Benthic Life Research Articles

Stock Dynamics of Female Red King Crab in a Small Bay of the Barents Sea in Relation to Environmental Factors.

Stock-recruitment relationships depend on the total abundance of females, their fecundity, and patterns of their maturation. However, the effects of climatic conditions on the abundance, biomass, and mean weight of female red king crabs, Paralithodes camtschaticus, from the introduced population (Barents Sea) have not yet been studied. For this reason, we analyzed long-term fluctuations in stock indices and the average weight of an individual crab in a small bay of the Barents Sea and related these parameters to the dynamics of temperature conditions (temperature in January-December, mean yearly temperature, and temperature anomaly) in the sea. The average weight of a crab at age 6-9 had strong negative correlations with water temperature at lags 8 and 9, indicating faster female maturation in warm periods. Positive relationships were registered between temperature and stock indices for 15-19-year-old females at lag 4 and for 10-14-year-old females at lag 10, supporting the idea of higher survival rates of juveniles and their rapid development being a response to a pool of warm waters. Both redundancy and correlation analyses revealed seawater temperatures in June-August being the most important predictors of female abundance and biomass, indicating that favorable temperature conditions in the first 3 months of crab benthic life result in high survivorship rates for red king crabs.

Clam Genome and Transcriptomes Provide Insights into Molecular Basis of Morphological Novelties and Adaptations in Mollusks.

Bivalve mollusks, comprising animals enclosed in two shell valves, are well-adapted to benthic life in many intertidal zones. Clams have evolved the buried lifestyle, which depends on their unique soft tissue structure and their wedge-shaped muscular foot and long extendible siphons. However, molecular mechanisms of adaptative phenotype evolution remain largely unknown. In the present study, we obtain the high-quality chromosome-level genome of Manila clam R. philippinarum, an economically important marine bivalve in many coastal areas. The genome is constructed by the Hi-C assisted assembly, which yields 19 chromosomes with a total of 1.17 Gb and BUSCO integrity of 92.23%. The de novo assembled genome has a contig N50 length of 307.7 kb and scaffold N50 of 59.5 Mb. Gene family expansion analysis reveals that a total of 24 single-copy gene families have undergone the significant expansion or contraction, including E3 ubiquitin ligase and dynein heavy chain. The significant expansion of transposable elements has been also identified, including long terminal repeats (LTR) and non-LTR retrotransposons. The comparative transcriptomics among different clam tissues reveals that extracellular matrix (ECM) receptors and neuroactive ligand receptors may play the important roles in tissue structural support and neurotransmission during their infaunal life. These findings of gene family expansion and tissue-specific expression may reflect the unique soft tissue structure of clams, suggesting the evolution of lineage-specific morphological novelties. The high-quality genome and transcriptome data of R. philippinarum will not only facilitate the genetic studies on clams but will also provide valuable information on morphological novelties in mollusks.

The benthic and epiphytic marine dinoflagellates of Aotearoa New Zealand and Rangitāhua Kermadec Islands, an updated checklist from 2018 to 2024

ABSTRACT A checklist collating records of New Zealand’s benthic and epiphytic dinoflagellate species was published on-line in 2018 [Rhodes L, Smith KF. 2019. A checklist of the benthic and epiphytic marine dinoflagellates of New Zealand, including Rangitāhua/Kermadec Islands. N Z J Mar Freshw Res. 53:258–277. doi:10.1080/00288330.2018.1492425]. Over the last six years, seventeen species from nine genera (three newly reported genera) have been documented, including sand-dwelling species. Isolation and identification of species using traditional microscopic techniques combined with analysis of DNA sequencing data has been supplemented by high-throughput sequencing techniques (i.e. metabarcoding). Toxin data, based on liquid chromatography mass spectrometry (LC-MS/MS), and toxicity of isolates are included where applicable. Forty-two benthic and epiphytic dinoflagellate genera, including genera having benthic life stages, have now been recorded in Aotearoa New Zealand coastal waters including Rangitāhua Kermadec Islands (new record genera in bold): Adenoides , Alexandrium, Amphidinium, Archaeperidinium, Azadinium, Biecheleria, Blastodinium, Bysmatrum, Cachonina, Coolia, Crypthecodinium, Cryptoperidiniopsis, Dinophysis, Durinskia, Ensiculifera, Fukuyoa, Fragilidium, Gambierdiscus, Gonyaulax, Gymnodinium, Gyrodinium, Heterocapsa, Karenia, Karlodinium, Kryptoperidinium, Lepidodinium, Ostreopsis, Pelagodinium, Pentapharsodinium, Pfiesteria, Polarella, Prorocentrum, Protodinium, Protoperidinium, Pseudadenoides , Pseudopfiesteria, Scrippsiella, Symbiodinium, Thecadinium , Togula, Vulcanodinium and Woloszynskia.

