Intertidal Mussel Beds Research Articles

Drone-based monitoring of intertidal blue mussel beds in the Wadden Sea – comparison of a threshold and two machine learning approaches

In the Wadden Sea, intertidal mussel beds of the blue mussel (Mytilus edulis) and the Pacific oyster (Magallana gigas) form distinct epibenthic communities and local hotspots of high biomass and biodiversity. To detect and evaluate natural and anthropogenic processes, a ground-based monitoring program started over 25 years ago in the German Wadden Sea. In this study, we describe the potential of drones and machine learning approaches for a remote sensing-based integration into an existing monitoring program of intertidal mussel beds. A fixed wing drone was used to cover an area of up to 39ha in a single flight, with an overall time saving potential of 50%. Applying machine learning approaches, a detailed extraction of the intertidal blue mussel bed coverage with an overall accuracy (OA) up to 95.6% was reached, applying a Support Vector Machine (SVM). The application of a multispectral sensor improved the classification performance. Compared to ground-based monitoring, the drone-based method provided significantly more information on the area extension, coverage, and associated algae of the mussel beds. The results show that drones can provide a non-invasive way to survey large and difficult to access areas providing detailed maps of mussel beds and their internal structures.

Non-native barnacle accelerates the recovery from disturbance of intertidal mussel beds

The barnacle Balanus glandula is a non-native species inhabiting Argentinian rocky shores. The native mussel Brachidontes rodriguezii forms extensive beds in the mid-intertidal zone of these shores, generating a physical structure that determines the diversity of the assemblage. Yet, this native foundation species is prone to mortality due to disturbances associated with extreme climatic events. The aim of this study was to experimentally investigate the role of early-colonizing, non-native B. glandula in the succession process and the recovery of mussel beds following disturbance. Experimental plots were demarcated in the mussel bed and initially cleared of mussels, to produce exposed rock surfaces similar to those that form after a disturbance event. Half of these plots were kept barnacle-free throughout the experiment by removing all recruiting B. glandula, whereas all recruits were allowed to develop in the remaining plots. Our results showed that mussel cover at the end of the experiment was higher in the plots with barnacles. The plots with and without barnacles followed different successional trajectories, with increasing limpet densities and reduced cover of crustose algae in the presence of barnacles during early successional stages. The results indicate that the presence of B. glandula at the early stages of succession can alter successional dynamics and facilitate the recovery of mussel bed cover after disturbance events. More broadly, this study also shows that non-native species, although frequently considered a ‘nuisance’, can accelerate the recovery of foundation species that characterize entire communities and sustain the greatest share of their diversity.

Identifying how restoration measures influence the presence of shorebirds: a case study on the use of artificial structures for restoring mussel reefs

Artificial structures are often used as a tool for habitat restoration and the recreation of degraded coastal ecosystems and their associated food webs. However, it is often unknown if and how these artificial structures may influence the habitat use of target species, thereby hampering restoration goals. In this study, we test how artificial barriers, deployed to enhance the creation of an intertidal mussel bed, influenced the mussel‐habitat use by two bird species under pressure, Eurasian oystercatchers and Eurasian curlews. Average bird presence was monitored using time‐lapse camera's from the start of the mussel bed restoration in August 2018 until April 2019. We found that in the first few months of the experiment, both oystercatchers and curlews avoided the restored mussel beds containing artificial structures in the form of metal barriers that act as traps for dislodged mussels. Thereafter, the presence of barriers had no negative influence on the average presence of oystercatchers or curlews. In fact, curlews were significantly attracted to the mussel beds with barriers in January and February. In addition, we found a negative effect of the presence of European herring gulls on the presence of oystercatchers and curlews. The higher herring gull densities in the first 2 months of the experiment might explain the lower‐than‐expected curlew and oystercatcher densities observed in August. To our knowledge, no other studies have investigated the effect of artificial restoration structures on the abundance or habitat use of specific shorebirds.

Intraspecific variation in a predator changes intertidal community through effects on a foundation species.

