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Parasites and coral‐associated invertebrates that impact coral health
Abstract
Globally coral reefs are in decline, largely driven by local anthropogenic pressures combined with broader cumulative impacts from climate change. Coral aquaculture will play an important role in active reef restoration and attempts to preserve some semblance of coral reefs in highly impacted areas. Achieving maximum growth and survivorship of cultured corals is necessary to achieve optimal results. This is not possible without the study of coral pests and diseases which can be detrimental to coral health. Here we review the complex relationships between corals and their associated symbiotic organisms, identify invertebrates that may harm the corals and suggest known management techniques in captivity. Groups considered included acoels (Xenacoelomorpha: Acoela), digeneans (Trematoda: Digenea), polyclads (Rhabditophora: Polycladida), gastropods (Mollusca: Gastropoda), decapods (Malacostraca: Decapoda), copepods (Hexanauplia: Copepoda) and pyrgomatids (Cirripedia: Pyrgomatidae). There are few empirically validated management techniques for coral pests, particularly in terms of large‐scale aquaculture, emphasizing the need for further directed research in this area. Information generated through the ornamental trade and hobbyists is valuable to inform future research direction targeted towards captive coral husbandry, reef ecosystem management and restoration strategies.
... Corals are cultured primarily for ornamental aquaria or for the restoration of natural coral reefs [62,63]. Many coral reefs are under threat of degradation and this has led to increased research on active intervention strategies in an attempt to restore reefs and build ecosystem resilience [64]. Several studies have attempted to demonstrate the feasibility of large-scale coral aquaculture to provide a source of corals to transplant onto degraded coral reefs [64]. ...
... Many coral reefs are under threat of degradation and this has led to increased research on active intervention strategies in an attempt to restore reefs and build ecosystem resilience [64]. Several studies have attempted to demonstrate the feasibility of large-scale coral aquaculture to provide a source of corals to transplant onto degraded coral reefs [64]. The parasitic species affecting corals were reviewed in Barton [64], and include some species of Acoela, Digenea, Polycladida, Gastropoda, Crustacea, and starfish. ...
... Several studies have attempted to demonstrate the feasibility of large-scale coral aquaculture to provide a source of corals to transplant onto degraded coral reefs [64]. The parasitic species affecting corals were reviewed in Barton [64], and include some species of Acoela, Digenea, Polycladida, Gastropoda, Crustacea, and starfish. Some of the gastropods and crustacea may be more like predators than parasites [64]. ...
Parasites are very diverse and common in both natural populations and in stocks kept in aquacultural facilities. For most cultured species, there are important bacteria and viruses causing diseases, but eukaryotic parasites are also very important. We review the various combinations of aquacultured species and eukaryotic parasitic groups and discuss other problems associated with aquaculture such as eutrophication, zoonotic species, and invasive species, and we conclude that further development of aquaculture in a sustainable manner must include a holistic approach (One Health) where many factors (e.g., human health, food safety, animal health and welfare, environmental and biodiversity protection and marketability mechanisms, etc.) are considered.
... As such it is possible that, at the higher densities recorded here, coral parasites could depress coral population growth rates and expansion into adjacent habitats, further supported by high parasite loads where Acropora corals were rare. At high parasite loads, endolithic barnacles can negatively impact host fitness, causing stress or damage (Fig. 1) to nearby coral polyps (Benzoni et al. 2010) and inhibiting coral growth (Barton et al. 2020), fecundity (Thamrin and Nojima 2001) and heterotrophic feeding (Barton et al. 2020), in this region where Acropora corals are often seen tentacle feeding during the day. Endolithic organisms also weaken coral skeletons and make them more susceptible to breakage (Fig. 1) and bioerosion (Rice et al. 2020;Li et al. 2022), which has been linked to lack of reef development at high latitudes (Harriott and Banks 2002). ...
... As such it is possible that, at the higher densities recorded here, coral parasites could depress coral population growth rates and expansion into adjacent habitats, further supported by high parasite loads where Acropora corals were rare. At high parasite loads, endolithic barnacles can negatively impact host fitness, causing stress or damage (Fig. 1) to nearby coral polyps (Benzoni et al. 2010) and inhibiting coral growth (Barton et al. 2020), fecundity (Thamrin and Nojima 2001) and heterotrophic feeding (Barton et al. 2020), in this region where Acropora corals are often seen tentacle feeding during the day. Endolithic organisms also weaken coral skeletons and make them more susceptible to breakage (Fig. 1) and bioerosion (Rice et al. 2020;Li et al. 2022), which has been linked to lack of reef development at high latitudes (Harriott and Banks 2002). ...
The role of species interactions in setting species range limits is rarely empirically explored. Here, we quantify host and parasite densities in subtropical eastern Australia (26.65°–30.20°S) to examine whether parasitism might contribute to range limitation of Acropora corals at their cold-range boundary. 79% of Acropora corals had endolithic barnacles (family Pyrgomatidae), with higher parasite load in larger corals and up to 141 barnacles per coral. Parasite load increased poleward and closer to the mainland and was greater in cooler and high nutrient environments. Parasite burden was higher at sites with fewer Acropora corals, broadly consistent with the hypothesis that parasites can fragment host populations where host densities are low, and the parasite is a better disperser than the host. Whilst the mechanism is unclear, our findings suggest that at the high densities recorded here, coral-barnacles could influence range dynamics of Acropora corals at their poleward range limit.
... While our findings suggest that larger gastropods were more likely to consume hosts entirely and were more likely occurring alone or in smaller aggregations than smaller gastropods, rapid population increases have been found to lead to mortality of coral hosts under ex situ conditions. While widespread infestation and coral-health impacts in situ by associated gastropods remains rare, records show a growing number of cases of significant coral loss in aquaria and other ex situ environments (Barton et al. 2020;Wang et al. 2020;Cabrito et al. 2022;Knapp et al. 2022). These cases highlight the potential impact of outbreaks driven by large aggregations of gastropods typically seen feeding on relatively small amounts of coral tissue. ...
... To date, no other obligate parasite of Acropora corals has been found in Thai waters, however, this is possibly due to the high cryptic nature of known acroporid parasites. For example, one of the most documented obligate parasites of Acropora corals is the flatworm Prosthiostomum acroporae (Rawlinson et al. 2011), which has a broad geographic range and is a highly cryptic pest on both natural and aquarium corals (Barton et al. 2020), but has yet to be documented in Thai waters. Acropora corals can also become infested by acoel flatworms of the genus Waminoa Winsor, 1990, which have demonstrated high degrees of speciation and host specifity (Kunihiro et al. 2019), and also have a reputation as negatively impacting coral health (Hoeksema and Farenzena 2012;Ponti et al. 2016;Maggioni et al. 2022). ...
Recent years have seen a rapid increase in the study of coral-associated gastropods. In particular, the description of several new species in conjunction with their host specificity or dietary variability, has raised questions pertaining to their impact on reef health. These corallivores have been labelled as both ‘parasite’ and ‘predator’ by different studies, due to the tendency of some species to entirely consume their ‘host’ corals. Here we present new findings of corallivory and parasitism based on surveys conducted on the reefs of Koh Tao, Gulf of Thailand. A total of 6566 corals were assessed for their tendency to host gastropods of the nudibranch genus Phestilla and the caenogastropod family Epitoniidae. Thirteen gastropod species were found to be associated with 20 scleractinian coral species, including six that do not match the original description of previously known taxa. Herein we describe one of them, the first nudibranch proven to be associated with corals of the scleractinian genus Acropora and discuss conservation implications of these coral/gastropod relationships. Additionally, we explore the complex topic of defining these relationships as parasitic versus predatory and the merits of using these labels to better understand the ecology of these relationships.
... From ecological and conservational perspectives, it is important to understand the impact of epifauna on their hosts. In some associations, the epibiont offers protection against predators and diseases (DeVantier et al., 1986;Ben-Tzvi et al., 2006;Montano et al., 2017;Samsuri et al., 2018) or provides cleaning services (Stewart et al., 2006), while in others they wound their hosts, obstruct the host's growth, or smother them entirely (Shima et al., 2010;de Bakker et al., 2018;Turicchia et al., 2018;Barton et al., 2020;Allchurch et al., 2022). ...
... The settlement process of the barnacles is disadvantageous for the host as their larvae penetrate the coral tissue with their antennules, which triggers a physical defence response (Liu et al., 2016). It is also thought that occupying host surface by the barnacles might inhibit coral growth (Barton et al., 2020). Besides these negative influences, hydrocorals acting as hosts were thought to recycle organic material excreted by the barnacles, indicating a mutualistic symbiosis (Cook et al., 1991). ...
Coral-associated invertebrates contribute much to the biodiversity of Caribbean coral reefs. Although the nature of their symbiotic relation is usually not fully understood, they can cause damage to their hosts, especially when they occur in high densities. The abundance of seven groups of coral-associated invertebrates was investigated on reefs along the leeward side of Curaçao, southern Caribbean. In particular, coral barnacles (Pyrgomatidae), boring mussels (Mytilidae: Leiosolenus spp.), gall crabs (Cryptochiridae), and Christmas tree worms (Serpulidae: Spirobranchus spp.) were recorded together with their host corals by means of a photo survey across four depths (5, 10, 15, 20 m) and across seven sites with high and five with low eutrophication values (based on δ¹⁵N isotope measurements). Feather duster worms (Sabellidae: Anamobaea), coral blennies (Chaenopsidae: Acanthemblemaria), and worm snails (Vermetidae: Petaloconchus) were insufficiently abundant for thorough quantitative analyses. The results show a decrease in the number of barnacles and Christmas tree worms per host over depth, which could be related to the availability of their host corals. Sites with high δ¹⁵N values show a higher abundance of barnacles and Christmas tree worms per host than sites with low values. This indicates that eutrophication could be favourable for these filter feeding organisms but when their densities become too high, they tend to overgrow their hosts and may become a threat to them.