Hidden gems: Scattered knowledge hampered freshwater jellyfish research over the past one-and-a-half centuries.

Freshwater jellyfish (= limnic medusa-budding hydrozoans, FWJ) are a small group of cnidarians found on all continents except Antarctica in temperate to tropical latitudes. Members of this group belong primarily to three genera: Astrohydra, Craspedacusta, and Limnocnida. While Astrohydra and Limnocnida are typically restricted to the islands of Japan, Africa, and the Indian subcontinent, one species or potential species complex, Craspedacusta sowerbii, became globally invasive. Despite research going back about one-and-a-half centuries, little is known about their phylogeny and ecology compared to marine jellyfish. Recent species distribution modelling, however, showed that by 2050, C. sowerbii will potentially extend their distribution ranges due to global warming to high-latitude ecosystems and be present (medusa stage) for an extended time in the seasonal limnic production cycle. An increase in their relative ecological importance with temporal and spatial spreading is hypothesised. Only recently, it has been shown that the trophic roles of polyps and medusae and their prey overlap with other ecosystem members. In addition, medusa behaviour may cause trophic cascades and alter vertical nutrient distributions. However, polyps and other benthic life cycle stages are understudied. In globally, changing freshwater ecosystems that may become more accommodating for FWJ, an improved understanding of their population biology and ecosystem ecology is urgently needed. In this integrative review, we, therefore, explore reasons for the hampered historical research progress, contrast developments with those of marine cnidarians, compile and publish alongside an extensive and unprecedented literature database, and formulate avenues for future directions in FWJ research.

Intra and interspecies discrimination of three teleost species collected from the Komo Estuary in Gabon in relation to living depth levels using otolith shape analysis

ABSTRACT This study aimed to examine otolith shape and fluctuating asymmetry (FA) in pelagic Ethmalosa fimbriata, demersal Galeoides decadactylus, and benthic Cynoglossus monodi and assess their population status to inform on management procedures and verify whether or not otolith shape differs with living depth levels of these species in Lebe fishing site located along Komo Estuary, central-western Gabon. At intraspecies level, otolith shape analysis showed a bilateral asymmetry only in left and right otoliths between males and females of E. fimbriata and C. monodi. DFA separated between left and right and left-left and right-right otoliths shape of males and females within each species. At interspecies level, a significant bilateral asymmetry in left and right otolith shape was found among males and females of each species. DFA completely separated the left and right otoliths of both males and females of three species and confirmed the presence of three separate populations representing the three species, which should be managed separately. A significant FA on right and left otolith shapes was found among males and females at intra and interspecies levels. Accordingly, results indicated a close relationship between asymmetry of otolith shape and pelagic and benthic life characteristics of E. fimbriata and C. monodi.

