On the food of the European eel, Anguilla anguilla (L.), in the upper zone of the Tagus estuary, Portugal

The estuarine food habits of the European eel, Anguilla anguilla (L.), in the upper zone of the Tagus estuary have been studied through the analysis of 210 specimens collected during 1988. Eels, measuring from 136 to 627 mm in total length, fed on prey organisms ranging from 2.0 to 76.0 mm in length. Amphipods and the shore crab, Carcinus maenas (L.), were the most important food items found. In more saline muddy bottom areas polychaetes, bivalves and shrimp increased their importance as prey, replacing the amphipods as preferential food. Fish were always a secondary, although significant, prey item. The occurrence of seasonal variations in eels' diet could be attributed to fluctuations in prey densities. There was evidence of a close relationship between the quantity of prey organisms in the benthos and the composition of eels' stomach contents, but a certain degree of food selection based on size, concealment capacity and motility of prey, was found.     

The importance of intraspecific competition in a Littorina littorea population in the Wadden Sea

Two field experiments were carried out totest whether effects of intraspecific competition ina Littorina littorea population can be detectedin a short-term investigation. Different size classesof L. littorea showed no significant differencein preferences when offered four kinds of eitherpossible food or substrata (Fucus vesiculosus,Ulva lactuca, Carcinus maenas, brick).Large and medium winkles preferred Fucusvesiculosus, followed by Ulva lactuca. Deadshore crabs (Carcinus maenas) were the leastpreferred objects for all size classes. On the firstday of the experiment bricks were more attractive tosmall littorines than to larger ones. Considering allfour days, the same ranking occurred for all sizeclasses: Fucus vesiculosus > Ulvalactuca > brick > Carcinus maenas. The reactionofjuveniles to increased densities was examined using anin situ caging experiment on a mussel bed. Meshsize of the cages allowed adult densities to beincreased while juveniles could escape by passingthrough the meshes. However, there was no significantemigration of small winkles even from cages with 10 to20 times natural density of large individuals. Ofgreater importance was the original number of winklesat the site. The available resources on the musselbeds appear to be sufficient to maintain a highpopulation density. Intraspecific competition does notseem to play a major role in this L. littorea-population.     

Relationships between trophic organization of benthic communities and organic matter content in Tyrrhenian Sea sediments

The organic content of sediments, often considered as an important trophic source for the benthos, can be used as a measurement of the trophic status of marine ecosystems. Soft-bottom communities were studied between Leghorn and Elba Island, from 5 to 500 m depth. Total biomass and trophic structure (percent dominance of trophic guilds) were related to organic carbon content and C/N ratio of sediments. Sediment organic matter, depending on its quantity and quality, could act as a food source or a stress source for the community.     

Absence or masking of metabolic fractionations of 13C in a freshwater benthic food web

1. Although marine research has indicated that metabolic fractionations of ¹³C due to differences in organismal trophic position and proximal composition can complicate the isotopic interpretation of energy flow pathways, such potentially confounding problems have never been examined in freshwater benthic food webs.
2. The δ¹³C values of animals comprising a littoral benthic food web composited from four Canadian Shield lakes showed no relationship with either individual trophic position (δ¹⁵N) or lipid content (C/N ratios).
3. Differences in the relative incorporation of autochthonous and allochthonous energy sources by freshwater benthic organisms will alter their δ¹³C and δ¹⁵N values, thereby masking any possibility of observing ¹³C trophic enrichment.
4. Removal of the possibly confounding influences of lipids through either empirical correction or by analytical extraction may be unnecessary in studies of freshwater benthic food webs. Likewise, a priori adjustments in δ¹³C for freshwater benthic organisms in order to accommodate trophic fractionations which are presumed to occur, based on data from marine offshore food webs, may also be inappropriate.     

