Growth and reproduction of Mytilus edulis (Linnaeus) on the two sides of the Strait of Belle Isle

Abstract

A comparative growth study of Strait of Belle Isle Mytilus edulis populations was undertaken, with the hypothesis that the surface water temperature difference between the two sides of the Strait (4-8 C) results in differences in growth rates. Results of the study show that Mytilus edulis collected at four sites, (two on each side of the Strait) from the high, low, and subtidal zones, displays the type of spawning, growth, and population structure, typical of north-temperate, exposed-coast mussel populations. Linear shell growth rates were similar between the two sides of the Strait. Growth rates were low (maximum of 6-8 mm per year) and were highly variable within populations (average range in length of 10 mm per year class). -- Winter growth was negligible as evidenced by pronounced, external shell check-marks, and despite the large spring-summer water temperature difference between sides of the Strait of Belle Isle, the annual spring start of linear shell growth was similar between mussels on the two sides. The seasonal progression of the internal growth line in M. edulis was relatively synchronous within populations, and timing of deposition was similar between sides of the Strait. -- Spawning was synchronized and occurred later (July-August) than at more southern latitudes. Subsequent settlement in 1981 resulted in large numbers of post-larvae over-wintering on algae and adult mussel beds at sizes < 2 mm in shell length. There were large differences in fecundity between sites, however, the range in fecundity was similar on both sides of the Strait. Age-specific fecundity was higher in the low intertidal than in the high intertidal (e.g. 160 and 115 mg gamete dry weight respectively, at Pte. Amour). -- Mussels < 15 mm in shell length dominated the intertidal zone while contributing little to meat weight biomass. At the sampling scale used in this study (200 cm¹), meat dry weight biomass and reproductive output were similar between high and low intertidal zones. Individual meat weight values were similar between the two sides of the Strait and Pte. Amour meat weight values were highest of those in the intertidal zones while similar to values at other sites subtidally.