The effects of temperature and light on the gametogenesis and spawning of four sea urchin and one sea cucumber species on coral reefs in Kenya

Abstract

Seasonality in reproduction in temperate marine invertebrates is well recognized, but reproduction at the equator where environmental variability is lower is typically assumed to be continuous. This paper reviews studies of the reproductive cycles of four species of sea urchins and one species of sea cucumber to test for seasonality and sexual synchrony along the Kenyan coast (10S - 50S). Gonad index measurements and macro and microscopic observations of gonads were used to evaluate monthly changes in gonad growth. The urchin Echinometra mathaei and sea cucumber Holothuria arenacava displayed a seasonal reproductive pattern with gametogenesis commencing in July during the southeast monsoons and spawning peaking between March-April during the northeast monsoons. Monthly temperature and light significantly correlated with gonad index in these species but light displayed a stronger response. The sympatric urchins Diadema savignyi and D. setosum had a monthly gametogenic cycle with D. savignyi spawning after full moon and D. setosum spawning in the last quarter. These species also showed seasonal gonad growth with D. savignyi following a pattern similar to E. mathaei. The life history strategies of these species included a high level of sexual synchrony and spawning at the time most favorable for larval growth.