Stock-recruitment relationships in pocilloporid corals are likely disrupted by thermal stress

Abstract

Pocilloporids have short larval dispersal—an important mechanism in creating localized stock-recruitment relationships, whereby the rate of recruitment increases with size of the adult stock. Therefore, population recovery can occur quickly from even a small source. Here, we explore the existence of a stock-recruitment pattern in brooding species (Pocilloporidae) across 10 sites, separated by about 500 m, within a semi-continuous reef system spanning 4 km, in the east of Palau, Micronesia. Twenty settlement tile structures were deployed at each site for two consecutive years (2020–2021), and the nearby benthic community was assessed using photo quadrats. Brooding pocilloporid cover and settlement decreased significantly in 2021, by 0.6-fold and 0.4-fold respectively (P < 0.001 for both). A positive stock-recruitment relationship between adult brooder cover and settlement was identified in 2020 (GLMM: P < 0.001), but in 2021 this relationship was no longer significant (GLMM: P = 0.58). In late 2020, the reef was impacted by a modest bleaching event, which led to a 2.5-fold increase in the cover of dead corals in 2021 (GLMM: P < 0.001). We calculated the proportion of newly dead coral in 2021 to obtain a bleaching stress index for every site. Pocilloporid settlement in 2021 was significantly negatively correlated to the stress index (R = −0.42, P = 0.05). Our results identify a stock-recruitment relationship in brooding corals at the scale of sites and are consistent with studies on thermal stress impacts on coral fecundity and reproductive output. Given that brooders are increasing their dominance on coral reefs, understanding their recovery dynamics will help us identify locations where interventions might be prioritized.