Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
9483447 | Journal of Marine Systems | 2005 | 17 Pages |
Abstract
Hydrographic conditions, phytoplankton composition and biomass, photosynthetic parameters and primary production were determined in the RÃa de Vigo and adjacent shelf waters during April-May 1997 and September 1998. The sampling was designed to find the seasonal downwelling-upwelling and upwelling-downwelling transition periods characteristic of spring and autumn phytoplankton blooms. There was upwelling relaxation event followed by downwelling during both spring and autumn cruises. Temperature and salinity distributions showed that rÃa and shelf waters formed two distinct domains, which were separated by a thermohaline front at the mouth of the rÃa. The phytoplankton composition was completely different in the two environments. Cyanobacteria dominated on the shelf and constituted 46-66% of total phytoplankton biomass, while large phytoplankton (diatoms and dinoflagellates) were more abundant in the rÃa, especially during upwelling relaxation. However, the high shelf-rÃa exchange induced by a strong downwelling event on 7 September 1998 removed large phytoplankton (mainly diatoms) from the water column in the rÃa. Chlorophyll-specific maximum photosynthetic rates (PmB) were significantly higher in the rÃa domain during upwelling relaxation, when autotrophic microplankton dominated in the interior. Primary production varied from 0.63 to 2.6 g C mâ2 dayâ1 during the spring cruise and between 0.32 and 2.09 g C mâ2 dayâ1 during the autumn cruise, with the highest values in the rÃa during both cruises. Primary production was relatively constant on the shelf with no significant differences between cruises, whereas differences were significant in the rÃa, with higher values during upwelling relaxation periods and lower values during downwelling. Analysis of light saturation parameters and light absorbed by phytoplanton in the water column suggests that photosynthesis was not light-limited either on the shelf or in the rÃa. It is concluded that upwelling-downwelling cycles were the main driving force, through changes in autotrophic microplankton biomass in the rÃa, that caused the variability observed in the rÃa-shelf system.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Oceanography
Authors
Luisa M. Lorenzo, Belén Arbones, Gavin H. Tilstone, Francisco G. Figueiras,