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1.
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2.
  1. Marine ecosystems are highly affected by several human stressors. In this context, beyond passive restoration measures such as the creation of marine protected areas, it is urgent that we explore active restoration measures to enhance and accelerate the recovery of sessile marine species.
  2. Bryozoans are among the most common sessile invertebrates in rocky bottom ecosystems and are considered habitat‐forming species that are highly vulnerable to physical disturbances, such as recreational diving, ghost fishing nets, and global warming, which makes them highly vulnerable to other impacts. Despite their ecological importance and vulnerability, to date restoration actions for bryozoans have rarely been explored.
  3. In this study, different restoration techniques were developed and tested, with a focus on two types of effective methodologies previously applied to other marine invertebrates: recruitment enhancement and the transplantation of adult colonies, in both cases using the Mediterranean bryozoan Pentapora fascialis as a model species.
  4. First, different types of artificial surfaces were installed in different coralligenous habitats to test the enhancement of recruitment, concluding that plastic grids are the best substrate in terms of facilitating the recruitment of new bryozoan colonies.
  5. Second, different methodologies were tested for adult transplantation. The most successful was to fix colonies to a suitable substrate with a nylon thread attached to the colony ex situ (i.e. on the boat).
  6. Using this technique a trial restoration programme was undertaken, involving transplanting adult colonies collected from a ghost fishing net trapped on the bottom, which showed a high survival rate of ~50% after 6 months.
  7. The low economic cost of the implementation of the proposed techniques as well as the successful results obtained highlight the viability of restoring bryozoan populations over long temporal and spatial scales.
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3.
  1. Gorgonians dwelling on the Mediterranean continental shelf are among the most frequent fishing bycatch taxa. These species display several traits, such as long lifespans and slow growth, which make them very vulnerable to the impacts caused by fishing activities with far‐reaching and long‐lasting effects.
  2. Hence, restoration and mitigation actions are crucial to enhance and speed up the natural recovery of damaged cold‐water coral gardens. Given the growing concern to develop effective and affordable restoration actions, the present study aims to propose and technically validate a new large‐scale and cost‐effective restoration method.
  3. This technique, named ‘badminton method', consists of attaching bycatch Eunicella cavolini colonies to cobble supports and returning them to the continental shelf by gently throwing the gorgonian transplants directly from a boat.
  4. Two consecutive field experiments were conducted in order to find the best cobble type support and gorgonian size to be used: first, to evaluate the landing efficiency of gorgonian transplants at different depths (from 5 to 30 m) and second, to evaluate their capability to maintain a correct position over time.
  5. Natural cobbles with large gorgonians attached were the best option. Field results and modelling approaches suggest that the transplants would correctly land on the continental shelf seabed in a predicted area of around 60 m2. Moreover, they would successfully maintain an upright position ensuring gorgonian survival over time.
  6. The success of this method highlights the feasibility of large‐scale and low‐cost restoration actions with promising results for the conservation and recovery of cold‐water coral gardens.
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4.
  1. Removal of instream woody habitat (IWH) is one factor attributed to declines in fish populations worldwide. Restoration of IWH to help fish populations recover is now common; however, quantitative predictions about the outcomes of these interventions is rare. As such, quantitative links between IWH and fish abundance is of interest to managers to inform conservation and restoration activities.
  2. Links between instream habitat attributes, especially IWH, and selected fish species of recreational, cultural, and ecological significance were explored at 335 sites spanning eight streams across south‐eastern Australia. Data were collected on fish abundance and length, IWH density and a range of other habitat attributes at a scale that incorporated at least one of each of the major mesohabitat types (functional river elements). The data were analysed using Bayesian hierarchical generalized linear mixed models to examine fish habitat associations and used to make quantitative predictions of responses to future restoration.
  3. Strong positive relationships were found between fish abundance and IWH density and the strength of this relationship varied between species and waterways. Murray cod (Maccullochella peelii), a species commonly targeted by IWH interventions, displayed the strongest association with IWH density. River blackfish (Gadopsis marmoratus) also showed a significant relationship with IWH, but this effect was waterway specific. Fish length was only related to IWH for river blackfish. These results may reflect differences in the life histories of these two species. We suggest that differences in habitat association through ontogeny may be more relevant at smaller spatial scales.
