Toward an Ecological Geography of the Sea
Abstract
This book presents an in-depth discussion of the biological and ecological geography of the oceans. It synthesizes locally restricted studies of the ocean to generate a global geography of the vast marine world. Based on patterns of algal ecology, the book divides the ocean into four primary compartments, which are then subdivided into secondary compartments. *Includes color insert of the latest in satellite imagery showing the world's oceans, their similarities and differences *Revised and updated to reflect the latest in oceanographic research *Ideal for anyone interested in understanding ocean ecology -- accessible and informative.
... Three regions in the tropical Pacific Ocean are identified based on the statistically significant spatial patterns of chlorophyll to investigate the controlling mechanisms by which ENSO events affected simulated surface (Longhurst, 1998), accounting for a considerable contribution to the primary and export productions of the tropical Pacific (Pennington et al., 2006;Stanley et al., 2010). ...
The present study aims to investigate the influences of El Niño and Southern Oscillation (ENSO) events on chlorophyll biomass in the tropical Pacific under historical and RCP8.5 scenarios with simulations from the Community Earth System Model Large Ensemble (CESM‐LE) project. Large variance in surface chlorophyll concentrations is identified across the Peruvian Upwelling (PU), Equatorial Upwelling (EU), and Western Pacific (WP) regions within the tropical Pacific. Results suggest that responses of surface chlorophyll to ENSO in these regions are governed by different mechanisms. The increasing chlorophyll during La Niña is a consequence of increasing nutrients, influenced by local upwelling systems in the PU and EU regions, while the supplementary nutrients in the WP region arise from the eastern Pacific through stronger surface westward currents. Under RCP8.5 scenario, stronger water warming in the eastern equatorial Pacific leads to a remarkable reduction in the amplitudes of seasonal cycles and interannual variations of chlorophyll in both PU and EU regions. This results in less responsiveness of the chlorophyll biomass to El Niño and moderate La Niña compared to the historical period. However, though warming induces a decrease in chlorophyll concentrations in the WP region, the interannual variations of chlorophyll have shown an improvement in correlation with ENSO events. Meanwhile, despite the small phytoplankton‐dominated community being observed under future scenario, species dominance is likely to shift back to diatoms once extreme La Niña occurs, which is unseen in all El Niño and moderate La Niña cases.
... Globally, there have been multiple efforts to classify and map marine regions, habitats and ecosystem types (Gregr and Bodtker, 2007;Longhurst, 2007;Howell, 2010;Last et al., 2010;Gregr et al., 2012;Hu et al., 2021;Nikolopoulou et al., 2021). Approaches include those with a focus on biogeography (Spalding et al., 2007) or bio-physical habitats (McArthur et al., 2010;Sayre et al., 2017;Nikolopoulou et al., 2021), with more capacitated countries possessing substantial datasets increasingly applying statistical methods to support classification, mapping and dissemination Dove et al., 2018;Gerovasileiou et al., 2019). ...
... At large spatial (e.g., national) scales, species and habitats can differ considerably among biogeographic regions with distinct physical, biological, and ecological characteristics, [54][55][56][57] which often also have distinct responses to management actions. 58 Depending on the size of the area being evaluated, it may be uninformative to treat the protected areas as belonging to a single network. ...
... Higher TP values relative to adults including values that exceeded expected values based on previous feeding studies(Torres-Rojas et al., 2014;Tripp-Valdéz et al., 2015) suggest that juveniles from this area might be recent migrants from areas with higher baselines, such as the Gulf of California(Richert et al., 2015). Further, the Mexican coastline (Cabo San Lucas) includes a boundary for three Longhurst provinces (CCAI, PNEC and CAMR)(Longhurst, 2007), so juveniles in this region could forage in different isoscapes without undertaking long geographical displacements.Trophic diversity and uncertainties regarding TDF estimations across taxa will be constant biases on the application of bulk SIA techniques, when baseline isotope values are used to estimate the trophic position of predators. Nonetheless, this analysis utilizing Δ 15 N dolphinfish-copepod as a proxy for spatial movements and population dispersal across locations and sizes provided insight into the movement capabilities of the species. ...
The dolphinfish (Coryphaena hippurus) is a globally distributed marine predator that supports one of the most important coastal fisheries along the Eastern Tropical Pacific (ETP), but its spatial movements in this area are poorly understood. Stable isotope values (δ¹³C and δ¹⁵N) of white muscle from dolphinfish (n = 220) captured at different locations across the ETP (i.e., Mexico, Costa Rica, Ecuador, Peru and oceanic areas) were normalized to copepod baseline stable isotope values to estimate dolphinfish trophic position, movements and population dispersal. Movement or residence patterns were inferred from the difference in δ¹⁵N values (Δ¹⁵Ndolphinfish‐copepod‰) between copepods and dolphinfish muscle. Baseline corrected isotope values (δ¹³Cdolphinfish‐copepod and δ¹⁵Ndolphinfish‐copepod) of dolphinfish muscle were used to estimate isotopic niche metrics and infer population dispersal across isoscapes. Values of δ¹³C and δ¹⁵N differed between juvenile and adult dolphinfish and across the ETP. Trophic position estimates ranged from 3.1 to 6.0 with a mean of 4.6. Adults and juveniles had similar trophic position estimates, whereas isotopic niche areas (SEA ‰²) of adults were greater relative to juveniles in every location. Adult dolphinfish showed “moderate movement by some individuals” in all locations based on Δ¹⁵Ndolphinfish‐copepod values, except for Costa Rica where adults were classified with “high degree of movement by some individuals” whereas juveniles showed “limited movement” in all areas except Mexico. Population dispersal based on Δ¹⁵Ndolphinfish‐copepod values showed “moderate” and “high” dispersal for adults and “no dispersal” for most juveniles, except for Mexico. This study provides insight into potential dolphinfish spatial mobility across an area of interest for multiple nations, which can help to improve stock assessments and management of the species.