... Das et al. Regional Studies in Marine Science xxx (xxxx) 103904 epibionts (Barton et al., 2020). IGs have sometimes been synonymized as "Known GAs" (Beeden et al., 2008). ...
... The first documented case of P. acroporae infestation in the wild occurred off Lizard Island, Australia (Rawlinson et al. 2011). Additionally, this species has been widely observed, infecting Acropora colonies at multiple sites along the Great Barrier Reef (Barton et al. 2020). P. acroporae typically feed on coral tissue, leaving behind circular pale feeding scars approximately 1 mm in size (Nosratpour 2008;Rawlinson et al. 2011). ...
Coral reefs serve as vital ecosystems, playing a crucial role in supporting diverse marine life and sustaining human livelihoods. However, human-induced pressures and climate change disturbances have led to coral decline, necessitating concerted efforts and innovative solutions. Coral aquaculture, also known as coral farming or coral gardening, has emerged as a focal point in marine conservation initiatives, aiming to reduce the growing threats to coral reefs worldwide. Innovative techniques in coral aquaculture encompass both in situ and ex situ cultivation methods. In situ coral aquaculture involves cultivating corals within their natural habitats to enhance coral cover and health conditions. Conversely, ex situ coral aquaculture entails controlled coral cultivation in aquarium environments, aiming to optimize coral production. This industry has evolved into large-scale systems, meeting the demands of various sectors, including marine aquariums, pharmaceuticals, and reef restorations. The applications of coral aquaculture extend beyond environmental conservation, contributing significantly to economic growth by generating employment opportunities for the local communities. Additionally, the diverse array of secondary bioactive metabolites found within corals has led to the discovery of novel drugs, enhancing the pharmaceutical industry. Despite its promising potential, coral aquaculture faces challenges such as sediment impact from dredging activities as well as various types of emerging diseases and compromised health. By exploring these aspects, the review emphasizes the potential for coral aquaculture to make a sustainable contribution to both marine conservation and human being.
... It was not until the use of phylogenetic analyses, based on nuclear and mitochondrial genetic markers, that this ambiguity was clarified (Laumer and Giribet, 2014).Thus, some genera (e. g., Theama Marcus, 1949 andCestoplana Lang, 1884) that were originally included in the Acotylea suborder, were later transferred to the Cotylea one, thanks to the phylogenetic analyses based on the large subunit of the ribosome (28 S) nuclear marker and the mitochondrial Cytochrome c Oxidase Subunit I (COI) molecular markers (Laumer et al., 2015;Laumer and Giribet, 2014;Rawlinson et al., 2011;Rawlinson and Stella, 2012;Yuki and Hiroshi, 2020). The polyclads encompass different species that feed on invertebrates (e.g., Arthropoda, Cnidaria, Mollusca) (Barton et al., 2020;Gallani et al., 1980;Lee, 2006;Teng et al., 2022) and within molluscs, the commercial bivalves are some of the most threatened by these flatworms, causing massive mortality and serious damage in aquaculture facilities (Vieira et al., 2020). Among cultured bivalves, mussels, oysters and clams are the most common groups actively hunted by polyclads (Lee, 2006;Teng et al., 2022), leading to important economic losses (Vieira et al., 2020). ...
Harbours and marinas are optimal places for the detection of the arrival of Non-Indigenous Species (NIS) in the
early stages of introduction. Marine traffic serves as a route for species movement among different regions, while
the species settlement in the ports is facilitated due to habitat degradation. Among NIS, polyclads flatworms are
active hunters of bivalves, posing a threat to recipient environments and aquaculture. They can either use their
pharynx and mucus to penetrate the mussels and oysters, or enter molluscs while they filter, making the management
of the species difficult. In this regard, this work aims to report the first morphological and molecular
identification of a new NIS polyclad native to the Pacific Ocean in Europe, specifically in the Ría de Avil´
es and
the Gij´
on Port (North of Spain, Cantabrian Sea, Bay of Biscay). The occurrence of mature ovigerous specimens
and the collection of specimens of various sizes from different times of the year, evidence a reproductively-active
population in the area. The external morphological characters, as the ruffled pharynx and the cephalic eyes, and
the internal ones, as the male copulatory apparatus, fit with the description of Postenterogonia orbicularis. The
phylogenetic analysis based on the mitochondrial COI marker, placed the studied specimens from Avil´
es and
Gij´
on (Spain) and the recently described species Idiostylochus tortuosus from Arcachon Bay (France) within the
P. orbicularis clade (Ilyplanidae family). Therefore, our results suggest that I. tortuosus may be a synonym of the
New Zealander P. orbicularis. Finally, we discuss the possible ecological impacts of its introduction and provide
some management recommendations for controlling its influx in the recipient environments.
... They inhabit a variety of environments ranging from the intertidal zone to the deep-sea, such as rocky shores, sand/mud flats, coral reefs, and deep-sea hydrothermal vents (Newman and Cannon 2003;Wolff 2005;Quiroga et al. 2006). Polyclads are important predators in hard bottom environments (Rawlinson et al. 2011), and prey on crustaceans, ascidians, cnidarians, gastropods, and bivalves (Jennings 1957;Newman and Cannon 2003;Lee 2006; Barton et al. 2020;Teng et al. 2022). Some species feed on scallops and oysters (Newman et al. 1993;Heasman et al. 1998;Gutiérrez et al. 2023), damaging commercial shellfish farming (Sluys et al. 2005). ...
A new species of the polyclad genus Prosthiostomum is described from the intertidal zone of the South China Sea, Huidong, China, based on morphological and molecular analyses. Prosthiostomum huidongensesp. nov. is characterized by i) few marginal eyes scattered between the marginal band and the cerebral eyes; ii) sucker located at two-thirds of the body length, being removed from the female gonopore by twice the distance between the male and female gonopores; iii) shallow male atrium with slightly ruffled inner wall, positioned approximately perpendicular to the body wall. Molecular phylogenetic analyses based on 28S rDNA sequence showed that the new species was nested in a clade composed of Prosthiostomum species. The uncorrected p-distance of COI between P. huidongensesp. nov. and other Prosthiostomum species ranged from 20.3 to 24.3%, and the high genetic divergence further supports P. huidongense as a new species.
... From 2021 until 2030, the United Nations are asked to implement projects that combat climate to commensalism and parasitism. Parasites may stress the coral and, to some extent, may cause coral mortality through feeding and boring activities; some corallivores may also be able to spread diseases [35,36]. ...
Maldivian coral reefs have been experiencing significant degradation due to a combination of global climate change and local anthropogenic pressures. To enforce the conservation of coral reefs worldwide, coral restoration is becoming a popular tool to restore ecosystems actively. In the Maldives, restoration interventions are performed only around touristic islands, where there are economic resources available to support these projects. Unfortunately, on local islands, coral restoration does not benefit from the same support and is rarely boosted. A challenging coral restoration experiment has been performed, for the first time, on a local island of the Maldives affected by intense human pressures that caused the degradation of its reefs. A total of 242 coral fragments were collected from impacted colonies and transferred to the coral nursery of the island. Survival and growth rates of the fragments were monitored for 12 months. After one year, a survival rate of 70% was recorded. Although this rate might appear lower when compared to other restoration experiences, it is very promising considering the origin of the fragments and the poor quality of the environment where they have been transplanted. Some potential threats to the success of this restoration have also been identified, i.e., water temperature anomaly, diseases, and parasites, the latter being the leading causes of coral mortality. The procedure presented here is less expensive compared to the typical relocation of entire coral colonies from donor-healthy reefs to degraded reefs, thus providing an opportunity and a viable option for local islands to restore their reefs and preserve local biodiversity.
... At present, we cannot consistently differentiate microbiome changes that destabilize the host and cause coral death, from microbiome changes that are a response to coral demise due to other drivers or from changes that may involve the coral adapting to a changing environment by "trading-out" microbial associates. In numerous cases, it is not even clear if coral disease/demise is due to changes in bacterial, fungal, ciliates, flatworms, or other coral associates (Mera and Bourne, 2018;Barton et al., 2020;Vega Thurber et al., 2020). In these instances, field experiments with compounds targeting these different groups may be useful. ...
Tropical reefs are commonly transitioning from coral to macroalgal dominance, but the role of macroalgae in coral decline remains inadequately understood. A growing body of research suggests that algae may harm corals via disruptions to the homeostasis of the coral holobiont, including resident microbial communities, but the processes that mediate these potential microbial effects and the spatial scales at which they operate are uncertain. Resolving the relative importance and context dependencies of microbially-mediated algal-coral competition is critical for understanding and predicting coral dynamics as reefs further degrade. In this review, we examine the current state of knowledge surrounding algal impacts on corals via disruption of their microbiomes, with a particular focus on the mechanisms hypothesized to mediate microbial effects, the scales at which they are thought to operate, and the evidence from laboratory- and field-based studies for their existence and ecological relevance in the wild. Lastly, we highlight challenges for further advancing the field.
... Most polyclads are predators of other small invertebrates, such as crustaceans, ascidians, cnidarians, gastropods, or bivalves (Barton et al. 2020;Jennings 1957;Newman and Cannon 2003;Lee 2006;Teng et al. 2022). At present, the suborder Acotylea (Polycladida) is divided into three superfamilies: Discoceloidea Dittmann, Cuadrado, Aguado, Noreña and Egger, 2019;Leptoplanoidea Faubel, 1984;and Stylochoidea Poche, 1926. ...
