The Response of Surf Diatom Populations to Environmental Conditions. Changes in the Extent of the Planktonic Fraction and Surface. Patch Activity

Abstract

The population dynamics of the surf diatoms Anaulus birostratus and Asterionella glacialis were monitored over an 11-day period during which wave height decreased and then increased abruptly. Two main changes were observed in the populations, viz; 1) a diel periodicity in cell concentration that persisted throughout the study period, and 2) a meso-scale variability where both patch activity (i. e. the concentration of cells in the neuston which created discoloured patches) and planktonic cell concentrations in non-patch areas (background cells) decreased during falling wave energy, disappearing after 5 days. Immediately following the onset of a high wave energy event (approximately 8 h), patch activity resumed, together with an increase in background planktonic cell concentration.Time of day and wave height accounted for 51 % of the variance in background cell concentrations during the study. Wind direction and speed, tidal phase and sea and air temperature did not have any significant effect. The pattern of cell division in Anaulus birostratus indicates that the sequence of patch disappearance and reappearance did not involve any of the logarithmic growth or senescence that is the normal pattern of phytoplanktpn blooms. Instead the decrease and increase in cell concentration was brought about by cell advection into and out of the water column and neuston of the surf-zone. This advection appears to be directly related to wave energy. We therefore conclude that both the diel periodicity and meso-scale temporal features of the population involve migration and accumulation phenomena rather than growth.

Growth rates of five species of surf clams on a southern North Island beach, New Zealand

“…They concluded that the most likely cause of the different growth rates of New Zealand surf clams was that individual species occur and feed within a gradient of surf diatom density. The gradient is the result of the interaction of diurnal changes in the physiology of surf diatoms and wave action that can result in low concentrations of surf diatoms of 10 2 cells ml" 1 outside the breaker zone but high concentrations, 10 5 -10 6 cells ml" 1 , within the breaker zone (Talbot & Bate 1988;Talbot et al 1990). The three species of surf diatoms, Gonioceros armatus, Asterionella glacialis, and Aulacodiscus kittoni, that occur on New Zealand beaches show regional difference in abundance (Cassie-Cooper 1996).…”