Limpet Abundance Research Articles

Nutrient conditions determine the strength of herbivore-mediated stabilizing feedbacks in barrens.

Abiotic environmental conditions can significantly influence the way species interact. In particular, plant-herbivore interactions can be substantially dependent on temperature and nutrients. The overall product of these relationships is critical for the fate and stability of vegetated ecosystems like marine forests. The last few decades have seen a rapid spread of barrens on temperate rocky reefs mainly as a result of overgrazing. The ecological feedbacks that characterize the barren state involve a different set of interactions than those occurring in vegetated habitats. Reversing these trends requires a proper understanding of the novel feedbacks and the conditions under which they operate. Here, we explored the role of a secondary herbivore in reinforcing the stability of barrens formed by sea urchin overgrazing under different nutrient conditions. Combining comparative and experimental studies in two Mediterranean regions characterized by contrasting nutrient conditions, we assessed: (i) if the creation of barren areas enhances limpet abundance, (ii) the size-specific grazing impact by limpets, and (iii) the ability of limpets alone to maintain barrens. Our results show that urchin overgrazing enhanced limpet abundance. The effects of limpet grazing varied with nutrient conditions, being up to five times more intense under oligotrophic conditions. Limpets were able to maintain barrens in the absence of sea urchins only under low-nutrient conditions, enhancing the stability of the depauperate state. Overall, our study suggests a greater vulnerability of subtidal forests in oligotrophic regions of the Mediterranean and demonstrates the importance of environment conditions in regulating feedbacks mediated by plant-herbivore interactions.

He i‘a make ka ‘opihi: Optimal Foraging Theory, Food Choice, and the Fish of Death

Efficiency-based frameworks have a long history in archaeological research and have been used particularly by zooarchaeologists when interpreting forager behaviour. The use of optimality models, such as the prey- and patch-choice models in Optimal Foraging Theory (OFT), have the ability to identify episodes of resource depression, but also behavioural anomalies in the archaeological record that deviated from predicted optimal behaviour. Deviations may be the result of social, cultural, or environmental factors. We investigated prehistoric harvesting of the culturally-important Hawaiian limpet (Cellana spp.) across fourteen sites on the windward, north coast of Moloka‘i, Hawaiian Islands. Prehistoric harvest of the three endemic limpet species (C. exarata, C. sandwicensis, C. talcosa) is compared with OFT-predicted harvesting, natural limpet abundance, and contemporary traditional gathering. Our results indicate that prehistoric limpet abundance does not reflect efficiency-based predictions or natural abundance of limpet populations. Ancient limpet harvesting in Hawai‘i is instead similar to present-day gathering and may have been shaped by social and cultural influences.

Origin and genetic diversity of the invasive mussel Semimytilus algosus in South Africa, relative to source populations in Chile and Namibia

Worldwide, the spread of alien species in marine ecosystems has increased, with mussels frequently being involved. In South Africa, 91 alien and 39 cryptic marine and estuarine species, from 17 taxonomic groups, are known. Of these, three are associated with major invasions, including the Pacific mussel, Semimytilus algosus, which has rapidly spread and colonised the lower portions of rocky shores on the west coast. Semimytilus algosus is indigenous to Chile and has been introduced to Namibia. To determine the source and likely mode of introduction of S. algosus, we analysed the population genetic structure of eight populations on the west coast of South Africa and Namibia, as well as three populations in the native Chilean range. Using cytochrome c oxidase subunit I, we collected sequence data from 226 individuals sampled across the 11 localities. We detected no evidence for founder effects, as the South African and Namibian populations had comparable genetic variation to those sampled in Chile, pointing to large effective population sizes and high propagule pressure in the region. It is probable that the Namibian population originated from Chile, and that introduction took place from there to South Africa via a single and substantial natural larval dispersal that breached the biogeographic barrier created by the Luderitz upwelling cell; but we cannot discount the possibility that introduction associated with oyster aquaculture played a role. Based on comparisons with Mytilus galloprovincialis, we predict S. algosus will continue to spread in South Africa but will be confined to temperate regions; reduce limpet abundance by monopolising primary substratum and because it is too small for them to occupy its shells; and supplement food sources for predators such as oystercatchers and dogwhelks.

