Tissue fusion and enhanced genotypic diversity support the survival of Pocillopora acuta coral recruits under thermal stress

Abstract

Scleractinian coral recruitment provides critical support for reef persistence under the threat of global climate change. The high mortality rates exhibited in early life history stages are further increased under thermal stress, compromising reef recruitment. Tissue fusion with neighboring recruits is one potential early life history strategy that has been shown to support recruit survival (particularly in brooding species) by promoting rapid increases in colony size and potential opportunities for enhanced intracolonial genetic diversity. However, tissue fusion also presents risks in the cost of growth and maintenance of relationships between genetically distinct individuals. Although fusion is one potential strategy for recruit survival, the effects of colony size and enhanced genetic diversity achieved through fusion on survival under ocean warming conditions are not well understood. Here we tested the effect of tissue fusion on Pocillopora acuta recruit survival under ambient and high temperature stress by manipulating the size and parental genotypic richness in fused recruits. We provided opportunities for tissue fusion in groups of recruits with enhanced parental genotypic richness (1–4 parent genotypes) and size (1–4 recruits) and tracked subsequent growth and survival (N = 137). Under ambient temperature (1–15 days post-settlement), fusion significantly increased survivorship regardless of parental genotypic richness, while negative competitive effects existed between closely settled, but unfused recruits. Under high temperature (+ 2.5 °C; 16–47 days post-settlement), the median survival of fused recruits was 5 days longer than individuals, with 1.5 days added to median survival when composed of multiple parental genotypes. These results demonstrate that tissue fusion during coral recruitment can improve survival and provides insights on early life history strategies to increase tolerance to ocean warming.