Combined effects of urbanization and connectivity on iconic coastal fishes

Evaluating the influence of marine protected areas on surf zone fish

Marine protected areas (MPAs) globally serve conservation and fisheries management goals, generating positive effects in some marine ecosystems. Surf zones and sandy beaches, critical ecotones bridging land and sea, play a pivotal role in the life cycles of numerous fish species and serve as prime areas for subsistence and recreational fishing. Despite their significance, these areas remain understudied when evaluating the effects of MPAs. We compared surf zone fish assemblages inside and outside MPAs across 3 bioregions in California (USA). Using seines and baited remote underwater videos (BRUVs), we found differences in surf zone fish inside and outside MPAs in one region. Inside south region MPAs, we observed higher abundance (Tukey's honest significant difference [HSD] = 0.83, p = 0.0001) and richness (HSD = 0.22, p = 0.0001) in BRUVs and greater biomass (HSD = 0.32, p = 0.0002) in seine surveys compared with reference sites. Selected live-bearing, fished taxa were positively affected by MPAs. Elasmobranchs displayed greater abundance in BRUV surveys and higher biomass in seine surveys inside south region MPAs (HSD = 0.35, p = 0.0003 and HSD = 0.23, p = 0.008, respectively). Although we observed no overall MPA signal for Embiotocidae, abundances of juvenile and large adult barred surfperch (Amphistichus argenteus), the most abundant fished species, were higher inside MPAs (K-S test D = 0.19, p < 0.0001). Influence of habitat characteristics on MPA performance indicated surf zone width was positively associated with fish abundance and biomass but negatively associated with richness. The south region had the largest positive effect size on all MPA performance metrics. Our findings underscored the variability in species richness and composition across regions and survey methods that significantly affected differences observed inside and outside MPAs. A comprehensive assessment of MPA performance should consider specific taxa, their distribution, and the effects of habitat factors and geography.

A comparison of biomonitoring methodologies for surf zone fish communities

Surf zones are highly dynamic marine ecosystems that are subject to increasing anthropogenic and climatic pressures, posing multiple challenges for biomonitoring. Traditional methods such as seines and hook and line surveys are often labor intensive, taxonomically biased, and can be physically hazardous. Emerging techniques, such as baited remote underwater video (BRUV) and environmental DNA (eDNA) are promising nondestructive tools for assessing marine biodiversity in surf zones of sandy beaches. Here we compare the relative performance of beach seines, BRUV, and eDNA in characterizing community composition of bony (teleost) and cartilaginous (elasmobranch) fishes of surf zones at 18 open coast sandy beaches in southern California. Seine and BRUV surveys captured overlapping, but distinct fish communities with 50% (18/36) of detected species shared. BRUV surveys more frequently detected larger species (e.g. sharks and rays) while seines more frequently detected one of the most abundant species, barred surfperch (Amphistichus argenteus). In contrast, eDNA metabarcoding captured 88.9% (32/36) of all fishes observed in seine and BRUV surveys plus 57 additional species, including 15 that frequent surf zone habitats. On average, eDNA detected over 5 times more species than BRUVs and 8 times more species than seine surveys at a given site. eDNA approaches also showed significantly higher sensitivity than seine and BRUV methods and more consistently detected 31 of the 32 (96.9%) jointly observed species across beaches. The four species detected by BRUV/seines, but not eDNA were only resolved at higher taxonomic ranks (e.g. Embiotocidae surfperches and Sygnathidae pipefishes). In frequent co-detection of species between methods limited comparisons of richness and abundance estimates, highlighting the challenge of comparing biomonitoring approaches. Despite potential for improvement, results overall demonstrate that eDNA can provide a cost-effective tool for long-term surf zone monitoring that complements data from seine and BRUV surveys, allowing more comprehensive surveys of vertebrate diversity in surf zone habitats.