Seasonal variability in the population structure of a habitat-forming kelp and a conspicuous gastropod grazer: Do blue-rayed limpets (Patella pellucida) exert top-down pressure on Laminaria digitata populations?

Kelp forests dominate wave-exposed rocky reefs along mid-to-high latitude coastlines. The distribution and structure of kelp forests is determined by a range of physical and biological processes operating across varying spatial and temporal scales. Many kelp forest systems are strongly influenced by herbivory, and overgrazing by urchins, in particular, is a recognised driver of kelp forest distribution and structure. The ecological significance of herbivory by kelp-associated limpets, however, has received far less attention. We quantified seasonal population dynamics of Laminaria digitata and the blue-rayed limpet Patella pellucida on two rocky shores in North Devon, UK. For the kelp, we quantified density, percent cover, morphology, standing biomass, elongation and erosion rates, and C:N and phenol content. For the limpet, we measured abundance, biomass, and morphology, and for the limpet-kelp interaction we recorded observable grazing damage on the blade. Both populations exhibited typical seasonality with kelp growth rates peaking in spring, maximum standing biomass observed in summer and increased erosion rates in autumn. Blue-rayed limpets, which were recorded within kelp holdfasts as well as on stipes and blades, recruited in spring and peaked in abundance in late summer, with length and biomass generally increasing through the year. The area of kelp blade damaged by limpet grazing was low (a maximum of ~4%) and relatively consistent throughout the year, and the number and size of grazing scars exhibited limited seasonality. Survey data from other L. digitata populations in the UK suggested that the limpet abundances recorded in North Devon were comparable with other sites in the region. Although the impact of P. pellucida grazing on kelp blade tissue appears to be minimal, further research into cavity grazing by limpets on the stipe and in the holdfast is needed to formerly assess the impact these cavities have on dislodgement and fracture rates, especially when increased occupancy and grazing coincides with periods of intense wave action. We conclude that while herbivory is an important processes acting upon many kelp populations globally, the grazing pressure exerted by P. pellucida on L. digitata is unlikely to strongly influence population structure on UK rocky shores.

The exploitation of limpets in a Mediterranean Marine Protected Area: assessing the effectiveness of protection in the intertidal zone

Limpets are intertidal keystone grazers and their overexploitation could have significant consequences for intertidal communities. Limpets are harvested around the Sinis Peninsula (Sardinia, Italy) but harvesting is prohibited within the “Penisola del Sinis - Isola di Mal di Ventre” Marine Protected Area (MPA). This work assesses the effects of human harvesting on the population dynamics of three common Mediterranean species of Patella, namely, P. rustica, P. caerulea and P. ulyssiponensis, testing the effectiveness of the MPA and the role of site accessibility in limiting the intensity of such harvesting pressure. In the period between June 2015 and August 2016, limpet abundance and size were recorded on a monthly basis by means of photographic frames within linear transects at ten sites spread out along the coastline of the Sinis Peninsula to assess growth and temporal patterns. Limpets older than two years are extremely rare in the study area. Limpets are more abundant within the MPA in comparison with non-protected areas and within less accessible sites in comparison with areas where the intertidal zone is easily accessible from land. Despite this, overall human-induced mortality in the area is high, indeed the pool of limpets observed with a mean density of 104.3 ± 9.7 limpets/m2 during the first survey was reduced by 99.2%in less than one year. This work demonstrates that human harvesting strongly affects the population dynamics of Patella species in the area and that within the MPA this stressor is not efficiently reduced.

Long-term fluctuations in intertidal communities in an Irish sea-lough: Limpet-fucoid cycles

Long-term cyclical changes in rocky shore community structure were documented over two decades at sheltered shores in Lough Hyne Marine Reserve, County Cork, Ireland. Three peaks of abundance were recorded for the limpet, Patella vulgata (1990-5, 2002-6 and 2010-14) with oscillations that varied in amplitude and frequency among sites. The cover of the fucoid Fucus vesiculosus varied inversely with limpet abundance and showed the strongest negative correlation with a lag time of 0–2 years. The species complex Fucus spiralis/guiryi showed a weaker correlation with a lag time of 1–2 years. Two other fucoid species showed no such negative correlations despite their close proximity to limpets within the lough's compressed tidal range. There was no relationship between overall barnacle cover (dominated by Austrominius modestus) and the limpet-fucoid cycles, suggesting that the shelter provided by A. modestus for algae to escape from limpet grazing pressure may not be necessary for these cycles to occur on wave-sheltered shores.

