MEPS 281:79-92 (2004)  -  doi:10.3354/meps281079

ABSTRACT: The effects of 2 cold fronts on a shallow sublittoral system at the Island of Santa Catarina, southern Brazil, were investigated in June 2002. Atmospheric, pelagic and benthic data were taken daily covering the days before, during and after the passage of both fronts, for a total of 8 d of sampling. The passage of cold fronts, a short-term event, promotes changes in the entire shallow sublittoral ecosystem, i.e. both pelagic and benthic compartments. In the pelagic system, both fronts changed seston, nutrient and chl a concentrations. An increase in chl a just after the passage of the fronts probably resulted from phytoplankton retention and accumulation near the coast, from microphytobenthos resuspension and from an increase in nutrient availability. In the benthic system, sediment features and the 3 benthic components studied—microphytobenthos, meiofauna and macrofauna—were also affected by the passage of the cold fronts. The sediments at the site became more homogeneous. While mean grain size decreased, the fraction of fine sand gradually increased after the passage of the fronts. In contrast, sediment organic content was significantly higher immediately after the passage of the first cold front. Cold front effects in the benthos depended on the biological component, the vertical distribution of fauna and on the magnitude of the front. The sediment chl a concentration was lower exactly 1 d after the passage of the fronts, while phaeopigments were significantly higher. Both macrofauna and meiofauna, particularly nematodes, of the upper sediment layer exhibited a decrease in density and number of taxa during the passage of the first frontal system. The decrease in nematode abundance was mostly due to vertical migration to the deeper layers of the sediment, rather than being the result of erosion and transport during the passage of the cold fronts.

KEY WORDS: Cold front · Short-term disturbance · Phytoplankton · Microphytobenthos · Meiofauna · Nematodes · Macrofauna