Journal Description
Oceans
Oceans
is an international, peer-reviewed, open access journal of oceanography published quarterly online by MDPI.
- Open Access—free to download, share, and reuse content. Authors receive recognition for their contribution when the paper is reused.
- Rapid Publication: manuscripts are peer-reviewed and a first decision provided to authors approximately 30.2 days after submission; acceptance to publication is undertaken in 7.3 days (median values for papers published in this journal in the first half of 2021).
- Recognition of Reviewers: APC discount vouchers, optional signed peer review, and reviewer names published annually in the journal.
Latest Articles
Cold-Water Coral Reefs in the Langenuen Fjord, Southwestern Norway—A Window into Future Environmental Change
Oceans 2021, 2(3), 583-610; https://doi.org/10.3390/oceans2030033 - 25 Aug 2021
Abstract
Ocean warming and acidification pose serious threats to cold-water corals (CWCs) and the surrounding habitat. Yet, little is known about the role of natural short-term and seasonal environmental variability, which could be pivotal to determine the resilience of CWCs in a changing environment.
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Ocean warming and acidification pose serious threats to cold-water corals (CWCs) and the surrounding habitat. Yet, little is known about the role of natural short-term and seasonal environmental variability, which could be pivotal to determine the resilience of CWCs in a changing environment. Here, we provide continuous observational data of the hydrodynamic regime (recorded using two benthic landers) and point measurements of the carbonate and nutrient systems from five Lophelia pertusa reefs in the Langenuen Fjord, southwestern Norway, from 2016 to 2017. In this fjord setting, we found that over a tidal (<24 h) cycle during winter storms, the variability of measured parameters at CWC depths was comparable to the intra-annual variability, demonstrating that single point measurements are not sufficient for documenting (and monitoring) the biogeochemical conditions at CWC sites. Due to seasonal and diurnal forcing, parts of the reefs experienced temperatures up to 4 °C warmer (i.e., >12 °C) than the mean conditions and high CT concentrations of 20 µmol kg−1 over the suggested threshold for healthy CWC reefs (i.e., >2170 µmol kg−1). Combined with hindcast measurements, our findings indicate that these shallow fjord reefs may act as an early hotspot for ocean warming and acidification. We predict that corals in Langenuen will face seasonally high temperatures (>18 °C) and hypoxic and corrosive conditions within this century. Therefore, these fjord coral communities could forewarn us of the coming consequences of climate change on CWC diversity and function.
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(This article belongs to the Special Issue The Future of Coral Reefs: Research Submitted to ICRS 2020, Bremen, Germany)
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Open AccessFeature PaperArticle
Optimal Life Extension Management of Offshore Wind Farms Based on the Modern Portfolio Theory
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and
Oceans 2021, 2(3), 566-582; https://doi.org/10.3390/oceans2030032 - 24 Aug 2021
Abstract
The present study aims to develop a risk-based approach to finding optimal solutions for life extension management for offshore wind farms based on Markowitz’s modern portfolio theory, adapted from finance. The developed risk-based approach assumes that the offshore wind turbines (OWT) can be
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The present study aims to develop a risk-based approach to finding optimal solutions for life extension management for offshore wind farms based on Markowitz’s modern portfolio theory, adapted from finance. The developed risk-based approach assumes that the offshore wind turbines (OWT) can be considered as cash-producing tangible assets providing a positive return from the initial investment (capital) with a given risk attaining the targeted (expected) return. In this regard, the present study performs a techno-economic life extension analysis within the scope of the multi-objective optimisation problem. The first objective is to maximise the return from the overall wind assets and the second objective is to minimise the risk associated with obtaining the return. In formulating the multi-dimensional optimisation problem, the life extension assessment considers the results of a detailed structural integrity analysis, a free-cash-flow analysis, the probability of project failure, and local and global economic constraints. Further, the risk is identified as the variance from the expected mean of return on investment. The risk–return diagram is utilised to classify the OWTs of different classes using an unsupervised machine learning algorithm. The optimal portfolios for the various required rates of return are recommended for different stages of life extension.
