Article

The Ecology Of Rafting In The Marine Environment. Iii. Biogeographical And Evolutionary Consequences

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Abstract

Rafting of marine and terrestrial organisms has important ecological, biogeographical and evolutionary implications. Herein the general principles of rafting are described and how they contribute to population connectivity. Rafting dispersal has particular characteristics, which may differ substantially from those of species with planktonic larval dispersal. Dispersal distances achieved via rafting can vary considerably: journeys may be very short or in some cases extremely long, depending on currents and wind. Accumulation of rafts in convergence zones facilitates cohesion of travelling groups, possibly reducing the risk of founder populations being very small. This becomes particularly important over long distances where singular founder events could provoke strong reduction of the genetic variability in the founded population. The frequency of transport affects the degree of connectivity between local populations. Three important raftingroutes are distinguished: frequent, intermittent and episodic. Frequent rafting routes are found in bays, lagoons and estuaries, and they are typically facilitated by substrata of biotic origin (seagrass, saltmarsh vegetation, intermediate-sized algae and mangroves). Intermittent rafting routes are found along temperate continental shores where they are facilitated primarily by giant kelps. In the subtropics and the Arctic intermittent rafting routes facilitated by wood are particularly important. Episodic rafting routes, which often cross vast areas of open ocean (biogeographic barriers), are facilitated by volcanic pumice, floating trees and occasionally by giant kelps when these are pushed beyond intermittent routes by strong winds or currents. Dispersal events occur in a highly sporadic manner in this latter category of rafting route, but when they happen, large amounts of floating substrata and rafters may be dispersed simultaneously. Intervals between events can be decades, centuries or even millennia, and consequently populations resulting from these events may be isolated from each other for long time periods. Population connectivity on frequent, intermittent and episodic rafting routes is high, intermediate and low, respectively. Genetic studies support these predictions, and furthermore underline that rafting may contribute to population connectivity over a wide range of geographic scales, from <100 km up to >5000 km. Rafting also has a strong effect on evolutionary processes of the organisms dispersed by this means. It is suggested that local recruitment (consequence of direct development) contributes to enhanced rates of population diver- gence among local populations of common rafters, but occasionally high genetic diversity may result from secondary admixture. Isolation of colonisers after singular episodic rafting events facilitates allopatric speciation. Through these processes rafting dispersal may support local species richness and thus have an influence on local biogeography and biodiversity. Human activities affect rafting connections in the oceans either by reducing or enhancing the possibility of transport and landfall. In many cases it cannot be safely decided whether the appearance of a species in a new habitat is due to rafting or to other transport mechanisms, and genetic studies can help to identify the most likely causes. Future field and laboratory studies on the ecology of potential rafters in combination with genetic studies on different spatial and temporal scales will contribute to a better understanding of the mechanisms of rafting dispersal, consideration of which is crucial in developing efficient conservation measures in the marine environment.

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... Page 4 of 16 and success depend on a wide panoply of biotic and abiotic factors [for a review, see Winston (2012) and references therein]. In the open ocean, episodic rafting routes are the most significant for biogeographic purposes, allowing the dispersal of organisms across biogeographic barriers within deep waters (Thiel and Haye 2006). Rafting consists of the dispersal of organisms in floating biotic or abiotic substrata, propelled by sea currents and trade winds (Winston 2012;Ávila 2013). ...
... Rafting consists of the dispersal of organisms in floating biotic or abiotic substrata, propelled by sea currents and trade winds (Winston 2012;Ávila 2013). Extensive reviews by Thiel and Gutow (2005a, b) and Thiel and Haye (2006) showed that rafters tend to share some features: small size, substratum generalists, food generalists, asexual reproduction, or direct development. Therefore, rafting in seawater can act as a "pathway" for the dispersal of non-planktotrophic marine larvae and floating organisms across oceanic barriers and colonization of new locations (review in Ávila 2006; Ávila et al. 2019). ...
... Rafting is of major importance for range expansion of non-planktotrophic shallow-water epibenthic molluscs inhabiting subtropical and temperate Atlantic waters (Thiel and Haye 2006;Ávila et al. 2012;Ávila 2013). P. sauciatus is believed to be a good candidate for episodic rafting to remote islands for three reasons: (1) its ability to attach to floating substrata;, (2) its considerably small sizes (< 15 mm) until sexual maturity is reached (Rubal et al. 2014;Sousa et al. 2019b);and (3) inhabiting the intertidal zone, where it is easier to initiate the process (Ávila 2006). ...
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The marine topshell Phorcus sauciatus is currently found along the temperatesubtropical shores of the Northeast Atlantic Ocean. Although present in the Iberian Peninsula, Madeira and Canaries for centuries, P. sauciatus has only recently reached another oceanic volcanic archipelago in the region. In 2013, a small population was recorded for the first time in Santa Maria Island (Azores), widening its distribution around the entire island and to the neighbouring island of São Miguel in a short period of time. The success of such colonization of the remote archipelago by P. sauciatus still awaits an explanation. To better understand the populational dynamics of the species in the NE Atlantic Ocean, we used a molecular approach to evaluate the genetic structure of P. sauciatus aiming at the determination of a potential origin for the first individuals that reached the Azores. On the foundations of detailed oceanographic, palaeontological and ecological data, we discuss the impact of climate change as a trigger for colonization of remote oceanic islands and suggest a mechanism that might explain the long-distance dispersal of the non-planktotrophic gastropod P. sauciatus across important biogeographical barriers in the NE Atlantic.
... The colonization of different substrates, including marine litter, by micro-and macro-organisms such as algae and invertebrates occurs during their propagule or larval stages, which will then grow, compete for space, and reproduce (Thiel and Gutow, 2005;Thiel and Haye, 2006;da Gama et al., 2008). The colonization is mediated by the physical and chemical characteristics of the substrates, including their composition and roughness (Railkin, 2003;Skinner and Coutinho, 2005;Astudillo et al., 2009;Bravo et al., 2011;Fazey and Ryan, 2016). ...
... However, even today the dispersion of species by marine litter is still little known in relation to its effectivity (Vegter et al., 2014;Rech et al., 2016). The studies of Thiel and Gutow (2005), Thiel and Haye (2006); Gall and Thompson (2015), Carlton et al. (2017), Carlton and Fowler (2018) and Laeseke et al. (2020) cite in the literature the different asks related to the dispersal such as loss of biodiversity, economical and ecological impacts, the origin and distribution of species, the resistance of species to various environmental adversities such as storms and tsunamis and the potential for their colonization in new environments. ...
... If fouling species present in the marine litter can be transferred to a new environment, by reproduction and posterior recruitment to rocky shores, these species can be considered as exotic species. However, they are called invasive when they cause impacts on the native fauna of the region, such as competition and predation, acting in this way as an ecological succession process as cited by Thiel and Gutow (2005) and Thiel and Haye (2006). ...
Article
One of the underestimated consequences of marine litter presence on marine environment is the transportation of fouling species on detritus-a process known as rafting. We undertook a review of articles concerning rafting published between 1970 and 2020 to identify patterns and potential areas of study that could contribute to directing future research. We observed in 53 publications an increase in rafting studies from the 1990s but fewer studies have been undertaken in the Southern Atlantic. The main fouling organisms were algae, barnacles, bryozoans, mollusks and polychaetes. The transport of those organisms over time and distances, and the volumes of material transported, have been very irregular, reflecting oceanic movements and detritus generating events acting at local, regional, or trans-oceanic scales. No standardized methodologies for collecting marine litter and identifying and quantifying their fouling were observed, but are suggested in this review, to allow more accurate future comparisons among different studies.
... In contrast, the species is conspicuous between 30°S and the sub-Antarctic region of South America, although a patchy distribution is observed in some fjords and sounds of Patagonia and the Magellan region (personal observations). It was hypothesized that such a wide distribution is the result of both the global ecological success of M. pyrifera due to its large physiological and morphological variability (Graham et al., 2007) and its ability to disperse over large distances through rafting of fertile individuals (Macaya et al., 2005, Rothaüsler et al., 2011, Thiel and Haye, 2006Tala et al., 2016). Yet, the origin of its phenotypic variability, i.e plasticity or local adaptation, has never been clearly evaluated. ...
... This would be the case if a stabilizing selection is acting on a large spatial scale (Price et al., 2003). While dispersal through rafting of mature sporophytes is probably too rare to ensure an effective gene flow among populations, it allows the transport of individuals for several hundred (Thiel and Haye, 2006), and up to several thousands of kilometers (Macaya and Zuccarello, 2010). The subsequent release of spores then may occur in a very distinct habitat than the origin of the parental rafting sporophyte. ...
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This study aimed at testing the existence of local adaptation in the gametophytes of giant kelp, in regions separated by up to 4000km and strong thermal divergence.
... The New Zealand chiton Onithochiton neglectus Rochebrune, 1881, is a low intertidal species that often inhabits the holdfasts of benthic Durvillaea kelp (both D. antarctica and the closely related D. poha). Onithochiton neglectus has frequently been observed rafting on detached individuals of these kelp species, being transported for long distances among New Zealand's Sub-Antarctic Islands and the South Island (Creese, 1986;Thiel & Haye, 2006;Nikula et al., 2012;López et al., 2017López et al., , 2018Waters et al., 2018a). Previous studies have identified shared mitochondrial haplotypes between O. neglectus in the South Island and the Sub-Antarctic Islands, providing evidence that connectivity among O. neglectus populations is promoted by rafting on Durvillaea in the southern region (Nikula et al., 2012;Waters et al., 2018a), but populations north of Dunedin (45.88°S, 170.50°E) remain to be assessed. ...
... Previous studies have identified shared mitochondrial haplotypes between O. neglectus in the South Island and the Sub-Antarctic Islands, providing evidence that connectivity among O. neglectus populations is promoted by rafting on Durvillaea in the southern region (Nikula et al., 2012;Waters et al., 2018a), but populations north of Dunedin (45.88°S, 170.50°E) remain to be assessed. Due to O. neglectus' brooding behaviour and release of short-lived larvae with limited mobility (Creese, 1986), little connectivity is expected where kelp-rafting is infrequent (Thiel & Haye, 2006;Lopez et al., 2017Lopez et al., , 2018. ...
Article
Onithochiton neglectus is a morphologically variable, brooding chiton inhabiting coastal reefs throughout New Zealand and its Sub-Antarctic Islands. Southern O. neglectus populations are typically associated with buoyant kelp (Durvillaea spp.) and are potentially connected via kelp-rafting. Northern O. neglectus populations are less likely to raft, due to lower numbers of Durvillaea in northern New Zealand. To test for the impact of kelp-rafting on the spatial distribution of variation in O. neglectus, we undertook a combined analysis of morphological and genetic variation across the range of the species. Geometric morphometrics were used to assess shell shape. We detected a northern vs. southern split in shell shape, corresponding to the frequency of the O. neglectus/Durvillaea spp. association. To assess O. neglectus genetic patterns across New Zealand, we estimated phylogenetic trees with nuclear (ITS) and mitochondrial (COI and 16S) markers, which revealed distinct northern and southern lineages, and an additional lineage in central New Zealand. Neither the morphological nor genetic groups match existing O. neglectus subspecies, but are concordant with the patterns of association of O. neglectus with Durvillaea. We suggest that shell shape may be linked to O. neglectus’ regionally variable ecological association with kelp holdfasts.
... While termites are poor flyers unable to cross large water bodies actively [24,25], they often live in wood pieces that can float across oceans as rafts [26,27]. The ability of termites to disperse by rafting in wood pieces is evidenced by their presence on remote oceanic islands, such as the Easter [28] and Galapagos islands [29]. ...
... Many species of wood-feeding termites nest inside wood pieces or harvest the lignocellulose of dead branches, sometimes retaining the ability to produce secondary reproductive when isolated from their parent colony [74]. Washed-up branches and trees, which are generated in large quantities during typhoons, tsunamis and other cataclysmic events, can serve as rafts carrying wood-feeding termites across oceans [26]. On the contrary, soil-feeding termites are rarely associated with wood items able to float. ...
Article
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Termites feed on vegetal matter at various stages of decomposition. Lineages of wood- and soil-feeding termites are distributed across terrestrial ecosystems located between 45°N and 45°S of latitude, a distribution they acquired through many transoceanic dispersal events. While wood-feeding termites often live in the wood on which they feed and are efficient at dispersing across oceans by rafting, soil-feeders are believed to be poor dispersers. Therefore, their distribution across multiple continents requires an explanation. Here, we reconstructed the historical biogeography and the ancestral diet of termites using mitochondrial genomes and δ13C and δ15N stable isotope measurements obtained from 324 termite samples collected in five biogeographic realms. Our biogeographic models showed that wood-feeders are better at dispersing across oceans than soil-feeders, further corroborated by the presence of wood-feeders on remote islands devoid of soil-feeders. However, our ancestral range reconstructions identified 33 dispersal events among biogeographic realms, 18 of which were performed by soil-feeders. Therefore, despite their lower dispersal ability, soil-feeders performed several transoceanic dispersals that shaped the distribution of modern termites.
... A distinctive feature of both species is their honeycombed internal structure, which makes them highly buoyant (Fraser, Hay, Spencer, & Waters, 2009;Fraser, Spencer, & Waters, 2012). This buoyancy also means detached individuals can act as rafts (Thiel & Haye, 2006), potentially transporting a range of flora and fauna, including crustaceans (Fraser, Nikula, & Waters, 2011;Nikula, Fraser, Spencer, & Waters, 2010), limpets (Edgar & Burton, 2000), sea-slugs (Cumming, Nikula, Spencer, Waters, & Crame, 2014) and echinoderms (Waters, King, Fraser, & Garden, 2018). Depending on the extent, longevity and direction of strong wind and storm events, detached D. antarctica and D. poha are capable of dispersing long distances and traversing oceanographic barriers (Fraser, Morrison, et al., 2018;Garden, Currie, Fraser, & Waters, 2014). ...