Shell alterations in limpets as putative biomarkers for multi-impacted coastal areas

During the last years, shell alterations in gastropods have been proposed as tools to be used in monitoring programs. However, no studies were so far performed investigating the relationships among shell parameters and classical biomarkers of damage. The relationship between shell alterations (biometrics, shape and elemental composition) and biomarkers (LPO and DNA strand break) was evaluated in the limpet L. subrugosa sampled along a contamination gradient in a multi-impacted coastal zone from southeastern Brazil. Statistically significant differences were detected among sites under different pollution levels. The occurrence of shell malformations was consistent with environmental levels of several hazardous substances reported for the studied area and related to lipid peroxidation and DNA damage. In addition, considering the low mobility, wide geographic distribution, ease of collection and abundance of limpets in coastal zones, this putative tool may be a cost-effective alternative to traditional biomarkers. Thus, shell alterations in limpets seem to be good proxies for assessing biological adverse effects in multi-impacted coastal zones.

Exploitation promotes earlier sex change in a protandrous patellid limpet, Patella aspera Röding, 1798.

Exploitation of organisms can prompt the reduction in the number and size of target populations consequently affecting reproductive output and replenishment. Here, we investigated the effects of exploitation on the population structure of a protandrous patellid limpet, Patella aspera, an overexploited Macaronesian endemic. Timed dives were used to collect animals across eleven islands of Macaronesia. Individuals were inspected for sex, size, and gonad stage. Using catch effort (time per person) per island coastal perimeter as a surrogate for exploitation intensity, we found that limpet abundance (CPUE) and mean size tended to decrease with exploitation intensity. When considering the sex of animals separately, the size of the largest male, but not females, decreased with exploitation. In contrast, the size of the smallest male remained relatively consistent, whereas the size of the smallest female decreased significantly with exploitation. As exploitation is mostly targeting larger individuals, results suggest that males are compensating the removal of larger females, by undergoing sex change at smaller and presumably earlier sizes. These results have wider implications for the conservation of P. aspera, as a reduction in female size will likely affect the numbers of oocytes produced, hence fecundity. Regulations promoting the protection of the larger‐sized animals should be enforced to safeguard the replenishment of the population.

Consistent patterns of spatial variability between NE Atlantic and Mediterranean rocky shores

Examining how variability in population abundance and distribution is allotted among different spatial scales can inform of processes that are likely to generate that variability. Results of studies dealing with scale issues in marine benthic communities suggest that variability is concentrated at small spatial scales (from tens of centimetres to few metres) and that spatial patterns of variation are consistent across ecosystems characterized by contrasting physical and biotic conditions, but this has not been formally tested. Here we quantified the variability in the distribution of intertidal rocky shore communities at a range of spatial scales, from tens of centimetres to thousands of kilometres, both in the NE Atlantic and the Mediterranean, and tested whether the observed patterns differed between the two basins. We focused on canopy-forming macroalgae and associated understorey assemblages in the low intertidal, and on the distribution of Patella limpets at mid intertidal levels. Our results highlight that patterns of spatial variation, at each scale investigated, were consistent between the Atlantic and the Mediterranean, suggesting that similar ecological processes operate in these regions. In contrast with former studies, variability in canopy cover, species richness and limpet abundance was equally distributed among spatial scales, possibly reflecting the fingerprint of multiple processes. Variability in community structure of low intertidal assemblages, instead, peaked at the largest scale, suggesting that oceanographic processes and climatic gradients may be important. We conclude that formal comparisons of variability across scales nested in contrasting systems are needed, before any generalization on patterns and processes can be made.

