Shallow Coastal Habitats Research Articles

Impacts of estuarine habitat degradation on the modeled life history of marine estuarine-dependent and resident fish species.

Shallow coastal and estuarine habitats play an essential role in the life cycles of many fish species, providing spawning, nursery, feeding, and migration areas. However, these ecologically valuable habitats are increasingly threatened by anthropogenic activities, causing substantial changes in both habitat availability and quality. Fish species use these shallow coastal habitats and estuaries during various life stages, leading to their categorization into guilds based on how and when they rely on these areas. This differential functional use of estuaries means that changes to these habitats may affect each guild differently. To understand the impact of estuarine habitat degradation on fish populations, it is therefore necessary to consider the full life cycle of fish and when they rely on these coastal habitats. Here, we use conceptual size-structured population models to study how estuarine habitat degradation affects two functionally different guilds. We use these models to predict how reduced food productivity in the estuary affects the demographic rates and population dynamics of these groups. Specifically, we model estuarine residents, which complete their entire life cycle in estuaries, and marine estuarine-dependent species, which inhabit estuaries during early life before transitioning offshore. We find that total fish biomass for both guilds decreases with decreasing food productivity. However, the density of juveniles of the marine estuarine-dependent guild can, under certain conditions, increase in the estuary. This occurs due to a shift in the population biomass distribution over different life stages and a simultaneous shift in which life stage is most limited by food. At the individual level, somatic growth of juveniles belonging to the estuarine-dependent guild decreased with lower food supply in the estuary, due to increased competition for food. The somatic growth rates of fish belonging to the resident guild were largely unaffected by low food supply, as the total fish density decreased at the same time and therefore the per-capita food availability was similar. These outcomes challenge the assumption that responses to habitat degradation are similar between fish guilds. Our study highlights the need to assess not only fish biomass but also size distributions, survival, and somatic growth rates for a comprehensive understanding of the effects of habitat degradation on fish populations. This understanding is crucial not only for estuary fish communities but also for successful conservation and management of commercially harvested offshore population components.

Habitat distinctness doesn't influence on the abundance and relative growth of the juveniles Atherinella brasiliensis (Quoy & Gaimard, 1824) in a subtropical estuarine ecosystem

Shallow coastal habitats with and without vegetation may perform nursery function from distinct way for many species, raising questions about the role of vegetation on structuring nursery ground. Unfortunately, degradation and inappropriate human use of these areas associated with the lack of ecological data about fish populations can limit appropriate strategies to protect both species and habitats. In this paper we examine the nursery value of different estuarine habitats by comparing the abundance and relative growth of juveniles Atherinella brasiliensis. Fish were sampled once a month from November 2018 to October 2019 in five habitats: no vegetation close to the ocean, no vegetation close to the river, no vegetation and distant from other sampling points (control), mangrove and saltmarsh. Juveniles are present and abundant in all habitats and specimens had similar relative growth in the salt marsh, mangrove habitats and non vegetated habitats. The results indicate that estuarine habitats offers suitable conditions to A. brasiliensis in early stages of life, indicating that these sites have nursery value for juveniles of this species. Conservation and/or preservation of estuarine shallows habitats along the coast is important for A. brasiliensis and probably for other species, and the identification of priority areas could help to provide subsidies to management policies on conservation of coastal marine environments.

Nutritional qualities partially predict diet of amphipod grazers: implications for modern coastal biofilms in microbialite pools

