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- Oceanographic conditions limit the spread of a marine invader along Southern African shoresPublication . Assis, J.; Zupan, Mirta; Nicastro, Katy; Zardi, Gerardo I.; McQuaid, Christopher D.; Serrao, Ester A.Invasive species can affect the function and structure of natural ecological communities, hence understanding and predicting their potential for spreading is a major ecological challenge. Once established in a new region, the spread of invasive species is largely controlled by their dispersal capacity, local environmental conditions and species interactions. The mussel Mytilus galloprovincialis is native to the Mediterranean and is the most successful marine invader in southern Africa. Its distribution there has expanded rapidly and extensively since the 1970s, however, over the last decade its spread has ceased. In this study, we coupled broad scale field surveys, Ecological Niche Modelling (ENM) and Lagrangian Particle Simulations (LPS) to assess the current invaded distribution of M. galloprovincialis in southern Africa and to evaluate what prevents further spread of this species. Results showed that all environmentally suitable habitats in southern Africa have been occupied by the species. This includes rocky shores between Rocky Point in Namibia and East London in South Africa (approx. 2800 km) and these limits coincide with the steep transitions between cool-temperate and subtropical-warmer climates, on both west and southeast African coasts. On the west coast, simulations of drifting larvae almost entirely followed the northward and offshore direction of the Benguela current, creating a clear dispersal barrier by advecting larvae away from the coast. On the southeast coast, nearshore currents give larvae the potential to move eastwards, against the prevalent Agulhas current and beyond the present distributional limit, however environmental conditions prevent the establishment of the species. The transition between the cooler and warmer water regimes is therefore the main factor limiting the northern spread on the southeast coast; however, biotic interactions with native fauna may also play an important role.
- Biogeographical patterns of endolithic infestation in an invasive and an indigenous intertidal marine ecosystem engineerPublication . Ndhlovu, Aldwin; McQuaid, Christopher D.; Nicastro, Katy; Marquet, Nathalie; Gektidis, Marcos; Monaco, Cristián J.; Zardi, GerardoBy altering the phenotypic properties of their hosts, endolithic parasites can modulate the engineering processes of marine ecosystem engineers. Here, we assessed the biogeographical patterns of species assemblages, prevalence and impact of endolithic parasitism in two mussel species that act as important ecosystem engineers in the southern African intertidal habitat, Perna perna and Mytilus galloprovincialis. We conducted large-scale surveys across three biogeographic regions along the South African coast: the subtropical east coast, dominated by the indigenous mussel, P. perna, the warm temperate south coast, where this species coexists with the invasive Mediterranean mussel, M. galloprovincialis, and the cool temperate west coast dominated by M. galloprovincialis. Infestation increased with mussel size, and in the case of M. galloprovincialis we found a significantly higher infestation in the cool temperate bioregion than the warm temperate region. For P. perna, the prevalence of infestation was higher on the warm temperate than the subtropical region, though the difference was marginally non-significant. On the south coast, there was no significant difference in infestation prevalence between species. Endolith-induced mortality rates through shell collapse mirrored the patterns for prevalence. For P. perna, endolith species assemblages revealed clear grouping by bioregions. Our findings indicate that biogeography affects cyanobacteria species composition, but differences between biogeographic regions in their effects are driven by environmental conditions.
- Photoautotrophic Euendoliths and their complex ecological effects in marine bioengineered ecosystemsPublication . Dievart, Alexia M.; McQuaid, Christopher D.; Zardi, Gerardo I.; Nicastro, Katy; Froneman, Pierre W.Photoautotrophic euendolithic microorganisms are ubiquitous where there are calcium carbonate substrates to bore into and sufficient light to sustain photosynthesis. The most diverse and abundant modern euendolithic communities can be found in the marine environment. Euendoliths, as microorganisms infesting inanimate substrates, were first thought to be ecologically irrelevant. Over the past three decades, numerous studies have subsequently shown that euendoliths can colonize living marine calcifying organisms, such as coral skeletons and bivalve shells, causing both sub-lethal and lethal damage. Moreover, under suitable environmental conditions, their presence can have surprising benefits for the host. Thus, infestation by photoautotrophic euendoliths has significant consequences for calcifying organisms that are of particular importance in the case of ecosystems underpinned by calcifying ecosystem engineers. In this review, we address the nature and diversity of marine euendoliths, as revealed recently through genetic techniques, their bioerosive mechanisms, how environmental conditions influence their incidence in marine ecosystems and their potential as bioindicators, how they affect live calcifiers, and the potential future of euendolithic infestation in the context of global climate change and ocean acidification
- Canopy microclimate modification in central and marginal populations of a marine macroalgaPublication . Monteiro, Cátia; Zardi, Gerardo I.; McQuaid, Christopher D.; Serrao, Ester; Pearson, Gareth; Nicastro, KatyThe effects of environmental changes on species distribution are generally studied at large geographical scales. However, aggregations of individuals can significantly moderate the impact of the environment at smaller, organismal scales. We focused on the intertidal macroalga Fucus guiryi and carried out field and laboratory common garden experiments to evaluate how the different individual morphologies and canopy densities typical of central and peripheral populations modify microhabitat conditions and associated levels of stress. We show that F. guiryi canopies significantly alter environmental conditions (i.e., temperature, humidity and light regimes) and mitigate the levels of stress experienced by individuals within the group. Southern algae are more branched and form denser canopies but, unexpectedly, despite these considerable differences, the mitigating effects of northern and southern canopies did not differ significantly. Microhabitat conditions beneath canopies were more stressful at marginal locations, indicating that southern populations are not more effective than northern algae at mitigating the harsher climate at the edge of the species distribution. Our findings highlight the importance of assessing structural changes in aggregating species across their distribution and relating these to local climates to understand the impact of environmental changes at scales relevant to individual organisms.
