Marine Habitats Research Articles

Labile organic matter promotes nitrogen retention in natural and constructed gulf coast marshes

Coastal marshes mitigate allochthonous nitrogen (N) inputs to adjacent marine habitat; however, their extent is declining rapidly. As a result, marsh restoration and construction have become a major foci of wetland management. Constructed marshes can quickly reach similar plant biomass to natural marshes, but biogeochemical functions like N removal and retention can take decades to reach functional equivalency, often due to lags in organic matter (OM) pools development in newly constructed marshes. We compared denitrification and dissimilatory nitrate reduction to ammonium (DNRA) rates in a 32 year-old constructed marsh and adjacent reference marsh in the Northern Gulf of Mexico. Marsh sediments packed into 3 mm “thin discs” were subjected to three OM quality treatments (no OM addition, labile OM, or recalcitrant OM) and two N treatments (ambient nitrate or elevated nitrate) during a 13 day incubation. We found that OM addition, rather than marsh type or nitrate treatment, was the most important driver of nitrate reduction, increasing both denitrification and DNRA and promoting DNRA over denitrification in both marshes. Fungal and bacterial biomass were higher in the natural marsh across treatments, but recalcitrant OM increased fungal biomass in the constructed marsh, suggesting OM-limitation of fungal growth. We found that constructed marshes are capable of similar denitrification and DNRA as natural marshes after 30 years, and that labile OM addition promotes N retention in both natural and constructed marshes.Graphical Conceptual figure highlighting the findings of this experiment. Under control treatment with no C addition (bottom panel), constructed and natural marshes have similar rates of both DNRA and denitrification. The natural marsh has higher fungal and bacterial biomass, while fungal biomass is not detectable in the constructed marsh. Under labile OM additions (upper left panel), rates of both DNRA and denitrification are increased and DNRA becomes favored over denitrification in both marshes. Recalcitrant OM additions (upper right) increase denitrification, but do not affect DNRA or % denitrification. The addition of recalcitrant OM also increases the detectability of fungal biomass in the constructed marsh.

Seagrass-mediated rhizosphere redox gradients are linked with ammonium accumulation driven by diazotrophs.

Seagrasses are important marine habitats providing several ecosystem services in coastal waters worldwide, such as enhancing marine biodiversity and mitigating climate change through efficient carbon sequestration. Notably, the fitness of seagrasses is affected by plant-microbe interactions. However, these microscale interactions are challenging to study and large knowledge gaps prevail. Our study shows that redox microgradients in the rhizosphere of seagrass select for a unique microbial community that can enhance the ammonium availability for seagrass. We provide first experimental evidence that Rhizobia, including the symbiotic N2-fixing bacteria Bradyrhizobium, can contribute to the bacterial ammonium production in the seagrass rhizosphere. The release of O2 from rhizomes and roots also caused gradients of sulfide in rhizosphere areas with enhanced nifH transcription by sulfate-reducing bacteria. O2 release from seagrass root systems thus seems crucial for ammonium production in the rhizosphere via stimulation of multiple diazotrophic associations.

Looking for reliable species distribution models for low‐density cetacean species: Compared effectiveness of SDMs for G. griseus, G. melas, Z. cavirostris in the Mediterranean Sea based on long‐term fixed‐transect data

