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Dispersal of the Solitary Coral Balanophyllia Elegans by Demersal Planular Larvae
Ecology
Abstract
The solitary scleractinian coral Balanophyllia elegans has nonpelagic planulae which remain on the bottom for several days before attaching and undergoing metamorphosis. Laboratory observations and field experiments suggest that the mean larval dispersal distance is <0.5 m from the parent. An isolated, 16-yr-old artificial reef has not been colonized by B. elegans, although a breeding population is present 4 km away and transplant experiments showed that the species can live and reproduce there. The corals tend to be spatially aggregated, which may result from their very limited dispersal. The dispersal of B. elegans planulae from a point source on a large settling plant placed on the sea bottom can be described by a diffusion model assuming random movement and settling behavior of the larvae. The maximum rate at which the species can spread demersally, even assuming exponential population growth is occurring, is calculated to be <0.1 m/yr. Since such a rate would not allow dispersal over the coral's 2000-km range even over evolutionary time, occasional dispersal by other means is considered probable. Previous observations of morphological variation in B. elegans may be related to low rates of gene flow in this species with demersal larvae and sessile adults. Distributions of other Balanophyllia species in the eastern Pacific suggest that limited dispersal ability may have played a role in the evolution of this genus.
... The variation in larval dispersal capability among species can be enormous: the larvae of some species spend many I Present address: Department of Zoology and Physiology, Louisiana State University, Baton Rouge, Louisiana 70803-1725. weeks in the plankton (Strathmann 1987) and can be found thousands of kilometers offshore (Scheltema 1971(Scheltema , 1988; the larvae of other species settle literally in the shadow of their mothers (Ostarello 1976;Gerrodette 1981;Olson 1985;Grosberg 1987). Consequently, interspecific differences in the mode of larval development have been causally linked to differences in geographical range (Scheltema 1971(Scheltema , 1977Shuto 1974), rates of colonization (Scheltema 1977;Valentine and Jablonski 1983), and levels of gene flow (Scheltema 1977;Hedgecock 1986;Knowlton and Jackson 1993). ...
... Densities of P. stearnsii in these habitats may reach 25 per m? (Fadlallah and Pearse 1982a). Densities of B. elegans at similar depths can be an order of magnitude greater (Gerrodette 1981;Fadlallah 1983a). Both species are dioecious, with nearly even sex ratios, and exhibit reproductive peaks in the late winter and early spring (Fadlallah and Pearse 1982a,b). ...
... Female B. elegans brood up to 50 large (2-3 mm), nonfeeding planulae annually. These larvae disperse very locally, often attaching within 40 em of their mother after crawling over hard substrata for only a few days (Gerrodette 1981;Fadlallah 1983a). ...
When the level of gene flow among populations depends upon the geographic distance separating them, genetic differentiation is relatively enhanced. Although the larval dispersal capabilities of marine organisms generally correlate with inferred levels of average gene flow, the effect of different modes of larval development on the association between gene flow and geographic distance remains unknown. In this paper, I examined the relationship between gene flow and distance in two co-occurring solitary corals. Balanophyllia elegans broods large, nonfeeding planulae that generally crawl only short distances from their place of birth before settling. In contrast, Paracyathus stearnsii free-spawns and produces small planktonic larvae presumably capable of broad dispersal by oceanic currents. I calculated F-statistics using genetic variation at six (P. stearnsii) or seven (B. elegans) polymorphic allozyme loci revealed by starch gel electrophoresis, and used these F-statistics to infer levels of gene flow. Average levels of gene flow among twelve Californian localities agreed with previous studies: the species with planktonic, feeding larvae was less genetically subdivided than the brooding species. In addition, geographic isolation between populations appeared to affect gene flow between populations in very different ways in the two species. In the brooding B. elegans, gene flow declined with increasing separation, and distance explained 31% of the variation in gene flow. In the planktonically dispersed P. stearnsii distance of separation between populations at the scale studied (10-1000 km) explained only 1% of the variation in gene flow between populations. The mechanisms generating geographic genetic differentiation in species with different modes of larval development should vary fundamentally as a result of these qualitative differences in the dependence of gene flow on distance.
... Among Scleractinia, the genus Balanophyllia has~50 species and a world-wide distribution (Vaughan and Wells, 1943). The distribution of these species is the result of several factors (e.g., larval dispersal ability, environmental conditions) which had important consequences for biogeography and species evolution, which include intrinsic larval dispersal ability (Gerrodette, 1981). The genus Balanophyllia has colonized the Mediterranean Sea since the Miocene or at least the early Pliocene (Vertino et al., 2014). ...
... In particular, the current study was performed on two azooxanthellate corals, namely B. elegans and B. regia, and the zooxanthellate B. europaea. The first appearance in the fossil record of the species B. elegans dates back to the middle Pliocene (~5.3 to 2.6 Mya) on the Pacific Coast of North America (Gerrodette, 1981). The Pacific Ocean during the Paleogene (between 65 and 23 Ma) was connected to the other oceans (Lyle et al., 2008) until the closure of the Panama Gateway around 3 Ma (Coates and Obando, 1996). ...
The diversity in the skeletal features of coral species is an outcome of their evolution, distribution and habitat. Here, we explored, from macro- to nano-scale, the skeletal structural and compositional characteristics of three coral species belonging to the genus Balanophyllia having different trophic strategies. The goal is to address whether the onset of mixotrophy influenced the skeletal features of B. elegans, B. regia, and B. europaea. The macroscale data suggest that the presence of symbiotic algae in B. europaea can lead to a surplus of energy input that increases its growth rate and skeletal bulk density, leading to larger and denser corals compared to the azooxanthellate ones, B. regia and B. elegans. The symbiosis would also explain the higher intra-skeletal organic matrix (OM) content, which is constituted by macromolecules promoting the calcification, in B. europaea compared to the azooxanthellate species. The characterization of the soluble OM also revealed differences between B. europaea and the azooxanthellate species, which may be linked to diverse macromolecular machineries responsible for skeletal biosynthesis and final morphology. Differently, the crystallographic features were homogenous among species, suggesting that the basic building blocks of skeletons remained a conserved trait in these related species, regardless of the trophic strategy. These results show changes in skeletal phenotype that could be triggered by the onset of mixotrophy, as a consequence of the symbiotic association, displaying remarkable plasticity of coral skeletons which repeatedly allowed this coral group to adapt to a range of changing environments throughout its geological history.
... One of the earliest reports of limited dispersal is the solitary cup coral Balanophyllia elegans . The crawling larvae (i.e., nonpelagic) of this species have been observed to settle on average <0.5 m away from the maternal colonies (Gerrodette 1981 ;Fadlallah and Pearse 1982 ), which concurs with the low levels of gene fl ow among populations separated by as few as 4-30 m, and a pattern of isolation by distance (IBD) along most of the Pacifi c coast of North America (Hellberg 1994(Hellberg , 1996. ...
... At a slightly larger spatial scale , dispersal that is restricted to 1-10 km also appears to be more common among brooders than in broadcast spawners, albeit exceptions clearly exist Corallium rubrum : Costantini et al. ( 2007b ) and Ledoux et al. ( 2010a ) Balanophyllia elegans : Gerrodette ( 1981 ) and Hellberg ( 1994Hellberg ( , 1996 ( 2011 ), Pinzón et al. ( 2013 ) and Torda et al. ( 2013b ) For further detail about the spatial extent of dispersal in coral taxa please refer to the text, and reviews by van Oppen and Gates ( 2006 ) and Jones et al. ( 2009 ) (see below). The presence of population genetic structure at inter-reef and larger spatial scales (Hellberg 1996 ;Ayre and Hughes 2000 ;Underwood et al. 2009 ) suggests the commonness of localized recruitment over ecological time scales among brooding corals . ...
Concern about the future of coral reef communities, and the recognition that larval dispersal plays a key role in the resilience of populations has spurred research to determine whether populations are connected by larval exchange or instead maintained by local supply of larvae. In the process of these endeavors, the generalized belief that marine populations were well connected via larval dispersal gave way to the notion that local retention of larvae is common among many benthic species, and that patterns of population connectivity are very complex owing to the multitude of factors and scales involved in larval transport. This review synthesizes the progress in our understanding of the processes affecting dispersal and connectivity in anthozoans (primarily corals), and examines the caveats inherent to the genetic and modeling approaches used in most connectivity studies. Conclusions about the scales of larval dispersal in anthozoans are often species-specific and almost always location-specific. However, some generalities can be recognized. Extreme cases of larval philopatry are more common in brooders. Conversely, large-scale dispersal is seemingly more common in broadcast spawners where a pre-competency period and a potentially long-lived dispersal phase provides a template for more distant dispersal. In between these extremes the divide is less clear and complex patterns of connectivity are widespread between the two developmental modes. Resolving connectivity at scales relevant to demographics remains a major challenge and considerable methodological improvements are needed. Nevertheless, both genetic analyses and biophysical modeling are rapidly maturing and provide increasingly sophisticated analyses of connectivity.
... Glynn et al. (2008) observed that T. coccinea planulae settlement occurred from 1 to 3 d. In the laboratory planulae of Balanophyllia elegans attached to settling plates and began metamorphosis in 3 d (Gerrodette, 1981). Settlement-competency periods of 1-7 d are typical of tropical corals (Edmondson, 1946). ...
... Larvae of B. elegans dispersed a mean distance of ,0.5 m before settlement, indicating that its larval dispersal in the family may be very limited. However, since limited dispersal is neither a necessary nor a sufficient condition for aggregation, inferences about patterns of settlement cannot be made based on spatial distribution of adult colonies alone (Gerrodette, 1981). ...
The azooxanthellate sun corals Tubastraea coccinea and T. tagusensis are invasive species which were introduced into Brazilian shallow-water tropical rocky reefs by oil and gas platforms. Both species are simultaneous hermaphrodites and brooders. Histological analysis shows a continuous reproduction with the presence of different stages of development of oocytes, spermatic cysts and larvae occurring together in the same polyps (overlapping). Gametogenesis, embryogenesis, planulation and settlement were observed. Although most of the colonies showed only oocytes, none had only testes. Spermatic cysts were observed in 8.3% of T. coccinea colonies and in 5.5% of colonies of T. tagusensis. The maximum diameter of oocyte of T. tagusensis (1252.5 µm) was greater than T. coccinea (901.8 µm) and mature spermaries 700 µm in diameter formed the typical arrangement of ‘bouquets’. Although all colonies showed oocytes throughout the year, two reproductive peaks of 3–4 months duration were observed. The larvae of T. coccinea and T. tagusensis had a competency period of 18 d in aquaria and settled near the parental colony. The investigation of gametogenesis, temporal patterns of reproduction, fecundity and sexual maturation helps to explain the rapid expansion in to new habitats and high population growth in these invasive sun corals.
... There are two basic ways that population geneticists estimate gene flow. Direct measurements (sensu Slatkin 1985a) involve the tracking of individual or group movements (e.g., Gerrodette 1981;Burton and Swisher 1984;Olson 1985;Grosberg 1987Grosberg , 1991Stoner 1990;Willis and Oliver 1990;Jones et al. 1999;Swearer et al. 1999). In principle, these migration or dispersal patterns could then be translated into estimates of gene flow by determining whether the movements lead to successful breeding within the recipient population. ...
... The pattern of isolation by distance should be most apparent in species that live in continuously distributed habitats and whose propagules have limited dispersal potential (e.g., Ayre and Dufty 1994;reviewed in Knowlton and Jackson 1993). For instance, the cup coral Balanophyllia elegans internally broods large, sexually produced, demersal larvae, and lives in the shallow subtidal and low intertidal along the West Coast of North America (Gerrodette 1981;Fadlallah 1983). Hellberg (1994Hellberg ( , 1995Hellberg ( , 1996 found a highly significant negative relationship between genetic (M , inferred from allozymes) and geographic distance in B. elegans. ...
