Changes In Oceanographic Conditions Research Articles

Neural network approach for detecting spatial changes in catch probability of Engraulis ringens during El Niño‐Southern Oscillation events in northern Chile

AbstractEngraulis ringens (anchovy) is a small pelagic fish of the Family Engraulidae that inhabits the neretic‐coastal zone from northern Peru to south‐central Chile. It is the main resource species of industrial fishing of northern Chile, representing 80% of the annual landings of the purse seine fleet. The history of this fishery (1985–2023) shows a strong decrease in annual industrial landings, especially during extreme El Niño–Southern Oscillation (ENSO) events. The greatest decrease in landings in two decades occurred in 2020, coinciding with a cold La Niña event, which had not been observed in previous La Niña events. We evaluated whether the current decrease in annual landings of E. ringens is associated with oceanographic changes in northern Chile during El Niño or La Niña events. We applied a neuronal network model to identify the spatial and temporal distribution of E. ringens using the catch probability of each boat of the industrial purse seine fleet. The selected oceanographic variables (sea surface temperature, salinity, depth of the mixed layer, sea height and currents) for the 2003–2020 period were obtained from the Copernicus Marine Environment Monitoring Service (CMEMS program) and used as predictor variables of the monthly landings of E. ringens. The neural network model explained 97% of the monthly variability of catch probability of E. ringens by the industrial purse seine fleet. The spatial distribution of catch probability of E. ringens was analyzed independently for El Niño (2015), La Niña (2007, 2013, and 2020), and Neutral (2004) years. We found that catch probability extended further west during La Niña events (except for 2020), occupying a greater area, but were limited to a 10 nautical mile coastal strip during the El Niño event. The spatial distribution of catch probability in the Neutral condition was near the coast, although not as restricted as during the El Niño event. The higher catch probabilities in the La Niña event of 2020 were near the coast, in contrast to the previous La Niña events of 2007 and 2013, due to the restriction of the optimal habitat of E. ringens in response to changes in oceanographic conditions. The application of the results of this study will allow understanding and probably anticipating the consequences that extreme ENSO events could have on the catch probability of the industrial anchovy purse seine fleet in northern Chile.

Evolution and environment of Caribbean coastal ecosystems

Isolation of the Caribbean Sea from the tropical Eastern Pacific by uplift of the Isthmus of Panama in the late Pliocene was associated with major, taxonomically variable, shifts in Caribbean biotic composition, and extinction, but inferred causes of these biological changes have remained elusive. We addressed this through falsifiable hypotheses about how independently determined historical changes in oceanographic conditions may have been responsible. The most striking environmental change was a sharp decline in upwelling intensity as measured from decreases in intra-annual fluctuations in temperature and consequently in planktonic productivity. We then hypothesized three general categories of biological response based upon observed differences in natural history between the oceans today. These include changes in feeding ecology, life histories, and habitats. As expected, suspension feeders and predators became rarer as upwelling declined. However, predicted increases in benthic productivity by reef corals, and benthic algae were drawn out over more than 1 Myr as seagrass and coral reef habitats proliferated; a shift that was itself driven by declining upwelling. Similar time lags occurred for predicted shifts in reproductive life history characteristics of bivalves, gastropods, and bryozoans. Examination of the spatial variability of biotic change helps to understand the time lags. Many older species characteristic of times before environmental conditions had changed tended to hang on in progressively smaller proportions of locations until they became extinct as expected from metapopulation theory and the concept of extinction debt. Faunal turnover may not occur until a million or more years after the environmental changes ultimately responsible.

Dynamical oceanographic processes impact on reef manta ray behaviour: Extreme Indian Ocean Dipole influence on local internal wave dynamics at a remote tropical atoll