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(This article belongs to the Special Issue Sustainable Marine Structures)
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Open AccessFeature PaperArticle
A Conflict between the Legacy of Eutrophication and Cultural Oligotrophication in Hiroshima Bay
Oceans 2021, 2(3), 546-565; https://doi.org/10.3390/oceans2030031 - 16 Aug 2021
Abstract
Although the water quality in Hiroshima Bay has improved due to government measures, nutrient reduction has sharply decreased fisheries production. The law was revised in 2015, where the nutrient effluents from the sewage treatment plants were relaxed, yet no increase in fishery production
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Although the water quality in Hiroshima Bay has improved due to government measures, nutrient reduction has sharply decreased fisheries production. The law was revised in 2015, where the nutrient effluents from the sewage treatment plants were relaxed, yet no increase in fishery production was observed. Herein, we investigate the distribution of C, N, S, and P within Hiroshima Bay. Material loads from land and oyster farming activity influenced the C and S distributions in the bay sediments, respectively. Natural denitrification caused N reduction in areas by the river mouths and the landlocked areas whose sediments are reductive. The P content was high in the areas under aerobic conditions, suggesting metal oxide-bound P contributes to P accumulation. However, it was low in the areas with reducing conditions, indicating P is released from the sediments when reacting with H2S. In such reductive sediments, liberated H2S also consumes dissolved oxygen causing hypoxia in the bottom layer. It was estimated that 0.28 km3 of muddy sediment and 1.8 × 105 ton of P accumulated in Hiroshima Bay. There remains conflict between the ‘Legacy of Eutrophication’ in the sediment and ‘Cultural Oligotrophication’ in the surface water due to 40 years of reduction policies.
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(This article belongs to the Special Issue Current Advances and Challenges in Ocean Science—Feature Papers for the Founding of Oceans)
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Open AccessArticle
The Last 1200 Years of Rainfall/Runoff Variability along the Central Mexico Pacific Coast Associated with the North American Monsoon
Oceans 2021, 2(3), 530-545; https://doi.org/10.3390/oceans2030030 - 02 Aug 2021
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This study presents new evidence for long-term variability in the late Holocene North American Monsoon (NAM), Pacific coast of Mexico. We have carried out a rock magnetic study on two deep-sea sediment cores from the Pacific coast Pescadero Basin. The magnetic intensities estimate
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This study presents new evidence for long-term variability in the late Holocene North American Monsoon (NAM), Pacific coast of Mexico. We have carried out a rock magnetic study on two deep-sea sediment cores from the Pacific coast Pescadero Basin. The magnetic intensities estimate total magnetic material and are a proxy for total clastic sediment. Ratios of magnetic intensities estimate the grain size of magnetic material. The rock magnetic data show a decimeter scale, multi-decadal oscillation with fourteen cycles (A-N) over the last 1200 years. These oscillations reflect alternating intervals of stronger/coarser magnetic/clastic flux to the coastal ocean and intervals of weaker/finer magnetic flux. We think these variations are caused by variations in long-term dominance of the NAM; summer (wet) monsoons produce rainy conditions (with runoff) while winter (dry) monsoons produce significant offshore winds, increased upwelling/biological productivity. We can correlate our variability to two other published studies southeast of Pescadero Basin, coastal lake sediments in Laguna de Juanacatlan and a Juxtlahuaca Cave stalagmite. Both of these studies estimate local rainfall. We see evidence of the same pattern of multi-decadal rainfall-runoff variability in these records as we see in Pescadero Basin, which is synchronous to within ±25 years over the last 1200 years. The multi-dacadal pattern of hydrologic variability in all three records varies in cycle duration from ~90-years wet/dry cycles in the Little Ice Age (1400–1850 AD) to ~60-years cycles in the Medieval Climate Optimum (1100–1400 AD). This variability in cycle duration suggests some chaotic nature to the regional NAM climate pattern or some long-term non-linear forcing (PDO?).
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Open AccessArticle
The Status of the Coral Reefs of the Jaffna Peninsula (Northern Sri Lanka), with 36 Coral Species New to Sri Lanka Confirmed by DNA Bar-Coding
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, , , and
Oceans 2021, 2(3), 509-529; https://doi.org/10.3390/oceans2030029 - 26 Jul 2021
Abstract
Sri Lanka, an island nation located off the southeast coast of the Indian sub-continent, has an unappreciated diversity of corals and other reef organisms. In particular, knowledge of the status of coral reefs in its northern region has been limited due to 30
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Sri Lanka, an island nation located off the southeast coast of the Indian sub-continent, has an unappreciated diversity of corals and other reef organisms. In particular, knowledge of the status of coral reefs in its northern region has been limited due to 30 years of civil war. From March 2017 to August 2018, we carried out baseline surveys at selected sites on the northern coastline of the Jaffna Peninsula and around the four largest islands in Palk Bay. The mean percentage cover of live coral was 49 ± 7.25% along the northern coast and 27 ± 5.3% on the islands. Bleaching events and intense fishing activities have most likely resulted in the occurrence of dead corals at most sites (coral mortality index > 0.33). However, all sites were characterised by high values of diversity (H’ ≥ 2.3) and evenness (E ≥ 0.8). The diversity index increased significantly with increasing coral cover on the northern coast but showed the opposite trend on the island sites. One hundred and thirteen species of scleractinian corals, representing 16 families and 39 genera, were recorded, as well as seven soft coral genera. Thirty-six of the scleractinian coral species were identified for the first time on the island of Sri Lanka. DNA barcoding using the mitochondrial cytochrome oxidase subunit I gene (COI) was employed to secure genetic confirmation of a few difficult-to-distinguish new records: Acropora aspera, Acropora digitifera, Acropora gemmifera, Montipora flabellata, and Echinopora gemmacea.
