Composition of a molluscan assemblage associated with macrophytes in Menzel Jemil (Bizerte lagoon,SW Mediterranean Sea)

The molluscan species composition and diversity associated with macrophytes was studied throughout 1 year at Menzel Jemil station (Bizerte lagoon, north‐west of Tunisia). A total of 7,539 individuals belonging to 13 species were collected. The molluscan assemblage was mainly composed of gastropods (98.12%, nine species), followed by bivalves (1.88%, four species). Hydrobia acuta ranked first with 49.97% of total abundance, followed by Bittium reticulatum (17.97%), Tritia mutabilis (11.38%), Haminoea navicula (8.98%), Phorcus articulatus (5.17%) and Cerithium vulgatum (3.94%). The large number of juvenile molluscs collected confirms the importance of macroalgae and seagrass for mollusc recruitment. Significant temporal variations of species richness, density and diversity indices of the mollusc assemblage have been observed during the year. Multivariate analyses applied to our data revealed significant relationships between the macrophyte composition and associated molluscan assemblage. The BIOENV analysis indicated that water temperature, phosphates concentration and macrophyte biomass were environmental variables most closely associated with the temporal variation of molluscan assemblage.     

Topographic effects of coastal seas on the composition of the culturable bacterial communities in marine sediments

Five published indirect methods to estimate benthic secondary production of intertidal mudflats and a new proposed formulation based on quarter-power allometric scaling and the “Universal Temperature Dependence” of biological processes (UTD) were compared. For this purpose, a dataset consisting of an annual series of samples, taken from the Lagoon of Venice from March 1996 to March 1997, at sites characterised by different seagrass coverage was used. All methods resulted in that biomass and secondary production decreased progressively when moving from the seagrass meadow toward areas of unvegetated substrate, suggesting an influence of the available marine phanerogams on the neighbouring sites. The equation proposed in this paper gives results comparable with those obtained using empirical regression models from literature. The main conclusion from this study is that general equations proposed by the “metabolic theory of ecology” can be applied for indirect estimations of secondary production of benthic communities.     

Twentyfive years of changes in the distribution and biomass of eelgrass,Zostera marina,in Grevelingen lagoon,The Netherlands

The wax and wane of the eelgrass (Zostera marina L.) population in Grevelingen lagoon (East Atlantic; The Netherlands) has been documented for over 25 years, together with quantitative and semi-quantitative data on environmental variables. The population expanded after the closure of the Grevelingen estuary in 1971, but declined from 4600 ha surface area in 1978 to less than 100 ha in 1993. There is little causal evidence which factors are responsible for the observed dynamics of the population. The incomplete picture emerging from the data is that of an extremely impoverished eelgrass population, living under constant oligo-mesotrophic marine conditions. Both the sexual and the vegetative modes of reproduction are severely stressed by environmental variables, most likely a combination of low temperatures, high salinity, low dissolved silicate and low ammonium concentrations. Survival of the population asks for the restoration of moderate estuarine conditions.Contribution No. 2180 of the Netherlands Institute of Ecology, Nieuwersluis, The Netherlands.     

Distribution of introduced Japanese macroalgae Undaria pinnatifida,Sargassum muticum (Phaeophyta) and Antithamnion Pectinatum (Rhodophyta) in the Lagoon of Venice

The present distribution of invasive seaweeds Undaria pinnatifida (Phaeophyta, Laminariales) and Sargassum muticum (Phaeophyta, Fucales) in the Lagoon of Venice is updated in this work. The distribution of Antithamnion pectinatum (Rhodophyta, Ceramiales) is presented for the first time. All these species have quickly colonized the hard substrata competing with indigenous species. Competition acts differently in the two species, U. pinnatifida competing for the substratum and S. muticum for light. On tidal flats composed of silt and sand, the growth of two brown seaweeds is restricted owing to the lack of a solid substrata. While Undaria pinnatifida and Sargassum muticum have colonized only some areas of the lagoon in a short vertical range (from 0 to -3 m), Antithamnion pectinatum is present on the three portmouths, along the inner shores of the city of Venice, and in the lagoon islands with extensive vertical distribution (from +0.2 to -8 m). This revised version was published online in September 2006 with corrections to the Cover Date.     

