1,721,210 research outputs found
Piddocks (Mollusca: Bivalvia: Pholadidae) increase topographical complexity and species diversity in the intertidal
No full textBioerosion increases the topographic complexity of soft rock habitats, thereby increasingspecies diversity. This increase in species diversity may either be associated with an increase incomplexity or may simply be a consequence of the increase in available surface area for colonisation.The influence of habitat modification by piddocks on intertidal species richness was investigatedthrough field survey using fractal geometry to assess topographical complexity. The relationshipbetween topographical complexity and species diversity was examined using the species spacingtechnique, which uses fractal dimensions to normalise the species richness data in relation to topographicalcomplexity. Six sites were chosen, comprising either clay or chalk substratum, which had arange of rock hardness. Through their rock-boring activities, piddocks significantly increased thetopographical complexity of the shore. Associated with this increase was an increase in species richnessat all sites. Using species spacing, at 5 of the 6 sites, the increased species richness was found tobe area-independent, with more species being observed than would be expected for a simpleincrease in surface area alone. However, piddocks are also known to significantly increase the erosionof soft rock habitats, many of which are regarded as being of particular conservation importancebecause of their rarity within Europe. Piddocks thus increase intertidal biodiversity while at the sametime significantly contributing to erosion of the substratum
Rocky intertidal communities: past environmental changes, present status and predictions for the next 25 years
No full textRocky shores occur at the interface of the land and sea. Typically they are open ecosystems, with steep environmental gradients. Their accessibility to man has rendered them susceptible to a variety of impacts since prehistoric times. Access can be regulated, however, and they are more amenable to management than open ocean habitats. This review uses examples from throughout the world to demonstrate the extent to which rocky shores have been, and are currently, affected by pollution (examples used are endocrine disrupters, oil, eutrophication), over-collection of living resources, introduced alien species, modification of coastal processes (coastal defences, siltation) and global change (climate, sea level). These impacts are put into the context of natural fluctuations in time and variability in space of both the environment and the organisms. The relative magnitudes of some anthropogenic disturbances differ between the industrialized, developed world and the developing world. For example, in developed, industrialized countries pollution based impacts should diminish over the next 25 years due to improved regulation and a reduction in older 'dirtier' heavy industry. Conversely, in many developing countries pollution will increase as a consequence of growth in the human population and industrialization. Except for large-scale disasters such as oil spills, pollution tends mainly to influence embayed coastlines. Chronic effects such as eutrophication can have broader-scale impacts over whole coastlines and elevated nutrient levels have also been implicated in a trend of increasing frequency of catastrophic kills due to harmful algal. Direct removal of living resources has had major effects on coastlines at both local and regional scales and is likely to increase over the next 25 years, especially in developing countries where rapidly expanding human populations will put further pressure on resources. Impacts from recreational activities are likely to increase with greater leisure time in wealthier regions of the world, and cheaper travel will spread these impacts to poorer regions. Invasions by alien species have increased in frequency during the last 20 years leading to some dramatic effects on native assemblages. Problems associated with alien species, especially pathogens, will continue to increase over the next few decades. The proportion of the coastline modified by artificial structures (breakwaters, seawalls, groynes) will increase because of coastal development and defences against sea-level rise and the greater frequency of storms. This will increase connectivity between areas of rocky habitat. Siltation will continue to increase due to urbanization of catchments and estuaries, and changes in agricultural practice. This may have considerable impacts at local and regional scales, favouring sediment tolerant organisms such as turf algae and anemones. In the future, greater frequency of environmental extremes is likely, including large-scale events such as the El Nino Southern Oscillation (ENSO). Global change in temperature, sea-level rise and increases in the frequency of storms will affect rocky shores throughout the world, but this will occur over long time scales; over the next 25 years most of the responses by rocky shore communities will mostly be quite subtle. Thus rocky shores will be subject to increasing degradation over the next 25 