Fróðskaparrit - 01.01.2004, Page 278

276 THE gametogenic cycle and spawning in mytilus edulis in the faroe islands
JJASONDJFMAMJ
1996 1997
Fig. 5. Seasonal changes in mean monthly sea temperature at Eidi a site close to the study area at Svínáir and
the gametogenic cycle in Mytilus edulis/rora the study site, shown as the mean gonad index (temperature records,
courtesy of the Office ofPublic Works, Tórshavn).
served (February and March) and spawning
began in May when sea temperature was
increasing but had not reached its maxi-
mum. Similar results were found in a study
of farmed blue mussels on Suðuroy in the
Faroes in 1984 and 1985, with maximum
gonad index during the period late March
to early May (Gaard, 1986).
Changes in temperature have been found
to stimulate initiation of gonad development
(Bayne, 1975; Gray et al., 1997) as well
as spawning (Chipperfield, 1953; Sprung,
1983). Some authors have even suggested
that a critical temperature change is needed
for initiation of spawning (Kautsky, 1982;
Seed, 1976) while others have found little
or no evidence of this (Newell et al., 1982;
Seed and Suchanek, 1992). In the fíeld re-
productive activity of M. edulis has often
been correlated with rising water tempera-
tures (Kinne, 1970; Seed, 1976; Bayne,
1975; Hines, 1979).
Annual differences in reproductive con-
dition and fecundity have also been con-
nected with differences in annual food sup-
ply (Thompson, 1979; Newell etal., 1982).
Spawning has been considered timed such
that both larvae and adults have access to
abundant supplies of food (Thompson,
1979; Newell et al., 1982) and direct coup-
ling of mussel spawning with phytoplank-
ton blooms has been observed (Starr et al.,
1991).
Food supply in form of phytoplank-