Habitat Provision and Erosion Are Influenced by Seagrass Meadow Complexity: A Seascape Perspective

Habitat complexity plays a critical role in shaping biotic assemblages and ecosystem processes. While the impacts of large differences in habitat complexity are often well understood, we know less about how subtle differences in structure affect key ecosystem functions or properties such as biodiversity and biomass. The late-successional seagrass Posidonia australis creates vital habitat for diverse fauna in temperate Australia. Long-term human impacts have led to the decline of P. australis in some estuaries of eastern Australia, where it is now classified as an endangered ecological community. We examined the influence of P. australis structural complexity at small (seagrass density) and large (meadow fragmentation) spatial scales on fish and epifauna communities, predation and sediment erosion. Fine-scale spatially balanced sampling was evenly distributed across a suite of environmental covariates within six estuaries in eastern Australia using the Generalised Random Tessellation Structures approach. We found reduced erosion in areas with higher P. australis density, greater abundance of fish in more fragmented areas and higher fish richness in vegetated areas further from patch edges. The abundance of epifauna and fish, and fish species richness were higher in areas with lower seagrass density (seagrass density did not correlate with distance to patch edge). These findings can inform seagrass restoration efforts by identifying meadow characteristics that influence ecological functions and processes.

The role of inputs of marine wrack and carrion in sandy-beach ecosystems: a global review

Sandy beaches are iconic interfaces that functionally link the ocean with the land via the flow of organic matter from the sea. These cross-ecosystem fluxes often comprise uprooted seagrass and dislodged macroalgae that can form substantial accumulations of detritus, termed 'wrack', on sandy beaches. In addition, the tissue of the carcasses of marine animals that regularly wash up on beaches form a rich food source ('carrion') for a diversity of scavenging animals. Here, we provide a global review of how wrack and carrion provide spatial subsidies that shape the structure and functioning of sandy-beach ecosystems (sandy beaches and adjacent surf zones), which typically have little in situ primary production. We also examine the spatial scaling of the influence of these processes across the broader land- and seascape, and identify key gaps in our knowledge to guide future research directions and priorities. Large quantities of detrital kelp and seagrass can flow into sandy-beach ecosystems, where microbial decomposers and animals process it. The rates of wrack supply and its retention are influenced by the oceanographic processes that transport it, the geomorphology and landscape context of the recipient beaches, and the condition, life history and morphological characteristics of the macrophyte taxa that are the ultimate source of wrack. When retained in beach ecosystems, wrack often creates hotspots of microbial metabolism, secondary productivity, biodiversity, and nutrient remineralization. Nutrients are produced during wrack breakdown, and these can return to coastal waters in surface flows (swash) and aquifers discharging into the subtidal surf. Beach-cast kelp often plays a key trophic role, being an abundant and preferred food source for mobile, semi-aquatic invertebrates that channel imported algal matter to predatory invertebrates, fish, and birds. The role of beach-cast marine carrion is likely to be underestimated, as it can be consumed rapidly by highly mobile scavengers (e.g. foxes, coyotes, raptors, vultures). These consumers become important vectors in transferring marine productivity inland, thereby linking marine and terrestrial ecosystems. Whilst deposits of organic matter on sandy-beach ecosystems underpin a range of ecosystem functions and services, they can be at variance with aesthetic perceptions resulting in widespread activities, such as 'beach cleaning and grooming'. This practice diminishes the energetic base of food webs, intertidal fauna, and biodiversity. Global declines in seagrass beds and kelp forests (linked to global warming) are predicted to cause substantial reductions in the amounts of marine organic matter reaching many beach ecosystems, likely causing flow-on effects for food webs and biodiversity. Similarly, future sea-level rise and increased storm frequency are likely to alter profoundly the physical attributes of beaches, which in turn can change the rates at which beaches retain and process the influxes of wrack and animal carcasses. Conservation of the multi-faceted ecosystem services that sandy beaches provide will increasingly need to encompass a greater societal appreciation and the safeguarding of ecological functions reliant on beach-cast organic matter on innumerable ocean shores worldwide.

