Reproductive biology of the sea cucumber Holothuria grisea in Brazil: importance of social and environmental factors in breeding coordination

Sea cucumbers (Echinodermata: Holothuroidea) can contribute to the cycling of nutrients and play important roles as ecosystem engineers; many also have high commercial value. Their success at colonizing marine habitats from the shore to the abyss makes them ideal models for the study of breeding patterns. Here, the reproductive biology of the sea cucumber Holothuria grisea was studied at large and fine scales over 13 months on the northeastern Brazilian coast, to investigate the role of environmental and aggregative factors in this process. Gametogenic maturity peaked in December-February, as indices of spawning activity appeared and aggregative behavior was minimal. Mature individuals disappeared in June-July in both sexes, as the highest frequencies of aggregation and post-spawning stage were recorded. In August-September, gamete synthesis started to increase again in correlation with a higher frequency of individuals in the early gametogenic growth, while the degree of aggregation among individuals in the field was still high. Spawning occurred during the rainy season when chlorophyll-a concentrations were maximal, and the highest frequency of solitary individuals was recorded. The data are consistent with pre-spawning aggregative behavior as a strategy to help synchronize gametogenesis and phytoplankton bloom as a trigger of gamete release to optimize larval feeding. At finer scale, spawning occurred when high water levels coincided with sunset or night time, providing favorable conditions for free spawning and external fertilization. The influence of environmental factors and aggregation in the reproduction of H. grisea could potentially exacerbate its vulnerability to anthropogenic pressures (e.g., fisheries, pollution, habitat loss) along the coast of Brazil.