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The demand for bait by recreational fishers has led to significant commercial and recreational harvests of polychaete worms, primarily from wild resources. In this global review of over 200 papers, we identify 12 of the 81 families of polychaetes are used for bait (the most popular are Arenicolidae, Eunicidae, Nereididae and Onuphidae), and include over 60 species. There are clear regional patterns in the supply and demand for bait, reflected in harvest levels. For example, fisheries for polychaetes in many countries throughout Asia are focused on the supply and export of nereidids, yet in Japan, the nereidids are imported from China. Determining the sustainability and managing polychaete fisheries is extremely difficult due to: (1) a lack of a knowledge of the biology and population dynamics; (2) limited understanding of direct harvests as well as indirect impacts of harvesting; (3) reliance on wild harvest with few cultured species; and (4) problems with biosecurity associated with live exports. Improved understanding of the taxonomy, population connectivity, dynamics of polychaete populations and the fishery activities they support will support more effective and efficient management and secure more reliable access for user groups.

It has been widely shown that oyster reefs enhance local biodiversity and fisheries production. To determine the importance of intertidal remnant estuarine oyster reefs compared to unstructured sandy habitats over small spatial scales (<1 km) to fishes, assemblages were sampled with two nondestructive methods: baited underwater remote videos (BRUVs) and environmental DNA (eDNA) metabarcoding. Fish diversity from eDNA was characterized using three metabarcoding assays, and the assemblages differed with each, as well as to that detected by BRUVs. Overall, 112 fish genera were identified, with 78 more genera detected using eDNA metabarcoding than those observed with BRUVs. Both eDNA and BRUVs resolved a higher number of fish genera associated with oyster reefs than with sand sites, and a different fish composition between habitats was also resolved using each method. Furthermore, eDNA was shown to be useful toward characterizing the gamma diversity of the estuary, due to the intertidal nature and hydrodynamics of the system, as well as the alpha diversity associated with oyster reefs and sand sites. This study reinforces the importance of using multiple metabarcoding assays along‐side BRUVs for sampling assemblages of fishes and demonstrates the utility of using both methods in studies of biodiversity and future management of intertidal estuarine systems. To determine the importance of intertidal remnant estuarine oyster reefs compared to unstructured sand habitats over small spatial scales (<1 km) to fishes, assemblages were sampled with two non‐destructive methods: baited underwater remote videos (BRUVs) and environmental DNA (eDNA) metabarcoding. Fish diversity from eDNA was characterised using three metabarcoding assays, and the assemblages differed with each, as well as to that detected by BRUVs. eDNA was shown to be useful towards characterising the gamma diversity of the estuary, due to the intertidal nature and hydrodynamics of the system, as well as the alpha diversity localised to the oyster reefs and sand sites.

Background Shellfish reef restoration is relatively new in Australia, particularly to intertidal estuarine environments. In late 2019/early 2020 the first large-scale shellfish reef restoration project of the Sydney rock oyster, Saccostrea glomerata was undertaken in the Myall and Karuah Rivers, Port Stephens, on the mid north coast of New South Wales (NSW), Australia. The present study aimed to determine whether locally sourced clean conspecific oyster shells, and/or locally quarried rocks were better for natural recruitment of natural S. glomerata for large-scale oyster reef restoration, and subsequent recruitment of fishes and invertebrates. Over two years, recruitment of S. glomerata spat, and associated fishes and invertebrates were assessed on reefs made of: (1) rock, and (2) rock and shell. Results The mean (± SE) density of oyster spat on rock reefs (Myall River: 1790 ± 48, Karuah River: 1928 ± 68) was significantly greater (Myall River: ANOVA Si: MS 2, 18 = 31080167, F = 96.05, P  < 0.001, Karuah River: ANOVA Si x Ti: MS 18, 270 = 2965449, F = 5.99, P  < 0.001) than on rock and shell reefs (Myall River: 840 ± 40, Karuah River: 1505 ± 75). Rock reefs had significantly greater densities (Myall River: ANOVA Si x Ti: MS 18, 270 = 15657, F = 2.71, P  < 0.001, Karuah River: ANOVA Si x Ti: MS 18, 270 = 20322, F = 5.25, P  < 0.001) of the most abundant invertebrate, Bembicium auratum (Myall River: 85 ± 9, Karuah River: 100 ± 8) than reefs of rock and shell (Myall River: 59 ± 8, Karuah River: 44 ± 5), but there was no significant difference in the diversity and relative abundance of the most abundant species of fish, Acanthopagrus australis . Conclusions This study demonstrates that using locally sourced rock is better for S. glomerata recruitment than shells. Although shell might have benefits that were not investigated in the present study, such as elicit greater social licence for oyster reef restoration projects, but as shown here, it may not be beneficial from an ecological perspective. With the global expansion of the range of different native species of reef oysters for restoration, the appropriate material used for reef bases needs to be chosen for a specific species and purpose.

