Distribution, abundance, and size composition of phytoplankton off Westland, New Zealand, February 1982

Abstract

In late summer 1982 an intense dinoflagellate bloom occurred close inshore off West‐land, New Zealand. This bloom was essentially made up of a monospecific surface population of Prorocentrum micans. This species alone accounted for 92–98% of integrated phytoplankton cell carbon (PPC) close inshore. Dinoflagellates also formed the largest proportion of PPC further offshore, except off Karamea Bight where phytoflagellates predominated. Diatoms were most plentiful close inshore off Wanganui Bluff, coincident with the elevation of dissolved inorganic nitrogen in upwelled water. There was a general shift in the predominant phytoplankton size class from 25–30 μm nearshore to 0–5 μm further offshore. The size fractionation of chlorophyll a also showed a marked onshore‐offshore relationship — the proportion of 5–20 μm (nanoplankton) and 20–200 μm (microplankton) fractions decreased dramatically seawards while the proportion of 0.2–5 μm (picoplankton) fraction increased progressively seawards. Close inshore the >20 μm fraction accounted for >66% of total chorophyll a and >56% of total primary productivity, while < 20 μm fraction contributed to >89% of total chlorophyll a and >85% of the total offshore oceanic production.

Key words:

• late summer bloom
• Prorocentrum micans
• phytoplankton
• dinoflagellates
• diatoms
• phytoflagellates
• size fractionation
• cell carbon
• chlorophyll a
• primary productivity
• upwelling
• freshwater run‐off
• Westland
• New Zealand