Genetic structure in native and non-native populations of the direct-developing gastropod Crepidula convexa

In many marine invertebrate species, larval development plays an important role in population connectivity and gene flow: species with direct benthic development generally show more genetic structure than those with planktonic development. We used nuclear markers (microsatellites) to determine population genetic structure of the direct-developing snail Crepidula convexa (Gastropoda: Calyptraeidae) in seven populations with 15–85 individuals each within its native range of the northwest Atlantic and compared it to Crepidula fornicata, a congener with planktonic development. Our results are consistent with general expectations and previous work in these species with other markers: C. convexa had greater population structure and even at a regional scale shows significant isolation-by-distance, in contrast to C. fornicata. We also genotyped a single population of C. convexa introduced to the northeastern Pacific to investigate the prediction of reduced genetic diversity following introduction (founder effect). We did not find a reduction in genetic diversity, suggesting that this non-native population may be characterized by multiple introductions. This pattern is consistent with many other introduced populations of marine invertebrates, including C. fornicata.     

Attraction to prey and stimulus to attack in the predatory gastropod Urosalpinx cinerea

Urosalpinx cinerea (Say), accustomed to feeding on Balanus balanoides, were strongly attracted in a choice chamber by the effluents of B. balanoides and B. eburneus, were indifferent to the effluents of Crassostrea virginica, Crepidula fornicata and Mytilus edulis, and responded negatively to the effluent of their own species. Oyster drills from a population feeding on Crassostrea virginica were attracted to oyster effluent; when these snails were offered a choice between Crassostrea virginica and B. balanoides effluents, they responded in equal numbers to the two effluents. Concentrations of NH₄Cl-ammonia in the range 18.2 to 73.3 mol did not attract the snails, and their responses to animal effluents were not correlated with the ammonia and amino-acid concentrations of the effluents, which ranged from 11.8 to 21.0 mol. It is argued that these results deny ammonia the role of a nonspecific distance attractant. Confined separately with various potential prey species, Urosalpinx drilled Balanus balanoides, B. eburneus, Crassostrea virginica, Crepidula fornicata, C. plana, Mercenaria mercenaria, Modiolus demissus, Mya arenaria, Mytilus edulis, Spisula solidissima, and Yoldia limatula, but not Anomia simplex. The prey species that were the least attractive in running water were generally rendered attractive and subject to attack in standing water. Freshly shucked Crepidula fornicata shells were scarcely drilled unless continuously perfused by C. fornicata effluent, and then only in small numbers. Altering the texture of living C. fornicata shells by wrapping them in nylon netting, by polishing, or by roughening, did not make them immune to drilling. Oyster drills in contact with C. fornicata attacked only if they received the effluent of the living prey, proving that tactile stimuli alone are not adequate to induce drilling.     

Efficacité et sélectivité faunistique comparée de quatre appareils de prélèvements endo-, épi- et suprabenthiques sur deux types de fonds

Using data from 6 cruises from May to October 1972, we have compared the efficiency and selectivity of a double-scoop Holme bottom sampler, a Spatangue anchor dredge, a Hessler-Sanders epibenthic sled and a Macer-GIROQ suprabenthic sled, at comparable time intervals, on muddy sand at a depth of 18 to 26 m and on silty clay at 329 to 355 m in the Lower St. Lawrence Estuary, Quebec, Canada. Estimates of density and species proportions of most taxa except polychaetes allow an assessment of the stratification of autecological forms at the bottom-water interface. Estimates of species percentages are similar for the Holme sampler and the dredge, but only the former yields reliable density estimates. The dredge underdigs and overestimates density on harder ground, and overdigs and underestimates it on soft mud. Both types of estimates are comparable among suprabenthic samples not contaminated with mud, and the fauna therein (Crustacea account for 97% of individuals and 79% of species, excluding copepods) at both stations is markedly different from that of other sample types. Epibenthic and contaminated suprabenthic samples yield estimates somewhat transitional between those of endobenthic and non-contaminated suprabenthic samples. The Hessler-Sanders sled behaves somewhat like a dredge, depending on substrate firmness, and many mobile Crustacea can apparently evade it. No instrument adequately samples the 28 cm layer closest to the bottom.

