Abstract
Mussel commercial production depends on wild populations to obtain the seed. Therefore, any new farming initiative needs deep knowledge on reproductive cycle of native mussel populations. The reproductive cycle of Mytilus galloprovincialis Lmk. from five sites, three estuarine and two coastal, along the coast of the Basque Country were assessed using gonad index and stereology over 2 consecutive years (2010 and 2011). Sex ratios, developmental stages of gonads, as well as reserve tissue cycle were analyzed. The onset of gametogenesis was observed from winter to spring, with spawning occurring from spring till summer. A resting phase followed with an increase in reserve tissues (adipogranular cells) was observed in fall. Mussels stayed ripe during winter until favorable environmental conditions were met in spring. Differences in reproductive cycles were found among populations, and also, year-to-year variability was observed within each population. In two of the studied sites asynchrony in the timing of spawning was observed between genders. These timing differences, however, did not prevent mussels at those sites from reproducing successfully. The Bidasoa estuary points to the potential of such studied sites for becoming the main source of wild mussel spats for future expected commercial mussel farming in the Basque Country. To ensure year-to-year maximum reproductive output, however, wild mussels harvest should be avoided from spring to the end of summer in this region.
Highlights
Open-ocean aquaculture represents a promising alternative for sustainable cultivation of bivalve species (Polk 1996; Hesley 1997; Stickney R 1998; Bridger and Costa-Pierce 2003), especially in regions with restricted coastal space for farming activities such as the Basque Country (Azpeitia et al 2016)
The present study provides a detailed description of the reproductive cycle of five mussel populations inhabiting the coast of the SE Bay of Biscay (2 in coastal exposed waters and 3 in estuarine sheltered waters)
Along the Basque coast gametogenesis onset was observed from winter to spring, with spawning occurring from spring till summer
Summary
Open-ocean aquaculture represents a promising alternative for sustainable cultivation of bivalve species (Polk 1996; Hesley 1997; Stickney R 1998; Bridger and Costa-Pierce 2003), especially in regions with restricted coastal space for farming activities such as the Basque Country (Azpeitia et al 2016). Analyzing the health of wild mussel populations in relation to their reproductive cycle and spat production is important as mussel production relies on the annual collection of significant amounts of wild seeds, and farmers grow these seeds. Areas favorable for spat collection and/or targeting rope deployment periods for spat settlement is of particular relevance in mussel aquaculture and further, will be fundamental for developing future farming management strategies (e.g., protect native spawning stocks and/or larval settlement) (Gosling 1992; Dias et al 2009). Prudent regulation of harvesting will maximize reproductive output of wild and cultured mussel populations
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