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(This article belongs to the Special Issue The Future of Coral Reefs: Research Submitted to ICRS 2020, Bremen, Germany)
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Open AccessArticle
Minor Contribution by Biomineralizing Phytoplankton to Surface Ocean Biomineral Pools in the Late Stratified Period
Oceans 2021, 2(3), 489-508; https://doi.org/10.3390/oceans2030028 - 21 Jul 2021
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Vertical distributions of biogenic silica (bSi), particulate inorganic carbon (PIC) and key biomineral-forming phytoplankton indicate vertical zoning, or partitioning, during the late summer stratified period in the northeast Atlantic. Coccolithophores were generally more numerous in the surface mixed layer, whilst PIC concentrations were
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Vertical distributions of biogenic silica (bSi), particulate inorganic carbon (PIC) and key biomineral-forming phytoplankton indicate vertical zoning, or partitioning, during the late summer stratified period in the northeast Atlantic. Coccolithophores were generally more numerous in the surface mixed layer, whilst PIC concentrations were more homogenous with depth throughout the euphotic zone. Diatoms were notably more abundant and more diverse in the lower euphotic zone beneath the mixed layer in association with subsurface maxima in chlorophyll-a, bSi and oxygen concentrations. The four dominant coccolithophore species (Emiliania huxleyi, Gephyrocapsa muellerae, Syracosphera spp., and Rhabdosphaera clavigera) represented 78 ± 20% (range 31–100%) of the observed community across all sampled depths yet simultaneously contributed an average of only 13% to measured PIC pools. The diatom community, which was dominated by Pseudo-nitzschia spp. and by a species tentatively identified as Nanoneis longta, represented only ~1% of the bSi pool on average, with contributions increasing within the chlorophyll maximum. Despite a slow gradual deepening of the surface mixed layer in the period prior to observation, and adequate nutrient availability beneath the mixed layer, biomineral pools at this time consisted largely of detrital rather than cellular material.
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Open AccessFeature PaperArticle
Shallow-Water Species Diversity of Common Intertidal Zoantharians (Cnidaria: Hexacorallia: Zoantharia) along the Northeastern Coast of Trinidad, Southern Caribbean
Oceans 2021, 2(3), 477-488; https://doi.org/10.3390/oceans2030027 - 20 Jul 2021
Abstract
Zoantharians are colonial cnidarians commonly found in shallow tropical Caribbean coral reefs, and are known to be globally distributed. Common species in genera Zoanthus and Palythoa occur at Toco, Trinidad, where they are more abundant than their Scleractinia counterparts relative to benthic coverage.
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Zoantharians are colonial cnidarians commonly found in shallow tropical Caribbean coral reefs, and are known to be globally distributed. Common species in genera Zoanthus and Palythoa occur at Toco, Trinidad, where they are more abundant than their Scleractinia counterparts relative to benthic coverage. In this study, distribution, morphological and molecular data were collected to determine species and symbiont identification to provide more insight on zoantharians. The Line Intercept Point (LIT) transect method recorded coverage at three sites: Salybia (SB), Pequelle (PB), and Grande L’Anse (GA) Bays along the northeastern coast. Variations in morphology, such as tentacle count, oral disk color and diameter were collected from colonies in situ. All specimens were zooxanthellate, and molecular and phylogenetic analyses were done by sequencing the cytochrome oxidase subunit I (COI) gene, and the internal transcribed spacer (ITS) region for species and symbiont identification, respectively. Results showed mean Zoantharia percentage cover was 32.4% ± 5.1 (X ± SE) at SB, 51.3% ± 6.5 (PB), and 72.2% ± 6.1 at GA. Zooxanthellate zoantharians were identified as Palythoa caribaeorum, Palythoa grandiflora, Zoanthus pulchellus, and Zoanthus sociatus. Symbiodiniaceae genera were identified as Cladocopium and Symbiodinium in Palythoa and Zoanthus spp., respectively. Although this is the first molecular examination of zoantharians, and their symbionts in Trinidad, more research is needed to identify and document species distribution and symbiont biodiversity to understand their ecology in these dynamic ecosystems.