... As macroalgal rafts and stands support a range of intertidal species (Cumming et al., 2014;Morton & Miller, 1968;Thiel & Haye, 2006), the quick recovery of these species has implications for the timing of re-establishment of a range of dependent species, including invertebrate animals, that rely on Durvillaea for food, shelter, protection and passive dispersal (Edgar & Burton, 2000;Smith, 2002). As Durvillaea populations continue to recover, the ongoing dispersal of organisms via rafting could therefore result in shifts in the local communities, including changes in species diversity and abundance of epibiotic invertebrates. ...
Article
In species that form dense populations, major disturbance events are expected to increase the chance of establishment for immigrant lineages. Real‐time tests of the impact of disturbance on patterns of genetic structure are, however, scarce. Central to testing these concepts is determining the pool of potential immigrants dispersing into a disturbed area. In 2016, a 7.8 magnitude earthquake occurred on the South Island of New Zealand. Affecting approximately 100 km of coastline, this quake caused extensive uplift (several metres high), extirpating many intertidal populations, including keystone intertidal kelp species. Following the uplift, we set out to determine the geographic origins of detached kelp specimens which rafted into the disturbed zone. Specifically, we used genotyping‐by‐sequencing (GBS) approaches to compare beach‐cast southern bull‐kelp (Durvillea antarctica and D. poha) samples to established populations throughout the species’ ranges, and thus infer the geographic origins of potential colonists reaching the disturbed coast. Our findings reveal an ongoing supply of diverse lineages dispersing to the newly uplifted coastline, suggesting potential for establishment of ‘exotic’ lineages following disturbance. Furthermore, we found that some drifting individuals of each species came from far‐distant regions, some >1200 km away. These results show that diverse lineages – in many cases from very distant sources – have potential to compete for new space in the wake of an exceptional disturbance event, illustrating the potential of long‐distance dispersal as a key mechanism for re‐assembly of coastal ecosystems. Furthermore, our findings demonstrate that high‐resolution genomic baselines can be used to robustly assign the provenance of dispersing individuals.
... The increasing amount of floating marine anthropogenic litter in the marine environment has offered a high amount of distinct substrates to the colonization by various fouling organisms, starting from their propagule/larval stage (Bravo et al., 2011;Gracia et al., 2018;Rech et al., 2018aRech et al., , 2018bRech et al., , 2018c. These organisms establish themselves on these substrates, growing, competing with others, and resisting to the various adversities of the marine environment (Thiel and Guttow, 2005;Thiel and Haye, 2006;Bravo et al., 2011). The preference regarding the type of colonized material depends on the substrate characteristics such as buoyancy, surface, roughness, size, and composition (Fazey and Ryan, 2016;Battaglia et al., 2019). ...
... Most species found in the different types of marine anthropogenic litter in the Ilha Grande Bay are introduced and cryptogenic species, differing from the study by Rech et al. (2018aRech et al. ( , 2018bRech et al. ( , 2018c on Rapa Nui Island in the Pacific which did not find any invasive species. When non-indigenous species are introduced into a new environment, and if they affect the native fauna as a result of competition for food and space, resulting in changes in the ecosystem balance they can be considered as invasive (Thiel and Guttow, 2005;Thiel and Haye, 2006;Gall and Thompson, 2015). The sun coral Tubastraea spp. ...
Article
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The presence of floating marine anthropogenic litter in marine environments increase the possibility of transportation of fouling organisms using these substrates as a vector, mainly for those species with close affinities to artificial substrates. The objectives were to qualitatively and quantitatively report anthropogenic litter and its associated fouling groups arround Ilha Grande Bay (IGB). Litter was collected, classified and examined for the presence of fouling organisms on beaches located at two different levels of wave exposure during rainy and dry seasons. The types of litter do not differ among beaches, and the highest density and cover of fouling were reported on exposed beaches due the currents, winds, and storm waves. Bryozoans, barnacles, polychaetes, and mollusks were the most frequent fouling groups observed in litter and represents a potential vector for the dispersion of species in the IGB and adjacent coastal areas.
... We refer to this phenomenon as 'bailout', the term coined by Shanks et al. (1986) to describe the voluntary abandonment of a dislodged rock by gastropods. Bailout of mobile crustaceans from detached seaweeds is well documented, but research has focussed on the consequences of remaining on the host seaweed (Kingsford & Choat 1985, Thiel & Gutow 2005b, Thiel & Haye 2006, and the cue(s) that trigger bailout are unknown (Taylor 2015). ...
... A significant fraction of individuals elect to remain on their host when it detaches (Kingsford & Choat 1985, Gutow et al. 2009, and some even actively colonise floating seaweeds from attached plants via the water column (Ingólfsson 1998). The evidence of biogeographic-scale range expansion via seaweed rafts indicates that those individuals have at least a small chance of survival (Thiel & Haye 2006). At the species level, it may be beneficial to have a mixture of individuals that help to maintain local populations by bailing out promptly following detachment of their host, and others that disperse by remaining onboard. ...
Article
Small mobile crustaceans are abundant on seaweeds. Many of these crustaceans rapidly abandon their host if it is detached from the seafloor and floats towards the surface, but the trigger for this ‘bailout’ behaviour is unknown. We tested 2 potential cues, i.e. rapid change in light and rapid change in water pressure, using >1 mm epifauna on the brown seaweed Carpophyllum plumosum as a model system. Bailout occurred in response to reduced water pressure, but not to changing light, as (1) bailout occurred at similar rates in light and dark, (2) bailout occurred on the seafloor when water pressure was reduced within a transparent chamber by the equivalent of ~0.5 m depth or more, and (3) little bailout occurred when water pressure was held constant within the chamber while seaweeds were raised to the surface. Increase in pressure (simulating sinking) did not induce bailout. The rate of bailout increased with increasing magnitude of pressure reduction but was not influenced greatly by the rate of change of pressure within the range tested (up to an equivalent of 0.4 m depth s ⁻¹ ). The use of pressure rather than light as a cue for bailout is consistent with the need for seaweed-associated crustaceans to rapidly abandon a detached host and relocate to suitable habitat during both day and night.
... Seaweeds provide habitats, shelters, natural food sources, and nursery grounds for marine organisms (Anh, Vinh, Lan, & Hai, 2019;Mantri, Kavale, & Kazi,, & M. A., 2020;Thiel & Haye, 2006). Seaweeds are used as shelter for juvenile mud crabs at aquaculture farms have strongly positive effects on crab survival (Mirera & Moksnes, 2013). ...
... shelters, natural food sources, and nursery grounds for marine organisms in natural habitats Mantri et al., 2020;Thiel & Haye, 2006). The present study supports these findings because survival was higher for the treatments with seaweeds as shelter than for those without seaweed (control treatment). ...
Article
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Mud crabs (Scylla spp.) are considered luxury seafood and high market value; hence, mud crab farming is well known in Southeast Asia. However, the prevalence of cannibalistic behavior in crabs thus requires shelter in the culture system to reduce conspecific cannibalism and enhance the survival of crabs. This study aims to determine the suitability of various seaweed species as shelter to improve the survival and production of mud crab Scylla paramamosain crablets. The experiment consisted of seven treatments and was randomly designed in triplicate tanks. The control treatment had no shelter (i.e., without seaweed in the culture tank), and in the other six treatments, red seaweed (Gracilaria tenuistipitata) or green seaweed (Enteromorpha intestinalis) was placed in the rearing tanks at three density levels: 0.5, 1, and 2 kg/m². Instar 2 crablets were reared at a density of 300 ind/m², at salinity of 15 g/L, and with continuous aeration. Crablets were fed frozen Artemia biomass to satiation for 4 weeks. Results showed that the survival of crabs in all treatments sharply declined from Week 3 to Week 4 of culture, where the 1 and 2 kg Gracilaria groups showed less reduction than the other treatments. At the end of the experiment, the average survival of crabs in the control group was lowest (17.4%), while the survival of crabs was significantly improved, varying within the ranges of 53.3–70.7% and 27.8–35.9% in the Gracilaria and Enteromorpha groups, respectively. Notably, higher survival resulted in lower growth rates in the seaweed treatments, but enhanced biomass and production of crab juveniles. Moreover, concentrations of TAN, NO2⁻, NO3⁻, and PO4³⁻ in the Gracilaria treatments were much lower than in both the control and the Enteromorpha treatments that improved water quality in the rearing tanks. The present findings prove that red seaweed G. tenuistipitata could be considered a suitable shelter for the reliable production of mud crab juveniles in the nursery phase.
... Thus, the general absence of genetic divergence throughout the distribution of Z. exsargasso (albeit not examined over the entire distribution of the species) could suggest that randomness and regional hydrographic patterns can promote high population connectivity via the Gulf Stream. It has been suggested (Thiel and Haye 2006) that there may be convergence zones where multiple rafts arrive, thus favouring high levels of gene flow between distant populations and erasing the genetic signatures of founder effects. Such 'arrival' zones for eastward dispersal are likely to be the Macaronesian archipelagos (Bamber 2012a). ...
Article
In this study, the phylogeographic patterns of nuclear, ribosomal and mtDNA gene fragments of five tanaidacean species (Zeuxo, Tanaidae) from the Atlantic, Pacific and Mediterranean Sea were investigated. We aimed to interpret results in the framework of current hypotheses on the distribution of small invertebrates with very limited dispersal ability. Evidence for a surprisingly high genetic divergence was found for intertidal tanaidaceans from the North Atlantic. This is a result of poor dispersal potential, as tanaidaceans have direct development, no pelagic stage, and very limited swimming capacity. However, lower genetic divergence was found between an intertidal tanaid species from the North Atlantic and two from the North Pacific, which suggests a scenario of recent colonization following the last glacial maximum. The species Zeuxo normani was found to be a species complex consisting, at least, of Z. normani (California), Z. cf. normani (Japan), Z. cf. normani (Australia), Z. sp. A (Korea), and Z. holdichi (Spain and France). Our results showed that traditional species identification underestimates tanaidacean diversity and that what have been previously perceived as reliable diagnostic morphological characters, are, however, variable and unreliable.
... Plastic FMD items pose extensive ecological stressors including alteration of pelagic habitats and transport of alien species (Gregory, 2009;Fazey and Ryan, 2016;Tutman et al., 2017). Transport mechanisms for the introduction of marine species to non-native environments are ballast water (Carlton and Geller, 1993), hull fouling (Gollasch, 2002), aquaculture (Minchin, 2007), rafting (Thiel and Haye, 2006) and canals (Galil, 2012). But relatively little information is only available about rafting species (as biofouling) on FMD (Ojaveer et al., 2014;Vegter et al., 2014;Tutman et al., 2017;Santos and Reimer, 2018). ...
Article
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The floating marine debris (FMD) and the associated rafting communities are one of the major stressors to ecosystem services, global biodiversity and economy and human health. In this study, assemblages of encrusting organisms on different types of stranded FMD along the west coast of Qatar, Arabian/Persian Gulf (hereafter referred to as ‘Gulf’) were examined. The analysis showed 18 fouling species belonging to 5 phyla (Annelida, Anthropoda, Bryozoa, Mollusca and Porifera) on the FMD. The most abundant fouling species were the encrusting Amphibalanus amphitrite, polychaete Spirobranchus kraussii, Bryozoan species and Megabalanus coccopoma. More number of taxa were found on larger size FMD than on smaller FMD. Some of the barnacle rafting types were found to be non-indigenous species. The central and northwest parts of the Qatar had more FMD and fouled species than in other locations. Winds and the prevailing hydrodynamic conditions (waves and currents) played an important role in the transportation and distribution of FMD and associated organisms along the west coast of Qatar. The present study confirmed that huge amount of bio-fouled FMD items, causing great damage to biodiversity, drift in the surface layer of ocean and eventually strand onto the beaches. We propose a simple, but an effective management plan for FMD and associated organisms at regional scale to restore the biodiversity, sustainability and health of the marine ecosystem in the Gulf.
... Floating debris and ice rafts have long been recognized as a facilitating the dispersal of animals and plants along rivers and across open water (Eliasson 1992;Stemberger 1995;Johansen and Hytteborn 2001) in both marine (Jokiel 1990;Thiel and Haye 2006) and freshwater environments. Indeed, Darwin (1859) proposed ice rafting as a mechanism for seed dispersal. ...
Article
Passive transport has likely contributed to the post-glacial dispersal of species in temperate regions. However, identifying such processes from patterns can be obscured by confounding environmental conditions. We studied the distribution of ground beetles in Ontario’s Far North, a vast (450,000 km²) and largely intact region, to identify mechanisms that aid in species dispersal when confounding factors, such as temperature, are controlled. We tested a model of passive, riverine dispersal using recent records of flightless and flighted ground beetles from 34 sites across the region. The number of species declined with distance from main watershed rivers, as predicted from our model at the site level. Contrary to expectations, this pattern was evident with flighted species but not flightless species. The opposite pattern, with flightless species displaying a decrease with increasing distance from river, was evident at a regional level. These patterns are consistent with ground beetles carried along rivers since glacial retreat. We surmise that northward dispersal of these invertebrates into the boreal forest has been aided by vegetation and other debris flowing down rivers, including soil from eroded banks in which larvae and pupae reside. Biogeographic inferences, although often subtle, can be supported by broad-scale studies of intact landscapes.
... Benthic invertebrates have a wide variety of life histories (Godwin, 2003) and many have long larval stages, favoring transport of these species between areas separated by thousands of kilometers (Townsend et al., 2006;Çinar, 2013). Even benthic species without planktonic stage or with short-lived larvae can efficiently disperse using different ways of transportation (Jablonsky & Lutz, 1983;Winston, 2012), such as drifting, rafting, hitchhiking, creeping, and hopping (Thiel & Haye, 2006;Winston, 2012). ...
Article
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The introduction of non-indigenous marine species in new habitats is generally associated with ships arriving at ports, driven by species transported in ballast water and sediment and biofouling communities on ship hulls, drifting object and underwater surfaces in dock areas. The present paper reports the record of the specie Sternaspis aff. nana in the Atlantic Ocean, discussing its possible conservation status and method of arrival to Brazil. Sediments samples were collected in the external area (11 m depth) of the Suape Harbor (Brazil) in February 2018. Two individuals of Sternaspis aff. nana were recorded, representing the first record of this species in the Southwest Atlantic Ocean. The way S. aff. nana arrived in Brazilian waters cannot be easily determined, the short-lived lecithotrophic larvae of sternaspids suggest that the specimens found in Suape have arrived in ballast sediment. An increase in trade between Brazil and Asian countries since the 2000s has led to that more ships coming from China having arrived in Brazilian harbors. The arrival of S. aff. nana, originally described in the South China Sea, in the Suape harbor area may have resulted from this intense movement of ships between China and Brazil.