Abstract The EU regulative framework for the protection of marine biodiversity and habitats requires the assessment of species' conservation status and the identification of core habitats to design adequate conservation and management plans. However, the identification of distribution range and habitat‐use of pelagic large‐range, migratory species, such as cetaceans, is challenging. Species distribution models (SDMs) are increasingly used in conservation planning to identify species priority areas. However, the quality of SDMs varies widely depending on the representativeness of data and the appropriateness of the modelling techniques. Since 2007, the Fixed Line Transect Mediterranean Monitoring Network (FLT Med Net) has been continuously monitoring cetaceans throughout the year in the Mediterranean basin using passenger ferries as observation platforms that perform repetitive surveys along fixed trans‐border transects. With the aim of defining a standard analytical approach, the data collected by the FLT Med Net on rarer Mediterranean cetacean species (i.e., Grampus griseus, Globicephala melas, Ziphius cavirostris) are used here to assess the performance of commonly used SDMs, including GLM, GAM, GAM‐Negative Binomial, GAM‐tweedy, MaxEnt and Random Forest. Models were built and evaluated using a total of 296 FLT Med Net sighting data and cross‐validated using 145 independent data points. Under testing conditions, almost all methods exhibited good performance, with Random Forest being the best model in several cases. However, when evaluated with the independent dataset, many models yielded inconsistent results or notably low performance. Only MaxEnt demonstrated consistent efficiency and reliability in both cases, showing results less affected by unequal sampling or small sample size. Results confirm the importance of robust standard SDM approaches based on representative data such as the FLT Med Net data to identify reliable priority areas for the species and to assess the long‐term coherence and effectiveness of spatial protection measures.

Checklist of the marine malacofauna of Culuccia Peninsula (NW Sardinia, Italy), with notes on relevant species.

Culuccia is a small peninsula of about 3 km2 placed in north-western Sardinia (Italy) at the margin of the Maddalena Archipelago. The marine area surrounding this Peninsula is a Special Area of Conservation, included in the European Natura 2000 Ecological Network of protected areas, but until now, no information on biodiversity of this area is available. In 2021, a research project to study both terrestrial and marine biodiversity of Culuccia has started in order to fill this gap of knowledge. This work provides the first inventory of the marine malacofauna of the coast of Culuccia. Fifteen sites were sampled seasonally for one-year by using different sampling methods and the present study shows the results from approximately 50 scientific SCUBA and free dive surveys, carried out in all main marine habitats of the studied area. In total, 259 species of molluscs were recorded along the coasts of the Culuccia Peninsula (0-25 m depth), belonging to the classes Bivalvia, Gastropoda, Polyplacophora and Scaphopoda. Amongst the four classes recorded, gastropods were the most represented (66.90%; 173 species), followed by bivalves (28.10%; 73 species), polyplacophorans (4.60%; 12 species) and scapophods (0.40%; 1 species). Notes about distribution, conservation status and ecology for some valuable species are provided, together with images of representative species, consisting mainly of in situ photographs. Additionally, the present investigation recorded the presence of four alien species, whose Mediterranean distribution was extended to north-western Sardinia.

Salmon farming, overfishing and southern sea lion: Not so opportunistic responses of a top predator to human perturbations in the Patagonian Fjords

Pinnipeds are considered generalist predators that prey opportunistically on more abundant prey. Thus, their diet could be affected by natural and anthropogenic stressors, such as declines in native prey and increases in exotic prey such as escaped salmon. Using stable isotopes, we evaluated temporal and spatial variability in the diet of southern sea lion (Otaria flavescens), and assessed its response to seasonal and stochastic variability in native prey and escaped salmon. Demersal fishes (median contribution range = 50–79 %) and escaped salmon (6–44 %) were the most important prey, in all colonies and seasons examined. The median estimated contributions of caged salmon, Munida gregaria and Sprattus fuegensis were consistently lower than 10% in all colonies and seasons. Variability in the relative availability of stocked and escaped salmon, as well as in Merluccius australis and S. fuegensis, showed limited influence on the contribution of these prey to the diet. Thus, although a noticeable response was evident after a large-scale escape of farmed Atlantic salmon that occurred during the study period, the opportunistic behaviour of southern sea lion seems questionable. A better understanding of dietary responses to induced changes in prey availability may have management implications in marine habitats affected by overfishing and farming of exotic species.

