Conservation & Threats

The survival of T. cymodoce and all Trapezius species is dependent of Pocillopora coral. As such they are linked to the threats that afflict this coral species, which include: increased bleaching events, sea level rise and ocean acidification which are all linked to global climate change, and also increased nutrient input, overfishing and habitat degradation (Hughes et al., 2010, Pandolfi et al., 2003). Overfishing and increased nutrient input can lead to a shift in community structure from coral dominated reefs to macroalgae dominated reefs and lead to increased coral mortality as the coral are smothered by the macroalgae which have been left unchecked by the removal of herbivorous reef fish via overfishing (Hughes et al., 2007). Habitat degradation caused by flood plumes, tropical cyclones and destructive fishing practices leads to a reduction in the coral cover and the abundance of Pocillopora colonies persisting around reefs (Stella et al., 2011b).

Coral bleaching can also severely impact Pocillopora coral and has carry-on effects on the fauna that depend on these corals. T. cymodoce will actively move away from damaged and bleached coral colonies in preference of live colonies, with the amount on immigration away from bleached coral colonies increasing as the bleaching duration increases (Stella et al., 2011a). Female T. cymodoce individuals found living of bleached corals had reduced fecundity compared to females living on healthy coral, with egg clutch sizes40% lower in females living on bleached coral (Stella et al., 2011a). This is likely caused by reduced food quality in bleached coral colonies (Stella et al., 2011a).

The level of specialization shown by T.cymodoce and other Trapezia species may put them at great risk of extinction, especially since their preferred Procillopora host are one of the coral genera most susceptible to coral bleaching and mortality (Stella et al., 2010). Procillopora corals also benefit from Trapezia crabs thru the protection from predators and removal of sediment (Stewart et al., 2006, Glynn, 1976, Stella et al., 2011b). The loss of Pocillopora corals via bleaching or any other disturbance event could lead to strong feedback; in other words the loss of Trapezia species from Pocillopora colonies due to bleaching could then cause an increase in the mortality of Pocillopora colonies, since they no longer have the services provided by the crabs, which then in turn reduces Trapezia abundance since there are less coral hosts, and so on.