Composition and temporal succession of mesozooplankton communities in Kotor Bay (Montenegro)

PESTORIC, B.; MOLINERO, J. C.; LÓPEZ ABBATE, M. C.; LUCIC, D

Tirana

Congreso; MarCoastEcos; 2012

Mesozooplankton plays a key role in the ecosystem structure due to its quick response to abiotic conditions, especially in impacted environments, and provide a vital connection in marine trophic webs, transferring energy from autotrophic organisms or microzooplankton to higher trophic levels. Mesozooplankton communities of Mediterranean coastal areas are characterized by strong seasonal fluctuations in both total abundance and succession of dominant groups. Temporal mesozooplankton dynamics and driving mechanisms of their variability are highly susceptible to changes of the environmental variables, especially in shallow, semi-enclosed bay as Kotor Bay. This study was carried out from March 2009 to June 2010 weekly at one station in Kotor Bay. Hydrographic parameters were highly variable in upper 5m during the investigated period. Mean temperature was 16.58ºC and ranged between 6.30 ºC in January 2010 and 27.30ºC in July 2009. Very strong thermal stratification existed during summer months. In October, surface temperature rapidly decreased and in Kotor Bay temperature inversion occurred during winter months. Salinity in bottom layers does not exceed 37.5 except in March 2009 (38.5). Surface salinity was highly variable during investigated period because it is greatly driven by precipitation and fresh water discharge. The variability of zooplankton groups during the studied period (2009-2010) was addressed by PCA analysis. The total variance associated by the first four components (PCs) was 73%. Variability of PC1 was mainly due to Appendicularians, meroplankton larval stages, Siphonophores and Copepods, while PC2 was explained mainly by Ctenophores. PC3 and PC4 were better represented by Cladocerans and Chaetognaths respectively. PC1 showed the highest anomalies during warm seasons of 2009 and 2010, in which the involved groups were more abundant. The opposite was recorded for the PC3 and PC4. The downward trend of the PC2 is explained by the observed decrease in Ctenophores abundance during the studied period, which may be associated with the decrease in temperature during 2010, especially during spring time. This leaded to a release in grazing pressure which could have a synergistic effect with temperature, thus enhancing the strong upward trend of PC1 during 2010.