The seasonal planktonic cycle in coastal waters of the Canary Islands

Javier Arístegui,María F Montero,Santiago Hernández-León,May Gómez

doi:10.3989/scimar.2001.65s151

Abstract

The short-term temporal variation in the phytoplankton and mesozooplankton cycles was studied in a coastal area off east Gran Canaria Island. A small phytoplankton bloom, split into two peaks, appeared during late winter (end of February and March), coinciding with the lowest temperatures in the water column. A clear inverse relationship was observed between the biomasses in mesozooplankton and phytoplankton during the bloom period. The peaks in primary production and phytoplankton biomass were uncoupled in time, suggesting that biomass could depend on consumer control (grazing), and primary production on resource control (nutrients). Mesozooplankton grazing represented less than 20% of the primary production, an indication that small zooplankton and protozoans controlled the phytoplankton populations, dominated by picoplanktonic cells (> 60% of the primary production). The ratio between depth-integrated primary production and community respiration (P/R) covaried with primary production (P), showing that changes in P control the trophic status of the system. At P > 400 mgC m -2 day -1 the P/R ratio is > 1, switching the system from heterotrophy to autotrophy, a situation that takes place during the phytoplankton growth period.

Highlights

The temporal variability of planktonic cycles in subtropical waters is largely unknown, in comparison with temperate regions where many detailed studies on seasonal cycles have been done (e.g., Sverdrup, 1953; Purdie, 1996)
Subsamples were drawn for analysis of chlorophyll a, primary production (125 ml per incubation bottle) and the respiratory activity of the electron transport system (ETS) in microplankton (5 litres)
Two peaks in primary production were observed during the same period, uncoupled in time from the chlorophyll maxima (Fig. 2a)

Summary

Introduction

The temporal variability of planktonic cycles in subtropical waters is largely unknown, in comparison with temperate regions where many detailed studies on seasonal cycles have been done (e.g., Sverdrup, 1953; Purdie, 1996). Since subtropical regions have been frequently regarded as the least biologically variable waters, the few studies carried out in these regions (Menzel and Ryther, 1960; Jitts, 1969; Sournia, 1969; Owen and Zeitzschel, 1970; Bienfang et al, 1984) were designed with a monthly sampling strategy that barely represented the true variability in the structure and metabolism of planktonic communities. That plankton communities in the Canaries region may be influenced by mesoscale variability. Island eddies may pump nutrients into the surface waters (Arístegui et al, 1994; 1997); wind shearing in the boundaries of PLANKTONIC CYCLE IN THE CANARY ISLANDS 51 the islands increases vertical mixing along the coast (Arístegui et al, 1989); and upwelling filaments may export organic matter from the African coast into the surface Canary waters (Barton et al, 1998)

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