Trophic relationships of polychaetes associated with different algal growth forms

The trophic relations of the polychaete species associated with four different algal growth forms (filamentous, fan-shaped, bush-like and encrusting) were studied in the North Aegean Sea. Samples for the spatial analysis were collected in summer with a quadrate sampler (400 cm²) at a depth range of 15–40 m. Filamentous and encrusting forms were also seasonally sampled in order to detect the temporal changes. A total of 5,494 individuals belonging to 79 species were classified to 12 feeding guilds, considering the type of food, the feeding apparatus and the motility patterns involved. Carnivores dominated, followed by herbivores and filter-feeders, among all the algal forms studied, excepting the fan-shaped form where filter-feeders prevailed mainly due to a massive recruitment of spirorbids. With respect to the abundance of the various feeding guilds, filamentous and fan-shaped forms discriminated, whereas bush-like and encrusting forms showed high similarity. The occurrence of polychaete feeding guilds among both filamentous and encrusting forms showed seasonal changes, with summer and spring samples, respectively, discriminating. The results of the trophic group analysis conformed to previous information provided by a taxon composition analysis of the dominated by the same algae communities. However, a functional study can give additional information and is thus a useful tool for the study of hard bottom communities.     

Polychaetes associated with the sciaphilic alga community in the northern Aegean Sea: spatial and temporal variability

Polychaete biodiversity has received little attention despite its importance in biomonitoring. This study describes polychaete diversity, and its spatial and temporal variability in infralittoral, hard substrate assemblages. Seven stations were chosen in the central area of the northern Aegean Sea. At each station, one to three depth levels were set (15, 30 and 40 m). Five replicates were collected by scuba diving with a quadrat sampler (400 cm²) from each station and depth level during summer for the spatial analysis, and seasonally for the study of temporal changes. Common biocoenotic methods were employed (estimation of numerical abundance, mean dominance, frequency, Margalefs richness, Shannon-Weaver index and Pielous evenness). A total of 5,494 individuals, belonging to 79 species, were counted and classified. Diversity indices were always high. Clustering and multidimensional scaling techniques indicated a high heterogeneity of the stations, although these were all characterized by the sciaphilic alga community. A clear seasonal pattern was not detectable. Summer and autumn samples discriminate, while winter and spring form an even group. The abundance/biomass comparison indicated a dominance of k-strategy patterns, characteristic of stable communities.Communicated by H.-D. Franke     

Bionomy of Macrobenthic Molluscs in Evros Delta (North Aegean Sea)

The composition and distribution of the macrobenthic molluscs in Evros Delta (North Aegean Sea) were investigated by quantitative sampling. The molluscan distribution shows a zonation mainly related to the degree of “confinement”. Based on similarity in distribution among stations, 2 groups of species were distinguished. One group includes marine species (Tellina tenuis, Bittium reticulatum) found only in coastal stations and the second group is typical of estuarine species (Hydrobia acuta, Abra ovata and Cerastoderma glaucum) distributed in almost all stations. Spatial fluctuations of the 3 estuarine species reflect their preferences in the various parameters (“confinement”, salinity, grain size and organic matter of sediment). The most isolated stations support the highest values of total mollusc abundance and biomass.     

Macrozoobenthic Assemblages of the Evros Delta (North Aegean Sea)

The composition of the macrozoobenthic assemblages of the Evros Delta (North Aegean Sea) has been investigated by means of 4 replicate quantitative samples, collected at 35 sites. The information obtained from the numerical analysis of the faunal samples and the analysis of other data (values of the main physico-chemical parameters) revealed the presence of a single community. The faunal composition of this community varies locally according mainly to the salinity and secondly to the particle size of the substrate. The community is described on the basis of its biological parameters and compared with corresponding assemblages from other areas.     