... This generality is also true for marine crustaceans. Future studies may also assess the impact of oceanic rafting (e.g., hitching rides on seaweeds) on clades such as peracarids with direct development (Thiel and Haye 2006), and hence on LDG. ...
Chapter
The latitudinal diversity gradient (LDG) is a phenomenon acknowledged for over two centuries. The LDG of marine crustaceans has been studied often but without reaching consensus on its ultimate causative processes. We have undertaken a new synthesis to assess the generality of the LDG and evaluated how potential sampling and other biases, spatial scale, geographic regions, taxonomic aggregation, and differences between clades affect patterns. A meta-analysis of 186 datasets, encompassing 20 studies and 7 crustacean orders, revealed a strong effect size of the species richness-latitude correlation, supporting the existence of a “canonical” LDG. The effect size was sensitive to spatial scale, with studies conducted over shorter latitudinal ranges tending to show a weaker LDG. Correcting for sampling biases in the number of occurrences, taxonomic completeness and spatial heterogeneity did not affect the strength of the LDG, nor did the degree of taxonomic aggregation; effect sizes were similar at family and ordinal levels. However, between orders effect sizes varied strongly, with peracarid orders (Amphipoda, Cumacea, Isopoda) showing a weaker or inverse LDG compared with non-peracarid orders (Calanoida, Euphausiacea, Decapoda, Sessilia). Additional analyses based on a global dataset of >2 million occurrences of >13,000 species revealed patterns undetected by the meta-analysis, including: (1) the existence of a marked bi-modal LDG, with peaks of diversity in subtropical areas (Calanoidea, Decapoda, Sessilia) and in temperate areas (Amphipoda, Isopoda), (2) interhemispheric asymmetry, variable across groups and depths, and (3) ocean basin differences in the shape of the LDG, dependent on taxonomic clade. Both ecological and evolutionary processes play a part. The fossil record of Decapoda showed that its global canonical LDG can be explained by median and range of the age of genera, i.e., hotspots of diversity harbor both younger and older genera and contain a high proportion of genera originating during the Paleogene. In addition, the effect size was negatively related to family age, the LDG being stronger in older families of early Cenozoic and Mesozoic origin. Modes of larval development also played a significant part, taxa without planktonic larvae having weaker or inverse LDG compared with taxa with pelagic larvae. Because clades with direct development tend to show smaller bathymetric and latitudinal ranges than those with pelagic larvae, differences in diversification rates may be implied. Overall, our evidence suggested that the ultimate causes of the LDG are deeply tied to geographic differences in macro-evolutionary rates, i.e., greater rates of species origin and lower rates of extinction in the tropics than in higher latitudes combined with a strong tropical niche conservatism.
... Because most benthic hydroids are substrate generalist, and often occur on floating material (e.g. Calder et al. 2014), their wide distributions have been explained by long-distance rafting, which would significantly increase the dispersal potential of benthic species (Cornelius 1992a;Thiel and Haye 2006;. In fact, several recent studies suggest a central role for rafting in range expansion of hydroid species with benthic life cycles (e.g. ...
Article
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Connectivity among populations of widespread marine species is expected to be correlated with their dispersal potential but the evolution of reproductive barriers may account for variations in spatial genetic patterns. Marine benthic hydroid species are traditionally considered widespread, with long-distance rafting presumably increasing their dispersal potential. In this study, we investigated the relationship between genetic, morphological and environmental variability within three benthic marine hydroid species to evaluate current patterns of genetic variation and assess the existence of cryptic speciation. Although a long-lived planktonic stage is absent in all the lineages sampled and they have an overlapping geographical ranges, we observed contrasting patterns of genetic and phenotypic divergence: Orthopyxis sargassicola showed little genetic variation, while O. caliculata and O. crenata each contained high genetic differentiation, primarily suggesting limited dispersal potential. Significant covariation was observed between phenotypic and environmental data in all lineages, but different environmental variables were responsible for explaining morphological variation in each case. Genetic and morphological patterns within O. caliculata and O. crenata are suggestive of cryptic speciation, while phenotypic variation in O. sargassicola may be plastic. Thus, morphological and genetic patterns may potentially vary among related marine lineages with shared life history traits and habitat.
... Mangrove propagules are often viviparous or cryptoviviparous in nature, as they germinate on the tree prior to dispersal (Bhosale and Mulik 1991;Tomlinson 1994). Tides, currents, wind, and wave action are all important factors in determining dispersal distance and direction (Howe and Smallwood 1982;Huiskes et al. 1995;Thiel and Haye 2006). Mangrove dispersal has been documented at large temporal and spatial scales (reviewed by Van der Stocken et al. 2019, for specific examples -Duke 1993Duke et al. 1998), but only a limited number of studies have examined dispersal at smaller scales (Yamashiro 1961;Clarke 1993;Sousa et al. 2007;Peterson and Bell 2015;Van der Stocken et al. 2015a). ...
Article
Dispersal and establishment dynamics are critical in understanding shifts in species’ ranges. We seek to illuminate patch-level dispersal dynamics by examining the shifting salt marsh-mangrove ecotone. Specifically, we ask the following: (1) How are mangrove propagules dispersed, retained, and exported within a discrete patch? (2) How do differences across a flooding gradient influence propagule dispersal dynamics? (3) How does the distribution of established seedlings compare to propagule movements? Avicennia germinans is the most temperate mangrove species in the northern Gulf of Mexico forming an ecotone with Spartina alterniflora marshes in coastal Louisiana. Sets of 500 distinctively marked mangrove propagules were placed at five different elevations. After their release, we observed dispersal dynamics for 1 month. Retention was limited in the study area (< 10%) with ~ 70–80% of propagules exporting out of the system and ~ 20% propagule predation. Retained propagules largely remained at their original elevations and were generally found at the highest elevation. Seedling establishment was also studied and unlike propagule dispersal distributions, peak seedling density occurred at elevations flooded 20–40% of the time. Our study highlights the mass export of mangrove propagules, the disparity between dispersal and establishment dynamics, and the need to explore dispersal at biologically relevant temporal and patch-level spatial scales. By understanding dispersal and establishment dynamics within the ecotonal boundary, we provide one of the first studies on dispersal at a temperature-controlled latitudinal limit for mangroves and highlight some of the drivers needed to better connect plot-, patch-, and landscape-level dynamics at this and other range limits.
... Our findings indicate that the likely former native range of J. marmorata is the NW Atlantic region, and the likely former native range of J. slatteryi is the Northern Pacific (NW and NE) region. Due to the relatively fast travel speeds, extensive surface area, and independence of stochastic ocean currents (Haydar, 2012), shipping still appears to be the more successful vector of Jassa species dispersal on a global scale as compared to natural dispersal on a local level (e.g., rafting or drifting; Thiel & Haye, 2006). As with these two successful biofoulers, the occurrence of many other coastal benthic species with wide modern geographic distributions is probably the result of human shipping activities over the last centuries. ...
Article
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The geographic distributions of some coastal marine species have appeared as cosmopolitan ever since they were first scientifically documented. In particular, for many benthic species that are associated with anthropogenic substrata, there is much speculation as to whether or not their broad distributions can be explained by natural mechanisms of dispersal. Here, we focused on two congeneric coastal crustaceans with cosmopolitan distributions - the tube-dwelling amphipods Jassa marmorata and Jassa slatteryi. Both species are common elements of marine biofouling on nearly all kinds of artificial hard substrata in temperate to warm seas. We hypothesized that the two species' modern occurrences across the oceans are the result of human shipping activities that started centuries ago. Mitochondrial DNA sequences of the CO1 fragment of specimens from distinct marine regions around the world were analysed, evaluating genetic structure and migration models and making inferences on putative native ranges of the two Jassa species. Populations of both species exhibited considerable genetic diversity with differing levels of geographic structure. For both species, at least two dominant haplotypes were shared among several geographic populations. Rapid demographic expansion and high migration rates between geographically distant regions support a scenario of ongoing dispersal all over the world. Our findings indicate that the likely former native range of J. marmorata is the Northwest Atlantic, whereas the likely former native range of J. slatteryi is the Northern Pacific region. As corroborated by the genetic connectivity between populations, shipping still appears to be the more successful vector of the two species' dispersal when compared to natural mechanisms. Historical invasion events that likely started centuries ago, along with current ongoing dispersal, confirm these species' identities as true "neocosmopolitans".
... For example, lineage 'L' has been observed to often have a less dense coenosteum than lineage 'S' (Hidaka, 1992, Wewengkang et al., 2007. A softer coenosteum may lead to more frequent colony fragmentation and dispersal by rafting (Thiel and Haye, 2006), which would allow lineage 'L' to disperse to remote places more easily. Although the correlation with coenosteum density between 'L' and 'S' was not significant in a previous study (Wewengkang et al., 2007), morphological, life-history, and dispersal differentiation between the cryptic lineages may be more clear, if they will be reassessed in the light of the present findings regarding polyp size (Fig. 5) and more detailed genetic distinction within former lineage 'L' (Admixture lineages and DAPC clades, Figs. ...
Article
Stony corals (Scleractinia) form the basis for some of the most diverse ecosytems on Earth, but we have much to learn about their evolutionary history and systematic relationships. In order to improve our understanding of species in corals we here investigated phylogenetic relationships between morphologically defined species and genetic lineages in the genus Galaxea (Euphyllidae) using a combined phylogenomic and phylogeographic approach. Previous studies revealed the nominal species G. fascicularis included three genetically well-differentiated lineages (L, S & L+) in the western Pacific, but their distribution and relationship to other species in the genus was unknown. Based on genomic (RAD-seq) and mitochondrial sequence data (non-coding region between cytb and ND2) we investigated whether the morphological taxa represent genetically coherent entities and what is the phylogenetic relationship and spatial distribution of the three lineages of G. fascicularis throughout the observed species range. Using the RAD-seq data, we find that the genus Galaxea is monophyletic and contains three distinct clades: an Indo-Pacific, a Pacific, and a small clade restricted to the Chagos Archipelago. The three lineages of G. fascicularis were associated with different RAD-seq clades, with the ‘L’ lineage showing some morphological distinction from the other two lineages (larger more asymmetrical polyps). In addition to these, three more genetic lineages in G. fascicularis may be distinguished – a Chagossian, an Ogasawaran, and one from the Indian-Red Sea. Among nominal taxa for which we have multiple samples, G. horrescens was the only monophyletic species. The mitochondrial non-coding region is highly conserved apart of the length polymorphism used to define L, S & L+ lineages and lacks the power to distinguish morphological and genetic groups resolved with genomic RAD-sequencing. The polyphyletic nature of most species warrants a careful examination of the accepted taxonomy of this group with voucher collections and their comparison to type specimens to resolve species boundaries. Further insight to the speciation process in corals will require international cooperation for the sharing of specimens to facilitate scientific discovery.
... The use of a flagging system allowed retaining valuable data that should not be discarded. For instance, some large brown algae and seagrasses can often be found as rafts 43 , floating on the sea surface, hundreds of kilometers away from their original source 44,45 . While these records are not particularly suitable to build ecological models aimed for benthic species, they are highly valuable to address dispersal ecology. ...
Article
Full-text available
Species distribution records are a prerequisite to follow climate-induced range shifts across space and time. However, synthesizing information from various sources such as peer-reviewed literature, herbaria, digital repositories and citizen science initiatives is not only costly and time consuming, but also challenging, as data may contain thematic and taxonomic errors and generally lack standardized formats. We address this gap for important marine ecosystem-structuring species of large brown algae and seagrasses. We gathered distribution records from various sources and provide a fine-tuned dataset with ~2.8 million dereplicated records, taxonomically standardized for 682 species, and considering important physiological and biogeographical traits. Specifically, a flagging system was implemented to signal potentially incorrect records reported on land, in regions with limiting light conditions for photosynthesis, and outside the known distribution of species, as inferred from the most recent published literature. We document the procedure and provide a dataset in tabular format based on Darwin Core Standard (DwC), alongside with a set of functions in R language for data management and visualization.
... Thiel M, et al. [17] recognized three main types of rafts according the permanence and the availability in coastal areas: a) frequent b) intermittent and c) episodic. All that review is focused on the ecological implications of such a phenomenon, and its reflections on the species genetics. ...
... The combination of having a long-lived planktonic larva (from 2 weeks to 2 months), sexual (hermaphroditic zooids) and asexual reproduction, fast growth rates, effective food acquisition in a wide range of flow rates, ability to form large colonies and to colonize kelps make M. membranacea a successful disperser, colonizer, and invasive species [22][23][24] . Potentially, these kelp can be transported much farther than bryozoan larvae [25][26][27][28][29][30][31] . Furthermore, their heavy encrustations may have a negative impact on marine ecosystems by increasing the brittleness of kelp blades, followed by extensive losses of kelp canopy 21 , and by limiting the ability of the seaweeds to reproduce and grow, specifically interfering with spore release from the kelp blade 20 . ...
Article
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Antarctic shallow coastal marine communities were long thought to be isolated from their nearest neighbours by hundreds of kilometres of deep ocean and the Antarctic circumpolar current. the discovery of non-native kelp washed up on Antarctic beaches led us to question the permeability of these barriers to species dispersal. According to the literature, over 70 million kelp rafts are afloat in the Southern Ocean at any one time. These living, floating islands can play host to a range of passenger species from both their original coastal location and those picked in the open ocean. Driven by winds, currents and storms towards the coast of the continent, these rafts are often cited as theoretical vectors for the introduction of new species into Antarctica and the sub-Antarctic islands. We found non-native kelps, with a wide range of "hitchhiking" passenger organisms, on an Antarctic beach inside the flooded caldera of an active volcanic island. This is the first evidence of non-native species reaching the Antarctic continent alive on kelp rafts. one passenger species, the bryozoan Membranipora membranacea, is found to be an invasive and ecologically harmful species in some cold-water regions, and this is its first record from Antarctica. the caldera of Deception island provides considerably milder conditions than the frigid surrounding waters and it could be an ideal location for newly introduced species to become established. These findings may help to explain many of the biogeographic patterns and connections we currently see in the Southern ocean. However, with the impacts of climate change in the region we may see an increase in the range and number of organisms capable of surviving both the long journey and becoming successfully established.