years. They are, however, less vulnerable than many other aquatic habitats due to their hard substratum (rock), their relative lack of large biogenic structures and to their generally open nature. They are also remarkably resilient, and recTheir susceptibility to both terrestrial and marine disturbances does make them more vulnerable than sublittoral and offshore habitats. There are considerable gaps in knowledge, particularly of certain microhabitats such as crevices, boulders, sand-scoured areas and rock pools. These have been much less studied than more accessible assemblages on open, freely draining rock. More research is needed to establish the effects of increasing sediment loads, ultraviolet radiation and introduced species on rocky shore communities. Strategic and applied research programmes should integrate field experiments and carefully selected monitoring programmes to verify management regimes. Hindcasting from the palaeo-record would be valuable, to compare rates of predicted change with periods when change was rapid in the past. This information could, in principle, be used to help conserve rocky shores through networks of marine protected areas and a general reduction of environmental pollution
Physical stress and biological control regulate the producer-consumer balance in intertidal biofilms
No full textEpilithic biofilms play a key role in marine ecosystems. They also provide a tractable system to investigate the relative roles of environmental stressors, bottom-up physicochemical factors and top-down biological control in regulating communities. Patterns of photosynthetic microbial biomass were recorded over a four-year period at several tidal levels on shores in the Isle of Man. Photosynthetic biomass and the abundance of diatoms were consistently greater during winter than summer. Biomass Was negatively correlated with insolation stress and air temperature, but was not correlated with grazing intensity, dissolved nutrients, sea temperature, or planktonic chlorophyll. Field experiments confirmed that reducing insolation stress led to substantial increases in photosynthetic biomass, predominantly of diatoms and macroalgal germlings. Reducing grazing intensity also led to considerable increases in photosynthetic biomass, but reducing desiccation stress or increasing nutrient availability had no effect. Although grazing can regulate microalgal biomass, seasonal patterns of grazing activity were driven by temperature and were decoupled from photosynthetic biomass. Our study demonstrates the importance of physiological stresses for the direct and indirect regulation of the balance between primary producers and consumers. Based on these findings, we present a model that combines the roles of stressors together with bottom-up forcing and top-down regulation in controlling communities on wave-exposed shores
Predation by small mobile aquatic predators regulates populations of the intertidal limpet Patella vulgata (L.)
No full textHighly mobile aquatic predators are known to forage in the intertidal during periods of immersion. There is limited quantitative information, however, on the extent to which these predators influence the abundance of grazing molluscs which are known to have a key role in structuring intertidal assemblages. Our preliminary video observations revealed that crabs and small fish were abundant on shores in southwest England during high-tide. We then used manipulative experiments to quantify the effect of small mobile aquatic predators on the abundance of limpets (Patella vulgata L.). On the lower shore at two moderately sheltered rocky shores three treatments were established: complete cage, partial cage (cage control) and uncaged (natural condition). The complete cages excluded all predators. The partial cage treatment allowed full access to small predators and the uncaged treatment allowed access to all predators. After two months, limpet abundance in uncaged and partial cage treatments had declined by around 50% compared to the complete cage treatment. Population structure also changed with survival of larger individuals being greater than smaller individuals in the open and partial cage treatments compared to the complete cage treatment. The effects of excluding predators were consistent at small (meters) and large spatial scales (kilometres) and hence, it would appear that the outcomes of our research are generally applicable to similar shores in the region.To explore the mechanism behind the differential effects of predators according to prey size, we compared the detachment force required to remove limpets of differing sizes from the shore. This was around four times greater for larger individuals than for smaller ones indicating that smaller limpets were more vulnerable to predation. These effects were also consistent between locations. Subsequent laboratory observations showed that the crabs Carcinus maenas (L.), Necora puber (L.) and Cancer pagurus (L.) which are locally abundant predators of limpets, had differing handling behaviour but were all highly efficient at removing limpets from substratum. Hence, shell width and attachment force appeared to be critical factors influencing the vulnerability of limpets to predation by these crabs. Limpets are known to control the abundance of macroalgae on shores in the North-east Atlantic and so our conclusions about the role of mobile predators in regulating the abundance of these grazers are important to our broader understanding of the ecology of these shores
