1,721,019 research outputs found
Seventy years' observations of changes in distribution and abundance of zooplankton and intertidal organisms in the western English Channel in relation to rising sea temperature
No full text1. Extensive changes in marine communities in southwest Britain and the western English Channel have been recorded during the past 70 years.2. Over the same period there was a climatic warming from the early 1920s, then a cooling to the early 1980s, with recent resumption of warming; the change in annual mean temperature was approximately ±0.5°C.3. Marked changes occurred in plankton community structure; the distribution of both plankton and intertidal organisms was affected, with latitudinal shifts of up to 120 miles; there were increases or decreases of 2–3 orders of magnitude in abundance.4. Warm water species increased in abundance and extended their range during periods of warming, while cold-water species declined or retreated; the reverse occurred during the period of cooling.5. Climate change can influence marine communities by a combination of: direct effect on the organisms; effects mediated by biotic interactions; and indirectly through ocean currents.6. From climate models that indicate rises of mean temperature of 2°C in the next 50 years, and from the observed changes, we can expect future latitudinal shifts of 200–400 miles in distribution of plankton, fish and benthos, with extensive restructuring of planktonic, pelagic and benthic communities.7. Species common now in the Bay of Biscay will become common in the English Channel; those presently restricted to the western English Channel could colonise the central Irish Sea; changes in community structure could lead to lower abundances of infaunal benthos and fish.8. To fully prove the effects of global warming, future changes in the marine biota must exceed those recorded in the 1950s and 1960s
Larval development of the intertidal barnacles Chthamalus stellatus and Chthamalus montagui
No full textTwo recently-distinguished species of Chthamalus (Cirripedia) are found on rocky shores in the north-eastern Atlantic: C. stellatus predominant on islands and headlands and C. montagui more abundant in bays. Larvae of the two species were produced in laboratory cultures to describe and compare the morphology and to allow identification in plankton samples. Nauplius larvae of C. stellatus are up to 30% larger than those of C. montagui. Differences in setation are minor. The two species are easily distinguishable from the size and shape of the cephalic shield. Chthamalus stellatus has a subcircular shield with longer body processes in later stages while C. montagui is more ovoid. The former develop more slowly in culture than the latter. Chthamalus stellatus larvae in a culture at 19 °C reached stage VI in 16 d compared to 11 d for larvae of C. montagui at the same temperature. The morphology and longer development time of C. stellatus larvae suggests adaptation to a more oceanic lifestyle and wider dispersal to reach more fragmented habitats than larvae of C. montagui
Multidecadal signals within co-occurring intertidal barnacles Semibalanus balanoides and Chthamalus spp. linked to the Atlantic Multidecadal Oscillation
No full textFew links have been established between the Atlantic Multidecadal Oscillation and long-term dynamics of marine systems due to the scarcity of sustained biological time-series with sufficient multi-decadal coverage. The abundances of co-occurring boreal and Lusitanian species of barnacle have been recorded annually at a rocky shore in Devon, southwest England since 1953. Multidecadal cycles in relative abundances of the cold-water Semibalanus balanoides and warm-water Chthamalus spp. are strongly correlated with both local sea surface temperatures, and a ‘Warm Index’ of barnacle abundance shows strong links to the basin-scale Atlantic Multidecadal Oscillation. In contrast there are weak or no observed relationships with the North Atlantic Oscillation for either species. The shorter lifecycle of S. balanoides compared to the chthamalids and the increase in spring and summer temperatures to which newly settled S. balanoides recruits have been exposed during the last decade are likely mechanisms by which barnacle densities are responding to low-frequency temperature variability expressed in the Atlantic Multidecadal Oscillation
Measuring surface complexity in ecological studies
No full textHabitat complexity is a potential structuring force in benthic communities. Different studies often estimate complexity in different ways, and it is not always clear how precise the separate techniques are. Here we review three methods of estimating surface complexity: stereo photography, profile gauges, and lengths of chain contoured over the substratum. We derived fractal dimensions for the quadrats in the rocky intertidal zone using each technique. Complexity estimates from chains and profile gauges were related, but neither technique was correlated with the results from stereo photographs. Stereo photographs appeared to overestimate complexity on smooth surfaces. The variance of fractal dimension estimates increased nonlinearly with the mean fractal dimension in each quadrat. Recommendations for the number of replicates needed for a reliable estimate of fractal dimension from a quadrat, therefore, vary as a function of surface complexity. Within the range of complexities typically encountered on rocky shores, as few as three profiles or sets of chains can produce relatively reliable estimates of fractal dimension. The most robust and time effective method, however, would be to sample using as many chain profile sets per quadrat as is logistically feasible. Given the changes in precision with surface complexity, comparisons between studies need to take careful note of the number of replicates and the average level of surface complexity. A null result (no relationship between surface complexity and an ecological variable) could be produced by imprecise estimates of surface complexity based on too few replicate measurements per quadrat
Beyond the predation halo: small scale gradients in barnacle populations affected by the relative refuge value of crevices
No full textHaloes of bare space around crevices used as refuges by predators are a feature of many rocky shores. The presence of small scale spatial gradients in the demographic structure of prey populations is hypothesized for the region adjoining predation haloes. It is also suggested that halo effects in prey populations will change in response to environmental constraints on predator foraging behaviour. These hypotheses were tested by examining gradients in barnacle population structure around crevices high and low on the shore. The probability of encountering a barnacle above the local median size always increased with distance from a crevice. Foraging at sites high on a shore is assumed to be more risky to individual whelks. Initial probabilities of recording a large barnacle near a crevice increased more rapidly over small spatial scales at sites high on the shore than at sites low on the shore. The implications of small scale gradients in prey populations are discussed with reference to the role of topographic complexity in mediating predator–prey dynamics
Long-term changes in the geographic distribution and population structures of Osilinus lineatus (Gastropoda: Trochidae) in Britain and Ireland
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
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Macroalgae contribute to the diet of Patella vulgata from contrasting conditions of latitude and wave exposure in the UK
Full text linkAnalysis of gut contents and stable isotope composition of intertidal limpets (Patella vulgata) showed a major contribution of macroalgae to their diet, along with microalgae and invertebrates. Specimens were collected in areas with limited access to attached macroalgae, suggesting a major dietary component of drift algae. Gut contents of 480 animals from 2 moderately wave exposed and 2 sheltered rocky shores in each of 2 regions: western Scotland (55–56°N) and southwest England (50°N), were analysed in 2 years (n = 30 per site per year). The abundance of microalgae, macroalgae and invertebrates within the guts was quantified using categorical abundance scales. Gut content composition was compared among regions and wave exposure conditions, showing that the diet of P. vulgata changes with both wave exposure and latitude. Microalgae were most abundant in limpet gut contents in animals from southwest sites, whilst leathery/corticated macroalgae were more prevalent and abundant in limpets from sheltered and northern sites. P. vulgata appears to have a more flexible diet than previously appreciated and these keystone grazers consume not only microalgae, but also large quantities of macroalgae and small invertebrates. To date, limpet grazing studies have focussed on their role in controlling recruitment of macroalgae by feeding on microscopic propagules and germlings. Consumption of adult algae suggests P. vulgata may also directly control the biomass of attached macroalgae on the shore, whilst consumption of drift algae indicates the species may play important roles in coupling subtidal and intertidal production
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