Annual variations in biochemical composition of size fractionated particulate matter and zooplankton abundance and biomass in Mersin Bay, NE Mediterranean Sea

Seasonal changes in biochemical composition of different particle size classes (pico-, nano- and micro-particulate matter) and the zooplankton abundance and biomass were studied in NE Mediterranean between November 2004 and January 2006. Sampling was carried out at monthly intervals from two stations representing coastal and open water characteristics. Dominance of size fractions showed seasonal variations in each biochemical component but on annual average pico size fraction predominated and accounted for ≥ 40% of the chl-a and particulate organic matter (protein + lipid + carbohydrate) concentrations. At most of the sampling periods protein:carbohydrate ratio was < 1 at the stations revealed that the studied area was under the nutrient limitation, and nutrient deficiency was severe especially for nano size fraction. On annual average, total zooplankton abundance were 4968 ± 3538 and 603 ± 368 ind. m− 3, and total biomass were 22 ± 19 and 3 ± 1 mg m− 3 at stations 1 and 2, respectively. 200–500 and 112–200 µm size fractions were dominant in zooplankton abundance at both stations. Similarly, 200–500 µm size fraction was dominant in zooplankton biomass at the coastal, whereas > 1000 µm size fraction was at the open station. Copepods were the most abundant zooplankton group and determine the distribution of total zooplankton followed by crustacean nauplii, appendicularia, and cladocera.