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(This article belongs to the Special Issue The Future of Coral Reefs: Research Submitted to ICRS 2020, Bremen, Germany)
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Open AccessArticle
Otolith δ18O Composition as a Tracer of Yellowfin Tuna (Thunnus albacares) Origin in the Indian Ocean
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, , , , , , , and
Oceans 2021, 2(3), 461-476; https://doi.org/10.3390/oceans2030026 - 14 Jul 2021
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Yellowfin tuna of the Indian Ocean is overfished, and a better understanding of the stock structure is needed to enable sustainable management. Here, otolith δ18O values of young-of-the-year fish from known nursery areas of the equatorial Indian Ocean (West, Central and
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Yellowfin tuna of the Indian Ocean is overfished, and a better understanding of the stock structure is needed to enable sustainable management. Here, otolith δ18O values of young-of-the-year fish from known nursery areas of the equatorial Indian Ocean (West, Central and East) were used to establish a reference isotopic signature to predict the origin of sub-adult and adult individuals. Sub-adult tuna otolith δ18O values from Reunion Island were similar to the West nursery signature, but otolith δ18O values of sub-adults from Pakistan were unlike any of the nurseries sampled. Therefore, δ18O values from the Pakistan area samples were considered an additional nursery source for predicting the origin of adult tuna, using a multinomial logistic regression classification method. The western equatorial area was the most productive nursery for three fishing grounds sampled, with a minor contribution of Pakistan-like origin fish. Contribution of Central or East nurseries to the adult population was negligible. One adult otolith was analysed by secondary ion mass spectrometry along the otolith growth transect and results were compared with an isoscape approach to infer lifetime movements. This study is an important first step towards understanding the spatial structure and connectivity of the species.
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Heatwave Effects on the Photosynthesis and Antioxidant Activity of the Seagrass Cymodocea nodosa under Contrasting Light Regimes
Oceans 2021, 2(3), 448-460; https://doi.org/10.3390/oceans2030025 - 25 Jun 2021
Abstract
Global climate change, specifically the intensification of marine heatwaves, affect seagrasses. In the Ria Formosa, saturating light intensities may aggravate heatwave effects on seagrasses, particularly during low spring tides. However, the photophysiological and antioxidant responses of seagrasses to such extreme events are poorly
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Global climate change, specifically the intensification of marine heatwaves, affect seagrasses. In the Ria Formosa, saturating light intensities may aggravate heatwave effects on seagrasses, particularly during low spring tides. However, the photophysiological and antioxidant responses of seagrasses to such extreme events are poorly known. Here, we evaluated the responses of Cymodocea nodosa exposed at 20 °C and 40 °C and 150 and 450 μmol quanta m−2 s−1. After four-days, we analyzed (a) photosynthetic responses to irradiance, maximum photochemical efficiency (Fv/Fm), the effective quantum yield of photosystem II (ɸPSII); (b) soluble sugars and starch; (c) photosynthetic pigments; (d) antioxidant responses (ascorbate peroxidase, APX; oxygen radical absorbance capacity, ORAC, and antioxidant capacity, TEAC); (d) oxidative damage (malondialdehyde, MDA). After four days at 40 °C, C. nodosa showed relevant changes in photosynthetic pigments, independent of light intensity. Increased TEAC and APX indicated an “investment” in the control of reactive oxygen species levels. Dark respiration and starch concentration increased, but soluble sugar concentrations were not affected, suggesting higher CO2 assimilation. Our results show that C. nodosa adjusts its photophysiological processes to successfully handle thermal stress, even under saturating light, and draws a promising perspective for C. nodosa resilience under climate change scenarios.
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(This article belongs to the Special Issue Seagrass Ecosystems in a Changing World)
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Future Changes in Tropical Cyclone and Easterly Wave Characteristics over Tropical North America
Oceans 2021, 2(2), 429-447; https://doi.org/10.3390/oceans2020024 - 10 Jun 2021
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Tropical Cyclones (TCs) and Easterly Waves (EWs) are the most important phenomena in Tropical North America. Thus, examining their future changes is crucial for adaptation and mitigation strategies. The Community Earth System Model drove a three-member regional model multi-physics ensemble under the Representative
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Tropical Cyclones (TCs) and Easterly Waves (EWs) are the most important phenomena in Tropical North America. Thus, examining their future changes is crucial for adaptation and mitigation strategies. The Community Earth System Model drove a three-member regional model multi-physics ensemble under the Representative Concentration Pathways 8.5 emission scenario for creating four future scenarios (2020–2030, 2030–2040, 2050–2060, 2080–2090). These future climate runs were analyzed to determine changes in EW and TC features: rainfall, track density, contribution to seasonal rainfall, and tropical cyclogenesis. Our study reveals that a mean increase of at least 40% in the mean annual TC precipitation is projected over northern Mexico and southwestern USA. Slight positive changes in EW track density are projected southwards 10° N over the North Atlantic Ocean for the 2050–2060 and 2080–2090 periods. Over the Eastern Pacific Ocean, a mean increment in the EW activity is projected westwards across the future decades. Furthermore, a mean reduction by up to 60% of EW rainfall, mainly over the Caribbean region, Gulf of Mexico, and central-southern Mexico, is projected for the future decades. Tropical cyclogenesis over both basins slightly changes in future scenarios (not significant). We concluded that these variations could have significant impacts on regional precipitation.
