1,720,991 research outputs found
Temporal and spatial variation in the reproductive ecology of the vent-endemic amphipod Ventiella sulfuris in the eastern Pacific
No full textPopulations of the vent-endemic amphipod Ventiella sulfuris were compared from 6 East Pacific Rise (EPR) vent sites of different ages, 3 from the northern EPR and 3 from the southern EPR. Although vent age affected amphipod abundance, with no individuals at the oldest vent, other population/reproductive parameters were found to be site dependent rather than vent age dependent. There was little within-site variation in population structure and reproductive output, probably the result of high within-site motility. However, there were significant between-site and between-field differences, indicating a high degree of population and reproductive variability and a moderate degree of vent fidelity. Since population structure and reproductive output varied between sites, the possibility of their use as biomarkers of vent ‘condition’ is discussed. The reproductive ecology of V. sulfuris is described for the first time and compared to that of other vent amphipod species. Unlike other species studied, reproductive output is relatively high. Adults move to the periphery of vents to reproduce and brood; after brooding, they moult again, return to feed at vent habitats (e.g. mussel and tube worm beds), and undergo a new phase of gonad maturation and emigration
A reinterpretation of the taxonomy and zoogeography of Pakistanapseudes and Swireapseudes (Crustacea; Tanaidacea): Hong Kong taxa in the world context
No full textStructure and function of Halice hesmonectes (Amphipoda: Paraliscidae) swarms from hydrothermal vents in the eastern Pacific
No full textSwarms of the pardaliscid amphipod Halice hesmonectes were sampled at low-temperature hydrothermal vents in the Venture Hydrothermal Fields of the East Pacific Rise. In excess of 3000 individuals were collected from a range of sites/habitats, and at two points in time (December 1991 and March 1994). The structure of swarms was described in terms of growth stages, the development of primary and secondary sex characteristics and the accumulation of nutritional reserves. The results demonstrated that swarms contained a wide range of growth stages, but that small juveniles and mature males and females were absent. Swarm structure was interpreted as an equilibrium dependent on the relative proportion of time spent by each growth stage in the swarm habitat. This equilibrium swarm structure was very similar at different sites and times. Swarms dominated by small juveniles occurred at the northern sites in December 1991 following a period of eruption and new venting in April 1991. Equilibrium swarm structure had become re-established at these sites by March 1994. The function of swarming was considered. The results indicated that swarming was not associated with reproductive activity. The available evidence, though not conclusive, suggested that swarms were associated with feeding
Reproductive ecology of Bouvierella curtirama (Amphipoda: Eusiridae) from chemically distinct vents in the Lucky Strike vent field, Mid-Atlantic Ridge
No full textPopulations of the vent amphipod Bouvierella curtirama were compared from two sites in the Lucky Strike vent field on the Mid-Atlantic Ridge. The two sites (Sintra and Eiffel Tower) are chemically distinct, fed by different hydrothermal sources, but separated by only about 400 m. Both sites are characterized by dense beds of the mussel Bathymodiolus azoricus, though the proportion of methanotrophic and thiotrophic endosymbionts supported by the mussel and its isotopic composition vary significantly between the sites. Such differences presumably reflect the availability of primary resources and would be expected to impinge on other members of the mussel bed community, such as B. curtirama, which was abundant at both sites. A detailed comparative study of the amphipod showed that, although the overall population structure (in terms of growth stages) was similar at the two sites, reproductive output was significantly greater at Sintra, a result of females maturing at a smaller body size and producing more broods of a greater size. The reproductive output at both sites was relatively low, with a proportion of surviving females failing to mature. The plasticity of response of the two populations is discussed in relation to food availability (quantity and quality). Grazing predation, resulting in loss of antennal flagellum articles, was high at both sites. Such damage is discussed in terms of predation impact. Damage to the antennae of the holotype has resulted in an inaccurate species description, which is remedied here
The anemone, Nematostella vectensis, in Britain: considerations for conservation management
No full textThe genetic structure of the rare lagoonal sea anemone, Nematostella vectensis (Cnidaria; Anthozoa) in the United Kingdom based on RAPD analysis
No full textThe sea anemone Nematostella vectensis occurs in lagoons in the United States and along the southern and eastern coasts of the United Kingdom. In the United Kingdom it is considered rare and is threatened, principally through the destruction of lagoonal habitat. Random amplified polymorphic DNA (RAPD) data from populations across most of the rane of N. vectensis in the United Kingdom revealed that 61% of individuals had an identical genotype, the frequency of which varied from 0.01 to 1.00. These data provide strong evidence for predominantly clonal reproduction and for the existence of a 'general-purpose genotype' in the UK populations. Alternatively, the low levels of genetic variation observed in some N. vectensis populations may have resulted if they were founded from very few successful individuals from the United States. Analysis of molecular variance (amova) showed significant genetic differentiation between lagoons with no large-scale pattern of geographical variation. This result is consistent with occasional passive or anthropogenic dispersal of low numbers of individuals between lagoons followed by asexual proliferation of immigrants. Transplantation of individuals of the predominant (general-purpose) genotype, for conservation purposes, will probably stand a good chance of survival given its prevalence throughout the United Kingdom
Meiofauna in closed coastal saline lagoons in the United Kingdom: structure and biodiversity of the nematode assemblage