Intraspecific variation is an important form of biodiversity that can alter community and ecosystem properties. Recent work demonstrates the community effects of intraspecific variation in predators via altering prey communities and in foundation species via shaping habitat attributes. However, tests of the community effects of intraspecific trait variation in predators acting on foundation species are lacking despite the fact that consumption of foundation species can have strong community effects by shaping habitat structure. Here, we tested the hypothesis that intraspecific foraging differences among populations of mussel-drilling dogwhelk predators (Nucella) differentially alter intertidal communities through effects on foundational mussels. We conducted a 9-month field experiment where we exposed intertidal mussel bed communities to predation from three Nucella populations that exhibit differences in size-selectivity and consumption time for mussel prey. At the end of the experiment, we measured mussel bed structure, species diversity, and community composition. While exposure to Nucella originating from different populations did not significantly alter overall community diversity, we found that differences in Nucella mussel selectivity significantly altered foundational mussel bed structure, which in turn altered the biomass of shore crabs and periwinkle snails. Our study extends the emerging paradigm of the ecological importance of intraspecific variation to include the effects of intraspecific variation on predators of foundation species.

A comparative study on CNN-based semantic segmentation of intertidal mussel beds

Mussels are globally distributed and abundant species on intertidal habitats such as rocky shores where they form dense beds and provide a variety of ecosystem services. The ability to measure mussel abundance on shores with high efficiency and accuracy will enhance assessment of their facilitative services to intertidal ecosystems. Traditional sampling methods, however, are labour intensive and consequently limited in spatial and temporal coverage. To advance such monitoring and quantification processes, four state-of-the-art convolutional neural networks (CNN); namely U-Net, FastSCNN, DeepLab v3+, and HRNet, were compared in their performance to segment mussels at the pixel level either with or without Cityscapes pre-trained weights. All proposed CNN were trained on a photographic dataset of 1455 images generated from field images of mussel beds. CNN trained with the Cityscapes pre-trained weights showed an overall increased model performance as illustrated by mean intersection-over-union (mIoU), loss, overall accuracy (oAcc), and Cohen's kappa coefficient. DeepLab v3+ and HRNet with the combination of Cityscapes pre-trained weights achieved over 95% mIoU and 97% oAcc for assessing distribution and abundance of these important intertidal species. Such combination of approaches is, therefore, recommended for ecologists who wish to conduct image-driven surveys of intertidal ecosystems and the code for this study is available at: https://github.com/Vicellken/CNN-SS-mussel.

How climate-driven changes in disturbance frequency affect the recovery of intertidal mussel beds

Community and population recovery from disturbance depends on the intensity, spatial scales, and frequency of disturbance events. Moreover, foundation species, like bed-forming mussels in rocky intertidal shores, are especially prone to disturbance associated with extreme climatic events. The aim of the present study was to experimentally evaluate how the frequency of physical disturbances that generate gaps in beds of the mussel Brachidontes rodriguezii affects mussel recolonization and the succession process on two rocky shore sites of the Southwestern Atlantic. Experimental disturbances (removal of mussels and other forms of biotic cover) were applied to small plots (14 cm × 14 cm) at three different frequencies over two years: 1) only at the beginning of the experiment (i.e., 1× removal frequency), 2) at the beginning of the experiment and 12 months later (2× removal frequency) and, 3) at the beginning of the experiment and 6, 12, and 18 later (4× removal frequency). Unmanipulated areas were maintained as controls. Before applying the experimental disturbance, we measured the abundance of all organisms present in all plots, obtaining data every 6 months. The data were analyzed considering two factors associated with the disturbance frequency: the time since the last removal and the number of removals on the same plot. Our results indicate that increases in disturbance frequencies were sufficient to maintain mussel bed recovery below control levels and increased the cover of crustose algae at the end of the two-year experimental period in one of the rocky shores studied. The decreases observed in the mussel recovery rates under increased disturbance scenarios are expected to have cascading consequences on rocky shore biodiversity, such as reductions in the overall abundance of interstitial invertebrate species that depend on mussel bed habitats and increases in the abundance of sessile organisms that preferentially occur in gaps and are otherwise excluded by mussels, such as the non-native barnacle Balanus glandula.