Physical oceanographic observations were made with subsurface, taut-line moorings at Egmont Island, a tropical atoll within the Chagos Archipelago in the central Indian Ocean, to elucidate the dynamics of near-bed cold-water intrusions implicated in driving local aggregations of reef manta rays (Mobula alfredi). Manta have been previously shown to aggregate within ‘Manta Alley’, a lipped gully at 65 m depth along the north coast, at times when the surface to bottom temperature difference was highest. We here identify the dynamical processes driving these temperature differences and shaping the foraging landscape at Egmont, and equivalent small-scale atolls, improving our understanding of manta behavior at hotspots where they are most vulnerable to exploitation.The thermal regime within Manta Alley is shown to be governed at several spatiotemporal scales. The extreme 2019 Indian Ocean Dipole event drove a depression of the 26 °C isotherm to a depth of 115 m precluding the observation of cooling within the alley. As the thermocline shoaled with the change in phase of the IOD, near bed cold water flushing was seen with tidal periodicity within the gully. The internal tide is accompanied by high frequency internal waves with periods of O (5 min) which are shown to promote mixing through shear instability, evidenced by subcritical Richardson numbers, with surface-seabed temperature differences ∼4 °C observed throughout a tidal period.Our results highlight a level of heterogeneity in oceanographic dynamics at sub-atoll spatial scales within an environment in which these processes are rarely resolved. Whilst the physical mechanisms through which these dynamics drive foraging within the resident manta population remain unclear, the generation of turbulence by high frequency internal wave events as shown here may influence zooplankton distributions, improving feeding efficiency at discrete locations within atolls. Our results thus highlight the need to account for fine scale changes in oceanographic conditions when attempting to explain habitat utilization by mobile species.

Historical biogeography supports Point Conception as the site of turnover between temperate East Pacific ichthyofaunas.

The cold temperate and subtropical marine faunas of the Northeastern Pacific meet within California as part of one of the few eastern boundary upwelling ecosystems in the world. Traditionally, it is believed that Point Conception is the precise site of turnover between these two faunas due to sharp changes in oceanographic conditions. However, evidence from intraspecific phylogeography and species range terminals do not support this view, finding stronger biogeographic breaks elsewhere along the coast. Here I develop a new application of historical biogeographic approaches to uncover sites of transition between faunas without needing an a priori hypothesis of where these occur. I used this approach to determine whether the point of transition between northern and southern temperate faunas occurs at Point Conception or elsewhere within California. I also examined expert-vetted latitudinal range data of California fish species from the 1970s and the 2020s to assess how biogeography could change with the backdrop of climate change. The site of turnover was found to occur near Point Conception, in concordance with the traditional view. I suggest that recent species- and population-level processes could be expected to give signals of different events from historical biogeography, possibly explaining the discrepancy across studies. Species richness of California has increased since the 1970s, mostly due to species's ranges expanding northward from Baja California (Mexico). Range shifts under warming conditions seem to be increasing the disparity between northern and southern faunas of California, creating a more divergent biogeography.

Cetacean strandings in San Diego County, California, USA: 1851–2008

There were 717 cetacean strandings recorded in San Diego County, California, USA between 1851 and 2008. These strandings comprised 18 odontocete and 6 mysticete species. Common dolphins (both the short-beaked (Delphinus delphis) and long-beaked common dolphin (D. capensis)) were the most commonly stranded cetacean species (43.2%), followed by bottlenose dolphins (Tursiops truncatus) (16.5%), gray whales (Eschrictius robustus) (11.0%), and Pacific white-sided dolphins (Lagenorhyncus obliquidens) (7.0%). A higher number of strandings was observed in the La Jolla and Coronado/Imperial Beach areas, which likely reflects the influence of coastal protrusions in those regions. Strandings of bottlenose dolphin neonates suggests their calving season extends from May to September. Strandings of common dolphin species peaked in the early- to mid-1970s and in the late-1990s to 2008, coincident with cool oceanographic regimes. In addition, extralimital strandings of harbour porpoises and temporal changes in stranding rates of Dall’s porpoises (Phocoenoides dalli) and short-finned pilot whales (Globicephala macrorhynchus) may have been associated with changes in oceanographic conditions. Evidence of human interaction in strandings included entanglements, boat strikes, shootings and harpooning. Overall, the stranding record largely reflected the species composition of the Southern California Bight and provided confirmation for presence of cryptic species not previously recorded by aerial and ship surveys.