Effects of chemical disturbances on intertidal benthic assemblages

Contamination is a particular harmful type of chemical disturbance and predicting their effects on natural systems is very complex. Effects of disturbances vary in space and time and depend, among other things, on the type and age of organisms, the habitat being studied and the complex interactions occurring in the systems. Most impact analyses of contaminants are however still done with limited number of selected organisms under laboratory conditions. Manipulative experiments done in situ are important to measure ecologically relevant responses of contaminant effects on marine systems. Ecological approaches on contamination studies, accounting for interactions among species and the environment are essential to understand how such disturbances affect systems. We evaluated the effects of bleach and permethrin, two common and pervasive contaminants, on intertidal benthic assemblages in two different successional stages, mature and young. There were no impacts on the overall structure of assemblages, regardless of their age. The lack of effects on the structure of assemblages might be due to the intrinsic characteristic of the habitat studied, which provide few sinks for contaminants, as well as the inherent features of the organisms themselves. Bleach did cause, however, a decrease in the abundance of limpets, which can have further consequences to these systems. This study shows the importance of studies on chemical disturbances done under relevant natural scenarios and that efficient management policies of natural systems will only achieve successful responses with properly designed experiments under natural conditions.

Habitat Preference and Population Ecology of Limpets Cellana karachiensis (Winckworth) and Siphonaria siphonaria (Sowerby) at Veraval Coast of Kathiawar Peninsula, India

Present study reports the habitat preference and spatiotemporal variations in the population abundance of limpets Cellana karachiensis and Siphonaria siphonaria inhabiting rocky intertidal zones of Veraval coast, Kathiawar Peninsula, India. The entire intertidal zone of the Veraval coast was divided into five microsampling sites based on their substratum type and assemblage structure. Extensive field surveys were conducted every month in these microsampling sites and the population abundance of two limpet species was analyzed using belt transect method. The results revealed that C. karachiensis was the dominating species at microsampling Site-1 (having rocky substratum) possibly due to its ability to tolerate high desiccation, salinity, and temperature fluctuations, while the S. siphonaria was found to be the most dominating species at microsampling Site-2 (having rocky substratum with abundant algal population) possibly due to their preference for the perpetual wet areas. The study also indicated that S. siphonaria preferred upper littoral zone where the green algae were abundant while C. karachiensis preferred the spray zone, where it faces almost no competition for space and food with other molluscs. The condition of the spray zone is very harsh for other species to survive.

Spatial niche differentiation and coexistence at the edge: co-occurrence distribution patterns in Scurria limpets

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 483:185-198 (2013) - DOI: https://doi.org/10.3354/meps10293 Spatial niche differentiation and coexistence at the edge: co-occurrence distribution patterns in Scurria limpets Moisés A. Aguilera1,*, Nelson Valdivia2, Bernardo R. Broitman1 1Centro de Estudios Avanzados en Zonas Áridas (CEAZA), Facultad de Ciencias del Mar, Universidad Católica del Norte, Larrondo 1281, Coquimbo, Chile 2Instituto de Ciencias Marinas y Limnológicas and Laboratorio Costero de Recursos Acuáticos Calfuco, Facultad de Ciencias, Universidad Austral de Chile, Campus Isla Teja s/n, Valdivia, Chile *Email: moises.aguilera@ceaza.cl ABSTRACT: Examining the co-occurrence of taxonomically similar species can provide important information about their niches and coexistence. Segregation at smaller scales can be especially relevant for grazers living at the edge of their geographic distribution, because environmental factors can lead to similar distribution. Related grazer species may show dispersive, i.e. uniform, distribution at small scales (few centimetres) to reduce interference among individuals. We examined intra- and interspecific spatial distribution and habitat use in 2 phylogenetically related intertidal limpets, Scurria viridula and S. zebrina, at the polar and equatorial edge of their geographic distribution, respectively, and in S. araucana, a widely distributed species that overlaps the range of the other 2 species across the southeastern Pacific. S. viridula and S. zebrina overlapped in a narrow geographic zone (ca. 250 km) and reached relatively similar densities and sizes. Intraspecific spatial structure estimated through autocorrelation and individual-to-individual distances was random for S. viridula and variable for S. zebrina and S. araucana, depending on the scale considered; S. zebrina was aggregated at the individual-to-individual distances, while S. araucana was mostly random at this scale. Segregated distribution between S. viridula and S. zebrina was observed at the finer scale, whereas the association with S. araucana was random. Abundance of limpets loosely followed major habitats, namely bare rock and the alga Mazzaella laminarioides, which showed patchy distributions. We suggests that similarity in population traits between S. viridula and S. zebrina found in the overlap zone may be compensated by small-scale spatial segregation. Thus, at the edge of their geographic distribution, coexistence between related species may be influenced by spatial niche differentiation driven by habitat suitability or competition. KEY WORDS: Coexistence · Geographic edge · Grazers · Habitat type · Niche partitioning · Nearest neighbour · Spatial autocorrelation Full text in pdf format Supplementary material PreviousNextCite this article as: Aguilera MA, Valdivia N, Broitman BR (2013) Spatial niche differentiation and coexistence at the edge: co-occurrence distribution patterns in Scurria limpets. Mar Ecol Prog Ser 483:185-198. https://doi.org/10.3354/meps10293 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 483. Online publication date: May 30, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Biogeographical patterns in limpet abundance and assemblage composition in New Zealand