ABIOTIC LIGHT FACTOR TOWARDS FUTURE CRUSTACEAN AQUAFARMING TECHNOLOGY IN PREPARING FOR GLOBAL CLIMATE CHANGE

The ramifications of light on crustacean circadian rhythm are complex and multifaceted since light has three core elements included of photoperiod, spectrum and intensity. Most marine crustacean has a planktonic larval phase in their life cycle before metamorphosing into benthic juvenile, this ontogenetic shift from a planktonic to a benthic life requires a different level of light photoperiod, spectrum and intensity. Hence, this review is planned on the basis of referring to a large number of accumulated scientific findings and further emphasizes the light impacts on the different life stages (larva, juvenile and adult) of crustaceans with myriad approaches in the areas of growth, feeding, locomotion, spawning and immunity. In terms of photoperiod, there is a high tendency of larval crustaceans to favour longer photoperiods (more than 18 L) during the early stage. Later, up to a certain extent, perhaps amid the juvenile stage, photoperiod preference shifted towards shorter photoperiods as such later juvenile stage demonstrated a pressing need for dark photoperiod reflected the common nocturnal behaviour in crustaceans. In terms of light intensity, several previous studies convinced that more light intensity is requisite as a vital need to enhance larval growth, as well as emphasized the positive impact of light intensity on ovarian progression in adult female crustaceans. For the context of the light spectrum, former evidence deciphered the benefit of utilizing white light in terms of survival, growth and reduced stress, as well as rising antioxidant capacity in the crustacean. Simultaneously, instead of the white spectrum, adopting green, blue and cyan light spectrums perhaps had a high potential to be incorporated into aqua-farming. As a whole, for future studies, many experts need to take the initiative to engage in upgrading further existing research by prioritizing light intensity and light spectrum to better understand the light repercussions on crustaceans. Regarding future applications, the breakthrough from this review fosters and advocates farmers and researchers to shift to an enclosed system set-up in terms of optimization of myriads' light approach, including photoperiod, light intensity and light spectrum, in tandem with such system is resilient against catastrophic global climate change. This light optimization during crustacean culture is a pivotal avenue to enhanced farming productivity and providing assurance of food security preservation for the sake of the next generation.

Hedgehog signaling is required for larval muscle development and larval metamorphosis of the mussel Mytilus coruscus

Understanding the developmental processes and signaling pathways involved in larval myogenesis and metamorphosis is crucial for comprehending the life history and adaptive strategies of marine organisms. In this study, we investigated the temporal and spatial patterns of myogenesis in the mussel Mytilus coruscus (Mc), focusing on the emergence and transformation of major muscle groups during different larval stages. We also explored the role of the Hedgehog (Hh) signaling pathway in regulating myogenesis and larval metamorphosis. The results revealed distinct developmental stages characterized by the emergence of specific muscular components, such as velum retractor muscles and anterior adductor muscles, in D-veliger and umbo larvae, which are responsible for the planktonic stage. In the pediveliger stage, posterior ventral, posterior adductor, and foot muscles appeared. After larval metamorphosis, the velum structure and its corresponding retractor muscles degenerate, indicating the transition from planktonic to benthic life. We observed a conserved pattern of larval musculature development and revealed a high degree of conservation across bivalve species, with comparable emergence times during myogenesis. Furthermore, exposure to the Hh signaling inhibitor cyclopamine impaired larval muscle development, reduced larval swimming activity, and inhibited larval metamorphosis in M. coruscus. Cyclopamine-mediated inhibition of Hh signaling led to reduced expression of four key genes within the Hh signaling pathway (McHh, McPtc, McSmo, and McGli) and the striated myosin heavy chain gene (McMHC). It is hypothesised that the abnormal larval muscle development in cyclopamine-treated groups may be an indirect effect due to disrupted McMHC expression. We provide evidence for the first time that cyclopamine treatment inhibited larval metamorphosis in bivalves, highlighting the potential involvement of Hh signaling in mediating larval muscle development and metamorphosis in M. coruscus. The present study provides insights into the dynamic nature of myogenesis and the regulatory role of the Hh signaling pathway during larval development and metamorphosis in M. coruscus. The results obtained in this study contribute to a better understanding of the evolutionary significance of Hh signaling in bivalves and shed light on the mechanisms underlying larval muscle development and metamorphosis in marine invertebrates.

