Shore Assemblages Research Articles

Spatio-temporal patterns in stable isotope composition of a benthic intertidal food web reveal limited influence from salt marsh vegetation and green tide

Assessing fluxes of matter and energy in food webs within and across benthic habitats is important to understand the ecological functioning in bays and estuaries, where the productivity is favoured by a wide diversity of primary producers. The temporal variability (March vs September 2019) in the carbon and nitrogen stable isotope composition of primary food sources and benthic invertebrates consumers was investigated in a large intertidal area (Western English-Channel, France). The study area is influenced by megatidal conditions and characterised by salt marshes in the sheltered part, and seasonal Ulva spp. blooms. The spatio-temporal variability in the structure of the benthic food web was analysed at the scales of both the whole bay and the different assemblages, which constitute the mosaic of habitats. Inferences on potential sources fuelling the food web were supported by spatio-temporal patterns based on covariations and stable isotope trajectory analysis. Results highlighted that phytoplankton, microphytobenthos and SOM were, most likely, the main food sources. The trophic connectivity between salt marsh and benthic habitats within the bay was limited to some macrofauna species inhabiting muddy creeks within the salt marsh. Unexpectedly, the influence of Ulva spp. blooms appeared also limited. Spatial patterns illustrates the constancy of the spatial variability in the benthic pelagic coupling, with a higher influence of microphytobenthos in the upper shore compared to low shore assemblages. This first attempt to characterize intertidal benthic food web constitutes a relevant baseline for the conservation of the bay of Saint-Brieuc where a national Nature Reserve has been created in 1998 for the conservation of overwintering birds. The spatial and temporal patterns of the benthic food web observed in this study (1) confirm the importance to consider food web variability at spatial and temporal scales from sampling designs to data analysis, and (2) demonstrate the ability of the stable isotope trajectory analysis framework to highlight food web dynamics.

Natural and anthropogenic factors as possible drivers of variability in rocky shore assemblages at multiple spatial scales

Spatial and temporal variability in rocky shore assemblages at multiple scales can be driven by natural factors and anthropogenic disturbances, operating either separately to each other or in complex combinations. Using the shallow subtidal rocky habitat in Ilha Grande Bay (southeastern Brazil) as a model system, this study analyzed five natural and five anthropogenic variables as possible drivers of variability of cover in rocky shore assemblages, focusing on the following questions: (i) Which are the relevant horizontal scales of variation in assemblage structure?; (ii) Are patterns of horizontal variation consistent across a small depth range?; (iii) Are there significant relationships between spatial patterns of macroalgae and macroinvertebrates, and their potential natural and anthropogenic drivers? These issues were addressed through a hierarchical sampling strategy including five horizontal scales, namely quadrat (0.4–3 m), point (3–10 m), site (100–350 m), island (500–1000 m) and area (2000–6500 m), repeated at two depths (1–2 m and 3.5–4.5 m). The correlations of cover data of 21 groups of organisms and five natural and five anthropogenic variables were analyzed. Assemblages showed relevant variation among quadrats, points and sites, at both depths, while variation at the area scale was relevant only at 3.5–4.5 m depth, indicating that patterns of horizontal variation were not fully consistent between depths. Substrate rugosity, rocky shore extension, water movement, percentage of deforested land area and distance to urban center were the environmental variables that most explained spatial patterns of the assemblages. Our study highlights the potential role of such variables as drivers of variation in rocky subtidal assemblages at multiple spatial scales. For environmental protection programs, relevant scales of variation of target populations and assemblages need to be considered, to effectively capture their dynamics and underlying processes.