... In contrast, the zooxanthellate Balanophyllia europaea displays simultaneous hermaphroditism with asynchronous gametogenesis (Goffredo and Teló 1998;Goffredo et al. 2002). Of the three Balanophyllia species for whom reproduction has been characterized, all brood larvae, which then disperse as demersal planulae prior to metamorphosis (Gerrodette 1981). This dispersal mode results in limited dispersal and larvae settling close to their parent, potentially leading to high levels of self-fertilization and in-breeding (Hellberg and Taylor 2002;Goffredo et al. 2004). ...
Deep-sea scleractinian cup corals are prominent members of Southern Ocean megabenthic communities, though little is known about their life history. This study used paraffin histology and scanning electron microscopy to characterize the reproduction of the scleractinian coral Balanophyllia malouinensis (Squires, 1961) from Burdwood Bank in the Drake Passage. Samples were taken in April and May via otter trawls, Blake trawls, and dredges on three separate cruises: one on the RV Lawrence M. Gould in 2006, and two on the RV Nathaniel B. Palmer in 2008 and 2011. B. malouinensis is gonochoric with rare hermaphroditism. All four spermatocyst stages were seen simultaneously in males; similarly, most females contained oocytes at varying stages of development, though seasonality or periodicity could not be determined without a wider range of sample dates. Average fecundity was 241 ± 184 oocytes/individual (n = 38) and not correlated to cup size. Maturing larvae were found in the mesenteries and coelenteron of females, indicating B. malouinensis broods its larvae. This study was the first to characterize the reproduction of a deep-sea Balanophyllia species and adds to a small but growing body of work seeking to understand the unique benthic communities of Burdwood Bank.
... Field evidence also indicates that larvae can behave demersally and have limited dispersal distances. For instance, some planktotrophic larvae are known to draw close to the seabed during the latter part of their life cycle (Andrews, 1983;Baker, 2003;Welch, Forward, & Howd, 1999), and lecithotrophic Balanophyllia elegans coral larvae are demersal throughout their development (Gerrodette, 1981 (Prytherch, 1929). (Prytherch, 1929). ...
• Benthic marine invertebrates, such as oysters, rely on larval recruitment for their populations to persist. This can be by self‐recruitment to the natal population or recruitment from geographically distant populations.
• Marine invertebrate larvae are increasingly understood to influence their dispersal through vertical migrations, based on a combination of responses to external cues and the larvae's ontogenetic stage.
• This study examined the larval behaviour of the European oyster Ostrea edulis in laboratory experiments. The aim was to establish if larvae show systematic behaviour that could affect dispersal. Vertical distribution, swimming speeds, and behaviour of O. edulis larvae were quantified throughout their ontogenetic development, and under scenarios of light/dark, food/no food, and two temperatures.
• Most O. edulis larvae concentrated at the bottom of the aquarium, independent of developmental stage or treatment, and consistently over time. Larvae behaved actively in ~50% of all bottom observations, indicating a behavioural function other than resting. At the surface, larvae frequently formed aggregations. In the water column, larvae swam with high vertical directionality and their distribution was homogenous. Swimming speeds ranged from 0.001 to 9.07 mm s⁻¹.
• Advection close to the seabed is slower than in any other part of the water column. The demersal preference of O. edulis may be targeted towards increasing the likelihood of self‐recruitment, which is consistent with the larvae's preference to settle in the presence of conspecifics. Stronger hydrodynamic environments are likely to override the larvae's demersal behaviour. It is recommended to restore European oyster beds at sufficient scale, density, and rugosity to promote retention of larvae within the natal population and minimize larval loss and mortality, as well as to account for the observed behaviours in networks of restoration sites.
... Rapid settlement of A. palifera planulae has also been observed in the laboratory (Potts, 1984). Restricted larval dispersal (less than 0.5 to 1 m from the parent colony) has also been noted for non-pelagic (benthic) planula of a solitary coral Balanophyllia elegans (Gerrodette, 1981;Fadlallah and Pearse, 1982). Harii et al. (2002) found that Helioporacoerulea larvae settled close to the parent colony due to the larval competency period and the amount of energy (zooxanthellae) in the larval planulae. ...
In order to elucidate the patterns of dispersal in scleractinian coral Pocillopora damicornis near the northern limit of its latitudinal range, a total of 50 colonies (15-25 cm in diameter) of this coral were collected from Ooshima Island, Japan, and transplanted within one hour to the area of Satsuki, where they were not present before. Three concentric areas were established such as; the parental area (PA), intermediate area (IA) and outer area (OA). A total of 831 new corals were found in 1997 while 54.3% of these occurred in PA, 30.5% in IA and 15.1% in OA. In 1998, 52.3% of recruits settled in PA, 30.5% in IA and 17.2% in OA. A significant difference in the density of recruits was found among three areas, but recruit density was not significantly different between years and there was no interaction between area and year. There was no significant difference in the number of recruits among different directions, indicating no tendency for larvae to be concentrated in one particular direction. The present study suggests that the planulae of P. damicornis have limited dispersal distances at high-latitudes© Untuk menjelaskan pola penyebaran karang scleractinia Pocillopora damicornis yang berada di batas Utara penyebarannya, total 50 koloni (15-25 cm) dari karang ini dikumpulkan dari Pulau Ooshima, Jepang, dan di transplantasikan dalam waktu satu jam ke daerah Satsuki yang tidak ditemukan jenis ini. Tiga daerah ditetapkan yaitu, Daerah Induk (PA), Daerah Tengah (IA), dan Daerah Luar (OA). Sebanyak 831 karang baru ditemukan pada tahun 1997, sementara 54,3% ditemukan di PA, 30,5% di IA dan 15,1% di OA. Pada tahun 1998, 52,3% ditemukan di PA, 30,5% di IA, dan 17,2% di OA. Ditemukan perbedaan yang signifikan untuk kepadatan antara ketiga daerah tersebut, tetapi tidak ada perbedaan yang signifikan antar tahun dan tidak ada interaksi antara daerah dan tahun. Tidak ada perbedaan yang signifikan dalam jumlah pada arah yang berbeda sehingga hal ini menunjukkan tidak ada kecenderungan bagi larva untuk terkonsentrasi pada satu arah tertentu. Penelitian ini menunjukkan bahwa planula P.
... it can only disperse meters in a generation because females produce crawl-away young (Gerrodette, 1981;Fadlallah and Pearse, 1982;Fadlallah, 1983;Hellberg, 1994Hellberg, , 1995Bruno and Witman, 1996;Hellberg and Taylor, 2002). C. rubens is a brooding, aclonal, subtidal anemone (Siebert and Spaulding, 1976;Sanamyan et al., 2019) with no previously-published ecological work. ...
Hexacorallians are one of the most conspicuous and dominant suspension feeders in temperate and tropical environments. While temperate hexacorallians are particularly diverse in the northeast Pacific, little work has been done in examining their biology and ecology. Within this dissertation, I describe a novel method for marking soft-bodied invertebrates such as hexacorallians (Chapter 1), examine the prey selectivity of the competitively dominant anemone Metridium farcimen with DNA metabarcoding (Chapter 2), and explore the distribution of the most common hard-bottom hexacorallians in the San Juan Archipelago (Chapter 3). In the first chapter, I found that both methylene blue and neutral red make excellent markers for long-term monitoring of M. farcimen with marked individuals identifiable for up to six weeks and seven months, respectively. I also found that fluorescein is lethal in small dosages to M. farcimen and should not be used as a marker. Neutral red could be used for long-term monitoring of growth and survival in the field, and in combination with methylene blue could be used to mark individuals in distinguishable patterns for short-term studies such as examining predator-prey interactions, movement of individuals, and recruitment survival. In the second chapter, I found that M. farcimen captures a wider variety of prey than has been previously described, likely all prey that are large enough to detect and that cannot escape. Additionally, comparisons between DNA metabarcoding and published results from traditional gut sampling techniques showed that many more taxa can be found by DNA metabarcoding. Terrestrial prey were surprisingly high in abundance within the diet of M. farcimen, likely due to the animals living on floating docks. These data highlight the need for consideration of space and time in a sampling regime and the usefulness of the metabarcoding method in identifying prey within the gut of planktivorous animals. In the final chapter, I found that depth, light, flow, and substratum slope had significant impacts on the distribution of hard-bottom hexacorallians, whereas predation pressure and temperature had no detectable effect. Depth and light have a strong relationship with algal cover and most hexacorallians were conspicuously missing from high algal cover surfaces. Additionally, nearly every species increased in density with increased flow. These data call attention to the need for experimental studies examining the interactions between temperate hexacorallians and algae as well the effects of flow on distribution of anthozoans.
... Corals collected from PAC will be referred to as the HU (high upwelling) population and corals collected from GOL will be referred to as the LU (low upwelling) population [Colour figure can be viewed at wileyonlinelibrary.com] Baja California to Southeast Alaska (Gerrodette, 1981). The upwelling mosaic of the CCLME combined with B. elegans' nonplanktonic larval stage, which restricts gene flow, creates the potential for population variation through local adaptation or phenotypic plasticity when exposed to low pH (Sanford & Kelly, 2011). ...
Ocean acidification (OA), the global decrease in surface water pH from absorption of anthropogenic CO2, may put many marine taxa at risk. However, populations that experience extreme localized conditions, and are adapted to these conditions predicted in the global ocean in 2100, may be more tolerant to future OA. By identifying locally adapted populations, researchers can examine the mechanisms used to cope with decreasing pH. One oceanographic process that influences pH, is wind driven upwelling. Here we compare two Californian populations of the coral Balanophyllia elegans from distinct upwelling regimes, and test their physiological and transcriptomic responses to experimental seawater acidification. We measured respiration rates, protein and lipid content, and gene expression in corals from both populations exposed to pH levels of 7.8 and 7.4 for 29 days. Corals from the population that experiences lower pH due to high upwelling, maintained the same respiration rate throughout the exposure. In contrast, corals from the low upwelling site had reduced respiration rates, protein content, and lipid‐class content at low pH exposure, suggesting they have depleted their energy reserves. Using RNA‐Seq, we found that corals from the high upwelling site upregulated genes involved in calcium ion binding and ion transport, most likely related to pH homeostasis and calcification. In contrast, corals from the low upwelling site downregulated stress response genes at low pH exposure. Divergent population responses to low pH observed in B. elegans highlight the importance of multi‐population studies for predicting a species’ response to future OA.
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... Anthozoans exhibit both solitary and colonial species, and a variety of reproduction modes and life-cycle histories, including: self-fertilization, swimming planula with pelagic dispersal or benthic-crawling planula, and asexual reproduction for colonial growth and/or dispersal (Fautin 2002). Although broadcasting predominates in many anthozoans, internal brooding is also widespread in the group (Gerrodette 1981;Brazeau et al. 1998;Fautin 2002;Heltzel & Babcock 2002). Anthozoans have developed a variety of mechanisms for asexual propagation such as somatic/vegetative embryogenesis, budding, fission, and fragmentation, among others, but not all species reproduce asexually (Fautin 2002). ...
... Bryozoan lecithotrophic larvae also have a short swimming period which they spend within the bottom water layer (for different bryozoan species, from several hours up to 3-4 days-Shunatova, unpublished data; see also Ryland 1974Ryland , 1976Reed 1991). Pearse (1969) and Mileikovsky (1971) termed such larval type as demersal and both of them suggested that it may be more common for benthic invertebrates than previously thought (see also Gerrodette 1981). ...