The longevity of subtidal mussel beds in the Dutch Wadden Sea

Soft-bottom beds of the blue mussel (Mytilus edulis) are of high ecological importance in intertidal and subtidal habitats. They create habitat, shelter and food for other organisms, and play a dominant role in energy flow and nutrient cycling. Intertidal beds are much better studied than subtidal beds. Though it is often assumed that subtidal mussel beds resemble their intertidal counterparts, major differences in factors driving recruitment, growth and survival can be expected. The aim of our study was to estimate survival chances of the mussel beds in the subtidal parts of the Dutch Wadden Sea in relation to environmental variables, and to compare the results with those obtained previously from the intertidal areas. We used data from a long-term annual survey, resulting in a survival analysis of 365 individual subtidal mussel beds. The average life span of subtidal mussel beds, once they have survived their first winter, was estimated at 2.3 years. This is lower than what was found in the intertidal (3.4 years) in a previous study. However, the survival of subtidal mussel beds in less-saline areas is comparable to survival of intertidal mussel beds, whereas survival of subtidal mussel beds in more-saline areas is significantly lower. The strong, significant effect of salinity is most likely an indication of an effect from starfish predation, since starfish (Asterias rubens) are virtually absent from the intertidal and their abundance is strongly reduced in the subtidal at lower salinities. Furthermore, the survival of individual beds is positively correlated with their size. This may be a direct effect of the bed size itself, or also an indirect effect of environmental factors that can affect the size of newly settled beds. A secondary aim was to compare two methods, based on different types of field data: 1) empirical point data and 2) estimated bed contours based on the point data and additional sources of information. Both methods give similar results. Advantages and disadvantages of both methods are discussed.

Facilitation alters climate change risk on rocky shores.

A huge fraction of global biodiversity resides within biogenic habitats that ameliorate physical stresses. In most cases, details of how physical conditions within facilitative habitats respond to external climate forcing remain unknown, hampering climate change predictions for many of the world's species. Using intertidal mussel beds as a model system, we characterize relationships among external climate conditions and within-microhabitat heat and desiccation conditions. We use these data, along with physiological tolerances of two common inhabitant taxa (the isopod Cirolana harfordi and the porcelain crab Petrolisthes cinctipes), to examine the magnitude of climate risk inside and outside biogenic habitat, applying an empirically derived model of evaporation to simulate mortality risk under a high-emissions climate-warming scenario. We found that biogenic microhabitat conditions responded so weakly to external climate parameters that mortality risk was largely unaffected by climate warming. In contrast, outside the biogenic habitat, desiccation drove substantial mortality in both species, even at temperatures 4.4-8.6°C below their hydrated thermal tolerances. These findings emphasize the importance of warming-exacerbated desiccation to climate-change risk and the role of biogenic habitats in buffering this less-appreciated stressor. Our results suggest that, when biogenic habitats remain intact, climate warming may have weak direct effects on organisms within them. Instead, risk to such taxa is likely to be indirect and tightly coupled with the fate of habitat-forming populations. Conserving and restoring biogenic habitats that offer climate refugia could therefore be crucial to supporting biodiversity in the face of climate warming.

Ecological implications of variable energy storage in the keystone predator, Pisaster ochraceus

AbstractWe considered how environmental variation and adaption together constrain energy acquisition of a keystone predator and how the constraints might influence its ecological function. We tested the proposition that changing energy availability, occurring as shifts in shore level and size composition of the lower vertical boundary of intertidal mussel beds (Mytilus spp.), affects energy storage and growth of predatory sea stars, Pisaster ochraceus. Energy storage of Pisaster (mass of the pyloric caeca, PC) increased when highly variable inter‐annual mussel recruitment temporarily shifted the lower boundary of the mussel bed down‐shore; energy storage decreased when the lower boundary receded up‐shore. Greatest storage occurred during massive recruitment of juvenile mussels, which caused the largest downward extensions of the boundary. To test the causal basis of the storage–boundary correlation, sea stars collected from sites with natural episodes of massive mussel recruitment were tagged and translocated to sites with experimentally shifted boundaries. On mussel beds with lower boundaries artificially expanded downward, the sea stars sustained high energy storage over most of the range of initial sizes. On mussel beds left unaltered or experimentally recessed, they lost PC mass. The amounts of loss were similar between unaltered and recessed treatments. We suggest an explanation for this unexpected similarity. Pisaster aggregate and disperse in response to the inter‐annual variation in mussel recruitment, and this numerical response is integral to mechanisms holding stationary the lower boundary, imposing stability on the local mussel population. Inter‐annual episodes of massive mussel recruitment, which have the potential to abruptly destabilize the lower boundaries, (1) elicit the strongest numerical response and (2) incur the greatest energy storage. The amount of energy storage in the season of active foraging is approximately proportional to the reproductive output in the subsequent reproductive season. Therefore, we propose that the system property of prey population stability originates in energy constraints underpinning Darwinian fitness of a keystone predator. Study limitations and further tests of the hypothesis are described.