Latitudinal patterns of species diversity on South American rocky shores: Local processes lead to contrasting trends in regional and local species diversity

AbstractAimWe evaluated whether patterns of species diversity (α, β and γ) of rocky shore assemblages followed latitudinal gradients (i.e. LDGs) along the South American coasts, and tested hypotheses related to potential processes sustaining or disrupting the expected LDG pattern at various spatial scales.LocationCoasts of South America.TaxonMacroalgae and sessile/slow‐moving macrofauna on intertidal rocky shores.MethodsWe evaluated changes in species composition across 143 sites. The degree of replacement and loss of species at different spatial scales (i.e. coasts, regions and sites) were estimated to help distinguish among ecological, historical and evolutionary hypotheses for explaining LDGs. Furthermore, components of diversity and taxonomic distinctness were measured, and variability in these measures was decomposed using analysis of covariance. Finally, we examined relationships between diversity and a suite of environmental and anthropogenic variables to identify potential mechanisms that may be responsible for the reported spatial relationships.ResultsSpecies composition varied with latitude, and this variability was relatively consistent on both coasts. At all spatial scales, replacement of species was the dominant phenomenon (>95%), rather than loss in the total number of species (<5%). LDGs were strongly dependent on the diversity component and the spatial scale: generally, positive for regional β‐diversity, negative for α‐diversity and site β‐diversity. Sea surface temperature (SST) was the variable that best explained patterns of diversity along both coasts (14%–22%), but other regional and local environmental variables associated with river discharges, upwelling, confluence of currents, tides and anthropogenic pressures also accounted for an important portion of variation (5%–14% each).Main conclusionsSpecies diversity of South American rocky shores followed, with interruptions, LDGs. The trend of those LDGs, however, depended on the scale and metric used to describe diversity. It is proposed that patterns of LDGs at various scales are not the result of a single overarching process but are strongly influenced by local and regional processes. Although the most evident environmental gradient was the decrease in SST towards the south, it was demonstrated that regional and local environmental variables were also important for understanding the increase in regional β‐diversity towards the tropics.

The role of competitor, stress-tolerant and opportunist species in the development of indexes based on rocky shore assemblages for the assessment of ecological status

Abstract The existence of three different ecological strategies (competitor, stress-tolerant, opportunist) has been widely recognized in the scientific literature and in the development of several biotic indexes using marine macroinvertebrates. However, its use has been totally neglected in the creation of indexes dealing with macroalgal assemblages and developed to fulfill the requirements of the European Water Framework Directive. In this study we apply a new method considering these different ecological strategies to assess the Ecological Status (ES) in rocky shores, which are mostly macroalgal-dominated. We use a large data set consisting of 653 samples collected between 1999 and 2017 in Catalonia (northwestern Mediterranean). In this approach we distinguish four basic strategies (competitor, indifferent, stress-tolerant and opportunist). Our results emphasize the importance in the distinction between competitor and stress-tolerant species when calculating the ES and highlight the importance of good natural history knowledge prior to appropriately assign every species to the proper ecological strategy. On the other hand, the comparison of ES obtained with the application of the new method based on the four strategies and the Ecological Evaluation Index (EEI-c) and R/P ratio Index (R/P rt. I) shows that the combination of eco-physiological traits, morphology and life-history strategies involved in EEI-c and R/P rt. I indices does not work in detecting differences in ES. Finally, if we take into account not only the algae but also the invertebrates that sometimes are dominant organisms in rocky shore assemblages (e.g. mussels), results become more accurate.

Algal Epibionts as Co-Engineers in Mussel Beds: Effects on Abiotic Conditions and Mobile Interstitial Invertebrates

Mussels and macroalgae have long been recognized as physical ecosystem engineers that modulate abiotic conditions and resources and affect the composition of rocky shore assemblages. Their spatial distributions in the intertidal zone frequently overlap, as many algal species thrive as epibionts on mussel beds. Nonetheless, their potential for combined engineering effects has not been addressed to date. Here we illustrate that Porphyra sp.—a desiccation-resistant macroalga that develops mostly epiphytically onto mussel beds—affects temperature, desiccation levels, and mobile interstitial invertebrates in mussel beds. Specifically, we observed that Porphyra cover (a) reduced temperature at the surface of the mussel bed but not at their base, (b) reduced desiccation both at the surface and base of the mussel bed and, (c) increased the densities of an abundant interstitial species—the amphipod Hyale grandicornis—in several study sites/dates. Additionally, we found that the positive responses of these grazing amphipods to Porphyra were driven by physical habitat modification (engineering) rather than food availability. This suggests that co-engineering by Porphyra and mussels generates abiotic states and focal species responses that would not be predictable from their individual effects. We expect that increased appreciation of co-engineering aids our understanding of complex ecological dynamics.