Absence or masking of metabolic fractionations of 13C in a freshwater benthic food web

1. Although marine research has indicated that metabolic fractionations of ¹³C due to differences in organismal trophic position and proximal composition can complicate the isotopic interpretation of energy flow pathways, such potentially confounding problems have never been examined in freshwater benthic food webs.
2. The δ¹³C values of animals comprising a littoral benthic food web composited from four Canadian Shield lakes showed no relationship with either individual trophic position (δ¹⁵N) or lipid content (C/N ratios).
3. Differences in the relative incorporation of autochthonous and allochthonous energy sources by freshwater benthic organisms will alter their δ¹³C and δ¹⁵N values, thereby masking any possibility of observing ¹³C trophic enrichment.
4. Removal of the possibly confounding influences of lipids through either empirical correction or by analytical extraction may be unnecessary in studies of freshwater benthic food webs. Likewise, a priori adjustments in δ¹³C for freshwater benthic organisms in order to accommodate trophic fractionations which are presumed to occur, based on data from marine offshore food webs, may also be inappropriate.     

Cryptic invasions of the crab Carcinus detected by molecular phylogeography

Coastal marine ecosystems world-wide are threatened by invasions of nonindigenous species. The ubiquity of marine sibling species identifiable only by genetic analysis suggests that many invasions are cryptic and therefore undetected, causing an underestimation of the actual number and impacts of invading species. We test this hypothesis with European crabs in the genus Carcinus that have invaded five regions globally. Partial 16S ribosomal RNA gene sequences confirm sibling species status of morphologically similar Atlantic C. maenas and Mediterranean C. aestuarii . Based on 16S rRNA haplotypes, crabs from California, New England and Tasmania were all C. maenas . However, we report the cryptic multiple invasion of both species in Japan and South Africa, where only C. aestuarii and C. maenas , respectively, were previously recognized.     

The distribution and orientation of epizoic barnacles on crabs

The distribution and orientation of Balanus crenatus on Carcinus maenas is described. Elminius modestus was also found on C. maenas but it was not common. Both species of barnacle were also found on Cancer pagurus, although neither species of barnacle appeared to be as common on Cancer as on Carcinus. Possible reasons for this are discussed.
Treating the carapaces of similar sized C. maenas as sampling units it is clear that the distribution of B. crenatus over these sampling units is not random but is aggregated. This probably arises because of the gregarious nature of the cyprids when they settle out but other possibilities are considered. B. crenatus on the carapace of C. maenas is found exclusively in the grooves and depressions on the carapace and this is because the cyprids preferentially settle in concavities.
The orientation of B. crenatus also shows a consistent pattern, with the cirral nets facing predominantly backwards. This pattern could arise because the barnacle cyprids orientate to water currents, generated by the exhalant respiratory currents, flowing forwards over the carapace.     

Effects of water activity on oxygen-binding in high-molecular weight,extracellular invertebrate hemoglobin and hemocyanin

We have investigated the effects of water activity on oxygen-binding properties of giant invertebrate oxygen-binding proteins: hemocyanins from the intertidal crab, Carcinus maenas and the terrestrial snail, Arion ater and hemoglobin from the marine polychaete, Arenicola marina, using the osmotic stress method. We show that in contrast to the water-sensitive dimeric or tetrameric hemoglobins from humans, fish and cyclostomes, changes in water activity exert small effects on the oxygen affinity of these polymeric proteins, indicating that their deoxygenated and oxygenated states are almost similarly hydrated. The small effects of water activity may correlate with small surface to volume ratios in these high-molecular-weight proteins that pose a limit to water-accessible sites, and suggest smaller quaternary structural changes associated with oxygenation compared to those in dimeric and tetrameric hemoglobins.     

