Plankton Dynamics in the South-Central Caribbean Sea: Strong Seasonal Changes in a Coastal Tropical System

Abstract

Between September 1999 and May 2000, seasonal changes of plankton communities were assessed in two contrasting tropical systems: Salamanca Gulf and Tayrona Natural National Park at the coastal, south-central Colombian Caribbean Sea. We measured hydrographic characteristics of the water column, size fractionated phytoplankton biomass, protein/carbohydrate ratios (P/C) of the particulate organic material, phytoplankton (>55 µm), and mesozooplankton composition and density. Between zones no change was detected in water column characteristics, but there were changes among seasons (rainy and dry) in both areas. High chlorophyll a concentrations in the phytoplankton community prevailed during both seasons. The phytoplankton taxonomic composition, mesozooplankton assemblages, as well as P/C ratio, differed between seasons. This variability was derived from differences in fresh and brackish water input to the continental shelf (rainy season) and potentially upwelling (dry season). Albeit differences in the intensity of the oceanographic processes, Salamanca Gulf and Tayrona Natural National Park varied similarly by climatic season. Our results showed strong seasonal differences in the plankton community, contrasting with the general perspective of tropical Caribbean systems where plankton communities are usually considered of low variability and concentration all year long.