Dataset and database biodiversity of plankton community in Lebanese seawater (Levantine Basin, East Mediterranean)

Oceanographic data were obtained from ship cruises conducted from 1965 until 2003 in the neritic and oceanic Lebanese waters (Levantine Basin). They include, in addition to Plankton community diversity and abundance, main hydrographic data such as temperature, salinity, dissolved oxygen, water transparency, chlorophyll a, nitrates and phosphates. The purpose of this work was to elaborate a dataset and database for the biodiversity of the plankton community in relation to the hydrological conditions of the area and the abundance of species populations. Spatial and temporal qualitative and quantitative distributions of the species and groups are strongly correlated to seasonal variations of hydrological parameters. The thermal annual cycle splits up in two different phases: a cold phase in winter (December-March) and a warm phase in summer (June-November), separated by a short spring inter-season. During the winter period, isothermal conditions prevailing in the 0-200 m water column are characterized with relative low temperature and salinity averages, poor plankton productivity and low biomass contrasting the high species diversity. The warm phase in summer is characterized by high surface water temperatures and salinity, accompanied with the formation of a thermocline in the layer 35-75m and a water layer stratification, which creates a hydro-thermal barrier avoiding exchange of water masses and vertical migration of organisms and low plankton biomass and diversity. A short spring period (April-June) is characterized by optimal hydrographic conditions that induce phytoplankton growth leading sometimes to little blooms, followed by high zooplankton production contrasting the low species diversity. During the long-term survey we noticed certain hydrological changes in the Levantine Basin, expressed by small rises in temperature (ΔT=0.4°C) and salinity (ΔS= 0.35‰) and increasing migration. To date 400 phytoplankton species and more than 750 zooplankton taxa, were identified in the area, of which dozens of introduced exotic species are of Indo-Pacific origin. These changes induced some ecological evolutions in the marine ecosystems and are due to the regulation of the water level of the Nile by the Aswan High Dam by reducing the amount of freshwater outflow in the Mediterranean, and the deepening of the Suez Canal accelerates the northward current and thus facilitates the migration process. Global warming may also contribute to these hydrological changes in generating a certain “tropicalisation” of the Levantine Sea.