Mobile metazoans in the Phanerozoic transformed shallow coastal habitats covered in biofilms into bioturbated mixed grounds. Benthic biofilms during this time rarely preserved into the fossil record as microbialites, and more specifically their layered form, stromatolites. Living microbialites are rare for this reason, in addition to other factors such as unfavourable modern geochemical conditions. Counterintuitively, macroinvertebrate grazers and laminated stromatolites coexist along the Nelson Mandela Bay coastline, South Africa. Here we aimed to determine if nutritional qualities of algae in these microbialite pools are linked to the diet of a dominant amphipod grazer, Melita zeylanica Stebbing, 1904. We assessed this in 3 microbialite pools using stable isotopes coupled to seasonal shifts in abundant food resources of microbialite biofilms and exposed (bleached and rimstone) or submerged (pool) macroalgae, Ulva spp. Amphipod diet was proportional to the quantity available (biomass) and nutritional properties of available algal food (energy, protein, total phosphorus and C:N ratios). Macroalgae in all states were the most nutritious, and the diet of M. zeylanica was dominated by submerged macroalgae. Although microbialite material had the worst nutritional profile, it was consumed in larger quantities compared to exposed bleached and rimstone macroalgae. Therefore, factors unrelated to nutritional profiles, such as predation, allelopathy or exposure risks, likely drive food choices. High levels of grazing on nutritious pool macroalgae likely releases most of the grazing pressure on the microbialite biofilm, therefore partially explaining why the microbialites can persist in this environment instead of being bioturbated through foraging.

Quantifying spatiotemporal variation of nearshore forage fish schools with aerial surveys in Prince William Sound, Alaska

AbstractObjectiveChanges in abundance and distribution of schooling forage fish, such as the Pacific Sand Lance Ammodytes hexapterus and Pacific Herring Clupea pallasii, can be difficult to document using traditional boat‐based methods, especially in the shallow, nearshore habitats frequented by these species. In contrast, nearshore fish schools are easily observed and quantified from aircraft when light and sea conditions are favorable. We used aerial shoreline surveys to assess interannual variability in the distribution and abundance of schooling forage fish in Prince William Sound, Alaska, during the summers of 2010 and 2012–2022.MethodsDuring the surveys, aerial observers classified fish schools by their size, species, and (in some cases) age‐class. All observations were georeferenced along the flight path, converted to estimated surface area (m2) based on school diameter, and standardized by effort (shoreline kilometers surveyed).ResultPacific Herring were widely distributed, and school densities varied annually; there were several spikes in school density of up to 54.38 m2/km interspersed among years of lower average densities (7.73–25.57 m2/km). In contrast, Pacific Sand Lance were usually limited in their distribution to a few predictable locations. School density in these consistent areas varied across years, from a high of 50.98 m2/km in 2010 to a low of 0.15 m2/km in 2017. We validated 88 schools during aerial surveys conducted in 2014–2016 and 2019–2022, of which 76 (86%) were correctly identified to species.ConclusionHere, we provide indices of Pacific Herring and Pacific Sand Lance school density over time in shallow nearshore coastal areas of Prince William Sound, Alaska. These indices were generated from aerial surveys, which offer an effective alternative to boat‐based surveys for tracking forage fish schools when they occur in shallow and nearshore coastal habitats.

Ingestion and respiration rates of a common coastal mysid respond differently to diurnal temperature fluctuation

AbstractAnimals face strong environmental variability even on short time scales particularly in shallow coastal habitats, forcing them to permanently adjust their metabolism. Respiration rates of aquatic ectotherms are directly influenced by water temperature, whereas ingestion rates might additionally be influenced by behavior. We aim to understand how respiration and ingestion rates of an aquatic invertebrate respond to changing temperature during a diurnal thermal fluctuation cycle and how both processes are related. We studied the benthopelagic mysid Neomysis integer as an important food web component of coastal ecosystems. Mysids were collected at the southern Baltic Sea coast and exposed in the laboratory to either constant temperature of 15°C or daily temperature fluctuation of 15 ± 5°C. Short‐term (1–2 h) respiration and ingestion rates were measured at four equidistant time points within 24 h and did not differ among time points at constant temperature, but differed among time points in the fluctuating treatment. Respiration was highest at the thermal maximum and lowest at the thermal minimum. Ingestion rates showed the opposite pattern under fluctuation, likely due to differences in underlying thermal performance curves. When temperature transited the average, the direction of temperature change influenced the animals' response in respiration and ingestion rates differently. Our results suggest that respiration is not only instantaneously affected by temperature, but also influenced by the previously experienced direction of thermal change. Our experiment, using an important non‐model organism, delivered new insights on the relationship between the crucial organismal processes ingestion and respiration under thermal variability.

