δ 13C and δ 15N variations in organic matter pools, Mytilus spp. and Macoma balthica along the European Atlantic coast

Stable carbon (δ ¹³C) and nitrogen (δ ¹⁵N) isotope (SI) values of sedimentary organic matter (SOM), seston and two dominant bivalves, Mytilus spp. and Macoma balthica, were studied at 18 stations along the European coast in spring and autumn 2004. Three main regions, the Baltic Sea (BS), the North Sea and English Channel (NS), and the Bay of Biscay (BB), were tested for possible geographic (latitudinal) differences in the SI values. In spring, only BS showed lower δ ¹³C values of seston and Mytilus spp., and higher δ ¹⁵N values of SOM, than NS and BB. No significant differences between the 3 regions were found in autumn. Irrespective of season and regions, Mytilus spp. was more ¹³C-depleted than M. balthica. δ ¹³C values of M. balthica, but not those of Mytilus spp., were significantly correlated with SOM. These results are consistent with differences in feeding behavior of Mytilus spp. and M. balthica, as the two species are known as obligatory-suspension and facultative-deposit feeders, respectively. In contrast, no differences in the δ ¹⁵N values of Mytilus spp. and M. balthica were found at individual stations, indicating the same trophic level of the two bivalves within the food webs. At some stations, irrespective of geographic location, both bivalves showed δ ¹⁵N values up to 18–20 ‰. These were two trophic levels higher than those found at the other stations, indicating local and/or episodic eutrophic conditions, probably due to waste water discharge, and the effectiveness of both Mytilus spp. and M. balthica as bio-indicators of anthropogenic eutrophication. Overall, our results suggest that pathways of energy flow from OM pools to dominant bivalves is more related to local environmental conditions than to geographic regions across the European coastline. This has implications for food web studies along the Atlantic coast because most of the values are consistent over a large area and show no significant differences. Therefore, the present study can be used twofold for the determination of trophic baselines and for the correction of the trophic position of consumers higher up in the food web in the case of differences in waste water discharge.     

Modelling of the contribution of dissolved inorganic nitrogen (DIN) from litterfall of adjacent mangrove forest to Hooghly–Matla estuary,India

Hooghly–Matla estuarine ecosystem of India is very rich in natural resources and receives large amount of nutrients through litterfall from adjacent mangrove forest. Nitrogen as an important nutrient occurs in various forms and plays a crucial role in the regulation of productivity in this estuarine system. Modelling of nitrogen dynamics from mangrove litterfall and particularly the release of dissolved inorganic nitrogen in this estuarine system is important because of its role in augmenting growth of phytoplankton and other higher plants and all other biological components of grazing food chain.     

Growth dynamics of Saccharina latissima (Laminariales,Phaeophyceae) in Aarhus Bay,Denmark, and along the species’ distribution range

Growth dynamics of Saccharina latissima in a Danish embayment (56°03.793N, 10°16.148E) were investigated through an annual cycle (March 1999–March 2000) and related to patterns found in previous studies covering the distribution range of the species. The kelps exhibited meristematic growth as well as distal tissue loss all year around. Elongation rate peaked in spring (March–May, 0.75 cm day^?1), whereas maximum biomass growth occurred in May–July at higher insolation. S. latissima accumulated nitrogen (N) in November–March, when ambient N levels were high and the fast growth in March–July was followed by a depletion of these reserves. Light regimes and seasonal fluctuations of nutrients were, thus, major factors explaining the seasonal growth pattern of S. latissima in this temperate bay. Differences in light and exposure along depth gradients affected the growth, loss and storage product dynamics. High losses of N and carbon (C) through summer abscission of distal tissue question the efficiency of translocation, especially at shallower depths, where losses are accelerated by, e.g., high temperature. A large-scale comparison further highlighted that warming advanced the timing, increased the level of peak growth and also seemed to expand the growth period. Growth rates of the studied Danish population fell in the low end of the range for similar latitudes and temperatures, probably due to sub-optimal salinities (avg. 23.3 psu) in combination with periodically high summer temperatures (max. 21.1 °C).     