Kelps are ecosystem engineers and thus enhance biodiversity and subsidize food webs in nearshore areas. Numerous studies describing diversity and abundance of biota associated with kelp have focused on sub-tropical and temperate waters while kelp forests at high latitudes, where kelp is predicted to expand in distribution, remain mostly unexplored. Kelp forests contribute significantly to regional biodiversity, and associated fauna and the kelp themselves play ecologically important roles as habitat and feeding areas. Here, we report patterns in diversity, abundance and seasonal dynamics of fouling organisms associated with different regions of Saccharina latissima and nearby substrates (including stones of the barren ground). The study was conducted in Kongsfjorden, a high Arctic fjord on the west coast of Spitsbergen; and samples were taken five times between September 2013 and January 2015. Trends in species richness of epifauna were similar for stones and holdfasts: higher in winter (due the presence of rare species), and lower in spring and autumn. Species richness and abundance demonstrated a clear tendency to increase in accordance with substrate stability. Stones housed the most diverse biota compared to living substrates. Holdfasts demonstrated similar patterns in species composition and abundance as stones due their close spatial arrangement and presence of demersal larvae in most of fouling organisms. Similarly, assemblages on blades in prostrate kelp forests are influenced by the species inhabiting stones of the barren ground. Both biotic and abiotic factors, including habitat stability and proximity to source populations, contribute to these spatial and temporal patterns in faunal abundance and diversity.
... Most marine invertebrates develop through either a lecithotrophic (nonfeeding) or planktotrophic (feeding) larval phase, and it is generally accepted that feeding larvae spend more time in the plankton than nonfeeding larvae (e.g., Strathmann, 1985). This development time, or larval duration (we use larval duration instead of the commonly used pelagic larval duration because many invertebrate larvae are demersal and neritic, not pelagic), constrains the upper limit of larval transport, with potentially greater spatial scales of larval transport for longer-lived species (Scheltema, 1989), and clearly, species with very short larval life cannot translocate long distances (Gerrodette, 1981). Therefore, a simple relationship between larval duration and dispersal distance is expected (Scheltema 1989), and plots describing such relationships have been offered in the literature (Siegel et al., 2003;Shanks, front would be shorter than for those larvae that are advected but did not accumulate (Figure 11.3). ...
Larval transport is fundamental to several ecological processes, yet it remains unresolved for the majority of systems. We define larval transport, and describe its components, namely larval behavior and the physical transport mechanisms accounting for advection, diffusion, and their variability. We then discuss other relevant processes in larval transport, including swimming proficiency, larval duration, accumulation in propagating features, episodic larval transport, and patchiness and spatial variability in larval abundance. We address challenges associated with understanding larval transport, and recent approaches, including autonomous sampling, imaging, ’omics’, and the exponential growth in the use of poorly-tested numerical simulation models to examine larval transport and population connectivity. Thus, we discuss the promises and pitfalls of numerical modelling, concluding with recommendations to move forward, including a need for more process-oriented understanding of the mechanisms of larval transport, and use of emergent technologies.
... This solitary, azooxanthellate coral is a conspicuous and common member of temperate intertidal and subtidal communities in the northeast Pacific Ocean (Gerrodette 1979). Unlike many other corals, the gonochoric B. elegans broods relatively few and large larvae that tend to disperse over short (<1 m) distances (Gerrodette 1981, Fadlallah 1983). This feature, together with its indeterminate growth and longevity (6−11 yr;Fadlallah 1983), permits an instructive contrast to the relative wealth of information on short-lived and highly fecund taxa (e.g. ...
Reductions in body size are hypothesized to be a universal response to climate warm- ing, yet the proximate causes of change remain unresolved. In this study, we combined field evi- dence and demographic models to explore mechanisms relevant to temperature-related declines in the body size of an ectotherm exhibiting indeterminate growth. Our field data demonstrate that the body size of cup corals Balanophyllia elegans has decreased by ~35% over nearly 4 decades (1969−2007), during which seawater temperatures have increased by 0.6°C in the San Juan Islands, Washington State, USA. We developed a modeling framework, based on the Arrhenius equation and temperature−size theory, to explore the thermal dependence of maximum body size. Our models identified the growth rate of corals as a key demographic leverage point for changes in maximum body size, but temperature alone was likely insufficient to cause the observed mag- nitude of change. Our case study provides a simple template for integrating detailed demographic data with predictions derived from the temperature−size theory, in order to evaluate empirically the magnitude of body size decline in the context of climate warming.
... In the eastern PaciWc, T. coccinea occurs abundantly in the Gulf of California (Reyes Bonilla (Cortés and Jiménez 2003;Maté 2003;Reyes Bonilla and Barraza 2003), along the coasts of Colombia and Ecuador (Reyes Bonilla 2002;Glynn 2003), and at the Galápagos Islands (Glynn and Wellington 1983). Gerrodette (1981) suggested that the »2,000 km range of the temperate dendrophylliid coral Balanophyllia elegans, with demersal larvae capable of only limited dispersal (<0.1 m year ¡1 ), achieved its broad distribution through passive dispersal or rafting. A possible example would be the dispersal of an adult coral on a rock held in a drifting kelp holdfast. ...
The reproductive ecology of Tubastraea coccinea Lesson, an azooxanthellate tropical scleractinian coral, was studied over various periods from 1985 to 2006 at four principal eastern Pacific locations in Costa Rica, Panama, and the Galapagos Islands (Ecuador). This small (polyp diameter 0.8–1.0 cm), relatively cryptic species produced ova and planulae year round, including colonies with as few as 2–10 polyps. Of 424 colonies examined histologically, 13.7% contained both ova and sperm. Mature ova varied in diameter from ∼300 to 800 μm and the time from spawning and fertilization of oocytes to release of brooded planulae was about 6 weeks. Planulae were 0.5–1.5 mm long and they settled and metamorphosed on a variety of substrates after 1–3 days. Spermaries, though more difficult to distinguish in histological sections, were present throughout the year. Spent spermaries were never observed in sections, but several colonies in Panama and the Galapagos Islands released sperm from night one to night five after full moon, indicating the potential for cross-fertilization among colonies. Planula release was observed at Uva Island (Panama) in March, May, June, and July, and in general planula presence was higher at warm ocean temperatures at all sites, whether or not the sites were influenced by seasonal upwelling. Annual fecundity estimates for T. coccinea are comparable with other high fecundity brooding species, including the zooxanthellate Porites panamensis, with which it co-occurs in Panama. Tubastraea coccinea is widely distributed in the tropical Indo-Pacific and has colonized substrates in the western Atlantic. In addition to the reproductive characteristics described in the present study, other features of the biology of T. coccinea, such as an ability to withstand conditions that produce bleaching and mortality in zooxanthellate species, may account for its widespread, low-latitude distribution in multiple oceans.
... In response to the need for estimates of planktonic durations in the field, a range of approaches have been developed. Some researchers have followed individual larvae directly and simultaneously estimated planktonic mortality, larval movement, and planktonic duration (Gerrodette 1981, Olson 1985, Young 1986, Davis & Butler 1989, Bingham & Young 1991, Stoner 1992. Such approaches are valuable, but are necessarily restricted to species with conspicuous larvae with relative short larval durations (e.g. ...
Planktonic larval durations (PLDs) affect the ecology and evolution of benthic marine populations through their effects on dispersal distance, the spread of sibling larvae, the level of larval mortality, and population connectivity. Despite the importance of PLDs, field estimates of PLDs in marine invertebrates are rare and restricted to specific taxa. The size of the first post-metamorphic feeding structure (the ancestrula lophophore) in Bugula neritina has been shown previously to decline with increases in larval duration. We hypothesised that if the relationship between larval duration and the size of the ancestrula lophophore can be estimated in the laboratory, then it should be possible to infer the PLD of B. neritina settlers in the field. We manipulated the length of the larval period in the laboratory and quantified the relationship between larval duration and the volume of the ancestrula lophophore. We then measured the size of lophophores in field-settled individuals at 2 sites on multiple days over a 2 yr period, and predicted their planktonic durations based on our laboratory-derived classifications. The average percentage of individuals in the field with short (0 to 1.5 h), intermediate (1.5 to 6.5 h), and long (6.5 to 32 h) PLDs was 54, 27, and 19%, respectively. Despite being competent to settle upon release from the colony, a significant proportion of settlers in the field experienced metamorphic delays that would incur significant post-settlement costs. Furthermore, there was a positive relationship between settlement density and the proportion of settlers in any one cohort that had experienced short PLDs. The extended planktonic periods that we predicted are likely to affect the dynamics of adult populations directly via reductions in settlement density and indirectly via reductions in the post-settlement performance of individuals that experienced a metamorphic delay before settling.
... The height (h) was measured (d) and volume was calculated using Eq. (1.) juvenile corals (Fig. 1a, b), usually within a few centimeters of the mother (Gerrodette, 1981). B. elegans is an azooxanthellate species (lacking photosynthetic symbiotic algae) depending on heterotrophic feeding on zooplankton or dissolved organic molecules for all of its energy and nutrients. ...
Ocean acidification, the assimilation of atmospheric CO2 by the oceans that decreases the pH and CaCO3 saturation state (Omega) of seawater, is projected to have severe adverse consequences for calcifying organisms. While strong evidence suggests calcification by tropical reef-building corals containing algal symbionts (zooxanthellae) will decline over the next century, likely responses of azooxanthellate corals to ocean acidification are less well understood. Because azooxanthellate corals do not obtain photosynthetic energy from symbionts, they provide a system for studying the direct effects of acidification on energy available for calcification. The solitary azooxanthellate orange cup coral Balanophyllia elegans often lives in low-pH, upwelled waters along the California coast. In an 8-month factorial experiment, we measured the effects of three pCO(2) treatments (410, 770, and 1220 mu atm) and two feeding frequencies (3-day and 21-day intervals) on "planulation" (larval release) by adult B. elegans, and on the survival, skeletal growth, and calcification of newly settled juveniles. Planulation rates were affected by food level but not pCO(2). Juvenile mortality was highest under high pCO(2) (1220 mu atm) and low food (21-day intervals). Feeding rate had a greater impact on calcification of B. elegans than pCO(2). While net calcification was positive even at 1220 mu atm (similar to 3 times current atmospheric pCO(2)), overall calcification declined by similar to 2545 %, and skeletal density declined by similar to 35-45% as pCO(2) increased from 410 to 1220 mu atm. Aragonite crystal morphology changed at high pCO(2), becoming significantly shorter but not wider at 1220 mu atm. We conclude that food abundance is critical for azooxanthellate coral calcification, and that B. elegans may be partially protected from adverse consequences of ocean acidification in habitats with abundant heterotrophic food.
... This kind of larva is considered Aplanic (a= without). Examples of aplanic larvae include forms that emerge from the adult with the capability to settle, but also include some lecithotrophic larvae in which development occurs completely during encapsulation or while crawling on the seabed, as happens in some corals (Gerrodette, 1981;Fadlallah & Pearse, 1982). ...
A very important objective of ecological research is to explain the evolution of life histories, more specifically how natural selection modifies reproduction and development in order to generate the patterns that are observed in nature. With few exceptions, the reproductive mechanisms and patterns found in deep-water echinoderms are entirely similar to those found in shallow-water species. The aims of this study were 1) to examine the reproductive biology of the many deep-sea asteroids found on the continental slope to the west of Europe in order to determine if the reproductive adaptations are a function of depth, distribution or are phylogenetically controlled, and 2) to conduct experiments on the effects of pressure and temperature on larval development of Atlantic asteroids, to investigate the physiological potential for deep sea invasion by shallow-water species. Eggs of the shallow-water asteroids Asterias rubens Linnaeus and Marthasterias glacialis (Linnaeus) were fertilized in vitro and incubated through the early embryonic cleavages until the larval stage. They were subjected to different temperature/pressure regimes. Early embryos were able to tolerate pressures up to 150 atm at 15oC and 100 atm at 10oC. Survivorship of A. rubens swimming bipinnaria remained high (> 70%) after incubation at all the pressure/temperature combinations. In M. glacialis the highest survival of swimming larvae was 100% at 1 atm/5, 15 and 20oC and 50 atm/15 and 20oC. Data for the temperature and pressure effects on the later stages of development suggest that all the larval stages are more temperature/pressure tolerant than the early embryos and survivorship becomes greater with larval age. Therefore, the larvae of these two species could survive transport to deeper waters and these species may be capable of sending colonists to the deep sea. In the deep NE Atlantic the habitat has selected for species with specific reproductive traits, which provide them with successful and advantageous life history strategies. This can be clearly observed in the upper bathyal zone between 700 and 1100 m, where the environmental conditions have selected for small species with low fecundity and large eggs, plus habits related directly or indirectly with suspension feeding. These species exhibit reproductive features with trends to the opportunistic strategy and are distinctive of unpredictable environments, although their large egg size probably follows the general trend observed in species from cold waters in order to provide the larvae with energy sufficient for a high survival possibility. Conversely, phylogenetic and evolutionary factors are also important and seem to be decisive at the deepest waters where basically mainly species belonging to the strict deep-sea family Porcellanasteridae are found. All these species possess a mixture of features typical of classical K strategists and equilibrium strategists, which enable them to persist in a relatively stable environment with low energy availability. A comprehensive knowledge of the reproductive processes of the deep-sea fauna is essential in order to evaluate the level of variability caused in the environment principally by human activity and the possible effects on life-history of the species.