A species distribution model for Paracentrotus lividus: predicted projections of habitat suitability

A species distribution model for Paracentrotus lividus: predicted projections of habitat suitability

Allometric differences on the shell shape of two scorched mussel species along the Atlantic South American Coast

Scorched mussels (Bivalvia: Mytilidae) are an important component of rocky shore assemblages around the world. The mussel beds of the mid-intertidal coasts of the south-western Atlantic are composed of two species of scorched mussels, which dominate the physiognomy and structure of the rocky shore communities. The present study investigates the variation in the shell-shape allometric trajectories of both species of mussels throughout their distributional range in the southwestern Atlantic coast, from latitude 34°S to 53°S. Shells of Brachidontes rodriguezii were collected at two Uruguayan localities and four Argentinean localities, while shells of Perumytilus purpuratus were collected at six Argentinean localities. Shell shapes of the specimens were studied by geometric morphometrics using landmark and semi-landmark methods. Different evolutionary histories and thermal regimes characterize these two species. Brachidontes rodriguezii seems to have a long history in the region and is present in a restricted area, the warm temperate region of the south-western Atlantic, while P. purpuratus seems to have a recent history and is present in a wide thermal range, involving the cold-temperate regions of the south-western Atlantic and south-eastern Pacific and the warm-temperate region of the south-eastern Pacific. Based on these considerations, we prompt the hypothesis that allometric trajectories of P. purpuratus shell shape is more variable and adapted to a specific habitat than B. rodriguezii. The impact of allometry was larger in P. purpuratus than in B. rodriguezii. Graphical evidence was gathered, showing that these two species differ in allometric growth forms and that the allometric shell morphology changes reflect environmental constraints and adaptation. While the intertidal mussel beds of the South American coasts are ecologically similar in appearance, we found that the allometric variation of the scorched mussels occurs in response to diverging evolutionary processes such as phenotypic plasticity in P. purpuratus and canalization in B. rodriguezii.

Intertidal zonation and latitudinal gradients on macroalgal assemblages: Species, functional groups and thallus morphology approaches

Macroalgae are unavoidable biological elements when monitoring and assessing costal environments. However, these tasks can be difficult to address because macroalgae a) present a high natural variability across a range of spatial and temporal scales, b) they imply a high sampling and laboratory processing effort and good taxonomical expertise (as they are a very diverse group of species), and c) there is insufficient knowledge about their structural and functional characteristics. This work addressed how the vertical (intertidal zonation) and horizontal (latitudinal gradient) variability of macroalgae assemblages are structured across continental Portugal, as well as how some surrogates for species-level biodiversity measures (namely functional groups and thallus morphology approaches) respond to such large-scale variability. Particularly, it was tested if intertidal zonation patterns are higher than fine-scale horizontal variation, and however, if vertical variation decreases along broad-scale horizontal variation. To do so, cover per species was taken (using a photographical and GIS methodological approach) from five sites located along the shoreline and along respective upper- mid- and lower-intertidal zones. The work findings include that both intertidal and latitudinal gradients impose deep structural changes on assemblages patterns. That is, broad-scale processes along Portuguese latitudes act as strongly as vertical stress gradients on assemblages patterns. Functional groups and thallus morphology approaches were useful to generalize the latitudinal assemblages patterns, where some groups emerge at the expense of others, and may improve biodiversity understanding and ecological synthesis. Because these surrogates decrease taxonomical expertise needs and can provide insight into the functional structure of macroalgal communities, their patterns founded may be particularly useful as reference data for further monitoring, so that shifts in such patterns might represent early warning surrogate approaches to detect environmental impact changes. Ultimately, to generate broader databases on rocky shore assemblages diversity (from species-level to functional groups and thallus morphologies approaches) can be useful for large-scale comparisons and for establishing ecological reference conditions, including for monitoring programs and environmental impact studies.