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(This article belongs to the Special Issue Tropical Cyclone Future Projections)
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Open AccessReview
Offshore Geological Hazards: Charting the Course of Progress and Future Directions
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, , , , , , , , , , , , , , , , , , , , , , , and
Oceans 2021, 2(2), 393-428; https://doi.org/10.3390/oceans2020023 - 31 May 2021
Abstract
Offshore geological hazards can occur in any marine domain or environment and represent a serious threat to society, the economy, and the environment. Seismicity, slope sedimentary instabilities, submarine volcanism, fluid flow processes, and bottom currents are considered here because they are the most
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Offshore geological hazards can occur in any marine domain or environment and represent a serious threat to society, the economy, and the environment. Seismicity, slope sedimentary instabilities, submarine volcanism, fluid flow processes, and bottom currents are considered here because they are the most common hazardous processes; tsunamis are also examined because they are a secondary hazard generated mostly by earthquakes, slope instabilities, or volcanic eruptions. The hazards can co-occur and interact, inducing a cascading sequence of events, especially in certain contexts, such as tectonic indentations, volcanic islands, and canyon heads close to the coast. We analyze the key characteristics and main shortcomings of offshore geological hazards to identify their present and future directions for marine geoscience investigations of their identification and characterization. This review establishes that future research will rely on studies including a high level of multidisciplinarity. This approach, which also involves scientific and technological challenges, will require effective integration and interplay between multiscale analysis, mapping, direct deep-sea observations and testing, modelling, and linking offshore observations with onshore observations.
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(This article belongs to the Special Issue Current Advances and Challenges in Ocean Science—Feature Papers for the Founding of Oceans)
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Open AccessCommunication
Humpback Whale Instigates Object Play with a Lion’s Mane Jellyfish
Oceans 2021, 2(2), 386-392; https://doi.org/10.3390/oceans2020022 - 24 May 2021
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Cetaceans are well-known for their intelligence, charismatic nature, and curiosity. Many species, particularly odontocetes, are known to investigate and manipulate novel objects they encounter. Yet, disentangling the drivers of these behaviors and distinguishing between those that are simply playful and those which serve
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Cetaceans are well-known for their intelligence, charismatic nature, and curiosity. Many species, particularly odontocetes, are known to investigate and manipulate novel objects they encounter. Yet, disentangling the drivers of these behaviors and distinguishing between those that are simply playful and those which serve a specific function remains challenging due to a lack of direct observations and detailed descriptions of behaviors. This is particularly true for mysticetes such as humpback whales (Megaptera novaeangliae), as records of object use are far less common than in odontocetes. Here, we present evidence of novel object use from a first of its kind encounter between an individual humpback whale and a large lion’s mane jellyfish (Cyanea capillata) in the coastal waters off New England. We detail the interaction and discuss possible drivers for the behavior, with a focus on cetacean innovation, ectoparasite removal, and wound healing.
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Open AccessFeature PaperArticle
The Interactive Role of Hydrocarbon Seeps, Hydrothermal Vents and Intermediate Antarctic/Mediterranean Water Masses on the Distribution of Some Vulnerable Deep-Sea Habitats in Mid Latitude NE Atlantic Ocean
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, , , , , , , , , , , , , and
Oceans 2021, 2(2), 351-385; https://doi.org/10.3390/oceans2020021 - 26 Apr 2021
Abstract
In this work, we integrate five case studies harboring vulnerable deep-sea benthic habitats in different geological settings from mid latitude NE Atlantic Ocean (24–42° N). Data and images of specific deep-sea habitats were acquired with Remoted Operated Vehicle (ROV) sensors (temperature, salinity, potential
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In this work, we integrate five case studies harboring vulnerable deep-sea benthic habitats in different geological settings from mid latitude NE Atlantic Ocean (24–42° N). Data and images of specific deep-sea habitats were acquired with Remoted Operated Vehicle (ROV) sensors (temperature, salinity, potential density, O2, CO2, and CH4). Besides documenting some key vulnerable deep-sea habitats, this study shows that the distribution of some deep-sea coral aggregations (including scleractinians, gorgonians, and antipatharians), deep-sea sponge aggregations and other deep-sea habitats are influenced by water masses’ properties. Our data support that the distribution of scleractinian reefs and aggregations of other deep-sea corals, from subtropical to north Atlantic could be dependent of the latitudinal extents of the Antarctic Intermediate Waters (AAIW) and the Mediterranean Outflow Waters (MOW). Otherwise, the distribution of some vulnerable deep-sea habitats is influenced, at the local scale, by active hydrocarbon seeps (Gulf of Cádiz) and hydrothermal vents (El Hierro, Canary Island). The co-occurrence of deep-sea corals and chemosynthesis-based communities has been identified in methane seeps of the Gulf of Cádiz. Extensive beds of living deep-sea mussels (Bathymodiolus mauritanicus) and other chemosymbiotic bivalves occur closely to deep-sea coral aggregations (e.g., gorgonians, black corals) that colonize methane-derived authigenic carbonates.
