Cryptochiridae Research Articles

An Indo-West Pacific Distribution for the Coral-Dwelling Gall Crab Lithoscaptus doughnut (Decapoda: Cryptochiridae)

Coral-dwelling gall crabs (Cryptochiridae) are common inhabitants of scleractinian corals. Several species have been described as new in recent years, including Lithoscaptus doughnut, which was described from Hong Kong based on a single female retrieved from the coral Plesiastrea peroni. Here we extend the distribution range of L. doughnut with nine additional localities throughout the Indo-West Pacific, from the Red Sea to the Coral Triangle and Japan. We describe a male specimen of L. doughnut for the first time, based on a specimen from Malaysia, and provide photographs of life and preserved material. Haplotype networks based on COI mtDNA (n = 12) and 16 rRNA sequences (n = 12) were created. We retrieved eleven COI haplotypes and six 16S haplotypes, however no clear geographic distribution pattern was discerned. Intraspecific variation in L. doughnut was 1.4% for COI and 0.2% for 16S. Lastly, the first colour photos and records of associated parasites of this species are provided.

Dining on corals: stable isotope evidence for close trophic connection between gall crabs (Cryptochiridae) and their stony coral hosts

The exact nature of the relationship between symbiont fauna and their hosts is often unclear, but knowing more about these intricate ecological interactions is vital to understand the trophic positions of host-associated fauna, and can aid in accurate constructions of food-webs on coral reefs. Scleractinian corals are hosts to hundreds of symbiont taxa, including fish and many invertebrate species. Some of these associated fauna are beneficial to their coral host(s), whereas other taxa can have detrimental effects, yet their impact is often difficult to determine. Coral-dwelling gall crabs (Cryptochiridae) are obligate, often host-specific, symbionts of scleractinian corals but the nature of this relationship is still under debate. Three Atlantic gall crab species (Kroppcarcinus siderastreicola, Opecarcinus hypostegus and Troglocarcinus corallicola) and their coral hosts’ tissue/mucus were collected from reefs in Guadeloupe. Stable carbon and nitrogen isotope values were measured for 57 crabs inhabiting host coral colonies belonging to seven different coral species (although only 27 colonies from five coral species were collected), alongside other potential food sources (epilithic algal matrix, plankton and particulate organic matter). The carbon and nitrogen isotope values of gall crabs relative to those of their respective coral host(s) and other possible food sources showed that coral tissue/mucus was the main food source for the crabs. The results of the mixing models further supported this finding, suggesting that corals are responsible for 40–70% of the crabs’ diet. In T. corallicola, the isotopic signature differed significantly between sexes, possibly caused by the high sexual dimorphism observed in this species. Here we showed that Atlantic gall crabs mainly dine on coral tissue and/or mucus excreted by their coral hosts, highlighting their nutritional dependence on their host. However, since coral mucus is continuously exuded by scleractinians, hence the energetic or metabolic drain for corals is expected to be minimal. Gall crabs depend on their coral hosts for settlement cues as larvae, for habitat as adults and - highlighted by this study - for food, essential for their subsistence. This obligate dependence on their hosts for all parts of their life makes them extremely vulnerable to reef degradation, and underlines the importance in understanding the exact nature of a relationship between symbiont and coral host.

Phylomitogenomics elucidates the evolution of symbiosis in Thoracotremata (Decapoda: Cryptochiridae, Pinnotheridae, Varunidae).

Thoracotremata belong to the large group of "true" crabs (infraorder Brachyura), and they exhibit a wide range of physiological and morphological adaptations to living in terrestrial, freshwater and marine habitats. Moreover, the clade comprises various symbiotic taxa (Aphanodactylidae, Cryptochiridae, Pinnotheridae, some Varunidae) that are specialised in living with invertebrate hosts, but the evolutionary history of these symbiotic crabs is still partially unresolved. Here we assembled and characterised the complete mitochondrial genomes (hereafter mitogenomes) of three gall crab species (Cryptochiridae): Kroppcarcinus siderastreicola, Opecarcinus hypostegus and Troglocarcinus corallicola. A phylogenetic tree of the Thoracotremata was reconstructed using 13 protein-coding genes and two ribosomal RNA genes retrieved from three new gall crab mitogenomes and a further 72 available thoracotreme mitogenomes. Furthermore, we applied a comparative analysis to characterise mitochondrial gene order arrangement, and performed a selection analysis to test for selective pressure of the protein-coding genes in symbiotic Cryptochiridae, Pinnotheridae, and Varunidae (Asthenognathus inaequipes and Tritodynamia horvathi). The results of the phylogenetic reconstruction confirm the monophyly of Cryptochiridae, which clustered separately from the Pinnotheridae. The latter clustered at the base of the tree with robust branch values. The symbiotic varunids A. inaequipes and T. horvathi clustered together in a clade with free-living Varunidae species, highlighting that symbiosis in the Thoracotremata evolved independently on multiple occasions. Different gene orders were detected in symbionts and free-living species when compared with the ancestral brachyuran gene order. Lastly, the selective pressure analysis detected two positively selected sites in the nad6 gene of Cryptochiridae, but the evidence for positive selection in Pinnotheridae and A. inaequipes and T. horvathi was weak. Adaptive evolution of mitochondrial protein-coding genes is perhaps related to the presumably higher energetic demands of a symbiotic lifestyle.