New Zealand is an isolated landmass which straddles two major marine biogeographic provinces, across which eleven biogeographic regions have been identified. It also supports a high biodiversity of endemic rocky intertidal species. Although the distributions of many of these species were qualitatively described several decades ago, little quantitative data on abundance, distribution and diversity has been collected across a range of spatial scales from local to biogeographical. Without such data it is difficult to assess range dynamics and connectivity of endemic and climate-sensitive species and assemblages, and thus predict responses to future impacts of climate warming, sea level rise, coastal squeeze and ocean acidification. This paper documents the geographic distributions, abundances and assemblage patterns of intertidal limpets at 63 sites around the New Zealand coast. Limpets are key functional components of most temperate ecosystems, influencing patterns of invertebrate–macroalgal dominance, carbon cycling and biodiversity. In contrast to continental-scale studies in other temperate systems, limpet assemblages were not more similar at the level of the biogeographic province, and only weak associations were found with biogeographic region. Limpet assemblages did differ between sites, but no spatial pattern was evident. Species distributions and assemblage structures did also not appear to be strongly influenced by environmental factors including temperature, coverage of key structural taxa including barnacles, mussels and macroalgae, or other potentially competing grazers. Limpet diversity was highest at some exposed locations, but there was no national trend. In general, the high variability we observed in individual species abundances at local, regional and biogeographic scales suggests that small scale, local factors rather than broad biogeographic drivers determine New Zealand rocky intertidal limpet assemblages. This creates a challenge for ecological forecasting of future responses to global environmental change.

Exploitation of intertidal grazers as a driver of community divergence

Summary 1. The possibility that different assemblages of species may represent alternative stable states has been the subject of much theoretical and empirical work. Alternative stable states may in theory arise from a perturbation of sufficient magnitude that pushes an assemblage from one stable equilibrium point to another. Overfishing is one such disturbance that can lead to cascading community‐level effects. Yet, whether these different assemblages represent alternative stable states or are the consequence of chronic disturbance from fishing is still a matter of debate. Understanding the mechanisms that drive community stability is fundamental if we are to assess the consequences of anthropogenic impacts on the structure and function of ecosystems to better inform management of disturbed habitats. 2. To investigate the extent to which present‐day community state is stable versus being maintained by chronic exploitation, we manipulated the time and intensity of physical disturbance and grazing by limpets in a system where over‐harvesting of limpets has led to a regional‐scale shift in community structure to one in which algal turfs have replaced barnacles as the primary space occupier in the mid‐intertidal. 3. After a 1‐year period since disturbance was applied, assemblages in disturbed areas were significantly different from undisturbed areas, but the timing of disturbance and its intensity had little effect on the outcome of succession. Undisturbed areas were highly resistant to new colonization and persisted unchanged throughout the study period. 4. Manipulation of limpet abundance in disturbed patches showed that, where present, limpets successfully prevented the recolonization of space by algal turfs. Moreover, there was evidence that grazing by limpets at the turf/open‐rock boundary effectively pushed the turfs back, extending the area of open‐rock. 5. Synthesis and applications. Our findings provide evidence that in this system the dominance by algal turfs does not represent an alternative stable state but that chronic exploitation of limpets leads to the persistence of this community. Conservation strategies aimed at protecting or enhancing limpet abundances (e.g. no‐take marine reserves) should allow the gradual restoration of this community to its pre‐disturbed state.

Predation: a regulating force of intertidal assemblages on the central Portuguese coast?

