Contributions of nano- and picophytoplankton to the phytoplankton biomass in Saudi Arabian waters of the Arabian Gulf

The two smallest size classes of phytoplankton, namely, nano- and picophytoplankton, can play an important role in marine primary production, particularly in warm and nutrient-poor waters. The Arabian Gulf, with its high temperatures, could provide good growth conditions for these two size classes; however, so far, phytoplankton research in the Arabian Gulf has largely focussed on the biggest size class, microphytoplankton. This study presents data on the annual cycle of chlorophyll-a (Chl-a) at three stations in Saudi Arabian waters of the Arabian Gulf, focussing on the contribution of the three phytoplankton size classes to total Chl-a, and identifies environmental parameters affecting these contributions. Whereas dominance of nanophytoplankton was observed during summer, highest contributions of picophytoplankton were found during winter and spring. A close link between nano- and microphytoplankton was noted on the basis of optimum correlation models. The models for both size fractions included photosynthetically active radiation, salinity and phosphate concentration, but with opposing algebraic signs in the two models. By contrast, picophytoplankton was negatively correlated with temperature, indicating that the contribution of this size class could decrease under a future climate-change scenario in the Arabian Gulf.