Tienderen, K.M. van

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.

Date
2017
Data type
Scientific article
Theme
Research and monitoring
Geographic location
Curacao

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.

Date
2016
Data type
Scientific article
Theme
Research and monitoring
Journal
Geographic location
Curacao

A mesophotic record of the gall crab Opecarcinus hypostegus from a Curacaoan reef

Curaçao, Dutch Caribbean, is home to three species of gall crabs belonging to Cryptochiridae, a family obligatorily associated with a wide range of scleractinian host species. Gall crabs are reliant on their host coral; females are sedentary and never leave their dwelling (van der Meij 2014a). One of the three Atlantic gall crab species is Opecarcinus hypostegus (Shaw and Hopkins, 1977), which inhabits corals of the genus Agaricia. Corals of this genus are abundant in the photic zone (<30 m), but also in the mesophotic zone (30–150 m), where they predominantly belong to Agaricia grahamae Wells, 1973 and Agaricia lamarcki Milne- Edwards and Haime, 1851. The latter was found to be most abundant at depths of 25–60 m (Bongaerts et al. 2013). 

During a survey on 31 March, 2014, with the manned CuraSub submersible launched from Substation Curaçao (12°05 ́04.14 ̋N, 68°53 ́53.16 ̋W), a colony of A. lamarcki was observed at approximately 60 m depth (Panel B) exhibiting the characteristic tunnel formed by O. hypostegus. The shape of this tunnel is virtually identical to those found with O. hypostegus crabs in A. lamarcki at shallower depths (Panel A: Slangenbaai, Curaçao). Hence, we contend that this is strong evidence of O. hypostegus at mesophotic depth. 

The present finding is relevant in the light of the “deep reef refugia” hypothesis, which states that mesophotic reefs may act as a refuge in the face of global reef decline (Bongaerts et al. 2010), as it furthers our knowledge on the communities that presently thrive on these deep reefs. 

 

 

Date
2015
Data type
Scientific article
Geographic location
Curacao