LONG-TERM REGULATING MECHANISMS OF PHYTOPLANKTON BIOMASS IN A TRADITIONAL SHELLFISH AQUACULTURE AREA.

Using 14 years of environmental data, we investigated distribution of thermohaline properties and phytoplankton biomass in Mali Ston Bay, which is the major shellfish farming area on the eastern Adriatic coast. Sampling was conducted biweekly during summer and monthly during the rest of the year throughout period 1999-2012. Due to strong river inflow and many submarine springs, continuous thermohaline stratification was recorded throughout the entire investigated period. The salinity effect on stratification was more pronounced compared to temperature effect which was mostly expressed in summer. Phytoplankton biomass increased throughout the period 1999-2012, while a negative trend in salinity was observed for the surface layer. Seasonal biomass pattern showed two biomass peaks: the first in late winter/early spring and the second (less pronounced) in the autumn. Regarding phytoplankton size fraction; such as microplankton and nanoplankton, each component was equally represented in all seasons. Despite continuous enrichment from the Neretva River and underwater springs, lack of significant correlation between phytoplankton biomass and nutrients indicate that nutrients are quickly utilized by phytoplankton and transferred further into food web. Water column was well oxygenized throughout investigated period having high transparency and high diversity of phytoplankton taxa. According to all investigated parameters, and the fact that Mali Ston Bay is naturally productive area, and also aquaculture area, it is hypothesized whether this area could be considered as oligotrophic environment or not. [ABSTRACT FROM AUTHOR]