In situ and laboratory growth by a population of blue mussel larvae (Mytilus edulis L.) from a Danish embayment, Knebel Vig

The aim of this study was to investigate if the growth rate of Mytilus edul is larvae was food limited during the summer period. Populations of M. edul is veliger larvae were investigated during two intensive periods in 1994 an d 1995 in the embayment Knebel Vig, Denmark. The abundance of veligers vari ed from 1.7-40.4 ind. 1(-1) (1994) and 2.7-99.0 ind. 1(-1) (1995), generall y declining throughout the sampling periods. Exponential disappearance rate s for the M. edulis larvae were estimated as 0.06 d(-1) and 0.23 d(-1) for the two years, presumably caused by predation and settlement. In situ water temperature in the embayment was between 21-23 degrees C both years of inv estigation. In the laboratory, larvae were fed three different food rations : filtered sea water, natural sea water and natural sea water enriched with added algal culture (Isochrysis galbana) ad libitum. All laboratory experi ments were conducted at 22+1 degrees C. Larval mean+/-s.e. shell lengths in creased at significantly different rates (5% significance level) (Kruskal-W allis analysis of variance followed by multiple comparisons) of 4.3+/-0.4 m u m d(-1) in filtered sea water, 9.1+/-0.2 mu m d(-1) in natural sea water, and 13.1+/-2.8 mu m d(-1) in enriched sea water, respectively. Under in si tu conditions mean+/-s.e. shell growth rates were estimated as 5.6+/-0.3 mu m d(-1) and 7.6+/-1.3 mu m d(-1) in 1994 and 1995, respectively, the latte r not significantly different from the laboratory growth rate performed wit h natural sea water. During the sampling periods, the chlorophyll a content of the bay water was 0.5-4.5 mu g 1(-1) (mean 2.8 mu g 1(-1)) which is wel l within the summer range of Danish coastal waters. In order to calculate t he specific growth rates of the larvae, a shell length-carbon content regre ssion was carried out with in situ larvae from 1994 giving W(mu gC)= 3.06 X 10(-8) X L(mu m)(2.88) (L = 175-450 mu m), where W is individual carbon co ntent and L is shell length. Specific growth rates in situ were 0.062 d(-1) in 1994 and 0.064 d(-1) in 1995. In the laboratory, the specific growth ra tes were estimated to be 0.04 d(-1), 0.08 d(-1) and 0.11 d(-1) in filtered, natural and enriched sea water, respectively. The investigations lead us t o suggest that growth of M. edulis veligers is commonly limited by food sup ply in the embayment during the summer. (C) 1999 Elsevier Science BN. All r ights reserved.