Reproduction and growth of Isostichopus fuscus (Echinodermata: Holothuroidea) in the southern Gulf of California, México

The reproduction and growth of Isostichopus fuscus (Ludwig, 1875) at Isla Espíritu Santo, Baja California Sur, México from July 1992 to September 1993 and from August 1996 to July 1997 were analyzed. The reproductive cycle was monitored by using histological analysis. Five gonadal stages were described according to cell types present in the gonad; undetermined, gametogenesis, maturity, spawning and post-spawning. This holothurian reproduces annually during summer (July to September), when sea surface temperature reaches 27 °C. The gonad index is related to the gonadal stages. The first sexual maturity for I. fuscus was calculated at 367 g (4 to 5 years old) according to the von Bertalanffy equation, and nearly all the specimens at Isla Espíritu Santo were 5 to 7 years old (including some individuals over 35 years old). Data of the length–weight relationship showed that I. fuscus grows allometrically at the studied site (b = 1.83). The mortality rate was relatively high (M = 0.51), indicating that in a typical cohort, 40% of the recruits does not survive the first year, and less than 20% reaches maturity. Received: 15 July 1998 / Accepted: 19 August 1999     

Modelling of coastal vulnerability in the stretch between the beaches of Porto de Mós and Falésia, Algarve (Portugal)

Coastal systems are characterized by high geophysical and biophysical sensitivity as being their massive occupation a serious issue concerning their self-regulation. Worldwide coastal areas are exposed to problems such as coastal erosion, degradation and destruction of marine habitats, pollution and rising sea level. Thus, it is crucial to design models of coastal vulnerability assessment to ensure a better management of coastal areas. This study characterizes the vulnerability of the coastal stretch between the beaches of Porto de Mós and Falésia in the Algarve, corresponding to 52?km of the south coast of Portugal. The expansion of urban areas was modelled using a Cellular Automata (CA) based approach. Results show that 65% of the coastal stretch has high and very high vulnerability caused by both physical and human factors. Results further indicate that urban growth may interfere with the natural evolution of the coastal geomorphology. The scenario of urban expansion for the year 2015 highlights the need to develop effective urban planning processes to ensure a correct balance between the geophysical resilience of coastal systems and the promotion of the coastal sector as a strategic asset for the regional and national economy.     

Heavy metal contents of the sperm whale physeter macrocephalus and the bottle‐nosed dolphin tursiops truncatus beached on Languedoc‐Roussillon seaside (Mediterranean,France)

The contamination of Sperm Whale Physeter macrocephalus and bottle‐nosed dolphin Tursiops truncatus by lead is less than detection limit, insignificant by cadmium and nickel, not very high by copper and quite high by zinc. On the other hand, the concentration of mercury, very low for Sperm Whale, is very high for bottle‐nosed dolphin.

The pollution of Physeter macrocephalus is significantly lower than that of dolphin Stenella coeruleoalba and probably that of other species of cetaceans living near the coast; this might be due to its pelagic life and its diet.

The mercury pollution of Tursiops truncatus (especially that of one of the two subjects analyzed) is quite similar to that of Stenella coeruleoalba. This might be due to the fact that Tursiops truncatus can live in the open sea just as well as close to the seashore.     

In situ characterization of sulphur in gill-endosymbionts of the shallow water lucinid Codakia orbicularis (Linné, 1758) by high-pressure cryofixation and EFTEM microanalysis

In this study, Codakia orbicularis gill-tissues were cryo-fixed by using high-pressure freezing, a freeze substitution process and finally by cryo-embedding in Lowicryl. Ultrathin sections were then used for an EFTEM microanalysis. Results show that intracellular bacterial symbionts contain elemental sulphur in periplasmic vesicles as indicated by conventional TEM. When sulphur is temporarily depleted in the environment, such structures may act as energy sources for bacterial metabolism. Moreover, sulphate was detected in the cytoplasm of the bacterial symbionts, suggesting the oxidation of elemental sulphur, located in periplasmic granules, to sulphate (the final step in sulphur oxidation) by these chemoautotrophic bacteria. To assess the effects of host starvation on the bacterial sulphur content, adult individuals of C. orbicularis were maintained in starvation for 6 weeks in sterile artificial seawater depleted in sulphur. During starvation, both (1) the number of bacteria inside the bacteriocytes and (2) the number of periplasmic granules per prokaryotic cell decreased. The content of the remaining periplasmic granules had been modified to sulphate. This observation suggests that bacterial gill-endosymbionts used the elemental sulphur in their periplasmic granules as stored substrate for oxidation in order to produce energy in case of sulphur depletion.