Uneven declines between corals and cryptobenthic fish symbionts from multiple disturbances

Abstract

With the onset and increasing frequency of multiple disturbances, the recovery potential of critical ecosystem-building species and their mutual symbionts is threatened. Similar effects to both hosts and their symbionts following disturbances have been assumed. However, we report unequal declines between hosts and symbionts throughout multiple climate-driven disturbances in reef-building Acropora corals and cryptobenthic coral-dwelling Gobiodon gobies. Communities were surveyed before and after consecutive cyclones (2014, 2015) and heatwaves (2016, 2017). After cyclones, coral size and goby group size decreased similarly by 28-30%. After heatwave-induced bleaching, coral size decreased substantially (47%) and the few gobies recorded mostly inhabited corals singly. Despite several coral species still occurring after bleaching, all goby species declined, leaving 78% of corals uninhabited. These findings suggest that gobies, which are important mutual symbionts for corals, are unable to cope with consecutive disturbances. This disproportionate decline could lead to ecosystem-level disruptions through loss of key symbiotic services to corals.

Habitat health, size and saturation do not alter movement decisions in a social coral reef fish

“…Our results demonstrate that coral gobies are clearly specialized, not only to a particular type of habitat but also to specific habitats that they are familiar with. Such specificity might prove disadvantageous under conditions of rapid habitat degradation, particularly due to cyclones and bleaching [16,21,26], because maintaining plasticity in habitat utilization would enable these fish to reside in any habitat available following environmental disturbances [39]. Unlike other social fishes, however, G. quinquestrigatus opted to pay high costs of movement by returning to familiar corals rather than adopting other suitable corals nearby.…”

“…For each trial, a different focal fish and live coral were used. To assess where the focal goby moved and whether any movement decisions were based on the level of saturation of neighbouring corals in the study plot, we surveyed all Acropora corals larger than 7-cm in diameter [26] within a 10-m radius from the dead coral in each trial. Additional covariables were recorded and accounted for in data analysis (see Suppl Methods).…”

Habitat size, health and saturation do not alter movement decisions or the preference for familiarity in a social coral-reef fish

“…To assess where the focal goby moved and whether any movement decisions were based on the level of saturation of neighbouring corals in the study plot, we surveyed all Acropora corals larger than 7-cm in diameter [26] within a 10-m radius from the dead coral in each trial. Additional covariables were recorded and accounted for in data analysis (see Suppl Methods).…”