Recovery of ghost crabs metapopulations on urban beaches during the Covid-19 "anthropause"

The majority of government authorities initially responded to COVID-19 pandemic by declaring lockdown to facilitate social distancing and minimize virus spreading. This period termed "anthropause" provided a unique opportunity to evaluate the recovery of wildlife in the absence of stressors on urban ecosystems. We assessed whether the anthropause associated with beach closures during the COVID-19 pandemic resulted in repopulation of the Atlantic ghost crab Ocypode quadrata (Fabricius, 1787) on urban beaches. For this purpose, we compiled a historic dataset (2013-2019) of the ghost crab density and performed biweekly burrow measurements from June/2020 to May/2021. Recovery of ghost crab metapopulation during the lockdown occurred even in more human-modified beaches. Burrow abundance significantly increased in urban sectors, but not in control site along with the time of pandemic. The reduction in the mean burrow opening diameter during this period evidenced that young metapopulation have thrived on urban beaches when recreational activities ceased. Our results show that urban beaches should not be exclusively managed for recreational purposes. Initiatives with a focus on wildlife conservation including spatial-temporal controlled beach closures may increase the biodiversity resilience.

Cumulative stressors impact macrofauna differentially according to sandy beach type: A meta-analysis

Many studies have demonstrated human impacts on sandy beach macroinvertebrates. However, little is known about causative drivers among multiple co-occurring stressors and how these interact with natural habitat conditions to yield specific faunal responses. We performed a global meta-analysis to shed light on how interactions between human disturbances and beach morphodynamics shape macroinvertebrate populations. We found that supralittoral forms (Talitridae and Ocypodidae) responded more negatively to the Human Modification Metric (a proxy for urbanization) on dissipative beaches, whereas intertidal organisms (Hippidae and Cirolanidae) showed more negative responses on non-dissipative beaches. Based on these findings we propose the Cumulative Harshness Hypothesis (CHH), which predicts higher sensitivity of beach macroinvertebrates to human disturbances when inhabiting a harsher physical environment according to their life histories. Secondly, we compared the response of macroinvertebrates to urbanization levels from local to larger scales (from 500 to 50000 m). Supralittoral families responded more negatively to local urbanization, which leads to habitat loss due to removal or reduction of upper beach zones. Conversely, intertidal organisms with planktonic larval stages were more affected by urbanization at the largest spatial scales, which we hypothesize disrupts metapopulation dynamics by impacting the supply of larvae that could colonize human-disturbed beaches. The differential effects of human disturbances on macroinvertebrates according to beach morphodynamics suggest that the efficiency of these ecological indicators for beach monitoring is context-dependent. Focusing on multiple stressors rather than on a single one is also critical to mitigate human impacts on these threatened ecosystems.

Mapping and assessment of future changes in the coastal and marine ecosystem services supply in Lithuania

Assessing and mapping ecosystem services (ES) became an integral part of coastal and marine management practices. Hence, quantitative and validated approaches are lacking, especially to address future conditions. The objective of this study is to apply further existing and develop new methodological frameworks to quantitatively assess and map the current and future supply of 3 ES in the coastal zone of Lithuania: coastal flood protection, nutrient regulation, and maintenance of nursery conditions. For coastal flood ES modelling, 2 time periods (1990 and 2018) and 4 scenarios (A0, A1 A2, A3 - based on future socio-economic changes in Lithuania) were analysed. The coastal flood protection ES model was validated (r² = 0.30) using tree cover density. The results showed spatial differences among the analysed periods but no statistical differences. High supply areas are located in the southern coastal area, while the central part displays a low supply. For nutrient regulation and maintenance of nursery conditions, 7 time periods were analysed: a historical period and 6 scenarios based on Representative Concentration Pathway 4.5 and 8.5 and 3 Shared Socioeconomic Pathways. The nutrient regulation ES model was validated (r² = 0.85) using in situ nutrient. Statistical differences were observed for this ES, but a similar spatial distribution of high and low supply areas. A decrease in the supply was observed comparing the historical period and future scenarios. Maintenance of nursery conditions was validated (r² = 0.72) based on the protection status of the coastal zone. Results show no statistical differences and similar spatial patterns among the periods. Rocky and sandbank areas show a high supply for this ES. Limitations of our work are mainly related to the resolution of the utilised indicators. Nevertheless, the information obtained from our models can support spatial planning and decision-making processes.