A robotic molecular method for in situ detection of marine invertebrate larvae

Knowledge of the temporal and spatial abundance of invertebrate larvae is critical to understanding the dispersal capabilities and recruitment potential of marine and aquatic organisms. Traditional microscopic analyses are time-consuming and difficult given the diversity of larval species and a frequent lack of discriminating morphological characteristics. Here, we describe a sensitive rRNA targeted sandwich hybridization assay (SHA) that uses oligonucleotide probes to detect and enumerate the larvae of invasive green crabs (Carcinus maenas), native blue mussels (Mytilus), native barnacles (Balanus) and polychaetes (Osedax and Ophelia) that occur in the Monterey Bay National Marine Sanctuary, California. Laboratory-based assays demonstrate specificity, high sensitivity, and a quantitative response to cultured samples from three of the target organisms. Oligonucleotide probes were then printed in arrays on nitrocellulose membranes and deployed in our robotic Environmental Sample Processor (ESP) to detect larvae in situ and autonomously. We demonstrate that the SHA-detection method and ESP robot can be used for near real-time, in situ detection of larval species in the marine environment.     

Alteration of cytochrome C oxidase activity during spermatogenesis in Carcinus maenas

During spermatogenesis in the crab, Carcinus maenas, mitochondria in the developing spermatids degenerate. In close association with mitochondrial fragments in late spermatids, an elaborate lattice-like complex of fused membranes is formed and lies in a position adjacent to the acrosome. Mature sperm possess no mitochondria, but a whorl of membranes is present alongside the acrosome in the diffuse nucleus. To ascertain whether or not cytochrome c oxidase activity is lost as the mitochondria disintegrate, differentiating Carcinus maenas spermatids and mature sperm have been studied cytochemically. Cytochfome c oxidase activity was localised by means of the osmophilic compound 3,3'-diaminobenzidine (DAB). Cytochrome c oxidase activity is confined to the cristae of mitochondria in the testis. As spermatids mature most mitochondria are lost. A few mitochondrial fragments may be caught up within the lamellar complex. While they are recognisalbe as mitochondria they retain cytochrome c oxidase activity. The lamellar complex does not show this enzyme activity. These results therefore suggest that the mature sperm of Carcinus maenas do not contain the enzymes normally incorporated in the mitochondrial membrane, capable of oxidative phosphorylation.     

Experimental evidence for latent developmental plasticity: intertidal whelks respond to a native but not an introduced predator

Animals with highly inducible traits may show no inducible response when exposed to a related but wholly novel cue. This appears to be true for the intertidal whelk Nucella lamellosa faced with a voracious introduced predator. In the laboratory, we exposed whelks to effluent from two species of predatory crab, the native red rock crab Cancer productus and the invasive European green crab Carcinus maenas. Nucella and Cancer have a long shared history in the northeast Pacific, whereas potential interaction with Carcinus began here less than 10 years ago. Although Nucella responded adaptively to Cancer effluent by increasing shell thickness and decreasing somatic growth, there was no such response to Carcinus. Furthermore, thicker shelled Nucella were less likely to be eaten by Carcinus. Because Nucella produces thicker shells when exposed to Cancer cues, its ability to respond similarly to Carcinus depends only on the coupling of the Carcinus cue to the existing developmental pathways for adaptive changes in shell form. Such coupling of latent plasticity to a novel cue -- via genetic changes or associative learning -- could explain many cases of rapid phenotypic change following a sudden shift in the environment.     

海洋细菌抗菌和细胞毒活性的初步研究

从不同海域的生物、海水和海泥中分离海洋细菌,利用琼脂扩散法和MTT法对细菌培养液的乙酸乙酯提取物进行了抗菌和细胞毒活性筛选。比较了活性菌株与来源的相关性．结果表明,在分离的341株海洋细菌中。42株细菌的代谢产物具有抗菌活性,7株具有细胞毒活性,其中来源于海洋无脊椎动物和海藻的活性菌株比例(22％和11％)大于来源于海水和海泥的细菌(7％和5％)．细菌分类鉴定结果显示,具有活性的细菌大部分属于假单胞菌属、发光杆菌属、梭状芽孢杆菌属、交替单胞菌属和黄杆菌属．     