  4. The results generated in this study can be used to guide waterway restoration and develop quantitative predictions about how fish might respond to IWH interventions across south‐eastern Australia. This approach provides a powerful quantitative framework within which to explore management options and objectives, and to test our predicted responses to habitat restoration.
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5.
  1. Evidence-based decisions relating to effective marine protected areas as a means of conserving biodiversity require a detailed understanding of the species present. The Caribbean island nation of St Lucia is expanding its current marine protected area network by designating additional no-take marine reserves on the west coast. However, information on the distribution of fish species is currently limited.
  2. This study used baited remote underwater stereo-video to address this shortcoming by investigating the effects of depth and seabed habitat structure on demersal fish assemblages and comparing these assemblages between regions currently afforded different protection measures.
  3. From the 87 stations visited a total of 5,921 fish were observed comprising 120 fish taxa across 22 families. Species richness and total abundance were higher within the highly managed region, which included no-take reserves. Redundancy analysis explained 17% of the total variance in fish distribution, driven predominantly by the seabed habitats. The redundancy analysis identified four main groups of demersal fishes each associated with specific seabed habitats.
  4. The current no-take marine reserves protected two of these groups (i.e. fishes associated with the ‘soft corals, hard corals or gorgonians’ and ‘seagrass’ groups). Importantly, habitats dominated by sponges, bacterial mats, algal turfs or macroalgae, which also supported unique fish assemblages, are not currently afforded protection via the marine reserve network (based on the five reserves studied). These results imply that incorporation of the full breadth of benthic habitat types present would improve the efficacy of the marine reserve network by ensuring all fish assemblages are protected.
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6.

7.
  1. In the context of the River Rhône restoration programme, the objective of this study was to assess the dispersal and population connectivity of the European chub, Squalius cephalus (Linnaeus, 1758) in a section of the natural, free-flowing part of the lower River Rhône.
  2. The elemental water signatures for Sr:Ca and Ba:Ca were measured at seven stations within the river section, including its tributaries and backwaters, to determine whether they could be differentiated by microchemistry. From August to October the signatures differed among three sectors of the study reach: the Rhône; the Ardèche; and the backwaters.
  3. The elemental signatures of the otoliths of 178 young-of-the-year (YOY) chub from the stations were measured to assess spawning areas and identify early migratory life histories. Analyses of otolith microchemistry identified the natal origin of 95% of the fish. Sr:Ca signatures of otoliths showed early downstream migration for 30.4% of the YOY chub; however, 70% of the fish recruited relatively close to their spawning origin suggesting a potential inshore retention of fish.
  4. The results showed (i) a non-negligible contribution of the tributaries and backwaters in the recruitment of fish into the main channel; and (ii) the ability of chub to migrate over several kilometres during their first few months of life.
  5. This study shows that the combination of water and otolith microchemistry analyses of fish growth increases the understanding of fish life history. Moreover, the study revealed that half of the YOY fish from this river section came from the tributaries and the other half came from reproduction in the River Rhône (despite its high anthropization).
  6. These methods offer promising future applications of otolith microchemistry for river management in the context of ecological rehabilitation, especially to assess the effectiveness of measures applied in the restoration of floodplain connectivity for riverine fish population conservation.
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8.
  1. The implementation of marine protected areas (MPAs) has been widely used as a tool to manage and conserve marine resources and services. Yet, to date, the reserve effect is still weakly evaluated, particularly for soft-sediment habitats.
  2. The Arrábida MPA, considered as a biodiversity hotspot, was fully established in 2009 on the west coast of Portugal and is characterized by large expanses of soft-sediment habitats. This MPA was established to protect biodiversity and to ensure the livelihood of the local small-scale fisheries community.