... Limited larval dispersal does not preclude other means of dispersal for many colonial benthic animals. Some colonies are dispersed by drifting of partial or whole colonies or by rafting (Keough & Chernoff, 1987;Thiel & Haye, 2006;Winston, 2012;Worcester, 1994). Rafting varies in frequency and distance but can be frequent and exceed the usual dispersal distance of the larvae. ...
Article
Many colonial marine animals care for embryos by brooding them on or in their bodies. For brooding to occur, features of the animals must allow it, and brooding must be at least as advantageous as releasing gametes or zygotes. Shared features of diverse colonial brooders are suspension feeding and a body composed of small modules that are indefinitely repeated and can function semi-autonomously, such as polyps or zooids. Suspension feeding permits capture of sperm for fertilization of ova that are retained by the parent. Distribution of broods among numerous small polyps, zooids, or other small modules facilitates supply of oxygen to embryos that are retained and protected by the parent. Brooding increases survival of offspring, controls dispersal, and can provide other developmental advantages. Colonial ascidians, pterobranch hemichordates, and entoprocts brood; most bryozoans and many colonial cnidarians brood. An unanswered question is why so many colonial anthozoans do not brood. Sponges share with colonies capacities for capturing sperm and separating numerous retained embryos yet many do not brood. Hypotheses for nonbrooding by colonies and sponges necessarily must apply to particular taxa. Few have been tested.
... Fucoid seaweeds have no planktonic dispersal stage and have restricted gamete dispersal (Serrão et al., 1997). However, adult individuals can achieve long distance gene flow via the rafting of whole or partially detached thalli with reproductive structures (Thiel and Haye, 2006;McKenzie and Bellgrove, 2008), a form of population connectivity strongly influenced by hydrodynamic forces and coastal topography. Currently, F. ceranoides is distributed from northern Portugal to northern Norway (Lein, 1984) and Iceland (Munda, 1999), covering both past non-glaciated and glaciated regions of Europe. ...
Article
Genetic structure in biogeographical transition zones can be shaped by several factors including limited dispersal across barriers, admixture following secondary contact, differential selection, and mating incompatibility. A striking example is found in Northwest France and Northwest Spain, where the estuarine seaweed Fucus ceranoides L. exhibits sharp, regional genetic clustering. This pattern has been related to historical population fragmentation and divergence into distinct glacial refugia, followed by post-glacial expansion and secondary contact. The contemporary persistence of sharp ancient genetic breaks between nearby estuaries has been attributed to prior colonization effects (density barriers) but the effect of oceanographic barriers has not been tested. Here, through a combination of mesoscale sampling (15 consecutive populations) and population genetic data (mtIGS) in NW France, we define regional genetic disjunctions similar to those described in NW Iberia. Most importantly, using high resolution dispersal simulations for Brittany and Iberian populations, we provide evidence for a central role of contemporary hydrodynamics in maintaining genetic breaks across these two major biogeographic transition zones. Our findings further show the importance of a comprehensive understanding of oceanographic regimes in hydrodynamically complex coastal regions to explain the maintenance of sharp genetic breaks along continuously populated coastlines.
... Lacking a planktonic life history stage, colonization of the NEP was presumably accomplished by rafting of adults or egg masses on floating biological debris (Knox, 1960;Johannesson, 1988;O'Foighil et al., 1999;Collin, 2001;Colson & Hughes, 2004;Waters & Roy, 2004;Thiel & Haye, 2006;Gordillo & Nielsen, 2013;Cumming et al., 2014). Although both the ABC and full-likelihood methods yielded similar results, the arrival of L. sitkana in North America is probably best estimated by the full-likelihood methods (Hickerson, Dolman & Moritz, 2006). ...
Article
Full-text available
The demographic history of a species can have a lasting impact on its contemporary population genetic structure. Northeastern Pacific (NEP) populations of the rocky shore gastropod Littorina sitkana have very little mitochondrial DNA (mtDNA) sequence diversity and show no significant population structure despite lacking dispersive planktonic larvae. A contrasting pattern of high mtDNA diversity in the northwestern Pacific (NWP) suggests that L. sitkana may have recently colonized the NEP from the NWP via stepping-stone colonization through the Aleutian-Commander Archipelago (ACA) following the end of the last glacial 20,000 years ago. Here, we use multi-locus sequence data to test that hypothesis using a combination of descriptive statistics and population divergence modeling aimed at resolving the timing and the geographic origin of NEP populations. Our results show that NEP populations share a common ancestor with a population of L. sitkana on the Kamchatka Peninsula ∼46,900 years ago and that NEP populations diverged from each other ∼21,400 years ago. A more recent population divergence between Kamchatka and NEP populations, than between Kamchatka and other populations in the NWP, suggests that the ACA was the most probable dispersal route. Taking into account the confidence intervals for the estimates, we conservatively estimate that L. sitkana arrived in the NEP between 107,400 and 4,100 years ago, a range of dates that is compatible with post-glacial colonization of the NEP. Unlike other congeners that are relatively abundant in the Pleistocene fossil record of the NEP, only one report of L. sitkana exists from the NEP fossil record. Although broadly consistent with the molecular data, the biogeographic significance of these fossils is difficult to evaluate, as the shells cannot be distinguished from the closely-related congener L. subrotundata.
... Furthermore, it also seems highly unlikely that freshwater fishes dispersed over long marine distances using floating rafts (Gayet, 2001;Thiel & Haye, 2006) or by the means of rare, local and untestable phenomena, such as rains of fishes (Gudger, 1929;Bajkov, 1949) or transportation of their eggs by waterbirds (Hirsch et al., 2018 and references cited therein). ...
Article
The Afrotropics house a diverse freshwater ichthyofauna with > 3000 species, almost all of which are endemic. Recent progress in dated phylogenetics and palaeontology of several groups of Afrotropical freshwater fishes (AFFs) has allowed the testing of palaeoecology- and palaeogeography-based hypotheses explaining their early presence in Africa. Seven hypotheses were tested for 37 most-inclusive monophyletic groups of AFFs. Results indicated that ten lineages originated from direct, but asynchronous, marine-to-freshwater shifts. These lineages contribute < 2% to the current AFF species richness. Eleven lineages colonized the Afrotropics from the Orient after the Afro-Arabian plate collided with Eurasia in the early Oligocene. These lineages contribute ~20% to the total diversity. There are seven sister relationships between Afrotropical and Neotropical taxa. For only three of them (4% of the species diversity), the continental drift vicariance hypothesis was not rejected. Distributions of the other four younger trans-Atlantic lineages are better explained by post-drifting long-distance dispersal. In those cases, I discuss the possibility of dispersal through the Northern Hemisphere as an alternative to direct trans-Atlantic dispersal. The origins of ten AFF lineages, including the most species-rich Pseudocrenilabrinae (> 1100 species), are not yet established with confidence.
... Our analyses have found that these crinoid colonies studied could have existed for more than 10 years, even up to 20 years, exceeding the life expectancy of modern documented raft systems with possible implications for the role of modern raft communities in the biotic colonization of oceanic islands and intercontinental dispersal of marine and terrestrial species. modern global patterns of species distributions [1][2][3][4]. Extant communities have been recorded lasting up to 6 years [5]. However, the deep time ecology of these communities has never been investigated using the latest quantitative methods to test these different hypotheses [6] empirically. ...
Article
Full-text available
Pseudoplanktonic crinoid raft colonies are an enigma of the Jurassic. These raft colonies are thought to have developed as floating filter-feeding communities due to an exceptionally rich oceanic niche, high in the water column enabling them to reach large densities on these log rafts. However, this pseudoplanktonic hypothesis has not been quantitatively tested, and there remains some doubt that this mode of life was possible. The ecological structure of the crinoid colony is resolved using spatial point process analyses and the duration estimates of the floating system until sinking using moisture diffusion models. Using spatial analysis, we found that the crinoids would have trailed preferentially positioned at the back of the floating log in the regions of least resistance, consistent with a floating, not benthic ecology. Additionally, we found using a series of moisture diffusion models at different log densities and sizes that ecosystem collapse did not take place solely due to colonies becoming overladen as previously assumed. Our analyses have found that these crinoid colonies studied could have existed for more than 10 years, even up to 20 years, exceeding the life expectancy of modern documented raft systems with possible implications for the role of modern raft communities in the biotic colonization of oceanic islands and intercontinental dispersal of marine and terrestrial species.
... These distributional ranges are much lower than for the swimming isopod families Desmosomatidae and Munnopsidae. As a typical walking haploniscid isopod, the body plan of Haploniscusdoes not show adaptations specific to swimming or burrowing, and the animals are found in close association with the sediment surface (Brix et al., 2020, Thiel andHaye, 2006). This suggests comparably poor dispersal capabilities of the adults as well. ...
Preprint
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The isopod species Haploniscus bicuspis (G.O. Sars, 1877) shows circum-Icelandic distribution in a wide range of environmental conditions and along well-known geographic barriers, such as the Greenland-Iceland-Faroe (GIF) Ridge. We wanted to explore population genetics, phylogeography and cryptic speciation as well as to investigate whether previously described, but unaccepted subspecies have any merit. Using the same set of specimens, we combined mitochondrial COI sequences, thousands of nuclear loci (ddRAD), and proteomic profiles, plus selected morphological characters using Confocal Laser Scanning Microscopy (CLSM). Five divergent genetic lineages were identified by COI and ddRAD, two south and three north of the GIF Ridge. Assignment of populations to the three northern lineages varied and detailed analyses revealed hybridization and gene flow between them, suggesting a single northern species with a complex phylogeographic history. No apparent hybridization was observed among lineages south of the Ridge, inferring the existence of two more species. Differences in proteomic profiles between the three putative species were minimal, implying an ongoing or recent speciation process. Population differentiation was high, even among closely associated populations, and higher in mitochondrial COI than nuclear ddRAD loci. Gene flow is apparently male-biased, leading to hybrid zones and instances of complete exchange of the local nuclear genome through immigrating males. This study did not confirm the existence of subspecies defined by male characters, which probably characterize different male developmental stages present in all species.
... The position of islands relative to prevailing currents may play a significant role in the beaching of raft materials and potential colonization. East Brother Island is in the direct line of out-going flow (at low tide) from San Pablo Bay (McGann et al. 2013) and appears to benefit from higher frequencies of intersection between raft materials and landform (Vences et al. 2003;Thiel and Haye 2006;Measey et al. 2006) than other islands in the bay. We think it likely that drifting debris that periodically washes up on the north side of the island has enabled these salamanders to colonize through rafting (See: Anderson 1960; Measey et al. 2006). ...
Article
Full-text available
The origin of island populations of herpetofauna is often unclear for some species. Successful colonization events are rare, and likely stochastic, but establishment does occur if current site conditions are suitable. We detected a breeding population of Arboreal Salamanders (Aneides lugubris) on a small rock island in the San Francisco Bay. The origin of this population is unknown, but it appears to be thriving amid anthropogenic structures and an altered landscape
... Some lobster larvae are known to ride upon jellyfish (Wakabayashi and Tanaka, 2012) and rafting on marine debris could be used for the dispersal of late larvae or even adults of some crab species (Pfaller et al., 2019). Genetic studies support that rafting may contribute to population connectivity up to >5000 km, with a strong effect on evolutionary processes of the organisms dispersed by this means (Thiel and Haye, 2006). ...
Article
Grapsus grapsus and Grapsus adscensionis are supralittoral crabs that are known to inhabit oceanic islands and depend on surface currents to recruit in the rocky shores. The ornamentation of the cephalothorax is very distinct among species, but morphological differences are controversial, and integrative studies with different approaches are needed. This study investigated the genetic variation among the populations of G. grapsus from Saint Peter and Saint Paul Archipelago (SP), Fernando de Noronha (FN), Rocas Atoll (RA) and Trindade Island (TR) in the western Atlantic, and G. adscensionis from the islands of Ascension (AI) and Saint Helena (SH) in the mid-Atlantic. Morphology was assessed by geometric morphometric analyses of the carapace and chelae, and numerical analyses of tubercles in the frontal plate of SP, FN, RA, TR and AI populations. In addition, dispersal of the larvae in the Atlantic Ocean was simulated performing a Lagrangian analysis using HYCOM reanalysis dataset as the ocean surface velocity field. The data obtained for the mitochondrial D-loop gene confirmed the distinctness of the two putative species and demonstrated the connectivity between the populations of G. grapsus from the three equatorial islands. The TR population presented unique haplotypes, as well as AI and SH. The geometric morphometric analyses showed differentiation between the carapace shapes for G. grapsus and G. adscensionis, however, the chelae shape does not allow to distinguish between the species or the population. The morphometric and molecular results were consistent with the pattern of particles dispersion in the Atlantic ocean. The larvae of SP, FN and RA mix after two months of drift, while the larvae of TR, AI, SH circulate only around the respective islands. The results reinforce the validation of the two species and the isolation of populations of G. grapsus in TR and of G. adscensionis in AI and SH. The populations of these islands might be maintained by self-recruitment, through larval behavior associated with the local current system, and therefore should be the target of conservation measures.
... In the years following, an unprecedented number of poriferan, cnidarian, arthropod, molluscan, bryozoan, and other species were found rafting on debris transported by this tsunami to the Pacific coast of the U.S.A. (Calder et al. 2014;Elvin et al. 2018;Miller et al. 2018a;Tanaka et al. 2018). Dispersal events like this have important implications for marine biogeography and long-term evolutionary consequences due to expanded gene flow (Briggs 1974;Thiel & Haye 2006). ...