Diversity and distribution of benthic dinoflagellates in Tonga include the potentially harmful genera Gambierdiscus and Fukuyoa

Benthic dinoflagellates that can cause illness, such as ciguatera poisoning (CP), are prevalent around the Pacific but are poorly described in many locations. This study represents the first ecological assessment of benthic harmful algae species in the Kingdom of Tonga, a country where CP occurs regularly. Surveys were conducted in June 2016 in the Tongatapu island group, and in June 2017 across three island groups: Ha'apai, Vava'u, and Tongatapu. Shallow subtidal coastal habitats were investigated by measuring water quality parameters and conducting quadrat surveys. Microalgae samples were collected using either macrophyte collection or the artificial substrate method. Benthic dinoflagellates (Gambierdiscus and/or Fukuyoa, Ostreopsis, and Prorocentrum) were counted using light microscopy, followed by molecular analyses (real-time PCR in 2016 and high throughput sequencing (metabarcoding) in 2017) to identify Gambierdiscus and Fukuyoa to species level. Six species were detected from the Tongatapu island group in 2016 (G. australes, G. carpenteri, G. honu, G. pacificus, F. paulensis, and F. ruetzleri) using real-time PCR. Using the metabarcoding approach in 2017, a total of eight species (G. australes, G. carpenteri, G. honu, G. pacificus, G. cheloniae, G. lewisii, G. polynesiensis, and F. yasumotoi) were detected. Species were detected in mixed assemblages of up to six species, with G. pacificus and G. carpenteri being the most frequently observed. Ha'apai had the highest diversity with eight species detected, which identifies this area as a Gambierdiscus diversity ‘hotspot’. Vava'u and Tongatapu had three and six species found respectively. Gambierdiscus polynesiensis, a described ciguatoxin producer and proposed causative agent of CP was found only in Ha'apai and Vava'u in 2017, but not in Tongatapu in either year. Ostreopsis spp. and Prorocentrum spp. were also frequently observed, with Prorocentrum most abundant at the majority of sites. In 2016, the highest number of Gambierdiscus and/or Fukuyoa cells were observed on seagrass (Halodule uninervis) from Sopu, Tongatapu. In 2017, the highest numbers of Gambierdiscus and/or Fukuyoa from artificial substrate samples were recorded in the Halimeda dominant habitat at Neiafu Tahi, Vava'u, a low energy site. This raised the question of the effect of wave motion or currents on abundance measurements from artificial substrates. Differences in detection were noticed between macrophytes and artificial substrates, with higher numbers of species found on artificial substrates. This study provides a baseline of benthic dinoflagellate distributions and diversity for Tonga that may be used for future studies and the development of monitoring programmes.

Predicting lake bathymetry from the topography of the surrounding terrain using deep learning

AbstractLake morphometric features like surface area, volume, mean, and maximum depth are important predictors of many physical, biological, and ecological processes. Lake bathymetric maps that present the lake basin contours are thus an integral part of limnological investigations. Accurate but cumbersome traditional bathymetric surveys measure the depth using a lead line or echosounder. Recently, airborne bathymetric mapping using imagery or laser scanning has been attempted in shallow freshwater and coastal habitats. However, these methods depend on the ability of light to penetrate the water column, which can be problematic in eutrophic lakes and shallow lakes. To alleviate these issues, we developed and tested a deep learning model (based on the U‐net) using data from 153 lakes in Denmark to predict bathymetry using the topography of the surrounding terrain. The deep learning model performed much better (pixel‐wise mean absolute error: validation set = 1.75 and test set = 2.15 m) than baseline interpolation approaches (validation set = 3.12 m). In addition, the deep learning model generated more realistic bathymetry maps that did not suffer from interpolation artifacts. We find that the model performance improves slightly with increasing model size (number of trainable parameters) and the extent of the surrounding terrain. In addition, our pretraining procedure improved performance and reduced the time for model convergence. Because the model only relies on digital elevation data which are widely available, it can be fine‐tuned and used to predict lake bathymetry in other geographical regions.

