Zooplankton diversity and distribution in a deep and anoxic Mediterranean coastal lake

Abstract

The variation of the smaller size fraction of zooplankton was investigated during a two-year period in a brackish deep and anoxic coastal lake of western Greece (Aitoliko), along with the specific environmental characteristics of this ecosystem. The zooplanktonic community comprised a relatively small number of taxa and it was dominated by brackish-water calanoid copepods (Paracartia latisetosa, Calanipeda aquaedulcis) and in certain periods by rotifers and tintinnids. The zooplankton abundance showed an increase in the warmer period starting from late spring and reached maximum values in July. In the well oxygenated surface layer, temperature was the most important parameter influencing the seasonal cycles of all groups. In contrast, the oxygen depletion a few meters under the surface affected the vertical distribution of most of the zooplankton groups, which were found restricted in the surface layer, especially from spring until autumn. Only the meroplanktonic larvae of polychaetes presented increased proportions in the deeper layers. Salinity has not significantly influenced the zooplanktonic assemblages. The results reveal the degraded status of the Aitoliko basin, where the hypoxic/anoxic layers resulted in a high portion of dead organic material identified as copepod carcasses; they also underline the necessity of monitoring this ecosystem.

Response of Zooplankton Population to Environmental Forcing: Case of Southern and Northern Coasts of Sfax, Tunisia

“…In fact, a significant difference was observed in water temperature from Northern to Southern part (ANOVA; F = 76.86, p < 0.001, df = 3.027). In addition, water temperature is one of the most important ecological factors affecting the abundance, composition and diversity of zooplankton communities [45][46][47][48][49]. The low pH values can reasonably be attributed to the industrial activity still settled along the Southern in TF and IF coast whereas it was reduced in the North part (MZ).…”

“…was markedly evident in FI suggests their high adaptability to trophic and hydrologic conditions in this interface zone. The highest copepod eggs production rates and egg concentrations of cyclopoida occurred at the FI indicating that the front is also a favorable area for increases of secondary production These coexisting species exhibited certain strategies (e.g., shifting the feeding habit) in their opportunistic behaviors, in order to adapt to a highly variable marine environment of this coastal region [48,[81][82][83]. Copepod nauplii, unlike copepodites and adults, have limited energy reservoirs and inefficient feeding appendages, and given that its survival depends on high concentrations of phytoplankton, they could achieve high survival rates in the FI where the highest chl-a values are registered.…”