Age and growth of an Iberian cyprinodont, Aphanius iberus (Cuv. & Val.), in its most northerly population

Age and growth of an Iberian cyprinodont, Aphanius iberus (Cuv. & Val.), in its most northerly population, La Rubina lagoon (Alt Empordà wetlands, NE Spain), was studied. The age groups for this Mediterranean population (O +, 1 + and 2 +) agree with those reported for the Atlantic population (R. Guadalquivir marshes), in the southern limit of the species distribution in the Iberian peninsula. Differences in age structure between these populations and the one previously studied in La Tancada lagoon (R. Ebro delta marshes) can be attributed to age estimation bias. Male A. iberus data appear to fit similarly to a Gompertz growth function and to a von Bertalanffy growth function, but L _x, was clearly underestimated. A Gompertz growth function was not a good fit for females, perhaps because female growth is clearly faster and less attenuated than male growth. The life history and growth pattern ofthis species is similar to that in other cyprinodontiform fishes, typified by a short longevity. The growth model of this species does not seem to fit types I and II of Sebens's classification, which are characteristic of fish.     

Interpretation of the seasonal variations of nutrients in a mediterranean lagoon: étang de Thau

A network of 63 stations was used on four occasions (June 1986, October 1986, February 1987, and May 1987) to study the spatio-temporal distribution of inorganic nutrients in Thau Lagoon (l'étang de Thau), which covers 7500 hectares on the French Mediterranean coast. Three environmental factors, revealed by multiple regression models, govern the distributions observed. Allochthonous inputs from the watershed enrich the environment with nitrogen and phosphorus compounds in the winter and autumn. Internal sources are essentially localized in the shellfish breeding zone of the lagoon. In the summer, shellfish excretions and the rapid remineralization of organic deposits produce ammonium ions. Uptake by phytoplankton has a much larger impact on the seasonal variation of inorganic nitrogen than on that of phosphorus; the latter is present in excess in the lagoon waters. Thus, nitrogen appears to be the primary limiting nutrient for the development of the chorophyllous biomass.     

Patterning limnological characteristics of the Chilika lagoon (India) using a self-organizing map

In this study, a self-organizing map (SOM) was utilized to classify habitats in the Chilika lagoon located in India, the largest lagoon ecosystem in Asia (maximum length, 64.3 km; mean width, 20.1 km). The lagoon was marginally eutrophic (nitrate, 0.25 ± 0.22 mg L⁻¹; orthophosphate, 0.26 ± 0.22 mg L⁻¹; n = 1,980, respectively) for six years (1999–2004), and it used to be warm, shallow, turbid and predominantly brackish. The SOM model successfully identified the changing patterns of limnology in the lagoon using the monthly limnological dataset from 30 study sites (July 1999–December 2004). Comparative re-sectoring evaluation of current monitoring sites was accomplished based on the outcome of the modeling. The new site clustering that emerged from the model was similar to conventional ones, and several sites were reorganized. Water physicochemistry was affected by freshwater inflow during monsoon and the new lagoon mouth constructed in September 2000, which resulted in variations in site characteristics in terms of limnology. The results of this study may provide information on the limnological patterns in Chilika lagoon, and they leave room for further study into functional changes in the lagoon ecology with respect to changes in climatic factor, freshwater flow and lagoon morphology.     

Can Coral Cover be Restored in the Absence of Natural Recruitment and Reef Recovery?

