Disentangling the identities and distribution patterns of the introduced beachfleas Orchestia gammarellus and Platorchestia platensis (Crustacea: Amphipoda: Talitridae) in South Africa

Two introduced beachfleas, Orchestia gammarellus and Platorchestia platensis, have been recorded from South Africa, but have been misidentified by some earlier researchers and, prior to this study, each was also known from just a few, scattered observations, such that their true distributions remained obscure. We illustrate both species to clarify the features that identify and distinguish them and determine their true distributions by re-examining historical samples and by collecting new material from estuaries and lagoons along the west and south coasts of South Africa. Adult males of O. gammarellus have slender antennae and characteristic expanded, flattened, oar-like distal segments on pereopod 7. Adult males of P. platensis have the peduncle of antenna 2 strongly swollen and have bulbous, but not flattened, distal segments on pereopod 7. Both species occur under wrack and other debris along the banks of estuaries and sheltered lagoons. Orchestia gammarellus is found only along the south-west coast, in the Berg River Estuary, Langebaan Lagoon and the Diep River Estuary. Previous records from Knysna were misidentifications of P. platensis. Platorchestia platensis is found at one west coast site, Langebaan Lagoon, but is widely distributed from Cape Point eastwards to at least Algoa Bay. Both species share the same habitats as several other native beachfleas and competitive interactions between native and introduced species merit investigation.     

Defensive Metabolites from Antarctic Invertebrates: Does Energetic Content Interfere with Feeding Repellence?

Many bioactive products from benthic invertebrates mediating ecological interactions have proved to reduce predation, but their mechanisms of action, and their molecular identities, are usually unknown. It was suggested, yet scarcely investigated, that nutritional quality interferes with defensive metabolites. This means that antifeedants would be less effective when combined with energetically rich prey, and that higher amounts of defensive compounds would be needed for predator avoidance. We evaluated the effects of five types of repellents obtained from Antarctic invertebrates, in combination with diets of different energetic values. The compounds came from soft corals, ascidians and hexactinellid sponges; they included wax esters, alkaloids, a meroterpenoid, a steroid, and the recently described organic acid, glassponsine. Feeding repellency was tested through preference assays by preparing diets (alginate pearls) combining different energetic content and inorganic material. Experimental diets contained various concentrations of each repellent product, and were offered along with control compound-free pearls, to the Antarctic omnivore amphipod Cheirimedon femoratus. Meridianin alkaloids were the most active repellents, and wax esters were the least active when combined with foods of distinct energetic content. Our data show that levels of repellency vary for each compound, and that they perform differently when mixed with distinct assay foods. The natural products that interacted the most with energetic content were those occurring in nature at higher concentrations. The bioactivity of the remaining metabolites tested was found to depend on a threshold concentration, enough to elicit feeding repellence, independently from nutritional quality.     

Could artificial structures such as fish passes facilitate the establishment and spread of the ‘killer shrimp’ Dikerogammarus villosus (Crustacea: Amphipoda) in river systems?

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Broad_scale,dense amphipod tube aggregations on the sea bed: implications for resource species that utilize benthic habitats

During a research cruise to Georges Bank in 1999 to study the areas closed to fishing, broad areas of the sea floor (3000_km²) were found to have a high percentage cover of emergent invertebrate tubes. Most of these tubes were attributable to the tubicolous epifaunal amphipod, Ericthonius rubricornis. Our data show the spatial extent that dense clumps of amphipod tubes could cover the sea floor on Georges Bank. When some of the same sites were sampled 1_yr later, in June 2000, the percent cover of the tube clumps on the sea floor was significantly reduced. Biogenic structures, such as invertebrate tubes, are important features of benthic habitats and may provide protection for juvenile fish and invertebrate resource species. Our observations reiterate that biogenic habitat characteristics are not spatially and temporally stable and this needs to be recognized by fisheries managers when managing the living marine resources that utilize these habitats.     

三种深渊钩虾肠道微生物组成与群落结构

针对马里亚纳海沟、玛索海沟、新不列颠海沟东部、新不列颠海沟中部等4个采样点的3种钩虾共120个样品,利用16S rRNA-RFLP分析方法对不同样品间的微生物组成进行研究,并比较了4个采样点的细菌群落结构多样性。结果表明:4个采样点钩虾肠道的微生物多样性有着显著差别。马里亚纳海沟Hirondellea gigas钩虾肠道细菌的优势菌群为嗜冷单胞菌属(Psychromonas sp.)和Uncultured bacterium,分别占37.05%和18.52%。玛索海沟Bathycallisoma(syn.Scopelocheirus)schellenbergi钩虾肠道细菌的优势菌群为Uncultured Mollicutes bacterium和Uncultured deep-sea bacterium,分别占62.5%和25%。新不列颠海沟东部Alicella gigantean钩虾肠道细菌的优势菌群为Uncultured Mollicutes bacterium和Uncultured Mycoplasmataceae bacterium,含量分别占到50%和44.44%。新不列颠中部的A.gigantean钩虾肠道细菌的优势菌群为Psychromonas sp.、Uncultured Mollicutes bacterium、Uncultured Mycoplasmataceae bacterium和Uncultured bacterium,含量分别为39.29%、32.14%、14.29%和10.71%。Uncultured Mollicutes bacterium在玛索海沟S.schellenbergi肠道内占了62.5%,在新不列颠海沟东部A.gigantean肠道内的含量为50%,在新不列颠海沟中部A.gigantean肠道内含量为32.14%,而在马里亚纳海沟H.gigas肠道中仅占3.7%。由此可见,4个采样点3种钩虾肠道内微生物多样性丰富、且存在较大的差异,马里亚纳海沟H.gigas肠道内微生物物种最丰富、且种群结构最复杂,玛索海沟S.schellenbergi钩虾和新不列颠海沟A.gigantean钩虾次之。     