Article
Previous studies documented colonies of the cheilostome bryozoan Biflustra irregulata rafting across the Pacific Ocean on debris from the 2011 Great East Japan megathrust earthquake and resulting tsunami. They arrived in the eastern Pacific on floating non-biodegradable tsunami debris from 2014 to 2016. Based on a newly discovered occurrence of this species off the west coast of Mexico, we report that this species has successfully expanded its range from the Indo-Pacific to the northeast Pacific following this dispersal event. Colonies were found encrusting barnacles on spiny lobsters from the southeastern Gulf of California.
... However, when the spatial extent of kelp loss is widespread (i.e., the scale of loss exceeds the typical scale of dispersal, but see Kinlan et al. 2003;Thiel et al. 2006;Hawes et al. 2017), or when kelp removal and/or inhibition persists through time, the strength of feedback processes that stabilize kelp forests can be degraded, and other processes may strengthen to stabilize the barren state (Filbee-Dexter and Scheibling 2014b; Ling, Kriegisch, et al. 2019;McPherson et al. 2021). ...
Thesis
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How the direct and indirect effects of species interactions cascade to affect community structure, functioning, and stability is a fundamental question in ecology. In temperate kelp forests, species interactions, in conjunction with environmental processes, produce rich spatiotemporal dynamics. Arguably the most dramatic of these are abrupt shifts in community state, where forested locations are grazed by herbivorous urchins to establish what is known as an “urchin barren”. The increasing frequency and intensity of perturbation events associated with climate change have increased the frequency of shifts towards the barren-state. Understanding not only the mechanisms precipitating state shifts but also those that stabilize both the forested and barren states is essential to guide effective kelp-forest conservation and management strategies. Central to urchin barren establishment is a switch in behavior, where urchins leave cracks and crevices to move across the seafloor and graze upon kelp. While it is known that urchin predators can control urchin density and behavior, it is less clear how resource availability affects urchin behavior, or how the switch in behavior affects kelp-forest dynamics at large. This dissertation evaluated urchin behavior, the “bottom-up” processes controlling it, and the subsequent effects upon kelp-forest dynamics and stability from three distinct directions. In Chapter 2, I analyzed 38 years of kelp-forest community data and found distinct spatiotemporal patterns: certain sites exhibited abrupt shifts in state, others exhibited resilient kelp-forest persistence. I suggest that substrate complexity (the rugosity of the benthic substrate) modified both “top-down” and “bottom-up” processes regulating urchin density and behavior. In particular, I suggest that substrate complexity altered the retention of drift algae (also known as kelp detritus, and henceforth, drift)—the senescent form of kelp that has detached from the seafloor. Urchins are believed to prefer drift, such that when drift is abundant urchin remain inactive, consume the drift, and do not graze live kelp. Variation in the retention of drift may thus in-part be responsible for the urchin behavioral switch that leads to the establishment and stabilization of the barren state. In Chapter 3, I used a one-consumer (urchins) two-resource (kelp and drift) model to test if and how a switch in urchin grazing can precipitate kelp-forest dynamics such as alternative stable states and the emergence of kelp population cycles. Under the assumption that urchins prefer drift over live kelp, results demonstrated that all shifts in state are associated with urchins switching between resources. In Chapter 4, I experimentally tested the core assumption from Chapter 3, i.e., that urchins “prefer” drift. Specifically, I used a subtidal caging experiment to evaluate the density-dependent effects of drift and kelp upon urchin consumption rates. Results demonstrated a strong preference in urchins to consume drift, that kelp consumption is controlled by the availability of drift (not by kelp itself), and that urchins exhibit a rank switch—a switch in the proportion of resources consumed as total biomass increases—from kelp to drift. Altogether, this dissertation used long-term monitoring, dynamical modeling, and subtidal experimentation to evaluate the influence of grazer-resource behavior, interactions, and feedbacks upon kelp-forest dynamics and stability. While urchin predators are predominantly thought to control the switch in urchin behavior, I demonstrate how resource availability can also control this behavioral switch. This may help explain shifts to the urchin barren state at locations where urchin predator abundances remain unchanged. Furthermore, my inferences involving substrate complexity and drift as a preferred urchin resource point towards potential strategies with which to conserve or restore kelp-forest ecosystems.
... In addition, 642 proceedings papers were also classified as articles. The book chapters document type had the highest CPP 2019 of 84, which can be attributed to the five highly cited book chapters with a TC 2019 of 100 or more [36] by Alongi [13], Balasubramanian et al. [42], Feller et al. [43], Thiel and Haye [44], and Manson et al. [45], with a TC 2019 of 302, 159, 156, 148, and 124, respectively. The data papers document type had the highest APP of 7.0. ...
Article
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Mangroves are one the most productive ecosystems on Earth, and they are geographically located in the tropics and sub-tropics. Notwithstanding their critical role in providing a large number of environmental services and benefits as well as livelihood provisions, mangrove forests are being lost globally at an alarming rate. At the same time, they are increasingly recognized as a cost-effective nature-based climate solution for their carbon sequestration and storage capacity. Despite their enormous importance to people’s lives and the ecosystem, no bibliometric study on this topic has been published to our knowledge. Here, we provide a bibliometric analysis of the research on mangroves with research trends, most influential research based on citation count, and the origins (country and institution) of major research. Using the Science Citation Index Expanded (SCI-EXPANDED) database of the Web of Science Core Collection (Clarivate Analytics), we identified 13,918 documents published between 1990 and 2019. Nevertheless, 12,955 articles met our final criteria and were analyzed in detail. Six publications and their citations per publication (CPP2019) were applied to evaluate the publication performance of countries and institutes. When considering the top ten Web of Science subject categories, articles published on the ecology of mangroves had the highest CPP2019 of 28. Environmental sciences have been the major category since 2013. The USA dominated the total articles and single-author articles. The USA was also the most frequent partner of international collaborative publications. China published the most single-country articles, first-author articles, and corresponding-author articles. However, articles by the USA and Australia had a higher CPP2019. Sun Yat Sen University in China was the most active university. The Australian Institute of Marine Science dominated all kinds of publications with the top CPP2019. Together with the USA, Australia, China, India, Brazil, and Japan ranked both the top six on total publications and total publications in 2019. Our bibliometric study provides useful visualization of the past and current landscape of research on mangroves and emerging fields, to facilitate future research collaboration and knowledge exchange.
... Organisms here must contend with wave action and unique chemical [2][3][4][5] and physical properties [4]. The surface is utilized by a wide range of species, from various fish and cetaceans, to species that ride on ocean debris (termed rafters) [6][7][8]. Most prominently, the surface is home to a unique community of free-living organisms, termed "neuston" (from the Greek word, υεω, which means both to swim and to float. ...
Article
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Life on the ocean's surface connects worlds. From shallow waters to the deep sea, the open ocean to rivers and lakes, numerous terrestrial and marine species depend on the surface ecosystem and the organisms found therein. Organisms that live freely at the surface, termed "neuston," include keystone organisms like the golden seaweed Sargassum that makes up the Sargasso Sea, floating barnacles, snails, nudibranchs, and cnidarians. Many ecologically and economically important fish species live as or rely upon neuston. Species at the surface are not distributed uniformly; the ocean's surface harbors unique neustonic communities and ecoregions found at only certain latitudes and only in specific ocean basins. But the surface is also on the front line of climate change and pollution. Despite the diversity and importance of the ocean's surface in connecting disparate habitats, and the risks it faces, we know very little about neustonic life. This Essay will introduce you to the neuston, their connections to diverse habitats, the threats they face, and new opportunities for research and discovery at the air-sea interface.
... In addition, amphipods may disperse for long-distances as part of fouling communities on floating materials. Globally, at least 108 amphipod species have been reported to passively disperse by such rafting for up to 10,000 km (Thiel & Gutow, 2005;Thiel & Haye, 2006). ...
Article
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Amphipod crustaceans are an essential component of tropical marine biodiversity. However, their distribution and biogeography have not been analysed in one of the world's largest tropical countries nested in the Coral Triangle, Indonesia. We collected and identified amphipod crustaceans from eight sites in Indonesian waters and combined the results with data from 32 additional sites in the literature. We analysed the geographic distribution of 147 benthic amphipod crustaceans using cluster analysis and the 'Bioregions Infomaps' neural network method of biogeographic discrimination. We found five groups of benthic amphipod crustaceans which show relationships with sampling methods, depth, and substrata. Neural network biogeographic analysis indicated there was only one biogeographic region that matched with the global amphipod regions and marine biogeographic realms defined for all marine taxa. There was no support for Wallaces or other lines being marine biogeographic boundaries in the region. Species richness was lower than expected considering the region is within the Coral Triangle. We hypothesise that this low richness might be due to the intense fish predation which may have limited amphipod diversification. The results indicated that habitat rather than biogeography determines amphipod distribution in Indonesia. Therefore, future research needs to sample more habitats, and consider habitat in conservation planning.
... (a), (d), (e) and (f) were taken with a CLSM. Scale bar = 100 µm surface Thiel & Haye, 2006). This suggests comparably poor dispersal capabilities of the adults as well. ...
Article
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The crustacean marine isopod species Haploniscus bicuspis (G.O. Sars, 1877) shows circum‐Icelandic distribution in a wide range of environmental conditions and along well‐known geographic barriers, such as the Greenland‐Iceland‐Faroe (GIF) Ridge. We wanted to explore population genetics, phylogeography and cryptic speciation as well as to investigate whether previously described, but unaccepted subspecies have any merit. Using the same set of specimens, we combined mitochondrial COI sequences, thousands of nuclear loci (ddRAD), and proteomic profiles, plus selected morphological characters using Confocal Laser Scanning Microscopy (CLSM). Five divergent genetic lineages were identified by COI and ddRAD, two south and three north of the GIF Ridge. Assignment of populations to the three northern lineages varied and detailed analyses revealed hybridization and gene flow between them, suggesting a single northern species with a complex phylogeographic history. No apparent hybridization was observed among lineages south of the Ridge, inferring the existence of two more species. Differences in proteomic profiles between the three putative species were minimal, implying an ongoing or recent speciation process. Population differentiation was high, even among closely associated populations, and higher in mitochondrial COI than nuclear ddRAD loci. Gene flow is apparently male‐biased, leading to hybrid zones and instances of complete exchange of the local nuclear genome through immigrating males. This study did not confirm the existence of subspecies defined by male characters, which probably characterize different male developmental stages.
... Numerous studies have shown that anthropogenic waste is a suitable substrate for the colonization and growth of numerous marine organisms such as bryozoans, polychaeta, barnacles, hydrozoans (e.g., Thiel and Gutow, 2005;Thiel and Haye, 2006;da Gama et al., 2008;Zettler et al., 2013;Fazey and Ryan, 2016). To date, only one paper has analyzed and described the macrozoobenthic fauna associated with deep litter in Italian waters (Crocetta et al., 2020), but this study did not analyze the association between species and categories of waste. ...
Article
Marine litter is a serious global environmental threat that has received increasing attention in the last decades from the academic world, intergovernmental organizations and agencies due to its impact on ecosystems, fisheries and, ultimately, human health. The Mediterranean Sea is characterized by one of the highest densities of marine litter in the world: although much research has been conducted on floating litter, little data exist on benthic litter and its associated macrozoobenthic fauna and only one study has investigated the matter in Italian waters. In the present work, marine litter was collected through demersal trawl nets in the coastal sector of Civitavecchia (northern Tyrrhenian sea, GSA 9) at 50-120 m of depth with the aim of i) describing the marine litter-associated macrozoobenthic community, ii) identifying the associations between macrozoobenthic species and litter categories and iii) evaluating the presence of unrecorded and/or non-indigenous species (NIS) associated with marine litter. Marine litter was recovered from all hauls, confirming its ubiquity and global dispersion in coastal areas, with plastic materials being the most frequently retrieved category. The highest and lowest litter items density were 2125 and 312.50 items/Km2. A total of 656 litter items weighing 15.8 Kg were classified according to the MSFD Technical Group on Marine Litter categories and analyzed. Their associated fauna consisted of 1536 benthic organisms belonging to 62 species. Species abundance-wise, Bryozoans were the dominant taxon followed by Polychaeta, Bivalvia, Ascidiacea and Anthozoa. Six non-indigenous species (NIS) were retrieved on anthropogenic substrates and, among them, two bryozoans species previously unreported in Italian waters were herein recorded. At last, our results highlight the possible selective association between some sessile species and specific marine litter categories, even though further validation is needed.
... Third, there are numerous examples of species lacking pelagic larval stages with broad distributional ranges, including established populations on isolated shores (Johannesson 1988;Martel and Chia 1991). Non-pelagic disperses may be able to reach these distant shores by rafting on, or in, items like seaweed, driftwood, boats, ships, and anthropogenic debris, or even aided by mobile organisms like birds (Martel and Chia 1991;Thiel and Haye 2006;Fraser et al. 2011). ...
Article
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Phylogeography provides insights into how historical and contemporary processes influence the genetic structure and gene flow in marine organisms around the globe. In benthic marine invertebrates, a species’ reproductive strategy can strongly impact phylogeographic patterns and distribution, with some direct-developing (non-planktonic) dispersers demonstrating strong genetic structure but also broad geographic spread. While seemingly paradoxical, past work has shown ovoviviparous species, like Littorina saxatilis, can be more successful colonizers of remote locations than species with planktonic larvae, like L. littorea. Both Littorina species overlap in much of their North Atlantic ranges but have different colonization histories: L. saxatilis is native on both North Atlantic coasts and islands, and L. littorea is native to the eastern Atlantic but introduced to the west. Using an extensive mitochondrial dataset (1236 sequences; 85 sites), we examined how their opposing reproductive strategies correspond to their distributions and phylogeographies. Littorina saxatilis exhibited a heterogeneous genetic structure reflecting post-glacial recolonization from multiple refugial sites, while L. littorea had a homogeneous structure with a post-glacial history characterized by recolonization from one main refugial area in the northeast Atlantic. Further, haplotype diversity was significantly depressed in northwest Atlantic L. littorea populations, signifying a strong bottleneck characteristic of a human-mediated introduction. In contrast, haplotype diversity in L. saxatilis was similar between the two regions, demonstrating long-term history on both coasts. Thus, our study suggests contrasting life-history characteristics were a major structuring force in the phylogeographic patterns of these related species following large-scale disturbances (natural and anthropogenic) that compel contraction and redistribution over large areas.