Climate presses and pulses mediate the decline of a migratory predator

Long-term climate changes and extreme climate events differentially impact animal populations, yet whether and why these processes may act synergistically or antagonistically remains unknown. Disentangling these potentially interactive effects is critical for predicting population outcomes as the climate changes. Here, we leverage the "press-pulse" framework, which is used to describe ecological disturbances, to disentangle population responses in migratory Magellanic penguins to long-term changes in climate means and variability (presses) and extreme events (pulses) across multiple climate variables and life history stages. Using an unprecedented 38-y dataset monitoring 53,959 penguins, we show for the first time that the presses and pulses of climate change mediate the rate of population decline by differentially impacting different life stages. Moreover, we find that climate presses and pulses can work both synergistically and antagonistically to affect animal population persistence, necessitating the need to examine both processes in concert. Negative effects of terrestrial heat waves (pulses) on adult survival, for example, were countered by positive effects of long-term changes in oceanographic conditions in migratory grounds (presses) on juvenile and adult survival. Taken together, these effects led to predicted population extirpation under all future climate scenarios. This work underscores the importance of a holistic approach integrating multiple climate variables, life stages, and presses and pulses for predicting the persistence of animals under accelerating climate change.

Assessing the benefits of the marine protected area of Punta Coles, southern Peru (south‐east Pacific) on productivity of conspicuous benthic species using pre‐image population analysis

Abstract The coastal marine protected ecosystem at Punta Coles (as a part of the Reserva Nacional de Islas, Islotes y Puntas Guaneras) is located in a highly exploited area in southern Peru and contains several commercial, bioengineering and other benthic species. Pre‐image population analysis was used to estimate the transient values of intrinsic growth rate (r) based on biomass and density time series as a proxy of productivity to assess the effectiveness of protection. The outcomes obtained showed that the gastropods Concholepas concholepas, Fissurella latimartiginata and the tunicate Purya chilensis showed a reduction of productivity during recent years, whilst the sea urchin Loxechinus albus, the barnacle Balanus laevis and the bivalve Semimytilus algosus showed an opposite pattern. Several species exhibited a chaotic dynamic, coinciding with the highest productivity values. In 2016 and 2017, several species exhibited a reduction of their abundance which could be delayed responses explained by changes in oceanographic conditions (reduction of coastal upwelling), La Niña event and illegal harvest. The above notwithstanding, the results suggest that effective protection of benthic species in the protected ecosystem of Punta Coles have been partially accomplished. Therefore, this work could be considered a baseline study, permitting the subsequent monitoring of productivity of the main species inhabiting the coastal area of Punta Coles. Pre‐image population analysis could be used as a complimentary analytical tool since it enables the evaluation of transient population parameters (e.g. productivity) thus aiding population management, conservation and monitoring decisions.

In situ imaging across ecosystems to resolve the fine‐scale oceanographic drivers of a globally significant planktonic grazer

AbstractDoliolids are common gelatinous grazers in marine ecosystems around the world and likely influence carbon cycling due to their large population sizes with high growth and excretion rates. Aggregations or blooms of these organisms occur frequently, but they are difficult to measure or predict because doliolids are fragile, under sampled with conventional plankton nets, and can aggregate on fine spatial scales (1–10 m). Moreover, ecological studies typically target a single region or site that does not encompass the range of possible habitats favoring doliolid proliferation. To address these limitations, we combined in situ imaging data from six coastal ecosystems, including the Oregon shelf, northern California, southern California Bight, northern Gulf of Mexico, Straits of Florida, and Mediterranean Sea, to resolve and compare doliolid habitat associations during warm months when environmental gradients are strong and doliolid blooms are frequently documented. Higher ocean temperature was the strongest predictor of elevated doliolid abundances across ecosystems, with additional variance explained by chlorophyll a fluorescence and dissolved oxygen. For marginal seas with a wide range of productivity regimes, the nurse stage tended to comprise a higher proportion of the doliolids when total abundance was low. However, this pattern did not hold in ecosystems with persistent coastal upwelling. The doliolids tended to be most aggregated in oligotrophic systems (Mediterranea and southern California), suggesting that microhabitats within the water column favor proliferation on fine spatial scales. Similar comparative approaches can resolve the realized niche of fast‐reproducing marine animals, thus improving predictions for population‐level responses to changing oceanographic conditions.