Expansion of intertidal mussel beds following disease-driven reduction of a keystone predator

Disease shapes community composition by removing species with strong interactions. To test whether the absence of keystone predation due to disease produced changes to the species composition of rocky intertidal communities, we leverage a natural experiment involving mass mortality of the keystone predator Pisaster ochraceus from Sea Star Wasting Syndrome. Over four years, we measured dimensions of mussel beds, sizes of Mytilus californianus, mussel recruitment, and species composition on vertical rock walls at six rocky intertidal sites on the central California coast. We also assessed the relationship between changes in mussel cover and changes in sea star density across 33 sites along the North American Pacific coast using data from long-term monitoring. After four years, the lower boundary of the central California mussel beds shifted downward toward the water 18.7 ± 15.8 cm (SD) on the rock and 11.7 ± 11.0 cm in elevation, while the upper boundary remained unchanged. In central California, downward expansion and total area of the mussel bed were positively correlated with mussel recruitment but were not correlated with pre-disease sea star density or biomass. At a multi-region scale, changes in mussel percent cover were positively correlated with pre-disease sea star densities but not change in densities. Species composition of primary substrate holders and epibionts below the mussel bed remained similar across years. Extirpation of the community below the bed did not occur. Instead, this community became limited to a smaller spatial extent while the mussel bed expanded.

A Histopathological–Biochemical Health Assessment of Blue Mussel Mytilus edulis

Aquaculture of the blue mussel Mytilus edulis in the Gulf of Maine is a growing industry at a time when wild mussel populations are threatened by a rapidly changing ocean. Intertidal mussel beds have largely disappeared in the region raising concerns over the long-term viability of mussel farming. Histology and lipid fatty acid analysis were used to assess gametogenesis, energy investment, and pathology of farmed mussels collected twice monthly for three years in Casco Bay, ME. Energy investment in reproduction and storage differed significantly between years, suggesting interannual variability. Wet weight of fatty acids such as DHA and EPA corresponded to pre-spawning periods, when gonad tissue was most abundant. Overall, pathology assessment showed low levels of common pathogens, parasites, and cellular abnormalities. The survey did, however, reveal high levels of oocyte atresia, a probable indicator of physiological or environmental stress from unfavorable spawning conditions. In addition, the presence of the potentially damaging digenetic trematode Proctoeces maculatus was documented using histology, marking the northernmost detection in the Northwest Atlantic and a likely climate-driven range expansion. These trends may signal a challenging future for blue mussels in the Gulf of Maine. Forward-looking farm mitigation practices informed by these results should be developed to ensure future sustainability of this industry.

Foul-weather friends: Modelling thermal stress mitigation by symbiotic endolithic microbes in a changing environment.