  3. Beyond before–after-control–impact (BACI) analyses were carried out on catch data (abundance and biomass) of 351 trammel net sets from experimental fishing campaigns (2007–2019) to study the reserve effect on demersal fish populations.
  4. The results show a declining trend in abundance inside and outside the protected area, with significant positive effects only found for undersize commercial species and Solea senegalensis, and a general increase in fish species total length. Despite the lack of any obvious reserve effect, the increase in fish length can be considered as a first sign.
  5. Anthropogenic pressures are generalized around the area, and transgressions of the restrictions are frequently observed inside the no-take zone. These can, among other aspects, delay or prevent the expected reserve effects. Therefore, enforcement and/or modification of the spatial plan must be incentivized to achieve the goals of the MPA.
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9.
  1. To understand the ecological factors behind the decline of functionally important threatened species with complex life cycles, many different life‐cycle stages need to be investigated. The highly threatened unionoid freshwater mussels, with their complex life cycle, including a parasitic stage on host fish, often have a large influence on biodiversity and ecosystem functioning.
  2. The overall aim of the present article is to summarize and discuss the impact of two articles published in Aquatic Conservation: Marine and Freshwater Ecosystems (AQC) on biotic interactions and adaptation of a threatened unionoid mussel (Margaritifera margaritifera) to its host fish (Salmo trutta).
  3. The two AQC publications described research on the influence of population size and density of mussels and host fish, and host–parasite interactions between mussels and their host fish, on the recruitment of juvenile mussels.
  4. The results from these publications filled gaps in knowledge and resulted in recommendations and incentives for conservation. The results and method development have been used in practical conservation work with threatened mussel species and have been implemented and cited in management handbooks. The outcome of the publications has been implemented in large conservation and restoration projects, and in several recent scientific publications.
  5. Specifically, the results from one publication showed that ecological parameters such as mussel and host fish density and population size influenced recruitment of the threatened freshwater pearl mussel. The results from the second publication showed that understanding host–parasite interactions is important for comparing the suitability of host fish strains, and that host fish strains differ in their suitability for mussel infestations. In combination, the articles show that integrating ecological parameters of threatened mussels and their host fish with host–parasite interaction experiments can be an important influence on conservation recommendations, adaptive management and national management programmes for threatened species.
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10.
  1. Most research on anadromous fishes has been invested in their freshwater life‐phases, resulting in a relatively sparse understanding of their spatial ecology during marine life‐phases. However, understanding the marine dispersal of anadromous fishes is essential to identify threats and to implement conservation measures that fully encompass their lifecycle.
  2. The twaite shad Alosa fallax is an anadromous fish increasingly imperilled across its range due to pollution, harvesting, and impediments to freshwater migration, but little is known about its distribution and movements during its marine life‐phase. Here, the application of acoustic telemetry provided novel insights into the coastal dispersal of twaite shad in the UK and Ireland during 2018–2019, and the freshwater entry of individuals during the 2019 spawning season.
  3. Of 73 twaite shad acoustic‐tagged during their upstream migration in the River Severn in May 2018, 58 emigrated from the river. Twelve were subsequently detected 200 km to the south‐west at the Taw–Torridge Estuary between July 2018 and April 2019, where estuarine movements up to 5.8 km inland occurred in summer, winter, and spring. One was subsequently detected in the Munster Blackwater Estuary (Ireland) and then in the River Severn, indicating a minimum movement distance of 950 km. Thirty‐four (59%) of the emigrating individuals from 2018 re‐entered fresh water in the rivers Severn (n = 33) and Wye (n = 2) in April and May 2019.
  4. These results suggest year‐round use of estuarine and nearshore habitats by at least a subset of the twaite shad population during their marine phase, providing evidence of potential range overlap between populations that spawn in different areas in the UK and Ireland, which may be facilitated by substantial dispersal. The results also highlight the potential of telemetry for estimating freshwater and marine mortality, and the benefits of sharing detection data across networks.
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11.
  1. Small‐scale fisheries may pose a serious threat to the conservation of marine mammals. At the same time various factors have led to the decline of small‐scale fisheries, often making them unsustainable. Current rates of biodiversity loss and the reduction of fish stocks and fisheries dictate a thorough understanding of fisheries‐related issues and the implementation of effective management actions.