... However, studies have found several instances where direct developing gastropods have either colonized new areas before species with a pelagic larval stage (Johannesson 1988, Johannesson et al. 1995 or where depleted areas have quickly regained their genetic diversity (Colson and Hughes 2004). Rafting of individuals on seaweed is one possible explanation for these contradictions (Johannesson 1988, Ingólfsson 1992, 1995, Marko 2004, Thiel and Haye 2006. However, since the common whelk is a benthic species, it is more likely that egg-masses come loose from the substrate to which the females have attached them, and drift with the currents (Donald et al. 2015). ...
Thesis
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Variation in morphology of shelled marine gastropods across small spatial scales may reflect restricted population connectivity, resulting in evolutionary or plastic responses to environmental heterogeneity. Species delimitation of shelled gastropods is often based solely on shell characteristics; therefore, morphological variation can lead to taxonomic confusion and inaccurate estimates of species diversity. A comprehensive delimitation approach based on both phenotypic and genotypic information is needed in the face of such taxonomic uncertainty. The common whelk Buccinum undatum, a subtidal gastropod ubiquitous in the North Atlantic, exhibits considerable spatial variation in shell morphology and color. The purpose of the current project was to perform a comprehensive analysis of phenotypic differentiation across the whelk’s distribution and compare with a revised analysis of molecular genetic differentiation among the populations. Phylogenetic reconstruction revealed monophyletic Eastern and Western North Atlantic whelk lineages, which diverged early in the Pleistocene glaciation (~2.1 Mya). Species screening indices indicated cryptic speciation as a result of allopatric divergence. Genetic distances between populations from the two continents were similar to or greater than interspecific genetic distances across several North Pacific and North Atlantic Buccinum species. Morphological differentiation in whelk populations across the North Atlantic reflected this genetic split. Concordant with observed genetic differentiation, Canadian and Icelandic whelk reared in a common garden experiment revealed consistent morphological differences between juveniles from the two continents. Finally, analysis of fine-scaled phenotypic variation of common whelk in Breiðafjörður, Iceland, revealed that shell color diversity, shape and proportion of striped individuals were all related to depth.
... These deviations from the geographical pattern indicate a recent colonization from the Central group or the recent exchange of individuals due to unusual patterns of circulation between these island groups. Therefore, even though the Azorean islands are relatively isolated for long periods of times, occasional dispersal events of rafting and extreme weather might allow the exchange of individuals among distant populations [2,48,122]. ...
Article
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Background In the marine realm, dispersal ability is among the major factors shaping the distribution of species. In the Northeast Atlantic Ocean, the Azores Archipelago is home to a multitude of marine invertebrates which, despite their dispersal limitations, maintain gene flow among distant populations, with complex evolutionary and biogeographic implications. The mechanisms and factors underlying the population dynamics and genetic structure of non-planktotrophic gastropods within the Azores Archipelago and related mainland populations are still poorly understood. The rissoid Cingula trifasciata is herewith studied to clarify its population structure in the Northeast Atlantic Ocean and factors shaping it, with a special focus in intra-archipelagic dynamics. Results Coupling microsatellite genotyping by amplicon sequencing (SSR-GBAS) and mitochondrial datasets, our results suggest the differentiation between insular and continental populations of Cingula trifasciata, supporting previously raised classification issues and detecting potential cryptic diversity. The finding of connectivity between widely separated populations was startling. In unique ways, dispersal ability, habitat type, and small-scale oceanographic currents appear to be the key drivers of C. trifasciata’s population structure in the remote Azores Archipelago. Dispersal as non-planktotrophic larvae is unlikely, but its small-size adults easily engage in rafting. Although the typical habitat of C. trifasciata, with low hydrodynamics, reduces the likelihood of rafting, individuals inhabiting algal mats are more prone to dispersal. Sea-surface circulation might create dispersal pathways for rafts, even between widely separated populations/islands. Conclusions Our results show that gene flow of a marine non-planktotrophic gastropod within a remote archipelago can reveal unanticipated patterns, such that the understanding of life in such areas is far from well-understood. We expect this work to be the starting of the application of SSR-GBAS in other non-model marine invertebrates, providing insights on their population dynamics at distinct geographical scales and on hidden diversity. How transversal is the role played by the complex interaction between functional traits, ecological features, and sea-surface circulation in the population structure of marine invertebrates can be further addressed by expanding this approach to more taxa.
Article
Locomotor activity rhythms of one hyalid and six talitrids were deterermined extending published rhythms to species in three new ecotopes previously not examined in this way: eulittoral – the hyalid, Apohyale prevosti (H. Milne Edwards 1830) with a circatidal rhythm, supralittoral/palustral – the talitrid, ‘Orchestia’ grillus Bosc 1802 and supralittoral/xylophagous talitrid, Macarorchestia remyi (Schellenberg 1950), where activity was random in both. A xylophagous-acclimated population of Platorchestia platensis (Krøyer 1845) living in a secondary ecotope also exhibited random activity. Endogenous diel rhthyms with maximum activity during darkness were present in the supralittoral wrack generalists [P. platensis and Orchestia gammarellus (Pallas 1766)] and sand-burrowing specialists [Americorchestia longicornis (Say 1818) and A. megalophthalma (Spence Bate 1862)]. The tentative order for talitrids examined here and in the literature, from high to low, in their susceptibility to passive, natural dispersal in wrack/driftwood is therefore as follows: O. gammarellus + P. platensis > O. mediterranea Costa 1853 > marsh-hoppers > sand-hoppers > driftwood-hoppers.
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Discoveries of persistent coastal species in the open ocean shift our understanding of biogeographic barriers. Floating plastic debris from pollution now supports a novel sea surface community composed of coastal and oceanic species at sea that might portend significant ecological shifts in the marine environment.
Article
Jonathan Waters provides an introduction to seaweed rafts and their role in the dispersal of marine and coastal species.
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Marine plastic debris floating on the ocean surface is a major environmental problem. However, its distribution in the ocean is poorly mapped, and most of the plastic waste estimated to have entered the ocean from land is unaccounted for. Better understanding of how plastic debris is transported from coastal and marine sources is crucial to quantify and close the global inventory of marine plastics, which in turn represents critical information for mitigation or policy strategies. At the same time, plastic is a unique tracer that provides an opportunity learn more about the physics and dynamics of our ocean across multiple scales, from the Ekman convergence in basin-scale gyres to individual waves in the surfzone. In this review, we comprehensively discuss what is known about the different processes that govern the transport of floating marine plastic debris in both the open ocean and the coastal zones, based on the published literature and referring to insights from neighbouring fields such as oil spill dispersion, marine safety recovery, plankton connectivity, and others. We discuss how measurements of marine plastics (both in situ and in the laboratory), remote sensing, and numerical simulations can elucidate these processes and their interactions across spatio-temporal scales.
Article
The ecology and biogeography of the invertebrate epifauna related to floating Sargassum in the East China Sea were studied. Floating algal rafts composed of only Sargassum horneri (Turner) C. Agardh were collected in the East China Sea in March 2012 when the rafts were distributed not only on the continental shelf but also, unusually, south and east of the Kuroshio Current in the Pacific Ocean. In total, 71 samples collected at 11 stations were studied. Of the 11 invertebrate taxa recognized, harpacticoid copepods were most abundant, followed by malacostracans, and cirripedes. The densities of these three taxa were higher than those of other invertebrates. The number of invertebrate taxa was not correlated with the algal wet weight. There were more invertebrate taxa in the coastal area around Amami-Oshima Island than in other areas. The trajectories of drifting buoys indicated that the algal rafts collected in this area floated longer than those in other areas, allowing the colonization of invertebrates from the surrounding water.
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Termites are major decomposers in terrestrial ecosystems and the second most diverse lineage of social insects. The Kalotermitidae form the second-largest termite family and are distributed across tropical and subtropical ecosystems, where they typically live in small colonies confined to single wood items inhabited by individuals with no foraging abilities. How the Kalotermitidae have acquired their global distribution patterns remains unresolved. Similarly, it is unclear whether foraging is ancestral to Kalotermitidae or was secondarily acquired in a few species. These questions can be addressed in a phylogenetic framework. We inferred time-calibrated phylogenetic trees of Kalotermitidae using mitochondrial genomes of ∼120 species, about 27% of kalotermitid diversity, including representatives of 21 of the 23 kalotermitid genera. Our mitochondrial genome phylogenetic trees were corroborated by phylogenies inferred from nuclear ultraconserved elements derived from a subset of 28 species. We found that extant kalotermitids shared a common ancestor 84 Mya (75–93 Mya 95% HPD), indicating that a few disjunctions among early-diverging kalotermitid lineages may predate Gondwana breakup. However, most of the ∼40 disjunctions among biogeographic realms were dated at less than 50 Mya, indicating that transoceanic dispersals, and more recently human-mediated dispersals, have been the major drivers of the global distribution of Kalotermitidae. Our phylogeny also revealed that the capacity to forage is often found in early-diverging kalotermitid lineages, implying the ancestors of Kalotermitidae were able to forage among multiple wood pieces. Our phylogenetic estimates provide a platform for critical taxonomic revision and future comparative analyses of Kalotermitidae.
Article
Globally, species distributions are shifting in response to environmental change,1 and those that cannot disperse risk extinction.2 Many taxa, including marine species, are showing poleward range shifts as the climate warms.3 In the Southern Hemisphere, however, circumpolar oceanic fronts can present barriers to dispersal.4 Although passive, southward movement of species across this barrier has been considered unlikely,5,6 the recent discovery of buoyant kelp rafts on beaches in Antarctica7,8 demonstrates that such journeys are possible. Rafting is a key process by which diverse taxa-including terrestrial, e.g., Lindo,9 Godinot,10 and Censky et al.,11 and marine, e.g., Carlton et al.12 and Gillespie et al.13 species-can cross oceans.14 Kelp rafts can carry passengers7,15-17 and thus can act as vectors for long-distance dispersal of coastal organisms. The small numbers of kelp rafts previously found in Antarctica7,8 do not, however, shed much light on the frequency of such dispersal events.18 We use a combination of high-resolution phylogenomic analyses (>220,000 SNPs) and oceanographic modeling to show that long-distance biological dispersal events in Southern Ocean are not rare. We document tens of kelp (Durvillaea antarctica) rafting events of thousands of kilometers each, over several decades (1950-2019), with many kelp rafts apparently still reproductively viable. Modeling of dispersal trajectories from genomically inferred source locations shows that distant landmasses are well connected, for example South Georgia and New Zealand, and the Kerguelen Islands and Tasmania. Our findings illustrate the power of genomic approaches to track, and modeling to show frequencies of, long-distance dispersal events.
Article
Aim Historical patterns of ocean circulation in the Southern Hemisphere have been well‐studied, but the effects of coastal oceanography on marine biogeography in this region remain poorly understood relative to northern latitudes. Our study investigates historical and contemporary patterns of migration and dispersal across the Tasman Sea. Location Coastal regions of the Tasman Sea including southeastern Australia, Tasmania and New Zealand. Taxon Hippocampus abdominalis, the pot‐bellied seahorse, one of the most broadly distributed seahorse species, and the only seahorse to have successfully colonized New Zealand from Australia across 2,000 km of open ocean. Methods We used a multilocus genetic dataset to measure population diversity and differentiation from seahorses across the full species range to investigate contemporary and historical demography, and to reconstruct colonization routes across the Tasman Sea. Results Genetic data indicate that seahorses colonized New Zealand from Australia during the previous interglacial‐glacial cycle (12,000–120,000 ybp), and have evolved in relative isolation since the initial establishment event. Contemporary effective population sizes in the newly colonized range are substantially larger than those inferred in Australia, and both appear to be reduced relative to ancestral levels. Australian seahorses are genetically diverse and show high levels of population connectivity, while the distribution of genetic variation in New Zealand suggests an initial colonization of the South Island following by northward migration. Importantly, despite clear evidence that New Zealand seahorses are descendent from Australian ancestors, patterns of contemporary genetic diversity are consistent with trans‐Tasman migration from New Zealand to Australia, suggesting that genetic variation accumulated in the newly colonized range may be contributing to the genetic diversity of Australian seahorses. Main conclusions Despite a largely independent evolutionary trajectory of seahorses separated by the Tasman Sea, haplotype sharing between populations in Australia and New Zealand suggests that secondary genetic exchange is contributing to the contemporary phylogeography of the species. Patterns of genetic structure in H. abdominalis mirror those found in other rafting species, suggesting that adult dispersal via rafting has been an important vector of marine dispersal in this species.
Article
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Populations of the colonial hydroid Obelia geniculata in the White Sea reproduce asexually by frustule formation. Young medusae appear in the plankton during July and August. The number of medusae rarely exceeds 36 per m3, and the average number varies every year from 0.4 to 10 per m3. The size of medusae is smaller than reported from other regions. The umbrella of the largest recorded medusa was only 0.57 mm in diameter and the specimen had just 35 tentacles. Only a few mature medusae were found during the study. The colonies in the White Sea are epiphytic and grow only on laminarian thalli. At the beginning of July there are no colonies on thalli from the upper subtidal zone. By the end of August, colonies of O.␣geniculata had increased in density to 30 per m2. Hydroid recruitment was attributed to active frustule production by colonies living below that zone. The frustules detach from the stems of the hydroids and are found in plankton. Production of frustules on branches occurs continuously during colony growth until water temperatures climb above 0 °C. We found that water temperature in this Arctic environment is generally too low for medusa maturation and planula development in the species. Propagation by frustule formation is the principal means of reproduction in Obelia geniculata within the White Sea, and this phenomenon accounts for the species being a dominant epiphyte on laminarian thalli there.
Conference Paper
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Conference Proceedings; Gordon, D.P., Smith, A.M. and Grant-Mackie, J.A. 1996. Bryozoans in Space and Time. 10th International Bryozoology Conference, Wellington, New Zealand, 1995. National Institute of Water and Atmospheric Research Ltd. Wellington 442p.
