Habitat with small inter-structural spaces promotes mussel survival and reef generation

Spatial variability and context-dependence of fouling communities in recreational marinas: A study in the Western Mediterranean with a focus on non-indigenous species (NIS)

Fouling communities were studied in twenty-six recreational marinas located along the continental and island coasts of Tuscany as well as Corsica (Western Mediterranean), focusing on the occurrence of non-indigenous species (NIS), in order to assess the variability of these assemblages at different spatial scales. Among the 560 taxa identified, 32 were alien or cryptogenic, with six new records for the study area. Results of this survey showed remarkable spatial variability of fouling community structure and NIS assemblage i) between marinas located on the mainland with respect to those on the islands (sectors), ii) among marinas within the same sector, and iii) among areas within the most of marinas. Macroalgae resulted the main drivers for the associated community, especially NIS, with variability level depending on different contexts. The high spatial variability observed suggests context-dependent fouling dynamics, where unique local conditions shape the structure of these communities and NIS occurrence.

A global synthesis of predation on bivalves

Predation is a dominant structuring force in ecological communities. In aquatic environments, predation on bivalves has long been an important focal interaction for ecological study because bivalves have central roles as ecosystem engineers, basal components of food webs, and commercial commodities. Studies of bivalves are common, not only because of bivalves' central roles, but also due to the relative ease of studying predatory effects on this taxonomic group. To understand patterns in the interactions of bivalves and their predators we synthesised data from 52 years of peer-reviewed studies on bivalve predation. Using a systematic search, we compiled 1334 studies from 75 countries, comprising 61 bivalve families (N = 2259), dominated by Mytilidae (29% of bivalves), Veneridae (14%), Ostreidae (8%), Unionidae (7%), and Dreissenidae and Tellinidae (6% each). A total of 2036 predators were studied, with crustaceans the most studied predator group (34% of predators), followed by fishes (24%), molluscs (17%), echinoderms (10%) and birds (6%). The majority of studies (86%) were conducted in marine systems, in part driven by the high commercial value of marine bivalves. Studies in freshwater ecosystems were dominated by non-native bivalves and non-native predator species, which probably reflects the important role of biological invasions affecting freshwater biodiversity. In fact, while 81% of the studied marine bivalve species were native, only 50% of the freshwater species were native to the system. In terms of approach, most studies used predation trials, visual analysis of digested contents and exclusion experiments to assess the effects of predation. These studies reflect that many factors influence bivalve predation depending on the species studied, including (i) species traits (e.g. behaviour, morphology, defence mechanisms), (ii) other biotic interactions (e.g. presence of competitors, parasites or diseases), and (iii) environmental context (e.g. temperature, current velocity, beach exposure, habitat complexity). There is a lack of research on the effects of bivalve predation at the population and community and ecosystem levels (only 7% and 0.5% of studies respectively examined impacts at these levels). At the population level, the available studies demonstrate that predation can decrease bivalve density through consumption or the reduction of recruitment. At the community and ecosystem level, predation can trigger effects that cascade through trophic levels or effects that alter the ecological functions bivalves perform. Given the conservation and commercial importance of many bivalve species, studies of predation should be pursued in the context of global change, particularly climate change, acidification and biological invasions.

A wind of change for soft-sediment infauna within operational offshore windfarms

In this study, "artificial reef" (AR) impacts of offshore windfarms (OWFs) on the surrounding soft-sediments were investigated. Benthic grab samples were collected at nearby (37.5 m) and distant (500 or 350 m) positions from turbines of two Belgian OWFs (Belwind: monopiles and C-Power: jackets). Higher macrobenthos abundance and species richness were found nearby jacket foundations of C-Power compared to distant positions and differences were most pronounced within deeper sediments (i.e., gullies between sandbanks) at intermediate levels of fine sand fractions (10-20%) and total organic matter (0.5-0.9%). Strong benthic enrichment (>1000 ind. m^-2, >20 spp. sample^-1) was also linked with higher fine sand fractions (>20%) near the jackets. Moreover, nearby sediments showed higher occurrences of coastal species and habitat diversification was promoted by Mytilus edulis shell debris and alive organisms ("biofouling drop-offs"). The lack of similar results around monopiles (Belwind) confirms that the extent of detectable AR-effects depends on site- and turbine specific factors.

Are we there yet? Management baselines and biodiversity indicators for the protection and restoration of subtidal bivalve shellfish habitats

Biodiversity loss and degradation of natural habitats is increasing at an unprecedented rate. Of all marine habitats, biogenic reefs created by once-widespread shellfish, are now one of the most imperilled, and globally scarce. Conservation managers seek to protect and restore these habitats, but suitable baselines and indicators are required, and detailed scientific accounts are rare and inconsistent. In the present study the biodiversity of a model subtidal habitat, formed by the keystone horse mussel Modiolus modiolus (L.), was analysed across its Northeast Atlantic biogeographical range. Consistent samples of 'clumped' mussels were collected at 16 locations, covering a wide range of environmental conditions. Analysis of the associated macroscopic biota showed high biodiversity across all sites, cumulatively hosting 924 marine macroinvertebrate and algal taxa. There was a rapid increase in macroinvertebrate biodiversity (H') and community evenness (J) between 2 and 10 mussels per clump, reaching an asymptote at mussel densities of 10 per clump. Diversity declined at more northern latitudes, with depth and in coarser substrata with the fastest tidal flows. Diversity metrics corrected for species abundance were generally high across the habitats sampled, with significant latitudinal variability caused by current, depth and substrate type. Faunal community composition varied significantly between most sites and was difficult to assign to a 'typical' M. modiolus assemblage, being significantly influenced by regional environmental conditions, including the presence of algal turfs. Within the context of the rapid global increase in protection and restoration of bivalve shellfish habitats, site and density-specific values of diversity are probably the best targets for conservation management and upon which to base monitoring programmes.

