Observations of Synchronized Spawning, Larval Survival and Settlement in Corals of the Genus <i>Acropora</i> in Lakshadweep, India

Abstract

Reports of synchronous spawning in corals of Lak-shadweep reefs, India have been purely anecdotal. To understand factors that underlie coral spawning in Lakshadweep, we studied four Acropora species ( A. muricata, A. cytherea, A. hemprichii and A. nobilis ) in Kavaratti atoll from February to March 2018. These species were observed in situ for oocyte maturation, and the larvae of species A. muricata and A. cytherea were assessed for survival and settlement rates. Observations on oocyte maturation indicated possible spawning closer to the immediate full moon of species in which 7–28 % of the colonies had mature oocytes. Thus, A. muricata, A. cytherea and A. hemprichii spawned on 25 and 26 February 2018, demonstrating multi-specific synchronous spawning, whereas A. nobilis spawned on 21 March 2018. Larval survival rates revealed a steep die-off beginning on day 12 post-spawning and maximum survival up to 24–27 days. Settlement occurred between 12 and 20 days for A. muricata and between 12 and 22 days for A. cytherea . The comparatively low survival duration and fewer larvae surviving for settlement show that maximum settlement could be heavily compromised. However, the study reveals that the comparatively late onset of settlement (from day-12, post-spawning) and the broader settlement window of 8–10 days could allow room for long-distance dispersal of larvae. Further studies on this front are required to gather a better picture.