Host specificity of coral-associated fauna and its relevance for coral reef biodiversity

Coral-associated fauna predominantly consists of invertebrates and constitutes an important component of coral reef biodiversity. The symbionts depend on their hosts for food, shelter and substrate. They may act as parasites by feeding on their hosts, by overgowing their polyps, or by excavating their skeletons. Because some of these species partly reside inside their hosts, they may be cryptic and can easily be overlooked in biodiversity surveys. Since no quantitative overview is available about these inter-specific relationships, this present study adresses variation in host ranges and specificity across four large coral-associated taxa and between the Atlantic and Indo-Pacific oceans. These taxa are: coral barnacles (Pyrgomatidae, n = 95), coral gall crabs (Cryptochiridae, n = 54), tubeworms (Serpulidae, n = 31), and date mussels (Lithophaginae, n = 23). A total of 335 host coral species was recorded. An index of host specificity (STD) was calculated per symbiont species, based on distinctness in taxonomic host range levels (species, genus, family, etc.). Mean indices were statistically compared among the four associated taxa and the two oceanic coral reef regions. Barnacles were the most host-specific, tubeworms the least. Indo-Pacific associates were approximately 10 times richer in species and two times more host-specific than their Atlantic counterparts. Coral families varied in the number of associates, with some hosting none. This variation could be linked to host traits (coral growth form, maximum host size) and is most probably also a result of the evolutionary history of the interspecific relationships.

Lithoscaptus aquarius sp. nov. (Decapoda: Cryptochiridae) Described from a Catalaphyllia jardinei (Scleractinia) out of the Aquarium Trade

A new species of gall crab collected from elegance coral, Catalaphyllia jardinei, is described in this paper. The male holotype was collected from a reef tank in Germany in 2016, and it is described here using integrative taxonomy. This species, named Lithoscaptus aquarius sp. nov., is the thirteenth assigned to the genus. It is morphologically and phylogenetically closest to Lithoscaptus semperi, a cryptochirid associated with Trachyphyllia geoffroyi. Like L. semperi, it has a large, broad W-shaped depression on the anterior half of the carapace, but the carapace surface of L. aquarius sp. nov. is smooth overall, lacking spines or tubercles. This new species is so named because it was found in a reef tank after searching in vain for material during fieldwork campaigns over the course of several years.

A Red Sea Depth Record of the Coral-Dwelling Crab Opecarcinus (Decapoda: Cryptochiridae) in the Mesophotic Zone

Coral-dwelling gall crabs (Cryptochiridae) are obligate symbionts of stony corals and occur on shallow and deep reefs across the tropical belt. The circumtropical genus Opecarcinus associates with Agariciidae corals, a dominant component of Mesophotic Coral Ecosystems (MCEs). Here, we report the first Red Sea mesophotic record, with 89 m as the deepest record to date, for Opecarcinus—collected from Leptoseris cf mycetoseroides—from the NEOM marine area in Saudi Arabia. This observation reconfirms the depth range flexibility of Opecarcinus species and highlights the need for further mesophotic explorations of reef-associated fauna.

Interspecific coral competition does not affect the symbiosis of gall crabs (Decapoda: Cryptochiridae) and their scleractinian hosts.

