Ch. Lucas et al., SEASONAL DYNAMICS AND PRODUCTION OF THE HYDROMEDUSAN CLYTIA-HEMISPHAERICA (HYDROMEDUSA, LEPTOMEDUSA) IN SOUTHAMPTON WATER, Estuaries, 18(2), 1995, pp. 362-372
In 1990 and 1991, a zooplankton sampling program revealed the presence
of the hydromedusan Clytia hemisphaerica (Hydromedusa: Leptomedusa) f
rom early May through late September throughout Southampton Water. The
most notable aspects of the population dynamics of C. hemisphaerica i
n Southampton Water were the considerable interannual variation in pea
k abundance-10.65 m(-3) in 1990 and 2.44 m(-3) in 1991-and temporal pa
tterns of mean bell diameter. The suggestion of almost continuous repr
oduction in 1990, as indicated by high abundance and large size range
on each sampling date, is in contrast to 1991, where at the Cracknore
site, five cohorts were produced at 21 d to 80 d intervals. The maximu
m bell diameter attained in each generation was typically 10-11 mm. At
the Cracknore site in 1991, in situ bed diameter growth was linear wi
thin each cohort. A trend of increased growth rate with each subsequen
t cohort, from 26 mu g DW d(-1) to 106 mu g DW d(-1) was coincident wi
th increasing water temperature. Annual production ranged from 0.98 mg
C m(-3) yr(-1) to 1.08 mg C m(-3) yr(-1) in 1990 and 0.35 mg C m(-3)
yr(-1) to 0.48 mg C m(-3) yr(-1) in 1991. Daily P:B ratios varied in e
ach cohort from 0.05 to 0.35.