A New Polyclad Flatworm, Idiostylochus tortuosus gen. nov., sp. nov. (Platyhelminthes, Polycladida) from France. Can this Foreign A new species of polyclad flatworm, Idiostylochus tortuosus gen. nov., sp. nov. (Polycladida, Idioplanidae), from Arcachon Bay (France) is described. This description is based on a morphological analysis and a molecular analysis using partial sequences of the 28S and cytochrome Oxidase I (COI) genes. After the molecular analysis Idiostylochus gen. nov. appears to be the second genus of the Family Idioplanidae and closely related to the family Latocestidae as well as the genera Leptostylochus and Mirostylochus. The molecular data revealed that the new species may belong to an Indonesian or Indo-Pacific family, closely related to genera with origins in South Pacific Ocean waters. This species was found feeding on the oysters and mussels of the Arcachon farms. A new polyclad flatworm, Idiostylochus tortuosus gen. nov., sp. nov. (Platyhelminthes, Polycladida) from France. Can this foreign flatworm be responsible for the deterioration of oyster and mussel farms? Zool Stud 62:15.
... are coral predators notorious for their substantial damage to corals [6,7]. Moreover, some flatworms and nudibranchs are also potential threats to coral reefs [8][9][10]. ...
A corallivorous nudibranch from the South China Sea reproduced explosively and caused extensive damage to Porites in our aquarium. In this study, morphological and molecular analyses of the nudibranch were conducted and described. Morphologically, this nudibranch was nearly consistent with Pinufius rebus in its characteristics intermediate between arminids and aeolids. The only detected difference was that the hook-like denticles on the masticatory border of P. rebus were absent in this nudibranch. In a molecular analysis, phylogenetic results based on the cytochrome oxidase subunit-I, 16S rRNA, and histone H3 gene sequences showed that this nudibranch and P. rebus form a well-supported sister clade under the superfamily Fionoidea, with significant interspecific divergence (0.18). Thus, we presumed that this nudibranch is a new species of Pinufius. Our results extend the distribution of Pinufius to the South China Sea, support the current taxonomic status of Pinufius under the superfamily Fionoidea, and imply that the species composition of Pinufius is more complex than previous records. Moreover, as a corallivorous nudibranch, the potential threat of Pinufius to coral health cannot be neglected.
... Currently, coral diseases and disease management have seen limited research advancements, particularly in large-scale coral aquaculture. These limitations drive for a new research direction in this area (Barton et al., 2020). Coral ciliate infection is one of the most important diseases affecting the survival of corals. ...
Coral disease is a serious challenge for the survival of both wild and farmed corals. Ciliate infection causes severe damage on the coral health. The present study is the first report on the non-specific infection potential of ciliate parasites on four kinds of corals. The ciliates were isolated from an infected coral, Euphyllia glabrescens and re-infected to various coral species (Acropora muricata, Goniopora columna, Lemnalia fiava, Heteroxenia pinnata). This study aims to bring insights on ciliate infection rate, specific characteristics of infections, and infection pathway of ciliate in corals. In addition, the study also assessed the nature of parasitization in multiple corals, which could be helpful for a significant risk assessment on large-scale coral aquaculture. The 18S rRNA ciliate gene identification results showed about 99% sequence similarity with the Philaster lucinda found in Acropora coral. The purified ciliate was fed with 5 × 10⁶ cell mL⁻¹ of zooxanthellae and could achieve good proliferation. The specific growth rate of the ciliates was increased after 18 h of infection in the E. glabrescens, reaching 828.33 ± 26.10 cell mL⁻¹. Subsequently, the atrophy of coral polyps was observed after 12 h. After 24 h of infection, the coral began to die as the amount/number of zooxanthellae and chlorophyll a were significantly decreased. The coral suffered with 100% mortality within 72 h of infection. The histological study revealed that ciliate parasitized to coral's endoderm while entering the coral coelenteron via its mouth. Tests of ciliate infection revealed that four types of cultured corals were infected by this ciliate and rapidly rot and die, which suggests its non-specific parasitism potential. Furthermore, this study confirmed their onset of infection on different corals simultaneously, which is an important aspect for future coral research, ensuring coral disease management and designing drugs for ciliate prevention.
... According to a recent review paper on polychaete toxins, no relevant information appears to be available on the negative effect of sabellid mucus on other organisms [104]. In contrast, coral-dwelling worm snails, which occupy the same ecological niche as the feather duster worms of the present study [20], are well known for their venomous mucus and the damage this may inflict on the host corals [105,106]. ...
Some coral-associated invertebrates are known for the negative impact they have on the health of their hosts. During biodiversity surveys on the coral reefs of Curaçao and a study of photo archives of Curaçao, Bonaire, and St. Eustatius, the Caribbean split-crown feather duster worm Anamobaea sp. (Sabellidae) was discovered as an associate of 27 stony coral species (Scleractinia spp. and Millepora spp.). The worm was also found in association with an encrusting octocoral (Erythropodium caribaeorum), a colonial tunicate (Trididemnum solidum), various sponge species, and thallose algae (mainly Lobophora sp.), each hypothesized to be secondary hosts. The worms were also common on dead coral. Sabellids of the genera Bispira and Sabellastarte were all found on dead coral. Some of them appeared to have settled next to live corals or on patches of dead coral skeleton surrounded by living coral tissue, forming pseudo-associations. Associated Anamobaea worms can cause distinct injuries in most host coral species and morphological deformities in a few of them. Since Anamobaea worms can form high densities, they have the potential to become a pest species on Caribbean coral reefs when environmental conditions become more favorable for them.
... Waminoa spp. are found mainly on scleractinian corals, but also on octocorals, sea anemones, corallimorpharians, zoantharians, and echinoderms [8][9][10][11][12][13][14][15], and they show a circumtropical distribution, with the exception of the Caribbean [16]. Waminoa flatworms are characterized by the presence of intracellular dinoflagellate symbionts, which have also been found in the worm oocytes, suggesting that these symbionts are inherited via a vertical transmission and not obtained from the host coral [8][9][10]. ...
Waminoa spp. are acoel flatworms mainly found as ectosymbionts on scleractinian corals. Although Waminoa could potentially represent a threat to their hosts, not enough information is available yet regarding their ecology and effect on the coral. Here, the Waminoa sp.–coral association was analyzed in Singapore reefs to determine the prevalence, host range, and preference, as well as the flatworm abundance on the coral surface. Moreover, the impact of Waminoa sp. on the expression of putative immune- and stress-response genes (C-type lectin, C3, Hsp70 and Actin) was examined in the coral Lobophyllia radians. The association prevalence was high (10.4%), especially in sites with lower sedimentation and turbidity. Waminoa sp. showed a wide host range, being found on 17 coral genera, many of which are new association records. However, only few coral genera, mostly characterized by massive or laminar morphologies appeared to be preferred hosts. Waminoa sp. individuals displayed variable patterns of coral surface coverage and an unequal distribution among different host taxa, possibly related to the different coral growth forms. A down-regulation of the expression of all the analyzed genes was recorded in L. radians portions colonized by Waminoa individuals compared to those without. This indicated that Waminoa sp. could affect components of the immune system and the cellular homeostasis of the coral, also inhibiting its growth. Therefore, Waminoa sp. could represent a potential further threat for coral communities already subjected to multiple stressors.
... In comparison, acroporids, like A. palmata, grow much faster than boulder corals and can reach 7 cm 2 in 6 months (Merck personal observation). It is during this varying grow-out period that opportunities arise for biological stressors to negatively affect the coral (Barton et al., 2020;Cassidy, 2009;Sweet, Jones & Bythell, 2011;Sweet et al., 2013). These stressors can include algal and cyanobacterial blooms that outgrow/smother coral (Cassidy, 2009), as well as outbreaks of marine pests, such as Aiptasia and hydrozoans. ...
Large scale ex situ propagation of coral colonies for reef restoration is a relatively new and developing field. One of the many advantages of utilizing ex situ coral nurseries is the ability to optimize water quality conditions for coral health and survival. Slight alterations in environmental parameters (light, pH, temperature etc.) can affect the health and grow-out time of cultured coral, ultimately influencing production rates. However, corals are also subjected to pests associated with culture facilities such as ciliates, cyanobacterial blooms, and infectious diseases. Therefore, adjusting environmental parameters to optimize coral growth for a shorter ex situ residency time will lead to greater survival and faster restoration. Studies indicate that some coral species demonstrate parabolic tissue growth in response to increasing sea-surface temperatures until the maximum temperature tolerance is reached, whereafter they bleach. To maximize coral growth in Mote Marine Laboratory’s ex situ system, we tested the effect of two water temperature treatments (high temperature: 29.5 ± 0.03 °C; control: 25.2 ± 0.08 °C) on two coral species commonly used in reef restoration. To quantify this, we used four replicates of three genotypes each of Montastraea cavernosa ( n = 12) and Acropora palmata ( n = 12). Two-dimensional tissue area was recorded monthly using ImageJ and survival rates within each treatment were documented for 7 months. Results found that M. cavernosa had greater growth rates and equal survivorship in the high temperature treatment compared to the control treatment. A. palmata grew faster and had equal survivorship in the control treatment compared with the high temperature treatment. These results suggest that temperature preferences exist among coral species within ex situ systems and restoration practitioners should consider species-specific temperature regimes to maximize ex situ coral growth rates. This information is critical for optimizing production when corals are in the grow-out stage and should also be considered when designing ex situ systems to ensure temperature regulation can be controlled on a species-specific basis.
... Sowerby I, 1825), previously known as Dendropoma maxima, which dwells on scleractinians, blue corals, and fire corals [14][15][16]. This species is notorious because of its harmful effect on the growth, survival, and photophysiology of host corals [17][18][19][20]. There are only a few other coral-vermetid records from the Indo-Pacific, including Petaloconchus [21], Thylacodes hadfieldi (W.C. ...
