ABSTRACT
Mussel larval densities
may fluctuate considerably on both small spatial and short temporal scales. So
far, only few and scattered data on the occurrence of mussel larvae have been
reported from Danish waters. However, seasonal variation in density of blue
mussel (Mytilus edulis) larvae as related to environmental factors
(temperature, salinity, phytoplankton biomass) is basic information of
relevance for future line-mussel farming in Danish waters. Here we report on
the density of mussel larvae in a number of potential farming sites in the
inner Danish waters. The mussel larval density measured in Skive Fjord, an
eutrophicated inner branch of Limfjorden, during a period of 20 years, from
1989 to 2009, along with corresponding temperatures and chlorophylla,
makes up the most important series of data reported here. In most years, a
pronounced spring density peak and a subsequently lower autumn peak could be
seen in Skive Fjord, but most conspicuous in the period 1993 to 2002 where the
mean maximum spring larval density was 319 ± 260 ind·l-1. Further,
data on mussel larval densities have been recorded on 4 locations in the Great
Belt region: Kerteminde Bay in 2008 to 2011, and in 2008 at 3 other locations:
Musholm Bay, Svendborg Sund, and Horsens Fjord. The maximum spring densities in
the studied waters were observed in Skive Fjord, typically in May, whereas 10
to 100 times lower peak densities were found at the other locations studied.
The reported observations show that mussel larvae are omnipresent in the
studied areas and it is suggested that the
larval density is sufficient forrecruitment to future line-mussel farms.