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Mass Occurence of the Noctiluca scintillans (dinoflagellate), Salpa fusiformis (tunicate) in the open South Adriatic in spring 2009

This study was conducted on April and June 2009 at three stations (P-100, P-300, P-1200) in the South Adriatic using a Nansen net (250 um mesh, 1 m in diameter and 255 cm in length). In April 2009, abundance of N. scintillans and S. fusiformis was exceptionally high in the upper 50 m, 93 and 21 ind.m-3, respectively. In June 2009, S. maxima (avg 10 cm in length) accumulated in high numbers near the surface. According to the net samples from 0-50 m, we could estimate their abundance as 1 in.m-3 but, it is possible that this estimation is not accurate because of their superficial accumulation. At the same time, phytoplankton biomass expressed as Chl-a concentration was 0.11 and 0.10 mg m-3 from 0 to 50 m in April and June, respectively. In April 2009 calanoid copepod abundance was also relatively high with 150 ind. m-3 in the 0-50 m layer suggesting that there was enough food available for herbivorous zooplankton. Contrary, in June 2009, under high feeding pressure of S. maxima and due to competition for the same food only 1 ind. m-3 of calanoid copepods was found. Occurence of the mixotrophic dinoplagellate Noctiluca scintillans in unusual high abundance for the open sea and herbivorous tunicates Salpa fusiformis and S. maxima may indicate that open South Adriatic ecosystem is becoming more eutrophic. This could be in a close connection with hydroclimatic changes in the East Mediterranean in last two decades.

mass occurence; Noctiluca scintillans; Salpa fusiformis; South Adriatic

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