Two-year seasonality (2017, 2018), export and long-term changes in coccolithophore communities in the subtropical ecosystem of the Gulf of Aqaba, Red Sea

A two-year (2017, 2018) study of coccolithophores was undertaken in the Gulf of Aqaba in the northern Red Sea to 1) determine the local diversity and community succession patterns with high temporal and taxonomic resolution, 2) determine the contribution to exported inorganic carbon and 3) evaluate changes in communities relative to those in the mid-1970's reported in Winter et al. (1979). As typical, the oceanographic conditions in the Gulf alternated between stratified, oligotrophic through spring/summer, and mesotrophic during winter due to deep convective mixing. Noticeably, the second summer of 2018 was warmer resulting in a more pronounced thermocline. Overall, the coccolithophore dynamics followed the seasonal changes in oceanographic conditions. During the mixing period, coccolithophores were denser (>25 coccospheres mL−1) and were estimated to account on average for 3.46% of the total Chl-a. The communities were fairly homogeneous through depths and over time with a marked dominance of Emiliania huxleyi and Gephyrocapsa ericsonii. During the stratified season, coccolithophore densities were lower, particularly at the surface, such that coccolithophores were estimated to represent on average 0.72% of the total Chl-a. However, the diversity was higher and a clear vertical zonation developed with well-defined upper, intermediate and deep-dwelling communities. These included Umbellosphaera spp., Rhabdosphaera clavigera, a variety of Syracosphaera spp., holococcolithophores and Florisphaera profunda, respectively, as typical in oligotrophic systems. This further underscores the pelagic nature of the Gulf of Aqaba. Noticeably, however, coccolithophores declined in abundances and diversity during 2018, possibly due to the warmer conditions. The relative export of inorganic carbon by coccolithophores largely correlated with the density of living communities, representing <4% and <10% of total inorganic carbon exports during the stratified and mixing periods, respectively. A marked differentiation between different coccolithophore life phases was also detected. Broadly, holococcolithophores inhabited preferentially shallow, oligotrophic water layers in the stratified season, while heterococcolithophores prevailed in deeper water layers or in winter. Yet, species-specific deviations to this pattern were also detected. Finally, comparisons with the 1970's revealed marked changes compared to current communities. G. ericsonii appeared less prevalent and Umbellosphaera spp. displayed a wider temporal residence through spring/summer. Moreover, F. profunda and other deep dwelling species absent in the past are now common during the peak of summer. These observations are indicative of changes in local microbial communities, possibly linked to the ongoing rise in sea temperatures. This study provides a detailed baseline information on coccolithophores for future reassessments of community changes in the GoA.

Delayed response to environmental conditions and infra-seasonal dynamics of the short-beaked common dolphin distribution.

Cetaceans adjust their distribution and abundance to encountered conditions across years and seasons, but we poorly understand such small-scale changes for many species, especially in winter. Crucial challenges confront some populations during this season, such as the high levels of fisheries-induced mortality faced by the common dolphin (Delphinus delphis) in the Northeast Atlantic shelves. For such species, understanding the winter fine-scale dynamics is crucial. We aimed to identify the dolphin distribution drivers during the winters of 2020 and 2021, with a focus on determining the lag between changes in oceanographic conditions and dolphin distribution. The changes were related to temporal delays specific to the nature and cascading effects that oceanographic processes had on the trophic chain. By determining the most important conditions and lags to dolphin distributions, we shed light on the poorly understood intrusions of dolphins within coastal waters during winter: they displayed a strong preference for the coastal-shelf waters front and extensively followed its spatial variations, with their overall densities increasing over the period and peaking in March-April. The results presented here provide invaluable information on the winter distribution dynamics and should inform management decisions to help reduce the unsustainable mortalities of this species in the by-catch of fisheries.

Shearwaters' nest attendance patterns throughout the lunar cycle: Are oceanographic conditions decisive for timing of nest arrival?

The moon cycle has long been recognized as a driving factor of animals' behavioural patterns. However, its influence on seabirds' nocturnal behaviour remains poorly understood. Using a long-term GPS tracking dataset from Cory's and Cape Verde shearwaters (Calonectris borealis and Calonectris edwardsii, respectively) in the Berlengas, Azores, Madeira and Cape Verde archipelagos, North Atlantic Ocean, we investigated nest attendance patterns of breeding birds in relation to oceanographic and natural light conditions during mid-chick rearing. We intended to understand if inter-annual changes in oceanographic conditions around each colony were related with timing of nest arrival and respective light intensity at burrow entrance. For this, oceanographic conditions were evaluated using proxies for marine productivity and metrics of shearwaters' foraging effort. We also wanted to investigate if birds adjusted nest attendance in relation to moonlight throughout the lunar cycle, and whether these patterns changed with contrasting oceanographic conditions. Shearwaters stayed longer at sea after sunset in years of good oceanographic conditions, returning ashore earlier in years of poor conditions, mostly under twilight. Breeding birds also seemed little influenced by moonlight at colonies, although this did not seem to be the case at sea. In particular, they adjusted nest arrivals with the onset of waning moon nights (nights starting without moon), but delayed nest entrances throughout waxing moon nights (nights entailing a growing period of moonlight until moonset). However, this pattern was not extensible to years of poor foraging conditions, when birds returned ashore regardless of moonlight conditions. Combined, these results show that the nest attendance behaviour is mediated by moonlight in Cory's and Cape Verde shearwaters, a pattern that seems to be regulated by prevailing oceanographic and foraging conditions.