Article
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One way to summarize the evolutionary dynamics of species introductions is to estimate how levels of genetic diversity in non-native populations are dif- ferent from those of their source populations. While it is typically assumed that a significant loss of diversity will be associated with species introduc- tions, the actual effect may be more complex, depending on propagule pressure and patterns of diversity and population structure in the native range of a species. We review a number of studies of animal species introductions in which allelic diversity and heterozygosity in the non-native and source ranges of each species can be compared, and find that the typical loss of diversity is minimal. The generality of this pattern may provide new insight into debates over the prevalence of stochastic processes in generating novel phenotypes or coadapted gene complexes in founder populations. These results suggest that the response of founder populations to natural selection in a novel environ- ment is generally more important than the stochastic effects of the founder event itself in determining the evolutionary trajectory of a population.
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Of 59 pieces of flotsam picked up at sea 0.5-16 km from its nearest probable origin, 25% contained at least one live terrestrial animal and 6% had three or more species; one green plant contained 12 species. In many cases a number of conspecific individuals occurred in the same drift item. The animals represented included 19 families of insects, as well as psuedoscorpions, snails, spiders, mites, millipedes, isopods, and worms. Some families were represented by several (up to five) species. Eight drift items recovered approximately 120 km from the nearest land lacked terrestrial animals. A piece of bamboo which washed up on the beach of Cayo Ahogado contained a dipteran and a beetle. Flotsam transport is clearly a significant biogeographic factor among the islands of the Puerto Rican Bank.
Book
This volume results from a symposium entitled "Species and Ufe History Patterns: Geographic and Habitat Variation", held during the National Meeting of the Entomo­ logical Society of America in Denver, Colorado, USA in November, 1979. The stimu­ lus to assemble papers on this theme emerged from continuing discussions with col­ leagues concerning controversies in ecology and evolutionary biology, namely those associated with plant-herbivore interactions, life history theory, and the equilibrium status of communities. The study organisms used in this series of reports are all either herbivorous insects or those intimately associated with plants. In this volume we stress the variation found in life history traits and address some of the problems inherent in current life history theory. We include as life history traits not only traditional variables such as fecundity, size of young, and age to first and peak reproduction, but also diapause and migration, traits that synchronize reproduction with favorable plant resources. Because life history traits of phytophagous insects are influenced in part by spatial and temporal variation in the quality and availability of their host plants, we also consider the role that dis­ continuities in plant quality play in reducing insect fitness. Lastly, much of the tra­ ditional life history theory concerns itself with differences between the evolution of traits or constellations of traits when populations incur primarily density-independent, compared to density-dependent, mortality. Consequently, we address this issue and attempt to shed light on the equilibrium status of several phytophagous insect com­ munities.
Article
It is shown that for allele frequency data a useful measure of the extent of gene flow between a pair of populations is M∘=(1/FST-1)/4, which is the estimated level of gene flow in an island model at equilibrium. For DNA sequence data, the same formula can be used if FST is replaced by NST . In a population with restricted dispersal, analytic theory shows that there is a simple relationship between M̂ and geographic distance in both equilibrium and non-equilibrium populations and that this relationship is approximately independent of mutation rate when the mutation rate is small. Simulation results show that with reasonable sample sizes, isolation by distance can indeed be detected and that, at least in some cases, non-equilibrium patterns can be distinguished. This approach to analyzing isolation by distance is used for two allozyme data sets, one from gulls and one from pocket gophers.
Article
Both mtDNA variation and allozyme data demonstrate that geographic groupings of different color morphs of the starfish Linckia laevigata are congruent with a genetic discontinuity between the Indian and Pacific Oceans. Populations of L. laevigata sampled from Thailand and South Africa, where an orange color morph predominates, were surveyed using seven polymorphic enzyme loci and restriction fragment analysis of a portion of the mtDNA including the control region. Both allozyme and DNA data demonstrated that these populations were significantly genetically differentiated from each other and to a greater degree from 23 populations throughout the West Pacific Ocean, where a blue color morph is predominant. The genetic structure observed in L. laevigata is consistent with traditional ideas of a biogeographic boundary between the Indian and Pacific Oceans except that populations several hundreds kilometers off the coast of north Western Australia (Indian Ocean) were genetically similar to and had the same color morphs as Pacific populations. It is suggested that gene flow may have continued (possibly at a reduced rate) between these offshore reefs in Western Australia and the West Pacific during Pleistocene falls in sea level, but at the same time gene flow was restricted between these Western Australian populations and those in both Thailand and South Africa, possibly by upwellings. The molecular data in this study suggest that vicariant events have played an important role in shaping the broadscale genetic structure of L. laevigata. Additionally, greater genetic structure was observed among Indian Ocean populations than among Pacific Ocean populations, probably because there are fewer reefs and island archipelagos in the Indian Ocean than in the Pacific, and because present-day surface ocean currents do not facilitate long-distance dispersal.
Article
The Pacific marine biota, particularly species with long planktonic larval stages, are thought to disperse widely throughout the Pacific via ocean currents. The little genetic data available to date has supported this view in that little or no significant regional differentiation of populations has been found over large geographical distances. However, recent data from giant clams has demonstrated not only significant regional differentiation of populations, but routes of gene flow that run perpendicular to the main present-day ocean currents. Extensive surveys of genetic variation at eight polymorphic loci in 19 populations of the giant clam Tridacna maxima, sampled throughout the West and Central Pacific, confirmed that the patterns of variation seen so far in T. gigas were not unique to that species, and may reflect a fundamental genetic structuring of shallow-water marine taxa. Populations of T. maxima within highly connected reef systems like the Great Barrier Reef were panmictic (average FST < 0.003), but highly significant genetic differences between reef groups on different archipelagos (average FST = 0.084) and between West and Central Pacific regions (average FST = 0.156) were found. Inferred gene flow was high (Ne m usually > 5) between the Philippines and the Great Barrier Reef, between the Philippines and Melanesia (the Solomon Islands and Fiji), and between the Philippines and the Central Pacific island groups (Marshall Islands, Kiribati, Tuvalu and Cook Islands). Gene flow was low between these three sets of island chains (Ne m < 2). These routes of gene flow are perpendicular to present-day ocean currents. It is suggested that the spatial patterns of gene frequencies reflect past episodes of dispersal at times of lower sea levels which have not been erased by subsequent dispersal by present-day circulation. The patterns are consistent with extensive dispersal of marine species in the Pacific, and with traditional views of dispersal from the Indo-Malay region. However, they demonstrate that dispersal along present-day ocean surface currents cannot be assumed, that other mechanisms may operate today or that major dispersal events are intermittent (perhaps separated by several thousands of years), and that the nature and timing of dispersal of Pacific marine species is more complex than has been thought.
Article
Unlike populations of many terrestrial species, marine populations often are not separated by obvious, permanent barriers to gene flow. When species have high dispersal potential and few barriers to gene flow, allopatric divergence is slow. Nevertheless, many marine species are of recent origin, even in taxa with high dispersal potential. To understand the relationship between genetic structure and recent species formation in high dispersal taxa, we examined population genetic structure among four species of sea urchins in the tropical Indo-West Pacific that have speciated within the past one to three million years. Despite high potential for gene flow, mtDNA sequence variation among 200 individuals of four species in the urchin genus Echinometra shows a signal of strong geographic effects. These effects include (1) substantial population heterogeneity; (2) lower genetic variation in peripheral populations; and (3) isolation by distance. These geographic patterns are especially strong across scales of 5000-10,000 km, and are weaker over scales of 2500-5000 km. As a result, strong geographic patterns would not have been readily visible except over the wide expanse of the tropical Pacific. Surface currents in the Pacific do not explain patterns of gene flow any better than do patterns of simple spatial proximity. Finally, populations of each species tend to group into large mtDNA regions with similar mtDNA haplotypes, but these regional boundaries are not concordant in different species. These results show that all four species have accumulated mtDNA differences over similar spatial and temporal scales but that the precise geographic pattern of genetic differentiation varies for each species. These geographic patterns appear much less deterministic than in other well-known coastal marine systems and may be driven by chance and historical accident.
Article
Within the sea urchin genus Heliocidaris, changes in early embryonic and larval development have resulted in dramatic differences in the length of time larvae spend in the plankton before settling. The larvae of one species, H. tuberculata, spend several weeks feeding in the plankton before settling and metamorphosing into juveniles. The other species, H. erythrogramma, has modified this extended planktonic larval stage and develops into a juvenile within 3-4 days after fertilization. We used restriction site polymorphisms in mitochondrial DNA to examine the population genetic consequences of these developmental changes. Ten restriction enzymes were used to assay the mitochondrial genome of 29 individuals from 2 localities for H. tuberculata and 62 individuals from 5 localities for H. erythrogramma. Within H. tuberculata, 11 mitochondrial genotypes were identified. A GST analysis showed high levels of genetic exchange between populations separated by 1,000 kilometers of open ocean. In contrast, in H. erythrogramma, 13 mitochondrial genotypes differing by up to 2.33% were geographically partitioned over spatial scales ranging from 800 to 3,400 kilometers. Between distant localities, there was complete mitochondrial lineage sorting and large sequence divergence between resulting clades. Over much smaller spatial scales (< 1,000 km), genetic differentiation was due to the differential sorting of very similar genotypes. This pattern of mitochondrial variation suggests that these population differences have arisen recently and may reflect the historical interplay between the restricted dispersal capabilities of H. erythrogramma and the climatic and geological changes associated with Pleistocene Ice Ages.
Article
Excirolana braziliensis is a dioecious marine isopod that lives in the high intertidal zone on both sides of tropical America. It lacks a dispersal phase and displays a remarkable degree of genetic divergence even between localities less than 1 km apart. Nine populations of this nominal species from both sides of the Isthmus of Panama and one population of the closely allied species, Excirolana chamensis, from the eastern Pacific were studied for 2 yr for allozymic temporal variation in 13 loci and for 3 to 4 yr for morphological variation in nine characters. The genetic and morphological constitution of 9 out of 10 populations remained stable. Allele frequencies at two loci and overall morphology in a tenth beach occupied by E. braziliensis changed drastically and significantly between 1986 and 1988. The change in gene frequency is too great to explain by genetic drift occurring during a maximum of 14 generations regardless of assumed effective population size; drift is also unlikely to have caused observed changes in morphology. Selective survival of a previously rare genotype is more plausible but still not probable. The most credible explanation is that the resident population at this locality became extinct and that the beach was recolonized by immigrants from another locality. Such infrequent episodes of extinction and recolonization from a single source may account for the large amount of genetic divergence between local populations of E. braziliensis. However, the low probability of large temporal genetic change even in a species such as this, in which gene flow between local demes is limited and generation time is short, suggests that a single sample through time is usually adequate for reconstructing the genetic history of populations.
Article
Numerous studies of population structure in sessile clonal marine invertebrates have demonstrated low genotypic diversity and nonequilibrium genotype frequencies within local populations that are monopolized by relatively few, highly replicated genets. All of the species studied to date produce planktonic sexual propagules capable of dispersing long distances; despite local genotypic disequilibria, populations are often panmictic over large geographic areas. The population structure paradigm these species represent may not be typical of the majority of clonal invertebrate groups, however, which are believed to produce highly philopatric sexual propagules. I used allozyme variation to examine the population structure of the temperate soft coral, Alcyonium rudyi, a typical clonal species whose sexually produced larvae and asexually produced ramets both have very low dispersal capabilities. Like other clonal plants and invertebrates, the local population dynamics of A. rudyi are dominated by asexual reproduction, and recruitment of new sexually produced genets occurs infrequently. As expected from its philopatric larval stage, estimates of genetic differentiation among populations of A. rudyi were highly significant at all spatial scales examined (mean θ = 0.300 among 20 populations spanning a 1100-km range), suggesting that genetic exchange seldom occurs among populations separated by as little as a few hundred meters. Mapping of multilocus allozyme genotypes within a dense aggregation of A. rudyi ramets confirmed that dispersal of asexual propagules is also very limited: members of the same genet usually remain within < 50 cm of one another on the same rock surface. Unlike most previously studied clonal invertebrates, populations of A. rudyi do not appear to be dominated by a few widespread genets: estimates of genotypic diversity (Go ) within 20 geographically distinct populations did not differ from expectations for outcrossing, sexual populations. Despite theoretical suggestions that philopatric dispersal combined with typically small effective population sizes should promote inbreeding in clonal species, inbreeding does not appear to contribute significantly to the population structure of A. rudyi. Genet genotype frequencies conformed to Hardy-Weinberg expectations in all populations, and inbreeding coefficients (f) were close to zero. In general, the population structure of A. rudyi did not differ significantly from that observed among outcrossing sexual species with philopatric larval dispersal. Age estimates suggest, however, that genets of A. rudyi live for many decades. Genet longevity may promote high genotypic diversity within A. rudyi populations and may be the most important evolutionary consequence of clonal reproduction in this species and the many others that share its dispersal characteristics.
Article
Viviparous, branching corals such as Seriatopora hystrix are expected to generate most recruits through asexual reproduction (fission or fragmentation) but are expected to use sexual reproduction to produce widely dispersed colonists. In this study, allozyme electrophoresis was used to test for variation in the relative contributions of sexual and asexual reproduction to recruitment and to assess the apparent scale of larval dispersal (gene flow) in the central Great Barrier Reef. Fifty-seven collections (within ≤ 25 m(2) ) of fragments from sets of approximately 40 colonies were made (where possible) within each of five habitats on each of 12 reefs. These reefs, within the central region of the Great Barrier Reef, were separated by up to 90 km and included one inner-shelf continental island and groups of seven midshelf reefs and four outer-shelf reefs. Most collections contained a high level of multilocus genotypic diversity and hence showed little evidence of recruitment through fragmentation, although the majority of collections displayed large and consistent deficits of heterozygotes. Allele frequencies varied greatly among collections (FST = 0.43), and this variation was sufficient to explain two-thirds of observed deficiencies of heterozygotes via a Wahlund effect. A hierarchical assessment of FST values revealed that 45% of allelic variation occurred among reefs (FST = 0.20), and only 16% of variation within reefs was explained by variation among five major habitat types (FST = 0.05). A relatively small component of the total variation among samples was attributable to across-shelf variation among the groups of middle- and outer-shelf reefs (FST = 0.03); however, the outer-shelf reefs form a single UPGMA cluster separate from all but 4 of the other 43 collections. These data imply that widespread dispersal does occur but that the direction or magnitude of gene flow may be influenced by the along-shelf movement of major ocean currents and weather-dependent currents on or near reefs. Each reef, therefore, forms a partially isolated and highly subdivided population.