... This suggests that the species with the greatest potential for widest dispersal will not necessarily exhibit the highest population densities and widest geographic distribution. Some species with crawling larvae and apparently highly limited dispersal capabilities exhibit a very broad geographic range (Sammarco, 1994), such as some gastropods (Hoskin, 1997), teredinid bivalves (Calloway and Turner, 1983), and corals (e.g., Balanophyllia elegans; Gerrodette, 1981). Pocillopora damicornis, a brooding coral, has among the widest geographic range of any known coral, extending from the Red Sea to the eastern Pacific. ...
Cover image by Gregory S. Boland from video
"Contributing Authors" not in primary citation but listed on page iii of report (related to government publication issues).
Abbreviated Executive Summary follows:
ADULT CORAL COMMUNITY STUDY
There are approximately 3,200 oil and gas platforms in the northern Gulf of Mexico (GOM). These platforms provide hard substratum that extends throughout the euphotic zone, in a region where such has been rare in recent geological time. In this study, we attempted to determine whether extensive scleractinian coral populations have colonized these platforms, quantify them, and determine their population and community characteristics. We also examined the relationship between these variables and distance from the FGB, platform age, and depth. Surveys were performed on 13 oil or gas production platforms down to 33 m depth, encompassing an ellipse around the FGB. Corals occurred in abundance on most of the platforms. Eleven species were found: eight hermatypic scleractinians, two ahermatypic scleractinians, and one hydrozoan coral. Platforms have facilitated expansion of coral populations in the GOM. Such platforms have intrinsic environmental value through the presence of coral populations and this may influence future decisions about their decommissioning (removal).
CORAL SETTLEMENT STUDY
To assess coral recruitment rates on oil and gas platforms around the FGB, terracotta settlement plates were mounted on racks, deployed on, and retrieved from six platforms at depths of 15 and 27 m for a period of one to two years. Plates were analyzed in the laboratory with a dissecting microscope for taxonomic identification, distribution, and abundance. Density of coral spat settling on plates on the platforms was extraordinarily low when compared with other Caribbean sites or the Great Barrier Reef-averaging <1/450 cm2 -over a period of 10-12 months. There was no significant difference between platforms with respect to spat density, suggesting that the distance between the platforms and the E-FGB-their potential larval source, was large enough to allow diffusion of larvae, suppressing larval densities. There was a significant difference between coral spat densities on the platforms compared with those directly on the E-FGB (derived from a sister experiment). Only three species of coral spat were found: T. coccinea, Montastraea sp. (most likely Montastraea cavernosa), and Madracis sp. (most likely M. decactis), in order of abundance. This species composition varied substantially from the dominant genera of spat observed on the E-FGB: Agaricia and Porites.
MOLECULAR GENETICS STUDY
Here, we conduct molecular genetic analyses on adult scleractinian corals on the FGB coral reefs (~180 km S-SE of Galveston, Texas [TX]) and on surrounding oil and gas platforms. We have attempted to determine the degree of genetic affinity among the natural populations and those on the surrounding platforms. The three species collected were the most abundant hermatypic scleractinians: M. decactis, D. strigosa, and M. cavernosa. Tissue samples were collected from the E-FGB and W-FGB, and seven platforms within a 65 km radius, at a depth range of 5-37 m. Genetic variation was assessed using Amplified Fragment Length Polymorphisms (AFLPs). The AMOVA analyses indicated that the E and W-FGB were genetically homogeneous for M. decactis and D. strigosa populations. M. cavernosa populations, however, were significantly different between banks. In all species, genetic distance (ΦST) increased significantly with geographic distance between populations. In the brooding species M. decactis, this pattern was even stronger when one considered the shortest distance between platforms and the nearest perimeter of the FGB, particularly the nearest FGB, suggesting that the FGB may be a source of larvae for platform populations. The AFLPOP analyses showed that the degree of self-allocation to home sites also increased with inter-site distance. The low degree of genetic affinity exhibited by all species on the platforms may be attributed to genetic drift/founder effect or relatively small population sizes, although total populations were sampled. In general, genetic affinity decreased with inter-site distance.
... The same author also reported the solitary scleractinian coral Balanophyllia elegans. Demersal planula larvae of this species crawl over the benthic substratum at a speed of 1-4 mm min -1 (Gerrodette 1981), which cannot explain the widespread distribution of this species. The author suggested that rafting of adults on stones held by the haptera of detached kelps might be a possible dispersal mechanism for this species. ...
Rafting of marine and terrestrial organisms has been reported from a variety of substrata and from all major oceans of the world. Herein we present information on common rafting organisms and on ecological interactions during rafting voyages. An extensive literature review revealed a total of 1205 species, for which rafting was confirmed or inferred based on distributional or genetic evidence. Rafting organisms comprised cyanobacteria, algae, protists, invertebrates from most marine but also terrestrial phyla, and even a few terrestrial vertebrates. Marine hydrozoans, bryozoans, crustaceans and gastropods were the most common taxa that had been observed rafting. All major feeding types were represented among rafters, being dominated by grazing/boring and suspension-feeding organisms, which occurred on all floating substrata. Besides these principal trophic groups, predators/scavengers and detritus feeders were also reported. Motility of rafting organisms was highest on macroalgae and lowest on abiotic substrata such as plastics and volcanic pumice. Important trends were revealed for the reproductive biology of rafting organisms. A high
proportion of clonal organisms (Cnidaria and Bryozoa) featured asexual reproduction, often in combination with sexual reproduction. Almost all rafting organisms have internal fertilisation, which may be due to the fact that gamete concentrations in the rafting environment are too low for successful fertilisation of external fertilisers. Following fertilisation, many rafting organisms incubate their offspring in/on their body or deposit embryos in egg masses on rafts. Local recruitment, where offspring settle in the immediate vicinity of parents, is considered an important advantage for establishing persistent local populations on a raft, or in new habitats. Some organisms are obligate rafters, spending their entire life cycle on a raft, but the large majority of reported rafters are considered facultative rafters. These organisms typically live in benthic (or terrestrial) habitats, but may become dispersed while being confined to a floating item. Substratum characteristics (complexity, surface, size) have important effects on the composition of the rafting community.
While at sea, ecological interactions (facilitation, competition, predation) contribute to the community succession on rafts. Organisms capable to compete for and exploit resources on a raft (space and food) will be able to persist throughout community succession. The duration of rafting voyages is closely related to rafting distances, which may cover various geographical scales. In chronological order, three features of an organism gain in importance during rafting, these being ability to (1) hold onto floating items, (2) establish and compete successfully and (3) develop persistent local populations during a long voyage. Small organisms that do not feed on their floating substratum and, with asexual reproduction or direct development, combine all these features appear to be most suited for long-distance dispersal on rafts and successful colonisation after reaching new habitats. All available evidence suggests that rafting is an important process for the population dynamics of many organisms and that it also has had and continues to have a strong influence on coastal biodiversity.
... Since ecologists have recognised the fundamental role of dispersal in the regulation and persistence of populations (see Cowen and Sponaugle, 2009 for review), understanding the processes that contribute to the dispersal of pelagic larvae, including the quantification of dispersal dynamics at different scales, has become an important topic (e.g. Gerrodette, 1981;Kinlan et al., 2005;Cowen et al., 2006). Recently, generalised explanations of connectivity models have focussed on dispersal and hydrodynamics and the resulting bio-physical relationships (Metaxas andSaunders, 2009, Carson et al., 2010). ...
... The height (h) was measured (d) and volume was calculated using Eq. (1.) juvenile corals (Fig. 1a, b), usually within a few centimeters of the mother (Gerrodette, 1981). B. elegans is an azooxanthellate species (lacking photosynthetic symbiotic algae) depending on heterotrophic feeding on zooplankton or dissolved organic molecules for all of its energy and nutrients. ...
Ocean acidification, the assimilation of atmospheric CO2 by
the oceans that decreases the pH and CaCO3 saturation state
(Ω) of seawater, is projected to have severe consequences for
calcifying organisms. Strong evidence suggests that tropical
reef-building corals containing algal symbionts (zooxanthellae) will
experience dramatic declines in calcification over the next century. The
responses of azooxanthellate corals to ocean acidification are less well
understood, and because they cannot obtain extra photosynthetic energy
from symbionts, they provide a system for studying the direct effects of
acidification on the energy available for calcification. The orange cup
coral Balanophyllia elegans is a solitary, azooxanthellate scleractinian
species common on the California coast where it thrives in the low pH
waters of an upwelling regime. During an 8 month study, we addressed the
effects of three pCO2 treatments (410, 770, and 1230 μatm)
and two feeding frequencies (High Food and Low Food) on adult
Balanophyllia elegans planulation (larval release) rates, and on the
survival, growth, and calcification of their juvenile offspring.
Planulation rates were affected by food level but not pCO2,
while juvenile survival was highest under 410 μatm and High Food
conditions. Our results suggest that feeding rate has a greater impact
on calcification of B. elegans than pCO2. Net calcification
was positive even at 1230 μatm (~ 3 times current atmospheric
pCO2), although the increase from 410 to 1230 μatm reduced
overall calcification by ~ 25-45%, and reduced skeletal density by ~
35-45%. Higher pCO2 also altered aragonite crystal morphology
significantly. We discuss how feeding frequency affects azooxanthellate
coral calcification, and how B. elegans may respond to ocean
acidification in coastal upwelling waters.
... Although dispersal is typically two-dimensional, heterogeneous, and anisotropic , our preliminary analyses indicated that both N MAP and N VP were primarily a function of in-water distance L between the source and the collector (or model grid cell) locations, allowing estimation of a greatly simplified single-variable dispersal kernel (e.g., Gerrodette, 1981;Largier, 2003). The estimates of the observed number (N) of MAPs or VPs are presented in a semilog manner (log e N as a function of L) and consistent with the linear relation log e N ¼ b À aL. ...
... Caffey 1985) and this patchiness is likely to be reduced or magnified by the dispersal stage. Direct developers with limited dispersal ability can clump around benthic egg capsules (Gosselin and Chia 1995) or parental females (Gerrodette 1981). The dispersal of adults could result in an over-dispersed distribution if territorial, or a highly clumped distribution if, for example, they bring a brood of juveniles into the new habitat. ...
My dissertation work involves the study of how marine communities develop in the context of local and regional processes. In particular, I am interested in how diversity in a community can be affected through processes such as habitat destruction, community density, and migration, using pen shells and their inhabitants as a model system. In St. Joe Bay, Florida, pen shells (Atrina rigida) are the most abundant source of hard substrate, and the shell provides habitat for approximately 70 species. These communities are discrete habitats that differ from the surrounding seagrass beds and sandy areas. Sixty-six percent of the species found on pen shells are not found in the habitat surrounding pen shells. Pen shells provide shelter for many motile species and hard substrate for settling sessile species and egg-laying fishes. I first demonstrate the role of the pen shell community within sea grass ecosystems. Results suggest that a large component of species found on pen shells are only found with pen shells, and those that are found in the surrounding habitat tend to occur at much lower densities. I then carried out an experiment that showed that the age of the community can affect diversity at local and regional scales. Results also showed that more motile species were more sensitive to these spatial scales, and showed changes in the spatial relationship through time; while for sessile species, the local-regional diversity relationship did not change with succession. In 2003 I performed an experiment that tested successional patterns on pen shells that occurred at high and low densities, as well as a pen shell region that suffered habitat destruction. Local community density did affect local diversity as predicted. Further, motile and sessile species had different responses to habitat destruction. What was interesting from this study is the way individual species responded to different regional sizes. It seems that species’ changes in abundance and distribution (number of shells occupied) differed between the common species and the rare species. The pattern and probability of successful dispersal among habitats can therefore be crucial in determining whether local populations will become rare or increase in abundance. I studied three amphipod species that disperse at different life stages: Neomegamphopus hiatus and Melita nitida disperse as adults, while Bemlos unicornis disperses as juveniles. The metapopulation dynamics of the three species seems highly dependent on the life history stage involved in dispersal.
