Island Stirring Effects on Phytoplankton Growth

Abstract

It has long been suspected that the disturbance of the flow caused by the presence of an oceanic island may be responsible for increased biomass and production near the island. Doty and Oguri (1956), reporting observations near Oahu, Hawaii, coined the phrase “island mass effect” to describe such enhancement, which they explained with the suggestion that benthic algae or corals on the island’s flanks might concentrate inorganic nutrients from the passing waters, grazing eventually making these nutrients available to phytoplankton. They drew on older literature (e.g. Gran, 1912) reporting an increase in oceanic plankton near continental margins. Dandonneau and Charpy (submitted), in a detailed statistical analysis of data from the S.W. Pacific, could find only occasional and weak relationships between sea-surface photosynthetic pigment concentration and distance from the nearest island. Remote sensing of pigments has not yet been used extensively to observe biomass distributions around islands (but see Simpson and Tett, this volume, for an example of the exciting possibilities in this area). Other accounts of island mass effects are anecdotal and often unsupported by measurements of the physical structure and flow field. It thus appears to remain true, as Gilmartin and Revelante (1974) remarked in a further study of the Hawaiian islands, that ‘except for the work of Doty and Oguri (1956), the so-called ‘island mass’ effect is neither well documented nor are the causes for the increases clear.’