  2. The Mediterranean monk seal is one of the most endangered marine mammals on Earth; its survival in the eastern Mediterranean Sea is threatened by negative interactions with fisheries. A nationwide questionnaire survey among fishers and port police authorities was carried out in Greece to describe the main characteristics of small‐scale fisheries, and to understand the nature and assess the magnitude of negative interactions between the monk seal and these fisheries. Questionnaire information was verified by a second round of interviews during landings.
  3. The main attributes of the fishers, their fishing boats, and their practices were characteristic of the small‐scale fisheries sector. Overfishing was considered the main reason for fish‐stock reduction, and negative interactions with marine mammals was considered the main issue for the fishing sector.
  4. Monk seals were present, caused damage, and got accidentally entangled in fishing gear throughout Greece. Damage to fishing gear was recorded mainly during spring and summer, and on average affected 21% of all fishing trips and 1% of nets deployed during a fishing trip.
  5. Based on these results, the implementation of general and specific nationwide fishery management and conservation actions are proposed. These actions are mainly aimed at improving fish stock status, changing the behaviour of the fishers, and mitigating seal–fishery interactions in Greece, while promoting the recovery of the Mediterranean monk seal in the eastern Mediterranean Sea.
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12.
  1. Coral reef biodiversity is rapidly decreasing as a result of the loss of coral cover, which modifies the structure and functioning of the ecosystem. Understanding how coral reef communities respond in space and over the long term is essential in order to implement management strategies and reduce the effects of biodiversity loss on coral reefs.
  2. Fish, coral, and algae communities were used as indicators to evaluate changes in coral reef systems. The variation of these communities was studied in a marine protected area composed of three management zones in Cozumel Coral Reef National Park in Quintana Roo, Mexico, over a period of 11 years (2004–2014). The following parameters were monitored annually: (i) total fish density; (ii) fish trophic group densities; (iii) species richness and three fish diversity indices; (iv) relative scleractinian coral cover; and (v) relative macroalgae cover.
  3. In the years in which coastal development, such as the construction of a marina, took place, an increase in the abundance of territorial herbivorous and planktivorous fish was observed. As the coral recovered, macrocarnivores and sessile benthic invertivores were re‐established, whereas scraper herbivores showed no changes in the period of study in any of the three management zones.
  4. Coral cover recovery showed rapid phase‐shift reversal (phase‐shift, macroalgae dominance over coral) in the three zones. Even though the fish density and coral cover recovered, the diversity indices of each fish trophic group exhibited a reduction in the three management zones over time.
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13.
  1. Technological advancements in data collection and analysis are producing a new generation of ecological data. Among these, computer vision (CV) has received increased attention for its robust capabilities for rapidly processing large volumes of digital imagery.
  2. In marine ecosystems, the study of fish connectivity provides fundamental information for assessing fisheries stocks, designing and implementing protected areas and understanding the impact of habitat loss. While the field of fish connectivity has benefited from technological advancements, the extent to which novel techniques, such as CV, have been utilized has not been assessed. To inform future directions and developments, this study reviewed the current use of CV in fish connectivity research, quantified how the implementation of such technology in fish connectivity research compared with other areas of marine research and described how this field could benefit from CV.
  3. The review found that the use of remote camera systems in fish connectivity research is increasing, but the implementation of automated analysis of digital imagery has been slow. Successful implementation and expansion of CV frameworks in aquaculture and coral reef ecology suggest that CV techniques could greatly benefit fish connectivity research.
  4. A case study of potential use of CV in fish connectivity research, scaling up optimal foraging models to predict marine population connectivity, highlights how beneficial it could be.
  5. The capacity for CV techniques to be adopted alongside traditional approaches, the unparalleled speed, accuracy and reliability of these approaches and the benefits of being able to study ecosystems along multiple spatial–temporal scales, all make CV a valuable tool for assessing connectivity. Ultimately, these technologies can assist data-driven decisions that directly influence the health and productivity of marine ecosystems.