Distinguishing globally-driven changes from regional- and local-scale impacts: The case for long-term and broad-scale studies of recovery from pollution

Marine ecosystems are subject to anthropogenic change at global, regional and local scales. Global drivers interact with regional- and local-scale impacts of both a chronic and acute nature. Natural fluctuations and those driven by climate change need to be understood to diagnose local- and regional-scale impacts, and to inform assessments of recovery. Three case studies are used to illustrate the need for long-term studies: (i) separation of the influence of fishing pressure from climate change on bottom fish in the English Channel; (ii) recovery of rocky shore assemblages from the Torrey Canyon oil spill in the southwest of England; (iii) interaction of climate change and chronic Tributyltin pollution affecting recovery of rocky shore populations following the Torrey Canyon oil spill. We emphasize that “baselines” or “reference states” are better viewed as envelopes that are dependent on the time window of observation. Recommendations are made for adaptive management in a rapidly changing world.

Combined impacts of natural and human disturbances on rocky shore communities

Most ecosystems are subject to both natural and human disturbances that can combine to influence populations and assemblages in complex ways. Assessing the relative influences and combined impacts of natural and human disturbance is crucial for managing human uses of ecosystems against the backdrop of their natural variability. We evaluated the separate and combined influences of disturbance from storm waves and disturbance associated with human trampling of rocky shores by conducting an experiment mimicking controlled levels of trampling at sites with different wave exposures, and before and after a major storm event in central California, USA. Results show that trampling and storm waves affected the same taxa and have comparable and additive effects on rocky shore assemblages. Both disturbance types caused significant reduction in percent cover of mussels and erect macroalgae, and resulted in significant re-organization of assemblages associated with these habitat-forming taxa. A single extreme storm event caused similar percent cover losses of mussels and erect macroalgae as did 6–12 months of trampling. Contrary to a predicted synergistic effect of trampling and storm damage, we found that impacts from each disturbance combined additively. Mussel beds in wave-exposed sites are more vulnerable to trampling impacts than algal beds at protected sites. Mussels and erect macroalgae recovered within five years after trampling stopped. These results suggest that impacts from local human use can be reversed in relatively short time frames, and that cumulative impacts can be reduced by setting recreational carrying capacities more conservatively when ecosystems are already exposed to frequent and/or intense natural disturbances.

Effects of simulated human exploitation of a key grazer, Patella vulgata, on rocky shore assemblages

Exploitation of key consumers can have major consequences for community and ecosystem functioning. Limpets are key grazers exploited in regions such as Macaronesia, southern Africa, Chile and California. Here we describe a field experiment designed to simulate human exploitation of British limpets that are unexploited and used as model populations. Our aim was to evaluate the effects of size-selective harvesting on the composition of the rocky shore community of non-target species. Limpet populations were subjected to simulated exploitation of large size classes for 18 mo at 2 locations in the southwest of England, by systematic removal at 2 different intensities: low and high exploitation compared with unexploited plots. The exploitation of limpets led to establishment of Fucus spp. to differing degrees at each location, but while variation in percentage cover of Fucus spp. decreased over the course of the experiment in unmanipulated control plots, it increased in plots with either low or high exploitation. Multivariate analyses showed that communities at the 2 locations responded differently to the same intensity of exploitation: unmanipulated controls were similar to low-exploitation treatments at Constantine, while at Trevone low-exploitation treatments were similar to high-exploitation treatments. This was mainly due to increases in percentage cover of F. vesiculosus var. evesiculosus with exploitation, indicating that site-specific differences in assemblage structure and the size structure of the harvested populations will determine its assemblage-level responses. Therefore, reductions in density of grazers may have divergent consequences for different rocky shore communities.