Human Health and Ocean Pollution

Background

Pollution - unwanted waste released to air, water, and land by human activity - is the largest environmental cause of disease in the world today. It is responsible for an estimated nine million premature deaths per year, enormous economic losses, erosion of human capital, and degradation of ecosystems. Ocean pollution is an important, but insufficiently recognized and inadequately controlled component of global pollution. It poses serious threats to human health and well-being. The nature and magnitude of these impacts are only beginning to be understood.

Goals

(1) Broadly examine the known and potential impacts of ocean pollution on human health. (2) Inform policy makers, government leaders, international organizations, civil society, and the global public of these threats. (3) Propose priorities for interventions to control and prevent pollution of the seas and safeguard human health.

Methods

Topic-focused reviews that examine the effects of ocean pollution on human health, identify gaps in knowledge, project future trends, and offer evidence-based guidance for effective intervention.

Environmental Findings

Pollution of the oceans is widespread, worsening, and in most countries poorly controlled. It is a complex mixture of toxic metals, plastics, manufactured chemicals, petroleum, urban and industrial wastes, pesticides, fertilizers, pharmaceutical chemicals, agricultural runoff, and sewage. More than 80% arises from land-based sources. It reaches the oceans through rivers, runoff, atmospheric deposition and direct discharges. It is often heaviest near the coasts and most highly concentrated along the coasts of low- and middle-income countries. Plastic is a rapidly increasing and highly visible component of ocean pollution, and an estimated 10 million metric tons of plastic waste enter the seas each year. Mercury is the metal pollutant of greatest concern in the oceans; it is released from two main sources - coal combustion and small-scale gold mining. Global spread of industrialized agriculture with increasing use of chemical fertilizer leads to extension of Harmful Algal Blooms (HABs) to previously unaffected regions. Chemical pollutants are ubiquitous and contaminate seas and marine organisms from the high Arctic to the abyssal depths.

Ecosystem Findings

Ocean pollution has multiple negative impacts on marine ecosystems, and these impacts are exacerbated by global climate change. Petroleum-based pollutants reduce photosynthesis in marine microorganisms that generate oxygen. Increasing absorption of carbon dioxide into the seas causes ocean acidification, which destroys coral reefs, impairs shellfish development, dissolves calcium-containing microorganisms at the base of the marine food web, and increases the toxicity of some pollutants. Plastic pollution threatens marine mammals, fish, and seabirds and accumulates in large mid-ocean gyres. It breaks down into microplastic and nanoplastic particles containing multiple manufactured chemicals that can enter the tissues of marine organisms, including species consumed by humans. Industrial releases, runoff, and sewage increase frequency and severity of HABs, bacterial pollution, and anti-microbial resistance. Pollution and sea surface warming are triggering poleward migration of dangerous pathogens such as the Vibrio species. Industrial discharges, pharmaceutical wastes, pesticides, and sewage contribute to global declines in fish stocks.

Human Health Findings

Methylmercury and PCBs are the ocean pollutants whose human health effects are best understood. Exposures of infants in utero to these pollutants through maternal consumption of contaminated seafood can damage developing brains, reduce IQ and increase children's risks for autism, ADHD and learning disorders. Adult exposures to methylmercury increase risks for cardiovascular disease and dementia. Manufactured chemicals - phthalates, bisphenol A, flame retardants, and perfluorinated chemicals, many of them released into the seas from plastic waste - can disrupt endocrine signaling, reduce male fertility, damage the nervous system, and increase risk of cancer. HABs produce potent toxins that accumulate in fish and shellfish. When ingested, these toxins can cause severe neurological impairment and rapid death. HAB toxins can also become airborne and cause respiratory disease. Pathogenic marine bacteria cause gastrointestinal diseases and deep wound infections. With climate change and increasing pollution, risk is high that Vibrio infections, including cholera, will increase in frequency and extend to new areas. All of the health impacts of ocean pollution fall disproportionately on vulnerable populations in the Global South - environmental injustice on a planetary scale.

