Temporal and spatial distribution of larval and post-larval blue mussels (Mytilus edulis/Mytilus trossulus) and starfish (Asterias vulgaris) within four Newfoundland mussel culture sites

Pryor, Miranda Leigh (2004) Temporal and spatial distribution of larval and post-larval blue mussels (Mytilus edulis/Mytilus trossulus) and starfish (Asterias vulgaris) within four Newfoundland mussel culture sites. Masters thesis, Memorial University of Newfoundland.

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Abstract

As the blue mussel farming industry in Newfoundland continues to grow, farmers anticipate problems regarding spat collection and the presence of predatory starfish on collectors, based on past experience. The objectives of this study were to examine the temporal and spatial patterns of planktonic larval and post-set stages of both mussels and starfish to determine if a consistency in timing of spawning, settlement and abundance exists between these two organisms. -- During 1998, four sites were chosen throughout the province, with weekly larval and spat/juvenile samples taken from May to November. Mussel larvae were abundant at three sites, located on the North coast, from mid-June through late August, with starfish larvae appearing from late June through late August. While some trickle spawning events were recorded, most larger pulses of mussel larvae were generally followed by a larger pulse in spat settlement, ~4-6 weeks later. Size data for these sites also indicated the presence of a major influx of larvae early in summer with some smaller events occurring in late summer to early autumn. Mussel spat settlement and starfish juvenile settlement subsequently occurred at varying times for all three sites, with peak starfish settlement occurring about 2-3 weeks after peak mussel settlement. -- For the fourth site, located on the southern shore, mussel spawning was sporadic resulting in low settlement on collectors. As well, no starfish were observed on this site. While larval numbers were highest among sites along the North coast of Newfoundland, geographic location alone does not seem to be the major factor determining larval procurement and spat settlement. The one sample site along the South coast had very low larval numbers throughout 1998 but, without experiencing any loss of spat over the winter months, anticipated spat available for socking in the spring would be comparable to the other three sites. -- During 1999, larval size and abundance was examined over a 12-hour tidal cycle, on two of the sites examined in 1998 (one on the North Coast, one on the South Coast) and the results indicated that larval numbers changed often over the tidal cycle, at both sites, with observable changes in the abundance of such fouling organisms as starfish and saxicave clam larvae also recorded. This study demonstrated the importance of a standardized and accurate method for monitoring larval abundances on shellfish culture sites with the timing, occurrence and relationship of abundance between larvae and spat/juveniles of mussels and starfish being site specific throughout Newfoundland.

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