Phytoplankton biomass in the sub-Antarctic area of the Straits of Magellan (53°S), Chile during spring-summer 1997/1998

In order to provide a better understanding of the dynamics of phytoplankton in the coastal regions of high latitudes, a study was carried out to estimate the dynamics of carbon biomass of autotrophic and heterotrophic algal groups over the austral spring-summer 1997/1998 period. At a fixed station located in the central basin (Paso Ancho) of the Straits of Magellan (53 degreesS), surface water samples were collected at least once a week from September 1997 (early spring) to March 1998 (late summer). Quantitative analysis of biomass of phytoplankton was estimated from geometric volumes, using non-linear equations, and converted to biomass. The pattern of chlorophyll a showed a strong temporal variability, with maximum values (mean 2.5 mg m(-3)) at the austral spring phytoplankton increase bloom (October/November) and minimum values during early spring (September: <0.5 mg m(-3)) and summer (January/March: 0.5-1.0 mg m(-3)). During the spring bloom, diatoms made up to 90% of the total phytoplankton carbon (0.01-189 <mu>g l(-1)), followed by a maximum of thecate dinoflagellates (0.08-34 mug l(-1)), and sporadic high biomass of phytoflagellates during summer. Heterotrophic algal groups such as Gymnodinium and Gyrodinium spp. dominated (70%, in the 5- to 25-mum size range) shortly before the main diatom bloom, and small peaks were observed within spring and early summer periods (0-0.4 mug l(-1)). Phytoflagellates dominated earlier (spring) with higher carbon biomass (8 mug l(-1)) and post-bloom periods (summer) when carbon biomass ranged between 1 and 4 mug(-1).