A decision-support framework for the restoration of Cystoseira sensu lato forests

Macroalgal forests characterised by species of the genus Cystoseira sensu lato form important shallow coastal rocky habitats in the Mediterranean Sea. These forests support a high biodiversity and provide important ecosystem services and societal benefits. Currently these habitats are often in a poor condition in many areas, due to loss and degradation from both anthropogenic and climate stressors. Restoration has recently moved to the forefront of the United Nations and European Union agendas to reverse this trend, particularly in the last decade with the implementation of various international policies. However, this has been in the form of generic targets (e.g., restoration of 30% of degraded habitats by 2030) and has not been linked to specifically what habitat or species to restore, where and how. Initial targets have been missed, new targets are expected through the proposed EU Nature Restoration Law, but overall guidance is still lacking. There are few specific guides to marine habitat restoration limited to mostly seagrass, corals and shellfish. As a priority action for the recovery of coastal marine ecosystems a decision-support framework has been developed for the restoration of Mediterranean macroalgal forests, comprising a stepwise decision tree with additional descriptions of key elements to be considered for a restoration action. The decision tree includes steps concerning current and historical forest presence, site local condition assessment and choice of actions. Key considerations include restoration implementation (competence, society and support, finance and governance), success evaluation (at the target species and the ecosystem level) and long-term management. The framework builds on existing work on Cystoseira s.l. restoration, the work carried out in the EU AFRIMED project, but also on principles and guidelines in place for both generic and specific marine habitats. The work reported here has involved the expertise of scientists and information from stakeholders. Gaps were identified and recommendations were made, dealing with stressors, coordinating and networking stakeholders, integrating top down policy and bottom up initiatives, funding of restoration actions, establishing synergies between restoration, conservation and marine spatial planning and finally communication and publicity.

Ontogenetic changes in green turtle (Chelonia mydas) diet and home range in a tropical lagoon

Ontogenetic changes in habitat and diet are widespread among marine species. Most species of sea turtles are characterized by extreme ontogenetic changes in habitat use and diet, with large changes occurring in early developmental stages (e.g., neonates to juveniles). Changes can continue even after recruitment to shallow coastal habitats. In places where substantial transitions in habitat occur across short distances, it is possible that the distances of developmental movements from one habitat to another could be short. We investigated ontogenetic changes in home range size, home range location and diet of Chelonia mydas in a tropical coastal lagoon in north-western Australia by combining acoustic telemetry with stable isotope analysis. There was a substantial (but nonlinear) increase in home-range size (kernel utilization distribution: KUD) with length, and an increase in the average distance of the center of home ranges from shore with length: larger turtles tended to occupy larger areas further from the shore. These patterns were accompanied by complex nonlinear changes in δ13C, δ15N and δ34S of red blood cells and nails; changes were rapid from 36 cm (the length of the smallest individual captured) to 50 cm, before reversing more gradually with increasing size. δ15N and δ34S (but not δ13C) of red blood cells and nails increased monotonically with KUD and distance from shore. Seagrass was likely an important food for all sizes, macroalgae was potentially important for small (< 60 cm CCL) individuals, and the proportion of scyphozoan jellyfish in diet increased monotonically with size. The combination of acoustic telemetry and stable isotope analysis revealed ontogenetic shifts in use of space and diet across short distances in a tropical coastal lagoon.