REPRODUCTIVE SUCCESS OF FUCUS VESICULOSUS (PHAEOPHYCEAE) IN THE BALTIC SEA

Marine organisms colonizing brackish habitats such as the Baltic Sea must cope with the negative effects of low salinities on reproductive success because these may reduce gamete viability and/or increase polyspermy. Reproductive characteristics of the marine seaweed Fucus vesiculosus L. were studied in several brackish habitats, particularly in the northern Baltic Sea, to understand its ability to reproduce where few other marine species survive. Polyspermy and fertilization success were variable at the boundary of the continuous distribution of F. vesiculosus in the Baltic Sea, and polyspermy was high (10%–30%) when fertilization was successful. A strong female bias (80%–86%, ca. 5.5:1) was found at the northernmost limit of Baltic F. vesiculosus. Electrophysiological studies showed that many eggs have a high input resistance (519 ± 150 MΩ[mean ± SE, n = 14] at Drivan, 1995), which may be helpful in preventing polyspermy in this brackish habitat. The polyspermy block remains sodium-dependent in the northern Baltic. Sperm bound quickly to northern Baltic eggs in natural water, but fertilization was delayed compared to marine F. vesiculosus. A subset of northern Baltic eggs studied during an optimal reproductive period (7–11 July 1995) had a membrane potential (E_m) of ca. −100 mV and an effective fertilization potential (FP) of ca. 2 min with a plateau of −25 mV, but repolarized too rapidly for the FP to be protective. Pronuclear migration and cell wall secretion occurred more slowly in Baltic than in marine zygotes. The reproductive success of theseboundary populations may be dependent upon windows of opportunity when there are favorable combinations of the levels of salinity, water motion, population density, and sex ratio. These factors and the short duration of the reproductive season in the northern Baltic Sea may result in reproductive failure in some years.     

Seasonal variations of microphytoplankton assemblages and environmental variables in the coastal zone of Bozcaada Island in the Aegean Sea (NE Mediterranean Sea)

Seasonal changes in the microphytoplankton assemblages were examined in the coastal zone of Bozcaada Island with regard to some major physical and chemical variables. Samples were collected from May 2000 to December 2001 at four stations. A total of 108 dinoflagellates, 102 diatoms, 1 chrysophycean, 3 dictyochophycean, and 1 prasinophycean species were identified and quantified during the study period. Diatoms and dinoflagellates were the most important in terms of species number and abundance. The maximum values of total microphytoplankton were observed at 0.5 m depth (46.2 × 10³ cells l⁻¹ at st. 3) in May as this was the month when the diatom Pseudo-nitzschia pungens bloomed. Chlorophyll (chl) a concentration ranged between 0.08 (August) and 0.78 μg l⁻¹ (February). May was another important month in which chlorophyll a increased (0.41–0.47 μg l⁻¹). Species diversity values (H′_log2) ranged from 1.66 bits (June, 20 m) to 4.11 bits (November, 0.5 m). The increase was attributed to a more balanced distribution of abundance among species. The amounts of nitrate + nitrite (0.6−3.7 μg-at N l⁻¹), phosphate (0.2−0.6 μg-at P l⁻¹) and silicate (0.7−2.5 μg-at Si l⁻¹) were recorded on each sampling occasion. Nutrient concentrations and chl a values of the research area were found to be poorer than those of the many other coastal areas in the northeastern Mediterranean. The mean atomic ratio of nitrogen to phosphorus varied from 1.3 (June) to 12.9 (February). This ratio was lower than the Redfield ratio of 16 for ocean phytoplankton, and phytoplankton was potentially limited by nitrogen for most of the months. The result of this study confirms and emphasizes the oligotrophic nature of the eastern Mediterranean.     

Pelagic larvae of bivalve mollusks and polychaetes in winter plankton of the Kara Sea

Quantitative zooplankton samples were obtained by vertical tows with a Juday plankton net, in the southern Kara Sea, from November 28 to December 11, 2005 (by an expedition of the Murmansk Marine Biological Institute KSC RAS aboard the nuclear ice-breaker “Soviet Union”). The most abundant meroplankton forms were juveniles of Bivalvia and larvae of Polychaeta (the maximum abundances were 106.2 ind/m³ and 7.5 ind/m³, respectively). The results are discussed in relation to changes in the thermal regime of the Arctic Ocean observed during the recent decades.     

