No-take marine reserves control the recovery of sea urchin populations after mass mortality events

Mesophotic zone as buffer for biodiversity protection: A promising opportunity to enhance MPA effectiveness

Coastal areas conservation strategies often left deeper habitats, such as mesophotic ones, unprotected and exposed to anthropogenic activities. In this context, an approach for including the mesophotic zone inside protection plans is proposed, considering 27 Italian Marine Protected Areas (MPAs) as a model. MPAs were classified considering their bathymetries, exposure to marine heat waves (MHWs), mass mortality events (MMEs) and, using a local ecological knowledge (LEK) approach, the estimated resilience of certain sessile species after MMEs. Only 8 MPAs contained considerable mesophotic areas, with stronger MHWs mainly occurring in shallower MPAs, and MMEs mostly affecting coralligenous assemblages. Even with only a 10% response rate, the LEK approach provided useful information on the resilience of certain species, allowing us to suggest that the presence of nearby mesophotic areas can help shallower habitats facing climate change, thus making the "deep refugia" hypothesis, usually related to tropical habitats, applicable also for the Mediterranean Sea.

Diversity of Molluscan Assemblage in Relation to Biotic and Abiotic Variables in Brown Algal Forests

Canopy-forming macroalgae, mainly those belonging to the order Fucales, form the so-called brown algal forests, which are among the most productive assemblages in shallow coastal zones. Their vertical, branching canopies increase nearshore primary production, provide nursery areas for juvenile fish, and sustain understory assemblages of smaller algae and both sessile and vagile fauna. The majority of benthic invertebrates inhabiting these forests have larval stages that spend some time floating freely or swimming in the plankton. Therefore, canopy-forming macroalgae play an important role as species collectors related to larval supply and hydrodynamic processes. During the past several decades, brown algal forests have significantly reduced their extension and coverage in the Mediterranean basin, due to multiple interacting natural and anthropogenic pressures, with negative consequences also for the related fauna. The aim of this research was to examine how differences in macrophyte abundance and structure, as well as environmental variables, affect the associated molluscan communities in the shallow northern Adriatic Sea. Sampling sites with well-developed vegetation cover dominated by different canopy-forming species were selected in the shallow infralittoral belt of the northern Adriatic Sea in the spring–summer period of the years 2019 and 2020. Our results confirm the importance of algal forests for molluscan assemblage, with a total of 68 taxa of molluscs found associated with macrophytes. Gastropods showed the highest richness and abundance, followed by bivalves. Mollusc richness and diversity (in terms of biotic indices) were not related with the degree of development of canopy-forming species (in terms of total cover and total volume), nor with the ecological status of benthic macroalgae at different depths. On the contrary, the variability in molluscan taxa abundances was explained by some environmental variables, such as temperature, pH, light, and nitrates concentration.

Sea urchin harvest inside marine protected areas: an opportunity to investigate the effects of exploitation where trophic upgrading is achieved

Background

Marine protected areas (MPAs) usually have both positive effects of protection for the fisheries' target species and indirect negative effects for sea urchins. Moreover, often in MPAs sea urchin human harvest is restricted, but allowed. This study is aimed at estimating the effect of human harvest of the sea urchin Paracentrotus lividus within MPAs, where fish exploitation is restricted and its density is already controlled by a higher natural predation risk. The prediction we formulated was that the lowest densities of commercial sea urchins would be found where human harvest is allowed and where the harvest is restricted, compared to where the harvest is forbidden.

Methods

At this aim, a collaborative database gained across five MPAs in Sardinia (Western Mediterranean, Italy) and areas outside was gathered collecting sea urchin abundance and size data in a total of 106 sites at different degrees of sea urchin exploitation: no, restricted and unrestricted harvest sites (NH, RH and UH, respectively). Furthermore, as estimates made in past monitoring efforts (since 2005) were available for 75 of the sampled sites, for each of the different levels of exploitation, the rate of variation in the total sea urchin density was also estimated.

Results

Results have highlighted that the lowest sea urchin total and commercial density was found in RH sites, likely for the cumulative effects of human harvest and natural predation. The overall rate of change in sea urchin density over time indicates that only NH conditions promoted the increase of sea urchin abundance and that current local management of the MPAs has driven towards an important regression of populations, by allowing the harvest. Overall, results suggest that complex mechanisms, including synergistic effects between natural biotic interactions and human pressures, may occur on sea urchin populations and the assessment of MPA effects on P. lividus populations would be crucial to guide management decisions on regulating harvest permits. Overall, the need to ban sea urchin harvest in the MPAs to avoid extreme reductions is encouraged, as inside the MPAs sea urchin populations are likely under natural predation pressures for the trophic upgrading.