The presence of associated endofauna can have an impact on the health of corals. During fieldwork on the southern Caribbean island of Curaçao in 2021, the presence of an unknown coral-dwelling worm snail was discovered, which appeared to cause damage to its hosts. A study of photo archives revealed that the species was already present during earlier surveys at Curaçao since 2014 and also in the southern Caribbean island of Bonaire in 2019. It was not found in St. Eustatius, an island in the eastern Caribbean, during an expedition in 2015. The vermetid snail was preliminarily identified as Petaloconchus sp. Its habitat choice resembles that of P. keenae, a West Pacific coral symbiont. The Caribbean species was observed in 21 host coral species, more than reported for any other vermetid. Because Petaloconchus sp. is a habitat generalist, it is possible that it was introduced from an area with another host-coral fauna. The unknown vermetid is considered to be cryptogenic until future studies reveal its actual identity and its native range.
Sponges are fundamental components of coral reef communities and, unfortunately,
like other major benthic members, they too have been impacted by epizootic and panzootic events.
We report on the prevalence of disease-like conditions affecting populations of the giant barrel
sponge Xestospongia muta across shallow and mesophotic coral reefs off La Parguera Natural Reserve
(LPNR) and Mona Island Marine Reserve (MIMR) in Puerto Rico. Four different conditions affecting
X. muta were observed during our surveys, of which 3 have been previously reported: cyclic
spotted bleaching (CSB; apparently non-lethal), Xestospongia-tissue wasting disease (X-TWD; apparently
lethal), and sponge orange band disease (SOB; sparsely associated with X-TWD infected
individuals). Additionally, we describe a fourth condition, Xestospongia-tissue hardening condition
(X-THC), a previously unreported disease recently observed along the insular shelf margin off
LPNR and MIMR. Within LPNR, a total of 764 specimens of X. muta were inspected and measured.
Of these, 590 sponges (72.2%) had CSB, 25 (3.27%) had signs of X-TWD, 7 (0.92%) had SOB, and
the remaining 142 (18.6%) were apparently healthy. Three colonies inhabiting upper mesophotic
depths on the LPNR insular shelf showed signs of CSB and X-TWD. At MIMR, video-transect surveys
revealed a total of 514 colonies, of which 40 (7.78%) had signs of CSB and/or X-TWD, 14
(2.72%) were affected by X-THC, while the remaining 460 (89.5%) showed no external signs of disease
and appeared healthy. The presence of 4 concomitant disease-like conditions in barrel sponges
of Puerto Rico is alarming, and indicative of the deteriorating status of Caribbean coral reefs.
Allopodion ryukyuensis is a gall-inducing copepod of Montipora coral that has been collected from the coral reefs of Sesoko Island, Okinawa, Japan. The current study was conducted to elucidate its geographic distribution along the Ryukyu Archipelago from Yonaguni Island to Amami Island, including Green Island, Taiwan. The result shows that A. ryukyuensis was found from Montipora collected from all study sites.
Phestilla subodiosussp. nov. (Nudibranchia: Trinchesiidae) is a novel species that feeds on corals in the genus Montipora (Scleractinia: Acroporidae) which are economically important in the aquarium industry. Nuclear-encoded H3, 28SC1-C2, and mitochondrial-encoded COI and 16S markers were sequenced. Phylogenetic analysis, Automatic Barcode Gap Discovery (ABGD), morphological data, and feeding specialization all support the designation of Phestilla subodiosussp. nov. as a distinct species. Although new to science, Phestilla subodiosussp. nov. had been extensively reported by aquarium hobbyists as a prolific pest over the past two decades. The species fell into a well-studied genus, which could facilitate research into its control in reef aquaria. Our phylogenetic analysis also revealed Tenellia chaetopterana formed a well-supported clade with Phestilla . Based upon a literature review, its original morphological description, and our phylogenetic hypothesis, we reclassified this species as Phestilla chaetopteranacomb. nov.
Coral aquaculture is expanding to supply the marine ornamental trade and active coral reef restoration. A common pest of Acropora corals is the Acropora-eating flatworm Prosthiostomum acroporae, which can cause colonial mortality at high infestation densities on Acropora spp. We investigated the potential of 2 biological control organisms in marine aquaria for the control of P. acroporae infestations. A. millepora fragments infested with adult polyclad flatworms (5 flatworms fragment-1) or single egg clusters laid on Acropora skeleton were cohabited with either sixline wrasse Pseudocheilinus hexataenia or the peppermint shrimp Lysmata vittata and compared to a control (i.e. no predator) to assess their ability to consume P. acroporae at different life stages over 24 h. P. hexataenia consumed 100% of adult flatworms from A. millepora fragments (n = 9; 5 flatworms fragment-1), while L. vittata consumed 82.0 ± 26.76% of adult flatworms (mean ± SD; n = 20). Pseudocheilinus hexataenia did not consume any Prosthiostomum acroporae egg capsules, while L. vittata consumed 63.67 ± 43.48% (n = 20) of egg capsules on the Acropora skeletons. Mean handling losses in controls were 5.83% (shrimp system) and 7.50% (fish system) of flatworms and 2.39% (fish system) and 7.50% (shrimp system) of egg capsules. Encounters between L. vittata and P. hexataenia result in predation of P. acroporae on an Acropora coral host and represent viable biological controls for reducing infestations of P. acroporae in aquaculture systems.
As coral aquaculture is increasing around the world for reef restoration and trade, mitigating the impact of coral predators, pathogens and parasites is necessary for optimal growth. The Acropora coral-eating flatworm (AEFW), Prosthiostomum acroporae (Platyhelminthes: Polycladida: Prosthiostomidae) feeds on wild and cultivated Acropora species and its inadvertent introduction into reef tanks can lead to the rapid death of coral colonies. To guide the treatment of infested corals we investigated the flatworm’s life cycle parameters at a range of temperatures that represent those found in reef tanks, coral aquaculture facilities and seasonal fluctuations in the wild. We utilized P. acroporae from a long-term in vivo culture on Acropora species to examine the effects of temperature (3°C increments from 21 to 30°C) on flatworm embryonation period, hatching success, hatchling longevity, and time to sexual maturity. Our findings show that warmer seawater shortened generation times; at 27°C it took, on average, 11 days for eggs to hatch, and 35 days for flatworms to reach sexual maturity, giving a minimum generation time of 38 days, whereas at 24°C the generation time was 64 days. Warmer seawater (24–30°C) also increased egg hatching success compared to cooler conditions (21°C). These results indicate that warmer temperatures lead to higher population densities of P. acroporae. Temperature significantly increased the growth rate of P. acroporae, with individuals reaching a larger size at sexual maturity in warmer temperatures, but it did not influence hatchling longevity. Hatchlings, which can swim as well as crawl, can survive between 0.25 and 9 days in the absence of Acropora, and could therefore disperse between coral colonies and inter-connected aquaria. We used our data to predict embryonation duration and time to sexual maturity at 21–30°C, and discuss how to optimize current treatments to disrupt the flatworm’s life cycle in captivity.
During 1½ year the biology of Corallonoxia longicauda , a copepod endoparasitic in the stony coral Meandrina meandrites was studied in Curaçao, Netherlands Antilles.
Recent large-scale analyses suggest that local management actions may not protect coral reefs from climate change, yet most local threat-reduction strategies have not been tested experimentally. We show that removing coral predators is a common local action used by managers across the world, and that removing the corallivorous snail Coralliophila abbreviata from Caribbean brain corals (Pseudodiploria and Diploria species) before a major warming event increased coral resilience by reducing bleaching severity (resistance) and post-bleaching tissue mortality (recovery). Our results highlight the need for increased evaluation and identification of local interventions that improve coral reef resilience.
Marine viruses are the largest, but most poorly explored genetic reservoir on the planet. They occur ubiquitously in the ocean at an average density of 5–15 × 106 viruses per mL of seawater, which represents abundances an order of magnitude higher than those of bacteria. While viruses are known agents of a number of diseases in the marine environment, little is known about their beneficial function to corals. Herein, we briefly introduce the topic of viruses as potential drivers of coral bleaching and disease.
Interaction modifications can arise when a third species alters the physical and chemical environment within which two other species interact. On coral reefs, corals and algae commonly interact amid a suite of other species that may modify their interaction. Massive Porites coral and algal turfs often are covered by mucus nets cast by the vermetid gastropod, Ceraesignum maximum. Previously, vermetid mucus nets have been shown to have deleterious effects on corals. Here, we hypothesized that vermetids not only have direct effects on coral, but they also change the local physical and chemical environment establishing the potential for interaction modifications by intensifying the effects of algae on corals. To test this, we examined the effect of vermetids on physical and chemical aspects of the environments. We quantified light penetration, water flow, diffusive boundary layer (DBL) thickness, and oxygen concentrations in the presence and absence of vermetid nets. Vermetid nets did not affect light levels. Because we observed reduced water flow and increased DBL thickness in the presence of nets, we also expected to observe high oxygen concentration over coral surfaces. Instead, we observed no difference in oxygen concentrations in the presence of mucus nets. To explain the lower than expected oxygen concentrations, we hypothesize that nets decreased photosynthesis and/or increased respiration of corals and algae and their associated microbiota. This is the first study to explore mechanisms underlying the deleterious effects of vermetids on corals, and shows that vermetid mucus nets may modify coral–algal interactions by intensifying physical and chemical conditions.