Globally, oyster reef restoration is on the rise. In many instances, restoration is occurring alongside established oyster aquaculture industries that grew to prominence following oyster reef demise. This paper examines the potential positive and negative interactions between the two industries and identifies key factors that may promote positive interactions. Interactions between the two industries result from shared resource requirements (e.g., space, clean water, brood-stock, breeding programs), shared knowledge requirements (e.g. around threats and their mitigation, factors optimizing growth/survival) and biological interactions (e.g. over-catch, disease spill-over, competition for resources). Many of these interactions are reciprocated, and can shift from positive to negative depending on environmental, biological and socio-economic conditions. From our examination, three key factors emerge as shaping the strength and direction (positive or negative) of interactions: (1) whether the focal species is common or different between the two industries; (2) the physicochemical and socio-economic environment in which the two industries are occurring; and (3) whether there is open dialogue and consultation between the two industries and relevant stakeholders. Positive interactions can be maximized where the two industries are able to co-invest in and share infrastructure (e.g. hatcheries, breeding programs), resources (e.g. spat, broodstock, shell) and knowledge (e.g. optimal conditions of growth) – an easier task where the target oyster species is in common. Positive interactions may also be maximized by utilizing marine spatial planning tools, such as suitability modelling, to inform optimal siting of the two industries. As the two industries continue to grow, open and inclusive dialogue between these and key stakeholders will be essential for mitigating risk and maximising positive synergies.

Ecological theory predicts that positive interactions among organisms will increase across gradients of increasing abiotic stress or consumer pressure. This theory has been supported by empirical studies examining the magnitude of ecosystem engineering across environmental gradients and between habitat settings at local scale. Predictions that habitat setting, by modifying both biotic and abiotic factors, will determine large‐scale gradients in ecosystem engineering have not been tested, however. A combination of manipulative experiments and field surveys assessed whether along the east Australian coastline: (1) facilitation of invertebrates by the oyster Saccostrea glomerata increased across a latitudinal gradient in temperature; and (2) the magnitude of this effect varied between intertidal rocky shores and mangrove forests. It was expected that on rocky shores, where oysters are the primary ecosystem engineer, they would play a greater role in ameliorating latitudinal gradients in temperature than in mangroves, where they are a secondary ecosystem engineer living under the mangrove canopy. On rocky shores, the enhancement of invertebrate abundance in oysters as compared to bare microhabitat decreased with latitude, as the maximum temperatures experienced by intertidal organisms diminished. By contrast, in mangrove forests, where the mangrove canopy resulted in maximum temperatures that were cooler and of greater humidity than on rocky shores, we found no evidence of latitudinal gradients of oyster effects on invertebrate abundance. Contrary to predictions, the magnitude by which oysters enhanced biodiversity was in many instances similar between mangroves and rocky shores. Whether habitat‐context modifies patterns of spatial variation in the effects of ecosystem engineers on community structure will depend, in part, on the extent to which the environmental amelioration provided by an ecosystem engineer replicates that of other co‐occurring ecosystem engineers.

Organisms with different life-histories and abilities to disperse often utilise habitat patches in different ways. We investigated the influence of the size of patches of rock (separated by stretches of sand) on the density of pulmonate limpets (Siphonaria spp.) along 1500 km of the linear landscape of the South African coastline. We compared the influence of patch-size on two congeneric species with different modes of development, S. serrata a direct developer, and S. concinna a planktonic developer. We tested the spatial and temporal consistency of the effects of patch-size by sampling 7 independent regions spanning the distributional range of both species of limpets, and by sampling one region at monthly intervals for 1 year. Within each region or month, 4 small patches (<20 m in length) interspersed with the 4 large patches (>60 m in length) were sampled. Across the entire geographic range and throughout the year, there were more of both species of limpets in large patches than in small patches. In most regions, there was greater variability in large patches than small patches. Variability within patches in a single region was similar throughout the year, with greater variability of both species in large than in small patches. We found little influence of the mode of development on the response of limpets to patch-size. Our findings highlight the importance of understanding patterns of distribution of species with respect to habitat heterogeneity in linear landscapes, and contradict the idea that organism mobility at an early ontogenetic stage directly affects habitat use.

Source-sink theory has contributed to our understanding of the function of protected areas, particularly due to their role as population sources. Marine reserves are a preferred management tool for the conservation of natural populations, creating areas of good quality habitat and thus improving population connectivity by enhancing larval supply and recruitment among shores. Despite recent advances in the study of protected areas in the context of the source-sink theory, rigorous and empirical testing of marine reserves as metapopulation sources for the adjacent areas remain largely unexplored. We investigated the role of marine reserves as population sources, whether there was spill-over beyond the reserve boundaries and if so, whether spill-over was directional. We measured percentage cover and recruitment of mussels ( Perna perna ) at two reserves and two comparably sized exploited control areas on the south-east coast of South Africa where unprotected populations are severely affected by artisanal exploitation. Adult abundances were enhanced within reserves, but decreased towards their edges. We predicted that recruitment would mirror adult abundances and show directionality, with northern shores having greater recruitment following the prevalent northward flow of near-shore currents. There were, however, no correlations between adult abundances and recruitment for any months or shores, and no clear spatial patterns in recruitment (i.e. similar patterns occurred at reserves and controls). The results emphasise that, while reserves may act as important refuges by protecting adult abundances, their influence on promoting recovery of near-by exploited shores through larval spill-over may be overestimated.

