engleski

MASS OCCURRENCE EVENT OF THE CTENOPHORE BOLINOPSIS VITREA (L. AGASSIZ, 1860) IN THE NEARSHORE SOUTHERN ADRIATIC SEA (KOTOR BAY, MONTENEGRO)

Plankton sampling (125-µm mesh Nansen plankton net) and hydrographic measurements were carried out weekly from March 2009 to July 2010 at a fixed station in the Kotor Bay, Montenegro (N 42026’ ; W 18045’). A bloom of ctenophore Bolinopsis vitrea was noted in the spring and summer of 2009. B. vitrea has been observed before in the Mediterranean, although it has not been reported to be dominant or to occur in massive blooms. During our investigation, ctenophores were only found below 5 m depth, where the hydrographic conditions were more stable. Results of the investigation indicate that mass occurrence of B. vitrea could have a great impact on the Kotor Bay ecosystem. Their predation on copepods would reduce grazing pressure on phytoplankton, favouring an uncommon bloom of the latter. It is evident that B. vitrea are capable of altering rapidly the composition and biomass of coastal plankton communities when present in large masses. Disappearance of B. vitrea from the Kotor Bay coincided with the appearance of their predator, the ctenophore Beoroe ovata, in December 2009. During 2010, neither Bolinopsis vitrea nor Beoroe ovata was observed in the bay system. This first evidence of such events for Bolinopsis vitrea along with recurrent recent blooms of the invasive ctenophore Mnemiopsis leidyi in the Mediterranean Sea may indicate changes in the functioning of this enclosed marine ecosystem. Gelatinous plankton blooms may thus pose an area of concern for the region indicating a risk of failure to achieve GES (Good Environmental Status) as high level objective of the MSFD (Marine Strategy Framework Directive).

gelatinous zooplankton; blooms; microphytoplankton; nanophytoplankton; copepods; Mediterranean Sea

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