Grazing by microzooplankton in Concepción Bay, Gulf of California, Mexico

Abstract

Microzooplankton (< 200 µm) grazing over phytoplankton, play an important role in the trophodinamic of pelagic system. In order to determine the relevance of this process in Concepción Bay, we used estimations of chlorophyll-a of highperformance liquid chromatography (HPLC) and microscopy to estimate growth and grazing rates obtained with the dilution technique. Phytoplankton growth and microzooplankton grazing was evaluated in the middle region of bay. Seasonal rates of growth (µ) of nanno and microphytoplankton, determined by microscopy were, respectively: 1.04 y 1.06 d-1 (spring), 1.02 y 1.04 d-1 (summer), 1.01 y 1.03 d-1 (autumn), 1.05 y 1.00 d-1 (winter). The grazing by microzooplankton (g) of nano and microfitoplankton were respectively: 1.06 and 1.12 d-1(Spring); 1.02 d-1 and 1.07 d-1 (Summer); 1.03 d-1 and 1.10 d-1 (Autumn); 1.14 d-1 and 1.02 d-1 (Winter). The estimations of µ and g of chlorophyll-a (Chl-a) performed through HPLC were, respectively: 2.47 y 1.33 d-1 (Spring), 1.31 y 1.00 d-1 (Summer), 2.55 y 1.89 d-1 (Autumn), y 0.29 y 0.05 d-1 (Winter). We do not observe a clear preference by size class for the consumption of the potential primary production removed (PPPr), according to the microscopy analysis. Between the assessments of the phytoplankton growth (µ) and microzooplankton grazing (g) by microscope and HPLC, the PPPr were very similar (98.0% for nanophytoplankton, 97.2% for microphytoplankton, and 99.7% for HPLC). These results may be associated with the dominance of nanophytoplankton fraction along the year.