Coastal oceans are increasingly eutrophic, warm and acidic through the addition of anthropogenic nitrogen and carbon, respectively. Among the most sensitive taxa to these changes are scleractinian corals, which engineer the most biodiverse ecosystems on Earth. Corals' sensitivity is a consequence of their evolutionary investment in symbiosis with the dinoflagellate alga, Symbiodinium. Together, the coral holobiont has dominated oligotrophic tropical marine habitats. However, warming destabilizes this association and reduces coral fitness. It has been theorized that, when reefs become warm and eutrophic, mutualistic Symbiodinium sequester more resources for their own growth, thus parasitizing their hosts of nutrition. Here, we tested the hypothesis that sub-bleaching temperature and excess nitrogen promotes symbiont parasitism by measuring respiration (costs) and the assimilation and translocation of both carbon (energy) and nitrogen (growth; both benefits) within Orbicella faveolata hosting one of two Symbiodinium phylotypes using a dual stable isotope tracer incubation at ambient (26 °C) and sub-bleaching (31 °C) temperatures under elevated nitrate. Warming to 31 °C reduced holobiont net primary productivity (NPP) by 60% due to increased respiration which decreased host %carbon by 15% with no apparent cost to the symbiont. Concurrently, Symbiodinium carbon and nitrogen assimilation increased by 14 and 32%, respectively while increasing their mitotic index by 15%, whereas hosts did not gain a proportional increase in translocated photosynthates. We conclude that the disparity in benefits and costs to both partners is evidence of symbiont parasitism in the coral symbiosis and has major implications for the resilience of coral reefs under threat of global change.
Tropical reef systems are transitioning to a new era in which the interval between
recurrent bouts of coral bleaching is too short for a full recovery of mature
assemblages. We analyzed bleaching records at 100 globally distributed reef locations
from 1980 to 2016. The median return time between pairs of severe bleaching events
has diminished steadily since 1980 and is now only 6 years. As global warming has
progressed, tropical sea surface temperatures are warmer now during current La Niña
conditions than they were during El Niño events three decades ago. Consequently,
as we transition to the Anthropocene, coral bleaching is occurring more frequently in all
El Niño–Southern Oscillation phases, increasing the likelihood of annual bleaching in
the coming decades.
Research on the coral-eating crown-of-thorns starfish (CoTS) has waxed and waned over the last few decades, mostly in response to population outbreaks at specific locations. This review considers advances in our understanding of the biology and ecology of CoTS based on the resurgence of research interest, which culminated in this current special issue on the Biology, Ecology and Management of Crown-of-Thorns Starfish. More specifically, this review considers progress in addressing 41 specific research questions posed in a seminal review by P. Moran 30 years ago, as well as exploring new directions for CoTS research. Despite the plethora of research on CoTS (>1200 research articles), there are persistent knowledge gaps that constrain effective management of outbreaks. Although directly addressing some of these questions will be extremely difficult, there have been considerable advances in understanding the biology of CoTS, if not the proximate and ultimate cause(s) of outbreaks. Moving forward, researchers need to embrace new technologies and
opportunities to advance our understanding of CoTS biology and behavior, focusing on key questions that will improve effectiveness of management in reducing the frequency and likelihood of outbreaks, if not preventing them altogether.
Some Tenellia nudibranchs are known to be corallivores (Cella et al. 2016) that prey on poritid and dendrophylliid corals (Ritson-Williams et al. 2003). We report here the first record of a Tenellia nudibranch feeding on an agariciid coral, Pavona decussata. These nudibranchs (max. length observed ~10 mm) were first found during detailed examination of transplanted coral fragments of P. decussata in Chek Chau, Hong Kong, southern China. They were subsequently also found on natural coral colonies, inflicting feeding scars along the path of their movement. These nudibranchs display excellent mimicry (Fig. 1). Their body pattern of alternating brown and white stripes closely resembles the septa of P. decussata (Fig. 1b, c). Their cerata are also very similar to the tentacles of P. decussata, which are usually extended, even in daytime. Clumps of white egg capsules (each ~2 mm in length) (Fig. 1c) were also observed on the surface of coral colonies all year round.
High densities (>1 individual cm−2) of Tenellia caused rapid and heavy mortality of P. decussata colonies grown in our laboratory aquaria. However, very low densities (<1 individual m−2) of nudibranchs were found on natural colonies of P. decussata encountered in our field surveys. Coral tissue damage caused by the nudibranchs in nature was therefore limited. Predation by fishes and crustaceans could have limited the abundance of nudibranchs on natural coral surfaces (Gochfeld and Aeby 1997). Algae were observed rapidly growing over Tenellia egg masses (Fig. 1d), potentially affecting their hatching success. The prevalence of Tenellia corallivory on P. decussata in other tropical and subtropical coral communities remains to be verified.
Snails of the genus Coralliophila (Muricidae: Coralliophilinae) are common corallivores in the Caribbean, feeding on a wide range of host species. In the present study, the morphological and genetic variation in C. galea and C. caribaea were studied in relation to their association with host coral species at Curaçao. Differences in shell shape among snails living on different hosts were quantified using geometric morphometric and phylogenet-ic relationships were studied using two mitochondrial markers (12S and COI). Based on these analyses, a new species, C. cura-caoensis sp. nov., was found in association with the scleractinian coral Madracis auretenra. Both C. galea and C. caribaea showed host-specific differences in shell shape, size, and shell allometry (i.e. changes in morphological development during growth). Shell spire variability contributed foremost to the overall variation in shell shape. In C. caribaea minor genetic differences existed between snails associated with scleractinian and alcyonacean cor-als, whereas in C. galea such intraspecific variation was not found. These results shed more light on morphological and genetic differences among coral-associated fauna living on different host species.
Environmental stressors often interact, but most studies of multiple stressors have focused on combinations of abiotic stressors.Herewe examined the potential interaction between a biotic stressor, the vermetid snail Ceraesignum maximum, and an abiotic stressor, high sedimentation, on the growth of reefbuilding corals. In a field experiment, we subjected juvenile massive Porites corals to four treatments: (i) neither stressor, (ii) sedimentation, (iii) vermetids or (iv) both stressors. Unexpectedly, we found no effect of either stressor in isolation, but a significant decrease in coral growth in thepresence of both stressors. Additionally, seven times more sediment remained on corals in the presence (versus absence) of vermetids, likely owing to adhesion of sediments to corals via vermetid mucus. Thus, vermetid snails and high sedimentation can interact to drive deleterious effects on reef-building corals. More generally, our study illustrates that environmental factors can combine to have negative interactive effects even when individual effects are not detectable. Such 'ecological surprises' may be easily overlooked, leading to environmental degradation that cannot be anticipated through the study of isolated factors. © 2017 The Author(s) Published by the Royal Society. All rights reserved.
The term “microbiome” was first coined in 1988 and given the definition of a characteristic microbial community occupying a reasonably well defined habitat which has distinct physio-chemical properties. A more recent term has also emerged, taking this one step further and focusing on diseases in host organisms. The “pathobiome” breaks down the concept of “one pathogen = one disease” and highlights the role of the microbiome, more specifically certain members within the microbiome, in causing pathogenesis. The development of next generation sequencing has allowed large data sets to be amassed describing the microbial communities of many organisms and the field of coral biology is no exception. However, the choices made in the analytical process and the interpretation of these data can significantly affect the outcome and the overall conclusions drawn. In this review we explore the implications of these difficulties, as well as highlighting analytical tools developed in other research fields (such as network analysis) which hold substantial potential in helping to develop a deeper understanding of the role of the microbiome in disease in corals. We also make the case that standardization of methods will substantially improve the collective gain in knowledge across research groups.
The Cnidaria have more symbiotic copepods than any other group of invertebrates, and the greatest numbers of these associates occur on hard corals. A review of the scattered literature on the diversity and taxonomic composition of scleractinian-associated copepods and their hosts revealed a total of 148 coral species, representing 66 genera and 15 families that serve as hosts to copepods. At present, 363 copepod species, representing 99 genera, 19 families and three orders, have been recorded as associates of scleractinian corals. The total included 288 cyclopoids, 68 siphonostomatoids and seven harpacticoids. Within the Cyclopoida the representation of species varied greatly among the 13 families, with a disproportionate number of species belonging to the Anchimolgidae (141 species) and Xarifiidae (92 species). Data on host utilization and geographical distribution of all copepods living symbiotically with hard corals is synthesized and host specificity patterns are highlighted. The prevalence, intensity, density, and biodiversity of copepod infection of 480 colonies of the reef-building coral Pocillopora damicornis (Linnaeus, 1758) from Nanwan Bay, southern Taiwan were documented between July 2007 and November 2008. It was hypothesized that certain environmental factors and physiological coral traits, such as the density of Symbiodinium, could influence these infection parameters. Analysis revealed that ectoparasitic copepods were the most likely to infect P. damicornis, and that Asteropontius minutus Kim, 2003 accounted for more than 50% of total copepod density in July-September 2007 when temperatures were high and bleaching occurred in similar to 75% of the sampled colonies. The data further showed that copepod virulence may be related to their life history strategies, as well as to Symbiodinium density, surface area of the host coral colonies, and concentration of nitrate and chlorophyll-a in the surrounding seawater. By tracking the abundance, diversity, and performance of infectious copepods prior, throughout, and after a natural bleaching event, the potential to use these parasites as bioindicators for predicting the future physiological performance of P. damicornis in response to environmental change, particularly bleaching events, may ultimately be further explored, developed and maximized. Humesimyzon Kim, 2010, previously placed in the Asterocheridae, is tentatively transferred to the recently resurrected family Coralliomyzontidae. The authorship and spelling of Pseudanthessius thorellii (Brady, 1880) are corrected.
Reports of coral disease have increased dramatically over the last decade; however, the biological mechanisms that corals utilize to limit infection and resist disease remain poorly understood. Compromised coral tissues often display non-normal pigmentation that potentially represents an inflammation-like response, although these pigments remain uncharacterized. Using spectral emission analysis and cryo-histological and electrophoretic techniques, we investigated the pink pigmentation associated with trematodiasis, infection with Podocotyloides stenometre larval trematode, in Porites compressa. Spectral emission analysis reveals that macroscopic areas of pink pigmentation fluoresce under blue light excitation (450 nm) and produce a broad emission peak at 590 nm (±6) with a 60-nm full width at half maximum. Electrophoretic protein separation of pigmented tissue extract confirms the red fluorescence to be a protein rather than a low-molecular-weight compound. Histological sections demonstrate green fluorescence in healthy coral tissue and red fluorescence in the trematodiasis-compromised tissue. The red fluorescent protein (FP) is limited to the epidermis, is not associated with cells or granules, and appears unstructured. These data collectively suggest that the red FP is produced and localized in tissue infected by larval trematodes and plays a role in the immune response in corals.