Coral reefs accommodate a myriad of species, many of which live in association with a host organism. Decapod crustaceans make up a large part of this associated fauna on coral reefs. Among these, cryptochirid crabs are obligately associated with scleractinian corals, in which they create dwellings where they permanently reside. These gall crabs show various levels of host specificity, with the majority of cryptochirids inhabiting a specific coral genus or species. Here, we report the first records of gall crabs living in association with two different Porites species in the Red Sea. Crescent-shaped dwellings were observed in Porites rus and a Porites sp. in situ, and colonies with crabs were collected for further study in the laboratory. Using a combination of morphology and DNA barcoding, the crabs were identified as belonging to Opecarcinus, a genus only known to inhabit Agariciidae corals. The coral skeleton was bleached and studied under a stereo microscope, which revealed that the Porites corals overgrew adjoining agariciid Pavona colonies. We hypothesize that the gall crab originally settled on Pavona, its primary host of choice. Due to coral interspecific competition the Porites colony overgrew the adjacent Pavona colonies, resulting in a secondary and never before reported association of Opecarcinus with Porites. These findings suggest that cryptochirid crabs can adapt to the new microenvironment provided by a different coral host and survive competition for space on coral reefs.

Abundance of coral-associated fauna in relation to depth and eutrophication along the leeward side of Curaçao, southern Caribbean

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 at four depths (5, 10, 15, 20 m) and across seven sites with high and five sites with low eutrophication values (based on δ15N isotope data). 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.

Observation of a coral-dwelling gall crab (Cryptochiridae) in a dead coral host highlights their vulnerability to reef degradation

Coral-associated fauna contributes greatly to coral reef biodiversity. Many species are obligately associated with their hosts on which they depend for food and/or refuge from predators. Their close relationship with their hosts makes them vulnerable to coral mortality. Here I report a coral-dwelling gall crab (Cryptochiridae) inhabiting a partially dead Echinopora Lamarck, 1816 coral, at Magoodhoo Island, Faafu Atoll, Maldives. Cryptochirids are thought to feed off the mucus provided by their coral host, although some questions about their feeding biology remain. This observation highlights that these crabs remain associated with a dead host, even if it can no longer provide nutrients. The strong host association makes gall crabs vulnerable to widespread habitat degradation.

Morphology and reproduction in the Hapalocarcinus marsupialis Stimpson, 1859 species complex (Decapoda: Brachyura: Cryptochiridae)

Abstract Symbiotic relationships contribute considerably to the high biodiversity found on coral reefs. Coral-dwelling gall crabs (Cryptochiridae) represent a prime example of coral-associated invertebrates that exhibit obligate relationships with their host. The induction of a skeletal modification in the coral, used as a dwelling by the crab, is the most remarkable aspect of this close association. Here we examined Hapalocarcinus marsupialisStimpson, 1859, collected from Pocillopora and Stylophora corals in the Saudi Arabian Red Sea. Specimens were DNA barcoded, and five distinct clades were revealed, providing further evidence for the hypothesis that H. marsupialis is a species complex. Divergence (COI) between the clades ranged from 3.2 to 15.7%. The putative species were tested for differences in morphology and reproduction. Crabs were examined regarding morphometric characters (carapace length and width, pleon (abdomen), chelae, and growth patterns) and reproductive traits. The data were pooled and analysed by host genus and putative species, which revealed significant differences for most of the measured variables in female crabs. Specimens retrieved from Pocillopora were significantly larger (up to 49 %) and had higher fecundity than those inhabiting Stylophora. For reproductive output (RO) no differences at species- or host-genus level were detected. The average RO of ~70% over all specimens is high compared to other brachyurans, supporting the assumption that symbiotic brachyurans invest more energy in reproduction than their free-living counterparts. Discrepancies with published data on growth and reproduction of Hapalocarcinus are discussed. Our results demonstrate the usefulness of morphometric traits and fecundity in separating the clades in the H. marsupialis complex, and prepare the ground for further morphometric studies on the genus and other symbiotic brachyurans. Moreover, it highlights the need to check for the presence of cryptic species when studying aspects of the biology of a species.