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Contribution au programme du GIROQ (Groupe interuniversitaire de Recherches océanographiques du Québec)     

Spatio-temporal variations of biomass and abundance in bathyal non-crustacean megafauna in the Catalan Sea (North-western Mediterranean)

The spatio-temporal variations in diversity, biomass and abundance of bathyal invertebrates (excluding decapod crustaceans, which have been analysed elsewhere) from the North-western Mediterranean margin are described. The upper canyon (∼450 m), middle slope (∼650 m) and lower slope (∼1,200 m) habitats were investigated throughout the year. The first two sites are visited daily by a specialised commercial fisheries’ fleet, while the deeper site has not been impacted by fishing activities. A total of 140 species from 12 phyla were collected from the 3 study areas. Of these, the Mollusca, Echinodermata, Polychaeta and Cnidaria were the most speciose groups. The patterns of species diversity (H′) and evenness (E) were similar in time and space. The upper canyon and middle-slope sites were dominated by echinoderms and molluscs, while the lower-slope site was dominated by cnidarians and sponges. Multifactorial ANOVA showed significant spatio-temporal differences in the biomass and/or abundance only in echinoderms, molluscs, cnidarians and polychaetes. The faunal differences observed were explained by habitat type, but not by season. The role of submarine canyons and commercial fishing on shaping the diversity and biomass of bathyal Mediterranean invertebrates is discussed. Luis Dantart: Deceased March 2005     

Parasitism as a determinant of community structure on intertidal flats

The burrowing and movement ability of the New Zealand cockle Austrovenus stutchburyi is reduced when infected by echinostome trematodes. Previous experimental evidence from a single site suggests that this parasite-induced behavioural change of a key bivalve can affect the structure of the surrounding benthic community. By using multiple regression analyses on data collected from 17 intertidal flats, we here show that cockle parasitism is associated with macrozoobenthic community structure on a larger spatial scale. Regressions were performed for animal abundance, biomass, species diversity and species richness separately, entering cockle parasitism (infection intensity), presence/absence of ghost shrimps (Callianassa filholi), cockle density, primary producer abundance and organic content, particle size, sorting coefficient and gravel content of the substrate as predictors. Next to ghost shrimps, cockle parasitism was the best predictor of animal abundance by affecting (mainly positively) 8 of the 49 most widespread species significantly. Cockle parasitism was also associated with the biomass of anthozoans (positively), nemerteans (negatively) and bivalves (positively), whereas overall animal biomass was positively related to the sorting coefficient of the substrate. Species diversity was positively associated with cockle parasitism and gravel content of the substrate. Species richness was significantly associated with cockle parasitism (positively), ghost shrimps (negatively) and abundance of primary producers (positively) in combination. The impact of cockle parasitism on benthic community structure is believed governed directly or indirectly by (1) reduced sediment disturbance, (2) increased surface structural complexity and (3) availability of larval trematodes as an additional food source.     

Substrate supply, fine roots, and temperature control proteolytic enzyme activity in temperate forest soils