At-sea distribution, movements and diving behavior of Magellanic penguins reflect small-scale changes in oceanographic conditions around the colony

At-sea distribution, movements and diving behavior of Magellanic penguins reflect small-scale changes in oceanographic conditions around the colony

Modeling the Habitat Distribution of Acanthopagrus schlegelii in the Coastal Waters of the Eastern Taiwan Strait Using MAXENT with Fishery and Remote Sensing Data

Black sea bream, Acanthopagrus schlegelii, is among the most commercially valuable species in the coastal fishery industry and marine ecosystems. Catch data comprising capture locations for the gillnet fisheries, remotely sensed environmental data (i.e., sea surface temperature, chlorophyll-a concentration, and current velocity), and topography (bathymetry) from 2015 to 2018 were used to construct a spatial habitat distribution of black sea bream. This species is concentrated in coastal waters (&lt;3 nm) from December to April (spawning season). The maximum entropy (MaxEnt) method and corresponding habitat suitability index among seasons were used to clarify the species’ spatial distribution and identify the seasonal variations in habitat selection. The patterns corresponded closely to the changes in oceanographic conditions, and the species exhibited synchronous trends with the marine environment’s seasonal dynamics. Chlorophyll-a concentration and bathymetry substantially influenced (80.1–92.9%) black sea bream’s habitat selection. By applying the MaxEnt model, the optimal habitats were identified with four variables including depth and satellite-derived temperature, current velocity and chlorophyll-a concentration, which provides a foundation for the scientific assessment and management of black sea bream in coastal waters of the Eastern Taiwan Strait.

Emerging roles of circRNAs in regulating thermal and hypoxic stresses in Apostichopus japonicus (Echinodermata: Holothuroidea)

Some sea cucumbers are economically and ecologically important, but they are threatened by thermal and hypoxic stress in changing oceanographic conditions. We construct circRNAs profiles, reveal circRNAs characters, and illustrate the potential regulatory roles of circRNAs in one commercially important species of sea cucumber, Apostichopus japonicus. Reads are distributed in intergenic (44.14%), exonic (48.26%) and intronic (7.60%) regions of the genome. A total of 1684 circRNAs were identified, and the most common spliced length is 269 nt in the present study. In three treatments (HT [thermal stress], LO [hypoxic stress], and HL [combined thermal and hypoxic stress]), 24, 27 and 27 differentially expressed (DE) circRNAs were identified, respectively. Five novel DE-circRNAs commonly occur in these treatments (novel_circ_0003311, novel_circ_0000229, novel_circ_0003944, novel_circ_0001458 and novel_circ_0000707), and based on them, potential circRNA-miRNA binding pairs were predicted. Sanger sequencing, RNase R treatment experiment and qPCR validation identified the accuracy of the circRNAs. Key circRNAs identified in the present study were covalently closed and were more stable under RNase R treatment than linear RNAs. Based on function analysis, circRNAs could regulate metabolic process, signal transduction, and ion responses in A. japonicus when exposed to thermal and hypoxic stress, and ‘regulation of response to stimulus’ is a common gene ontology (GO) term that is significantly enriched in each treatment; GO terms for ‘DNA’ and ‘stress’ are commonly enriched in heat-related treatments (HT and HL); and GO terms for ‘protein’ are commonly enriched in hypoxia-related treatments (LO and HL). When environmentally stressed, ‘metabolism,’ ‘transport and catabolism,’ ‘membrane transport,’ and ‘signal transduction’ were significantly responded in sea cucumber based on KEGG analysis. We provide insights into circRNA functions in stress regulation and lay a foundation for invertebrate circRNA research.

