REPRODUCTION OF BIVALVE MOLLUSCS IN A CHANGING ENVIRONMENT: IMPACT OF HARMFUL ALGAL BLOOMS AND IMPLICATIONS FOR AQUACULTURE  

As coastal suspension-feeders, bivalve molluscs provide a variety of ecosystem services. Several species of bivalves are ecosystem engineers and have considerable commercial value, harvested through fishery- and aquaculture-based industries. During the past century, many bivalve populations have suffered tremendous decline due to overfishing, pollution, diseases, and physical alterations of their habitats. Recently, harmful algal blooms (HAB), mainly those afflicting temperate and tropical coastal regions, have been exerting negative effects on bivalve populations either via the synthesis of potent toxins and/or via high biomass levels. Mass mortalities, alterations of vital physiological functions, increased susceptibility to diseases have all been associated with HAB exposure of bivalves.

A growing body of scientific evidence have been showing that HAB are detrimental to early-developmental stages of bivalves. In particular, the sensitivity of bivalve larvae to certain HAB species in terms of survival and performance as juvenile can translate into substantial reduction in adult populations and into reduction in the top-down regulation of phytoplankton assemblage and in the control of HAB. In addition, a few and very recent studies have demonstrated deleterious effects of HAB on embryos, larvae, fertilization, gametes, and the reproductive output of broodstock.

In spite of the development of hatcheries, the culture of bivalves still relies, and in some cases relies solely on the collection of spat from the natural environment. In the present paper, we review the state of knowledge of the interactions of HAB with the early-life development of bivalve molluscs, focusing on species of importance to aquaculture (oysters, mussels, clams, and scallops). We also present the results of our research with the Japanese pearl oyster, Pinctada fucata martensii. The implications of HAB for aquaculture and the future of aquaculture in environments witnessing climate-driven changes, including warming and acidification, will be summarized to open a discussion on such interactions.