Influence of wind, rainfall, temperature, and primary productivity, on the biomass of the bivalves Spisula solida, Donax trunculus, Chamelea gallina and Ensis siliqua

Coastal bivalve populations are characterized by large temporal fluctuations, driven by recruitment success dependent on environmental conditions. The present study evaluated the relationship of rainfall, chlorophyll-α, sea surface temperature (SST) and wind, with the biomass of four commercial bivalve species (Spisula solida, Donax trunculus, Chamelea gallina and Ensis siliqua) that occur both along the Barlavento (western region), and the Sotavento (eastern region), along the South coast of Portugal, between 1999 and 2011. Multiple regression models were used to test two hypotheses: a) the association between environmental conditions three months prior to the spawning period and the biomass in the following year (response variable) and b) the association between environmental conditions during the spawning season plus one month and the biomass in the following year. Wind was not included in the model to test a). The environmental variables considered were not important for E. siliqua. In the period prior to spawning, temperature was significant for S. solida (both study areas), rain for D. trunculus and C. gallina (western area) and chlorophyll-α for C. gallina (western area). All the correlations were positive. During the spawning period, rain was significant for all three species but with different trends. The correlation with rain in months early in the spawning season was positive for S. solida (both areas) and D. trunculus (western area). The correlation with the rain in months towards the end of the spawning period was negative for D. trunculus, and C. gallina (western area). Chlorophyll-α in months at later stages of spawning was significant and positive for D. trunculus (both areas) and C. gallina (western area). The wind, expressed as an index developed to indicate the overall occurrence of winds blowing parallel to the coast (assumes to favour the retention of larvae in appropriate environments), was negatively correlated with biomass for mid to late spawning season for S. solida (eastern area) and D. trunculus (western area). For C. gallina there was a positive correlation with wind early in the spawning season. The SST was not an important variable during the spawning period with the exception of D. trunculus where the temperature at mid spawning season was significant with a negative correlation in the western coast and positive in the eastern coast. This study highlighted the annual spatial distribution of four commercially important bivalves and how environmental factors are likely to play an important role on both biomass and location of the fishing beds. Monitoring of the environmental variables could provide information to predict biomasses of bivalve species, an important tool for its management, as well as predict trends and plan strategies in response to global environmental changes.