Coral-associated invertebrates are the most significant contributors to the diversity of reef ecosystems, but no studies have examined how larvae manage to settle and grow in their coral hosts. Video recordings were used to document this process in the coral barnacle Darwiniella angularis associated with the coral Cyphastrea chalcidicum. Settlement and metamorphosis in feeding juveniles lasted 8-11 days and comprised six phases. The settling cyprid starts by poking its antennules into the tissue of the prospective host (I: probing stage). The coral releases digestive filaments for defence, but tolerating such attack the cyprid penetrates further (II: battling stage). Ecdysis is completed 2 days after settlement (III: carapace detachment). The barnacle becomes embedded deep in the coral tissue while completing metamorphosis between 4 and 6 days (IV: embedding stage), but reappears as a feeding juvenile 8-11 days after settlement (V: emerging stage; VI: feeding stage). Cyprids preferably settle in areas between the coral polyps, where they have a much higher survival rate than on the polyp surfaces. © 2016 The Author(s) Published by the Royal Society. All rights reserved.
This study describes the association between the obligatory symbiont coral gall crab Hapalocarcinus marsupialis and its stony coral hosts Seriatopora sp. within the Great Reef of Toliara in Madagascar and attempts to discuss their symbiotic status through comparison with previous studies. These corals are inhabited by crabs living in galls that can be categorised in four distinct morphological stages, where the first one corresponds to a small bud and the last one represents a completely closed gall surrounding the crab inside. Within the reef, 563 colonies of Seriatopora species were observed by scuba-diving at ten different stations: 37.8% of them were infested by H. marsupialis, with a total of 763 galls, and with a majority of stage 4 galls. Galls are monopolised by females that can have different morphologies. Females store the sperm in two spermathecae and are fertilised when their morphology and size are similar to males and the gall is not closed. Histological observations coupled with scanning electronic microscopy analyses show that closed galls are made of an external living tissue, a mid skeletal layer and an internal living tissue. The internal living tissue includes polyps similar to the external tissue, some of them being sexually mature. Nitrogen and carbon isotopic signatures confirmed that these crabs are filter-feeders and do not feed on their host. This association perfectly highlights the difficulties to define the symbiotic status of a symbiont if one considers inflexible the three categories of symbiosis commonly defined.
Symbiont community assembly is driven by host–symbiont and symbiont–symbiont interactions. The effects that symbionts exert on their hosts are often context‐dependent, and existing theoretical frameworks of symbiont community assembly do not consider the implications of variable outcomes to assembly processes.
We hypothesized that symbiont–symbiont interactions become increasingly important along a parasitism/mutualism continuum because; (i) negative outcomes favour host resistance which in turn reduces symbiont colonization and subsequently reduce symbiont–symbiont interactions, whereas (ii) positive host outcomes favour tolerance and consequently higher symbiont colonization rates, leading to stronger interactions among symbionts. We found support for this hypothesis in the cleaning symbiosis between crayfish and ectosymbiotic branchiobdellidan worms.
The symbiosis between crayfish and their worms can shift from parasitism/commensalism to mutualism as crayfish age. Here, field surveys identified changes in worm density, diversity and composition that were concomitant to changing symbiosis outcomes. We conducted several laboratory experiments and behavioural assays to relate patterns from the field to their likely causal processes.
Young crayfish typically hosted only two relatively small worm species. Older crayfish hosted two additional larger species. In laboratory experiments, young crayfish exhibited a directed grooming response to all worm species, but were unable to remove small species. Conversely, adult crayfish did not exhibit grooming responses to any worm species. Relaxed grooming allowed the colonization of large worm species and initiated symbiont–symbiont intraguild predation that reduced the abundance and altered the behaviour of small worm species. Thus, the dominant processes of symbiont community assembly shifted from host resistance to symbiont–symbiont interactions through host ontogeny and a concomitant transition towards mutualism.
This work shows that host resistance can have a prevailing influence over symbiont community assembly when symbiosis is disadvantageous to the host. However, when symbiosis is advantageous and resistance is relaxed, symbiont colonization rate and consequently abundance and diversity increases and interactions among symbionts become increasingly important to symbiont community assembly.
Aquaculture of coral offers an alternative to wild harvest for the ornamental trade and shows considerable promise for restoring reefs and preserving biodiversity. Here, we compare advantages and disadvantages of asexually derived fragments versus sexually derived propagules and in situ versus ex situ nursery phases for the ornamental trade and reef restoration. Asexual propagules, sourced from a donor coral colony that is cut into smaller parts and attached to artificial substrate, are most commonly used. The most suitable corals are typically branching species, although fragments from species with other growth forms can be successful, albeit slower growing. Sexually derived propagules are collected from the wild or from colonies in aquaria during spawning, with an artificial substrate provided for settlement. The timing of spawning is known for many broadcast spawning corals, but opportunities for collection of gametes are generally limited to only once or a few times per year. Brooding species with multiple periods of larval release provide better options for culture of sexually derived propagules. Propagation techniques have developed considerably over the past 20 years, yielding faster growth rates, reduced mortality and reduced detachment from substrates. Simple and cost–effective propagation techniques can be used to restore denuded reefs, preserve endangered species, provide live corals to the international ornamental trade, enable livelihood diversification for coastal communities and provide experimental materials for marine research. This review provides a comprehensive synthesis of recent developments in aquaculture propagation techniques for the purpose of ornamental trade and coral reef restoration, including asexual and sexual propagation, nursery and transplantation stages.
In recent decades, the cover of fleshy macroalgae has increased and coral cover has decreased on most Caribbean reefs. Coral mortality precipitated this transition, and the accumulation of macroalgal biomass has been enhanced by decreased herbivory and increased nutrient input. Populations of Acropora palmata (elkhorn coral) and A. cervicornis (staghorn coral), two of the most important framework-building species, have died throughout the Caribbean, substantially reducing coral cover and providing substratum for algal growth. Hurricanes have devastated local populations of Acropora spp. over the past 20–25 years, but white-band disease, a putative bacterial syndrome specific to the genus Acropora, has been a more significant source of mortality over large areas of the Caribbean region.
Paleontological data suggest that the regional Acropora kill is without precedent in the late Holocene. In Belize, A. cervicornis was the primary ecological and geological constituent of reefs in the central shelf lagoon until the mid-1980s. After constructing reef framework for thousands of years, A. cervicornis was virtually eliminated from the area over a ten-year period. Evidence from other parts of the Caribbean supports the hypothesis of continuous Holocene accumulation and recent mass mortality of Acropora spp. Prospects are poor for the rapid recovery of A. cervicornis, because its reproductive strategy emphasizes asexual fragmentation at the expense of dispersive sexual reproduction. A. palmata also relies on fragmentation, but this species has a higher rate of sexual recruitment than A. cervicornis If the Acropora spp. do not recover, macroalgae will continue to dominate Caribbean reefs, accompanied by increased abundances of brooding corals, particularly Agaricia spp. and Porites spp. The outbreak of white-band disease has been coincident with increased human activity, and the possibility of a causal connection should be further investigated.
The Hoekiini Ross and Newman, 1995 includes four genera of coral-eating, pyrgomatid barnacles. They parasitise only the zooxanthellate, scleractinian coral Hydnophora Fischer, 1807, which occurs throughout most of the Indo-West Pacific. All of the known species have an irregularly shaped shell found nestled cryptically beneath the tissues between the hydnons of the coral. These barnacles are readily distinguished from the setose-feeding pyrgomatids not only by subsisting on the soft tissues of the host that cover the minute orifice, but also in apparently being absorptive parasites. Until now Hydnophora of the Great Barrier Reef was not known to be infected by these parasites. The few samples available not only harbour a far greater concentration of individuals than noted previously, but also display a distinctive morphology. These represent a new genus and species for which we propose Australhoekia cardenae.
The coral-eating barnacle Hoekia monticulariae (Gray, 1831), the only internal parasite among the Thoracica described to this day, is characterized by an irregularly-shaped shell nestled cryptically between the polyps of the hermatypic coral Hydnophora Fischer, 1807, which occurs throughout most of the Indo-West Pacific. Because of its protean form, cirripedologists have failed to appreciate the diversity of taxa related to Hoekia, a presumed monotypic genus. We describe seven new species divided between Hoekia and three new genera, Eohoekia, Parahoekia, and Ahoekia for which the Tribe Hoekiini is proposed. As in other pyrgomatids, calcareous overgrowth by the coral is inhibited around the edge of the wall and aperture. But in Hoekiini a pseudopolyp, upon which the barnacle feeds with modified trophi, covers the wall and aperture. Furthermore, rather than articulating with a calcareous basis, the wall is suspended in coral tissue. Its hypertrophied lateral margin (= basal margin), in contact with the host's tissue, is the site where metabolic activities are inferred to take place. In Hoekia and Ahoekia, the wall develops simple or connecting tubes that lead to openings in the margin, which serve as circulatory pathways. A hypertrophied margin and elaborated circulatory system suggests that the Hoekiini may not be wholly dependent on feeding directly on host tissue and/or coelenteronic material, but may also be absorptive parasites. Although other pyrgomatids, in the tribes Pyrgopsellini nov. and Pyrgomatini nov., exercise some control over their hosts by an apertural frill and through discontinuities between the shell and basis, they are still planktotrophic.
