New Zealand Journal of Marine and Freshwater Research abstracts
Vertical distribution of zooplankton > 39 um in relation to the physical
environment off the west coast of South Island,
New Zealand
J. M. BRADFORD-GRIEVE1
R. C. MURDOCH1
M. R. JAMES2
M. OLIVER1
J. HALL3
National Institute of Water & Atmospheric
Research Ltd
1P. O. Box 14-901, Kilbirnie
Wellington, New Zealand
2P. O. Box 8602, Riccarton
Christchurch, New Zealand
3P. O. Box 11-115, Hillcrest
Hamilton, New Zealand
Abstract Data sets of pump-sampled zooplankton > 39 um
were obtained for early August 1987, late July 1988, and late June 1990, along
with environmental data in 1987 and 1990, off the west coast of South Island,
New Zealand. The environmental circumstances favourable to zooplankton species
known to be food for hoki larvae (Macruronus novaezelandiae) were
investigated. We found that a major proportion of the vertical distribution of
the epipelagic zooplankton off Westland is influenced by passive interaction
with physical processes against a background of the distribution of autotrophic
particles. Multivariate analysis classified stations into continental slope
(Group I), outer-mid shelf (Group II), and neritic (Group III) stations/depths.
Contrasting with other stations in Group I (the habitat of hoki larvae), the
physical conditions of one station differed in that winter mixing had hardly
begun (indicated by relatively low nutrients), concentrations of 20-200 um
autotrophic particles were low, as were concentrations of copepod nauplii, and
Calocalanus spp. Deep mixing in early winter, in subtropical water along
the outer shelf and slope of the west coast of South Island, may be necessary
to promote the growth of zooplankton species important in the diet of hoki.
This promotion of copepod growth may have been mediated through the growth of
autotrophic particles > 20 um in a higher nutrient environment and/or the
changing light environment which could have differentially favoured the growth
of various phytoplankton size fractions, and therefore their predators. The
1990 year class of hoki did not make a strong contribution to the fishery for
adults. In 1990 the onset of winter mixing (from model results) occurred 2
weeks later than in 1987 and 1988, years when hoki year classes contributed
strongly to the fishery.
Keywords New Zealand; zooplankton; vertical distribution;
winter mixing; food; Macruronus novaezelandiae; copepods;
tintinnids
New Zealand Journal of Marine and Freshwater Research, 1996, Vol 30:
285-300
0228-8330/96/3003-0285 $2.50/0 (c) The Royal Society of New Zealand
1996
PDF file of entire paper: medium quality (1087K); (scanned from paper original: notes about this process)
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