Burrow morphology, biometry, age and growth of piddocks (Mollusca: Bivalvia: Pholadidae) on the south coast of England
No full textBiometry and growth of three piddock species Pholas dactylus, Barnea candida and B. parva, from chalk and clay substrata were investigated between 1999 and 2000 at five low shore locations along the south coast of England. Piddock burrow shape was significantly different (P < 0.01) amongst the locations. Burrows at Lyme Regis showed the largest (height/maximum diameter) ratio (4.86 +/- 2.00) whilst those at Compton the lowest (3.73 +/- 1.62). Using the method of Bhattacharya, the population structure of P. dactylus, B. candida and B. parva was separated into eight, three and five modal size classes, respectively. Age and shell growth were determined from the number and spacing, respectively, of annual growth lines present in acetate peel replicas of shell sections. The von Bertalanffy growth (VBG) equation fitted the size at age data obtained for P. dactylus and B. candida (L-infinity and K were 79.3 +/- 13.8 mm and 0.0011 +/- 0.22 and 29.6 +/- 1.5 mm and 1.17 +/- 0.47, respectively) whilst the size at age data for B. parva were linearly related and did not fit the assumptions of the VBG equation. Male and female gonads were mature and piddocks competent to spawn between June and September 1999, with settlement of juveniles observed between November 1999 and February 2000. A significant relationship between burrow aperture diameter and age of the occupant piddock was established for the three species. Burrow morphology and spatial distribution of burrows were influenced by substratum hardness and population density. Based on estimates at Lyme Regis, piddocks are capable of removing up to 41% of the shore substratum to a depth of 85 mm over their lifespan (12 years), significantly compromising the structural stability of the soft rock shores they inhabit and contributing to bioerosion
Use of the intertidal zone by mobile predators: influence of wave exposure, tidal phase and elevation on abundance and diet
No full textLinkages between predators and their prey across the subtidal-intertidal boundary remain relatively unexplored. The influence of tidal phase, tidal height and wave exposure on the abundance, population structure and stomach contents of mobile predatory crabs was examined on rocky shores in southwest Britain. Crabs were sampled both during the day and at night using traps deployed at high tide and by direct observation during low tide. Carcinus maenas (L.), Necora puber (L.) and Cancer pagurus (L.) were the most abundant species, being mainly active during nocturnal high tides. C. maenas was the only species that was active during nocturnal low tides, when it was observed mainly on the lower shore feeding on limpets. Individuals of all 3 species sampled during high tide were considerably larger than those sampled during low tide. Thus, sampling crab populations at low tide is likely to underestimate abundance and the extent of predation by crabs on rocky-shore assemblages. During immersion, the relative abundance of each species was influenced by exposure to wave action and tidal elevation. All species were more abundant on the lower shore; C. maenas and N. puber were more abundant in sheltered locations, while C. pagurus was more abundant in exposed locations. Analyses of stomach contents from individuals captured at high tide revealed that chitons and limpets were the most common hard-shell prey taxa in the diet of these predators. The relative abundance of prey in gut contents was, however, not correlated with patterns of prey abundance. Our study indicates the importance of crabs as key intertidal predators and illustrates the strong trophic linkages between the subtidal and intertidal zones, which is likely to be a key factor influencing community structure on European shores
Problems in extraction and spectrophotometric determination of chlorophyll from epilithic microbial biofilms: towards a standard method
No full textA variety of methods are available to extract chlorophyll from epilithic biofilms using solvents. The relative efficiency of these has not been determined simultaneously and there is no recognized standard procedure. In this paper techniques for sample collection, storage, preparation and extraction are reviewed and compared experimentally.Extraction of chlorophyll was incomplete unless biofilms were fully hydrated. This factor was highly significant for all the solvents tested, with at least three times more pigment being extracted from hydrated samples than from dry ones. Methanol was the most efficient solvent, releasing over 96% of the total chlorophyll during a single extraction; hot ethanol extracted 86%, while acetone extracted less than 50%. Sonicating samples during extraction did not release any additional pigment. Centrifuging to remove suspended material did not alter estimates and was not advantageous. Rugose rock surfaces released more chlorophyll than smooth ones. However, a simple method to quantify surface rugosity at an appropriate scale was not available.Based on these observations, a standard method for chlorophyll extractions from epilithic biofilms using 100% methanol at room temperature (20°C) is proposed. This technique requires considerably less supervision than previously preferred methods and gave a chlorophyll extract which was stable for 15 h