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(This article belongs to the Special Issue Current Advances and Challenges in Ocean Science—Feature Papers for the Founding of Oceans)
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Open AccessArticle
After the Fall: The Demographic Destiny of a Gorgonian Population Stricken by Catastrophic Mortality
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, , , , , and
Oceans 2021, 2(2), 337-350; https://doi.org/10.3390/oceans2020020 - 19 Apr 2021
Abstract
In recent years, the frequency of mass mortality events in marine ecosystems has increased, and several populations of benthic organism have been affected, reducing their density and changing their size and age structure. Few details are known about the dynamics of these populations
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In recent years, the frequency of mass mortality events in marine ecosystems has increased, and several populations of benthic organism have been affected, reducing their density and changing their size and age structure. Few details are known about the dynamics of these populations over long time intervals. In late summer of both 1999 and 2003 two drastic mass mortality events, co-occurring with anomalous temperature increases, affected the northwestern Mediterranean rocky coastal communities. Due to these events the Paramuricea clavata population living at the western edge of La Spezia Gulf (Italy) was stricken, and 78% of the colonies died. This population was monitored from 1998 (pre-mortality) until 2013. This paper deals with the photographic sampling of permanent plots carried out in 2013. The findings were compared with those from the previous sampling series. This long-term, non-destructive sampling highlights the demographic trajectory of the octocoral population there after two anomalous mortality events, indicating that some new drop-point between local extinction and complete recovery may be have been reached. Long-term monitoring (including pre-mortality data) could allow evaluating the effects of global climate change on the conservation of impacted populations.
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(This article belongs to the Special Issue The Future of Coral Reefs: Research Submitted to ICRS 2020, Bremen, Germany)
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Open AccessArticle
Measurements of Bicarbonate in Water Containing Ocean-Level Sulfate Using a Simple Multi-Pass Optical Raman System
Oceans 2021, 2(2), 330-336; https://doi.org/10.3390/oceans2020019 - 06 Apr 2021
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The concentration of dissolved inorganic carbon in the oceans at depths of a few meters to thousands of meters is a critical parameter for understanding global warming. The concentration is both pH dependent and depth dependent. Current analysis that employs pH meters must
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The concentration of dissolved inorganic carbon in the oceans at depths of a few meters to thousands of meters is a critical parameter for understanding global warming. The concentration is both pH dependent and depth dependent. Current analysis that employs pH meters must account for several other parameters, such as salinity, temperature, pressure, and the dissolved carbon’s form, carbon dioxide, bicarbonate, or carbonate. Recently, Raman spectroscopy has been used to measure these forms directly in water at ~1000 ppm, which is unfortunately insufficient for typical ocean concentrations, such as ~115 ppm bicarbonate near the surface. Here, we employed a simple multi-pass optical system, a flat mirror to reflect the laser back through the sample, and a concave mirror opposite the entrance slit that effectively doubled the laser power and the collected Raman photons, respectively. This multi-pass optical Raman system with a 1.5 W, 532 nm laser was used to measure 30 ppm bicarbonate in water that contained 2650 ppm sulfate to simulate ocean water, a bicarbonate concentration well below that near the ocean surface. Furthermore, spectral analysis employed the bicarbonate C=O symmetric stretch at 1360 cm−1 instead of the C–OH stretch at 1015 cm−1 to avoid the intense, overlapping sulfate SO4 symmetric stretch at 985 cm−1. The calculated standard deviation of ~5 ppm for the described approach suggests that accurate measurement of bicarbonate in situ is possible, which has been, heretofore, either calculated based on pH or measured in a lab.