Diversification and distribution of gall crabs (Brachyura: Cryptochiridae: Opecarcinus) associated with Agariciidae corals

Coral reefs are home to the greatest diversity of marine life, and many species on reefs live in symbiotic associations. Studying the historical biogeography of symbiotic species is key to unravelling (potential) coevolutionary processes and explaining species richness patterns. Coral-dwelling gall crabs (Cryptochiridae) live in obligate symbiosis with a scleractinian host, and are ideally suited to study the evolutionary history between heterogeneous taxa involved in a symbiotic relationship. The genus Opecarcinus Kropp and Manning, 1987, like its host coral family Agariciidae, occurs in both Indo-Pacific and Caribbean seas, and is the only cryptochirid genus with a circumtropical distribution. Here, we use mitochondrial and nuclear DNA gene fragments of Opecarcinus specimens sampled from 21 Indo-Pacific localities and one Atlantic (Caribbean) locality. We applied several species delimitation tests to characterise species diversity, inferred a Bayesian molecular-clock time-calibrated phylogeny to estimate divergence times and performed an ancestral area reconstruction. Time to the most recent common ancestor (tMRCA) of Opecarcinus is estimated at 15−6 Mya (middle Miocene—late Miocene). The genus harbours ~ 15 undescribed species as well as several potential species complexes. There are indications of strict host-specificity patterns in certain Opecarcinus species in the Indo-Pacific and Atlantic, however, a robust phylogeny reconstruction of Agariciidae corals—needed to test this further—is currently lacking. The Indo-West Pacific was inferred to be the most probable ancestral area, from where the Opecarcinus lineage colonised the Western Atlantic and subsequently speciated into O. hypostegus. Opecarcinus likely invaded from the Indo-West Pacific across the East Pacific Barrier to the Atlantic, before the full closure of the Isthmus of Panama. The subsequent speciation of O. hypostegus, is possibly associated with newly available niches in the Caribbean, in combination with genetic isolation following the closure of the Panama Isthmus.

The growth and reproductive biology of the coral gall crab, Hapalocarcinus marsupialis Stimpson, 1859 (Crustacea: Cryptochiridae) from Gulf of Aqaba, Red Sea, Egypt

BackgroundGall crabs were described 150 years ago, but little is known about their biology, ecology, and taxonomy. Studying the breeding season can facilitate the understanding of the adaptive strategies and reproductive potential of gall crab and its relationship with the environment and other species.ResultsGrowth and reproductive biology of the coral gall crab, Hapalocarcinus marsupialis, were studied at Gulf of Aqaba, Red Sea, Egypt. A total of 209 specimens were collected from different reef depths during 2014. Relationship between carapace width (CW) and total body wet weight (W) was represented as log W = 0.190 + 2.87 log CW. Growth generally shows negative allometric pattern. While the relation between CW and CL is represented by log CL = 0.019 + 1.009 log CW. This relation is linear and shows an isometric regression coefficient. The overall value for “Kn” is varied from 0.8 to 1.24, with an average of 1.11 ± 0.13, and denotes fitness for females. H. marsupialis shows clear sexual dimorphism and has lengthy definite breeding season characterized by carrying eggs throughout the year. The incubated eggs are semi spherical in shape, with diameter ranges according to maturity stages between 10 and 50 μm. The color of incubated eggs is also varied according to the developmental stage. Most females attain sexual maturity between 2.0 and 2.49 mm CW. Juveniles were recorded during year except the months of January and October. Fecundity varied from 10 to 740 eggs, with an average of 230 ± 173 eggs/female, showing linear relation with carapace width. Significant relationship between carapace width and fecundity was represented by log F = 0.22 + 2.39 log CW.ConclusionThe present study emphasized the reproductive biology of H. marsupialis and explained the size structure, sexual dimorphism, breeding season, fecundity, size at first maturity, and juvenile’s recruitments in the three selected sites Dahab, Nuweiba and Taba along the Gulf of Aqaba.

The stony coral Agaricia tenuifolia Dana, 1848 as a new gall crab host (Decapoda: Cryptochiridae)

Abstract Infrequently studied coral species are seldom mentioned as host organisms of associated fauna. Here we report on the stony coralAgaricia tenuifoliaDana, 1848 hosting a gall crab (Cryptochiridae) for the first time. This coral-dwelling crab was observed at the southern coast of Bonaire in the Dutch Caribbean. Based on the shape of the dwelling, and the host specificity of cryptochirids, the crab is tentatively identified asOpecarcinus hypostegus(Shaw & Hopkins, 1977).