Guardians of the seabed: Nature-inclusive design of scour protection in offshore wind farms enhances benthic diversity

In the past, a large part of the seabed of the southern North Sea was covered by hard substrates, including oyster beds, coarse peat banks, and glacial erratics. Human activities, particularly bottom trawl fisheries, led to the disappearance of most of these hard substrates, resulting in the loss of its associated diverse benthic life as well. However, the introduction of human-made structures such as offshore wind farms in the North Sea, offers a chance to provide habitat of similar functionality as the former hard substrates. The offshore wind farm infrastructure generally contains layers of rock material deployed at the base of the wind turbine foundations and cable crossings, so-called scour protection, aiming to prevent seabed erosion. The scour protection offers a unique habitat for rock-dwelling benthic organisms in an otherwise mostly soft-bottom environment. By designing the scour protection to be more nature-inclusive, the biodiversity of benthic life can be increased. In this study we examined the effect of substrate material and grading of the scour protection on the epibenthic biodiversity in situ. This was done by deploying research cages containing crates (n = 15) with different types of substrates (concrete, granite, and marble) on the scour protection within an offshore wind farm in the Dutch North Sea. The study revealed a significant (p < 0.05) positive relation between available substrate surface (pebble size) and taxonomic richness. Furthermore, a biological trait assessment of living habits (Tube dwelling, Burrowing, Free living, Crevice dwelling, Epi/endobiotic, and Attached) revealed variations in habit modes across substrate types, with marble and concrete samples showing greatest divergence. Marble samples contained a higher prevalence of tube dwelling organisms, whereas concrete samples contained a relatively higher prevalence of free living, epi/endobiotic and crevice dwelling organisms. The findings support the value of nature-inclusive scour protection designs, emphasizing that both taxonomic and functional diversity can be enhanced by increasing the available surface area of the scour protection and incorporating a variety of substrate types. By adopting these nature-inclusive design components, the coexistence of renewable energy production and a diverse marine benthic community can be further optimized.

Adverse effects of crushed seafloor massive sulphide deposits on the boreal deep-sea sponge Geodia barretti Bowerbank, 1858 and its associated fauna

Abundant mineral resources in the deep sea are prospected for mining for the global metal market. Seafloor massive sulphide (SMS) deposits along the Mid-Atlantic Ridge are one of the potential sources for these metals. The extraction of SMS deposits will expose adjacent marine ecosystems to suspended particle plumes charged with elevated concentrations of heavy metals and other potentially toxic compounds. Up to date there is no information about the impact of mining activities on deep-sea benthic ecosystems such as abundant deep-sea sponge grounds in the North Atlantic Ocean. Sponge grounds play a major role in benthic-pelagic coupling and represent an important habitat for a diversity of vertebrates, invertebrates and microorganisms. To simulate the effects of mining plumes on benthic life in the deep sea, we exposed Geodia barretti, a dominant sponge species in the North Atlantic Ocean, and an associated brittle star species from the genus Ophiura spp. to a field-relevant concentration of 30 mg L−1 suspended particles of crushed SMS deposits. Three weeks of exposure to suspended particles of crushed SMS resulted in a tenfold higher rate of tissue necrosis in sponges. All brittle stars in the experiment perished within ten days of exposure. SMS particles were evidently accumulated in the sponge's mesohyl and concentrations of iron and copper were 10 times elevated in SMS exposed individuals. Oxygen consumption and clearance rates were significantly retarded after the exposure to SMS particles, hampering the physiological performance of G. barretti. These adverse effects of crushed SMS deposits on G. barretti and its associated brittle star species potentially cascade in disruptions of benthic-pelagic coupling processes in the deep sea. More elaborate studies are advisable to identify threshold levels, management concepts and mitigation measures to minimize the impact of deep-sea mining plumes on benthic life.

Resemblance of the global depth distribution of internal-tide generation and cold-water coral occurrences