- Intraspecific genetic lineages of a marine mussel show behavioural divergence when exposed to microplastic leachatesPublication . Cozzolino, Lorenzo; Nicastro, Katy R; Hubbard, Peter; Seuront, Laurent; McQuaid, Christopher D.; Zardi, Gerardo IWorldwide, microplastic pollution has numerous negative implications for marine biota, exacerbating the effects of other forms of global anthropogenic disturbance. Mounting evidence shows that microplastics (MPs) not only cause physical damage through their ingestion, but also act as vectors for hazardous compounds by leaching absorbed and adsorbed chemicals. Research on the effects of plastic pollution has, however, largely assumed that species respond uniformly, while ignoring intraspecific diversity (i.e., variation within a single species). We investigated the effects of plastic leachates derived from factory-fresh (virgin) and beached microplastics on the behavioural responses of two genetic lineages of the Mediterranean mussel Mytilus galloprovincialis. Through laboratory behavioural experiments, we found that during exposure to leachates from beached microplastics (beached MPLs), Atlantic specimens moved significantly less than Mediterranean individuals in terms of both (i) proportion of individuals responding through movement and (ii) net and gross distances crawled. In contrast, no significant intraspecific differences were observed in the behaviour of either adults or recruits when exposed to MPLs from virgin microplastics (virgin MPLs). Additionally, the reception of cues from three amino acids (Lcysteine, proline and L-leucine) at increasing concentrations (10-5 M to 10-3 M in charcoal-filtered seawater) was tested by electrophysiological analysis using mussels exposed to beached MPLs or control seawater. We found significant intraspecific differences in response to 10-3 M L-cysteine (regardless of treatment) and 10-4 M L-cysteine (in mussels exposed to beached MPLs) and to 10-3 M proline (in mussels exposed to beached MPLs) and 10-5 M L-leucine. Our study suggests that intraspecific variation in a marine mussel may prompt different responses to plastic pollution, potentially triggered by local adaptation and physiological variability between lineages. Our work highlights the importance of assessing the effects of intraspecific variation, especially in environmental sentinel species as this level of diversity could modulate responses to plastic pollution.
- Strong upwelling conditions drive differences in species abundance and community composition along the Atlantic coasts of Morocco and Western SaharaPublication . Lourenco, Carla R.; Nicastro, Katy; McQuaid, Christopher D.; Krug, Lilian; Zardi, Gerardo I.Upwelling strongly influences the composition and dynamics of coastal communities by affecting species abundances, recruitment, dispersal and distribution. Coastal upwelling areas are key model regions to study the responses of coastal species to climate change because they are characterized by cooler water conditions and experience lower warming rates than adjacent regions, making them effective 'control' or refuge sites. This is particularly true for the benthic species of rocky shores in upwelling areas because they are sedentary, inhabit the interface between marine and terrestrial habitats, are exposed to extremely severe and variable environmental conditions and often live near their tolerance limits. We sampled roughly 2000 km of the Atlantic coast of Morocco and Western Sahara to assess the influence of upwelling cells on patterns of diversity and abundance of northern African rocky shore species. We recorded 186 taxa, providing clarification of the distribution of 141 algae and documenting nine new species records for Morocco and Western Sahara. The results emphasize the influence of upwelling on the abundance and distribution of these organisms. The contrast between non-upwelling and upwelling areas highlights the direct and indirect importance of water temperature in shaping these communities, pointing to the consequences of large-scale warming. Such warming is likely to threaten intertidal species that already live close to their thermal tolerance limits and are not buffered by the effects of upwelling.