Temperature and substrate availability constrain the activity of the extracellular enzymes that decompose and release nutrients from soil organic matter (SOM). Proteolytic enzymes are the primary class of enzymes involved in the depolymerization of nitrogen (N) from proteinaceous components of SOM, and their activity affects the rate of N cycling in forest soils. The objectives of this study were to determine whether and how temperature and substrate availability affect the activity of proteolytic enzymes in temperate forest soils, and whether the activity of proteolytic enzymes and other enzymes involved in the acquisition of N (i.e., chitinolytic and ligninolytic enzymes) differs between trees species that form associations with either ectomycorrhizal or arbuscular mycorrhizal fungi. Temperature limitation of proteolytic enzyme activity was observed only early in the growing season when soil temperatures in the field were near 4 degrees C. Substrate limitation to proteolytic activity persisted well into the growing season. Ligninolytic enzyme activity was higher in soils dominated by ectomycorrhizal associated tree species. In contrast, the activity of proteolytic and chitinolytic enzymes did not differ, but there were differences between mycorrhizal association in the control of roots on enzyme activity. Roots of ectomycorrhizal species but not those of arbuscular mycorrhizal species exerted significant control over proteolytic, chitinolytic, and ligninolytic enzyme activity; the absence of ectomycorrhizal fine roots reduced the activity of all three enzymes. These results suggest that climate warming in the absence of increases in substrate availability may have a modest effect on soil-N cycling, and that global changes that alter belowground carbon allocation by trees are likely to have a larger effect on nitrogen cycling in stands dominated by ectomycorrhizal fungi.     

Research On Zooplankton in the Gulf of Rapallo

Zooplankton samples, collected in autumn 1996 from two stations in the Gulf of Rapallo, Ligurian Sea (Rapallo Harbour and Prelo Bay, which is a more open site with lower human impacts) were analysed. at both stations, the community was dominated by copepods (mainly juveniles and adults of different species of Acartia and Oithona) and meroplankton (mainly polychaete larvae). Total zooplankton abundance in the harbour waters was significantly higher than in the nearby bay. the occurrence of Acartia grani in Rapallo Harbour and Pteriacartia josephinae in Prelo Bay is noteworthy, as they are reported for the first time in the Ligurian Sea, and A. grani has not previously been recorded to the Italian coastline. A three-day benthic chamber experiment aimed to quantify nutrient fluxes between the sediment and water column was performed in the Rapallo Harbour: the profound effects of confinement on the composition and abundance of zooplankton within the incubation chamber are discussed.     

Null model analysis of species associations using abundance data

The influence of negative species interactions has dominated much of the literature on community assembly rules. Patterns of negative covariation among species are typically documented through null model analyses of binary presence/absence matrices in which rows designate species, columns designate sites, and the matrix entries indicate the presence (1) or absence (0) of a particular species in a particular site. However, the outcome of species interactions ultimately depends on population-level processes. Therefore, patterns of species segregation and aggregation might be more clearly expressed in abundance matrices, in which the matrix entries indicate the abundance or density of a species in a particular site. We conducted a series of benchmark tests to evaluate the performance of 14 candidate null model algorithms and six covariation metrics that can be used with abundance matrices. We first created a series of random test matrices by sampling a metacommunity from a lognormal species abundance distribution. We also created a series of structured matrices by altering the random matrices to incorporate patterns of pairwise species segregation and aggregation. We next screened each algorithm-index combination with the random and structured matrices to determine which tests had low Type I error rates and good power for detecting segregated and aggregated species distributions. In our benchmark tests, the best-performing null model does not constrain species richness, but assigns individuals to matrix cells proportional to the observed row and column marginal distributions until, for each row and column, total abundances are reached. Using this null model algorithm with a set of four covariance metrics, we tested for patterns of species segregation and aggregation in a collection of 149 empirical abundance matrices and 36 interaction matrices collated from published papers and posted data sets. More than 80% of the matrices were significantly segregated, which reinforces a previous meta-analysis of presence/absence matrices. However, using two of the metrics we detected a significant pattern of aggregation for plants and for the interaction matrices (which include plant-pollinator data sets). These results suggest that abundance matrices, analyzed with an appropriate null model, may be a powerful tool for quantifying patterns of species segregation and aggregation.     