Ambient fauna impairs parasite transmission in a marine parasite-host system

To understand possible factors controlling transmission of trematode larvae between first and second intermediate hosts we examined the impact of ambient fauna on parasite transmission in a marine intertidal parasite-host association. Cockle hosts (Cerastoderma edule) kept together with selected co-occurring macrozoobenthic species in mesocosms acquired a lower parasite load compared to cockles kept alone, when targeted by cercariae of the trematode Himasthla elongata. The reduction of parasite load in the cockles differed between the 7 macrozoobenthic species tested and was between 35 and 91%. Three different types of reduction could be distinguished: (1) predators (Carcinus maenas, Crangon crangon) actively preying upon cercariae, (2) non-host filter feeders (Crepidula fornicata, Mya arenaria, Crassostrea gigas) filtering cercariae but not becoming infected and (3) alternative hosts (Mytilus edulis, Macoma balthica) becoming infected by the cercariae and thus distracting cercariae from the target hosts. In addition, interference competition may occur in the form of disturbance of cockles by ambient organisms resulting in lower filtration rates and subsequently lower parasite loads. Our results suggest that the species composition and relative abundance of the ambient fauna of parasite-host systems play an important role in controlling trematode transmission rates in benthic marine systems.     

Habitat effects on the relative importance of trait- and density-mediated indirect interactions

Classical views of trophic cascades emphasize the primacy of consumptive predator effects on prey populations to the transmission of indirect effects [density-mediated indirect interactions (DMIIs)]. However, trophic cascades can also emerge without changes in the density of interacting species because of non-consumptive predator effects on prey traits such as foraging behaviour [trait-mediated indirect interactions (TMIIs)]. Although ecologists appreciate this point, measurements of the relative importance of each indirect predator effect are rare. Experiments with a three-level, rocky shore food chain containing an invasive predatory crab ( Carcinus maenas ), an intermediate consumer (the snail, Nucella lapillus ) and a basal resource (the barnacle, Semibalanus balanoides ) revealed that the strength of TMIIs is comparable with, or exceeds, that of DMIIs. Moreover, the sign and strength of each indirect predator effect depends on whether it is measured in risky or refuge habitats. Because habitat shifts are often responsible for the emergence of TMIIs, attention to the sign and strength of these interactions in both habitats will improve our understanding of the link between individual behaviour and community dynamics.     

Purification and characterisation of four polypeptides with neurotoxic activity from Condylactis aurantiaca.

Four toxic polypeptides, Toxins I, II, III and IV were isolated in pure form from the sea anemone Condylactis aurantiaca (Actinaria). Toxin isolation was achieved by alcoholic extraction of the homogenised sea anemones, batchwise adsorption onto cation exchangers, gel filtration on Sephadex G-50 and G-25 and ion-exchange chromatography on SP-Sephadex and QAE-Sephadex. Toxins from Condylactis aurantiaca all contain between 49 and 51 amino acids. Their amino acid compositions were compared to those of the Anemonia sulcata toxins. The toxins were tested on the shore crab Carcinus maenas by intramusclar injection. Crabs react highly sensitively to sea anemone toxins with muscle cramps and paralysis. For Condylactis toxins LD100 ranges from 2 to 6.6 mug/kg Carcinus maenas.     

Biological methylations in the crab Carcinus maenas; in vitro inhibition by a fraction purified from androgen gland extracts]

Extracts from muscles, testis, seminal vesicles and ovaries of the Crab, Carcinus maenas, have been studied in vitro, in presence of [14C]-methyl S-adenosylmethionine, with an E. coli tRNA as methyl acceptor. The highest level of methylases is found in the testis. It has been reported previously that a purified fraction extracted from the androgenic glands of Carcinus maenas inhibits the vitellogenesis in ovaries. We now show that the same fraction inhibits tRNA methylation in an extract of testis as methylase; a 50% inhibition is obtained with about 10 mug of a purified fraction corresponding to 15 glands. With an enzymatic preparation from the ovaries, a 50% inhibition of the tRNA methylase is observed with the purified extract from 4 glands.     

