Pelagic larval traits of the amphidromous goby Sicyopterus lagocephalus display seasonal variations related to temperature in La Réunion Island

Amphidromous gobies represent a substantial part of freshwater fish diversity throughout islands of the Indo-Pacific region. They display a marine pelagic phase during several months before recruiting in rivers. Understanding the relationship between larval traits and environmental conditions is a major challenge for the evaluation of a spatial scale of connectivity and populations’ dynamics, especially in a climate change context. In this study, the larval traits of Sicyopterus lagocephalus were examined and related to the sea surface temperature (SST), over three consecutive years in La Reunion Island (Mascarene archipelago). The pelagic larval duration (PLD, range from 96 to 293 days), the size-at-recruitment (range from 26.5 to 37 mm TL) and the larval growth rate (range from 0.112 to 0.293 mm·day−1 TL) varied seasonally depending on hatching date. The larval growth rate was inversely correlated to the fluctuations of PLD and size. Larvae living in high sea water temperatures exhibited a faster growth, shorter PLDs and smaller sizes-at-recruitment than those living in cool water temperatures. The instantaneous daily growth was assessed by the study of otolith increment widths. The daily growth was not linear throughout larval life and was positively correlated to SST. We showed high amplitude of PLD periodic fluctuations (170.39 ± 43.75 days) related to temperature (12.8% PLD drop per degree), which could affect dispersal and induce intermittent connectivity between distant populations. This high plasticity of larval traits is likely to be advantageous to respond to the wide range of environmental conditions encountered throughout the species distribution range.