... ← 10, Davis and Butler (1989); 11, Dayton (1973); 12, E. Demartini (personal communication); 13, Deysher and Norton (1982); 14, Epifanio et al. (1998); 15, Espinoza (1990); 16, Gerrodette (1981); 17, Grosberg (1987); 18, Grosholz and Ruiz (1995); 19, Grosholz and Ruiz (1996); 20, Harrison and Bigley (1982); 21, Hicks and Tunnell (1995); 22, Jones and Barb (1968); 23, Kenchington et al. (1998); 24, Keough and Chernoff (1987); 25, Knoepffler-Peguy et al. (1985); 26, Knowlton and Keller (1986); 27, Luczak et al. (1993); 28, Marliave (1986);29, McDermott (1998); 30, Meinesz et al. (1993); 31, Miller (1996); 32, Noel et al. (1997); 33, Olson (1983); 34, Olson (1985); 35, Olson and McPherson (1987); 36, Paine (1979); 37, Pfister (1997); 38, Prince et al. (1987); 39, Randall (1987); 40, Randall et al. (1993); 41, Reed et al. (1988); 42, Sammarco and Andrews (1989); 43, Scheltema (1971); 44, Stoner (1990); 45, Stoner (1992); 46, Thorson (1946); 47, Vandermeulen and DeWreede (1986); 48, Vermeij (1978); 49, Worcester (1994); 50, Zechman and Mathieson (1985). losus larvae (point D, Fig. 1) aggregate near the shore (within one to several m), tend to cluster behind promontories that deflect the flow, and swim against the local current (Marliave 1986). ...
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 5 0.7776, r 2 5 0.60, df 5 1, 25, P 5 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 52 1.29, t 52 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 , 1k m or.;20 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 10- 20 km apart should be close enough to capture propagules released from adjacent reserves.
... Likewise, the strictly demersal planulae of Balanophyllia elegans remain on the substrata for several days before attachment and metamorphosis. Lab and field experiments indicated that the mean larval dispersal distance in this species is even lower than in H. coerulea and is ≤ 0.5 m from the parent (Gerrodette, 1981). ...
The life-cycle of reef-building corals, as is true for many benthic marine invertebrates, includes a planktonic larval phase that is critical to the maintenance of adult populations. Interest in understanding the biology of this larval phase has taken on a heightened sense of urgency as the unprecedented decline of reef-building corals throughout the world raises fears that the supply of sexually produced larvae may no longer be sufficient to sustain reef ecosystems. Here we provide an overview of coral larval biology by integrating advances that have been made using both physiological and ecological approaches. The primary areas addressed include 1) a brief survey of reproductive modes as well as aspects of development, including the onset of competence, 2) an analysis of the abiotic and biotic factors that affect planula larvae during dispersal and an assessment of the spatial scales over which these various parameters act, and 3) an accounting of the exogenous synthetic and tentative endogenous factors that induce larva-to-polyp transformations in vitro as well as efforts to decipher the underlying signaling pathways. We conclude that the relatively recent discovery of mass spawning events exhibited by many of the major reef-building corals throughout the Pacific and Caribbean has done much to advance our understanding of coral larval biology because it has allowed researchers to obtain gametes that can be used in a wide range of physiological and ecological studies. We also recommend the following as high priority research areas: 1) the mechanisms involved in developing metamorphic competence, 2) the synergistic effects of biotic and abiotic factors on the dispersal and settlement of coral larvae, and 3) comparative studies of the putative endogenous morphogens that orchestrate larva-to-polyp metamorphosis.
Little is known about the biology of cold-water corals (CWCs), let alone the reproduction and early life stages of these important deep-sea foundation species. Through a three-year aquarium experiment, we described the reproductive mode, larval release periodicity, planktonic stage, larval histology, metamorphosis and post-larval development of the solitary scleractinian CWC Caryophyllia (Caryophyllia) huinayensis collected in Comau Fjord, Chilean Patagonia. We found that C. huinayensis is a brooder releasing 78.4 ± 65.9 (mean ± standard deviation [SD]) planula larvae throughout the year, a possible adaptation to low seasonality. Planulae had a length of 905 ± 114 µm and showed a well-developed gastrovascular system. After 8 ± 9.3 days (d), the larvae settled, underwent metamorphosis and developed the first set of tentacles after 2 ± 1.5 d. Skeletogenesis, zooplankton feeding and initiation of the fourth set of tentacles started 5 ± 2.1 d later, 21 ± 12.9 d, and 895 ± 45.9 d after settlement, respectively. Our study shows that the ontogenetic timing of C. huinayensis is comparable to that of some tropical corals, despite lacking zooxanthellae.
p>The Ivory Tree Coral Oculina varicosa, forms extensive bioherms (reefs) of azooxanthellate colonies at depths of 70-100m along the edge of the Florida Hatteras slope. Deepwater Oculina reefs support invertebrate and fish communities as diverse as those of tropical coral reefs, and are a critical spawning habitat for a number of commercial fisheries species. A different morphological variant of O. varicosa inhabits the near-shore limestone ledges, and these shallow-water colonies were included in the study as an ecological comparison of conspecific populations exploiting different habitats, as a preliminary reproductive model for the less accessible deep reefs. Colonies from the two populations were confirmed as conspecific using Internal Transcribed Spacer (ITS) sequences of the nuclear ribosomal gene from deep and shallow colonies.
Growth rates (skeletal deposition) of samples from both populations were measured under varying temperature and light regimes. The results showed a significant difference between the two populations under different light conditions. Temperature had no significant effect on growth however. This warrants further investigation, since photosynthetically enhanced calcification did confer an advantage to the shallow zooxanthellate samples, but temperature had no consistent effect on calcium deposition.
Oculina varicosa is a gonochoristic broadcast spawning species, with small eggs (<100mm) and a high fecundity of approximately 4,000-8,000 eggs per cm-2 of skeletal surface area for both populations. The gametogenic cycle begins in the early summer and spawning occurs during late summer and fall, with no obvious relationship to lunar or tidal phase. Histological analysis of gonad sections revealed concurrent gametogenic cycles in both populations; however, the deeper populations generally spawned later (September) than their shallow counterparts (July-August).</p
Does the dispersal of planktonic larvae promote strong connections between marine populations? Here we describe some of the most commonly used population- and individual-based genetic methods that have enhanced our understanding of larval dispersal and marine connectivity. Both approaches have strengths and weaknesses. Choosing between them depends on whether researchers want to know about average effective rates of connectivity over long timescales (over hundreds to thousands of generations) or recent patterns of connectivity on shorter timescales (one to two generations). The use of both approaches has improved our understanding of larval dispersal distances, the relationship between realized dispersal (from genetics) and dispersal potential (from planktonic larval duration), and the crucial distinction between genetic and demographic connectivity. Although rarely used together, combining population- and individual-based inferences from genetic data will likely further enrich our understanding of the scope and scale of larval dispersal in marine systems.
Although the propagules of many sessile organisms have the capacity to disperse over large distances, dispersal is often spatially restricted. In this paper, I document, using a combination of mark/recapture techniques and histocompatibility assays, dispersal distance of the planktonic larvae of the sessile, colonial sea squirt Botryllus schlosseri. Both of these methods indicate that most larvae remain within a meter of their birthplace. Such limited dispersal should lead to increased matings among relatives, and the potential for inbreeding depression. However, the success of: 1) fertilization, 2) embryogenesis, and 3) larval metamorphosis all decrease as distance between mated colonies increases. The spatial scale over which this decrease in mating success occurs is concordant with the estimates of dispersal distance based on the larval mark/recapture data and histocompatibility assays. Taken together, these results imply that inbreeding depression is not a necessary consequence of limited dispersal and consanguineous matings in B. schlosseri.
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.
The genetic structure of populations of sessile and sedentary organisms is often characterized by microgeographic differentiation in gene frequencies and deviations from panmixia. In many terrestrial botanical systems, restricted gene flow via seed and pollen dispersal may have an important role in promoting such genetic patterns. Until recently, however, limited dispersal of the sexual propagules of benthic invertebrates has not been considered to play a comparable role in aquatic systems. Based on paternity analyses in the field using rare allozyme markers, it appears that concentrations of sibling sperm of the sessile, colonial ascidian Botryllus schlosseri decline rapidly within 50 cm of a source colony. In combination with spatially restricted dispersal of brooded larvae, limited dispersal of sperm should enhance the potential for genetic diversification and inbreeding. However, analysis of allelic and genotypic frequencies at three independent, polymorphic allozyme loci using F-statistics provides little evidence for microgeographic variation in gene frequencies. This lack of differentiation can be explained in terms of the absolute number (rather than concentration) of gametes and larvae dispersing from a point source, which-depending on diffusion and geometric assumptions-may actually increase with distance. In contrast to the absence of differentiation, levels of inbreeding are high, even within the confines of 25 times 25-cm quadrats. The absence of genetic diversification and presence of inbreeding caution against inferring levels and causes of gene flow from indirect analysis of genetic structure and, conversely, making predictions about genetic and breeding structure based solely on direct analysis of gene flow.
When the dispersal capability of a species is considerably less than its geographic range, genetic differences between populations should increase with the distance separating those populations. This pattern should be most evident in linearly distributed species. The sessile solitary cup coral Balanophyllia elegans lives along nearly the entire Pacific coast of North America, yet its crawling larvae usually settle within 40 cm of their birthplace. In this paper, I document geographic patterns of allozyme differentiation within and among populations of B. elegans and estimate the proportion of observed geographic pattern attributable to gene flow between adjacent populations. Genetic subdivision among localities separated by up to 3000 km was high (FST = 0.283, SE = 0.038). Inferred gene flow between pairs of localities (M∘, individuals per generation) correlated inversely with the geographic distance between those localities, consistent with the pattern expected for a species at equilibrium in which gene flow occurred exclusively between adjacent localities. Within localities, patches separated by 4 to 30 m were also significantly subdivided, but genetic differentiation between patches did not vary significantly with the distance separating them. Simulations revealed that the power to detect genetic pattern expected from gene flow between adjacent populations increased with both the number of loci used to infer gene flow and the heterozygosity of those loci. Simulations also verified that when geographic distance poorly approximated the number of steps between populations, reduced major-axis regression more accurately portrayed the structural relationship between gene flow and separation than did ordinary least-squares regression. Attenuation of gene flow with distance explained 15% of the between-locality pattern of genetic differentiation in B. elegans. The remaining variation appeared to be due to neither natural selection nor a recent rangewide recolonization. Loci from the northern sampled localities, however, had fewer alleles than those from the remainder of the range, suggesting these localities had been recolonized recently following Pleistocene cooling.
Bases of attachment of Archimedes colonies are very rare, but many colonies show evidence of origination from a pre-existing set of branches. The evidence consists of spiralled supports (axial screws) originating from fragments of pre-existing sets of branches, proximal taper of colonies or axial screws to a diameter smaller than that of bases of attachment, early stages of new colonies originating from the whorl margins of older colonies, and sets of laterally fused colonies. In the most favorable environments Archimedes populations were dominated by a few genets that consisted of hundreds to perhaps thousands of genetically identical colonies.