Feeding and swimming of lysianassid amphipods in a shallow cold-water bay

The potential for dispersal by lysianassid amphipods and their localization to carrion in a shallow cold-water bay in the Middle Saint Lawrence Estuary were assessed by means of endobenthic sampling, SCUBA observations, measures of swimming speeds, and by exposure of bait (50–100 g of fish) in traps. Seventy-five to 99.9% of animals attracted to traps were lysianassid amphipods belonging to five species. Lysianassid species were spatially segregated in the Bay at low tide but all were more or less dispersed at high tide. Second cohortAnonyx sarsi Steele and Brunel,Boeckosimus edwardsi andOnisimus littoralis (Krøyer) were more dispersed than the small first cohort individuals. Second cohortA. sarsi were crawlers or low (0–0.5 m off the bottom) suprabenthic swimmers in the day, but upper (0.5–2 m) suprabenthic swimmers at night. In contrast, first cohortA. sarsi were crawlers or low suprabenthic swimmers day-and-night, whileOrchomenella pinguis (Boeck) followed this swimming pattern at night but were generally akinetic in the day. Mean swimming speeds ofA. sarsi (13.6 cm s^-1) andOn. littoralis (12.1 cm s^-1) were 2 to 3 times greater than those ofOr. pinguis (7.4 cm s^-1) andPsammonyx nobilis (Stimpson) (4.4 cm s^-1). Catchability coefficients (i.e. ratio number of individuals per trap:endobenthic abundance) were 74 (A. sarsi), 8 (On. littoralis), 7 (Or. pinguis), and 0.7 (P. nobolis) m² of bottom. Gut content analysis indicated thatA. sarsi fed mostly on large carrion, whileOn. littoralis were markedly opportunistic, andOr. pinguis andP. nobilis relied on detritus, algae, and small crustaceans.     

Meiofauna on the seagrass Thalassia testudinum: population characteristics of harpacticoid copepods and associations with algal epiphytes

The composition and abundance of bladedwelling meiofauna was determined over a 15 mo period (1983–1984) from a Thalassia testudinum Banks ex König meadow near Egmont Key, Florida, USA. Harpacticoid copepods, copepod nauplii, and nematodes were the most abundant meiofaunal taxa on T. testudinum blades. Temporal patterns in species composition and population life-history stages were determined for harpacticoid copepods, the numerically predominant taxon. Sixteen species or species complexes of harpacticoid copepods were identified. Harpacticus sp., the most abundant harpacticoid, comprised 47.8% of the total copepods collected, and was present throughout the study. Copepodites dominated the population structures of the blade-dwelling harpacticoid species on most collection dates. Ovigerous females and/or copepodites were always present, indicating continuous reproductive activity. Results suggest that epiphytic algae influence meiofaunal abundance on seagrass blades, as densities of most meiofaunal taxa at Egmont Key were positively associated with percent cover of epiphytic algae throughout the study. The majority of significant correlations between meiofaunal density and cover of epiphytic algae involved filamentous algae, although encrusting algae dominated the epiphytic community. It appears that resources provided by epiphytic algae to seagrass meiofauna (additional food, habitat, and/or shelter from predation) may be associated with algal morphology.     

Predicting structural complexity of reefs and fish abundance using acoustic remote sensing (RoxAnn)

This study determined whether the acoustic roughness of Caribbean reef habitats is an accurate proxy for their topographic complexity and a significant predictor of their fish abundance. Fish abundance was measured in 25 sites along the forereef of Glovers Atoll (Belize). At each site, in situ rugosity (ISR) was estimated using the “chain and tape” method, and acoustic roughness (E1) was acquired using RoxAnn. The relationships between E1 and ISR, and between both E1 and ISR and the abundance of 17 common species and the presence of 10 uncommon species were tested. E1 was a significant predictor of the topographic complexity (r ² = 0.66), the abundance of 10 common species of surgeonfishes, pomacentrids, scarids, grunts and serranids and the presence of 4 uncommon species of pomacentrids and snappers. Small differences in E1 (i.e. ∆0.05–0.07) reflected in subtle but significant differences in fish abundance (~1 individual 200 m⁻² and 116 g 200 m⁻²) among sites. Although we required the use of IKONOS data to obtain a large number of echoes per site, future studies will be able to utilise RoxAnn data alone to detect spatial patterns in substrate complexity and fish abundance, provided that a minimum of 50 RoxAnn echoes are collected per site.     

