Pacific Coastal Biome
439
abundance of the small photosynthetic cells: prokaryotes are normally within the range
5–7 × 10
7 cells liter
−1 , which is at least twice the relative variability normally observed
for the small eukaryotes. In general, and as occurs elsewhere, maximum prokaryote cell
numbers occur deep in the mixed layer and in association with a nitracline. In the inshore
phytoplankton, biomass is more evenly distributed among the size classes. Chang et al.
(1992) suggest that the 20- to 200-mm fraction contributes here as much as 55% of total
phytoplankton nitrogen because high nitrate levels favor the growth of diatoms. Cell
division rates among large cells are actually higher here than for the smaller fractions: at
surface irradiance, the 20–200 mm fraction = 0.5 doublings d
−1 , the 2–20 mm fraction
= 0.22 doublings d
−1 , and the <2 mm fraction = 0.18 doublings d
−1 .
Both the Westland and the Cape Kahurangi (Cook Strait) upwelling blooms support
populations of herbivorous macrozooplankton, as might be anticipated. Here, crustacean
herbivores are dominated by small copepods (species of Acartia, Paracalanus, Clausocalanus, Oithona, and Centropages) and a euphausiid (Nyctiphanes australis), which is an
important component in the pelagic food web both here and in the AUSE Province. At
Cape Kahurangi, Acartia may form up to 60% of net zooplankton biomass, and on the
Westland coast it dominates the inshore crustacean plankton; offshore in the upwelling
water a mixture of oceanic and neritic species is normally encountered. Off Westland,
zooplankton grazing represents 0.3–20% of algal production, with consumption being
relatively higher inshore. Nyctiphanes manages its diel migration in the inshore-offshore
transport associated with upwelling cells so as to place its eggs and larvae inshore, whereas
the main feeding population of older larvae and adults remains offshore. In the Taranaki
Bight, south of the upwelling at the Cape, Nyctiphanes may comprise more than half of
all zooplankton biomass (James and Wilkinson, 1988; Bradford and Chapman, 1988).
A 3-year study in the Hauraki Gulf revealed between-year differences that were probably significant for the recruitment ecology of spring- and summer-spawned fish larvae
(Zeldis et al., 1995); during the first two summers the salps Thalia democratica and Salpa
fusiformis dominated the later summer zooplankton biomass, whereas in the third year
salps were very rare. The presence of salps induced a small phytoplankton biomass with
a very deep DCM, well below the mixed layer. Without salps, mixed-layer chlorophyll
biomass was much greater and the DCM lay at the base of the mixed layer. The betweenyear differences in stratification were minor, and the effects observed were due to the
effect of salp grazing. Nevertheless, where salps were relatively sparse in the first 2 years,
phytoplankton were not correspondingly abundant: modeling studies suggested that the
incorporation of nutrients into salp biomass, and its sedimentation down through the
pycnocline, sufficiently reduced mixed-layer nutrients as to inhibit phytoplankton growth
even in those places where salp consumption rate was low. This situation is in stark
contrast with that more commonly found, in which ammonium excretion by microand mesozooplankton maintains some balance with the requirements of the autotrophic
community, as observed off Westland by James (1987).
On the east coast of North Island, where conditions are dominated by the effect of the
subtropical water of the western boundary current, especially during ENSO events, there
may be extensive coastal microalgal blooms of “nuisance” species: Mesodinium (a red
tide organism), Gonioceros, and Aulacodiscus are the main microalgae in these blooms. In
Tasman Bay, similar blooms occur after especially heavy coastal rainfall and runoff from
the land during summer.
Regional Benthic and Demersal Ecology
Benthic ecology, in the classical sense, seems to have survived longer off New Zealand
than in many other places, so here we have several modern studies of the macrobenthos
of the continental shelf and the relations between the fauna and deposit type. Early studies
439
abundance of the small photosynthetic cells: prokaryotes are normally within the range
5–7 × 10
7 cells liter
−1 , which is at least twice the relative variability normally observed
for the small eukaryotes. In general, and as occurs elsewhere, maximum prokaryote cell
numbers occur deep in the mixed layer and in association with a nitracline. In the inshore
phytoplankton, biomass is more evenly distributed among the size classes. Chang et al.
(1992) suggest that the 20- to 200-mm fraction contributes here as much as 55% of total
phytoplankton nitrogen because high nitrate levels favor the growth of diatoms. Cell
division rates among large cells are actually higher here than for the smaller fractions: at
surface irradiance, the 20–200 mm fraction = 0.5 doublings d
−1 , the 2–20 mm fraction
= 0.22 doublings d
−1 , and the <2 mm fraction = 0.18 doublings d
−1 .
Both the Westland and the Cape Kahurangi (Cook Strait) upwelling blooms support
populations of herbivorous macrozooplankton, as might be anticipated. Here, crustacean
herbivores are dominated by small copepods (species of Acartia, Paracalanus, Clausocalanus, Oithona, and Centropages) and a euphausiid (Nyctiphanes australis), which is an
important component in the pelagic food web both here and in the AUSE Province. At
Cape Kahurangi, Acartia may form up to 60% of net zooplankton biomass, and on the
Westland coast it dominates the inshore crustacean plankton; offshore in the upwelling
water a mixture of oceanic and neritic species is normally encountered. Off Westland,
zooplankton grazing represents 0.3–20% of algal production, with consumption being
relatively higher inshore. Nyctiphanes manages its diel migration in the inshore-offshore
transport associated with upwelling cells so as to place its eggs and larvae inshore, whereas
the main feeding population of older larvae and adults remains offshore. In the Taranaki
Bight, south of the upwelling at the Cape, Nyctiphanes may comprise more than half of
all zooplankton biomass (James and Wilkinson, 1988; Bradford and Chapman, 1988).
A 3-year study in the Hauraki Gulf revealed between-year differences that were probably significant for the recruitment ecology of spring- and summer-spawned fish larvae
(Zeldis et al., 1995); during the first two summers the salps Thalia democratica and Salpa
fusiformis dominated the later summer zooplankton biomass, whereas in the third year
salps were very rare. The presence of salps induced a small phytoplankton biomass with
a very deep DCM, well below the mixed layer. Without salps, mixed-layer chlorophyll
biomass was much greater and the DCM lay at the base of the mixed layer. The betweenyear differences in stratification were minor, and the effects observed were due to the
effect of salp grazing. Nevertheless, where salps were relatively sparse in the first 2 years,
phytoplankton were not correspondingly abundant: modeling studies suggested that the
incorporation of nutrients into salp biomass, and its sedimentation down through the
pycnocline, sufficiently reduced mixed-layer nutrients as to inhibit phytoplankton growth
even in those places where salp consumption rate was low. This situation is in stark
contrast with that more commonly found, in which ammonium excretion by microand mesozooplankton maintains some balance with the requirements of the autotrophic
community, as observed off Westland by James (1987).
On the east coast of North Island, where conditions are dominated by the effect of the
subtropical water of the western boundary current, especially during ENSO events, there
may be extensive coastal microalgal blooms of “nuisance” species: Mesodinium (a red
tide organism), Gonioceros, and Aulacodiscus are the main microalgae in these blooms. In
Tasman Bay, similar blooms occur after especially heavy coastal rainfall and runoff from
the land during summer.
Regional Benthic and Demersal Ecology
Benthic ecology, in the classical sense, seems to have survived longer off New Zealand
than in many other places, so here we have several modern studies of the macrobenthos
of the continental shelf and the relations between the fauna and deposit type. Early studies