The growth and reproductive biology of the coral gall crab, Hapalocarcinus marsupialis Stimpson, 1859 (Crustacea: Cryptochiridae), from the Gulf of Aqaba, Red Sea, Egypt

BackgroundGall crabs were described 150 years ago, but little is known about their biology, ecology, and taxonomy. Studying the breeding season can facilitate the understanding of the adaptive strategies and reproductive potential of gall crab and its relationship with the environment and other species.ResultsGrowth and reproductive biology of the coral gall crab, Hapalocarcinus marsupialis, were studied at the Gulf of Aqaba, Red Sea, Egypt. A total of 209 specimens were collected from different reef depths during 2014. The relationship between the carapace width (CW) and total body wet weight (W) was represented as Log W = 0.190 + 2.87 Log CW. Growth generally shows a negative allometric pattern, while the relation between CW and the carapace length (CL) is represented by Log CL = 0.019 + 1.009 Log CW. This relation is linear and shows an isometric regression coefficient. The overall value for “kn” is varied from 0.8 to 1.24, with an average of 1.11 ± 0.13, which denotes fitness for females. H. marsupialis shows clear sexual dimorphism and has a lengthy definite breeding season characterized by carrying eggs throughout the year. The incubated eggs are semispherical in shape, with diameter ranges according to maturity stages between 10 and 50 μm. The color of incubated eggs is also varied according to the developmental stage. Most females attain sexual maturity between 2.0- and 2.49-mm CW. Juveniles were recorded during each month of the year except in January and October. Fecundity varied from 10 to 740 eggs, with an average of 230 ± 173 eggs/female, showing linear relation with the carapace width. A significant relationship between the carapace width and fecundity was represented by Log F = 0.22 + 2.39 Log CW.ConclusionThe present study emphasized the reproductive biology of H. marsupialis and explained the size structure, sexual dimorphism, breeding season, fecundity, size at first maturity, and juvenile’s recruitments in the three selected sites Dahab, Nuweiba, and Taba along the Gulf of Aqaba.

Extreme mitochondrial variation in the Atlantic gall crab Opecarcinus hypostegus (Decapoda: Cryptochiridae) reveals adaptive genetic divergence over Agaricia coral hosts

The effectiveness of migration in marine species exhibiting a pelagic larval stage is determined by various factors, such as ocean currents, pelagic larval stage duration and active habitat selection. Direct measurement of larval movements is difficult and, consequently, factors determining the gene flow patterns remain poorly understood for many species. Patterns of gene flow play a key role in maintaining genetic homogeneity in a species by dampening the effects of local adaptation. Coral-dwelling gall crabs (Cryptochiridae) are obligate symbionts of stony corals (Scleractinia). Preliminary data showed high genetic diversity on the COI gene for 19 Opecarcinus hypostegus specimens collected off Curaçao. In this study, an additional 176 specimens were sequenced and used to characterize the population structure along the leeward side of Curaçao. Extremely high COI genetic variation was observed, with 146 polymorphic sites and 187 unique haplotypes. To determine the cause of this high genetic diversity, various gene flow scenarios (geographical distance along the coast, genetic partitioning over depth, and genetic differentiation by coral host) were examined. Adaptive genetic divergence across Agariciidae host species is suggested to be the main cause for the observed high intra-specific variance, hypothesised as early signs of speciation in O. hypostegus.

The coral genus Caulastraea Dana, 1846 (Scleractinia, Merulinidae) as a new host for gall crabs (Decapoda, Cryptochiridae), with the description of Lithoscaptus tuerkayi sp. nov.

A new gall crab species is described from the stony coral genus Caulastraea, a new host coral genus for Cryptochiridae crabs. Specimens were collected during fieldwork off Kudat (Malaysian Borneo) and Okinawa (Japan). Further material was retrieved from the collections of the Institute of Oceanography in Nha Trang (Vietnam). The new species, here named Lithoscaptus tuerkayi sp. nov., is the tenth assigned to the genus in which it is tentatively placed. It can be separated from its congeners by the strongly demarcated, inverted V-shaped protuberance flanking the mesogastric region, with denuded spots on the anterolateral sides of this inverted V-shape, as well as the denuded area just below the frontal margin. Based on morphology and COI sequence data, the closest species to L. tuerkayi sp. nov. is determined to be Lithoscaptus helleri (Fize & Serène, 1957).

Possible links between white plague-like disease, scleractinian corals, and a cryptochirid gall crab.

