Ecology of the Subantarctic Islands: Subantarctic marine food cycles and their relation to discontinuous plankton concentrations

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In the New Zealand subantarctic zone, the area of land in proportion to ocean is extremely small, and as the Southern Ocean is highly pro-uctive in plankton and capable of supporting enormous numbers of animals directly or in- directly, the number of vertebrates competing for breeding territories on thl" small amount of land available is exceptionally high. At the Auckland Island, four species of seal and many species of seabird make up a vast vertebrate population of marine feeders dependent ultimately on plankton. The dense local concentrations of vertebrates and of plankton make the New Zealand subantarctic islands a particularly favourable site for noting at least some of the seasonal variations in the links of the marine food chain.
Plankton hauls through a twelve month period at the Auckland Islands gae the following picture of seasonal changes. During late summer and autumn, plankton tows were relatively uniform and poor both in species and in quantity with little phytoplankton. Minimum quantities of all species were found in winter. At the beginning of October there was a spectacularly sudden appear- ance of great numbers of diatoms which lasted until November, by late December diatoms were again relatively insignificant in the catch. After the peak of the diatom blooming, nauplius larvae of copepods appeared, becoming particularly abundant in the middle of November. In late November nauplii were replaced by adult Copepoda and zoaea larvae of decapod crustacea became prominent.