Changes in the non-crustacean zooplankton community in the middle Adriatic Sea during the East Mediterranean Transient

Abstract

Background and Purpose: Here we presented changes in the non-crustacean zooplankton community in the years characterized by the large scale changes in the thermohaline circulation in the East Mediterranean known as the Eastern Mediterranean transient (EMT) and stronger inflow of colder and less saline Modified Atlantic Water (MAW) into the Adriatic Sea.

Material and Method: Monthly samplings from February 1995 to February 1996, were performed at fixed station Stončica near the Island of Vis in the open oligotrophic Middle Adriatic waters. Zooplankton samples, taken vertically from 100 m to the surface using a Nansen net with 125-µm mesh size were analyzed in detail for the following zooplankton taxa: Hydromedusae, Calycophorae, Ctenophora, Pteropoda, Heteropoda, Polychaeta and Chaetognatha.

Results and Conclusions: Among the investigated non-crustacean zooplankton three species were registered for the first time, while one species reappeared after years of absence. Compared with earlier data there was a dramatic change in dominant species of calycophoran medusae, pteropods and polychaetes. Data presented herein provide baseline information that is essential for the evaluation of impact of hydroclimatic changes on the zooplankton community, which started in the East Mediterranean in the 1990s and are still on going.

Keywords: zooplankton, hydroclimatic changes, Middle Adriatic