Travelling away from home? Joining global change and recovery scenarios to anticipate the marine distribution of diadromous fish

Species Distribution Models (SDM) are useful tools providing results that can be extrapolated to anticipate species range shifts, under climate change scenarios. SDM studies integrating spatial constraints are significantly lacking in the marine environment, leading to optimistic predictions. This is particularly true for anadromous species in which marine distributions can be driven by their affinity to their natal rivers. Acipenser sturio is a critically endangered anadromous fish for which two stocked populations are currently maintained in the Gironde-Garonne-Dordogne (France) and Elbe (Germany) river systems. Benefiting from bycatch reports of A. sturio, we applied a SDM process that explicitly considers distance to home when evaluating habitat suitability. More precisely, we included the variable ‘distance to mouth of the natal river system’ into SDM inputs to test and characterize its influence on the marine distribution of A. sturio. We used this model to obtain the marine distribution under current climatic conditions with the two source populations and under population recovery scenarios (functional populations hypothesized to exist in ten currently unoccupied river systems). We projected the model under future conditions with two climatic scenarios (RCP 4.5 and 8.5) and three time slices over the 2023–2099 period. Constrained-ranges of both existing and hypothetical populations are projected to expand in the future. We observed an overall increase of habitat suitability, with new suitable sectors localized further from natal river mouths. By informing on the suitable marine surface that each hypothetical population holds and adds to the existing ones, our approach aims at informing about the feasibility of species recovery and marine habitats protection strategies. Our findings highlight the need for including dispersal information in marine SDM. The application of our dispersal-constrained approach may be considered for other less-well-known species for which dispersal point sources are identifiable, such as other diadromous species in different study areas.

Morphological and molecular analyses of Vaucheria section Piloboloideae (Xanthophyceae: Vaucheriaceae) indicate alternative species identities for broadly distributed taxa

ABSTRACT The discovery of a previously unrecorded Vaucheria species in subtidal marine habitats in Western Australia has led to a review of species included in Vaucheria section Piloboloideae, a taxon that includes several problematic invasive species. Molecular analyses placed this species in a clade including the New Zealand Vaucheria aestuarii and additionally indicated conspecificity with specimens from the North Sea that have been previously regarded as invasive V. longicaulis. However, our molecular analyses from the Californian type locality of V. longicaulis have shown that the North Sea taxon is not that species. Instead, it belongs to V. aestuarii, previously described from New Zealand, now also discovered by us at the coast of Western Australia. The sequences from the type locality of V. longicaulis, however, match those of an unidentified Vaucheria, coincidentally also found in the North Sea, reported as Vaucheria sp., and also recently referred to V. aff. compacta from Svalbard in the Arctic. Our work provides a taxonomic framework for two widespread invasive species and a key to all known species of the section Piloboloideae.

Molecular cloning, characterisation and molecular modelling of two novel T-synthases from mollusc origin.

The glycoprotein-N-acetylgalactosamine β1,3-galactosyltransferase, known as T-synthase (EC 2.4.1.122), plays a crucial role in the synthesis of the T-antigen, which is the core 1 O-glycan structure. This enzyme transfers galactose from UDP-Gal to GalNAc-Ser/Thr. The T-antigen has significant functions in animal development, immune response, and recognition processes. Molluscs are a successful group of animals that inhabit various environments, such as freshwater, marine, and terrestrial habitats. They serve important roles in ecosystems as filter feeders and decomposers but can also be pests in agriculture and intermediate hosts for human and cattle parasites. The identification and characterization of novel carbohydrate active enzymes, such as T-synthase, can aid in the understanding of molluscan glycosylation abilities and their adaptation and survival abilities. Here, the T-synthase enzymes from the snail Pomacea canaliculata and the oyster Crassostrea gigas are identified, cloned, expressed, and characterized, with a focus on structural elucidation. The synthesized enzymes display core 1 β1,3-galactosyltransferase activity using pNP-α-GalNAc as substrate and exhibit similar biochemical parameters as previously characterised T-synthases from other species. While the enzyme from C. gigas shares the same structural parameters with the other enzymes characterised so far, the T-synthase from P. canaliculata lacks the consensus sequence CCSD, which was previously considered indispensable.