Spatial and temporal patterns of subtidal and intertidal crabs excursions
No full textHighly mobile predators such as fish and crabs are known to migrate from the subtidal zone to forage in the intertidal zone at high-tide. The extent and variation of these habitat linking movements along the vertical shore gradient have not been examined before for several species simultaneously, hence not accounting for species interactions. Here, the foraging excursions of Carcinus maenas (L.), Necora puber (Linnaeus, 1767) and Cancer pagurus (Linnaeus, 1758) were assessed in a one-year mark-recapture study on two replicated rocky shores in southwest U.K. A comparison between the abundance of individuals present on the shore at high-tide with those present in refuges exposed at low-tide indicated considerable intertidal migration by all species, showing strong linkage between subtidal and intertidal habitats. Estimates of population size based on recapture of marked individuals indicated that an average of ~ 4000 individuals combined for the three crab species, can be present on the shore during one tidal cycle. There was also a high fidelity of individuals and species to particular shore levels. Underlying mechanisms for these spatial patterns such as prey availability and agonistic interactions are discussed. Survival rates were estimated using the Cormack-Jolly-Seber model from multi-recapture analysis and found to be considerably high with a minimum of 30% for all species. Growth rates were found to vary intraspecifically with size and between seasons. Understanding the temporal and spatial variations in predation pressure by crabs on rocky shores is dependent on knowing who, when and how many of these commercially important crab species depend on intertidal foraging. Previous studies have shown that the diet of these species is strongly based on intertidal prey including key species such as limpets; hence intertidal crab migration could be associated with considerable impacts on intertidal assemblages
Impacts of anthropogenic stress on rocky intertidal communities
No full textRocky shores provide a harsh environment for marine organisms and we briefly discuss natural sources of variation in community structure before considering anthropogenic impacts in detail. We review impacts caused by (a) acute disturbances: oil spills, toxic algal blooms and (b) chronic disturbances: nutrient pollution, oil, heavy metals, pesticides, antifouling paints, collecting, trampling/habitat degradation, siltation and introduced species. Community level effects are emphasised throughout and illustrative examples are drawn from field-based case studies. Particular attention is given to the lessons learned from oil spills and the effect of chronic pollution by tributyltin on dogwhelks, the impacts of which ranged from the biochemical to community levels of organisation. Impacts are placed in a global and historical perspective and the potential for the recovery of shores under appropriate management is discussed. Finally we consider the relative merits of the multivariate and univariate approaches to studying impacted communities and suggest priorities for future research
The influence of epilithic microbial films on the settlement of Semibalanus balanoides cyprids – a comparison between laboratory and field experiments
No full textBarnacle cypris larvae show considerable exploratory behaviour prior to habitat selection. The influence of natural epilithic microbial fouling organisms on the settlement of Semibalanus balanoides cyprids (Crustacea: Cirripedia) was examined using laboratory and field based investigations. In choice chambers, cues from microbial films were important; cyprids preferred surfaces with a mature microbial film to either unfilmed surfaces or those with a developing film. Cyprids also discriminated between filmed rocks from different tidal heights, preferentially selecting those from the mid-shore which is their usual zone. Filmed surfaces which had previously been colonised by barnacles were selected in preference to unfilmed surfaces, but the presence of an adult barnacle did not enhance settlement on either filmed or unfilmed surfaces. However, laboratory experiments were not consistent with settlement in the field which was predominantly influenced by the proximity of conspecifics and by traces of previous barnacle colonisation. These factors increased settlement, and seemed to over-rule cues from microbiota within the film. Difficulties in the application of laboratory based studies to settlement in the natural environment are discussed
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