A flatworm isolated from bleached colonies of the coral Coscinaraea marshae at Rottnest Island,
Western Australia, is described using a combination of morphological and molecular systematics.
This flatworm shares morphological features characteristic of the genus Waminoa (Acoelomorpha:
Acoela), including the presence of two algal symbionts, but appears to have genital regions different
from those of other described species of Waminoa. The design of new oligonucleotide primers
enabled the amplification of partial 18S rDNA of the Rottnest Island acoel specimens, and phylogenetic
analysis positioned them within Waminoa, confirming their placement in the genus. Furthermore,
Waminoa specimens from Rottnest Island grouped into a sister clade to Waminoa
brickneri, indicating that the morphological and genetic differences observed are most likely
intraspecific and due to geographic variation. As such, we name these Rottnest Island specimens
W. cf. brickneri, but highlight that key differences warrant further exploration before assignment to
this species can be confirmed. This is the first acoel flatworm described from Western Australia and
contributes to our understanding of the diversity and evolutionary relationship of the Acoela.
The infection dynamics and distribution of the ectoparasitic fish monogenean Neobenedenia sp. (Monogenea: Capsalidae) throughout its development was examined on barramundi, Lates calcarifer (Bloch) (Latidae), by labelling transparent, ciliated larvae (oncomiracidia) with a fluorescent dye. Replicate fish were each exposed to approximately 50 fluorescent oncomiracidia and then examined for parasites using an epifluorescence stereomicroscope at 10 time intervals post-exposure (15, 30, 60, 120 min, 24, 48 h, four, eight, 12, and 16 days). Fluorescent labelling revealed that parasites attached underneath and on the surface of the scales of host fish. Parasite infection success was 20% within 15 min, and peaked at 93% two days post-exposure, before gradually declining between four and sixteen days. Differences in parasite distribution on L. calcarifer over time provided strong evidence that Neobenedenia sp. larvae settled opportunistically and then migrated to specific microhabitats. Parasites initially attached (<24 h) in greater mean numbers on the body surface (13 ± 1.5) compared to the fins (4 ± 0.42) and head region (2 ± 0.41). Once larvae recruitment had ceased (48 h), there were significantly higher mean post-larvae counts on the head (5 ± 3.4) and fins (12 ± 3) compared to previous time intervals. Neobenedenia sp. aggregated on the eyes, fins, and dorsal and ventral extremities on the main body. As parasites neared sexual maturity, there was a marked aggregation on the fins (22 ± 2.35) compared to the head (4 ± 0.97) and body (9 ± 1.33), indicating that Neobenedenia sp. may form mating aggregations.
Coral-inhabiting gall crabs are either obligate symbionts or parasitic associates with their host corals. They form a variety of galls/pits inside the skeleton of living corals. Nine genera of gall crabs on several scleractinian corals were used to test the hypothesis that galls vary among cryptochirid genera. Phylogenetic and morphometric observations were combined to analyze the possible evolutionary significance of gall construction. A high degree of conservation of gall shapes was observed in relation to the gall crabs' phylogeny. Gall/pit morphology and fidelity was studied in each of the different species of gall crabs. In addition, the correlation analysis results showed a significant linear relationship between crab size (carapace width) and its gall/pit size (opening diameter of gall/pit) (p < 0.001), demonstrating that crabs have the ability to create the gall/pit size which suits to their own size. Phylogenetically related crab species exhibit similar gall shapes; thus, the galls/pit morphology can be considered as an extention of the crabs' phenotypes.
Pea crabs are globally ubiquitous symbionts in the marine environment that cause serious economic impact in the aquaculture production of several major bivalve species. However, little is known about their host-parasite interactions, especially the mating behaviour of these parasites that could prove useful for controlling their infestation in aquaculture. In this study, the mate location behaviour of male New Zealand pea crabs, Nepinnotheres novaezelandiae (Filhol, 1885), was observed when dwelling in its preferred host, the commercially important green-lipped mussel, Perna canaliculus. Given the cryptic behaviour of the male crabs, a novel trapping system was developed to determine whether male crabs would exit their mussel hosts in response to an upstream female crab. The presence of receptive female crabs placed upstream successfully attracted 60% of male crabs from their host over 24 h. Observations of the nocturnal mate-finding behaviour of male crabs were made in darkness using infrared video recordings. Males spent on average 49 min on empty hosts and never left a mussel containing a female conspecific once found, spending 200 min on average to gain entry to the mussel. Male crabs were often observed stroking the mantle edge of the mussel whilst attempting to gain entry, successfully increasing mussel valve gape during entry from 3.7 to 5.5 mm. A pheromone-based mate location system is likely used by this crab to greatly reduce the risks associated with the location of females.
© O. Trottier and A.G. Jeffs, published by EDP Sciences, 2015.
Coral mariculture involves time-consuming removal of fouling. On natural reefs, this service is provided by grazers. As natural reefs also harbour corallivores, it is debated whether reef-bound fish have a positive or negative effect on coral maricultured near natural reefs. This study quantified the net impact of herbivorous and corallivorous fish on coral mariculture. Nursery trees either uncaged, caged or as cage-control (15 per treatment) were placed near a patch reef at Wasini, Kenya, each hosting 10 Acropora verweyi fragments. From April to July 2016, survival and growth of the corals and bite marks on the corals were monitored. Using remote underwater video, bites by herbivorous and corallivorous fish were quantified. Upon termination of the experiment, dry weight of fouling from the nursery trees was determined. Caging of nurseries strongly reduced herbivory and corallivory. Results of cage-controls were not significantly different from uncaged trees. In caged nurseries, coral survival and growth were significantly lower than in uncaged nurseries, respectively 9% and 40% lower. Fouling was nearly 800% higher in caged nurseries. Herbivory was dominated by the surgeonfish Ctenochaetus striatus, which was responsible for 77% of the grazing. Monthly assessments showed bite marks on 10% of the uncaged coral fragments. Our study reveals that fouling control by herbivorous fish outweighs the costs of incidental corallivory on the survival and growth of A. verweyi. The vigour of unrestricted fouling, its negative impact on coral performance and the scarcity of corallivory justify the recommendation to place coral nurseries in Wasini near the reef.
The biodiversity of coral reefs is dominated by invertebrates. Many of these invertebrates live in close association with scleractinian corals, relying on corals for food, habitat or settlement cues. Given their strong dependence on corals, it is of great concern that our knowledge of coralassociated invertebrates is so limited, especially in light of severe and ongoing degradation of coral reef habitats and the potential for species extinctions. This review examines the taxonomic extent of coral-associated invertebrates, the levels of dependence on coral hosts, the nature of associations between invertebrates and corals, and the factors that threaten coral-associated invertebrates now and in the future. There are at least 860 invertebrate species that have been described as coral associated, of which 310 are decapod crustaceans. Over half of coral-associated invertebrates appear to have an obligate dependence on live corals. Many exhibit a high degree of preference for one or two coral species, with species in the genera Pocillopora, Acropora and Stylophora commonly preferred. This level of habitat specialization may place coral-associated invertebrates at a great risk of extinction, particularly because preferred coral genera are those most susceptible to coral bleaching and mortality. In turn, many corals are also reliant on the services of particular invertebrates, leading to strong feedbacks between abundance of corals and their associated invertebrates. The loss of even a few preferred coral taxa could lead to a substantial decline in invertebrate biodiversity and have far-reaching effects on coral reef ecosystem function. A full appreciation of the consequences of further coral reef degradation for invertebrate biodiversity awaits a more complete description of the diversity of coral-associated invertebrates, the roles they play in coral reef ecosystems, their contribution to reef resilience and their conservation needs. © R. N. Gibson, R. J. A. Atkinson, J. D. M. Gordon, I. P. Smith and D. J. Hughes, Editors Taylor & Francis. All rights reserved.
Podocotyloides stenometra Pritchard, 1966 (Digenea: Opecoelidae) is the only trematode known to infect anthozoan corals. It causes disease in coral polyps of the genus Porites Link (Scleractinia: Poritidae) and its life-cycle depends on ingestion of these polyps by butterflyfishes (Perciformes: Chaetodontidae). This species has been reported throughout the Indo-Pacific, from the Seychelles to the Galápagos, but no study has investigated whether multiple species are involved. Here, we recollect P. stenometra from its type-host and type-locality, in Hawaiian waters, and describe four new species from examination of 768 butterflyfishes from French Polynesia. On the basis of morphology, phylogeny and life-history, we propose Polypipapiliotrema Martin, Cutmore & Cribb n. gen. and the Polypipapiliotrematinae Martin, Cutmore & Cribb n. subf., for P. stenometra (Pritchard) n. comb., P. citerovarium Martin, Cutmore & Cribb n. sp., P. hadrometra Martin, Cutmore & Cribb n. sp., P. heniochi Martin, Cutmore & Cribb n. sp., and P. ovatheculum Martin, Cutmore & Cribb n. sp. Given the diversity uncovered here and the ubiquity, abundance and diversity of butterflyfishes on coral reefs, we predict that Polypipapiliotrema will prove to comprise a rich complex of species causing disease in corals across the Indo-Pacific. The unique life-cycle of these taxa is consistent with phylogenetic distinction of the group and provides evidence for a broader basis of diversification among the family. We argue that life-cycle specialisation, in terms of adoption of disparate second intermediate host groups, has been a key driver of the diversification and richness of the Opecoelidae, the largest of all trematode families and the group most frequently encountered in coral reef fishes.