Assessing the carbon storage value of kelp forest restoration in the Hauraki Gulf Marine Park, New Zealand: Lessons from no-take Marine Protected Areas

Anthropogenic CO2 emissions are one of the principal driving forces of climate change. Climate change leads to systematic changes of ecosystems that cause significant impacts on species interactions, ecosystem processes, and result in profound socio-economic consequences. While carbon offsetting of terrestrial forests and their monetary value are well accepted, the carbon offsetting potential and value of coastal and marine ecosystems (Blue Carbon, BC) remains excluded from the international carbon accounting framework. In this study, we estimated the carbon offsetting value of kelp forests (Ecklonia radiata) against urchin barrens (dominated by crustose coralline algae) using the standing stock biomass as a metric. We propose that standing stock biomass is a crucial next step in introducing BC to the general carbon offsetting framework. Our approach is informed by long-term ecological research conducted in a marine reserve, which highlights the potential of utilizing trophic cascades to limit the dominance of urchin barrens in shallow coastal habitats. We found that the value of carbon standing stock in current kelp forests with reforestation in the Hauraki Gulf Marine Park (HGMP) is worth up to $NZ 7.9 million, based on 2021 carbon market pricing in New Zealand. This simple step towards realizing the value of marine conservation and its multiple benefits to society highlights the missed opportunities when policy and plans do not align with ecology and economics. Including the ocean's contributions to carbon storage is a critical step in using monetization techniques to overcome climate change challenges. Monetizing the carbon offsetting value of kelp forests contributes to establishing funding mechanisms to attract diverse investments in marine ecosystem restoration while providing ecological benefits in ocean governance.

Plankton depletion by mussel grazing negatively impacts the fitness of lobster larvae

Bivalve aquaculture has rapidly expanded in shallow coastal habitats, leading to substantial changes in the natural environment. While the grazing pressure of mussels (Mytilus edulis) on phytoplankton and zooplankton has been well documented, cascading effects of plankton depletion on the development and survival of resident fish and invertebrate larvae remains largely unexplored. This study experimentally assessed the impact of control (no mussel grazing), low (20 mussels·m−3) and high (80 mussels·m−3) mussel densities on a model community composed of various phytoplankton and zooplankton and how changes in plankton characteristics influence the development and survival of lobster (Homarus americanus) larvae. Mussels fed primarily on nanophytoplankton, while the picophytoplankton experienced significantly less grazing. Zooplankton was readily ingested by mussels, showing a sharp decline under low mussel density, whereas it was eliminated from the plankton under high density of mussels. A 65% decrease of polyunsaturated fatty acids (∑ PUFA) was observed in the plankton under mussel filtration compared to control. Lobster larvae reared under control plankton conditions exhibited the fastest development, highest survival rate, carapace length, total lipid and ∑ PUFA contents, and TAG/ST (triacylglycerols/sterols) ratio, indicating the best nutritional condition. Larvae reared under low mussel density showed longer developmental time, lower survival rate and carapace length than that for controls. In addition, these larvae showed a significant reduction in total lipid, ∑ PUFA, and TAG/ST, which collectively suggests poor nutritional status due to limited dietary intake. Under high mussel density, larvae did not molt to stage II and died within 14 days, suggesting that the depleted plankton community was unable to sustain physiological requirements for survival and development of the larvae. Overall, mussel grazing altered the meroplankton community structure and its biochemical composition, ultimately impacting the development, survival, and quality of lobster larvae. These findings provide novel information on complex trophic interactions between bivalves and a meroplankton species and adds a new perspective to fuel discussions on energy and nutrient pathways, particularly long-chain PUFA, in ecosystem carrying capacity studies for shellfish aquaculture in shallow coastal habitats.