Resurvey of sea urchins and mussels at protected and harvested shores a decade after: A beyond-BACI approach

Comparing temporal patterns of distribution and abundance of target organisms between protected and harvested shores is essential to assess the extant effectiveness of marine protected areas (MPAs) and whether it is maintained through time. By means of an adapted Beyond-BACI approach, we compared the short- and long-term patterns of variation in the abundance of the sea urchin Paracentrotus lividus and the mussel Mytilus galloprovincialis at a protected shore (within the Parque Litoral Norte MPA, Portugal) and at three adjacent shores subject to intense harvesting over a decadal interval. Despite the existence of the MPA for more than 30 years, we did not obtain clear evidence of its persistent or recent effectiveness on intertidal species of commercial interest. We suggest the need for refining management options along the northern Portuguese coast, possibly by better enforcing current regulations and reconsidering the present design of protection schemes. Moreover, the adopted analytical approach may represent a methodological reference for similar investigations in systems where the perturbation of interest (protection or disturbance) would not occur at a given time during the course of the study, but has been operating since before the first sampling occasion and maintained until subsequent surveys.

First Restoration Experiment for Gongolaria barbata in Slovenian Coastal Waters. What Can Go Wrong?

The global decline of brown algal forests along rocky coasts is causing an exceptional biodiversity loss. Regardless of conservation efforts, different techniques have been developed for large-scale restoration strategies in the Mediterranean Sea. In this study we tested ex situ pilot restoration of Gongolaria barbata (=Treptacantha barbata) for the first time in Slovenian coastal waters. Healthy apical fronds of the species were collected and the development of recruits on clay tiles was followed under laboratory conditions for 20 days. Despite the experimental difficulties experienced, especially due to the lack of antibiotics to prevent the growth of the biofilm, G. barbata recruits were outplanted in the sea on two concrete plates with 48 tiles each, protected by purpose-built cages to avoid grazing by herbivorous fish. The high survival rate of juveniles after four months in the field (89% of the tiles on the plate that was constantly protected) suggests that outplanting G. barbata is an operable approach for restoration efforts in the northern Adriatic Sea. Our first experiment in Slovenian coastal waters provides new information for the optimization of the best practices during the laboratory cultivation and addresses the early steps of restoration and introduction of young thalli in the natural environment.

Invertebrate health in marine protected areas (MPAs)

Marine protected areas (MPAs) consist of various categories of safeguarded areas in the marine environment, from semi-protected areas to total no take zones. The reported effects of MPAs are overwhelmingly positive, with numerous reports of fish size (biomass), abundance (recovery) and diversity increases, however, literature is lacking on the role and consequences of MPAs on parasite and disease dynamics, and in particular, invertebrate health. The implementation of MPAs has been known to alter trophic cascades and community dynamics, and with invertebrates commonly at the base of these systems, it is vital that their status is investigated. Overcrowding in areas closed to fishing is known to have parasitological consequences in some scenarios, and land/water use change has been known to alter host and vector communities, possibly elevating disease risk. Equally, reserves can be used as tools for alleviating impacts of marine disease. This review aims to consolidate extant literature and provide a comprehensive viewpoint on how invertebrates (and their health status) can be affected by MPAs, which are increasingly being implemented based on the relative urgency now being placed on protecting global biodiversity. In highlighting the paucity of knowledge surrounding MPAs and disease, especially that of the unenigmatic invertebrate groups, this review, published in the Special Issue on 'Invertebrates as One Health Sentinels', provides an opportunity for wide dissemination and provocation of further research in this area.

Ecological traits, genetic diversity and regional distribution of the macroalga Treptacantha elegans along the Catalan coast (NW Mediterranean Sea)

The widespread decline of canopy-forming macroalgal assemblages has been documented in many regions during the last decades. This pattern is often followed by the replacement of structurally complex algal canopies by more simplified habitats (e.g., turfs or sea urchin barren grounds). Against all odds, the fucoid Treptacantha elegans, a large Mediterranean brown macroalga, broadened its depth range to deeper and exposed environments and displayed an unexpected range expansion along the northern coast of Catalonia over the last two decades. Here, we reconstruct the spread of T. elegans in time and space and unravel ecological and demographic traits such as population dynamics and genetic patterns to provide a comprehensive and integrated view of the current status and geographical expansion for this species. Fast-growing dynamics, early fertile maturity, and high turnover rate are the main competitive advantages that allow the exposed populations of T. elegans to colonize available substrata and maintain dense and patchy populations. We also provided evidence that the deeper and exposed populations of T. elegans constitute a single group across the Catalan coast, with little genetic differentiation among populations. This seems to support the hypothesis of a unique source of spread in the last decades from the Medes Islands No-Take Zone towards both southern and northern waters.