Rapidly changing climate regimes combined with other anthropogenic pressures are implicated in increased disease epizootics among reef building corals, resulting in changing habitat structure. These accumulated stressors directly contribute to disease outbreaks by compromising the coral host immune system, modulating virulence of microbial pathogens, and/or disrupting the balance within the microbiome of the holobiont. Disentangling coral disease causation has been challenging, and while progress has been made for certain diseases in terms of the roles the associated microorganisms play, it is evident that like in other marine or terrestrial systems, compromised host health cannot always be attributed to a single causative agent. Here, we summarise the current state in knowledge of microbial induced coral diseases, and discuss challenges and strategies to further disentangle disease causation. With the major environmental pressures coral reefs face over the next century, understanding interactions between host, environmental and microbial causative agent(s) that lead to disease, is still a priority to enable development of effective strategies for building resilience into coral populations. This article is protected by copyright. All rights reserved.
During 2015-2016, record temperatures triggered a pan-tropical episode of coral bleaching, the third global-scale event since mass bleaching was first documented in the 1980s. Here we examine how and why the severity of recurrent major bleaching events has varied at multiple scales, using aerial and underwater surveys of Australian reefs combined with satellite-derived sea surface temperatures. The distinctive geographic footprints of recurrent bleaching on the Great Barrier Reef in 1998, 2002 and 2016 were determined by the spatial pattern of sea temperatures in each year. Water quality and fishing pressure had minimal effect on the unprecedented bleaching in 2016, suggesting that local protection of reefs affords little or no resistance to extreme heat. Similarly, past exposure to bleaching in 1998 and 2002 did not lessen the severity of bleaching in 2016. Consequently, immediate global action to curb future warming is essential to secure a future for coral reefs.
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The Reef Aquarium Volume Three: Science, Art, and Technology Reefkeeping science involves the interplay of biology, chemistry, and physics. However, a reef aquarium is not simply a product of scientific knowledge. The application of engineering and its product technology, makes it possible to duplicate the specific biological, chemical, and physical requirements of a coral reef in a relatively small volume of water. This third volume in The Reef Aquarium series, provides the most thorough description of the science behind the creation of a captive reef, and critically reviews and explains the different philosophical approaches to reef aquarium design. It also describes and illustrates the existing as well as emerging technology for building reef aquariums, to help guide the selection of equipment, its proper use, and installation. While science and technology afford the blank canvas and tools to build a suitable life support system, the plants, animals, and of course the aquarist provide the final ingredient that we call art. This art also involves the system design as it relates to the living space, the aesthetic appearance of the display, and its ease of maintenance, safety, and functionality. To this end, this book provides a wealth of information regarding aquascaping techniques, which combine art, biology, and physics; and invaluable information regarding plumbing, electrical, and other aspects of the aquarium design that combine art and engineering. Lastly, this book discusses the benefits and potential environmental impacts of the marine aquarium hobby, the challenges for its future, and possible new directions. The Reef Aquarium volume three is the essential manual for all reef aquarium hobbyists, professional aquarists, and coral reef researchers who study, create, and enjoy coral reef ecosystems in the confines of an aquarium.
Many ecosystems around the world are rapidly deteriorating due to both local and global pressures, and perhaps none so precipitously as coral reefs. Management of coral reefs through maintenance (e.g., marine-protected areas, catchment management to improve water quality), restoration, as well as global and national governmental agreements to reduce greenhouse gas emissions (e.g., the 2015 Paris Agreement) is critical for the persistence of coral reefs. Despite these initiatives, the health and abundance of corals reefs are rapidly declining and other solutions will soon be required. We have recently discussed options for using assisted evolution (i.e., selective breeding, assisted gene flow, conditioning or epigenetic programming, and the manipulation of the coral microbiome) as a means to enhance environmental stress tolerance of corals and the success of coral reef restoration efforts. The 2014–2016 global coral bleaching event has sharpened the focus on such interventionist approaches. We highlight the necessity for consideration of alternative (e.g., hybrid) ecosystem states, discuss traits of resilient corals and coral reef ecosystems, and propose a decision tree for incorporating assisted evolution into restoration initiatives to enhance climate resilience of coral reefs.
A new species of aeolid nudibranch mollusc of the genus Phestilla (Tergipedidae) is described from the Bay of Panama, on the Pacific coast of tropical America. It feeds on the scleractinian coral Porites lobata and preliminary histological evidence suggests that it may have a symbiosis with zooxanthellac it removes from the Porites tissue.
The copepod Tegastes acroporanus is a notorious pest of captive corals in the genus Acropora. In recent years, infestations of T. acroporanus have become widespread among public aquaria and coral propagation facilities and have been largely controlled with the extra-label use of milbemycin oxime formulations (Carl 2008). Many of these drug formulations (which were intended for dogs) have been discontinued by their manufacturers in favor of multidrug products, many of which are unsuitable for corals, forcing experimentation with alternatives. This report provides the first data on populations of T. acroporanus treated with milbemycin oxime and documents the first known use of an otic solution, MilbeMite Otic (Novartis Animal Health U.S., Greensboro, North Carolina), against copepods on live corals. MilbeMite Otic was found to be soluble in seawater and successful at eradicating T. acroporanus in a large exhibit over the course of 6-h waterborne baths (n = 12) at 0.167 µg/L. The resident population of T. acroporanus was also quantified before each treatment to provide the first estimates of coral parasite burden in response to the application of a waterborne chemotherapeutic agent.
Received November 19, 2015; accepted June 7, 2016
Two species of the poecilostomatoid copepods, Allopodion ryukyuensis n. sp. and Xenomolgus varius Humes and Stock, are recorded from galls and crypts on the scleractinian corals Montipora informis and Porites sp.(p), respectively, in Okinawa, Japan. Allopodion ryukyuensis is distinguished from its sole congener, A. mirum Humes, by having shorter caudal rami and abdominal somites, rounded lateral margins of the female genital double-somite, and a greater number of setal elements on the third exopodal segment of legs 2-4. The morphological features of the galls and crypts on the scleractinian hosts inhabited by A. ryukyuensis and X. varius are described, and it is proposed that certain other scleractinian-associated copepods likely also make use of similar habitations.
White plague is one of the most devastating coral diseases in the Caribbean, and yet important aspects of its epidemiology, including how the disease transmits, remain unknown. This study tested potential mechanisms and rates of transmission of white plague in a laboratory setting. Transmission mechanisms including the transport of water, contact with macroalgae, and predation via corallivorous worms and snails were tested on the host species Orbicella annularis. Two of the tested mechanisms were shown to transmit disease: water transport and the corallivorous snail Coralliophila
abbreviata. Between these transmission mechanisms, transport of water between a diseased coral and a healthy coral resulted in disease incidence significantly more frequently in exposed healthy corals. Transmission via water transport also occurred more quickly and was associated with higher rates of tissue loss (up to 3.5 cm d−1) than with the corallivorous snail treatment. In addition, water that was in contact with diseased corals but was filtered with a 0.22-μm filter prior to being introduced to apparently healthy corals also resulted in the transmission of disease signs, but at a much lower rate than when water was not filtered. This study has provided important information on the transmission potential of Caribbean white plague disease and highlights the need for a greater understanding of how these processes operate in the natural environment.
Barnacles of the genus Galkinius occupy a large spectrum of host corals, making it one of the least host-specific genera within the Pyrgomatidae. Molecular analyses show that within the genus Galkinius there are highly supported clades, suggesting that the genus Galkinius is a complex of evolutionarily significant units (ESUs). The morphology of the opercular valves has been used as the basis for the separation of species of Galkinius. In this study, morphological variability was found both between specimens within ESUs extracted from different host species and between specimens extracted from the same colony. Identifications based on the opercular valves cannot therefore be assigned to different species despite being genetically distinguishable. It is proposed that in many cases the differences between valve morphology of different species of Galkinius are the outcome of ontogeny. Allometric growth of the valves has resulted in differences in the proportions of the parts of the valve.
Incidences of coral disease are increasing. Most studies which focus on diseases in these organisms routinely assess variations in bacterial associates. However, other microorganism groups such as viruses, fungi and protozoa are only recently starting to receive attention. This study aimed at assessing the diversity of ciliates associated with coral diseases over a wide geographical range. Here we show that a wide variety of ciliates are associated with all nine coral diseases assessed. Many of these ciliates such as Trochilia petrani and Glauconema trihymene feed on the bacteria which are likely colonizing the bare skeleton exposed by the advancing disease lesion or the necrotic tissue itself. Others such as Pseudokeronopsis and Licnophora macfarlandi are common predators of other protozoans and will be attracted by the increase in other ciliate species to the lesion interface. However, a few ciliate species (namely Varistrombidium kielum, Philaster lucinda, P. guamensis, a Euplotes sp., a Trachelotractus sp. and a Condylostoma sp.) appear to harbor symbiotic algae, potentially from the coral themselves, a result which may indicate they play some role in the disease pathology at the very least. Although, from this study alone we are not able to discern what roles any of these ciliates play in disease causation, the consistent presence of such communities with disease lesion interfaces warrants further investigation.
While the majority of acoels live in marine sediments, some, usually identified as Waminoa sp., have been found associated with corals, living closely appressed to their external surfaces. We describe a new species collected from the stony coral Plesiastrea laxa in the Red Sea. Waminoa brickneri n. sp. can infest corals in high numbers, often forming clusters in non-overlapping arrays. It is bronze-colored, owing to the presence of two types of dinoflagellate endosymbionts, and speckled white with small scattered pigment spots. Its body is disc-shaped, highly flattened and circular in profile except for a small notch at the posterior margin where the reproductive organs lie. The male copulatory organ is poorly differentiated, but comprises a seminal vesicle weakly walled by concentrically layered muscles, and a small penis papilla with serous glands at its juncture with the male pore. The female system comprises a separate female pore, ciliated vagina, seminal bursa, 4-8 weakly sclerotized nozzles, and paired ovaries. Similarities with Haplodiscus spp. as well as features characteristic of the Convolutidae, including similarity in 18S rDNA sequence, warrant reassigning Waminoa to the Convolutidae.