Abstract. Internal tides are known to be an important source of mixing in the oceans, especially in the bottom boundary layer. The depth of internal-tide generation therefore seems important for benthic life and the formation of cold-water coral mounds, but internal-tide conversion is generally investigated in a depth-integrated sense. Using both idealized and realistic simulations on continental slopes, we found that the depth of internal-tide generation increases with increasing slope steepness and decreases with intensified shallow stratification. The depth of internal-tide generation also shows a typical latitudinal dependency related to Coriolis effects. Using a global database of cold-water corals, we found that, especially in Northern Hemisphere autumn and winter, the global depth pattern of internal-tide generation correlates (rautumn = 0.70, rwinter = 0.65, p &lt; 0.01) with that of cold-water corals: shallowest near the poles and deepest around the Equator, with a decrease in depth around 25° S and N, and shallower north of the Equator than south. We further found that cold-water corals are situated significantly more often on topography that is steeper than the internal-tide beam (i.e. where supercritical reflection of internal tides occurs) than would be expected from a random distribution: in our study, in 66.9 % of all cases, cold-water corals occurred on a topography that is supercritical to the M2 tide whereas globally only 9.4 % of all topography is supercritical. Our findings underline internal-tide generation and the occurrence of supercritical reflection of internal tides as globally important for cold-water coral growth. The energetic dynamics associated with internal-tide generation and the supercritical reflection of internal tides likely increase the food supply towards the reefs in food-limited winter months. With climate change, stratification is expected to increase. Based on our results, this would decrease the depth of internal-tide generation, possibly creating new suitable habitat for cold-water corals shallower on continental slopes.

Early Jurassic extrinsic solar system dynamics versus intrinsic Earth processes: Toarcian sedimentation and benthic life in deep-sea contourite drift facies, Cardigan Bay Basin, UK

The Cardigan Bay Basin (UK) may have functioned as a deep and narrow strait, and thereby influenced Early Jurassic oceanic circulation through the northern and southern Laurasian Seaway, and between Boreal and Peri-Tethys domains. Toarcian hemipelagic deposits of the basin in the Mochras borehole show strongly bioturbated contourite facies. Trace fossils are strongly dominated by Phycosiphon incertum (represented by four morphotypes), which was produced by opportunistic colonizers. Thalassinoides, Schaubcylindrichnus and Trichichnus are common (the latter is a deep-tier trace fossil produced by filamentous sulfide-oxidizing bacteria with a high tolerance for dysoxia), accompanied by less common Zoophycos, Planolites, Palaeophycus, Teichichnus, Rhizocorallium, Chondrites, and dwelling and resting structures, such as cf. Polykladichnus, Siphonichnus, Skolithos, Arenicolites, Monocraterion and Lockeia. Ichnological and lithological signals suggest repetitive fluctuations in benthic conditions attributed to a hierarchy of orbital cycles (precession and obliquity [4th order], short eccentricity [3rd order], long eccentricity [2nd order] and Earth–Mars secular resonance [1st order]). The Pliensbachian–Toarcian transition appears to be a significant palaeoceanographic turning point in the Cardigan Bay Basin, starting a CaCO3 decline, and with the most severe oxygen crisis of the Tenuicostatum Zone (here dysoxic but not anoxic) ending at the onset, in the early Serpentinum Zone (Exaratum Subzone), of the Toarcian negative carbon isotope excursion (To-CIE—linked with the Toarcian Oceanic Anoxic Event occurring in the lower part in the Serpentinum Zone). This trend contrasts with the prevalence of anoxia synchronous with the To-CIE in many other settings. Minor dysoxia returned to the Mochras setting in the latest Thouarsense to Dispansum zone interval. Extreme climate warming during the To-CIE may have enhanced and caused a reversal in the direction of deep marine circulation, improving oxygenation of the sea floor. Spectral analysis of binary data on ichnotaxa appearances gives high confidence in orbital signals and allows refined estimation of ammonite zones and the duration of the Toarcian (minimum ~ 9.4 Myr).

Spiny dogfish, Squalus suckleyi, shows a good tolerance for hypoxia but need long recovery times.

