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In February 2023, a severe cold snap took place in Atlantic Canada and was followed by the mass loss of mussels at mid-to-high intertidal elevations on the southeastern Nova Scotia coast. This loss was concerning because mussels sustain upper trophic levels in coastal food webs and because mussel stands enhance local biodiversity by sheltering many small invertebrate species. Using photographs taken in the second summer after that cold snap (July 2024), this article provides visual evidence of active ongoing recolonization of intertidal mussels on this coast, including the incipient formation of new stands. These are encouraging signs of ecological resilience. Reaching historical values of abundance will likely depend on the future occurrence of weather extremes, which are becoming more frequent with the ongoing climate change. [ABSTRACT FROM AUTHOR]

In the early summer of 2021, an intense heatwave killed millions of intertidal mussels in British Columbia, Canada. Using photographs taken three years later (June 2024), this article provides visual evidence of active recovery of intertidal mussel stands in the Vancouver region, revealing the resilience of these intertidal systems. Future monitoring should evaluate their ability for long-term persistence in light of the ongoing climate change, which is expected to increase the frequency and intensity of heatwaves. [ABSTRACT FROM AUTHOR]

Rocky intertidal habitats occur worldwide and are mainly characterized by primary space holders such as seaweeds and sessile invertebrates. Some of these organisms are foundation species, as they can form structurally complex stands that host many small invertebrates. The abundance of primary space holders is known to vary along coastlines driven directly or indirectly by environmental variation. However, it is less clear if the invertebrate assemblages associated to a foundation species may remain relatively unchanged along coastlines, as similar stands of a foundation species can generate similar microclimates. We examined this question using abundance data for invertebrate species found in mussel stands of a similar structure in wave-exposed rocky habitats at mid-intertidal elevations along the Atlantic coast of Nova Scotia (Canada). While the most abundant invertebrate species were found at three locations spanning 315 km of coastline, species composition (a combined measure of species identity and their relative abundance) differed significantly among the locations. One of the species explaining the highest amount of variation among locations (a barnacle) exhibited potential signs of bottom-up regulation involving pelagic food supply, suggesting benthic–pelagic coupling. The abundance of the species that explained the highest amount of variation (an oligochaete) was positively related to the abundance of their predators (mites), further suggesting bottom-up forcing in these communities. Overall, we conclude that species assemblages associated to structurally similar stands of a foundation species can show clear changes in species composition at a regional scale. [ABSTRACT FROM AUTHOR]

This article discusses the mass disappearance of intertidal mussels in eastern Canada after an unusual winter cold snap in February 2023. The decline in mussel abundance is concerning due to its impact on coastal biodiversity. The cold snap, which saw temperatures drop below -20°C, is believed to be the main driver of the mass disappearance. Other factors such as predation, ice scour, and wave action were ruled out as causes. The article highlights the potential implications of climate change on the future of coastal ecosystems and emphasizes the need to study the frequency of extreme weather events. [Extracted from the article]

Anthropogenic CO2is decreasing oceanic pH and contributing to seawater warming. We tested the effects of low pH and high temperature at levels predicted for 2100 on an ecologically important predator–prey system (sea stars,Asterias rubens, and mussels,Mytilus edulis) from the NW Atlantic coast. Mussels are dominant competitors for space and important ecosystem engineers, while sea stars control mussel populations and thus local community structure. We found sea stars to be negatively affected in growth rate by low pH, with growth further reduced by a high temperature. In contrast, mussel growth rate was positively affected by low pH, with no response to temperature within the tested range. Predation of sea stars on mussels, measured as per-capita consumption rate, decreased in acidified conditions by 50%. Our study suggests that mussels may not be negatively affected by pH at the levels predicted for the end of this century and that mussels may be subjected to a reduced predation from sea stars under future conditions. [ABSTRACT FROM PUBLISHER]

We determined the distribution of two cryptic mussel species (Mytilus edulisandM. trossulus) along full gradients of wave exposure in northwest Atlantic rocky intertidal habitats. Research was conducted in Nova Scotia (Canada) and Maine (United States) and species were determined using genetic analyses. In very sheltered habitats, onlyM. edulisoccurred. In sheltered, exposed, and very exposed habitats, both species co-existed,M. edulispredominating in Maine andM. trossulusin Nova Scotia. Hybrids were absent or rare. The distribution of mussels regardless of species (Mytilusspp.) was remarkably consistent across levels of wave exposure in both regions. In very sheltered habitats, organisms were large (4–5 cm long, on average) and old (7–8 years, on average) and occurred in low densities. In sheltered, exposed, and very exposed habitats, organisms were small (< 1 cm, on average) and young (1–2 years, on average); density was low in sheltered and very exposed habitats, but high in exposed habitats. Abundance data for predatory snails (dogwhelks,Nucella lapillus) and canopy-forming algae (Ascophyllum nodosumandFucusspp.) suggest that predation and facilitation may explain some of the observed changes in mussel population traits along the wave exposure gradients. Our results could be useful as baseline information to predict the effects of the progressive increase in wave action caused by climate change on intertidal mussel populations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Aim We performed the first test of predictions from the abundant-centre model using north-west Atlantic coastal organisms. We tested the hypotheses that the density of intertidal mussels (Mytilus edulis and M. trossulus) and dogwhelks (Nucella lapillus) and mussel age and size would peak at an intermediate location along their distribution range. We also assessed the latitudinal variation in critical aerial exposure time. Location North-west Atlantic coast between Newfoundland (Canada) and New York (USA), covering 1800 km of shoreline. Methods Using a nested design, we measured mussel density, age and size and dogwhelk density in 60 wave-exposed rocky intertidal sites spread evenly in six regions. Critical aerial exposure times were determined using online data. Results Mytilus edulis peaked in abundance in Maine and was much less abundant in the other regions. Mytilus trossulus peaked in abundance in southern Nova Scotia and Maine, was less abundant in the other regions to the north, and was absent in the southernmost region (New York). Both mussel species were least abundant in a northern region (Cape Breton), although not in the northernmost region (Newfoundland). Critical aerial exposure times were negatively correlated with overall mussel density. Mussel age and size were similar among regions. Dogwhelks peaked in abundance in Maine and were much less abundant in the other regions, being positively correlated with overall mussel density across regions. Main conclusions Density data for M. edulis and N. lapillus provide limited support for an abundant-centre pattern, while M. trossulus shows a clear rampedsouth distribution. Critical aerial exposure times suggest that physiological stress during summer and winter low tides may be lowest in Maine and southern Nova Scotia, which might partially explain mussel predominance in those regions. Winter ice scour in Cape Breton may explain the abundance trough observed there. Mussel size and age may be more limited by wave exposure at our sites (as they all face open waters) than by regional differences in environmental stress. Dogwhelks, which prey on mussels, seem to respond positively to prey density at the regional scale. Our study supports the notion that, while the abundant-centre model is a useful starting point for research, it often represents an oversimplification of reality. [ABSTRACT FROM AUTHOR]