Biodiversity in the ecosystem of the Portuguese continental shelf: distributional ecology and the role of benthic amphipods

The biodiversity and distributional ecology of amphipod crustaceans were analysed from benthic surveys in 1985 and 1986 along the coast of Portugal, from the Tagus canyon to the coast of Minho, in order to determine their role in the ecosystem of the Portuguese continental self. In samples obtained from different types of substrate between 18 and 545 m, we identified 113 species belonging to 51 genera of 24 families. Seventeen of these species were new records for the Portuguese coast. The relative frequencies and number of individuals of all species were analysed. The genus Ampelisca clearly dominated the group of the most frequent and abundant species, which also exhibited a large range of vertical distribution. Most of the 113 species were found only down to 150 m depth, corresponding roughly to the lower limit of the continental shelf. Fifteen species exhibited clear bathyal traits, being consistently found deeper than 100 m, especially in the Tagus canyon and the upper zone of the continental slope. The most frequent and abundant species were found predominatly or in large numbers in medium to fine sand bottoms. This type of substrate also contained the highest number of species. The granulometric structure of the habitat could constitute the most important factor controlling both biodiversity and development of large amphipod populations, since oxygen level, water exchange, number of available shelters, and probably the quantity and quality of nutritional resources all vary as a function of substrate texture. Because of their dominance in both frequency and abundance, several Ampelisca species may constitute an important food source for many secondary consumers of the shelf sediments, especially for demersal fishes.     

福建北部海域浙闽沿岸流消亡期浮游植物的种类组成与分布特征

根据2009年4月在福建北部海域(24°47’17.0"~26°48’02.9"N,119°29’36.0"~120°57’13.8"E)所获浮游植物网采样品和同步观测的理化参数,并结合2007年"908专项"春季航次相应范围的调查资料,分析该海域浮游植物种类组成、分布特点、年际变化及其与环境因子的关系.本航次共记录浮游植物3个门类85种,其中硅藻75种、甲藻9种、蓝藻1种.物种组成以广温种为主(占47.06%),其次为暖水种(占36.47%),温带种仅占7.06%.调查区浮游植物丰度平均为137.89×104cells m-3,其平面分布呈现从近岸往外海、从北往南递增的态势.聚类分析显示本海区浮游植物可划分为2个群落,群落Ⅰ主要由近岸低盐种组成,仅分布于受浙闽沿岸流影响较直接的闽江口以北的近岸测站;群落Ⅱ主要为外海高盐种和广温广盐种,广泛分布于受台湾暖流影响较大的闽江口以南及三沙湾外侧水域.主成分分析(PCA)表明,对本海区浮游植物的分布起主导作用的是温度和盐度,而与营养盐的关系不密切,反映调查期间浙闽沿岸流已基本退出本海区,浮游植物的分布主要受制于台湾暖流.浮游植物丰度的平面分布格局与以往的调查结果基本一致,但其群落结构存在年际变化,"908专项"春季航次的优势种为近岸低盐种和广温广盐种,优势种突出,多样性指数低;而本次调查外海性广温种成为优势种之一,多样性指数(H’)和均匀度(J’)均较高,这可能与考察期间受东北季风强度所左右的浙闽沿岸流强弱有关.     