Using eDNA and SCUBA surveys for detection and monitoring of a threatened marine cryptic fish

Abstract Quantification of species’ spatial distributions and population trends is crucial for successful conservation efforts. Obtaining sufficient population data, however, is often difficult in the marine environment, especially for rare fish and invertebrate species that are small, cryptic and very difficult to detect. This study sought to understand the effort required to search for undiscovered populations of small, cryptic, marine species in shallow vegetated coastal habitats and track population numbers, using the Critically Endangered red handfish (Thymichthys politus) as a representative species. A sampling strategy was designed using a combination of environmental DNA (eDNA) and structured underwater scuba surveys of life‐like 3D‐printed ‘handfish replicas’ to estimate detectability and ultimately determine whether current population monitoring is adequately covering the remaining habitat occupied by the species. Tested over scales of hundreds of metres to kilometres, the eDNA assays performed relatively poorly in situ, detecting red handfish presence in only ~13% of samples collected from the centre of a known, yet low‐density, red handfish site. In contrast, underwater searches for independently placed handfish replicas by scuba divers indicated that mean detection probabilities at finer scales (~100 m) ranged from 57 to 97%. Near certain (95% probability) detection of an adult handfish was achievable with only one to three surveys (300 m2 belt transects), depending on the habitat complexity. While other species will vary in detectability using eDNA and underwater searches, these findings give insight into the general effort required for the detection of small, rare species inhabiting vegetated coastal environments. Such knowledge not only helps to refine monitoring and conservation efforts for known threatened species, but may also assist in identifying other inconspicuous species whose population declines may otherwise go unnoticed.

Benthic jellyfish act as suction pumps to facilitate release of interstitial porewater

Upside-down jellyfish, genus Cassiopea (Péron and Lesueur, 1809), are found in shallow coastal habitats in tropical and subtropical regions circumglobally. These animals have previously been demonstrated to produce flow both in the water column as a feeding current, and in the interstitial porewater, where they liberate porewater at rates averaging 2.46 mL h−1. Since porewater in Cassiopea habitat can be nutrient-rich, this is a potential source of nutrient enrichment in these ecosystems. This study experimentally determines that porewater release by Cassiopea sp. jellyfish is due to suction pumping, and not the Bernoulli effect. This suggests porewater release is directly coupled to bell pulsation rate, and unlike vertical jet flux, should be unaffected by population density. In addition, we show that bell pulsation rate is positively correlated with temperature, and negatively correlated with animal size. As such, we would predict an increase in the release of nutrient-rich porewater during the warm summer months. Furthermore, we show that, at our field site in Lido Key, Florida, at the northernmost limit of Cassiopea range, population densities decline during the winter, increasing seasonal differences in porewater release.

Population structure and genetic connectivity of the scalloped hammerhead shark (Sphyrna lewini) across nursery grounds from the Eastern Tropical Pacific: Implications for management and conservation.

Defining demographically independent units and understanding patterns of gene flow between them is essential for managing and conserving exploited populations. The critically endangered scalloped hammerhead shark, Sphyrna lewini, is a coastal semi-oceanic species found worldwide in tropical and subtropical waters. Pregnant females give birth in shallow coastal estuarine habitats that serve as nursery grounds for neonates and small juveniles, whereas adults move offshore and become highly migratory. We evaluated the population structure and connectivity of S. lewini in coastal areas and one oceanic island (Cocos Island) across the Eastern Tropical Pacific (ETP) using both sequences of the mitochondrial DNA control region (mtCR) and 9 nuclear-encoded microsatellite loci. The mtCR defined two genetically discrete groups: one in the Mexican Pacific and another one in the central-southern Eastern Tropical Pacific (Guatemala, Costa Rica, Panama, and Colombia). Overall, the mtCR data showed low levels of haplotype diversity ranging from 0.000 to 0.608, while nucleotide diversity ranged from 0.000 to 0.0015. More fine-grade population structure was detected using microsatellite loci where Guatemala, Costa Rica, and Panama differed significantly. Relatedness analysis revealed that individuals within nursery areas were more closely related than expected by chance, suggesting that S. lewini may exhibit reproductive philopatric behaviour within the ETP. Findings of at least two different management units, and evidence of philopatric behaviour call for intensive conservation actions for this highly threatened species in the ETP.