Temperature extremes are predicted to intensify with climate change. These extremes are rapidly emerging as a powerful driver of species distributional changes with the capacity to disrupt the functioning and provision of services of entire ecosystems, particularly when they challenge ecosystem engineers. The subsequent search for a robust framework to forecast the consequences of these changes mostly ignores within-species variation in thermal sensitivity. Such variation can be intrinsic, but can also reflect species interactions. Intertidal mussels are important ecosystem engineers that host symbiotic endoliths in their shells. These endoliths unexpectedly act as conditionally beneficial parasites that enhance the host's resistance to intense heat stress. To understand how this relationship may be altered under environmental change, we examined the conditions under which it becomes advantageous by reducing body temperature. We deployed biomimetic sensors (robomussels), built using shells of mussels (Mytilus galloprovincialis) that were or were not infested by endoliths, at nine European locations spanning a temperature gradient across 22°of latitude (Orkney, Scotland to the Algarve, Portugal). Daily wind speed and solar radiation explained the maximum variation in the difference in temperature between infested and non-infested robomussels; the largest difference occurred under low wind speed and high solar radiation. From the robomussel data, we inferred body temperature differences between infested and non-infested mussels during known heatwaves that induced mass mortality of the mussel Mytilus edulis along the coast of the English Channel in summer 2018 to quantify the thermal advantage of endolith infestation during temperature extremes. Under these conditions, endoliths provided thermal buffering of between 1.7°C and 4.8°C. Our results strongly suggest that sustainability of intertidal mussel beds will increasingly depend on the thermal buffering provided by endoliths. More generally, this work shows that biomimetic models indicate that within-species thermal sensitivity to global warming can be modulated by species interactions, using an intertidal host-symbiont relationship as an example.

Species coexistence in resource‐limited patterned ecosystems is facilitated by the interplay of spatial self‐organisation and intraspecific competition

The exploration of mechanisms that enable species coexistence under competition for a sole limiting resource is widespread across ecology. Two examples of such facilitative processes are intraspecific competition and spatial self‐organisation. These processes determine the outcome of competitive dynamics in many resource‐limited patterned ecosystems, classical examples of which include dryland vegetation patterns, intertidal mussel beds and subalpine ribbon forests. Previous theoretical investigations have explained coexistence within patterned ecosystems by making strong assumptions on the differences between species (e.g. contrasting dispersal behaviours or different functional responses to resource availability). In this paper, I show that the interplay between the detrimental effects of intraspecific competition and the facilitative nature of self‐organisation forms a coexistence mechanism that does not rely on species‐specific assumptions and captures coexistence across a wide range of the environmental stress gradient. I use a theoretical model that captures the interactions of two generic consumer species with an explicitly modelled resource to show that coexistence relies on a balance between species' colonisation abilities and their local competitiveness, provided intraspecific competition is sufficiently strong. Crucially, the requirements on species' self‐limitation for coexistence to occur differ on opposite ends of the resource input spectrum. For low resource levels, coexistence is facilitated by strong intraspecific dynamics of the species superior in its colonisation abilities, but for larger volumes of resource input, strong intraspecific competition of the locally superior species enables coexistence. Results presented in this paper also highlight the importance of hysteresis in understanding tipping points, in particular extinction events. Finally, the theoretical framework provides insights into spatial species distributions within single patches, supporting verbal hypotheses on coexistence of herbaceous and woody species in dryland vegetation patterns and suggesting potential empirical tests in the context of other patterned ecosystems.

The Hidden Biodiversity of Intertidal Mussel Beds under contrasting Wave Exposures

Photo 1: Intertidal mussel bed from the Atlantic coast of Nova Scotia, Canada, viewed at low tide. Photo credit: Ricardo A. Scrosati. This photograph illustrates the article “Abundance data for invertebrate assemblages from intertidal mussel beds along the Atlantic Canadian coast” published by Ricardo A. Scrosati, Lorena P. Arribas, and Luigia Donnarumma in Ecology. https://doi.org/10.1002/ecy.3137

Abundance data for invertebrate assemblages from intertidal mussel beds along the Atlantic Canadian coast.

This data set describes the abundance of 50 invertebrate taxa found in intertidal mussel beds along the Atlantic Canadian coast. This information resulted from a regional-scale study that investigated the effects of wave exposure on the richness and composition of invertebrate assemblages from intertidal mussel beds. Abundance data are provided for taxa representing the Annelida, Arthropoda, Bryozoa, Chordata, Cnidaria, Echinodermata, Mollusca, Nematoda, Nemertea, and Platyhelminthes. The data characterize mussel beds from wave-sheltered and wave-exposed locations spanning 315 km of the coast of Nova Scotia. Univariate and multivariate analyses revealed that the compositional structure of these invertebrate assemblages differed markedly depending on wave exposure. Overall, because of its taxonomic diversity, the inclusion of data for basal, intermediate, and top trophic levels, and the coverage of two extremes of environmental stress, this data set could be useful to test broader aspects of ecological theory. Areas of ecology that could advance using this data set are those concerning environmental stress models of community organization, abundance-occupancy relationships, species co-occurrence, species abundance distributions, dominance and rarity, spatial scales of population and community variation, and distribution of functional and phylogenetic diversity. Use of this data set for academic or educational purposes is allowed as long as the data source is properly cited. When used for academic or educational purposes, this data set should be cited using the title of this Data Paper, the names of the authors, the year of publication, and the corresponding volume and article numbers.