Conclusions

Ocean pollution is a global problem. It arises from multiple sources and crosses national boundaries. It is the consequence of reckless, shortsighted, and unsustainable exploitation of the earth's resources. It endangers marine ecosystems. It impedes the production of atmospheric oxygen. Its threats to human health are great and growing, but still incompletely understood. Its economic costs are only beginning to be counted.Ocean pollution can be prevented. Like all forms of pollution, ocean pollution can be controlled by deploying data-driven strategies based on law, policy, technology, and enforcement that target priority pollution sources. Many countries have used these tools to control air and water pollution and are now applying them to ocean pollution. Successes achieved to date demonstrate that broader control is feasible. Heavily polluted harbors have been cleaned, estuaries rejuvenated, and coral reefs restored.Prevention of ocean pollution creates many benefits. It boosts economies, increases tourism, helps restore fisheries, and improves human health and well-being. It advances the Sustainable Development Goals (SDG). These benefits will last for centuries.

Recommendations

World leaders who recognize the gravity of ocean pollution, acknowledge its growing dangers, engage civil society and the global public, and take bold, evidence-based action to stop pollution at source will be critical to preventing ocean pollution and safeguarding human health.Prevention of pollution from land-based sources is key. Eliminating coal combustion and banning all uses of mercury will reduce mercury pollution. Bans on single-use plastic and better management of plastic waste reduce plastic pollution. Bans on persistent organic pollutants (POPs) have reduced pollution by PCBs and DDT. Control of industrial discharges, treatment of sewage, and reduced applications of fertilizers have mitigated coastal pollution and are reducing frequency of HABs. National, regional and international marine pollution control programs that are adequately funded and backed by strong enforcement have been shown to be effective. Robust monitoring is essential to track progress.Further interventions that hold great promise include wide-scale transition to renewable fuels; transition to a circular economy that creates little waste and focuses on equity rather than on endless growth; embracing the principles of green chemistry; and building scientific capacity in all countries.Designation of Marine Protected Areas (MPAs) will safeguard critical ecosystems, protect vulnerable fish stocks, and enhance human health and well-being. Creation of MPAs is an important manifestation of national and international commitment to protecting the health of the seas.

Human-engineered hydrodynamic regimes as a driver of cryptic microinvertebrate assemblages on urban artificial shorelines

Urban shorelines undergo substantial hydrodynamic changes as a result of coastal engineering and shoreline armouring that can alter sedimentation, turbidity, and other factors. These changes often coincide with major shifts in the composition and distribution of marine biota, however, rarely are hydrodynamic-mediated factors confirmed experimentally as the mechanism underpinning these shifts. This study first characterized hydrodynamic-related distribution patterns among epilithic and epiphytic microinvertebrates on urban seawalls in Singapore. We found reduced microinvertebrate abundances and distinct microinvertebrate community structure within benthic turf algae in areas where coastal defences had reduced wave energy and increased sediment deposition, among other hydrodynamic-related abiotic changes. Low-exposure areas also had reduced densities of macroinvertebrate grazers and less dense turf algae (lower mass per cm²) than adjacent high-exposure areas. Using harpacticoid copepods as a model taxon, we performed a reciprocal transplant experiment to discern between the effects of exposure-related conditions and grazing. Results from the experiment indicate that conditions associated with restricted wave energy from shoreline engineering limit harpacticoid population densities, as transplantation to low-exposure areas led to rapid reductions in abundance. At the same time, we found no effect from grazer exclusion cages, suggesting harpacticoids are minimally impacted by exposure-related gradients in gastropod macrograzer densities over short time scales. Given the key role of intertidal microinvertebrates, particularly harpacticoids, in nearshore food webs, we postulate that human-engineered hydrodynamic regimes are an important factor shaping marine ecosystem functioning in urban areas.

