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Abundance and carbon biomass of different phytoplankton groups obtained by microscopy were compared with taxonomy derived from pigment measurements and CHEMTAX analysis of samples collected in June 2006 in the NW Black Sea. The diatom Chaetoceros curvisetus was dominant in terms of carbon biomass based on cell volume at inshore stations, while the coccolithophore Emiliania huxleyi was prevalent at offshore. Emiliania huxleyi reached bloom abundance of 3.3 × 106 cells L− 1. The chlorophyll a (chl a) concentration within phytoplankton groups as allocated by CHEMTAX was in agreement with microscopy derived carbon biomasses of the taxonomic groups diatoms, dinoflagellates and cryptophytes only. Carbon biomass of less abundant phytoplankton taxa (cyanophytes, euglenophytes and chlorophytes) did not correlate with group-specific chl a. It was not possible to detect E. huxleyi bloom by CHEMTAX analysis probably due to much higher biomass of other species containing 19’-hexanoyloxyfucoxanthin. Nutrient concentrations were generally high in the waters where diatom and dinoflagellates dominated the community but low in the area of E. huxleyi bloom. A good correlation between total carbon biomass of phytoplankton and chl a was found and the estimated C:chl a ratio of phytoplankton varied between 36 and 256 (in average 124 ± 50).

Monitoring for 6 years (2001–2006) showed that the population explosion of the alien ctenophore Mnemiopsis leidyi in the southern Caspian Sea coincided with a decline in the abundance and species number of mesozooplankton. While this decline appeared to have reduced the nourishment of sprat (also known as kilka), it seemed to have affected phytoplankton favorably mainly due to the decrease in grazing pressure. During 2001–2002, when M. leidyi abundance and biomass were at their highest levels, abundance of dinoflagellates and cyanophytes exceeded that of diatoms. Before the invasion (1996) and in some years after the invasion (2003, 2004 and 2006) diatom abundance was higher than the abundance of other groups. In September 2005, an unprecedented bloom of the toxic cyanophyte Nodularia sp. was observed in the southern Caspian Sea. Disappearance of edible zooplankton such as Eurytemora spp. was among the first changes observed after the expansion of M. leidyi in the area. Some changes in the macrobenthic fauna were also conspicuous after the increase of this ctenophore. While the biomass of some deposit feeders, such as the polychaete Nereis diversicolor and oligochaete species increased, benthic crustaceans decreased sharply in abundance during 2001–2003 and completely disappeared during 2004–2006. Iranian catches of kilka, the most abundant and widespread zooplanktivorous fish, decreased significantly in the southern Caspian Sea after 1999. Iranian landings of kilka dropped ~70% from 69,070 ± 20,270 t during 1995–2000 to 23,430 ± 12,240 t during 2001–2006, resulting in a loss of at least 125 million US dollars to the economy. There were also changes in the total catches of large predators such as the kutum and mullet, which mainly feed on kilka, between 1991 and 2006.

Effects of atmospheric deposition and other environmental factors on phytoplankton dynamics were evaluated from an open (having offshore characteristics) and a coastal station in the northeastern Mediterranean between December 2000 and December 2001. Data on phytoplankton, chlorophyll a, nutrients, temperature and salinity were obtained at bi-weekly or more intense intervals during 1 yr, whilst transport of Saharan dust towards the sampling region was monitored daily by SeaWiFS (sea-viewing wide field-of-view sensor) images. Diatoms were the group of highest average biomass during the entire investigation period. Although coccolithophores (mainly Emiliania huxleyi) numerically dominated at the open station during the study period, their maximum abundance was as low as 50 x 10 3 cells l -1 . The intensity of dust transport was observed to be highest in spring. Less intense transports were observed in summer and autumn. Several intense episodic dry and wet dust deposition events during the spring season observed by SeaWiFS images caused little or no increase in phytoplankton abundance and biomass in the following days and weeks. Nevertheless, it appears that less intense dust transport events increased phytoplankton abundance and biomass in August, September and October 2001, when water column stratification was at its peak. However, these increases were much weaker than the major winter-early spring bloom (in February and March), which was caused by upwelling, mixing the water column. We suggest that the impact of atmospheric nutrient input on phytoplankton in the Mediterranean is rather low on a yearly basis.

