Seasonal patterns of phytoplankton productivity and abundance in nearshore oligotrophic waters of the Levant Basin (Mediterranean)

Abstract

A biweekly sampling program from two stations at the eastern Levant Basin was carried out during a 1-year period (1983). The first station (neritic) was located 2 km offshore over the Israeli continental shelf, while the second (pelagic) was located 10 km offshore slightly beyond the continental shelf. It was found that during summer the relatively close pelagic waters had chlorophyll a concentrations comparable with the most oligotrophic deep sea regions of the world's oceans. During winter and spring, profound fluctuations were observed in both phytoplankton standing crop and primary productivity at the neritic station. This was in response to weather phenomena, such as heavy rains or storms, which did not affect the pelagic Station to such an extent. The picoplanklon size fraction (<3 μm) dominated at the neritic station during summer and fall, while the nanoplankton fraction (3–20 μm) dominated during spring. At the pelagic station the picoplankton fraction dominated almost all year round, but it is suspected that some portion of it was photosynthetically inactive.