Hierarchical partitioning of fish diversity and scale-dependent environmental effects in tropical coastal ecosystems

The spatial structure of the fish diversity and site-scale and landscape-scale environmental effects were investigated across hierarchical levels in tropical coastal ecosystems. Total diversity (γ) was hierarchically partitioned into α and β components using both the additive and multiplicative methods. A model selection based on the AICc was applied to generalized linear mixed models relating diversity measures to environmental variables and including random effects for hierarchical levels and season. Short-term seasonal effects were negligible. Spatial effects were more relevant at the site level and negligible at the subregion level, due to the high spatial heterogeneity and the natural pooling of ecosystems, respectively. Site-scale environmental effects were more relevant at the subregion level, with eutrophic conditions (continental influence) favoring the species richness (α and γ) and higher absence of species (β^A) in oligotrophic conditions (marine influence). At the system level, the positive effect of the distance from the ocean on γ and higher β^A in oligotrophic conditions reinforced the positive continental influence on fish diversity. Environmental homogenization processes were most likely associated with the negative effect of the pasture cover on α at the system level, and γ and β^A at the site level. The negative effect of the forest cover on the later diversity measure evidenced its relevance to maintain richer but more similar assemblages, whereas the positive continental influence was most likely due to the loss of stenohaline marine species. This study evidenced that disentangling spatial, land use, and marine vs. continental effects on diversity components is critical to understand the primary determinants of the fish diversity in tropical coastal ecosystems.

Effects of seascape connectivity on reserve performance along exposed coastlines

Seascape connectivity (landscape connectivity in the sea) can modify reserve performance in low-energy marine ecosystems (e.g., coral reefs, mangroves, and seagrass), but it is not clear whether similar spatial linkages also shape reserve effectiveness on high-energy, exposed coastlines. We used the surf zones of ocean beaches in eastern Australia as a model system to test how seascape connectivity and reserve attributes combine to shape conservation outcomes. Spatial patterns in fish assemblages were measured using baited remote underwater video stations in 12 marine reserves and 15 fished beaches across 2000 km of exposed coastline. Reserve performance was shaped by both the characteristics of reserves and the spatial properties of the coastal seascapes in which reserves were embedded. Number of fish species and abundance of harvested fishes were highest in surf-zone reserves that encompassed >1.5 km of the surf zone; were located < 100 m to rocky headlands; and included pocket beaches in a heterogeneous seascape. Conservation outcomes for exposed coastlines may, therefore, be enhanced by prioritizing sufficiently large areas of seascapes that are strongly linked to abutting complementary habitats. Our findings have broader implications for coastal conservation planning. Empirical data to describe how the ecological features of high-energy shorelines influence conservation outcomes are lacking, and we suggest that seascape connectivity may have similar ecological effects on reserve performance on both sheltered and exposed coastlines.

Coastal fish assemblages reflect marine habitat connectivity and ontogenetic shifts in an estuary-bay-continental shelf gradient

The success of marine management initiatives and our capability for dealing with environmental change largely depend on our understanding regarding the distribution of species and their habitat preferences. In the present study, we deployed baited remote underwater video systems (BRUVs) in a portion of Brazilian central coast (i.e., Todos os Santos Bay) to describe fish species-habitat associations along an estuary-bay-continental shelf gradient. Significant variation in the fish assemblage was found among three ecosystems, four depth classes, and eight different types of habitat, confirming that the structure and composition of fish assemblages is mediated by a set of habitat characteristics forming an ecological mosaic. The highest species richness and relative abundance were found in the mangroves and reefs. The data demonstrated that some species, such as Lutjanus jocu, Lutjanus synagris, Carangoides bartholomaei, Eucinostomus argenteus and Eucinostomus melanopterus had clear ontogenetic shifts among habitats and across ecosystems. Some species (Sphoeroides greeley, L. synagris, and Eucinostomus gula) were widespread along the ecosystem-level gradient and were observed in a number of different habitats, reflecting more generalist habitat associations. By contrast, a large number of species (54; e.g., Ptereleotris randali, Decapterus macarellus and Mugil curema) were recorded in a single habitat type, indicating they were habitat specialists. Despite this apparent habitat-related pattern, the size-mediated relationships found in many species indicate cross-migration along the ecosystem gradient. Our findings have implications for the conservation and monitoring of fish assemblages highlighting the role of the connectivity of marine habitats as a conservation priority toward to an ecosystem-based management strategy.