White plague (WP) is a highly destructive coral disease that rapidly kills susceptible coral species by mass tissue lysis. The pathogen and underlying causes of this disease are not known. In this laboratory-based study, we examined a small coral-associated gall crab from the family Cryptochiridae in terms of a possible association with WP-like lesions. A series of experiments was conducted after observations that 2 scleractinian coral species, Diploria labyrinthiformis and Pseudodiploria strigosa, developed signs of WP-like disease within a laboratory holding aquarium and that small gall crabs were physically present in the center of each lesion. Using fragments of D. labyrinthiformis, a crab from one of the lesions was sequentially removed and placed, under controlled conditions, onto apparently healthy coral colonies, resulting in the development of similar lesions. Next-generation sequencing of the 16S rRNA gene was performed to profile the bacterial communities associated with the crab, lesions, and healthy corals. The microbiota of the crab and lesions were highly similar while that of apparently healthy colonies were significantly different. Significant differences were largely due to an increase in Alphaproteobacteria in crab and lesion communities. In particular, the Roseobacter clade had a higher relative abundance in the crab and WP-like lesions. This study suggests that the cryptochirid gall crab may be associated with development of WP-like lesions.

Helioseris cucullata as a host coral at St. Eustatius, Dutch Caribbean

In order to demonstrate how scleractinian corals contribute to marine biodiversity by their host function, information on associated fauna was gathered during a biological survey at St. Eustatius, eastern Caribbean. This knowledge is especially urgent for a host coral such as Helioseris cucullata (Agariciidae), which has undergone strong declines in abundance at various Caribbean localities and has a poor record of associated fauna. New records of H. cucullata as host are presented for the coral gall crab Opecarcinus hypostegus (Cryptochiridae), the Christmas tree worm Spirobranchus giganteus (Serpulidae) and an unidentified serpulid tube worm of the genus Vermiliopsis. A second association record is reported for the coral barnacle Megatrema madreporarum (Pyrgomatidae). Coral-associated copepods were not found on H. cucullata despite a search for these animals. The new records were compared with previous records of other host coral species that showed elements of the same associated fauna. The present findings indicate that new discoveries concerning Caribbean coral reef biodiversity can still be made during field expeditions by targeting the assemblages of associated fauna of specific benthic host species.

Occurrence patterns of coral-dwelling gall crabs (Cryptochiridae) over depth intervals in the Caribbean.

Coral-associated invertebrates form a major part of the diversity on reefs, but their distribution and occurrence patterns are virtually unstudied. For associated taxa data are lacking on their distribution across shelves and environmental gradients, but also over various depths. Off Curaçao we studied the prevalence and density of coral-dwelling gall crabs (Cryptochiridae), obligate symbionts of stony corals. Belt transects (10 × 0.5m2) were laid out at 6, 12 and 18 m depth intervals at 27 localities. Twenty-one known host coral species were surveyed, measured, and the number of crab dwellings was recorded to study the influence of host occurrence, depth distribution, and colony size on the occurrence rates of three Atlantic gall crab species: Opecarcinus hypostegus, Troglocarcinus corallicola and Kroppcarcinus siderastreicola. The overall gall crab prevalence rate was 20.3% across all available host corals at all depths. The agariciid-associated species O. hypostegus was found to mostly inhabit Agaricia lamarcki and its prevalence was highest at deeper depths, following the depth distribution of its host. Kroppcarcinus siderastreicola, associated with Siderastrea and Stephanocoenia, inhabited shallower depths despite higher host availability at deeper depths. The generalist species T. corallicola showed no clear host or depth specialisation. These results show that the primary factors affecting the distribution and occurrence rates over depth intervals differed between each of the three Atlantic cryptochirid species, which in turn influences their vulnerability to reef degradation.

Old and new DNA unweave the phylogenetic position of the eastern Atlantic gall crabDetocarcinus balssi(Monod, 1956) (Decapoda: Cryptochiridae)

Phylogeny reconstructions based on mtDNA and nDNA have become the standard in studies on relationships between taxa. Difficulties in obtaining material, for example because of small endemic distributions, often lead to gaps in datasets. Collections in natural history museums can provide us with material to fill these gaps, but extracting DNA from historical specimens can be challenging. We used a PCR protocol for small amounts of sample material and high PCR yield on eggs of specimens of the coral-dwelling gall crab family Cryptochiridae collected in 1984, including material from the eastern Atlantic species Detocarcinus balssi. We obtained DNA sequences from seven older museum specimens using newly developed primers, which we combined with COI sequences from recently collected material. Results show that D. balssi is closest to the Indo-Pacific species Utinomiella dimorpha and not closely related to one of the other three Atlantic Cryptochiridae species. The remaining newly acquired DNA sequences from museum material cluster with the respective sequences from recently collected specimens.