Predation has long been recognized as an important biological force driving community patterns in intertidal rocky shores throughout the world. Little is known, however, about the role of predation by mobile marine predators in shaping intertidal prey populations in Portuguese rocky shores. The abundance and population structure of crabs were assessed during nocturnal low-tides on two rocky shores to characterize potential predator species. To assess the effect of predation on intertidal species including limpets, barnacles and mussels, predator exclusion experiments using full cage, partial cage and no cage treatments, were set up for two months on two shores on the central Portuguese coast. Pachygrapsus marmoratus (Fabricius) and Eriphia verrucosa (Forsskål) were the most abundant crabs. Results from predator exclusion experiments suggested that predators do not exert a significant control on abundance of limpets, mussels or barnacles on the midshore during the experimental period. Despite the fact that these crabs are known to feed on the analysed prey, several factors may account for the observed absence of impact on prey abundance and these are discussed.

Predation by small mobile aquatic predators regulates populations of the intertidal limpet Patella vulgata (L.)

Highly 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.

Subsidy by Ascophyllum nodosum increases growth rate and survivorship of Patella vulgata

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 366:43-48 (2008) - DOI: https://doi.org/10.3354/meps07453 Subsidy by Ascophyllum nodosum increases growth rate and survivorship of Patella vulgata Andrew J. Davies1,2,*, Mark P. Johnson1,3, Christine A. Maggs1 1School of Biological Sciences, Queen’s University, 97 Lisburn Road, Belfast BT9 7BL, UK 2Present address: Scottish Association for Marine Science, Dunstaffnage Marine Laboratory, Oban, Argyll PA37 1QA, UK 3Present address: The Martin Ryan Marine Science Institute, National University of Ireland, University Road, Galway, Ireland *Email: andrew.davies@sams.ac.uk ABSTRACT: Limpets, predominantly Patella vulgata, have been associated with damaged or receding canopies of Ascophyllum nodosum. Although damage results from limpet grazing, the benefits that limpets gain from this behaviour are unclear as A. nodosum is thought to be well defended from grazers by anti-herbivore compounds. In the present study, P. vulgata individuals were enclosed at densities between 80 and 320 m–2 at 2 sites within Strangford Lough, Northern Island. Limpet growth and limpet survival were compared between unsubsidised controls and treatments in which limpet diets were subsidised by fronds of A. nodosum. When subsidised, limpet residual growth rates were significantly higher and mortality was lower than in unsubsidised control treatments. Individual limpets consumed a similar amount of A. nodosum regardless of limpet density. Higher densities of limpets, therefore, consumed more A. nodosum per replicate. The effects of A. nodosum in maintaining limpet densities could resonate through sheltered rocky communities. The importance of a macroalgal subsidy in supporting limpet populations may have been underestimated or overlooked in earlier studies. Therefore, the extensive and productive macroalgal canopies that characterise many sheltered temperate rocky shores could be more sensitive to increased limpet abundances than previously thought. KEY WORDS: Limpets · Grazing · Fucoid · Subsidy · Biomass · Phlorotannin Full text in pdf format PreviousNextCite this article as: Davies AJ, Johnson MP, Maggs CA (2008) Subsidy by Ascophyllum nodosum increases growth rate and survivorship of Patella vulgata. Mar Ecol Prog Ser 366:43-48. https://doi.org/10.3354/meps07453 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 366. Online publication date: August 29, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.

The effects of temperature on producers, consumers, and plant–herbivore interactions in an intertidal community

Although global warming is acknowledged as a primary threat to populations and communities, the impact of rising temperature on community structure remains poorly understood. In this study, we investigated the direct and indirect effects of temperature on epilithic primary producers (micro- and macroalgae) and an abundant consumer, the rough limpet Lottia scabra, in the rocky intertidal zone in central and northern California, USA. We factorially manipulated temperature and limpet abundance in the field to determine the effects of temperature on herbivore growth and mortality, algal abundance, and the strength of plant–herbivore interactions. Microalgal growth was positively affected by shading at both locations, and negatively affected by limpet grazing at Pacific Grove but not at Bodega Bay. Macroalgae were only abundant at Bodega Bay, where changes in abundance were negatively related to grazing and independent of temperature. Despite temperature-related changes in microalgal food supply, there were no direct or indirect effects of temperature manipulation on L. scabra growth or mortality. Furthermore, temperature did not alter the importance of herbivory at either site. These results indicate that the influence of increasing temperature, as is predicted with climate change, will have differential effects on producers and consumers. However, thermal effects at one trophic level do not necessarily propagate through the food web to other trophic levels.