The ability to reproduce by colony fragmentation was probably an important cause of Archimedes ' abundance in the Chesterian seas of eastern North America, especially where it occurred in dense populations in the lee of submarine carbonate shoals. Colony fragmentation, the importance of which is becoming increasingly recognized in modern corals and bryozoans, was also of importance in Paleozoic seas.
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.
Coralla of the three species of solitary corals described herein from the Sinemurian (Lower Jurassic) of Sicily, i.e., Haimeicyclus haimei (Chapuis and Dewalque, 1853), Stylophyllopsis sp. cf. S. rugosa (Duncan and Wright, 1867), and Stylophyllopsis sp. A., conform to the overall stylophyllid morphology. Their septa consist of spines that are increasingly covered with sclerenchyme and low in the calice form compact blades. The pattern of diagenetic alteration of septa is diverse but consistent within particular taxa. it suggests that the spectrum of the original microstructures is wider than traditionally suggested for stylophyllids. In H. haimei, the septa are covered with dense granulations and completely recrystallized. Granulations also cover septal faces of Stylophyllopsis cf. rugosa and have rod-like foundations. In Stylophyllopsis sp. A., vestiges of the narrow mid-septal zone (similar to that in minitrabecular corals) occur in the proximal part of larger septa, whereas septal spines which are similar to those in Stylophyllopsis cf. rugosa occur in their distal parts. Similar diversity of microstructures is reported also in Triassic stylophyllids that have aragonitic coralla. The presence of distinct septal spines along with wide-ranging microstructural diversity of traditional Triassic-Jurassic stylophyllids, casts light on their possible evolutionary relationships, and can be a useful criterion for further revision of the group. For example, Jurassic thecocyathids, considered ancestral to caryophylliinans, share similar spiny/lobate septa with stylophyllids. Also Recent deep-water anthemiphylliids with spiny/lobate septa are strikingly similar to stylophyllids. Although this may be another example of parallel evolution, the separation of anthemiphylliids from other scleractinian clades on a mitochondrial 16S RNA tree topology suggests their ancient roots and enable us to suggest a stylophyllid ancestry. The supposed cyclic pattern of protoseptal insertion in Early Jurassic H. haimei supports the hypothesis of scleractinian-like (and not rugosan) ancestory of the stylophyllid evolutionary lineage.
In this paper we develop a model of the long-term prospects for the Pacific sardine (Sardinops sagax) in which the surplus growth of the stock is influenced by random fluctuations. This can have an enduring effect partly through a serial correlation in the environmental disturbances, but also, and more importantly, because the effect of these random disturbances is related to the size of the stock itself.We use the model to generate fluctuations in the sardine stock to compare alternative fishing strategies: (i) constant escapement; (ii) constant exploitation rate; and (iii) a hybrid of the two.We find that strategy (i) results in greater catches per year and greater variability than (ii). The hybrid, (iii), results in greater catches and greater variability than (i).We conclude that the model supports the existing management of the U. S. Pacific sardine fishery.
Echinoderm larvae clone (reproduce asexually), but the implications of this remarkable life history trait for larval dispersal have not been explored. We develop a simple model of larval dispersal, in which cloning can be incorporated into the numerator of the Gaussian distribution: P(x,t) = 1/2 root pi Dt e(-x2/4Dt) Each cloning event resets the time to final settlement. The timing of cloning and the number of sequential cloning events influence the dispersal distance, but neither the percent of larvae that clone nor larval mortality has an impact on distance traveled. The percent of larvae that clone and survive control the number (probability density) of larvae. The second moment (variance) in the model shows that the "spread" of the dispersion is linearly related to time (2Dt.), where the constant D is the diffusivity. We discuss the implications of a few clones traveling long distances. This may effectively homogenize the population genetics and facilitate invasions but may not affect fishery management. The life history feature of larval cloning results in a limitless larval period (assuming they survive) and may act to promote long distance dispersal of a few larvae.
This article reviews chemical and physical mechanisms by which non-motile marine invertebrates and marine algae inhibit the fouling of their surfaces. Inhibition of primary film formation (bacterial, diatoms and protozoans); and macrophyte and epizooite settlement are considered individually followed by discussion of their interactions. Emphasis is placed on ecological and evolutionary considerations, including the advantages and disadvantages for an organism in being fouled, variation in the defenses utilized by an organism and the likelihood of misinterpreting interactions among organisms. The study of natural antifouling defenses is an emerging field offering important theoretical and economic spin-offs.
Large-scale efforts to restore oyster (Crassostrea virginica) habitat rely on the creation of high-relief hard substrate to improve the natural recruitment of larvae originating from existing oyster populations. Delivery of competent larvae to reefs is influenced by larval behavior, which respond to elevated levels of turbulence by a downward swimming behavior. To determine the geographic dispersal of populations of oyster larvae and how swimming behavior of larvae alters settlement patterns within Virginia (USA) coastal bays, this study utilized a depth-averaged Delft3D(C) hydrodynamic model coupled to a larval behavior model which incorporates an increased downward swimming speed in response to elevated turbulence. Turbulence and flow measurements over oyster reefs, oyster restoration sites, and bare seafloor were quantified using velocimeters. Hydrodynamic cues were input into the larval behavior model to determine how changes in swimming behavior due to turbulence influence settlement patterns. Results indicate that alterations in settlement velocity, specifically maintaining approximate neutral buoyancy until larvae are both mature and over an existing reef, substantially increased the probability of settling on suitable substrate. We also found that oyster reefs in low velocity regions have a higher probability of self-colonization, while reefs found in less sheltered higher velocity environments receive comparatively little of their own larvae and depend upon connectivity with other areas. Data from in situ larval settlement plates agree with model results and indicate that rates of settlement are similar to 1.5 to 3x greater over existing reefs composed of primarily vertically oriented oysters than over restoration reefs that are less topographically complex.
Disturbances from anchoring and sedimentation generally produce Type 1 and Type 2 patches (sensu Sousa 1985, Connell and Keough 1985), respectively. Recolonization and recovery of these patches in deep-water environments are expected to vary in accordance with current models of succession, but inhibition responses likely will predominate in Type 1 patches, particularly high-relief (eg >1 m) areas, where regrowth from the margins often is possible from sheet-like or mound-like forms such as those represented by many sponge taxa. Recovery of Type 2 patches, particularly low-relief areas, also may be influenced primarily by inhibition responses, but the relative lack of nearby colonizers suggests greater numbers of species interactions in accordance with facilitation and tolerance models. Recovery is expected to require a few to several years to accomplish for these deep-water hard-substrate communities. -from Authors
Although the propagules of many sessile organisms have the capacity to disperse over large distances, dispersal is often spatially restricted. In this paper, I document, using a combination of mark/recapture techniques and histocompatibility assays, dispersal distance of the planktonic larvae of the sessile, colonial sea squirt Botryllus schlosseri. Both of these methods indicate that most larvae remain within a meter of their birthplace. Such limited dispersal should lead to increased matings among relatives, and the potential for inbreeding depression. However, the success of: 1) fertilization, 2) embryogenesis, and 3) larval metamorphosis all decrease as distance between mated colonies increases. The spatial scale over which this decrease in mating success occurs is concordant with the estimates of dispersal distance based on the larval mark/recapture data and histocompatibility assays. Taken together, these results imply that inbreeding depression is not a necessary consequence of limited dispersal and consanguineous matings in B. schlosseri.
When the level of gene flow among populations depends upon the geographic distance separating them, genetic differentiation is relatively enhanced. Although the larval dispersal capabilities of marine organisms generally correlate with inferred levels of average gene flow, the effect of different modes of larval development on the association between gene flow and geographic distance remains unknown. In this paper, I examined the relationship between gene flow and distance in two co-occurring solitary corals. Balanophyllia elegans broods large, nonfeeding planulae that generally crawl only short distances from their place of birth before settling. In contrast, Paracyathus stearnsii free-spawns and produces small planktonic larvae presumably capable of broad dispersal by oceanic currents. I calculated F-statistics using genetic variation at six (P stearnsii) or seven (B. elegans) polymorphic allozyme loci revealed by starch gel electrophoresis, and used these F-statistics to infer levels of gene flow. Average levels of gene flow among twelve Californian localities agreed with previous studies: the species with planktonic, feeding larvae was less genetically subdivided than the brooding species. In addition, geographic isolation between populations appeared to affect gene flow between populations in very different ways in the two species. In the brooding B. elegans, gene flow declined with increasing separation, and distance explained 31% of the variation in gene flow In the planktonically dispersed P. stearnsii distance of separation between populations at the scale studied (10-1000 km) explained only 1% of the variation in gene flow between populations. The mechanisms generating geographic genetic differentiation in species with different modes of larval development should vary fundamentally as a result of these qualitative differences in the dependence of gene flow on distance.
Three species of massive reef-building coral, Goniastrea aspera, G. favulus, and Platygyra sinensis, were studied on two fringing reef flats in the central Great Barrier Reef from 1982 to 1984. Total population sizes ranged from 25 to 292 colonies, and remained relatively constant. Population structures and dynamics based on both age and size were described. Differences between these two classifications were primarily due to tissue fission or shrinkage of colonies. In populations dominated by small size classes, young corals were not necessarily the most abundant. Similarly, populations dominated by the largest size classes were not always dominated by the oldest corals. In several populations, mean colony size decreased slightly with increasing age, though variability in size also increased. Mortality patterns were similar in all three species, with the youngest genets and smallest ramets suffering the highest death rates. While mortality in older or larger corals was low, the incidence of partial mortality and fission was higher in these groups. Age-specific fecundity increased rapidly once reproductive age was reached at @?5 yr, but fecundity decreased slightly in the older age classes due to the decrease in mean colony size. Estimated mean generation times ranged from 33 to 37 yr.
Methods for marking invertebrate larvae for use in dispersal studies include staining, tagging with calcium replacements, radiotracers and rare elements, and use of genetic, morphological, and parasite markers. The mark, release and recapture method provides a valuable approach to the study of larval movements but has been attempted only rarely, in part because of difficulties with larval recovery. Methodological and instrumentational advances may improve the feasibility of release and recovery efforts. Additional approaches to tracking larvae include visual tracking, use of isolated or point sources, Lagrangian and Eulerian methods, energetic calculations, hydro-graphic modeling and simulations. Recent emphases on physical transport mechanisms, and on the interrelationship of behavior and passive transport can be considered in the context of tracking methods. Newly-developed and recently-conceived techniques offer promise of considerable advance in our understanding of larval dispersal phenomena.
When the dispersal capability of a species is considerably less than its geographic range, genetic differences between populations should increase with the distance separating those populations. This pattern should be most evident in linearly distributed species. The sessile solitary cup coral Balanophyllia elegans lives along nearly the entire Pacific coast of North America, yet its crawling larvae usually settle within 40 cm of their birthplace. In this paper, I document geographic patterns of allozyme differentiation within and among populations of B. elegans and estimate the proportion of observed geographic pattern attributable to gene flow between adjacent populations. Genetic subdivision among localities separated by up to 3000 km was high (FST = 0.283, SE = 0.038). Inferred gene flow between pairs of localities (M, individuals per generation) correlated inversely with the geographic distance between those localities, consistent with the pattern expected for a species at equilibrium in which gene flow occurred exclusively between adjacent localities. Within localities, patches separated by 4 to 30 m were also significantly subdivided, but genetic differentiation between patches did not vary significantly with the distance separating them. Simulations revealed that the power to detect genetic pattern expected from gene flow between adjacent populations increased with both the number of loci used to infer gene flow and the heterozygosity of those loci. Simulations also verified that when geographic distance poorly approximated the number of steps between populations, reduced major-axis regression more accurately portrayed the structural relationship between gene flow and separation than did ordinary least-squares regression. Attenuation of gene flow with distance explained 15% of the between-locality pattern of genetic differentiation in B. elegans. The remaining variation appeared to be due to neither natural selection nor a recent rangewide recolonization. Loci from the northern sampled localities, however, had fewer alleles than those from the remainder of the range, suggesting these localities had been recolonized recently following Pleistocene cooling.