Article
This study compiled available information on the dispersal distance of the propagules of benthic marine organisms and used this information in the development of criteria for the design of marine reserves. Many benthic marine organisms release propagules that spend time in the water column before settlement. During this period, ocean currents transport or disperse the propagules. When considering the size of a marine reserve and the spacing between reserves, one must consider the distance which propagules disperse. We could find estimates of dispersal distance,for 32 taxa; for 25 of these, we were also able to find data on the time the propagules spent dispersing. Dispersal distance ranged from meters to thousands of kilometers, and time in the plankton ranged from minutes to months. A significant positive correlation was found between the log-transformed duration in the plankton and the log-transformed dispersal distance (r =. 0.7776, r(2) = 0.60, df = 1, 25, P = 0.000); the more time propagules spend in the water column the further they tend to be dispersed. The frequency distribution of the log-transformed dispersal distance is bimodal (kurtosis = -1.29, t = -4.062, P < 0.001) with a gap between 1 and 20 km. Propagules that dispersed <1 km spent less time in the plankton (<100 h), or if they remained in the plankton for a longer period, they tended to remain in the waters near the bottom. Propagules that dispersed >20 km spent more than 300 h in the plankton. The bimodal. nature of the distribution suggests that evolutionary constraints may reduce the likelihood of evolving mid-range dispersal strategies (i.e., dispersal between 1 and 20 km) resulting in two evolutionarily stable dispersal strategies: dispersal <1 km or >similar to20 km. We suggest that reserves be designed large enough to contain the short-distance dispersing propagules and be spaced far enough apart that long-distance dispersing propagules released from one reserve can settle in adjacent reserves. A reserve 4-6 km in diameter should be large enough to contain the larvae of short-distance dispersers, and reserves spaced 1020 km apart should be close enough to capture. propagules released from adjacent reserves.
Article
Geographical surveys of genetic variation provide an indirect means of tracing movements made between marine populations by larvae and other propagules. Genetic markers can provide strong evidence that populations are closed (self-recruiting) because genetic differentiation is highly sensitive to migration. However, inferences based on genetic data must necessarily be based on models that make assumptions concerning inheritance, selective neutrality of markers, and equilibrium between genetic drift, migration, and mutation. We briefly introduce the types of genetic markers that can be used to infer demographic connections between populations and the forces causing evolutionary changes in these markers, and then we outline six patterns revealed by geographic surveys of genetic markers in marine species. Four of these patterns represent the possible combinations of high or low migration rates and large or small effective population sizes; two others are due to history and natural selection. Future genetic surveys should include more detailed spatial and temporal sampling and employ analyses of DNA sequence data that can reveal the signatures of natural selection and historical changes.
Article
Driftwood is an important source of habitat and food for the marine ecosystem, including the deep-sea floor. Driftwood, during its seaward journey, is both habitat and food source for many aquatic and terrestrial plants and animals. In addition, some driftwood controls stream velocities, stabilizes stream banks, and creates and protects fish spawning areas. Part I of the book looks at some present-day actions, including damming streams and rivers, which prevent driftwood reaching the sea. Without driftwood, stream channels and coastal sand dunes are destabilized and wood is eliminated from the food chains of estuaries and the deep ocean. In part II the journey taken by water and wood from the mountains to the ocean is described. The story is set prior to the settlement of the Pacific Northwest by Europeans. Part III looks at the collision of European settlement with the environment. Settlement began immediately to affect the waterways and ancient forests of the Pacific Northwest, contributing to current environmental crises. -from Authors
Article
Three families, 5 genera and 7 species of termites were found in the Krakatau Islands. Between 1908-1982, 2 species seem to have been replaced by other congeneric species in Rakata Besar, the largest island of the group. Termites in the islands were characterized taxonomically by the dominance of lower termites (Kalotermitidae and Rhinotermitidae) and ecologically by wood feeders constructing their nests in the wood itself, whereas those of the mainland (W Java) were characterized taxonomically by the dominance of higher termites (Termitidae) and ecologically by wood or humus feeders constructing their nests in the soil. The importance of dispersal ability by rafting and asymmetrical interspecific competition is discussed in an attempt to explain the presence or absence of termite groups with different life types in the islands.-from Author
Article
Plant populations have long been noted to migrate faster than predicted based on their life history and seed dispersal characteristics (i.e., Reid's paradox of rapid plant migration). Although precise mechanisms to account for such phenomena are not fully known for all plant species, a combination of theoretical and empirically driven mechanisms often resolves this paradox. Here, we couple a series of direct and indirect field and laboratory exercises on one marine macrophyte, Zostera marina L. (eelgrass), to measured distances between new patches and established beds in order to elucidate the long-distance dispersal and colonization potential of this marine seagrass. Detached, floating reproductive shoots with mature seeds were found to remain positively buoyant for up to 2 wk and retain mature seeds for up to 3 wk before release under laboratory conditions. Analysis of the, detritus wrack along a remote shoreline found reproductive fragments with viable seeds up to 34 km from established, natural beds. Analysis of different regions of the Chesapeake Bay and coastal bays of the Delmarva Peninsula that once supported eelgrass populations, revealed natural patches at 13 sites ranging from 1 to 108 km from established populations. A combination of tidal currents and wind influences has the potential to move a passive particle at the surface (e.g., a floating reproductive fragment) up to 23 km in a 6-h tidal window suggesting that most unvegetated areas in this region that can support eelgrass are within the colonization potential envelope. We suggest that, when combined with earlier work on seed dispersal ecology of this species, eelgrass has strong qualities for high colonization potential of new habitat. The finding of natural patches at such great distances from established beds when studied in the context of the dispersal mechanism (currents and wind) make the dispersal distances of this species one of the highest for angiosperms, comparable in scale to mangroves and coconuts. This new understanding of the dispersal dynamics of eelgrass is critical in the context of seagrass restoration in areas distant from established beds, maintenance of existing populations threatened by anthropogenic inputs of sediments arid nutrients, and examining metapopulation concepts in seagrass ecology.
Chapter
In floatation experiments it appeared that seeds of some chenopods as well as those of Plantago maritima, Limonium vulgare, Spergularia maritima and Rumex crispus * remained afloat some hours only. Seeds (grains) of most grasses and fruits of Suaeda maritima and Atriplex prostrata as well as achenes of Aster tripolium were kept afloat some days up to some weeks. Fruits of Halimione tripolium were kept afloat some days up to some weeks. Fruits of Halimione portulacoides, Atriplex littoralis, Triglochin maritima, Plantago maritima, Limonium vulgare and Rumex crispus, some grains of Spartina anglica, together with seeds (nuts) of Matricaria maritima and achenes of Sonchus arvensis are well adapted to long-lasting floating in sea water (some weeks up to several months). Long-lasting floating in sea water and even long-lasting submersion will not destroy the germination power of most species. Two experiments with floating sunflower seeds (Helianthus annuus), performed under different weather conditions, showed that dispersal of floating seeds may take place in all directions and over considerable distances.
Chapter
The great majority of ecological literature assumes that communities are in equilibrium and that interspecific competition plays a primary role in their organization (e.g., Lotka 1931, Gause 1934, Slobodkin 1961, MacArthur and Wilson 1967, Schoener 1974, Hutchinson 1977). For insects, several hypotheses have been invoked when attempting to explain coexistence under equilibrium conditions. McClure and Price (1975) suggest that coexistence in a guild of sycamore-feeding leafhoppers may be partially explained by frequency-dependent competitive ability, since at high densities each species adversely affects its own fitness more than that of its competitors. However, by far the most common explanation for equilibrium existence is resource partitioning, whereby species reduce interspecific competition by exploiting different aspects of resources (e.g., Connell 1961, MacArthur 1972, Cody 1974, Schoener 1974, Harper 1977, Diamond 1978). As Strong points out in his contribution (Chapter 10), competition has been invoked primarily by ecologists working with vertebrates, plants or marine organisms rather than insects.
Article
This book had its origin when, about five years ago, an ecologist (MacArthur) and a taxonomist and zoogeographer (Wilson) began a dialogue about common interests in biogeography. The ideas and the language of the two specialties seemed initially so different as to cast doubt on the usefulness of the endeavor. But we had faith in the ultimate unity of population biology, and this book is the result. Now we both call ourselves biogeographers and are unable to see any real distinction between biogeography and ecology.
Article
Crepidula fornicata(Linné) was introduced into Britain and Europe with oysters early in this century. The source populations were probably from Long Island Sound of the Northwestern Atlantic, U.S.A. In order to determine the genetic similarity of the introduced and native populations, starch-gel electrophoresis was performed on 6 native populations from Maine to Long Island Sound. These results were compared with those for one population from Portsmouth, England. The degree of similarity among New England sites was not related to the geographical distance between sites. There were no clines in gene frequencies. The year-to-year variation at one site was often larger than variation between sites. Ail Nei's D values were very small, compared with those between species, ranging from 0.003 to 0.016 for New England samples. The English population had Nei's D values of 0.002 to 0.012 from the New England samples, and hence was not divergent. At no locus was the Portsmouth population significantly different in gene frequencies from all the new England samples. Genetic distances between species of Crepidula are usually in the range of 1.0–2.0. The differences between New England sites can be attributed to sampling error or to local variation in gene frequency caused by variation in source of recruitment. The species is unified by its planktonic larvae and a fairly uniform habitat within New England. Heterozygosity and other measures of genetic variation were lower for the Portsmouth population than for any of the New England samples. The absence of some alleles in the Portsmouth population could be due in part to sampling error associated with small sample size or the loss of some rare alleles from the population.
Article
The Recent members of the genus Nodilittorina in the eastern Pacific Ocean are revised. Hitherto eight to 10 species have been recognized, but this total is now increased to 18, of which three are named as new. The majority of the taxa fall into three species complexes: six in the N. porcata group, two in the N. modesta group, and six in the N. aspera group. Within each of these complexes, species identification from shells alone is difficult, as a result of remarkable intraspecific variation. Since all species of the genus have pelagic eggs and planktotrophic development, it is suggested that this variation may be partly of ecophenotypic origin. Discrimination is confirmed by species-specific characters of the penis and supported by some features of the spermatozoa and pallial oviducts. Radular characters are more constant throughout the genus. The four additional species are N. araucana, N. peruviana. N. galapagiensis, and N. fernandezensis. Anatomical features, radulae, and a range of shells are figured for each species. Geographical distributions are mapped in detail (from 777 samples examined) and cases of sympatric occurrence provide strong support for the discrimination of members of the three species complexes. There is insufficient morphological differentiation among the species to permit formal phylogenetic analysis. Some of them show similarities with congeners in the western Atlantic, but there are no obvious sister-species pairs. A species endemic to the oceanic islands off Chile, N. fernandezensis, shows a clear relationship with a largely temperate Southern Hemisphere group, the subgenus Austrolittorina (here redefined). Of particular interest are the distributions of the 15 Nodilittorina species within the Tropical Eastern Pacific Region (TEP; hitherto referred to as the "Panamic Province" in the molluscan literature). These strongly support the classification of the region into four provinces, Cortez. Mexican, Panamic (with a southern Ecuadorean element), and Galápagos, as previously suggested for fishes, which (like Nodilittorina species) are dependent upon shallow-water rocky substrates. The boundaries between these provinces correspond with habitat gaps, of either open water (Galápagos) or inhospitable coastline of sand, mud, and mangroves (Sinaloan, Central American and Colombian Gaps). The implications for processes of dispersal and speciation, and also for future systematic studies of the rocky-shore fauna, are discussed.
Article
The structure, abundance, and biomass of the community of macroinvertebrates on the oceanic floating substrata were studied in the northwestern part of the Pacific Ocean. A model of the dynamics of this community after Lepas pectinata settling was developed. A succession was revealed; namely, during the first two weeks, bryozoans are the dominant animals, and then, the barnacle L. pectinata prevails. By the end of the model time (26 days), the abundance and biomass of barnacles increase further. The climax state for the community was not reached. The coexistence mechanisms of different taxa of invertebrates on the oceanic floating substrata are discussed. It is stressed that coexistence is possible even if the food spectra are completely overlapped.
Article
Geochemically five distinct groups could be distinguished and some could be linked to specific eruptions. Group A pumice originated from a submarine eruption off Zavodovski Island in the South Sandwich Island Group in 1962. The source of Group B is unknown, but the Mid-Atlantic Ridge in the South Atlantic Ocean is indicated. The Group C pumice was found only on the west coast of Australia. The source is in the southern Indian Ocean, probably from the Mid-Indian Ridge. The fourth group originated from a submarine eruption along the Tonga Trench in the Pacific Ocean. Group E originated from the 1883 eruption of Krakatoa, and it is still the most abundant type of drift pumice that can be found.-from Authors
Chapter
Entanglement, ingestion, and ghost-fishing are well-documented biologically damaging effects of marine debris. Debris may also smother benthic communities on soft and hard bottoms (Parker 1990). For a number of organisms, however, plastic debris provides a positive opportunity, creating new habitats in the form of numerous, semipermanent floating islands, which are driven by winds and currents around the world’s oceans. Although these epibiotic assemblages seem to be most common in warm-water regions, biologically encrusted plastic items have already been found at sites ranging from the Subantarctic to the Equator (Gregory et al. 1984; Gregory 1990a, 1990b). This paper focuses on studies by the three authors at sites in the Western Atlantic and the Southern Pacific, with findings of worldwide relevance.
Article
Ocean-going ships carry, as ballast, seawater that is taken on in port and released at subsequent ports of call. Plankton samples from Japanese ballast water released in Oregon contained 367 taxa. Most taxa with a planktonic phase in their life cycle were found in ballast water, as were all major marine habitat and trophic groups. Transport of entire coastal planktonic assemblages across oceanic barriers to similar habitats renders bays, estuaries, and inland waters among the most threatened ecosystems in the world. Presence of taxonomically difficult or inconspicuous taxa in these samples suggests that ballast water invasions are already pervasive.