Effects of coral bleaching on the obligate coral-dwelling crab Trapezia cymodoce |
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Authors: | J S Stella P L Munday and G P Jones |
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Institution: | (1) ARC Centre of Excellence for Coral Reef Studies, and School of Marine and Tropical Biology, James Cook University, Townsville, QLD, 4811, Australia;(2) Climate Adaptation Flagship, CSIRO, Hobart, Tasmania, 7001, Australia |
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Abstract: | Corals are an essential and threatened habitat for a diverse range of reef-associated animals. Episodes of coral bleaching
are predicted to increase in frequency and intensity over coming decades, yet the effects of coral-host bleaching on the associated
animal communities remain poorly understood. The present study investigated the effects of host-colony bleaching on the obligate
coral-dwelling crab, Trapezia cymodoce, during a natural bleaching event in the lagoon of Lizard Island, Australia. Branching corals, which harbour the highest
diversity of coral associates, comprised 13% of live coral cover at the study site, with 83% affected by bleaching. Crabs
on healthy and bleached colonies of Pocillopora damicornis were monitored over a 5-week period to determine whether coral bleaching affected crab density and movement patterns. All
coral colonies initially contained one breeding pair of crabs. There was a significant decline in crab density on bleached
corals after 5 weeks, with many corals losing one or both crabs, yet all healthy colonies retained a mating pair. Fecundity
of crabs collected from bleached and healthy colonies of P. damicornis was also compared. The size of egg clutches of crabs collected from bleached hosts was 40% smaller than those from healthy
hosts, indicating a significant reduction in fecundity. A laboratory experiment on movement patterns found that host-colony
bleaching also prompted crabs to emigrate in search of more suitable colonies. Emigrant crabs engaged in aggressive interactions
with occupants of healthy hosts, with larger crabs always usurping occupants of a smaller size. Decreased densities and clutch
sizes, along with increased competitive interactions, could potentially result in a population decline of these important
coral associates with cascading effects on coral health. |
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