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14.
  1. Effectiveness of restoration/repopulation measures may be strongly hindered by the ability of the target species to cope with the environmental conditions of the receiving area.
  2. Although a species has been reported previously for a given area, the environmental conditions and human pressures may have changed, potentially making any restoration attempt ineffective. Evidence is provided showing that the endangered ferruginous limpet Patella ferruginea can complete its reproductive cycle in the northernmost sector of the western Mediterranean.
  3. This supports the idea that the reintroduction and the strict protection of P. ferruginea in the extreme north of its historical geographic range could be effective for the recovery of the species in this area and ultimately the establishment of reproductively viable and stable populations.
  4. Verification of gonadal maturation of specimens experimentally established on the Gulf of Genoa (Ligurian Sea) coastline, as well as evidence of sex change in one individual (the first outside the Alboran Sea), provides further support of the potential for individuals to complete their reproductive cycle in this area.
  5. The results support the potential of actions for the restoration of viable populations of the species along the Ligurian coasts through the introduction of juveniles obtained exclusively by aquaculture techniques, in order to mitigate any impact on donor sites.
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15.
  1. Concern for conservation of seagrass habitat has prompted international transplantation‐style restoration efforts. A recent review of these restoration efforts has highlighted the low success associated with small‐scale restorations, yet scaling up transplantation effort may be too costly for underfunded regions. Small‐scale transplant survival can be enhanced with alleviation of two underlying issues: restoration site selection and donor site selection.
  2. To investigate appropriate donor source selection, donor site environmental influence on seagrass (Halodule wrightii) transplant survival was examined by transplanting donor cores from two environmentally disparate sites to a transplantation site with limited environmental uncertainties. Donor sites were chosen to represent either end of a benthic light gradient (high versus low) to elucidate seagrass resilience to transplantation stress, with respect to donor site conditions.
  3. After total loss of the first trial, a second trial was conducted with stabilizing mesh placed over transplants to reduce stingray bioturbation. The second trial resulted in 100% survival of high light transplants after 12 months and moderate survival (30–60%) of low light transplants for the first six months.
  4. At 18 months, the second trial ended after sediment burial from a hurricane. One year post‐burial, a patch of H. wrightii recovered at the high light transplant site; after six years the patch expanded to approximately 74 m2, an area 37‐fold larger than originally planted.
  5. Results from this transplant experiment provide evidence that donor environment plays a role in transplant resilience. The transplants sourced from high light had 47% greater leaf area per shoot, were more resistant to transplantation stress, and recovered following an extreme event relative to low light transplants. Therefore, selection of donor plants with more resilience features, a transplantation site with limited environmental uncertainties, and adaptive intervention can enhance seagrass resilience at a small planting scale.
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16.
  1. Genidens barbus is a vulnerable marine migrant catfish with low fecundity, a complex life cycle (i.e. mouth breeding), and is the target of industrial and artisanal fisheries of several countries. This species regularly migrates from marine to freshwater environments of the south-western Atlantic.
  2. The aim of this work was to delve deeper into the migration ecology of G. barbus, characterizing both its timing and potential environmental drivers. Furthermore, aspects of the population structure and reproduction of migrants in the lower Uruguay River were studied and the presence of juveniles in the adjacent estuarine recruitment area was evaluated.
  3. Data from 11 years (2008–2018) of records of adult G. barbus captured by artisanal fisheries were used alongside relevant environmental variables that were recorded monthly. Reproductive biology (i.e. sex ratio, gonadosomatic index, fecundity, and oocyte size) was analysed for a period of 3 years (2016–2018). The juvenile abundance in the Río de la Plata estuary was evaluated seasonally.
  4. A total of 935 adult individuals of G. barbus were captured, representing a total biomass of 3,123 kg. The migration timing was from early spring to early summer. The abundance of migrants strongly increased with river discharge, suggesting that this variable regulates the upriver migration. Furthermore, pre- and post-spawn females and males displaying mouth breeding were recorded during the study period, confirming G. barbus reproduction in the lower Uruguay River.