Marine habitat use and movement in response to ocean warming by a threatened forest-nesting seabird

Although anthropogenic climate change has resulted in significant alterations of ocean environments, the degree to which marine organisms can respond behaviorally to climate effects remains poorly understood, especially for species with increased extinction risk. We monitored marine space use and movement of the threatened marbled murrelet (Brachyramphus marmoratus) along the central coast of Oregon, USA during the 2017–2019 breeding seasons to quantify marine habitat selection patterns across a range of ocean conditions. We hypothesized that marine locations characterized by upwelling, nearshore areas adjacent to old-growth forest nesting habitat, and protected marine areas would be preferentially selected by tagged birds. Using >4800 locations collected from >180 individuals, we found that murrelets selected areas near small estuaries and with localized upwelling (as characterized by decreased sea-surface temperatures and high salinity), both of which are expected to lead to greater food availability during periods when sea-surface temperatures are elevated and coastal upwelling is reduced (i.e., poor ocean conditions). In addition, we found that individuals did not preferentially select marine areas adjacent to potential old-growth nesting habitat, and that murrelets exhibited limited overlap with protected marine areas regardless of ocean conditions. Unexpectedly, the majority (62%) of tagged individuals moved beyond the boundaries of our 135-km long study area in the year with the poorest ocean conditions (2017), with 15% of birds moving >500 km from their capture location. Our results confirm that marine habitat selection in murrelets becomes decoupled from terrestrial nesting habitat during periods of poor ocean conditions, and that such conditions are associated with low breeding propensity and long-distance movements during the breeding season. In addition to demonstrating murrelets undertake fine- and coarse-scale movements to buffer against poor ocean conditions, our study also emphasizes the importance of considering broad spatial scales in the marine environment when undertaking measures to conserve murrelet populations.

Assessment of microplastic contamination in commercially available fishes

Plastics have widespread applications for human use, but their disposal poses a significant threat to living organisms and these plastics end up in the marine environment. They will be fragmented into small pieces as a result of ultraviolet exposure, climatic changes, and temperature changes; Microplastics (MPs) are plastics that are less than 5 mm in size. The level of MP (Microplastic) pollution in commercially harvested fish from different habitant in Vellore, India is currently unknown. Therefore, this study aimed to determine the presence and characteristics of ingested or inhaled MPs in marine and freshwater fishes highly consumed by the local population. Fish gills and gastrointestinal tracts were aseptically dissected and digested (30% hydrogen peroxide), then filtered and examined under a microscope for the presence of MPs. Further analysis was performed on the samples using Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Scanning Electron Microscopy (SEM) with Energy Dispersive X-Ray (EDAX). Of the samples analysed, a total of 875 MPs were recovered from 32 fishes, with 478 from marine fishes and 397 from freshwater fishes. The most common colours of the MPs were blue and black, while stereo microscopy analysis revealed that the majority of MPs were fibers (91%), followed by fragments (8%) and a small number of films. The ATR-FTIR analysis identified polyvinyl alcohol (39.76%), polyethylene (16.51%), methylcellulose (12.84%) and styrene (9.07%), as the predominant types of MPs in the fish samples. This study highlights the significant impact of MP pollution on marine ecosystems. The research provides insight into the nature and extent of MPs in fish from both marine and freshwater habitats, with an aim for policies and interventions aimed to reduce plastic pollution in the locality.

Tracing Organophosphate Ester Pollutants in Hadal Trenches─Distribution, Possible Origins, and Transport Mechanisms.

Unraveling the mysterious pathways of pollutants to the deepest oceanic realms holds critical importance for assessing the integrity of remote marine ecosystems. This study tracks the transport of pollutants into the depths of the oceans, a key step in protecting the sanctity of these least explored ecosystems. By analyzing hadal trench samples from the Mariana, Mussau, and New Britain trenches, we found the widespread distribution of organophosphate ester (OPE) flame retardants but a complex transport pattern for the OPE in these regions. In the Mariana Trench seawater column, OPE concentrations range between 17.4 and 102 ng L-1, with peaks at depths of 500 and 4000 m, which may be linked to Equatorial Undercurrent and topographic Rossby waves, respectively. Sediments, particularly in Mariana (422 ng g-1 dw), showed high OPE affinity, likely due to organic matter serving as a transport medium, influenced by "solvent switching", "solvent depletion", and "filtering processes". Amphipods in the three trenches had consistent OPE levels (29.1-215 ng g-1 lipid weight), independent of the sediment pollution patterns. The OPEs in these amphipods appeared more linked to surface-dwelling organisms, suggesting the influence of "solvent depletion". This study highlights the need for an improved understanding of deep-sea pollutant sources and transport, urging the establishment of protective measures for these remote marine habitats.