Variation in rocky shore assemblages and abundances of key taxa along gradients of stormwater input

Stormwater brings freshwater and terrestrially derived contaminants into coastal systems and is predicted to increase with climate change. This study aimed to characterise variation in rocky shore assemblages in relation to stormwater pollution. Intertidal assemblages were sampled in similar habitats at a range of distances (0 m, 10 m, 20 m, 60 m, and 100 m) from stormwater outfalls on three rocky shores north of Dublin. In general, taxon richness and algal cover increased after 20 m from a stormwater outfall. Limpet population structure and condition index showed no consistent patterns among shores. Assemblage structure at or near stormwater sites differed from that at sites 100 m away. These findings, ideally supplemented by experimental research, may be used to inform stormwater management and remediation approaches.

Vertical zonation is the main distribution pattern of littoral assemblages on rocky shores at a regional scale

Vertical variation in the distribution of rocky shore assemblages is greater than horizontal variation, as shown by univariate and multivariate analysis performed with data obtained along 1000 km of shoreline and covering from the upper supralittoral to the upper infralittoral zone (−1 m). Consequently, vertical littoral zonation is a consistent pattern at a regional scale within the same biogeographical zone. While their distribution varies at the same shore height, marine species and assemblages from rocky shores show a specific vertical sequence known as zonation. A key question in ecology is how consistent is zonation along large spatial scales. The aim of this study is to show distribution patterns of littoral assemblages at a regional scale and to identify the most relevant abiotic factors associated to such patterns. The study is based on a detailed and extensive survey at a regional scale on a tideless rocky shore. Benthic macroflora and macrofauna of 750 relevés were described along the vertical axis of 143 transects distributed across the shoreline of Catalonia (NW Mediterranean). The Detrended Correspondence Analysis (DCA) first axis is highly related to the height on the shore: species, relevés, and assemblages grade from lower to upper height (infralittoral to supralittoral). As observed in nature, different assemblages co-occur at the same height at different sites, which is shown along DCA second axis. The abiotic variables that best explain the assemblage distribution patterns are: height (75% of the model inertia), longitude (14.6%), latitude (7.2%) and transect slope (2.9%). The Canonical Correspondence Analysis (CCA) first axis is related to height on the shore and explains four times more variance than CCA second axis, which is related to the horizontal gradient. Generalized Lineal Model (GLM) results show that height on the shore is the factor explaining most of the variance in species presence. Most studied species show distribution patterns related to latitude and longitude, but always in a much smaller proportion than to height.

Impacts of sewage outfalls on rocky shores: Incorporating scale, biotic assemblage structure and variability into monitoring tools

Coastal systems, such as rocky shores, are among the most heavily anthropogenically-impacted marine ecosystems and are also among the most productive in terms of ecosystem functioning. One of the greatest impacts on coastal ecosystems is nutrient enrichment from human activities such as agricultural run-off and discharge of sewage. The aim of this study was to identify and characterise potential effects of sewage discharges on the biotic diversity of rocky shores and to test current tools for assessing the ecological status of rocky shores in line with the EU Water Framework Directive (WFD). A sampling strategy was designed to test for effects of sewage outfalls on rocky shore assemblages on the east coast of Ireland and to identify the scale of the putative impact. In addition, a separate sampling programme based on the Reduced algal Species List (RSL), the current WFD monitoring tool for rocky shores in Ireland and the UK, was also completed by identifying algae and measuring percent cover in replicate samples on rocky shores during Summer. There was no detectable effect of sewage outfalls on benthic taxon diversity or assemblage structure. However, spatial variability of assemblages was greater at sites proximal or adjacent to sewage outfalls compared to shores without sewage outfalls present. Results based on the RSL, show that algal assemblages were not affected by the presence of sewage outfalls, except when classed into functional groups when variability was greater at the sites with sewage outfalls. A key finding of both surveys, was the prevalence of spatial and temporal variation of assemblages. It is recommended that future metrics of ecological status are based on quantified sampling designs, incorporate changes in variability of assemblages (indicative of community stability), consider shifts in assemblage structure and include both benthic fauna and flora to assess the status of rocky shores.