Structure,composition and seasonal dynamics of the larval and juvenile fish community in the mangrove estuary of Tanshui River,Taiwan

The temporal and spatial patterns of species composition and abundance of fish larvae and juveniles in the Tanshui River mangrove estuary (Taiwan) were studied monthly using a drift bag-net in daylight. A total of 44591 individuals representing 55 families and 105 species were collected over 12 mo (August 1989 to July 1990). The community was dominated numerically by a few species. Sardinella melanura was most numerous, making up 70.15% of the total catch, followed by Stolephorus buccaneeri (19.59%), Thryssa kammalensis (2.96%), and Gerres abbreviatus (2.61%). These four species constituted ca. 95% of the total catch, the remaining 5% consisted of another 101 species. This estuary functions as a nursery and feeding area in the early life history of these fish. There was a separation in peak-immigration and seasonal utilization of the estuary by the dominant species. The abundance of fish larvae and juveniles decreased in an upstream direction.     

Feeding habits of pasiphaeid shrimps close to the bottom on the Western Mediterranean slope

The composition of the diet and daily cicle of predatory activity of pasiphaeid shrimps in the Northwestern Mediterranean were established; special attention was focussed on nocturnal feeding habits close to the bottom. Daily activity in both species was studied in two continuous 24-h sampling periods. Samples were obtained using bottom trawls between 1988 and 1990. Both species fed on benthic prey items at night. The nocturnal diet of Pasiphaea multidentata consisted of gammarid amphipods, isopods (Cirolana borealis) and macruran decapods (Calocaris macandreae). Nocturnal feeding activity was carried out only by large specimens (cephalothorax length >28 mm), which stayed close to the bottom during the nighttime. In contrast, the specimens collected during the daytime exhibited highly digested remains of pelagic prey (hyperiids, fishes, euphausiids, chaetognaths) ingested as a result of predatory higher activity in the water column the night before. The feeding strategy of P. sivado was parallel to that of P. multidentata. At night large specimens were located near the bottom and fed on suprabenthic gammarid amphipods. This nocturnal feeding activity by both these mesopelagic pasiphaeid species furnishes evidence of energy transfer from the benthos to the planktonic system in bathyal communities. Changes were observed in the diet of P. multidentata with depth. Crustaceans made up a larger share of the diet of P. multidentata on the lower slope than on the upper middle slope, probably because of changes undergone by bathyal communities with increasing depth. The feeding rate was higher in the submarine canyons, where the diet is also more specialised. Dietary overlap between the two pasiphaeids was very low, due to the different size range of prey exploited.     

Local changes in the composition and community structure of suprabenthic peracarid crustaceans on the bathyal Mediterranean: influence of environmental factors

Deep-water assemblages of suprabenthic peracarids were analyzed in the SW Balearic Islands (Algerian Basin, southwestern Mediterranean) between 249 and 1,622 m depth; the patterns of species composition, possible zonation, and trophic structure found in this area were compared with those exhibited by peracarids in the mainland side of the Catalan Sea slope (northwestern Mediterranean). One hundred and four peracarid species (plus one leptostracan) were identified on the Balearic Islands slope, amphipods being the most diversified taxon (45 species). On the Balearic slope, two distinct depth assemblages were distinguished: one at the upper slope (US), between 249 and 402 m depth and the second at the deep slope, between 543 and 1,620 m depth. A remarkable species substitution occurred at depths between 402 and 638 m. In the Catalan Sea, in addition to the US assemblage occupying depths between 208 and 408 m, a second boundary of faunal change was found around 1,250 m. Suprabenthos biomass increased from 242 to approximately 500 m. Suprabenthos attained the highest biomass values (100 g wet weight/10,000 m²) at intermediate depths between 504 and 1,211 m, as also occurred with the associated zooplankton collected with suprabenthos (peak biomass between 502 m and 898 m). Suprabenthos biomass did not show any significant correlation with any environmental water-column variable. In contrast, zooplankton (especially small fish and decapod crustaceans) showed a significant positive correlation with fluorometry and turbidity at different levels of the water column. The feeding guilds of species showed important differences between the two areas only on the US, with a higher abundance of deposit feeders in the Catalan Sea (20.4%) than in the Balearic Islands (4.2%). The low contribution of deposit feeders in the SW Balearic Islands may ultimately be a consequence of the lack of river discharges in this area.Communicated by S.A. Poulet, Roscoff     