Pacific spiny dogfish, Squalus suckleyi, move to shallow coastal waters during critical reproductive life stages and are thus at risk of encountering hypoxic events which occur more frequently in these areas. For effective conservation management, we need to fully understand the consequences of hypoxia on marine key species such as elasmobranchs. Because of their benthic life style, we hypothesized that S. suckleyi are hypoxia tolerant and able to efficiently regulate oxygen consumption, and that anaerobic metabolism is supported by a broad range of metabolites including ketones, fatty acids and amino acids. Therefore, we studied oxygen consumption rates, ventilation frequency and amplitude, blood gasses, acid-base regulation, and changes in plasma and tissue metabolites during progressive hypoxia. Our results show that critical oxygen levels (P crit) where oxyregulation is lost were indeed low (18.1% air saturation or 28.5Torr at 13°C). However, many dogfish behaved as oxyconformers rather than oxyregulators. Arterial blood PO2 levels mostly decreased linearly with decreasing environmental PO2. Blood gases and acid-base status were dependent on open versus closed respirometry but in both set-ups ventilation frequency increased. Hypoxia below Pcrit resulted in an up-regulation of anaerobic glycolysis, as evidenced by increased lactate levels in all tissues except brain. Elasmobranchs typically rely on ketone bodies as oxidative substrates, and decreased concentrations of acetoacetate and β-hydroxybutyrate were observed in white muscle of hypoxic and/or recovering fish. Furthermore, reductions in isoleucine, glutamate, glutamine and other amino acids were observed. After 6hours of normoxic recovery, changes persisted and only lactate returned to normal in most tissues. This emphasizes the importance of using suitable bioindicators adjusted to preferred metabolic pathways of the target species in conservation physiology. We conclude that Pacific spiny dogfish can tolerate severe transient hypoxic events, but recovery is slow and negative impacts can be expected when hypoxia persists.

Oceanographic Analysis for Optimal Lobster Artificial Reef Placement in Prigi Bay, East Java

Oceanographic states are closely related to marine biota’s distribution and breeding patterns, especially in the intertidal zone. This study analyses the water quality variability and their relationship in the water of Prigi Bay. Water quality data was collected in situ using a Water Quality Checker. The statistical analyses were performed by applying PAST software version 4.11. The suitable waters with the best tendency value for the placement of lobster artificial reefs are stations 2 (Karang Gongso) and 4 (Damas). It is not only explained by salinity and turbidity but also by the ORP role, which has the solution potential to transfer electrons from oxidants to reductants, thus affecting the chemical processes. The high potential suitability at 2 locations is due to the concentration of a supportive environment with variability in ORP concentrations, having more potential for electron transfer, which significantly affects the attached benthic life as a pioneer for the reef. Salinity stability is safer from the impact of water mixing from the estuary. Parameter concentrations are more stable according to water temperature standards for coralline algae growth and are affected by turbidity and dissolved oxygen. In addition, other research is needed, such as social factors and fishermen’s activities.

Using Multiple Metal Mixture Models to Predict Toxicity of Riverine Sediment Porewater to the Benthic Life Stage of Juvenile White Sturgeon (Acipenser transmontanus).

Five metal mixture dose-response models were used to predict the toxicity of porewater to young sturgeon at areas of interest in the Upper Columbia River (WA, USA/BC, Canada) and to evaluate these models as tools for risk assessments. Dose components of metal mixture models included exposure to free metal ion activities or metal accumulation by biotic ligands or humic acid, and links of dose to response used logistic equations, independent joint action equations, or additive toxicity functions. Laboratory bioassay studies of single metal exposures to juvenile sturgeon, porewater collected in situ in the fast-flowing Upper Columbia River, and metal mixture models were used to evaluate toxicity. The five metal mixture models were very similar in their predictions of adverse response of juvenile sturgeon and in identifying copper (Cu) as the metal responsible for the most toxic conditions. Although the modes of toxic action and the 20% effective concentration values were different among the dose models, predictions of adverse response were consistent among models because all doses were tied to the same biological responses. All models indicated that 56% ± 5% of 122 porewater samples were predicted to have <20% adverse response, 25% ± 5% of samples were predicted to have 20% to 80% adverse response, and 20% ± 4% were predicted to have >80% adverse response in juvenile sturgeon. The approach of combining bioassay toxicity data, compositions of field porewater, and metal mixture models to predict lack of growth and survival of aquatic organisms due to metal toxicity is an important tool that can be integrated with other information (e.g., survey studies of organism populations, life cycle and behavior characteristics, sediment geochemistry, and food sources) to assess risks to aquatic organisms in metal-enriched ecosystems. Environ Toxicol Chem 2024;43:62-73. Published 2023. This article is a U.S. Government work and is in the public domain in the USA.