The area‐independent effects of habitat complexity on biodiversity vary between regions

AbstractPotential explanatory variables often co‐vary in studies of species richness. Where topography varies within a survey it is difficult to separate area and habitat‐diversity effects. Topographically complex surfaces may contain more species due to increased habitat diversity or as a result of increased area per se. Fractal geometry can be used to adjust species richness estimates to control for increases in area on complex surfaces. Application of fractal techniques to a survey of rocky shores demonstrated an unambiguous area‐independent effect of topography on species richness in the Isle of Man. In contrast, variation in species richness in south‐west England reflected surface availability alone. Multivariate tests and variation in limpet abundances also demonstrated regional variation in the area‐independent effects of topography. Community composition did not vary with increasing surface complexity in south‐west England. These results suggest large‐scale gradients in the effects of heterogeneity on community processes or demography.

Sampling design begets conclusions: the statistical basis for detection of injury to and recovery of shoreline communities after the 'Exxon Valdez' oil spill

The joint effect of multiple initial decisions made about sampling design in evaluation of environmental impacts using observational field assessments influences the ability to detect and ac- curately estimate responses. The design can dictate in advance whether the study can identify even large impacts that truly exist. Following the 'Exxon Valdez' oil spill in 1989, 4 separate studies of ef- fects of the spill on the intertidal biota were conducted. Studies overlapped sufficiently in geographic area, shoreline habitat, and biological response variables to permit contrasts showing how the aggre- gate of multiple design decisions led to differences in conclusions. The SEP (Shoreline Ecology Pro- gram) supported by Exxon and the CHIA (Coastal Habitat Injury Assessment) funded by the Exxon Valdez Oil Spill Trustee Council shared a core approach of establishing a stratified random design of site selection. The Exxon-supported GOA (Gulf of Alaska) study and the NOAA (National Oceano- graphic and Atmospheric Administration) Hazmat (Hazardous Materials) study both chose to employ subjective choices of fixed sites. Despite many common goals, these 4 studies differed greatly in: (1) sampling effort (area covered per sample quadrat, sample replication within sites, numbers of study sites per category, numbers of samplings, and total areas sampled) and sampling design (philo- sophy of targeting sampling effort, complete randomization versus matched pair designs, sampling frame, treatment of habitat heterogeneity within sites, interspersion of sites, and control of shoreline treatment and oiling intensity); (2) analytical methodology (analysis of covariance versus paired designs, treatment of subsamples as replicates in F-ratios, logic of inferring recovery, and power cal- culations); and (3) choice of biological response variables (taxonomic level of analysis, aggregating versus splitting separate communities, and scope of communities and habitats examined). The CHIA and NOAA Hazmat studies of epibiotic responses in sheltered rocky shores of Prince William Sound made several decisions to enhance detection power and produced similar conclusions about large reductions in total biotic cover of intertidal space, Fucus cover, mussel abundance, abundance of the limpet Tectura persona and a balanoid barnacle, and increases in open space and abundance of an opportunistic barnacle, Chthamalus dalli. In contrast, the SEP study of this same habitat and geo- graphic region adopted design choices resulting in lower power of detection in 12 (vs CHIA and vs NOAA Hazmat) of 15 separate decisions (with one tie in each contrast). Accordingly, the SEP study was able to detect declines only in Fucus cover and occasionally in total limpet abundance but not in total epifaunal or mussel or balanoid barnacle abundance and, unlike the results of the other 2 stud- ies, most of the taxa analyzed showed apparent increases rather than decreases from oiling and shoreline treatment. The more powerful GOA and CHIA studies of impacts of oiling in the Gulf of Alaska, where oil grounded 1 to 8 wk later and in more weathered condition than in Prince William Sound, showed more consistent and larger reductions in intertidal biota in the sheltered rocky habitat than did the SEP study of Prince William Sound. Thus, the combined effects of many design decisions that reduced power to detect impacts in the SEP study led to failure to demonstrate large impacts of the spill documented by other studies of the same habitat in the same and the more remote region.