No full textCoastal saline lagoons are rare in North West Europe and tend to be closed, brackish water systems. Inthe United Kingdom they are small and isolated, each exhibiting extremely variable habitat conditions,both spatially and temporally. This paper represents the first species-level study of lagoonal nematodeassemblages in the UK. Samples were taken from seven ponds in a saline lagoon system on the southcoast of England in order to describe the nematode assemblage in relation to habitat type and to assessthe possibility of lagoonal specialisation. At each site samples were also taken, or data were alreadyavailable, for salinity, sediment granulometry, sediment organic carbon content, photosyntheticpigments and lagoon topography.A lagoonal specialist nematode fauna was not identified, but it was found that the nematode communitiesstrongly reflected the differences between environmental conditions in the lagoons. Sample andsite diversity were found to be relatively similar, but the importance of habitat networks was indicatedby the relatively high system diversity, species turnover being highest between lagoons with differentsalinity and/or granulometry regimes. Salinity was the principal factor correlated with assemblagestructure and species diversity was highest at the higher salinity sites. Median salinity (averaged fromweekly records over the previous 4 months) correlated more clearly with nematode assemblage structurethan salinity at the time of sampling. This shows the importance of considering historical as well ascontemporaneous data when undertaking ecological studies: Contemporary conditions may influencespecies fecundity, and therefore relative abundances, whilst historic conditions may influence speciesoccurrence through the effects of recruitment and survival
Persistent border: an analysis of the geographic boundary of an intertidal species
No full textThe biological performance of species close to their biogeographic boundaries is ofcritical interest in a period of rapid climate change and can inform predictions of future patterns ofdistribution. The classic view is that performance attributes (reproduction, growth, survival) willgradually decline from the centre towards the edge of a species range. A persistent discontinuity inthe distribution of the intertidal barnacle Chthamalus montagui on the central south coast of Englandhas enabled us to test hypotheses about its performance and recruitment as the range edge isapproached. Although adult density was reduced by over 5 orders of magnitude along a 200 km distance,there was little evidence of impaired performance at the range edge. There have been fluctuationsin abundance over the last 50 yr at shores approaching the border, which are associated withchanges in temperature and suggest thermal sensitivities. A study of recruitment in C. montagui andin other intertidal barnacles revealed a region of very low recruitment for all species close to the borderof C. montagui. We propose that reductions in larval supply caused by complex regional hydrographyand suboptimal habitat quality, not adult performance, is most likely responsible for a steepgradient in recruitment as the border is approached, although possible reductions in larval performancecannot be totally discounted. The location of ‘low recruitment cells’ caused by oceanographicprocesses that obstruct the dispersal of propagules needs to be identified when modelling the rate ofchange of biological assemblages and the location and spacing of reserves
Influence of recruitment and temperature on distribution of intertidal barnacles in the English Channel.
No full textMany warm-water (Lusitanian) species reach their limits in the central English Channel, failing to penetrateto the North Sea. We re-surveyed the eastern limits of the Lusitanian intertidal barnacles Chthamalus montaguiand C. stellatus, from 1994 to 2004, a decade of exceptionally high sea temperatures, and found range extensionson both sides of the Channel compared to the 1950s and 1970s. Annual recruitment of Chthamalus on theEnglish coast was monitored. There was a consistent gradient of low recruitment to the east of Portland Bill,with significant reductions coinciding with prominent headlands. Highest recruitment occurred during thewarmest years. Cluster analysis showed a high degree of similarity of annual recruitment within coastal cellssuggesting that local processes are also important. In 1999 we compared recruitment in the other commonintertidal barnacles, the boreal Semibalanus balanoides and the non-native Elminius modestus, with Chthamalus spp.All species showed low recruitment between Selsey Bill and Portland Bill, suggesting habitat limitations and/orhydrographic mechanisms. Annual recruitment of Chthamalus at existing limits on the Isle of Wight was positivelycorrelated with the number of days of westerly and south-westerly winds during the summer, coincidingwith the pelagic larval phase. A ‘pulse’ of high Chthamalus recruitment on the Isle of Wight, measured duringthe warm summer of 2000, reversed population decline. Only a higher frequency of such pulses will maintainpopulations at existing limits and increase the rate of range extension towards the North Sea. Such extensionwill be limited by lack of hard substrata, but proliferation of coastal defence schemes in recent years is increasingsuitable habitat for barnacles
Disturbance of intertidal soft sediment assemblages caused by swinging boat moorings
No full textThe impact of swinging boat moorings on intertidal benthic assemblages was investigated in a small estuary on the south coast of England. Mooring buoys fixed near low water mark on a muddy shore were attached to 5 m of galvanised steel chain and had not been let for 12 months. Core samples for macro-invertebrates and sediments were taken both within and outside the chain radius of each buoy. The assemblage structure, biomass and abundance of selected bird prey species were examined at a range of scales. The study revealed variation in the impact of mooring buoys relative to control areas at two different times of sampling. Prior to the removal of buoys, the assemblage structure within areas affected by the buoys was found to be significantly different from unaffected areas. The abundance of the amphipod Corophium volutator, an important bird prey species, was significantly less in the areas affected by the buoys. In the second sampling programme (15 months after removal of buoys), the impact of extant buoys remaining in commission was not detectable. Assemblage structure in areas from which buoys had been removed was distinct from control areas which had never had buoys. The removal of mooring buoys clearly affected the assemblage, yet convergence with control areas, indicative of recovery, was not complete after 15 months. It is suggested that the effect of swinging mooring chains scraping over the mud surface may modify sediments favouring the greater prominence of larger particles such as gravel and shell fragments. The ecological impact of swinging moorings on estuarine benthic assemblages in designated protected areas is discussed in the context of other spatial and temporal disturbances
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