Ma. Stjohn et T. Lund, LIPID BIOMARKERS - LINKING THE UTILIZATION OF FRONTAL PLANKTON BIOMASS TO ENHANCED CONDITION OF JUVENILE NORTH-SEA COD, Marine ecology. Progress series, 131(1-3), 1996, pp. 75-85
The effects of physical mixing processes on phytoplankton production i
n the marine environment are well established. However, the effects of
these processes on growth and condition of zooplankton and larval fis
h are at present poorly understood. In this study, we utilized phytopl
ankton group-specific fatty acid content to trace the phytoplankton gr
oup and mixing regime contributing to the condition of individual juve
nile North Sea cod. In order to establish a relationship between lipid
tracer content and algal utilization, post yolk-sac larval North Sea
cod were reared in the laboratory on food chains based on monocultures
of either the diatom Skeletonema costatum or the dinoflagellate Heter
ocapsa triquetra (algae dominating in the mixed and stratified regions
of the North Sea). In the laboratory, these algae were fed to culture
s of adult Acartia tonsa, the copepod eggs were collected, hatched and
the N1 nauplii from these different feeding regimes fed to post yolk-
sac larval North Sea cod. Post yolk-sac larval cod required 8 d on eit
her a Heterocapsa- or Skeletonema-based food chain before tracer Lipid
signals (the ratio of the lipids 16:1 omega 7 to 16:0) in the larvae
began to change from their original values to those similar to the alg
ae at the base of their respective food chains. The cod larvae display
ed a lipid tracer content similar to that of their algal food source a
fter 13 d on their respective feeding regimes. During a cruise in May
1992 to examine the distribution of larval and juvenile North Sea cod,
a subsample of 100 juvenile cod from the stratified, mixed and fronta
l regimes of the northeastern North Sea were examined for their conten
t of lipid biomarkers and condition (as determined by the ratio of tot
al lipid content to total length). Juvenile cod displaying a lipid tra
cer content indicating utilization of diatom-basea food webs (found in
proximity to regions of frontal mixing) were observed to be in signif
icantly better condition (p less than or equal to 0.05) than those con
taining a lipid signal indicative of utilization of flagellate-based f
ood webs (found in stratified regions of the North Sea).