Consequences of finger coral declines for coral specialists versus generalists
Theory predicts that extinction debt should vary depending on the degree of habitat specificity of associated species (Kuussaari et al. 2009, Hylander & Ehrlén 2013, Watts et al. 2020) with generalists characterized as having broad habitat requirements and specialists “largely dependent on one particular habitat type” (Watts et al. 2020). Specialists with low dispersal should have relatively short duration extinction debt, while generalists with high dispersal would have the longest extinction debt, as they could utilize other habitats after a disturbance. Of the Pocillopora associated community of fishes and mobile macroinvertebrates, we have sufficient information on small-scale (within-habitat) distribution to estimate that at least six species can be considered largely dependent on the Pocilloporahabitat. These include three species of Trapezia crabs which are known obligate Pocillopora mutualists (Glynn 1976, Hickman & Zimmerman 2000), the spider crab Telephyrs cristolipes described as inhabiting finger corals in Hickman & Zimmerman (2000), the corallivorous gastropod Babelomurex hindsii , and the coral hawkfish Cirrhitichthys oxycephalus, which is frequently observed in finger corals and among black corals in the Galapagos (J. Witman, pers. obs.). As in most communities of mobile species such as birds (Watts et al. 2020), insects (Hanski & Ovaskainen 2002), and reef fishes (Kritzer & Sale 2006), the community of fishes and macroinvertebrates associated with live and dead finger corals represents a mix of habitat and food specialists and generalists. Future research to identify habitat specialist species on Galápagos reefs is needed to understand those species most vulnerable to habitat loss and to overall biodiversity loss following future temperature stress from climate oscillations.