Use of shell-shape to discriminate betweenBrachidontes rodrigueziiandBrachidontes purpuratusspecies (Mytilidae) in the transition zone of their distributions (south-western Atlantic)

Mussels are important components of rocky shore assemblages throughout the world. Several mytilid species are found as multilayered beds in the intertidal along the coasts of the south-western Atlantic. However, in contrast to the north communities in the Pacific and Atlantic, those of the south-western Atlantic are dominated by species of small size, locally named mejillines. These mid-intertidal beds attached to consolidated substrates are dominated by virtual monocultures of two small-sized species ofBrachidontes: B. rodriguezii(d'Orbigny, 1842) andB. (Perumytilus) purpuratusLamarck, 1819, respectively distributed in the warm and cold temperate sectors of the south-western Atlantic; both coexisting in the transition zone between 40° and 44°S latitude. Nevertheless, there has been some confusion about the separation ofB. rodrigueziiandB. purpuratus, as well as about the boundaries of their distribution ranges in the south-western Atlantic. Here, on the basis of a morphogeometric analysis of shell morphology, we describe a feasible way for the identification of both species.

Biological aspects and ecological effects of a bed of the invasive non-indigenous mussel Brachidontes pharaonis (Fischer P., 1870) in Malta

No mussel beds were known to occur in the Maltese Islands previous to 2009, when a single bed of the Lessepsian immigrant Brachidontes pharaonis, first recorded from the islands in 1970, was discovered in Birzebbugia Bay. The population structure of B. pharaonis was investigated to assess its potential to spread and colonise new shores, while the biotic community at the mussel bed was compared to that present on uncolonised substratum to determine the effects of mussel bed establishment on the associated biota. Results indicate a lower species richness and slightly different community structure with greater small-scale heterogeneity at the mussel bed site compared to the adjacent rocky shore where mussels are present but where there is no bed formation. The B. pharaonis population had a peak density of 16550 ± 2051 ind.m-2 within the mussel bed and included recent recruits. These data suggest that the B. pharaonis population has the potential to expand. Establishment of extensive beds by this invasive mussel could change the structure of native rocky shore assemblages around the Maltese Islands and elsewhere in the Mediterranean.

Temporal stability of European rocky shore assemblages: variation across a latitudinal gradient and the role of habitat‐formers

Compensatory dynamics, overyielding and statistical averaging are mechanisms promoting the temporal stability of natural communities. Using the model of European intertidal rocky shore assemblages and collating 17 datasets, we investigated how the strength of these stability‐enhancing mechanisms varies with latitude and how it can be altered by the loss of habitat‐formers (e.g. canopy‐forming macroalgae). Community stability decreased with increasing latitude, mostly as a consequence of a greater synchronization of species fluctuations. Statistical averaging and overyielding (i.e. richness effect) promoted stability, but their strength did not vary with latitude. An experimental removal of macroalgal canopies caused a strengthening of the statistical averaging effect that was consistent across the latitudinal gradient investigated. Nonetheless, the loss of canopies depressed stability by enhancing the synchronization of species fluctuations on southernmost shores, while it had weak effects on shores at higher latitudes. Variation in life‐history traits among canopy‐forming species and/or in prevailing environmental conditions across a gradient of latitude could underlie variable effects of habitat‐formers on species fluctuations. Our study shows 1) that the stability of intertidal assemblages and strength of compensatory dynamics varies with latitude, 2) that canopy‐forming macroalgae, exerting a strong control on understorey species, can influence the strength of compensatory dynamics and 3) that biological forcing (i.e. facilitation) can be as important as environmental forcing in enhancing the synchronization of species fluctuations.