Decadal dynamics of subtidal barrens habitat

Rocky reef barrens that are devoid of macroalgae can be created by various mechanisms, and are often maintained in the long-term by grazing urchins. The persistence of barrens varies greatly among locations, although few studies have investigated the stability of this habitat over multiple decades, particularly at large spatial scales. We used aerial images to test for differences in temporal trajectories of shallow (2-10 m) barrens at 21 sites (average size 12 ha) over 30 years across 500 km of coastline in New South Wales, Australia. Longer-term (40-68 yr) trajectories of barrens cover were documented for five of the sites and these generally reflected the 30-year patterns. Averaged across all sites, barrens area increased at a rate of 19.9 ± 8.4 m² per year per hectare of reef from 1980s-2010s. Importantly, however, 55% of sites had stable or fluctuating (±10% cover) barrens over this period, rather than displaying continual increases. Although the extent of shallow barrens increases with latitude, the temporal dynamics of barrens did not differ among three latitudinal regions where barrens are the most extensive. Associations between variability in barrens cover and environmental variables indicated that reef topography might pay a role in influencing barrens. Examples of such long-term persistence of extensive barrens are relatively rare and potential reasons for this and possible future changes are discussed.

Long-term monitoring of temperate macroalgal assemblages inside and outside a No take marine reserve

Macroalgal communities have an essential role in the shallow benthic habitats of temperate seas, where changes in their composition can resonate through entire coastal ecosystems. As all major ecosystems on Earth, algal beds have already been affected by multiple disturbances. Passive conservation tools, such as marine protected areas or No-take zones, have the potential to reduce some of the anthropogenic impacts by limiting human activity. However, without a good knowledge of the natural community dynamics, it is not easy to discern between changes fruit of the intrinsic variability of biological communities and the ones caused by human-related stressors. In this study, we evaluated the natural variability of macroalgal communities' composition inside and outside a Mediterranean No-Take marine reserve during 15 years. We described their temporal dynamics considering their main drivers and we tested the effect of protection in seaweed beds. We did not find differences either in the composition of the macroalgal assemblages or the total algal cover between protected and non-protected locations over the fifteen years of study. Nevertheless, we observed a positive effect of the protection increasing the cover of some specific species, such as the canopy-forming Treptacantha elegans. Our results highlight the importance of obtaining long-term data in ecological studies to better understand the natural variability of marine communities. Accordingly, a robust understanding of the community dynamics would help us to avoid misinterpretations between 'impacted' or 'in-recovery' communities when recovery times are longer than the study periods.

Coastal fish assemblages and predation pressure in northern-central Chilean Lessonia trabeculata kelp forests and barren grounds

Kelp forests are declining in many parts of the globe, which can lead to the spreading of barren grounds. Increased abundances of grazers, mainly due to reduction of their predators, are among the causes of this development. Here, we compared the species richness (SR), frequency of occurrence (FO), and maximum abundance (MaxN) of predatory fish and their predation pressure between kelp forest and barren ground habitats of northern-central Chile. Sampling was done using baited underwater cameras with vertical and horizontal orientation. Two prey organisms were used as tethered baits, the black sea urchin Tetrapygus niger and the porcelanid crab Petrolisthes laevigatus. SR did not show major differences between habitats, while FO and MaxN were higher on barren grounds in vertical videos, with no major differences between habitats in horizontal videos. Predation pressure did not differ between habitats, but after 24 h consumption of porcelanid crabs was significantly higher than that of sea urchins. Scartichthys viridis/gigas was the main predator, accounting for 82% of the observed predation events on Petrolisthes laevigatus. Most of these attacks occurred on barren grounds. Scartichthys viridis/gigas was the only fish observed attacking (but not consuming) tethered sea urchins. High abundances of opportunistic predators (Scartichthys viridis/gigas) are probably related to low abundances of large predatory fishes. These results suggest that intense fishing activity on large predators, and their resulting low abundances, could result in low predation pressure on sea urchins, thereby contributing to the increase of T. niger abundances in subtidal rocky habitats.