With many coral reef areas being degraded whether by anthropogenic or natural causes, a search is on for resilient species of corals that can restore coral cover where needed, if coral reefs are to continue to provide adequate ecosystem services. A series of experiments were undertaken in two sites with different environmental attributes and substrates in a lagoonal area in the northwestern Philippines to test the potentials of a local species, Porites cylindrica, for reef rehabilitation. With the use of asexual fragmentation of donor colonies, different treatments were tested, particularly to determine if the species would survive on different substrates, that is, solid, massive versus digitate/anastomosing, dead colonies. The results after nearly 2 years of the experiment were extraordinarily successful, with survival of transplants ranging from a high of 98% to a low of 80% of colonies, resulting in extensive coral cover on both original and new or different substrate from the original. A subsequent observation after another 16 months showed the coral cover to have been complete or nearly complete in the experimental plots, with the transplanted colonies fusing, and with evident reef fish communities where there were none before. Had there been no intervention, it is highly likely that the reefs would have remained in a degraded state .     

In situ metabolic budget for the calanoid copepod Acartia clausi in a tropical brackish water lagoon (Ebrié Lagoon,Ivory Coast)

Simultaneous measurements of respiration, excretion and production rates were carried out several times over a year period at five representative stations of the Ebrié Lagoon. Assuming a constant assimilation efficiency rate of 69.4%, we derived metabolic budgets for carbon, nitrogen and phosphorus. Daily specific ingestion rates calculated were rather generally high, and ranged between 54 and 159% of body carbon, between 26 and 102% of body nitrogen and between 108 and 307% of body phosphorus. Regional and seasonal variations depended mainly upon variations in trophic conditions. Curvilinear relationships between ingestion production, or net production efficiency K2, and food concentration (as chlorophyll-a + phaeopigments) showed that food could have been a limiting factor. Furthermore, K2 were low when compared with data from the literature (mean of 21% in carbon, 39% in nitrogen and 11% in phosphorus).Complementary laboratory experiments carried out on adults fed with enriched natural particles or algal cultures (Tetraselmis sp. or Dunaliella sp.) showed similar production (egg-production) vs food concentration curvilinear relationships as in the field. However, considerably higher maximal ingestion and production rates were obtained for animals fed algal cultures suggesting that optima for food acquisition and transformation were not reached in field conditions.Consequently, A. clausi, which represents more than 50% of the zooplankton biomass, appears to be rather inefficient in transforming the abundant particulate organic matter produced in the lagoon. This results from its high level of metabolic expenditure through respiration or excretion (about 50% of ingestion in terms of carbon) and from the small size and poor trophic value of food particles (high percentage of detritus).     

The use of Cerastoderma glaucum as a sentinel and bioindicator species: Take-home message

Bivalves are frequently used to assess environmental contamination, and are often considered good sentinel and/or bioindicator species. For that reason the bioaccumulation and toxicity induced by metals and As in the cockle Cerastoderma glaucum, collected from areas with different contamination levels along the Óbidos lagoon (Portugal), were used to evaluate the use of this species as sentinel and/or bioindicator. The results showed that areas in the middle of the lagoon presented lower metals and As concentrations, lower total organic matter content and lower percentage of fine particles than areas in the Bom Sucesso arm. In all areas Cr, Pb and Cu were the most abundant elements, while Ni, As, Cd and Hg were less abundant. Results also showed a moderate correlation between total elements concentrations found in C. glaucum and in sediment, and thus caution should be taken when considering this species as a good sentinel species. The present study also revealed that, in general, C. glaucum from areas in the middle of the lagoon accumulated higher concentrations of metals and As (Biota-Sediment Accumulation Factor >1) than cockles from the most polluted areas located in the Bom Sucesso arm. However, in all areas, the majority of metals (Cu, Cr, Pb) were found in cockles insoluble fraction which may explain low cellular damage and reduced oxidative stress responses observed. Therefore, our results may further alert for caution when identifying C. glaucum as a good bioindicator species. Thus, our findings highlight the fact that studies should be cautious when selecting species for environmental monitoring, since good sentinels or bioindicators in highly polluted systems may not act in the same way in low or moderately contaminated areas. Furthermore, our study warns for the misclassification of cockles in different ecosystems.