Short-term colonization of fouling communities within the port of Livorno (Northern Tyrrhenian Sea, Western Mediterranean): Influence of substrate three-dimensional complexity on non-indigenous species establishment

The influence of substrate morphology on early stages of fouling development was assessed through submerged experimental substrates with different morphological complexity. The experiment was carried out within commercial and touristic harbours of the port of Livorno (Italy), analysing the communities at three steps of colonization (14, 28, 42 days). We assessed the effect of substrate complexity on recruitment of non-indigenous species (NIS), combined with the influence of port use destinations. NIS were recorded in both use destination areas since the first step of colonization. Substrate morphological complexity significantly affected fouling colonization and particularly NIS assemblages. We found that high-complexity substrates are particularly suitable for NIS establishment in comparison with less complex ones. The touristic harbour exhibited a potential for fouling colonization higher than the commercial harbour. These results contributed to the understanding of factors involved in NIS establishment and spread, as well as in their spatial-temporal dynamics within port environments.

Linking individual and population patterns of rocky-shore mussels

Individual traits and population parameters can be used as proxies of processes taking place within a range of scales, thus improving the way we can evaluate species response to environmental variability. In intertidal rocky shores, patterns at the within-site scale, i.e., between centimeters to hundreds of meters, are important for understanding the population response into these highly variable environments. Here, we studied a rocky-shore mussel population at the within-site spatial scale (1) to test how intertidal height and orientation of the shore affect individual traits and population parameters, (2) to infer the link between individual and population level features, and (3) to explore the upscaling mechanisms driving population structure and processes. We analyzed the patterns of six population parameters: density, biomass, crowding, median individual size, recruitment and mortality rate, and four individual traits: growth rate, spawning phenology, size and condition index. Crowding was defined as the degree of overlapping of individuals within a given area, for which we created a "crowding index". Mussels were studied along the intertidal height gradient in two rocky shores with contrasted orientation at one site over a full year. Our results showed a significant effect of intertidal height and shore orientation on most of individual traits and population parameters studied. In contrast, biomass contained in a full covered surface did not vary in space nor in time. This pattern likely results from relatively constant crowding and a trade-off between median individuals' size and density. We hypothesize that growth, mortality and recruitment rates may all play roles in the stability of the crowding structure of mussel aggregations. Variation in spawning phenology between the two shores in the study site was also observed, suggesting different temporal dynamics of microclimate conditions. Interestingly, despite the different population size distribution between the two shores, our estimates indicate similar potential reproductive output. We hypothesize that the structure of the patches would tend to maintain or carry a maximum of biomass due to trade-offs between density and size while maintaining and maximizing the reproductive output. The patterns of spatial variability of individual traits and population parameters in our study site suggest that heterogeneous within-site conditions influence variation in individual performance and population processes. These results provide insights about the relationship between individual traits and how these relationships make patterns at the population level emerge. They provide baseline information necessary to improve models of metapopulation with spatially explicit processes.

Habitat Complexity Affects the Structure but Not the Diversity of Sessile Communities on Tropical Coastal Infrastructure

Increasing human population, urbanisation, and climate change have resulted in the proliferation of hard coastal infrastructure such as seawalls and breakwaters. There is increasing impetus to create multifunctional coastal defence structures with the primary function of protecting people and property in addition to providing habitat for marine organisms through eco-engineering - a nature-based solutions approach. In this study, the independent and synergistic effects of physical complexity and seeding with native oysters in promoting diversity and abundances of sessile organisms were assessed at two locations on Penang Island, Malaysia. Concrete tiles with varying physical and biological complexity (flat, 2.5 cm ridges and crevices, and 5 cm ridges and crevices that were seeded or unseeded with oysters) were deployed and monitored over 12 months. The survival of the seeded oysters was not correlated with physical complexity. The addition of physical and biological complexity interacted to promote distinct community assemblages, but did not consistently increase the richness, diversity, or abundances of sessile organisms through time. These results indicate that complexity, whether physical or biological, is only one of many influences on biodiversity on coastal infrastructure. Eco-engineering interventions that have been reported to be effective in other regions may not work as effectively in others due to the highly dynamic conditions in coastal environment. Thus, it is important that other factors such as the local species pools, environmental setting (e.g., wave action), biological factors (e.g., predators), and anthropogenic stressors (e.g., pollution) should also be considered when designing habitat enhancements. Such factors acting individually or synergistically could potentially affect the outcomes of any planned eco-engineering interventions.

Using functional responses and prey switching to quantify invasion success of the Pacific oyster, Crassostrea gigas

Invasive alien species continue to proliferate and cause severe ecological impacts. Functional responses (FRs) have shown excellent utility in predicting invasive predator success, however, their use in predicting invasive prey success is limited. Here, we assessed invader success by quantifying FRs and prey switching patterns of two native predators, the common sea star, Asterias rubens, and the green crab, Carcinus maenas, towards native blue mussels, Mytilus edulis, and invasive Pacific oysters, Crassostrea gigas. Asterias displayed destabilising type II FRs, whereas Carcinus displayed stabilising type III FRs towards both prey species. Both predators exhibited greater search efficiencies and maximum feeding rates towards native compared to invasive prey. Both predators disproportionately consumed native mussels over invasive oysters when presented simultaneously, even when native mussels were rare in the environment, therefore indicating negligible prey switching. We demonstrate that invasion success may be mediated through differential levels of biotic resistance exerted by native predators.