A fresh look at kelp bed phytoplankton populations in an upwelling area

• Published in: Marine ecology. Progress series (Halstenbek) 1991, Vol.72 (1/2), p.167-177
• Main Authors: Fielding, P. J., Seiderer, L. J.
• Format: Article
• Language: English
• Subjects: Chlorophyllides; Chlorophylls; Diatoms; Estimation methods; Marine; Particulate matter; Phytoplankton; Pigments; Summer; Upwelling water; Winter
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps072167

Algal pigment concentrations in the water column of a southern Benguela kelp bed were measured daily during summer and winter using High Performance Liquid Chromatography (HPLC) and spectrophotometric methods. Chlorophyll a concentrations estimated by HPLC were significantly lower than those estimated by the trichromatic equations of Jeffrey & Humphrey (1975; Biochem. Physiol. Pflanz. 167: 191–194), although differences were relatively small. There was no significant difference between chlorophyll a concentrations estimated by HPLC and the spectrophotometric equation of Lorenzen (1967; Limnol. Oceanogr. 12: 243–246). Mean HPLC chlorophyll a concentrations were 1.64 μg 1−1 in summer and 1.78 μg 1−1 in winter. Previous spectrophotometric estimates of kelp bed chlorophyll a concentrations were generally comparable to those determined by HPLC. In summer, 5 d pulses of southeasterly winds caused upwelling of cold nutrient-rich water into the kelp bed, which resulted in phytoplankton blooms. Time series analysis indicated that HPLC chlorophyll a concentrations were positively correlated with the upwelling index of 5 d previously, swell height of the same day and sea temperature of the previous day. In winter, winds were mainly northwesterly, sea temperatures were stable, and chlorophyll a concentrations were negatively correlated with swell height of 2 d previously. Phaeopigment concentrations determined by the method of Lorenzen (1967) reached 7.04 μg 1−1 and were significantly higher than phaeophytin a concentrations determined by HPLC, which rarely exceeded 2 μg 1−1. Chlorophyllide a occured in 57 % of summer samples and 43 % of winter samples, and was more prevalent than phaeophytin a. Chlorophyllide a and chlorophyll a concentrations of the same day were significantly correlated in both summer and winter. Fucoxanthin concentrations reached 5.35 μg 1−1 in winter and 2.04 μg 1−1 in summer, and daily winter fucoxanthin concentrations were highly correlated with chlorophyll a concentrations. Fucoxanthin and chlorophyll c, pigments characteristic of kelps and diatoms, occurred in > 90 % of winter samples and in < 35 % of summer samples. The kelp bed particulate resource in winter was therefore qualitatively different from the summer particulate resource.