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.