Pesticides in the Great Barrier Reef catchment area: Plausible risks to fish populations.

Waterways that drain the Great Barrier Reef catchment area (GBRCA) transport pollutants to marine habitats, provide a critical corridor between freshwater and marine habitats for migratory fish species, and are of high socioecological value. Some of these waterways contain concentrations of pesticide active ingredients (PAIs) that exceed Australian ecotoxicity threshold values (ETVs) for ecosystem protection. In this article, we use a "pathway to harm" model with five key criteria to assess whether the available information supports the hypothesis that PAIs are or could have harmful effects on fish and arthropod populations. Strong evidence of the first three criteria and circumstantial weaker evidence of the fourth and fifth criteria are presented. Specifically, we demonstrate that exceedances of Australian and New Zealand ETVs for ecosystem protection are widespread in the GBRCA, that the PAI contaminated water occurs (spatially and temporally) in important habitats for fisheries, and that there are clear direct and indirect mechanisms by which PAIs could cause harmful effects. The evidence of individuals and populations of fish and arthropods being adversely affected species is more circumstantial but consistent with PAIs causing harmful effects in the freshwater ecosystems of Great Barrier Reef waterways. We advocate strengthening the links between PAI concentrations and fish health because of the cultural values placed on the freshwater ecosystems by relevant stakeholders and Traditional Owners, with the aim that stronger links between elevated PAI concentrations and changes in recreationally and culturally important fish species will inspire improvements in water quality. Integr Environ Assess Manag 2024;20:1256-1279. © 2023 Commonwealth of Australia and The Commonwealth Scientific and Industrial Research Organisation. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Krumholzibacteriota and Deltaproteobacteria contain rare genetic potential to liberate carbon from monoaromatic compounds in subsurface coal seams.

Biogenic methane in subsurface coal seam environments is produced by diverse consortia of microbes. Although this methane is useful for global energy security, it remains unclear which microbes can liberate carbon from the coal. Most of this carbon is relatively resistant to biodegradation, as it is contained within aromatic rings. Thus, to explore for coal-degrading taxa in the subsurface, this study reconstructed relevant metagenome-assembled genomes (MAGs) from coal seams by using a key genomic marker for the anaerobic degradation of monoaromatic compounds as a guide: the benzoyl-CoA reductase gene (bcrABCD). Three MAGs were identified with this genetic potential. The first represented a novel taxon from the Krumholzibacteriota phylum, which this study is the first to describe. This Krumholzibacteriota MAG contained a full set of genes for benzoyl-CoA dearomatization, in addition to other genes for anaerobic catabolism of monoaromatics. Analysis of Krumholzibacteriota MAGs from other environments revealed that this genetic potential may be common, and thus, Krumholzibacteriota may be important organisms for the liberation of recalcitrant carbon in a broad range of environments. Moreover, the assembly and characterization of two Syntrophorhabdus aromaticivorans MAGs from different continents and a Syntrophaceae sp. MAG implicate the Deltaproteobacteria class in coal seam monoaromatic degradation. Each of these taxa are potential rate-limiting organisms for subsurface coal-to-methane biodegradation. Their description here provides some understanding of their function within the coal seam microbiome and will help inform future efforts in coal bed methane stimulation, anoxic bioremediation of organic pollutants, and assessments of anoxic, subsurface carbon cycling and emissions.IMPORTANCESubsurface coal seams are highly anoxic, oligotrophic environments, where the main source of carbon is "locked away" within aromatic rings. Despite these challenges, many coal seams accumulate biogenic methane, implying that the coal seam microbiome is "unlocking" this carbon source in situ. For over two decades, researchers have endeavored to understand which organisms perform these processes. This study provides the first descriptions of organisms with this genetic potential from the coal seam environment. Here, we report metagenomic insights into carbon liberation from aromatic molecules and the degradation pathways involved and describe a Krumholzibacteriota, two Syntrophorhabdus aromaticivorans, and a Syntrophaceae MAG that contain this genetic potential. This is also the first time that the Krumholzibacteriota phylum has been implicated in anaerobic dearomatization of aromatic hydrocarbons. This potential is identified here in numerous MAGs from other terrestrial and marine subsurface habitats, implicating the Krumholzibacteriota in carbon-cycling processes across a broad range of environments.