The effects of nitrate, ammonium and phosphate on the abundance, chlorophyll a content (chl a), in vivo fluorescence, particulate organic carbon, nitrogen, phosphorus and cell morphology of the diatom Skeletonema costatum, the dinoflagellate Prorocentrum micans and the coccolithophore Emiliania huxleyi were investigated in the laboratory. The carbon:chlorophyll a ratio (as weight), a parameter often used in productivity estimates, differed substantially among the three species as well as at different nutrient concentrations at the end of the exponential growth phase. The cell chl a content was higher in the earlier phases of growth in all three species in agreement with previous investigations. Average chl a content per cell during the experiments was higher in P. micans (8 pg) than in S. costatum (0.4 pg) and E. huxleyi (0.2 pg). However, chl a content per unit volume was higher in E. huxleyi (~15 fg μm−3) than in S. costatum (~7 fg μm−3) and P. micans (~1 fg μm−3). Prorocentrum micans cultures reached the highest total biovolume (74 mm3 L−1 and was 3 and 5 times higher than S. costatum and E. huxleyi cultures, respectively) under high nutrient concentrations. Nevertheless, total chl a concentration of S. costatum culture was almost twice higher (122 μg L−1) than that of the other two species at the end of the exponential growth phase. Phosphate consumption by S. costatum occurred at higher rates compared to the other two species during the experimental period, probably showing that this nutrient was more favourable for this species. Our findings from these laboratory experiments emphasize that chl a values in the natural habitat may not accurately indicate actual phytoplankton biomass.

The species composition, abundance, and biomass of micro- (>15 μm) and nano- (

Lessardia elongata Saldarriaga & Taylor is identified for the first time in the north-western Black Sea in the present study. This species has probably been recorded with different names in the Black Sea due to lack of detailed investigations with scanning electron microscopy (SEM) or fluorescence microscopy. Our identification is based on observations with an electron microscope in September 2004 and with an epifluorescence and light microscope in June 2006. Cells were 5–10 µm wide, 22–30 µm long in formaldehyde fixed samples, fusiform, transparent, and had a faint broad girdle. Epitheca was slightly larger than the hypotheca and recently ingested prey could often be seen in the antapical half of the cell within very conspicuous vacuoles. Thin and faint thecal plates were hardly visible under epifluorescence microscope after staining the cells with fluorescence brightener 28 in the fixed samples. Cell abundances up to 18,400 cells l–1 and 87,000 cells l–1 were observed in September 2004 and June 2006, respectively.

The invasive ctenophore Mnemiopsis leidyi (Agassiz) which was transported from the Black Sea into the Caspian Sea at the end of the 1990s, has negatively affected the ecosystem of the Caspian Sea. Zooplankton abundance, biomass and species composition were evaluated on the Iranian coast of the Caspian Sea during 2001-2006. A total of 18 merozooplankton (13 species composed of larvae of benthic animals) and holozooplankton (4 Copepoda and 1 Cladocera) species were identified. The total number of zooplankton species found here was 50% less than in a previous investigation performed in the same region in 1996 before the introduction of M. leidyi into the Caspian Sea. Cladocera species seemed to be highly affected by the invasion of M. leidyi; only one species, Podon polyphemoides, remained in the study area, whereas, 24 Cladocera species were found in the study carried out in 1996. While Copepoda Eurytemora minor, E. grimmi, Calanipeda aquae dulcis and Acartia tonsa were abundant before the M. leidyi invasion, only A. tonsa (copepodites and adults) dominated the inshore and offshore waters after the invasion. The maxima in zooplankton abundance (22,088 ± 24,840 ind.m-3) and biomass (64.1 ± 56.8 mg.m-3) were recorded in December 2001 and August 2004, respectively. The annual mean zooplankton abundance during 2001-2006 was in the range of 3,361- 8,940 ind.m-3 which was 2-5 fold less than the zooplankton abundance in 1996. During 2001-2006, the highest abundance and biomass of M. leidyi were observed during summer-autumn coincident with warm temperatures and generally when abundance of other zooplankton organisms was low., JRC.H.5-Land Resources Management

The contribution of phytoplankton groups to total chlorophyll a (chl a) was derived using CHEMTAX from pigment measurements by HPLC and compared with the carbon (C) biomass estimations obtained from microscopy in the southern Baltic Sea in April 2005. Five different matrices of pigment:chl a input ratios, derived from the literature, were tested. Successive runs of CHEMTAX showed peridinin:chl a for dinoflagellates and fucoxanthin:chl a for diatoms to converge at 0.452 ±0.02 (mean ± SD) and 0.489 ± 0.03, respectively, with initial ratios varying by a factor of 2 to 3 across matrices. The 2 techniques were in relatively good agreement for the dominant phytoplankton groups. Peridinin, diadinoxanthin, chlorophylls c1 and c2 (here grouped together as chl c1+c2), fucoxanthin and alloxanthin were the principal accessory pigments; dinoflagellates, diatoms and cryptophytes were the groups forming the majority of the C biomass. Diadinoxanthin and chl c1+c2 were mainly associated with the dominant dinoflagellates rather than with other phytoplankton classes. Excluding cyanophytes, the correlation between carbon biomass of other minor phytoplankton groups and their chl a was either poor or not significant due to uncertainties in either microscopic counts or CHEMTAX classification. There was a good correlation between carbon biomass of phytoplankton and chl a. The estimated C:chl a ratio of total phytoplankton varied between 8 and 40 (in average 20 ± 7), with a higher value for dinoflagellates (30 ± 17) than for diatoms (9 ± 7). Fucoxanthin- containing small flagellates might have led to the overestimation of the diatom contribution by CHEMTAX at a few stations., JRC.H.3-Global environement monitoring