Composition and temporal fluctuations of inshore juvenile fish populations in the Kornati Archipelago, eastern middle Adriatic

Temporal fluctuations of species composition and abundance of fish juveniles in the National Park Kornati were studied over 12 months from January to December 1992. A total of 40 168 individuals, representing 24 families and 69 species, were collected using a 50 m long beach seine. The community was dominated numerically by a few species: Atherina hepsetus (45.90%), Sarpa salpa (21.21%), Diplodus vulgaris (10.49%), and Symphodus ocellatus (6.98%), constituting over 84.58% of the total catch. Similarity between patterns in the abundance of the 17 most common species were examined using correlation matrix-based principal component analysis. Results were compared to the abiotic factors leading to the conclusion that only a low amount of variation in the abundance field can be explained by temperature, salinity and dissolved oxygen. Received: 23 March 1997 / Accepted: 11 April 1997     

Spatial and temporal changes in the demersal fish community of the Ria de Arosa (NW Spain)

The demersal fish community was sampled seasonally in three habitats (beach, raft and middle) of the inner, middle, and outer Ria de Arosa (NW Spain). A total of 73 species of demersal fish, dominated by the family Gobiidae, were found. There were no important seasonal changes in abundance, with similarity values always higher than 60% between samples from two different sampling periods. Raft stations in the ria show the highest values of abundance all year, containing almost 1 individual m^-2 in winter. The highest diversity indices were those from beach areas (2.11 to 2.27) and the lowest ones those from middle areas (1.13 to 1.86). Similarity indices and factorial analysis revealed three major groupings of species and samples, related to water depth and nature of the bottom.     

Corallum morphology and composition of crustacean cryptofauna of the hermatypic coralMadracis mirabilis

The motile crustacean cryptofauna of the hermatypic coralMadracis mirabilis (Duchassaing and Michelotti) was examined from three sites on reefs along the west coast of Barbados in 1985. In addition to site differences in degree of eutrophication, two distinct with-in-corallum habitats were recognized, based on differences in the growth form of the coral host. One form grows in isolated, hemispherical heads, with short, robust, widely separated branches covered by 50 to 80% live tissue. The second form occurs within large continuous beds of long, thin, tightly spaced branches tipped by 20 to 30% live tissue. Coral habitats consisting of small isolated heads support a crustacean fauna of high decapod and amphipod diversity, with numerous rare and site endemic species and an abundance of relatively large decapods and amphipods. The continuous beds favour a community of lower decapod and amphipod diversity, fewer rare and site endemic species and with an abundance of smaller sized isopods and copepods. It is suggested that spatial separation of branches and colonies as well as food availability associated with corallum morphology are factors influencing the variation in species abundance and faunal composition of the two habitats.     

Seasonal variation of fish abundance and biomass in gillnet catches of an East Mediterranean lake: Lake Doirani

The seasonal variation of fish species composition and abundance in gillnet catches (14-90 mm knot-to-knot) from the Greek part of the transboundary Lake Doirani was studied during the period 2006-2007. A total of 8,419 specimens weighing 182.3 kg and belonging to 9 species were caught. Catch composition differed with season. Thus, Rhodeus meridionalis dominated in terms of NPUE the spring, Perca fluviatilis the summer and Albumus macedonicus the autumn and winter catches. Cyprinids were generally the most abundant, with the cyprinids:percids biomass ratio ranging from 1.7 in summer to 14.8 in winter, supporting the eutrophic character of the lake. Richness and Shannon-Wiener diversity and evenness indices differed seasonally (ANOVA; p < 0.05). The abundance-biomass comparative (ABC) curves showed that fish communities were dominated by one or a few opportunistic species (e.g. Rhodeus meridionalis, Albumus macedonicus), which while dominated in number did not dominate in biomass, being small bodied.