Enhancing UAV images to improve the observation of submerged whales using a water column correction method

Enhancing <scp>UAV</scp> images to improve the observation of submerged whales using a water column correction method

The role of macroalgae as nursery areas for fish species within coastal seascapes

Abstract One of the most critical ecosystem functions provided by shallow coastal habitats is as nurseries for the juveniles of fish. Many of the studies that have assessed the nursery function of structurally complex coastal habitats have compared seagrass with unstructured sand and mud and as such, seagrass has emerged as the most important coastal nursery habitat for juvenile fishes. Although considerably less work has focussed on the nursery provision of structurally complex macroalgae within coastal nursery seascapes, recent work has started to highlight that the nursery provision of canopy-forming macroalgae may in fact be comparable with that of seagrass. This review collates research published on the important nursery role of macroalgae within both tropical and temperate coastal seascapes and highlights the importance of smaller canopy-forming brown algae from the Fucalean genera (particularly Sargassum spp.) as core nursery areas for juvenile fishes, particularly emperors (Lethrinidae), rabbitfishes (Siganidae), wrasse and parrotfishes (Labridae), goatfishes (Mullidae), groupers (Serranidae), surgeonfish (Acanthuridae) and damselfish (Pomacentridae) within tropical back-reef systems. Similarly, in temperate nursery seascapes, fucoid (Cystoseira spp.) and macroalgae-dominated reefs were important nursery habitats for damselfish (Chromis chromis), groupers and numerous species of wrasse and sparids (Sparidae). Although the overall density of juvenile fish was not shown to be higher in kelp relative to other temperate nursery habitats, kelp was important in the recruitment of Notolabrus celiodotus (wrasse), Paralabrax clathrus (Serranidae), Brachyistius frenatus (Embiotocidae), Heterostichus rostratus (Clinidae) and Sebastes spp. (Scorpaenidae). Although not interchangeable (fish communities were often different), the nursery function of structurally complex macroalgae was found to be similar to that of seagrass in both temperate and tropical seascapes.

Using timelapse cameras and machine learning to enhance acoustic monitoring of small boat sound

Small recreational boats are an omnipresent source of sound pollution in shallow coastal habitats, which can impact the behavior and physiology of a wide array of taxa. However, effective monitoring of this stressor is currently limited by a lack of tools. The present study coupled passive acoustic monitoring (PAM) with timelapse imagery to provide a comprehensive analysis of sound pollution at two coastal sites varying in habitat structure: Goat (rocky reef) and Kawau (sandy bay) Islands. A convolutional neural network (CNN) was used to automatically count boats in each image, and the relationship between the soundscape and number of boats present was analysed using power spectral density and adaptive threshold analyses. Small boat activity was positively correlated with third octave level (TOL) root mean squared sound pressure levels (SPLRMS 63 – 5011 Hz), and this effect was frequency dependent, at both Goat (F7,9704 = 5.665, p < 0.001) and Kawau (F7,42488 = 325.33, p < 0.001) Islands. However, at Goat Island this interaction effect was driven by a significant difference between 63 Hz and all other TOLs (p < 0.05), whereas at Kawau Island the interaction effect of TOL and boat number was more variable. Furthermore, low frequency (∼50 – 300 Hz) biophony was found to influence the likelihood of boat sound being detected at Goat Island. Small boat impacts are contextual, likely due to habitat specific propagation conditions and the presence/absence of vocalising animals. As such, monitoring of sound pollution in coastal habitats requires a tailored approach which accounts for the localised nature of shallow coastal soundscapes. These findings demonstrate the potential for timelapse imagery to elucidate variability in boat sound, which may be particularly useful for remote sites which are ecologically rich, yet have no acoustic protections, such as many marine protected areas.