An exploration of the population characteristics and behaviours of the white shark in Guadalupe Island, Mexico (2014–2019): Observational data from cage diving vessels

Abstract In the eastern North Pacific, the Guadalupe Island Biosphere Reserve (GIBR) is one of the most renowned white shark (Carcharodon carcharias) aggregation sites studied to date, and an important tourism activity has been developed in the reserve. This study used tourist‐based cage diving activities to biologically monitor white sharks from 2014 to 2019 within the GIBR. The data indicated a gradual increase in the overall abundance of white sharks with an age‐structure shift, as young of the year and juvenile sharks were more prevalent during the latter part of the study period (2016–2019). The arrival of young of the year and juvenile white sharks coincided with regional changes in oceanographic conditions off California and Baja California. The arrival of adult female white sharks coincided with the seasonal peak in elephant seal abundance. Records of high‐risk white shark behaviours, a shift to sharks of younger ages, and the high prevalence of small individuals during cage diving activities supports the need for the continued revision of tourism operational protocols. This study highlights the importance of white shark biological monitoring to identify threats and challenges to the growing tourism industry and the management of the species in Guadalupe Island and in other aggregation sites.

High-Frequency Variability of the Surface Ocean Properties Off Central Chile During the Upwelling Season

The ocean off south-central Chile is subject to seasonal upwelling whose intensity is mainly controlled by the latitudinal migration of the southeast Pacific subtropical anticyclone. During austral spring and summer, the mean flow is equatorward favoring coastal upwelling, but periods of strong southerly winds are intermixed with periods of relaxed southerlies or weak northerly winds (downwelling favorable). This sub-seasonal, high-frequency variability of the coastal winds results in pronounced changes in oceanographic conditions and air-sea heat and gas exchanges, whose quantitative description has been limited by the lack of in-situ monitoring. In this study, high frequency fluctuations of meteorological, oceanographic and biogeochemical near surface variables were analyzed during two consecutive upwelling seasons (2016–17 and 2017–18) using observations from a coastal buoy located in the continental shelf off south-central Chile (36.4°S, 73°W), ∼10 km off the coast. The radiative-driven diel cycle is noticeable in meteorological variables but less pronounced for oceanographic and biogeochemical variables [ocean temperature, nitrate (NO3−), partial pressure of carbon dioxide (pCO2sea), pH, dissolved oxygen (DO)]. Fluorescence, as a proxy of chlorophyll-a, showed diel variations more controlled by biological processes. In the synoptic scale, 23 active upwelling events (strong southerlies, lasting between 2 and 15 days, 6 days in average) were identified, alternated with periods of relaxed southerlies of shorter duration (4.5 days in average). Upwelling events were related to the development of an atmospheric low-level coastal jet in response to an intense along-shore pressure gradient. Physical and biogeochemical surface seawater properties responded to upwelling favorable wind stress with approximately a 12-h lag. During upwelling events, SST, DO and pH decrease, while NO3−, pCO2sea, and air-sea fluxes increases. During the relaxed southerly wind periods, opposite tendencies were observed. The fluorescence response to wind variations is complex and diverse, but in many cases there was a reduction in the phytoplankton biomass during the upwelling events followed by higher values during wind relaxations. The sub-seasonal variability of the coastal ocean characterized here is important for biogeochemical and productivity studies.

Redefining the oceanic distribution of Atlantic salmon

Determining the mechanisms driving range-wide reductions in Atlantic salmon marine survival is hindered by an insufficient understanding of their oceanic ecology and distribution. We attached 204 pop-up satellite archival tags to post-spawned salmon when they migrated to the ocean from seven European areas and maiden North American salmon captured at sea at West Greenland. Individuals migrated further north and east than previously reported and displayed increased diving activity near oceanographic fronts, emphasizing the importance of these regions as feeding areas. The oceanic distribution differed among individuals and populations, but overlapped more between geographically proximate than distant populations. Dissimilarities in distribution likely contribute to variation in growth and survival within and among populations due to spatio-temporal differences in environmental conditions. Climate-induced changes in oceanographic conditions will alter the location of frontal areas and may have stock-specific effects on Atlantic salmon population dynamics, likely having the largest impacts on southern populations.