- Evidence for rangewide panmixia despite multiple barriers to dispersal in a marine musselPublication . Lourenço, Carla R.; Nicastro, Katy; McQuaid, Christopher D.; Chefaoui, Rosa; Assis, J.; Taleb, Mohammed Z.; Zardi, Gerardo I.Oceanographic features shape the distributional and genetic patterns of marine species by interrupting or promoting connections among populations. Although general patterns commonly arise, distributional ranges and genetic structure are species-specific and do not always comply with the expected trends. By applying a multimarker genetic approach combined with Lagrangian particle simulations (LPS) we tested the hypothesis that oceanographic features along northeastern Atlantic and Mediterranean shores influence dispersal potential and genetic structure of the intertidal mussel Perna perna. Additionally, by performing environmental niche modelling we assessed the potential and realized niche of P. perna along its entire native distributional range and the environmental factors that best explain its realized distribution. Perna perna showed evidence of panmixia across > 4,000 km despite several oceanographic breaking points detected by LPS. This is probably the result of a combination of life history traits, continuous habitat availability and stepping-stone dynamics. Moreover, the niche modelling framework depicted minimum sea surface temperatures (SST) as the major factor shaping P. perna distributional range limits along its native areas. Forthcoming warming SST is expected to further change these limits and allow the species to expand its range polewards though this may be accompanied by retreat from warmer areas.
- Latitudinal incidence of phototrophic shell-degrading endoliths and their effects on mussel bed microclimatesPublication . Lourenço, Carla R.; R Nicastro, Katy; McQuaid, Christopher D.; Sabour, Brahim; Zardi, Gerardo I.Aggregations of organisms commonly benefit their members by mitigating the effects of predators and environmental stresses. Mussel aggregations also form important intertidal matrices that support associated infaunal communities, the structures of which are largely shaped by the conditions within the interstitial spaces. Intertidal mussels are frequently parasitized by phototrophic endoliths that infest the shell and have thermoregulatory effects on both solitary and aggregated mussels by changing shell albedo. A large-scale sampling was carried out May June 2016 along Portuguese and Moroccan shores to investigate a latitudinal gradient of endolithic infestation of the intertidal mussel Mytilus galloprovincialis. Endolithic infestation increased towards lower latitudes most likely as a response of greater light availability. Additionally, artificial beds of either 100% non-infested or infested biomimetic mussels were used to test whether infestation alters the temperature and humidity of the interstitial spaces within beds, and if mussels surrounded by infested mussels experience lower body temperatures than those surrounded by non-infested ones. Conditions within beds of infested mussels were significantly cooler and more humid than in non-infested beds and individuals in the centre of infested mussel beds experienced significantly lower body temperatures. Under a scenario of warming climate, endolithic infestation of mussel beds might thus represent an ecological advantage not only for M. galloprovincialis as a species but also for the associated communities.
- Intraspecific diversity in an ecological engineer functionally trumps interspecific diversity in shaping community structurePublication . Nicastro, Katy; McQuaid, Christopher D.; Dievart, Alexia; Zardi, Gerardo, ICan intraspecific diversity functionally supersede interspecific diversity? Recent studies have established the ecological effects of intraspecific variation on a number of ecosystem dynamics including resilience and productivity and we hypothesised that they may functionally exceed those of species diversity. We focused on a coastal ecosystem dominated by two coexisting bioengineering mussel species, one of which, Perna perna, displays two distinct phylogeographic lineages. A manipulative field experiment revealed greater habitat structural complexity and a more benign microscale environment within beds of the eastern lineage than those of the western lineage or the second species (Mytilus galloprovincialis)
- Density-dependent and species-specific effects on self-organization modulate the resistance of mussel Bed ecosystems to hydrodynamic stressPublication . Zardi, Gerardo I.; Nicastro, Katy; McQuaid, Christopher D.; de Jager, Monique; van de Koppel, Johan; Seuront, LaurentSelf-organized, regular spatial patterns emerging from local interactions among individuals enhance the ability of ecosystems to respond to environmental disturbances. Mussels self-organize to form large, regularly patterned biogenic structures that modify the biotic and abiotic environment and provide numerous ecosystem functions and services. We used two mussel species that form monospecific and mixed beds to investigate how species-specific behavior affects self-organization and resistance to wave stress. Perna perna has strong attachment but low motility, while Mytilus galloprovincialis shows the reverse. At low density, the less motile P. perna has limited spatial self-organization compared with M. galloprovincialis, while when coexisting, the two species formed random spatial patterns. At high density, the two species self-organized in similar ways, while when coexisting, patterns were less strong. Spatial pattern formations significantly shaped resistance to hydrodynamic stress. At low density, P. perna beds with strong attachment and M. galloprovincialis beds with strong spatial organization showed higher retention rates than mixed beds. At high density, the presence of strongly attached P. perna significantly increased retention in mixed and P. perna beds compared with M. galloprovincialis beds. Our study emphasizes the importance of the interplay of species-specific behaviors to spatial self-organization and stress tolerance in natural communities.
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