Diel activity and vertical distribution of Lysianassoid amphipods dominant in Onagawa Bay, north-eastern Japan

ABSTRACT:   Baited traps were used over 24 h to reveal the diel activity and vertical distribution of three dominant lysianassoid amphipods ( Scopelocheirus onagawae , Anonyx omorii , Anonyx abei ) in Onagawa Bay, north-eastern Japan. The three species were the most dominant small crustacean scavengers in the bay. Most individuals were caught by traps deployed 0.3 m above the bottom, showing that they were active in the layers close to the sea bottom. No habitat segregation was found among species or developmental stages, suggesting that these scavengers rely on the food supply from bottom deposits. The three species increased remarkably in numbers of collected individuals at night, showing a rise in feeding activity. The two Anonyx species were collected only during the night, and S. onagawae was collected mostly during the night. The nocturnal activity appears to be an adaptation to reduce predation risks. However, juveniles of S. onagawae appeared even during the day, suggesting that feeding might take precedence over avoiding predation. Baited traps collected ovigerous females of S. onagawae but not of Anonyx species; the reason for the difference could not be determined.     

Protein from Northern krill (Thysanoessa inermis), Antarctic krill (Euphausia superba) and the Arctic amphipod (Themisto libellula) can partially replace fish meal in diets to Atlantic salmon (Salmo salar) without affecting product quality

The main objective of the present study was to evaluate the effect of using three different crustacean meals (Tysanoessa inermis, Euphausia superba, Themisto libellula) on product quality of Atlantic salmon (Salmo salar L.). In order to do this, a total of six iso‐protein, iso‐lipid and iso‐carotenoid diets were prepared. Two experimental diet series were prepared. In the first series, a control feed (K0) was compared with diets where 20%, 40% and 60% of the fish meal protein were replaced with protein from Northern krill T. inermis (K20, K40 and K60, respectively). In the second series, control feed (K0) was compared with diets where 40% of the dietary protein was replaced by protein from T. inermis (K40), Antarctic krill E. superba (AK40) and the Arctic amphipod T. libellula (AMP40). The salmon groups were fed the various diets for 160 days and the average weight of the fish increased from 410 g to around 1500 g. Fish given diets containing krill displayed a general better growth compared with the ones given pure fish meal diet. Replacing fish meal protein with protein from the crustacean sources had, in general, only minor effects on the flesh quality measured both by technical and sensory methods. However, some significant effects were noted. Postmortem muscle pH was generally lower (P < 0.05), for K20, K40, AMP40 in fish fed crustacean diets compared with those receiving the control diet. Increasing the replacement level of non‐fish meal protein from Northern krill (K20, K60) significantly reduced the rigor contraction. Fish given K20 had a slightly firmer meat texture, measured as resistance to post‐rigor compression, especially when compared with K60 (P < 0.05). Fish from the K20 and AMP40 groups had a deeper red flesh coloration [both light reflection (A*‐value and chroma) and flesh astaxanthin concentration] than fish fed K0 and higher inclusions of krill meal. The groups with the highest astaxanthin flesh content also showed the best growth and had the highest feed intake. Finally, a sensory panel analysis differed slightly from the technical measurements in that K0, rather than K20 was given the highest score for hardness and colour. In comparison with K0, AK40 got the lowest salty taste and hardness scores from the panellists relative to the control fish (P < 0.05). Despite minor effects on the present quality measures, it is concluded that meal from three different crustacean species can successfully replace fish meal up to 60% with Northern krill, and 40% of Antarctic krill and amphipod meal of dietary proteins.     

Natural Products from Antarctic Colonial Ascidians of the Genera Aplidium and Synoicum: Variability and Defensive Role

Ascidians have developed multiple defensive strategies mostly related to physical, nutritional or chemical properties of the tunic. One of such is chemical defense based on secondary metabolites. We analyzed a series of colonial Antarctic ascidians from deep-water collections belonging to the genera Aplidium and Synoicum to evaluate the incidence of organic deterrents and their variability. The ether fractions from 15 samples including specimens of the species A. falklandicum, A. fuegiense, A. meridianum, A. millari and S. adareanum were subjected to feeding assays towards two relevant sympatric predators: the starfish Odontaster validus, and the amphipod Cheirimedon femoratus. All samples revealed repellency. Nonetheless, some colonies concentrated defensive chemicals in internal body-regions rather than in the tunic. Four ascidian-derived meroterpenoids, rossinones B and the three derivatives 2,3-epoxy-rossinone B, 3-epi-rossinone B, 5,6-epoxy-rossinone B, and the indole alkaloids meridianins A–G, along with other minoritary meridianin compounds were isolated from several samples. Some purified metabolites were tested in feeding assays exhibiting potent unpalatabilities, thus revealing their role in predation avoidance. Ascidian extracts and purified compound-fractions were further assessed in antibacterial tests against a marine Antarctic bacterium. Only the meridianins showed inhibition activity, demonstrating a multifunctional defensive role. According to their occurrence in nature and within our colonial specimens, the possible origin of both types of metabolites is discussed.