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Reef-building species are recognized as having an important ecological role and as generally enhancing the diversity of benthic organisms in marine habitats. However, although these ecosystem engineers have a facilitating role for some species, they may exclude or compete with others. The honeycomb worm Sabellaria alveolata ( Linnaeus, 1767 ) is an important foundation species, commonly found from northwest Ireland to northern Mauritania, whose reef structures increase the physical complexity of the marine benthos, supporting high levels of biodiversity. Local patterns and regional differences in taxonomic and functional diversity were examined in honeycomb worm reefs from 10 sites along the northeastern Atlantic to explore variation in diversity across biogeographic regions and the potential effects of environmental drivers. While taxonomic composition varied across the study sites, levels of diversity remained relatively constant along the European coast. Assemblages showed high levels of species turnover compared to differences in richness, which varied primarily in response to sea surface temperatures and sediment content, the latter suggesting that local characteristics of the reef had a greater effect on community composition than the density of the engineering species. In contrast, the functional composition of assemblages was similar regardless of taxonomic composition or biogeography, with five functional groups being observed in all sites and only small differences in abundance in these groups being detected. Functional groups represented primarily filter-feeders and deposit-feeders, with the notable absence of herbivores, indicating that the reefs may act as biological filters for some species from the local pool of organisms. Redundancy was observed within functional groups that may indicate that honeycomb worm reefs can offer similar niche properties to its associated assemblages across varying environmental conditions. These results highlight the advantages of comparing taxonomic and functional metrics, which allow identification of a number of ecological processes that structure marine communities.

Equilibrium concepts and the expectation of compensatory density dependence remain fundamental to fisheries science, but stock collapses and an increasing appreciation of environmental factors have raised questions about their real-world applicability. To explore the demographic variability of harvested marine fishes, we have calculated metrics commonly used in conservation biology to describe the demographics for 77 assessed stocks from the North Atlantic and Northeast Pacific Oceans using life-tables. We found that median annual population growth rates ( λ ) were centered around 1, and surprisingly, they were only slightly higher when the effect of fishing was excluded. For most stocks, as abundance declined, λ tended to increase and become more variable as would be expected from compensatory dynamics. The population growth of several stocks was sustained by a limited number of years with exceptionally high rates. However, the ability of a stock to increase from low abundance appeared largely independent of life history characteristics and exhibited stronger geographical differences among stocks of the same species (notably Atlantic cod). Life history characteristics alone were poor predictors of annual population growth or future recovery potential, whereas regional factors appeared to be more influential. Overall, recovery potential remained relatively high, with simulations indicating that 62 of the stocks would be highly likely to double in size within 20 years in the absence of fishing. Low recovery potential was exclusively observed in stocks with a low median λ and low variability in λ . These results suggest that understanding stock-specific (rather than species-specific) demographic parameters is necessary to promote sustainable management or develop rebuilding plans for collapsed stocks.

Climate-driven changes in ocean currents have facilitated the range extension of the long-spined sea urchin (Centrostephanus rodgersii) from Australia’s mainland to eastern Tasmania over recent decades. Since its arrival, the destructive grazing of the urchin has led to widespread formation of sea urchin ‘barrens’. The loss of habitat, biodiversity and productivity for important commercial reef species in conjunction with the development of an urchin fishery has led to conflicting objectives among some stakeholders that pose complex challenges for regional management. Stakeholders representatives and managers were engaged via a participatory workshop and subsequent one-on-one surveys to trial a structured decision making process to identify effective ecosystem-based management strategies. We directly and indirectly elicited each preferences for nine alternative management strategies by presenting them with the 10-year consequences of each strategy estimated from an ecosystem model of Tasmanian reef communities. These preferences were included in cost-effectiveness scores that were averaged (across stakeholders) to enable strategy ranking from most to least cost-effective. Rankings revealed strategies that included sea urchin removal or translocation of predatory lobsters were the most cost-effective. However, assessment of stakeholders’ individual cost-effectiveness scores showed some disparity among preferences in high ranking strategies. Additionally, inconsistencies in strategy preferences using alternative (direct or indirect) ranking scores reveal conflicting objectives as the most plausible explanation. Our study illustrates how structured decision making can effectively facilitate ecosystem-based management by engaging stakeholders step-by-step towards management strategy implementation and promoting collective learning.

Aim In coastal marine systems, biogenic reef‐building species have great importance for conservation as they provide habitat for a wide range of species, promoting biodiversity, ecosystem functioning and services. Biogenic reef persistence and recovery from perturbations depend on recolonization by new recruits. Characterizing larval dispersal among distant reefs is key to understanding how connectivity shapes metapopulation structure and determines network coherence; all of which are of critical importance for effective conservation. Location Northeast Atlantic coast and western English Channel, France. Methods We used a biophysical transport model to simulate larval dispersal of the reef‐building polychaete Sabellaria alveolata. We combined dispersal modelling and network analysis into a framework aiming to identify key reef areas and critical dispersal pathways, whose presence in the network is vital to its overall coherence. We evaluated changes in dispersal pathways constrained by different connectivity thresholds, i.e., minimum dispersal rate for the presence of a connection. We tested scenarios of sequential loss of reefs: randomly, by habitat quality (a score for reef status and occupancy in an area) or by betweenness centrality metric (BC; quantifying the proportion of shortest paths connecting all areas that are passing through any given area). Results We found that the network of S. alveolata reefs forms two main regional clusters, the Atlantic coast and the English Channel, which are connected only through weak sporadic dispersal events. Within each cluster, the network is characterized by relatively high connectivity among neighbouring areas with reefs, maintained even under higher connectivity thresholds. Simulating scenarios of sequential loss of reefs further identified high centrality reefs, those with highest BC values, key to network coherence. Main conclusions Effective conservation of this important reef habitat requires a network of protected areas designed to sustain a combination of locally important source reefs, and those that act as stepping stones connecting distant reefs.