Effects of harvesting and an invasive mussel on intertidal rocky shore communities based on historical and spatial comparisons.

Intertidal rocky shores are the most accessible marine habitats and therefore heavily impacted by harvesting. In recent years, they have also been increasingly invaded by alien species, which compounds the effects of harvesting on rocky shore community composition and functioning. Recent survey data, combined with historical data from 1970, were used to assess temporal changes over the intervening period in rocky shore communities at two sites (Wireless Point and Wireless Island). Three kinds of changes emerged: (1) the appearance of alien species; (2) the effects of increased harvesting pressure; and (3) the direct and indirect effects of these changes on other species. A striking result was transformation of mid-shore zones on exposed shores by the appearance of the invasive Mediterranean mussel Mytilus galloprovincialis, and the indirect effects of this on the demography and vertical zonation patterns of the granular limpet Scutellastra granularis. Adult limpets have become excluded by the mussel, whereas juveniles find a secondary home on the shells of the mussel and their abundance has increased. To further disentangle the effects of harvesting from those of alien invasions, a spatial comparison was made between two currently unharvested no-take sites (Scarborough South and Scarborough North) and two regularly harvested sites (Kommetjie and Wireless Point). Harvesting has substantially depleted the granite limpet Cymbula granatina and Argenville's limpet Scutellastra argenvillei. This has led to the proliferation of opportunistic seaweeds, such as Ulva spp. The dual effects of alien invasive species and over-harvesting have major ecosystem effects but do not necessarily diminish biodiversity because the alternative habitats that have developed provide opportunities for colonisation by additional species.

Enabling coastal blue carbon in Aotearoa New Zealand: opportunities and challenges

Blue carbon is the carbon sequestered by coastal and marine habitats such as mangroves, saltmarsh, and seagrasses. The carbon sequestration service provided by these habitats could help to mitigate climate change by reducing greenhouse gas (GHG) emissions, as well as providing other important ecosystem services. Restoration of coastal habitats for the purpose of sequestering blue carbon can generate carbon credits, potentially offsetting the costs of restoration and any lost revenue for landowners. Coastal blue carbon projects have been successfully implemented overseas, but a blue carbon market has not yet been established in Aotearoa New Zealand (ANZ). Here we identify key data gaps that will be necessary to fill to develop a blue carbon market in ANZ. Calculation of carbon abatement through development of a standardised method is the first step and will allow economic assessment of potential restoration sites. Economic assessment will determine if the carbon credits generated will cover restoration costs and lost revenue from restored lands. Once economically feasible potential restoration sites have been identified, prioritisation of sites could be determined by the value of co-benefits produced (i.e., biodiversity). There are also legal uncertainties in ANZ and ownership of the foreshore has been a contentious topic. Current legislation provides that neither the Crown nor any other person owns or can own the common marine and coastal area, although Māori may apply for recognition of customary rights, interests, and title in the area. The legal status of property rights will have significant implications for privately owned land, as it is unclear whether land will be considered foreshore when inundated in future with sea level rise. Here, we discuss further policy enablers including the role of government and the insurance industry that could encourage uptake of carbon projects by private landowners. Filling these gaps in market assessments and recognising the key role of Indigenous owners and customary rights holders to coastal land can facilitate operationalising of coastal blue carbon opportunities in Aotearoa New Zealand.