A Tropical Macroalga (Halimeda incrassata) Enhances Diversity and Abundance of Epifaunal Assemblages in Mediterranean Seagrass Meadows

The introduction and successful expansion of tropical species into temperate systems is being exacerbated by climate change, and it is particularly important to identify the impacts that those species may have, especially when habitat-forming species are involved. Seagrass meadows are key shallow coastal habitats that provide critical ecosystem services worldwide, and they are threatened by the arrival of non-native macroalgae. Here, we examined the effects of Halimeda incrassata, a tropical alga that has recently colonized the Mediterranean Sea, on epifaunal assemblages associated with Cymodocea nodosa seagrass meadows of Mallorca Island (Western Mediterranean Sea). This invasive macroalga is an ecological engineer and thus has a high potential of modifying native habitats. A seagrass meadow colonized by H. incrassata exhibited important changes on associated epifaunal assemblages, with an increase in abundance and diversity, particularly driven by higher abundances of Gammaridae, Polychaeta, Copepoda and Caprellidae. Given the key ecological contribution of epifauna to food webs, these alterations will likely have important implications for overall food web structure and ecosystem functioning of native ecosystems.

The profiles of occupancy by fish fauna of four shallow coastal habitats at a limited regional scale in the south-western Mediterranean

The diversity of the ichthyofauna and the seasonal variations of its assemblages were studied in four different habitats on a limited geographical scale of the eastern coast of Algeria: one downright marine site (The Caroube beach) and three transitional waters, two estuaries (Boukhmira and Mafragh) and one lagoon (Mellah).From monthly samples taken between January and December 2016 using a 3 mm mesh beach seine (L = 14 m, H = 2 m), a total of 13240 fish was caught: 4148 individuals (43 species, 13 families) at The Caroube beach, 1452 (20 species, 11 families) in Boukhmira Wadi, 1218 (15 species, 10 families) in Mafragh estuary and 6422 (14 species, 8 families) in Mellah lagoon. Shannon–Wiener​ (H’) index showed a relatively high specific diversity at the Caroube beach in spring (H’ = 3.87) with a Pielou equitability index J’ = 0.77, while the lowest diversity was noted in spring at Mellah lagoon (H’ = 0.49) with J’ = 0.15. All localities showed a seasonal variation in fish abundance and in specific diversity, as well as in the distribution of the ecological and trophic guilds.The analysis of the seasonal hierarchical clusters differentiated the marine site from the transitional waters (lagoon and estuaries). This site is also characterized by an autumnal ichthyofauna different from that of other seasons. At the combined spatial and temporal scales, canonical correspondence analysis (CCA) revealed the requirements of the species with respect to the considered abiotic parameters (temperature, salinity, oxygen, bottom nature) and showed that the nature of the bottom is the most important factor affecting the distribution and the abundance of fish.

Movement patterns and catch trends of the diamond ray Gymnura natalensis (Dasyatidae) in South African waters

The diamond ray Gymnura natalensis is endemic to southern Africa where its preference for shallow coastal habitats makes it vulnerable to recreational shore-based angling. Although it makes up approximately 1% of the shore-based tag numbers, little is known about its movements, reproduction or population status in South Africa. This study used three independent long-term (34–41 years) datasets, including tagging by recreational anglers, competitive shore angling catches and shark net catches, to investigate the species’ movements, catch composition and population status in South Africa. Of the 3 739 individuals tagged (1984–2018), only 30 (1%) were recaptured after an average of 487 days at liberty. The majority (60%) of the recaptures occurred within 10 km of the release site, while 7% had moved more than 1 000 km along the coast. The longest recorded movements (1 577 and 1 756 km) were undertaken by adult rays tagged in the Western Cape Province moving to KwaZulu-Natal Province (KZN). The competitive shore angling catch (1977–2018; n = 9 150) from KZN was dominated by adult rays caught north of Durban, while the shark net catch in KZN (1981–2018; n = 584) was dominated by juvenile rays primarily from the central beaches of Durban. All the datasets exhibited strong seasonal trends with most catches taking place in summer. A risk assessment confirmed a stable to increasing population trend over four generations, suggesting that the population sampled along the east coast of South Africa should be classified as Least Concern.