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J, Tarazona and W. Arntz
The success of pioneer species is a result of both rapid growth rates in
nutrient-rich and turbulent environments and the composition and abundance of seed populations. Seeding of upwelling water may be a result of
the presence of bloom-forming diatoms with resistant spores that quickly
settle from the euphotic zone to the bottom, heteromorphic dinoflagellates
with planktonic and non-mobile benthic stages, and active migration of
the photosynthetic ciliate Mesodinium rubrum (Barber and Smith 1981).
Species dominance and succession of the phytoplankton community largely depend on the frequency and intensity of upwelling and are associated with spatial and temporal transitions from a turbulent to a stratified
water column. The stability of the water column increases along the axis of
an upwelling plume with increasing distance from the coast. Since in each
upwelling cell succession proceeds from small to large diatoms and dinoflagellates and from a dependence on new nitrogen to a dependence on
regenerated nitrogen, an upwelling area represents a mosaic of water masses with different stages of succession.
16.3.2 Zooplankton
The dominant species of the zooplankton community in coastal water
are copepods (Acartia tonsa, Centropages brachiatus) and larvae of polychaetes, brachiopods, cirripedes, and other crustaceans. At the margin of
the continental shelf and above the slope the dominant or conspicuous
taxa are represented by copepods (Paracalanus parvus, Calanus spp.,
Oncaea spp.) and large holoplankters such as siphonophores, chaetognaths, and euphausiids. Due to hypoxic conditions at greater depths, most
of the zooplankton is restricted to the uppermost 30m of the water
column; however, some species (i.e., the copepod Eucalanus inermis)
migrate to greater depths with low ( <0.1 mll- 1 ) oxygen concentration. The
volume of zooplankton decreases from north to south, though seasonal
variability is similar along the coast, with a marked increase in spring.
A fundamental characteristic of the Peruvian upwelling system is the
low (5 %) transfer efficiency from primary to secondary production.
Nevertheless, high primary production provides abundant food for grazers and sustains large populations of copepods, euphausiids, anchovies,
and also myctophiids at greater depth on the slope. Protozoans, principally ciliates and zooflagellates, also attain high biomass (up to 0.97 g C m- 2 ).
Bacterial and protozoan plankton seem to constitute the primary diet of
herbivorous mesozooplankton and the abundance of foraminiferans, coccolithophorids, and siliceous radiolarians in the sediments suggests their
importance in the benthic subsystem. Copepods and euphausiids quickly
J, Tarazona and W. Arntz
The success of pioneer species is a result of both rapid growth rates in
nutrient-rich and turbulent environments and the composition and abundance of seed populations. Seeding of upwelling water may be a result of
the presence of bloom-forming diatoms with resistant spores that quickly
settle from the euphotic zone to the bottom, heteromorphic dinoflagellates
with planktonic and non-mobile benthic stages, and active migration of
the photosynthetic ciliate Mesodinium rubrum (Barber and Smith 1981).
Species dominance and succession of the phytoplankton community largely depend on the frequency and intensity of upwelling and are associated with spatial and temporal transitions from a turbulent to a stratified
water column. The stability of the water column increases along the axis of
an upwelling plume with increasing distance from the coast. Since in each
upwelling cell succession proceeds from small to large diatoms and dinoflagellates and from a dependence on new nitrogen to a dependence on
regenerated nitrogen, an upwelling area represents a mosaic of water masses with different stages of succession.
16.3.2 Zooplankton
The dominant species of the zooplankton community in coastal water
are copepods (Acartia tonsa, Centropages brachiatus) and larvae of polychaetes, brachiopods, cirripedes, and other crustaceans. At the margin of
the continental shelf and above the slope the dominant or conspicuous
taxa are represented by copepods (Paracalanus parvus, Calanus spp.,
Oncaea spp.) and large holoplankters such as siphonophores, chaetognaths, and euphausiids. Due to hypoxic conditions at greater depths, most
of the zooplankton is restricted to the uppermost 30m of the water
column; however, some species (i.e., the copepod Eucalanus inermis)
migrate to greater depths with low ( <0.1 mll- 1 ) oxygen concentration. The
volume of zooplankton decreases from north to south, though seasonal
variability is similar along the coast, with a marked increase in spring.
A fundamental characteristic of the Peruvian upwelling system is the
low (5 %) transfer efficiency from primary to secondary production.
Nevertheless, high primary production provides abundant food for grazers and sustains large populations of copepods, euphausiids, anchovies,
and also myctophiids at greater depth on the slope. Protozoans, principally ciliates and zooflagellates, also attain high biomass (up to 0.97 g C m- 2 ).
Bacterial and protozoan plankton seem to constitute the primary diet of
herbivorous mesozooplankton and the abundance of foraminiferans, coccolithophorids, and siliceous radiolarians in the sediments suggests their
importance in the benthic subsystem. Copepods and euphausiids quickly