Formation and Dynamics of a Coherent Coastal Freshwater Influenced System

AbstractOn the Northwest European Shelf rivers provide freshwater to the coastal seas. This coastal freshwater can be misrepresented in ocean models without effective coastal resolution. This leaves an unanswered question; is freshwater retained around Scotland and what affects its variability? Here, we deploy and run an unstructured model with enhanced coastal resolution to simulate the Northwest European Shelf from 1993 to 2019, the Scottish Shelf Water‐Reanalysis Service (SSW‐RS) long‐time run. The unstructured nature of the model grid means it more accurately captures a “bubble” of Coastal Water than a 7 km structured grid model (the Atlantic Margin Model 7 km). Surface salinity in the SSW‐RS shows salinity fronts within 80 km of the coast around west and north Scotland that disintegrates east of Orkney. There are periods characterized by high coastal salinity when freshwater is more actively advected away from the coast. Empirical orthogonal function statistical analysis shows the first two modes in surface salinity account for 66% of the variance. The first mode correlates with North Atlantic Oscillation and the salinity driven velocity variability which change the salinity through advection and diffusion. The second mode correlates with Ekman transport variability where the north of Scotland acts as a wedge causing bipolar dynamics either side. Freshwater is trapped in the west, while saline water from the north reduces the freshwater pathway to the North Sea. This is important for salinity distribution, stratification in the North Sea, marine habitats and frontal transport.

Environmental DNA reveals temporal variation in mesophotic reefs of the Humboldt upwelling ecosystems of central Chile: Toward a baseline for biodiversity monitoring of unexplored marine habitats.

Temperate mesophotic reef ecosystems (TMREs) are among the least known marine habitats. Information on their diversity and ecology is geographically and temporally scarce, especially in highly productive large upwelling ecosystems. Lack of information remains an obstacle to understanding the importance of TMREs as habitats, biodiversity reservoirs and their connections with better-studied shallow reefs. Here, we use environmental DNA (eDNA) from water samples to characterize the community composition of TMREs on the central Chilean coast, generating the first baseline for monitoring the biodiversity of these habitats. We analyzed samples from two depths (30 and 60 m) over four seasons (spring, summer, autumn, and winter) and at two locations approximately 16 km apart. We used a panel of three metabarcodes, two that target all eukaryotes (18S rRNA and mitochondrial COI) and one specifically targeting fishes (16S rRNA). All panels combined encompassed eDNA assigned to 42 phyla, 90 classes, 237 orders, and 402 families. The highest family richness was found for the phyla Arthropoda, Bacillariophyta, and Chordata. Overall, family richness was similar between depths but decreased during summer, a pattern consistent at both locations. Our results indicate that the structure (composition) of the mesophotic communities varied predominantly with seasons. We analyzed further the better-resolved fish assemblage and compared eDNA with other visual methods at the same locations and depths. We recovered eDNA from 19 genera of fish, six of these have also been observed on towed underwater videos, while 13 were unique to eDNA. We discuss the potential drivers of seasonal differences in community composition and richness. Our results suggest that eDNA can provide valuable insights for monitoring TMRE communities but highlight the necessity of completing reference DNA databases available for this region.

The reproductive biology of Ellochelon vaigiensis from the Vietnamese Mekong Delta.