Repeatable patterns of small-scale spatial variation in intertidal mussel beds and their implications for responses to climate change

The interaction of ocean conditions and weather with small-scale physical features of a habitat can have profound effects on the experiences of individual organisms. On topographically complex shorelines, and particularly within dense aggregations of organisms such as mussel beds, a mosaic of environmental conditions can develop, and the resulting variation in conditions within the aggregation could drastically alter the performance of neighboring individuals. Using a suite of sensors mounted to individual Mytilus californianus mussels over two summer field deployments, we have characterized the temperature variation and valve gaping behavior differences found at two spatial scales: within a group separated by centimeters, and between groups of mussels located at the upper and lower extents of the natural mussel zone separated by meters. While temperature conditions near the lower edge of the mussel bed were generally more benign, temperature extremes were similar at both heights in the bed, and variation in body temperature among neighbors increased as the daily mean temperature increased. These patterns were similar across years despite a 3.8 °C difference in mean air and seawater temperatures between years. Gaping behavior was also highly variable among individuals, though that variability diminished at the high end of the mussel bed where the total time mussels spent submerged was much more constrained. These data indicate that an individual mussel's physiological status and past history can be drastically different than those of its nearby neighbors, complicating our ability to characterize representative conditions within a habitat. These observations also provide for the possibility that the impacts of future climate change will be highly specific to certain individuals based on their relative exposure or protection within the mosaic. To address such possibilities, future work must examine the correlation between genotypic and physiological traits that determine performance and individuals' unique experiences in their disparate micro-environments.

A Decade of Observations of Intertidal Benthic Communities at the Water Area of Vitino Specialized Marine Oil Port (Northern Part of Kandalaksha Bay, White Sea): A Methodological View

Studies of the intertidal benthos of the water area of the Vitino Specialized Marine Oil Port using typical hydrobiological methods were carried out for more than ten years. From the analysis of the structure of intertidal communities using different mathematical methods, a quasi-cyclic dynamics of their biomasses was found. The dynamics of the main features of the intertidal blue mussel bed was found at one particular sampling site. In addition, some analytical approaches to the expert assessments of the state of sea floor ecosystem are discussed specifically regarding the diagnostics of the anthropogenic influence. It was shown that a single sampling cannot serve as reliable assessment due to permanent quasi-cyclic processes taking place in the intertidal communities, and the applied methods based on a sampling taking into account the shifting alongside K-, r-axis should be used only with great precaution. Long-term monitoring is needed to make the proper conclusions. The number of samplings at each station should be set in a way that can help outweigh the aggregated distribution of particular species.

Effects of trampling on intertidal mussel beds: importance of disturbance intensity