Hydrostatic pressure induces transformations in the organic matter and microbial community composition of marine snow particles

In the hadal zone of the ocean (6–11 km), the characteristics of sinking marine snow particles and their attached microbial communities remain elusive, despite their potential importance for benthic life thriving at extreme pressures (60–110 MPa). Here, we used simulation experiments to explore how increasing pressure levels modify the microbial degradation, organic matter composition, and microbiome of sinking diatom aggregates. Individual aggregates were incubated in rotating tanks in which pressure was incrementally increased to simulate a descent from surface to hadal depth within 20 days. Incubations at atmospheric pressure served as controls. With increasing pressure, microbial respiration and diatom degradation decreased gradually and ceased completely at 60 MPa. Dissolved organic carbon leaked substantially from the aggregates at ≥40 MPa, while diatom lipid and pigment contents decreased moderately. Bacterial abundance remained stable at >40 MPa, but bacterial community composition changed significantly at 60–100 MPa. Thus, pressure exposure reduces microbial degradation and transforms both organic matter composition and microbiomes of sinking particles, which may seed hadal sediments with relatively fresh particulate organic matter and putative pressure-tolerant microbes.

Environmental assessment of oyster beds in the northern Arabian Gulf Coast of the United Arab Emirates

The United Arab of Emirates (UAE) hosts valuable coastal and marine biodiversity, and oysters are one of the habitants of its marine ecosystem. Oysters play an essential role in the nearshore coasts where they work as an active filter. They filter nutrients, phytoplankton, sediments, heavy metals, and toxins out of the water, which improves the water quality. This is the first study that characterizes oyster bed habitats in the UAE by analyzing water quality parameters, polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs)and heavy metals in water, sediments and oyster samples collected from five locations along the coasts of Sharjah, Ajman, and Umm al Quwain. Oyster bed areas supported a diverse assemblage of benthic life including oysters, scallops, pen shells, hard corals, and macroalgae. Mobile species in these habitats included groupers, emperors, snappers, sea snakes, among others. The phytoplankton assemblages were dominated by diatoms, dinoflagellates, and small cryptophytes. Harmful diatom Pseudonitzschia was found in all locations. No detectable concentrations of PAHs and OCPs were reported in this study, and water quality parameters were within the acceptable levels for the region. On the other hand, water quality index was reported marginal, mostly due to the presence of higher than acceptable concentrations of chromium and mercury in all sites studied. Bioconcentration factors concluded that oysters were able to bioconcentrate metals such as arsenic, cadmium, chromium, and zinc, when compared to water. No detectable concentrations of lead and mercury were reported in oysters, suggesting higher depuration rates for those metals.

Navigating a broken river: Understanding the ecological consequences of fragmentation on benthic life

AbstractHabitat fragmentation is emerging as a leading cause of biodiversity decline in riverine ecosystems. Several natural and human factors contribute to the fragmentation of rivers. River fragmentation is a growing problem that is widely spread and poses a significant challenge to the conservation of freshwater biodiversity, but its impact is not fully documented and acknowledged. Fragmentation impedes the movement of aquatic organisms and alters natural flow regimes, disrupting habitats and trophic supplies for aquatic biodiversity. It can also affect the adaptive ability of organisms to natural environmental changes, leading to a change in the structure and function of biotic communities. To understand the effects of fragmentation on river ecology, it is crucial to link its spatial and structural implications. This article examines the occurrence and frequency of fragmentation and its effects on the ecological community of benthic biota. This review aims to elucidate the overall effects of fragmentation on river ecology and recommends the possible measures to mitigate its impact. Urgent action is required to establish a comprehensive global network of free‐flowing river systems and revive previously exploited rivers in different regions to enhance the protection and sustainable utilization of river ecosystems.