  5. The results obtained suggest that G. barbus ascend to spawn in the freshwater environments upstream from the mouth of the Uruguay River. Then, adult males incubate and carry the embryos downstream, releasing juveniles in the Río de la Plata estuary.
  6. This relevant information will help with the implementation of effective management polices (e.g. fishing restrictions during the reproductive period) for the presently unregulated fishery of this vulnerable species in the lower Uruguay River.
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17.
  1. Passive acoustic monitoring (PAM) is a non‐invasive technique that uses hydrophones to monitor populations and ecosystem dynamics. Although many applications of PAM have been developed in recent years, it has never been used to identify a calling marine species.
  2. The south pass of Fakarava Atoll, French Polynesia, hosts spawning events of many reef fish species, including the camouflage grouper Epinephelus polyphekadion, with a spawning aggregation abundance exceeding 17 000 individuals during the full moons of June and July.
  3. The current study aimed to use PAM to distinguish camouflage grouper sounds among the vocal activities of all fish recorded during the aggregation periods. Audio recordings analysis resulted in the identification of 29 sound types, some of which showed diel and lunar patterns.
  4. Temporal analysis of these sounds in relation to spawning activities allowed the identification of camouflage grouper calls. These calls can be described as a single pulse or a series of ‘boom(s)’ with a pulse duration of ~44 ms and a low dominant frequency of 103 ± 31 Hz. Video recordings show that the camouflage grouper produces the ‘booms’ to initialize spawner ascent and to promote synchronous gamete release into the water column.
  5. The study highlights for the first time that PAM can be used to identify the previously unknown sound of a fish species. Moreover, we can use it to understand the phenology of some biological activities for improving the resolution of fish biodiversity assessments.
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19.
  1. Two migratory and endangered freshwater fish species, Salminus franciscanus and Brycon orthotaenia, are endemic to one of the most important basins for hydropower capacity in South America. These two fish are target species of conservation aquaculture programmes along the São Francisco River system.
  2. In order to implement effective strategies for the conservation of these species, microsatellite markers were developed and used to assess the genetic diversity and structure among wild groups. Fish were collected during the spawning season at four sampling sites, covering more than 1000 km.
  3. Polymorphism loci were assessed, and a total of 133 and 107 alleles were found for S. franciscanus and B. orthotaenia, respectively. Despite the critical conservation status, B. orthotaenia showed high levels of genetic diversity, comparable with those of other closely related species.
  4. Salminus franciscanus exhibited half of the genetic diversity of its sister species in terms of allelic diversity, indicating that this species will be more prone to genetic drift and inbreeding in conservation aquaculture programmes.
  5. The results of an analysis of molecular variance for microsatellite markers in these species (FST = 0.007 for S. franciscanus and FST = 0.003 for B. orthotaenia) and the estimated recent migration rates (>40% among sampling sites) support panmixia in both species, despite the heterogeneities of the riverscape.
  6. The results of this study and the microsatellites developed will play an important role in assisting agencies in making informed decisions on conservation aquaculture programmes.
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20.
  1. Invasive species threaten the conservation of marine environments, and urgent management strategies are needed to prevent their introduction, establishment and spread. Specifically, marine invasive predators destabilize ecological interactions and alter community structure and function. However, most of the evidence showing the effect of these predators is restricted to a few species and regions, while for others the information remains scarce.
  2. This study experimentally evaluated the ecological effects of the sea slug Pleurobranchaea maculata, a recently introduced invasive predator, on the fouling communities of a cold-temperate port in the South-western Atlantic.
  3. The results show that increasing predation pressure reduces significantly the abundance of sea anemones, which are among the preferred prey items.
  4. This study reveals new evidence to help better understand the effects of P. maculata on the biological communities of a recently invaded region. Furthermore, it provides the first experimental evidence supporting the hypothesis that marine invasive predators can induce a significant decrease in the abundance of native species in benthic communities of cold-temperate marine environments in the South-western Atlantic.
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