Impact of increasing sea surface temperature on skipjack tuna habitat in the Flores Sea, Indonesia

The Flores Sea is a water mass transfer route from two large oceans, namely the Pacific Ocean to the Indian Ocean known as Indonesian Throughflow (ITF). This flow certainly has an impact on the waters it passes through, including the Flores Sea, making the Flores Sea a hotspot for changes in oceanographic conditions. This study used satellite data to determine the increase in Sea Surface Temperature (SST) in the Flores Sea during 2015-2019. It used the Generalized Additive Model (GAM) analysis to analyze the effect of increasing SST on skipjack tuna habitat in the Flores Sea. The results showed that there had been an increase in SST of up to 2.5 °C over the past five 15 years in the Flores Sea. This increase has affected pelagic fish habitat in these waters. This increase in SST affects the tuna skipjack habitat, as evidenced by the decrease in catches in areas with warmer temperatures than usual. This study is important in considering the sustainable management of tuna fisheries, especially in tropical waters.

Seasonal shifts of microbial methane oxidation in Arctic shelf waters above gas seeps

AbstractThe Arctic Ocean subseabed holds vast reservoirs of the potent greenhouse gas methane (CH4), often seeping into the ocean water column. In a continuously warming ocean as a result of climate change an increase of CH4 seepage from the seabed is hypothesized. Today, CH4 is largely retained in the water column due to the activity of methane‐oxidizing bacteria (MOB) that thrive there. Predicted future oceanographic changes, bottom water warming and increasing CH4 release may alter efficacy of this microbially mediated CH4 sink. Here we investigate the composition and principle controls on abundance and activity of the MOB communities at the shallow continental shelf west of Svalbard, which is subject to strong seasonal changes in oceanographic conditions. Covering a large area (364 km2), we measured vertical distribution of microbial methane oxidation (MOx) rates, MOB community composition, dissolved CH4 concentrations, temperature and salinity four times throughout spring and summer during three consecutive years. Sequencing analyses of the pmoA gene revealed a small, relatively uniform community mainly composed of type‐Ia methanotrophs (deep‐sea 3 clade). We found highest MOx rates (7 nM d−1) in summer in bathymetric depressions filled with stagnant Atlantic Water containing moderate concentrations of dissolved CH4 (&lt; 100 nM). MOx rates in these depressions during spring were much lower (&lt; 0.5 nM d−1) due to lower temperatures and mixing of Transformed Atlantic Water flushing MOB with the Atlantic Water out of the depressions. Our results show that MOB and MOx in CH4‐rich bottom waters are highly affected by geomorphology and seasonal conditions.

Otolith chemical fingerprints of skipjack tuna (Katsuwonus pelamis) in the Indian Ocean: First insights into stock structure delineation.

The chemical composition of otoliths (earbones) can provide valuable information about stock structure and connectivity patterns among marine fish. For that, chemical signatures must be sufficiently distinct to allow accurate classification of an unknown fish to their area of origin. Here we have examined the suitability of otolith microchemistry as a tool to better understand the spatial dynamics of skipjack tuna (Katsuwonus pelamis), a highly valuable commercial species for which uncertainties remain regarding its stock structure in the Indian Ocean. For this aim, we have compared the early life otolith chemical composition of young-of-the-year (<6 months) skipjack tuna captured from the three main nursery areas of the equatorial Indian Ocean (West, Central and East). Elemental (Li:Ca, Sr:Ca, Ba:Ca, Mg:Ca and Mn:Ca) and stable isotopic (δ13C, δ18O) signatures were used, from individuals captured in 2018 and 2019. Otolith Sr:Ca, Ba:Ca, Mg:Ca and δ18O significantly differed among fish from different nurseries, but, in general, the chemical signatures of the three nursery areas largely overlapped. Multivariate analyses of otolith chemical signatures revealed low geographic separation among Central and Eastern nurseries, achieving a maximum overall random forest cross validated classification success of 51%. Cohort effect on otolith trace element signatures was also detected, indicating that variations in chemical signatures associated with seasonal changes in oceanographic conditions must be well understood, particularly for species with several reproductive peaks throughout the year. Otolith microchemistry in conjunction with other techniques (e.g., genetics, particle tracking) should be further investigated to resolve skipjack stock structure, which will ultimately contribute to the sustainable management of this stock in the Indian Ocean.