Long-term shifts in environmental conditions driven by climate change are predicted to persistently modify the distribution of a multitude of species. These range shifts can have significant effects on the functioning of ecological communities. Ocean warming along the southeast coast of Australia has seen a polewards shift in the distribution of the long-spined sea urchin Centrostephanus rodgersii . Barren areas formed by the destructive overgrazing of kelp beds by invading C. rodgersii are associated with a dramatic loss of habitat, species diversity and productivity. The ongoing range expansion of C. rodgersii will further increase sea urchin densities along the south eastern coast of Tasmania, where ‘incipient’ barrens have started to appear. As restoration of sea urchin barrens over a large-scale is costly and hard to achieve, effective management needs to focus on preventing further formation of extensive barrens. This study examines whether systematic culling of C. rodgersii in spatially discrete areas is effective to control their abundance. We show that systematic culling was highly effective in significantly reducing the mean density and aggregation of urchins in a discrete area which persisted for at least 12 months. Notably, there was no significant difference in the reduction of urchin density and aggregation when plots were culled twice rather than once. There was however an edge effect indicating a slow incursion of urchins back into the treatment plots. We also show that divers follow a classic prey-predator interaction with culling efficiency increasing with urchin density. Ultimately our results demonstrate that systematic culling is an effective method for controlling urchin abundance in discrete areas. The high cost and logistical constraints limit the application of a culling programme over large areas of reef. Culling, therefore, needs to be considered along with other management measures to control the effects of overgrazing by urchins over large scales.

The authors are retracting this article [1] because of confidentiality reasons. The article has been removed to protect the privacy of an individual. All authors agree to this retraction.

We present the distribution of the parthenopid crab species Distolambrus maltzami from the North-east Atlantic with a first record from UK seas. The distribution of D. maltzami in the Celtic-Biscay area in the eastern Atlantic, is both described based on recent records from survey data and estimated from modelling its environmental niche. The predicted probability of occurrence is greatest in areas with fluctuating tidal currents and water masses that are rich in chlorophyll-a, cold (minimum bottom temperature lower than 10°C) and oxygen-rich. We include a simple key to distinguish the two parthenopid crab species previously encountered in the region and highlight the importance of a multidisciplinary approach to fisheries data collection.

Climate-driven changes in ocean currents have facilitated the range extension of the long-spined sea urchin (Centrostephanus rodgersii) from Australia’s mainland to eastern Tasmania over recent decades. Since its arrival, destructive grazing by the urchin has led to widespread formation of sea urchin ‘barrens’. The loss of habitat, biodiversity and productivity for important commercial reef species in conjunction with the development of an urchin fishery has led to conflicting objectives among stakeholders, which poses complex challenges for regional management. Stakeholder representatives and managers were engaged via a participatory workshop and subsequent one-on-one surveys to trial a structured decision-making process to identify effective ecosystem-based management strategies. We directly and indirectly elicited each stakeholder’s preferences for nine alternative management strategies by presenting them with the 10-year consequences of each strategy estimated from an ecosystem model of Tasmanian reef communities. These preferences were included in cost-effectiveness scores that were averaged (across stakeholders) to enable strategy ranking from most to least cost-effective. Rankings revealed strategies that included sea urchin removal or translocation of predatory lobsters were the most cost-effective. However, assessment of stakeholders’ individual cost-effectiveness scores showed some disparity among stakeholders’ preferences in high ranking strategies. Additionally, evaluating inconsistencies within some stakeholders’ scores that included direct or indirect preferences revealed conflicting objectives and cognitive bias as the most plausible explanations for these inconsistencies. Our study illustrates how structured decision-making can effectively facilitate ecosystem-based management by engaging stakeholders step-by-step towards management strategy implementation, identifying psychological barriers to decision-making and promoting collective learning.

Aim To investigate some of the environmental variables underpinning the past and present distribution of an ecosystem engineer near its poleward range edge. Location >500 locations spanning >7,400 km around Ireland. Methods We collated past and present distribution records on a known climate change indicator, the reef‐forming worm Sabellaria alveolata (Linnaeus, 1767) in a biogeographic boundary region over 182 years (1836–2018). This included repeat sampling of 60 locations in the cooler 1950s and again in the warmer 2000s and 2010s. Using species distribution modelling, we identified some of the environmental drivers that likely underpin S. alveolata distribution towards the leading edge of its biogeographical range in Ireland. Results Through plotting 981 records of presence and absence, we revealed a discontinuous distribution with discretely bounded sub‐populations, and edges that coincide with the locations of tidal fronts. Repeat surveys of 60 locations across three time periods showed evidence of population increases, declines, local extirpation and recolonization events within the range, but no evidence of extensions beyond the previously identified distribution limits, despite decades of warming. At a regional scale, populations were relatively stable through time, but local populations in the cold Irish Sea appear highly dynamic and vulnerable to local extirpation risk. Contemporary distribution data (2013–2018) computed with modelled environmental data identified specific niche requirements which can explain the many distribution gaps, namely wave height, tidal amplitude, stratification index, then substrate type. Main conclusions In the face of climate warming, such specific niche requirements can create environmental barriers that may prevent species from extending beyond their leading edges. These boundaries may limit a species’ capacity to redistribute in response to global environmental change.