The Squaretail mullet, Ellochelon vaigiensis, is a commercial fish species distributed throughout the Indo-Pacific region. This species tolerates wide variations in salinity, having been reported from both freshwater and marine habitats. Although economically significant, there is little information on its reproduction, especially in the Vietnamese Mekong Delta (VMD), where it is heavily extracted. Our study elucidates the breeding pattern, seasonality, first length at maturity, as well as potential and relative fecundity of this species. Fish specimens were collected by trawl nets from November 2020 to October 2021 at four estuarine sites within the VMD. We found this species to be a synchronous spawner, with peaks in reproductive activity from June to September. In the populations we surveyed, there was significant dominance of males (1.26:1.00) based on 942 fish samples (526 males and 416 females). The length at 50% maturity for females was significantly higher than for males at all sites and ranged from 10.6 to 19.3 cm. The diameter of the eggs examined for this species exhibited slight variation, from 0.43 to 0.54 mm. The potential fecundity ranged from 246,254 ± 35,878 to 411,970 ± 54,370 eggs, corresponding to female length and weight of 26.7-32.6 cm and 102.97-234.19 g, respectively. Relative fecundity values were highest at Thanh Phu, Ben Tre (6388 ± 605 eggs), and Dong Hai, Bac Lieu (6461 ± 637 eggs), followed by Tran De, Soc Trang (4729 ± 408), and were found to be lowest at Duyen Hai, Tra Vinh (3117 ± 223 eggs). Information on reproductive behavior in this species has far-reaching impacts on sustainable extractions, stock conservation, and aquaculture.

Investigating human impacts on rocky reefs using measures of complexity and relief from 3D photogrammetry

AbstractThe structural complexity of a habitat is linked with the health and biodiversity of the ecosystem. Computational methods analyzing 3D representations of the environment allow for accurate measurement; however, rocky reef environments that feature gullies, arches, stacks, and ledges may be inaccurately represented using standard measures of complexity. This article presents a novel assessment of structural complexity through relief calculated from 3D reconstructions of marine environments, tailored for rocky reefs with vertical features. This method is tested in two case studies: a tropical coral reef in Indonesia and a rocky (chalk) reef in the United Kingdom. Chalk reef relief was not correlated with vector dispersion or fractal dimension and was weakly correlated with rugosity (); however, in two comparison tropical reef datasets, relief correlated moderately with vector dispersion on both coral reefs () and moderately‐strongly with rugosity (). On the chalk reef, tailored complexity metrics confirmed the previous finding that catch‐size Cancer pagurus abundance (≥115 mm) was correlated with fractal dimension (), indicating that adults preferred elevated, complex reefs. Analysis showed correlations between relief and low‐severity chalk damage () and between relief and abrasion damage (), whereas previous research had indicated that damage was not correlated with complexity (assessed computationally with rugosity, fractal dimension, and vector dispersion). Surveying marine environments with multicamera arrays and 3D photogrammetry can drastically reduce the time and cost of fieldwork surveys and provide accurate measures of complexity across survey sites. Adapting complexity metrics to habitat‐specific topography provides valuable insight (in this case, into rocky reef marine habitats). Findings from the UK case study support the continued monitoring of the Cromer Shoal Chalk Bed Marine Conservation Zone (MCZ).

Standardization of ALEX index for the ecological quality assessment under European Framework Directives in Mediterranean sensitive habitats affected by biological invasions

Abstract This paper aims at providing a standardized procedure to assess the ecological quality of Mediterranean marine habitats in relation to biological invasions by macroalgae through the employment of the ALEX index. Available data from previous ALEX applications were used to optimize the sampling design and to propose a standardized procedure. The procedure was applied to the main Mediterranean sensitive habitats, coralligenous reefs and meadows of the endemic seagrass Posidonia oceanica, at two sites in the north‐western Mediterranean Sea. A total of 73 native macroalgal taxa and four introduced taxa (the Chlorophyta Caulerpa cylindracea and the turf forming Rhodophyta Acrothamnion preissii, Womersleyella setacea and Asparagopsis spp.) were identified. Coralligenous reefs exhibited a higher abundance of both C. cylindracea and introduced turf species, while P. oceanica meadows were mostly affected by W. setacea and A. preissii. The application of ALEX for different years on coralligenous reefs highlighted the consistency of the index over time in the absence of further invasions. The use of ALEX index with other ecological quality indices showed similar patterns in both habitats. The concurrent assessment of the ecological quality of ecosystems by generic indices and the level of invasion through ALEX index may be a useful approach for answer to requirements of the European Directives and to plan even more complete and effective conservation programmes.