Community structure and food web based on stable isotopes (δN and δC) analysis of a North Eastern Atlantic maerl bed

Maerl beds are highly biodiverse biogenic substrata that have been receiving increasing attention in the last decade. Although maerl beds represent important nursery areas for commercial fishes and molluscs, little is known on the trophic web of their communities. Community structure parameters of maerl bed of the Bay of Brest (species richness, abundance, biomass and dominating species) were studied in parallel with the carbon and nitrogen isotopic composition of their main benthic species (macrofaunal, and megafaunal organisms) in order to assess the trophic levels and differences in the potential food sources of maerl inhabitants. The major potential sources of energy were identified to originate either from epiphytic macroalgae and microphytobenthos both growing on maerl thalli, together with sedimenting (sedimentary) particulate organic matter (POM) originating from the water column. The majority of the macro- and megafaunal organisms investigated were filter feeders, selective-deposit feeders and predators/scavengers. Filter feeders fall into three different groups representing different trophic pathways (i) sponges feeding directly on POM (water column filter feeders I), (ii) ascidians and holothurians feeding on POM and probably captured pelagic preys (water column filter feeders II), and (iii) filter feeding molluscs and crustaceans were hypothesised to feed on microphytobenthos or on decaying sedimented POM (Interface filter feeders). Selective deposit feeders were also divided into two subgroups. Carnivores were also distinguished between those with scavenging habits and true predators. Coupling of the trophic levels observed with the community biomass structure revealed that most of the benthic biomass derives its food from detritic sedimented POM and/or microphytobenthos, with interface filter feeders (23% of the biomass), selective deposit feeders (12%). Carnivores made up to 14% of the total biomass. Generally stable isotopes ratio mean values overlap and cover a large range within feeding types, indicating a strong overlap in food sources and a high degree of complexity of the food web presumably due to the diversity of the potential food sources.     

Hydrocarbons in the seawater and pelagic organisms of the Southern Ocean

Summary The aliphatic and aromatic hydrocarbon content of seawater and a selection of marine pelagic organisms from the Bransfield Strait, Antarctica were evaluated. The patterns of the hydrocarbons found indicated that their origin was biogenic and there was no evidence for anthropogenic hydrocarbons in the Antarctic marine ecosystem. Hydrocarbons which are constituents of man made materials are present throughout the region but not in the patterns characteristic of anthropogenic origin. Recent reports of an even carbon number predominance in Antarctic marine organisms were not corroborated in this study. A number of biogenic compounds were investigated as suitable markers to monitor pathways of hydrocarbons in the Antarctic food chain. Specific compounds (probably branched chain alkenes) were found to occur at more than one trophic level. Polyaromatic hydrocarbons were present in all organisms but were undetectable in 44% of the seawater samples.     

Life in a temperate Polar sea: a unique taphonomic window on the structure of a Late Cretaceous Arctic marine ecosystem

As the earth faces a warming climate, the rock record reminds us that comparable climatic scenarios have occurred before. In the Late Cretaceous, Arctic marine organisms were not subject to frigid temperatures but still contended with seasonal extremes in photoperiod. Here, we describe an unusual fossil assemblage from Devon Island, Arctic Canada, that offers a snapshot of a ca 75 Myr ago marine palaeoecosystem adapted to such conditions. Thick siliceous biogenic sediments and glaucony sands reveal remarkably persistent high primary productivity along a high-latitude Late Cretaceous coastline. Abundant fossil faeces demonstrate that this planktonic bounty supported benthic invertebrates and large, possibly seasonal, vertebrates in short food chains. These ancient organisms filled trophic roles comparable to those of extant Arctic species, but there were fundamental differences in resource dynamics. Whereas most of the modern Arctic is oligotrophic and structured by resources from melting sea ice, we suggest that forested terrestrial landscapes helped support the ancient marine community through high levels of terrigenous organic input.