Demosponge distribution in the eastern Mediterranean: a NW–SE gradient

The purpose of this paper was to investigate patterns of demosponge distribution along gradients of environmental conditions in the biogeographical subzones of the eastern Mediterranean (Aegean and Levantine Sea). The Aegean Sea was divided into six major areas on the basis of its geomorphology and bathymetry. Two areas of the Levantine Sea were additionally considered. All available data on demosponge species numbers and abundance in each area, as well as their vertical and general geographical distribution were taken from the literature. Multivariate analysis revealed a NW–SE faunal gradient, showing an apparent dissimilarity among the North Aegean, the South Aegean and the Levantine Sea, which agrees with the differences in the geographical, physicochemical and biological characteristics of the three areas. The majority of demosponge species has been recorded in the North Aegean, while the South Aegean is closer, in terms of demosponge diversity, to the oligotrophic Levantine Sea. The number of studies in the Aegean and Levantine subareas was positively correlated with the number of species recorded within each Aegean subarea. Demosponge species with an Altanto-Mediterranean distribution prevailed in the Aegean and the Levantine. The reduced contribution of the endemic component, as compared to the western Mediterranean, is consistent with the general NW–SE decrease in the number of endemic species in the Mediterranean. Demosponge distribution at the order level showed also a NW–SE gradient, similar to that observed in the entire Atlantic–Mediterranean region, suggesting a warm water affinity. Sublittoral, circalittoral and bathyal zones were clearly distinguishable in the Aegean Sea on the basis of their sponge fauna. The total number of species was an exponential negative function of depth.     

Intraspecific Variations in Size- and Age-at-maturity for Red Bandfish, Cepola macrophthalma

Intraspecific variations in size- and age-at-maturity were studied in red bandfish, Cepola macrophthalma, in two adjacent gulfs of the western Aegean Sea, in the southern of which the population of red bandfish is stunted. Samples were collected with a commercial trawler over a grid of 34 stations at depths ranging from 22 to 222m. The hypothesis tested was that length and age at 50% maturity, Lm50 and tm50 respectively, for males and females do not differ in the two regions. The results showed that the Lm50 of both males and females in the northern area was by 3.5cm larger than that in the southern area and the 95% confidence intervals of Lm50 in the two areas did not overlap. Although the tm50 of males was larger in the northern area, the 95% confidence intervals of tm50 overlapped in the two areas whereas for females, the tm50 was larger by 0.4 years in the northern area and the 95% confidence intervals of tm50 in the two areas did not overlap. Stunting of the red bandfish growth in the southern area is the result of the combination of an extremely low food availability with higher temperatures prevailing in that area. Implications of these fine spatial scale intraspecific differences for the fisheries management of the highly oligotrophic eastern Mediterranean Sea are also discussed.     

Influence of pollution on the harpacticoid copepods of two North Sea estuaries

Seasonal monitoring of the meiobenthos in the Dutch estuaries revealed an anomaly in density and diversity of harpacticoid copepods in the Westerschelde.Another Dutch estuary, the Eems Dollard, has comparable hydrodynamical, physical and sedimentological, characteristics and a similar fauna, but even in the severely organically polluted oligohaline mudflats of this estuary, annual average density and diversity of endo-epibenthic harpacticoid communities are higher than at similar less enriched meso- to polyhaline biotopes of the Westerschelde.Besides the concentrations of inorganic pollutants, such as phosphates and nitrates, the concentrations of pesticides, cyanide, detergents, phenoles, oils, polychlorobenzenes, polycyclic aromatic hydrocarbons and heavy metals were compared in both estuaries and compared to suggested permissive levels when available. From this it appears that these pollutants are present in the Westerschelde either in too low concentrations to be considered dangerous or at concentrations comparable to those occurring in the Eems Dollard, except for heavy metals.The load of a.o. Zn, Cu and Pb is distinctly and persistently higher in sediments and suspensions of the Westerschelde than in the Eems Dollard and copper is continuously present in a concentration at which, according to bioassays, egg production and larval development of planktonic copepods are severely affected. The remarkable scarcity of harpacticoid life on nutrient rich mudflats of the Westerschelde is thus probably due to heavy metal pollution.Since no other hardbodied meio- and macrobenthic taxa nor the plankton of this estuary show such a marked impoverishment, benthic harpacticoids prove to be suitable as indicators for the first stages of ecosystem-breakdown in estuarine and coastal zones polluted by trace-metals.     

Peracarida populations of hard substrate assemblages in ports of the NW Aegean Sea (eastern Mediterranean)

This study deals with the structure of Peracarida populations in four ports in the NW Aegean Sea, Greece, and with the degree this structure is influenced by the particular biotic and abiotic conditions that prevail in the ports. Quantitative samples were taken during summer and winter in two successive years from artificial hard substrates and were analysed using common biocoenotic methods. The examination of approximately 81,250 specimens revealed the presence of 24 Peracarida species, the most dominant of which were Corophium acutum, Leptochelia savignyi and Elasmopus rapax. All species are very common and have been reported from many sites and assemblages in the N Aegean Sea. The ratios of certain Peracarida genera are discussed as possible indicators of environmental health that may be used in long-term biomonitoring programmes on the impact of pollution in harbours.Communicated by H.-D. Franke