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Open AccessArticle
Mapping Sub-Metre 3D Land-Sea Coral Reefscapes Using Superspectral WorldView-3 Satellite Stereoimagery
Oceans 2021, 2(2), 315-329; https://doi.org/10.3390/oceans2020018 - 02 Apr 2021
Abstract
Shallow coral reefs ensure a wide portfolio of ecosystem services, from fish provisioning to tourism, that support more than 500 million people worldwide. The protection and sustainable management of these pivotal ecosystems require fine-scale but large-extent mapping of their 3D composition. The sub-metre
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Shallow coral reefs ensure a wide portfolio of ecosystem services, from fish provisioning to tourism, that support more than 500 million people worldwide. The protection and sustainable management of these pivotal ecosystems require fine-scale but large-extent mapping of their 3D composition. The sub-metre spaceborne imagery can neatly produce such an expected product using multispectral stereo-imagery. We built the first 3D land-sea coral reefscape mapping using the 0.3 m superspectral WorldView-3 stereo-imagery. An array of 13 land use/land cover and sea use/sea cover habitats were classified using sea-, ground- and air-truth data. The satellite-derived topography and bathymetry reached vertical accuracies of 1.11 and 0.89 m, respectively. The value added of the eight mid-infrared (MIR) channels specific to the WorldView-3 was quantified using the classification overall accuracy (OA). With no topobathymetry, the best combination included the eight-band optical (visible + near-infrared) and the MIR8, which boosted the basic blue-green-red OA by 9.58%. The classes that most benefited from this MIR information were the land use “roof” and land cover “soil” classes. The addition of the satellite-derived topobathymetry to the optical+MIR1 produced the best full combination, increasing the basic OA by 9.73%, and reinforcing the “roof” and “soil” distinction.
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(This article belongs to the Special Issue The Future of Coral Reefs: Research Submitted to ICRS 2020, Bremen, Germany)
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Open AccessFeature PaperArticle
Divergent Proteomic Responses Offer Insights into Resistant Physiological Responses of a Reef-Foraminifera to Climate Change Scenarios
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, , , , , , and
Oceans 2021, 2(2), 281-314; https://doi.org/10.3390/oceans2020017 - 01 Apr 2021
Abstract
Reef-dwelling calcifiers face numerous environmental stresses associated with anthropogenic carbon dioxide emissions, including ocean acidification and warming. Photosymbiont-bearing calcifiers, such as large benthic foraminifera, are particularly sensitive to climate change. To gain insight into their responses to near-future conditions, Amphistegina lobifera from the
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Reef-dwelling calcifiers face numerous environmental stresses associated with anthropogenic carbon dioxide emissions, including ocean acidification and warming. Photosymbiont-bearing calcifiers, such as large benthic foraminifera, are particularly sensitive to climate change. To gain insight into their responses to near-future conditions, Amphistegina lobifera from the Gulf of Aqaba were cultured under three pCO2 conditions (492, 963, 3182 ppm) crossed with two temperature conditions (28 °C, 31 °C) for two months. Differential protein abundances in host and photosymbionts were investigated alongside physiological responses and microenvironmental pH gradients assessed via proton microsensors. Over 1000 proteins were identified, of which > 15% varied significantly between treatments. Thermal stress predominantly reduced protein abundances, and holobiont growth. Elevated pCO2 caused only minor proteomic alterations and color changes. Notably, pH at the test surface decreased with increasing pCO2 under all light/dark and temperature combinations. However, the difference between [H+] at the test surface and [H+] in the seawater—a measure of the organism’s mitigation of the acidified conditions—increased with light and pCO2. Combined stressors resulted in reduced pore sizes and increased microenvironmental pH gradients, indicating acclimative mechanisms that support calcite test production and/or preservation under climate change. Substantial proteomic variations at moderate-pCO2 and 31 °C and putative decreases in test stability at high-pCO2 and 31 °C indicate cellular modifications and impacts on calcification, in contrast to the LBFs’ apparently stable overall physiological performance. Our experiment shows that the effects of climate change can be missed when stressors are assessed in isolation, and that physiological responses should be assessed across organismal levels to make more meaningful inferences about the fate of reef calcifiers.
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(This article belongs to the Special Issue Impacts of Climate Change on the Fitness and Survival of Marine Organisms)
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Open AccessArticle
Mediterranean Water Properties at the Eastern Limit of the North Atlantic Subtropical Gyre since 1981
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and
Oceans 2021, 2(1), 266-280; https://doi.org/10.3390/oceans2010016 - 15 Mar 2021
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A high-quality hydrographic CTD and Argo float data was used to study the property changes along the westward branch of the Mediterranean Outflow Water (MOW) in the northeast Atlantic between 1981 and 2018. In this period, the temperature and salinity are marked by
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A high-quality hydrographic CTD and Argo float data was used to study the property changes along the westward branch of the Mediterranean Outflow Water (MOW) in the northeast Atlantic between 1981 and 2018. In this period, the temperature and salinity are marked by periods of cooling/freshening and warming/salinification. Since 1981, the MOW properties at the core decreased by −0.015 ± 0.07 °C year and −0.003 ± 0.002 year . The different phases of the North Atlantic Oscillation (NAO) influence the main propagation pathways of the MOW into the North Atlantic basin, thus affecting the trends determined within different NAO-phases. The temperature and salinity show a strong correlation with NAO, with NAO leading the properties by 8 and 7 years, respectively, indicating a delayed response of the ocean to different forcing conditions. A decrease in oxygen concentration (−0.426 ± 0.276 μ mol kg year ) was calculated for the same period; however, no connection with the NAO was found.