Long-term comparison of algal assemblages dominated by Cystoseira crinita (Fucales, Heterokontophyta) from Cap Corse (Corsica, North Western Mediterranean)

Species composition and abundance of present rocky shore assemblages at Cap Corse (Corsica, North Western Mediterranean) dominated by the fucalean alga Cystoseira crinita are compared with similar data obtained almost 50 years ago. Fifteen sites at five different localities where dense C. crinita assemblages were present in the past were revisited in June 2007. Possible differences between the two sampling times were investigated, applying various multivariate analysis techniques available in the statistical package PRIMER v.6. Dense assemblages dominated by C. crinita were found at 14 out of the 15 surveyed sites, showing a similar structure and composition to the assemblages studied in the past. PERMANOVA indicated slight differences in species composition and abundances between old and new surveys. These differences can be summarized as a higher abundance of encrusting species (up to 3 times greater cover), and more sciaphilic turf-forming species (3 to 60-fold greater, depending on the species) and Cladophora spp. (20 times greater) in the present study than in the old study. Furthermore, the present assemblages showed a lower abundance of photophilic turf-forming species. These differences could be due to different taxonomic competence between observers, seasonal fluctuations or long-term changes. Assemblages dominated by Cystoseira crinita in Cap Corse were confirmed to be common, as they were found and sampled at 22 new sites around the island.

Use of the intertidal zone by mobile predators: influence of wave exposure, tidal phase and elevation on abundance and diet

Linkages 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 popula- tions 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 illus- trates the strong trophic linkages between the subtidal and intertidal zones, which is likely to be a key factor influencing community structure on European shores.

Resistance of rocky shore assemblages of algae and invertebrates to changes in intensity and temporal variability of aerial exposure

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 400:75-86 (2010) - DOI: https://doi.org/10.3354/meps08418 Resistance of rocky shore assemblages of algae and invertebrates to changes in intensity and temporal variability of aerial exposure Iacopo Bertocci1,2,*, Elena Maggi1, Stefano Vaselli1, Lisandro Benedetti-Cecchi1 1Dipartimento di Biologia, University of Pisa, CoNISMa, Via Derna 1, 56126 Pisa, Italy 2Present address: CIIMAR (Centro Interdisciplinar de Investigação Marinha & Ambiental), Rua dos Bragas 289, 4050-123 Porto, Portugal *Email: ibertocci@ciimar.up.pt ABSTRACT: Experimental investigations of biological responses to changes in mean intensity and temporal variability of environmental conditions are key to anticipating effects of predicted climate change. We examined the ability of rocky shore organisms to resist increased levels of aerial exposure due to prolonged periods of high barometric pressure and calm sea conditions. By temporarily transplanting assemblages from the lowshore environment to mid- and high-shore habitats and varying the temporal intervals between successive transplantations, we examined the effects of intensity and temporal variability of aerial exposure. Resistance was evaluated through comparisons of multivariate and univariate response variables between transplanted cores and reference assemblages in the lowshore habitat. When differences emerged from these comparisons, we hypothesized that assemblages could shift towards those occurring under natural conditions of more severe aerial exposure. This was tested by comparing transplanted assemblages to those occurring naturally higher on the shore. The study was repeated twice to test for the generality of outcomes. Although individual taxa showed mixed responses varying between experimental trials that in some cases made their abundances similar to those occurring higher on the shore, whole assemblages and the number of taxa did not generally respond to experimental treatments. Present findings add to the few experimental investigations of the interactive effects of mean intensity and temporal variance of climatic variables, contributing to refined predictions of responses of rocky shore organisms to climate change. KEY WORDS: Aerial exposure · Climate change · Disturbance · Environmental fluctuations · Resistance · Rocky shore · Mediterranean Sea Full text in pdf format Supplementary material PreviousNextCite this article as: Bertocci I, Maggi E, Vaselli S, Benedetti-Cecchi L (2010) Resistance of rocky shore assemblages of algae and invertebrates to changes in intensity and temporal variability of aerial exposure. Mar Ecol Prog Ser 400:75-86. https://doi.org/10.3354/meps08418Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 400. Online publication date: February 11, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.