We found that recruitment, abundance, and dominance within two subtidal epifaunal communities in southern New England, USA persist year after year over large areas of the bottom. This long-term persistence in both dominance and recruitment is not expected in such an open system with disturbances continually creating open patches for recruiting larvae whose identity and abundances change both temporally and spatially. We suggest that the persistence results from strong local control of recruitment that overrides any variability in larval production and dispersal of species from outside a site. Although local dynamics that control persistence involve all life-stages, we found that intense predation on post-settlement individuals has drastic effects. This predation alters the relative abundances of recruits, prevents the invasion of some species, and allows others to dominate. In addition, epifaunal communities are often dominated by species producing short-lived, poorly dispersed larvae. The continued local recruitment of these species at a given site can contribute to the long-term persistence of dominants already present. Based on these observations, we suggest that a system of locally reproducing, self-sustaining populations coupled with strong local environmental differences (e.g. predation on recruits) limiting the invasion of other species may better represent some subtidal benthic communities than a system with widely-dispersed larvae, recruitment dominated by production outside the community, disturbance creating continual changes in dominance, and little long-term persistence.
Colonies were found to be abundant on seagrasses in the N Gulf of Mexico from mid to late fall through winter. Populations increase in mid to late fall, roughly with the onset of cooler weather. They decline between midwinter and early summer, apparently when cold fronts pass. No colonies were found on seagrass in summer, but some large colonies attached to polychaete tubes lie dormant through summer, regenerating in fall. Spatial variation occurs on very small scales. Absence of B. neritina from patches of seagrass is not the result of poor survival of post-settlement individuals, but rather is likely due to poor dispersal of the lecithotrophic larvae. Local extinctions of Bugula populations are probably caused by storms; one such extinction was observed. The spatial pattern is maintained by restricted dispersal and population bottlenecks. Unoccupied seagrass patches are unlikely to be colonized by larvae, but rafting of mature colonies on seagrass occurs frequently, with the potential of seeding new habitats.-from Authors
Experiments show that the close proximity of a large live colony of Pocillopora meandrina Dana var. nobilis Verrill, 1864 decreases the survival of small colonies compared to the survival of small colonies in the open. The close proximity of either large dead colonies or clusters of small colonies did not affect the survival rate of individual small colonies. The existence of this form of interaction between large and small colonies of the same species raises the question of whether the phenomenon occurs in more diverse and complex coral communities and whether it is contributing to the maintenance of high diversity in such situations by preventing the development of pure stands.
Life cycles of clonal benthic animals are more complicated than those of aclonal species because there are more parameters to vary, and because an individual clone can grow in disconnected bits and pieces and widely different shapes. Consequently, the schedule of life-history events in clonal animals is as closely tied to their size as to their age. The bigger the animal the more likely it is to survive, and there is usually no limit to this advantage. Senescence is typically absent, or unmeasurable. Reproduction and recruitment of new individuals into local populations occurs by both sexually and asexually produced larvae, and by fragmentation. In general, asexual recruitment is more frequent. Larvae of clonal species are strongly philopatric whereas those of aclonal species are dispersed over considerable distances. These differences, and the high incidence of asexual reproduction, mean that parents, siblings, and clonemates may become mixed together within a small area. Under these conditions inbreeding is likely, and there is even evidence of selection for inbreeding in several clonal phyla. Nevertheless, clonal species tend to persist as long in the fossil record as do aclonal species. Thus the relative frequency of sexual reproduction among benthic animals, if not its incidence per se, would appear to have little or no macroevolutionary significance.
The early development of Odontaster validus at McMurdo Sound, Antarctica, is indirect and includes equal cleavage, a convoluted blastula, a free-swimming coeloblastula, a gastrula, and a feeding bipinnaria larva. Development differs from that of other asteroids in two respects: (1) The developmental rate is extremely slow; blastulae form nearly 2 days after fertilization, gastrulation begins after 7 days, and the bipinnaria develops in about 40 to 55 days. The slow developmental rate appears to be only partly related to the low environmental temperature (-1.5C). (2) The embryos and larvae are largely demersal. Such behavior may be an adaptation to keep the larvae out of antarctic surface waters, as does brooding in many other polar echinoderms.
The garibaldi, Hypsypops rubicunda, is a California pomacentrid fish inhabiting the rocky subtidal between 0 and 25 m. Garibaldi feed almost exclusively on benthic organisms. Adults defend a territory which includes a shelter hole, grazing area, and for some males, a nest site. The territory is defended all year and against some other species as well as other garibaldi. The nest site is a small patch of red algae cultured by the male. The same site is used over a period of several years by the same male and probably by his successors. The female is allowed in the territory only to spawn; the eggs are guarded by the male. The young receive no parental care; they disperse into the plankton and settle out in shallow water. Age estimates from scales indicate that garibaldi assume adult coloration and mature at age 5 or 6 years and may live 13 or more years. Garibaldi have no obvious important predators or diseases. From age structures of several populations the mortality rate is estimated at about 9% of the adult population per year. In most cases potential recruitment more than balances mortality, indicating that population density is limited by some resource in the area and regulated by some form of intraspecific competition. Density and dispersion of both fish and resources (food, shelter, and nest sites), sex ratio, and age structure were determined in several study areas. From these data and a series of repopulation experiments, the most likely limiting and regulating factors are proposed. Density of adult garibaldi can be limited by supply of resources for survival or, where these are abundant, by minimal space requirements of nesting males. Exclusion by territory defense helps regulate density to limits set by food, space, etc. There is no evidence of feedback between density and the density limiting or regulating effects of territorial behavior. Territorial behavior seems to have evolved as a means of increasing reproductive success. Population effects, though beneficial, are probably incidental. There is no support for the hypothesis that territorial behavior in the garibaldi has evolved because it limits or regulates density.
Gene-enzyme variation was examined, electrophoretically, at three non-specific esterase loci in 15 sympatric populations of the prosobranch gastropods: Littorina littorea L. obtusata, and L. saxatilis. Gene frequencies, determined by assuming a correspondence between bands on gels and alleles, revealed marked differences between the species. These differences appear to be correlated with the mechanisms and capabilities for larval disposal in these species.
1. Ten species of prosobranch gastropod veligers collected from the open waters of the North Atlantic Ocean have been identified by comparison of their larval shells with the protoconchs of identifiable juvenile or adult museum specimens. The larvae described are those of Cymatium parthenopeum (von Salis), Cymatium nicobaricum (Roding), and Charonia variegata (Lamarck) belonging to the family Cymatiidae; Tonna galea (Linne) and Tonna maculosa (Dillwyn) belonging to the family Tonnidae; Phalium granulatum (Born) belonging to the family Cassidae; Thais haemastoma (Linne), a muricid; Philippia krebsii (Morch), an architectonicidae; Smaragdia viridis (Linne), a neritid; and Pedicularia sicula Swainson belonging to the family Ovulidae.2. The geographical distribution of the veligers of these ten gastropod species has been determined in the North and tropical Atlantic from approximately eight hundred and fifty plankton tows. The relationship between the North and Equatorial Atlantic circulation and the dispersa...
Six gene loci were characterized by polyacrylamide gel electrophoresis of 5 protein systems in the mud snail, Nassarius obsoletus. Snail populations collected at 11 sites along an Atlantic coast transect from Cape Cod, Massachusetts to Beaufort, North Carolina were surveyed for genetic variability at these loci. Four loci from malate dehydrogenase, tetrazolium oxidase, and leucine aminopeptidase systems are monomorphic for the same alleles througout the transect. Two loci from lactate dehydrogenase (Lc-1) and general protein ((Gp-1) systems are polymorphic in all populations.The Lc-1 locus has 2 common and 1 rare codominant alleles and the Gp-1 locus segregates for 2 codominant alleles. Alleles of each locus segregate independently of those of the other. Chi-square homogeneity tests indicate homogeneity of allele and genotype frequency throughout the transect at both loci. All populations conform to Hardy-Weinberg equilibrium values, as do pooled populations without indication of Wahlund's effect. Populat...
An extension of the logistic model to a spatially varying carrying capacity and to include fixed regimes of dispersal and spatial competition is analyzed using the theory of linear filters. Dispersal and competition regimes influence the extent to which various scales or frequencies of spatial variation in carrying capacity can be represented in the spatial pattern of abundance. Specifically, increasing the size d an individual's resource-capture zone (e.g., territory or root area) increases the representation in the pattern of abundance of fine scales or high-frequency components of the carrying capacity variation. In contrast, increasing average dispersal, distance decreases representation of the high-frequency components in the spatial pattern of the carrying capacity. An illustration with data on the rusty lizard, Sceloporus olivaceus, (Blair 1960) is provided.
Infaunal bivalves able to live in depths of 1 meter or less have significantly wider geographic distributions than infaunal bivalves restricted to deeper waters (not including deep-sea species). Shallower species tolerate a wider range of environmental conditions and probably have longer-lived larvae than species limited to depths greater than 1 meter. As a result of differences in geographic distribution, species able to live as shallow as 1 meter should be less likely to speciate or go extinct than species restricted to deeper waters. Low-diversity species associations (⩽ 1 meter) should therefore also be evolutionarily more stable than high-diversity (>1 meter) associations. These predictions are supported by evidence from the fossil record.
Where reproductive effort subjects the parent to a risk, the benefit of some breeding activity's contribution to present fitness must be weighed against the loss to future fitness. With risk and benefit defined in terms of life-table parameters, a simple model for a long-lived iteroparous organism permits calculation of the quantitative relation between risk and benefit necessary if an increase in reproductive effort is to be selected for. Constraints on the maximal real benefit establish a corresponding risk ceiling which represents that lowest increment to reproductive cost which can not be compensated by any realizable cost-benefit ratio. Application of this model to data for some offshore-feeding seabirds indicates that an increased reproductive effort will be selected for in these organisms only if the fractional amount by which fledging success increases is at least 19 times greater than the fractional amount by which parental survivorship is decreased. The calculated margin of possibly compensable ...
Optimal migration and dispersal behavior is considered from a theoretical point of view. It is considered as a problem of an optimal choice between alternatives, the outcomes of which are random variables. Models for optimal migration behavior have been worked out for the case where only the density functions of the distributions of survival for the two alternatives are given, and for the case where conditions at the time the choice has to be made are correlated with subsequent survival. The conditions for dominance between the two alternatives have been derived analytically. The predictions of the two models are discussed and compared to natural patterns of migration and dispersal.
A vertical array of four equidistant current meters was used to measure horizontal currents in 18 m of water. The instruments resolved frequencies up to 15 cph for a period of 33 days in late summer 1974. Onshore (EW) and longshore (NS) currents were essentially uncorrelated at all depths. Longshore currents exhibit significant coherence with the surface tide but not at frequencies higher than the tidal frequencies. The effect of a southerly wind lasting over 3 days was evident as a northbound current that was most intense near the surface. The spectrum of onshore currents exhibits a peak at the semidiurnal frequency corresponding to internal tides, and there is a second lower, but broader, peak at frequencies between 1 cph and the buoyancy frequency. Onshore current amplitudes corresponding to the internal tides are on the order of 20 cm s−1, while the higher frequency fluctuations have amplitudes on the order of 3 cm s−1. There is significant coherence between all measurements of onshore current with a phase shift of π between surface and bottom currents. The onshore current measurements are consistent with the mode 1 oscillations of a three-layer model consisting of homogeneous surface and bottom layers separated by a layer having constant buoyancy frequency.