Improvement of genetic health and diversity of Zostera marina (eelgrass) in Barnegat Bay, New Jersey ten years after Hurricane Sandy: Support for the “storm stimulus” hypothesis

Hurricane Sandy struck the New York metropolitan region on October 29, 2012. The storm severely impacted the physical state of Barnegat Bay, New Jersey with its heavy storm surge, affecting many forms of benthic life and ripping up extensive beds of Zostera marina. Pre-Sandy studies of the genetic status of Z. marina in Barnegat Bay indicated low levels of heterozygosity and high levels of inbreeding. This present study examines the long-term effects of Hurricane Sandy on the eelgrass meadows of New Jersey. Heterozygosity analysis (mean Ho= 0.482 ± 0.013 and mean He= 0.498± 0.009) of the five Barnegat populations studied suggest an improvement in diversity from pre-Sandy values of 2008. Mean inbreeding levels (overall Fis = 0.077 ± 0.034) also indicated reduced inbreeding, and the fixation index (overall mean pairwise Fst = 0.064 ±0.006) suggested increased connectivity between populations with low levels of differentiation. Although we found no indication of bottlenecks in the last 2–3 years, by employing m-ratio calculations, there was strong evidence for long-term, historical bottlenecks in all populations, potentially due to the mass wasting disease epidemic in the 1930s. Unexpectantly, the post-Sandy genetic health and diversity of Z. marina in Barnegat Bay appears to have improved since it was last surveyed in 2008, supporting the “Storm Stimulus” hypothesis.

Management and ecology of the wedge clam (Donax trunculus) in the NW Mediterranean Sea: The case of Ebro Delta (NE Spain)

The wedge clam (Donax trunculus) is one of the most prized clam species fished in the EU. Clam fisheries have experienced a dramatic decline during the last decades on Spanish coasts resulting in the progressive closure of fishing grounds. The Ebro Delta (NW Mediterranean Sea) is one of the few areas of the Spanish coast where there is still some fishing activity. In this context, the main objectives of this study were: to provide novel data on the ecology of this species and to analyse the management of D. trunculus fisheries in the Ebro Delta. The results showed a depth segregation phenomenon and suggested that D. trunculus performs two migrations during its benthic life cycle, i.e., (1) the settlement of planktonic larvae occurs more intensely in the deepest part of its bathymetric distribution, where the survival was more intense. As clams progressively increase in size, they move to shallower areas; (2) adults tend to move back to the deepest part of their bathymetric distribution as they increase in size. The management of D. trunculus has improved significantly in the last decade. However, some issues are still unsolved (e.g., fishing gear limits are unclear; population boundaries do not coincide with political boundaries). Moreover, the shallower areas where juveniles are located concentrate the highest fishing pressure over the stock.

Verification of the Daily Periodicity of Microincrements Formation on the Otoliths of the Juvenilrs of the Ocellated Blenny &lt;i&gt;Opisthocentrus ocellatus&lt;/i&gt; (Stichaeidae) for a Retrospective Evaluation of the Period of Mass Hatching under the Conditions of Peter the Great Bay of the Japan Sea

Experiments were carried out on intravital otolith-tagging of juveniles of the ocellated blenny after transition to benthic life mode with Alizarin Red S. Marking at a dye concentration of 200 mg/L for 16–18 h at night, gave 100% formation of fluorescent marks with zero mortality of experimental individuals. Alizarin marks on the otoliths correspond to “stress” marks in the form of darker micro-increments, visible in transmitted light. The calculation of microincrements in the zone between two consecutive markings with an interval of 9 days confirmed the daily periodicity of their laying at this stage of development of the ocellated blenny. This allowed us to determine the period of hatching in natural conditions of juveniles in the Zhitkov Bay (Russky Island, the Peter the Great Bay, Japan sea). Hatching of larvae in 2017 in this species occurred, according to our estimates, from the last decade of March to the end of the second decade of April, with a peak in the first decade of April. Hatching begins even under the ice at a slightly negative water temperature of –1–0°C, but it proceeds mainly already at a temperature of 1–3°C, after the removal of ice from the bay. Taking into account the known timing of spawning of the ocellated blenny in the Peter the Great Bay (November–early December), we can state that the development of its eggs in this area is greatly slowed down at water temperatures below zero in December–March and can go on for 4–5 months, which is almost 3 times longer than the development time in more mild conditions of the south Hokkaido.