Across the globe, restoration efforts are stemming the loss of native oyster reefs and the ecosystem services they provide, but these efforts will need to consider climate change in order to be sustainable. South-eastern Australia is the focus of restoring the once abundant oyster Ostrea angasi. This region is also a climate change ‘hot spot’ where the ocean is warming rapidly, with the potential to be exacerbated by marine heatwaves and coastal acidification. In this study, the impact of near-future (~2050) elevated temperature and pCO₂ on O. angasi was determined and considered in context with concerns for the long-term sustainability of oyster reef restoration efforts. Oysters were exposed to ambient and elevated pCO₂ concentrations (mean ± SE: 408 ± 19.8 and 1070 ± 53.4 μatm) and ambient and elevated temperatures (22.78 ± 0.17 and 25.73 ± 0.21°C) for 10 wk in outdoor flow-through mesocosms. Shell growth, condition index, standard metabolic rate (SMR), extracellular pH and survival were measured. Elevated temperature caused high mortality (36%) and decreased the condition of oysters (33%). Elevated pCO₂ increased SMR almost 4-fold and lowered the extracellular pH of O. angasi by a mean 0.29 pH units. In combination, elevated pCO₂ and temperature ameliorated effects on SMR and survivorship of oysters. O. angasi appears to be living near the limits of its thermal tolerance. Restoration projects will need to account for the temperature sensitivity of this species and its changing habitat to ‘climate proof’ long-term restoration efforts.

Ocean acidification, rising temperatures, and increased intensity of rain events are occurring due to climate change. Individually, each of these stressors has the potential to influence the growth and survival of many marine organisms, particularly during early development. Together the interactive and multiple impacts of elevated p CO 2 , temperature, and salinity may be exacerbated by a lack of food. Life history traits are important in determining the response of organisms to climate change. Larvae that develop within a brood chamber, such as the flat oyster, Ostrea angasi , may be pre-exposed to living a higher CO 2 environment. This study determined the pH of the fluid surrounding the gills of adult oysters where larvae are brooded and investigated the interactive effects of the multiple climate-related stressors: ocean acidification, warming, hyposalinity, and reduced food availability, on development of O. angasi larvae. The fluid surrounding the larvae was of pH 7.88 ± 0.04, lower than that of surrounding sea water, and was significantly reduced (to pH 7.46 ± 0.05) when oysters remained closed as occurs in nature during periods of stress caused by low salinity. Elevated p CO 2 [853–1194 µatm (pH NBS 7.79)] resulted in larvae being 3 % smaller, but it had no effect on the timing of progression through developmental stages, percentage of abnormalities, or survival of larvae. Exposure to elevated p CO 2 together with increased temperature (+4 °C) or reduced salinity (20) had a negative effect on the time to the eyed larval stage and with an increase in the percentage of abnormal larvae. Unexpectedly, larvae did not meet their higher metabolic requirements to survive under elevated p CO 2 by eating more. In a sublethal effect of elevated p CO 2 , larval feeding was impaired. We found that O. angasi larva were relatively resilient to elevated p CO 2 , a trait that may be due to the acclimatisation of hypercapnic conditions in the brood cavity or because they are released from the brood cavity at an older, possibly less sensitive stage. This result contrasts with the larvae of broadcast spawning oysters which are extremely sensitive to elevated p CO 2 .

Temperature and primary production (often linked to nutrient supply) are two of the few factors influencing species diversity and abundances across mesoscale gradients, while at smaller scales the habitat complexity offered by bioengineers is important. Previous studies have illustrated effects of upwelling and biogeography on intertidal bioengineers, but it is not known if these processes influence assemblages associated with those bioengineers in a similar way. We examined the habitat structure offered by two species of mussels and their associated fauna in five regions across 3000 km and three biogeographic provinces of the South African coast, replicating upwelling and non-upwelling areas within each region. Upwelling and region influenced the structure of mussel beds (the density and size of mussels). In contrast, upwelling did not influence mesoscale differences in composition, abundance, and numbers of species of crustaceans, mollusks, or polychaetes in mussel beds. Regardless of trophic level or mode of reproduction, mussel bed fauna were influenced only by region. Regional differences were strongly influenced by biogeography. The associated fauna was, however, also strongly correlated with the structure of the habitats created by mussels. Our results support the importance of upwelling to a critical ecosystem engineer, but show that these effects do not extend directly to the assemblages of associated fauna, which are more influenced by regional-scale effects and biogeography. We suggest that mesoscale patterns in the associated fauna of this bioengineered habitat are driven by the direct effects of biogeography, combined with the influence of biogeography and upwelling on mussel bed structure.