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Open AccessFeature PaperArticle
Millennial-Scale Environmental Variability in Late Quaternary Deep-Sea Sediments from the Demerara Rise, NE Coast of South America
by
and
Oceans 2021, 2(1), 246-265; https://doi.org/10.3390/oceans2010015 - 05 Mar 2021
Abstract
We carried out a rock magnetic study of two deep-sea gravity cores from the Demerara Rise, NE South America. Our previous studies provided radiocarbon and paleomagnetic chronologies for these cores. This study presents detailed rock magnetic measurements on these cores in order to
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We carried out a rock magnetic study of two deep-sea gravity cores from the Demerara Rise, NE South America. Our previous studies provided radiocarbon and paleomagnetic chronologies for these cores. This study presents detailed rock magnetic measurements on these cores in order to characterize the rock magnetic mineralogy and grain size as indicators of the overall clastic fraction. We measured the magnetic susceptibility, anhysteretic remanence, and isothermal remanence and demagnetized the remanences at several alternating field demagnetization levels. The magnetic intensities estimate the magnetic material concentration (and indirectly the overall clastic fraction) in the cores. Ratios of rock magnetic parameters indicate the relative grain size of the magnetic material (and indirectly the overall clastic grain size). Rock magnetic intensity parameters and rock magnetic ratios both vary systematically and synchronously over the last 30,000 years in both cores. There is a multi-millennial-scale cyclicity, with intervals of high magnetic intensity (high magnetic and clastic content) with low magnetic ratios (coarser magnetic and clastic grain size), alternating in sequence with intervals of low magnetic intensity with high magnetic ratios (finer grain size). There is also a higher-frequency millennial-scale variability in intensity superposed on the multi-millennial-scale variability. There are nine (A–I) multi-millennial-scale intervals in the cores. Intervals A, C, E, G, and I have high magnetic and clastic content with coarser overall magnetic and clastic grain size and are likely intervals of enhanced rainfall and runoff from the NE South American margin to the coastal ocean. In contrast, intervals B, D, F, and H have lower clastic flux with finer overall grain size, probably indicating lower continental rainfall and runoff. During the Holocene, high rainfall and runoff intervals can be related to cooler times and low rainfall and runoff to warmer times. The opposite pattern existed during the Pleistocene, with higher rainfall and runoff during interstadial conditions and lower rainfall and runoff during stadial conditions. We noted a similar pattern of Pleistocene multi-millennial-scale variability in a transect of deep-sea sediment cores along the NE Brazilian margin, from the Cariaco Basin (~10 N) to the NE Brazilian margin (~1° N–4° S). However the NW part of this transect (Cariaco Basin, Demerara Rise, Amazon Fan) has an out-of-phase relationship with the SE part of the transect (NE Brazilian margin) between warm–cold and wet–dry conditions. One possible cause of the high–low rainfall and runoff patterns might be oscillation of the Intertropical Convergence Zone (ITCZ), with higher rainfall and runoff associated with a more southerly average position of the ITCZ and lower rainfall and runoff associated with a more northerly average position of the ITCZ.
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(This article belongs to the Special Issue Current Advances and Challenges in Ocean Science—Feature Papers for the Founding of Oceans)
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Severe Heat Stress Resulted in High Coral Mortality on Maldivian Reefs following the 2015–2016 El Niño Event
Oceans 2021, 2(1), 233-245; https://doi.org/10.3390/oceans2010014 - 03 Mar 2021
Abstract
Coral cover worldwide has been declining due to heat stress caused by climate change. Here we report the impacts of the 2015–2016 El Niño mass coral bleaching event on the coral cover of reefs located on central and northern atolls of the Maldives.
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Coral cover worldwide has been declining due to heat stress caused by climate change. Here we report the impacts of the 2015–2016 El Niño mass coral bleaching event on the coral cover of reefs located on central and northern atolls of the Maldives. We surveyed six reef sites in the Alifu Alifu (Ari) and Baa (South Maalhosmadulu) Atolls using replicate 20 m benthic photo transects at two depths per reef site. Live and recently dead coral cover identified from images differed between reef sites and depth. Recently dead corals on average made up 33% of the coral assemblage at shallow sites and 24% at deep sites. This mortality was significantly lower in massive corals than in branching corals, reaching an average of only 6% compared to 41%, respectively. The best predictors of live coral cover were depth and morphology, with a greater percentage of live coral at deep sites and in massive corals. The same predictors best described the prevalence of recently dead coral, but showed inverse trends to live coral. However, there was high variability among reef sites, which could be attributed to additional local stressors. Coral bleaching and resulting coral mortalities, such as the ones reported here, are of particular concern for small island nations like the Maldives, which are reliant on coral reefs.
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(This article belongs to the Special Issue The Future of Coral Reefs: Research Submitted to ICRS 2020, Bremen, Germany)
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