Summary1. In analysing the ecological conditions of an animal population we have above all to focus our attention upon the most sensitive stages within the life cycle of the animal, that is, the period of breeding and larval development.2. Most animal populations on the sea bottom maintain the qualitatively composition of the species composing them, over long periods of time, though the individual species use quite different modes of reproduction and development. This shows that species producing a large number of eggs have a larger wastage of eggs and larvae than those with only a few eggs. The wastage of eggs in the sea is much larger than on the land and in fresh water.3. In the invertebrate populations on the level sea bottom, large fluctuations in numbers from year to year indicate species with a long pelagic larval life, while a more or less constant occurrence indicates species with a very short pelagic life or a non-pelagic development.4. In most marine invertebrates which shed their eggs and sperm freely in the water, either (a) the males are the first to spawn, thus stimulating the females to shed their eggs, or (b) an ‘epidemic spawning’ of a whole population takes place within a few hours. Both methods greatly favour the possibility of fertilization of the eggs spawned and show that the heavy wastage of eggs and larvae takes place after fertilization, during the free swimming pelagic life.5. Embryos with a non-pelagic development may originate (a) from large yolky eggs, in which case all the hatching young of the same species will be at the same stage of development, or (b) from small eggs which during their development feed on nurse eggs, when the individual embryos of the same species may vary enormously in size at the stage of hatching.6. Three types of pelagic larvae are known: (a) Lecithotrophic larvae, originating from large yolky eggs spawned in small numbers by the individual mother animals; they are independent of the plankton as a source of food although growing during pelagic life, are absent from high arctic seas but constitute about 1o% of the species with pelagic larvae in all other seas, (b) The planktotrophic larvae with a long pelagic life, originating from small eggs spawned in huge numbers by the individual mother animal; they feed from, and grow in, the plankton, constituting less than 5% of high arctic bottom invertebrates, 55–65% of the species in boreal seas, and 8o-85 % of the tropical species, (c) The planktotrophic larvae with a short pelagic life having the same size and organization at the moment of hatching and at the moment of settling; these constitute about 5% of the species in all Recent seas.7. To find out the factors which cause the enormous waste of eggs and larvae, we thus have to study those forms (constituting 7o% of all species of bottom invertebrates in Recent seas) which have a long planktotrophic pelagic life, as only species reproducing in this way have really large numbers of eggs.8. The food requirements of the planktotrophic pelagic larvae are much greater than those of the adult animals at the bottom. The adaptability of the larvae to poor food conditions seems, nevertheless, to be greater than hitherto believed. The significance of starvation seems mainly to be an indirect one: poor food conditions cause slow growth, prolong larval life, and give the enemies a longer interval of time to attack and eat the larvae.9. At the temperatures to which they are normally exposed, northern as well as tropical larvae seem on an average to spend a similar time (about 3 weeks) in the plankton. The length of the pelagic life of the individual species may, however, vary significantly in nature. In the Sound (Denmark) the larvae are never exposed to temperatures outside the range which they are able to endure. The wastage caused by temperature, like that due to starvation, seems mainly to be an indirect one: low temperatures postpone growth and metamorphosis, and give the enemies a longer time to feed on the larvae.1o. When a larva feeding on a pure algal diet metamorphoses into a carnivorous bottom stage, a ‘physiological revolution’ occurs and a huge waste of larvae might be expected. Experiments have, however, shown that this is not the case.11. Young pelagic larvae are photopositive and crowd near the surface; larvae about to metamorphose are photonegative. Larval polychaetes, echinoderms, and presumably also prosobranchs, may prolong their pelagic life for days or weeks until they find a suitable substratum. Forced towards the bottom by their photonegativity and transported by currents over wide bottom areas, testing the substratum at intervals, their chance of finding a suitable place for settling is much better than hitherto believed.12. Continuous currents from the continental shelf towards the open ocean may transport larvae from the coast to the deep sea where they will perish. Such conditions may (for instance in the Gulf of Guinea) deeply influence the composition of the fauna, while in other areas (European western coast, southern California) they seem to be only of small significance.13. The toll levied by enemies appears to be the most essential source of waste among the larvae. A list of such enemies, comprising other pelagic larvae, holoplank-tonic animals and bottom animals, is given on p. 2o. A medium-sized Mytilus edulis, filtering 1–4 1. of water per hour, may retain and kill about 100,000 pelagic lamellibranch larvae in 24 hr. during the maximum breeding season in a Danish fjord.14. Species reproducing in a vegetative way, by fission, laceration, budding, etc., might be expected to have good chances of competition in such areas where conditions for sexual reproduction are unfavourable. Nevertheless, they only supply a rather small percentage of the animal populations of all Recent seas, probably because their intensity of reproduction is low and because they are unable to spread to new areas. Most forms reproducing in a vegetative way have sexual reproduction as well.15. Pelagic development is nearly or totally suspended in the deep sea, and is restricted to the shelf faunas. In the arctic and antarctic seas pelagic development is nearly or totally suppressed, even in the shelf faunas, but starting from here the percentage of forms with pelagic larvae gradually increases as we pass into warmer water, reaching its summit on the tropic shelves.16. In order to survive in high arctic areas a planktotrophic, pelagic larva has to complete its development from hatching to metamorphosis within I–I ½ months (i.e. the period during which phytoplankton production takes place) at a temperature below 2–4o C. Most larvae, that is in 95% of the species, are unable to do so and have a non-pelagic development, but if a pelagic larva is able to develop under these severe conditions the planktotrophic pelagic life seems to afford good opportunities even in the Arctic. Thus the 5 % of arctic invertebrates reproducing in this way comprise several of the species which quantitatively are most common within the area.17. The antarctic shore fauna has poor conditions similar to those of the Arctic. The longest continuous periods of phytoplankton production are 2 and 3 weeks respectively, and pelagic larvae have, in order to survive, to complete their development within this short space of time at a temperature between 1 and 4o C. Accordingly, non-pelagic development is the rule, but most arctic species are able to support their non-pelagic development by means of much smaller eggs than the antarctic species, where brood protection and viviparity is dominant. The antarctic fauna has apparently had a longer time to develop its tendency to abandon a pelagic life. The greater the size of the individual born, the smaller its relative food requirements and the better its chance of competing under poor food conditions.18. The relatively few data on reproduction in deep sea invertebrates point to a non-pelagic development. The larvae of such forms, in order to develop through a planktotrophic pelagic stage, would have to rise by the aid of their own locomotory organs through a water column 2000–4000 m. high or more (often with counteracting currents) to the food producing surface layer, and to cover the same distance when descending to metamorphose and settle.19. The ecological features common to the deep sea, the arctic and the antarctic seas, which enable the same animals to live and to reproduce there, contribute to explain the ‘equatorial submergence’ of many arctic and antarctic coastal forms.20. In the tropical coastal zones where the percentage of species with pelagic larvae reaches its maximum, the production of food for the larvae takes place much more continuously than in temperate and arctic seas, because light conditions enable the phytoplankton to assimilate all the year round. The tropical species of marine invertebrates breed (in contrast to temperate and arctic species) within such different seasons that their larval stock, taken as a whole, is more or less equally distributed in the plankton all the year round. This makes the competition in the plankton less keen.21. The fact that a mode of reproduction and development, well fit for an arctic area, is unfit in a temperate or tropical area of the sea is probably one of the main reasons for the restricted distribution of species.22. In most groups of marine invertebrates the individual species have only one mode of reproduction and development, which accordingly restricts their area of distribution. In the polychaetes, however, the individual species often show an astonishing lability in their mode of reproduction and development which enables them to compete in wide areas of the sea. Thus, out of the Western European species of polychaetes, 28-4% have been found also in the Indian Ocean, and 18%, at least, along the Californian coast, while the corresponding number of Western European echinoderms, prosobranchs and lamellibranchs found also in the Indian Ocean and California amounts to less than 2%.23. The pelagic or non-pelagic development of marine prosobranchs has proved to be a very fine ‘barometer’ for ecological conditions. Recent observations, still not elaborated, seem to indicate that the shape of the top whorls, the apex, of the adult shells of prosobranchs may show whether the species in question has a pelagic or a non-pelagic development. This discovery may also give us valuable information about the larval development in fossil species, and help us to form an idea about ecological conditions in sea areas from earlier geological periods.
The distribution of various types of larval development among marine bottom invertebrates has been discussed on the basis of ecological evidence by Thorson (1936, 1946, 1950, 1952) and Mileikovsky (1961b, 1965). The information at hand is reviewed anew in this paper and is re-evaluated in the light of modern pertinent literature. The interrelationships between certain larval types and their distribution are not as rigid and direct as originally assumed. This can be proved even by the copy book example of the distribution of the various forms of development among species of the coastal gastropod genus Littorina. Especially among species with wide distributional areas, local populations may exhibit greater diversity in larval types than has previously been thought. Different types of larval development have now become known to exist in different populations of opisthobranch gastropods and lamellibranchs, i.e., in invertebrate groups in which such variability had been ruled out by Thorson. Variability in the type of larval development within given species — as a function of geographical, seasonal and other environmental parameters —is also more common in other marine bottom invertebrates than formerly considered. Marine bottom invertebrates are characterized not only by the 3 main different types of larval development proposed by Thorson (pelagic, direct, viviparous), but also by a fourth type: demersal (free non-pelagic) development. This fourth type occurs at all water depths and in all geographic zones of the oceans. The most important of the 4 types is pelagic (planktotrophic) development. Thorson's rule (decrease in numbers of species possessing pelagic development from the Equator towards the Poles, and from shallow-shelf waters to greater oceanic depths) is well substantiated by new data. However, one correction is necessary: pelagic development is not completely absent in the abyssal zone, as was proposed by Thorson (1950, and later), but is represented in it by at least several species belonging to various groups of invertebrates, and is also fairly common in the bathyal zone. A detailed analysis of the distributional pattern of the different types of development of marine bottom invertebrates must further take into consideration asexual reproduction with all its different modifications. Asexual reproduction in benthonic invertebrates is ecologically significant because of its common occurrence in nature; in numerous species it is also important as a biological supplement to sexual reproduction. The vast majority of species inhabiting the shallow-shelf zone and, partly, the higher levels of the slope zone of ocean areas located roughly between the polar circles, reveals development by means of planktotrophic larval stages. In the highest latitudes and on the slopes to abyssal depths—characterized by low water temperatures, scarcity of food, increasing hydrostatic pressure and other environmental peculiarities—other types of larval development prevail and, progressively, replace pelagic development with increasing latitude or depth. The distributional patterns of the various types of development among marine bottom invertebrates form one of the most important factors determining the basic distributional dynamics of the whole benthos in all oceans, both in the geological past and at the present time.
Most animal and plant populations are divided into a number of local populations with some dispersal of individuals from one site to another. A theoretical investigation of the phenomenon of dispersal suggests the following consequences: Isolated and poorly accessible sites will tend to become less crowded than an average site as a result of dispersal. An episode of dispersal will result in uneven crowding at the various sites. Variation in the degree of crowding resulting from dispersal will depress the total population size of a species over its entire range. Variation in the carrying capacity with time will lead to an analogous depression of the mean population size. Spatial variation in the carrying capacities of the sites will favor a sensitive response leading to a rapid increase in the emigration rate with crowding, while variation with time will disfavor a response very sensitive to crowding. Variation in space will favor the emigration of a small fraction of the population, while variation in time will favor the emigration of a larger fraction.
The planula larva of the solitary coral Balanophyllia regia has an ectoderm of flagellate, diplosomal collar cells. The collar of these cells is composed of a ring of microvilli linked with mucus strands. Four types of flagellate gland cells, three types of nematocyst and spirocysts are present in the planula ectoderm. The function of these ectoderm cells is discussed. The mesogloeal muscular and packing tissues of the planula are briefly described. The tentacle of the adult coral, examined for comparison, has an ectoderm of flattened flagellate cells with a shallow collar. Collar cells similar to those of the planula are occasionally found on the tentacle and their function is not known. Independent sensory cells built on a modified collar cell plan with collar of thickened microvilli are common in the tentacle. These are quite separate from the three kinds of tentacular nematocyte. Distended glandular areas occur in the tentacle ectoderm. The flagellate tentacle gastrodermis, muscle and mesogloeal region are briefly described. The evolutionary significance of collar cell ectoderm in a planula is discussed and the occurrence of collar cells throughout the animal kingdom, reviewed.
Species longevity in Lower Tertiary volutids (Gastropoda) is primarily controlled by a combination of developmental type and environmental tolerance. Larval dispersal may be an important factor in molluskan evolutionary rates.