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 606:231-235 (2018) - DOI: https://doi.org/10.3354/meps12770 NOTE Effects of trampling on intertidal mussel beds: importance of disturbance intensity María M. Mendez1,2,*, Juan P. Livore1, Gregorio Bigatti1,2,3 1Laboratorio de Reproducción y Biología Integrativa de Invertebrados Marinos (IBIOMAR-CCT CONICET CENPAT), U9120ACV Puerto Madryn, Argentina 2Universidad Nacional de la Patagonia San Juan Bosco, Sede Puerto Madryn, U9120ACV Puerto Madryn, Argentina 3Universidad Espíritu Santo, 092301 Samborondón, Ecuador *Corresponding author: mendez@cenpat-conicet.gob.ar ABSTRACT: Trampling is one of the most frequent forms of human disturbance on rocky shores. This activity may directly reduce the abundance of dominant species, indirectly promote changes in the abundance of associated species and ultimately affect biological interactions. We assessed the effects of different intensities of human trampling on Brachidontes spp. mussel beds, a dominant feature on rocky intertidal flats of southwestern Atlantic coasts. We experimentally applied 6 levels of trampling intensity on a Patagonian rocky shore. Simulated trampling intensity ranged from 0 to 600 tramples per day, and plots were disturbed replicating local usage patterns (i.e. austral summer weekend recreation). By the end of the experiment, Brachidontes spp. coverage decreased as a result of increasing intensities of trampling and mostly replaced by bare rock. Even the lowest experimental intensity produced a loss of more than 40% of coverage. Changes in coverage were generally immediate and occurred after the first 2 trampling events, regardless of disturbance intensity. Our findings highlight that as few as 5 people walking on the mid-intertidal flat can produce a decline of the mussel bed cover in a specific area. Our findings also alert to the urgency of implementing effective management actions in this and other frequented areas dominated by similar habitat-forming species. KEY WORDS: Disturbance · Trampling · Mussel beds · Rocky shores · Southwestern Atlantic Full text in pdf format PreviousNextCite this article as: Mendez MM, Livore JP, Bigatti G (2018) Effects of trampling on intertidal mussel beds: importance of disturbance intensity. Mar Ecol Prog Ser 606:231-235. https://doi.org/10.3354/meps12770 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 606. Online publication date: November 15, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Large scale patterns in mussel beds: stripes or spots?

An aerial view of an intertidal mussel bed often reveals large scale striped patterns aligned perpendicular to the direction of the tide; dense bands of mussels alternate periodically with near bare sediment. Experimental work led to the formulation of a set of coupled partial differential equations modelling a mussel–algae interaction, which proved pivotal in explaining the phenomenon. The key class of model solutions to consider are one-dimensional periodic travelling waves (wavetrains) that encapsulate the abundance of peak and trough mussel densities observed in practice. These solutions may, or may not, be stable to small perturbations, and previous work has focused on determining the ecologically relevant (stable) wavetrain solutions in terms of model parameters. The aim of this paper is to extend this analysis to two space dimensions by considering the full stripe pattern solution in order to study the effect of transverse two-dimensional perturbations—a more true to life problem. Using numerical continuation techniques, we find that some striped patterns that were previously deemed stable via the consideration of the associated wavetrain solution, are in fact unstable to transverse two-dimensional perturbations; and numerical simulation of the model shows that they break up to form regular spotted patterns. In particular, we show that break up of stripes into spots is a consequence of low tidal flow rates. Our consideration of random algal movement via a dispersal term allows us to show that a higher algal dispersal rate facilitates the formation of stripes at lower flow rates, but also encourages their break up into spots. We identify a novel hysteresis effect in mussel beds that is a consequence of transverse perturbations.

Intertidal mussel beds from the South-western Atlantic show simple structure and uniform appearance: does environmental harshness explain the community?

ABSTRACTCommunities of the rocky mid-intertidal zone of the South-western Atlantic are uniform in appearance, dominated by dense monocultures of small-size mussels (Brachidontes rodriguezii and Perumytilus purpuratus). To explain this, two hypotheses have been advanced in the literature: environmental harshness due to high potential evaporation and historical contingency after the Last Glacial Maximum. In this study of Uruguayan and Argentine shores, we address the implications and predictions of these two hypotheses from a biogeographic perspective by studying the regional distribution and composition of mid-intertidal mussels. We conducted an extensive latitudinal sampling survey (21 locations, 34–54°S), along with a compilation of available information on mussel bed composition and mussel predators present along the coastline. Then we constructed latitudinal profiles of ecologically significant environmental variables with specific emphasis on potential evaporation, a proxy for desiccation stress. The results show that mussel beds are composed of two species of small mussels, which coexist over a biogeographic transition zone (40–42°S) related to sea surface water temperature. The distribution of mussels along the coastline studied is not consistent with the environmental harshness hypothesis. In addition, in the Central Patagonian zone (44–50°S), two invertebrate predators also inhabit the intertidal rocky shores. However, these localities showed higher environmental harshness (potential evaporation rate) than non-Patagonian localities. We suggest that further attention should be given to historical contingency in order to advance towards a hypothesis consistent with current knowledge on the post-glacial biogeographic history of the South-western Atlantic.