... Globally, there have been multiple efforts to classify and map marine regions, habitats and ecosystem types (Gregr and Bodtker, 2007;Longhurst, 2007;Howell, 2010;Last et al., 2010;Gregr et al., 2012;Hu et al., 2021;Nikolopoulou et al., 2021). Approaches include those with a focus on biogeography (Spalding et al., 2007) or bio-physical habitats (McArthur et al., 2010;Sayre et al., 2017;Nikolopoulou et al., 2021), with more capacitated countries possessing substantial datasets increasingly applying statistical methods to support classification, mapping and dissemination (Costello, 2009;Dove et al., 2018;Gerovasileiou et al., 2019). ...
South Africa has taken an iterative approach to marine ecosystem mapping over 18 years that has provided a valuable foundation for ecosystem assessment, planning and decision-making, supporting improved ecosystem-based management and protection. Iterative progress has been made in overcoming challenges faced by developing countries, especially in the inaccessible marine realm. Our aim is to report on the approach to produce and improve a national marine ecosystem map to guide other countries facing similar challenges, and to illustrate the impact of even the simplest ecosystem map. South Africa has produced four map versions, from a rudimentary map of 34 biozones informed by bathymetry data, to the latest version comprising 163 ecosystem types informed by 83 environmental and biodiversity datasets that aligns with the IUCN Global Ecosystem Typology. Data were unlocked through academic and industry collaborations; multi-disciplinary, multi-realm and multi-generational networks of practitioners; and targeted research to address key gaps. To advance toward a more transparent, reproducible and data-driven approach, limitations, barriers and opportunities for improvement were identified. Challenges included limited human and data infrastructure capacity to collate, curate and assimilate many data sources, covering a variety of ecosystem components, methods and scales. Five key lessons that are of relevance for others working to advance ecosystem classification and mapping, were distilled. These include (1) the benefits of iterative improvement; (2) the value of fostering relationships among a co-ordinated network of practitioners including early-career researchers; (3) strategically prioritizing and leveraging resources to build and curate key foundational biodiversity datasets and understand drivers of biodiversity pattern; (4) the need for developing, transferring and applying capacity and tools that enhance data quality, analytical workflows and outputs; and (5) the application of new technology and emerging statistical tools to improve the classification and prediction of biodiversity pattern. South Africa’s map of marine ecosystem types has been successfully applied in spatial biodiversity assessment, prioritization to support protected area expansion and marine spatial planning. These successes demonstrate the value of a co-ordinated network of practitioners who continually build an evidence base and iteratively improve ecosystem mapping while simultaneously growing ecological knowledge and informing changing priorities and policy.
Oceanic eddies are recognized as pivotal components in marine ecosystems, believed to concentrate a wide range of marine life spanning from phytoplankton to top predators. Previous studies have posited that marine predators are drawn to these eddies due to an aggregation of their forage fauna. In this study, we examine the response of forage fauna, detected by shipboard acoustics, across a broad sample of a thousand eddies across the world’s oceans. While our findings show an impact of eddies on surface temperatures and phytoplankton in most cases, they reveal that only a minority (13%) exhibit significant effects on forage fauna, with only 6% demonstrating an oasis effect. We also show that an oasis effect can occur both in anticyclonic and cyclonic eddies, and that the few high-impact eddies are marked by high eddy amplitude and strong water-mass-trapping. Our study underscores the nuanced and complex nature of the aggregating role of oceanic eddies, highlighting the need for further research to elucidate how these structures attract marine predators.
Microbial communities play a crucial role in ocean ecology and global biogeochemical processes. However, understanding the intricate interactions among diversity, taxonomical composition, functional traits, and how these factors respond to climate change remains a significant challenge. Here, we propose seven distinct ecological statuses by systematically considering the diversity, structure, and biogeochemical potential of the ocean microbiome to delineate their biogeography. Anthropogenic climate change is expected to alter the ecological status of the surface ocean by influencing environmental conditions, particularly nutrient and oxygen contents. Our predictive model, which utilizes machine learning, indicates that the ecological status of approximately 32.44% of the surface ocean may undergo changes from the present to the end of this century, assuming no policy interventions. These changes mainly include poleward shifts in the main taxa, increases in photosynthetic carbon fixation and decreases in nutrient metabolism. However, this proportion can decrease significantly with effective control of greenhouse gas emissions. Our study underscores the urgent necessity for implementing policies to mitigate climate change, particularly from an ecological perspective.
Thriving in both epipelagic and mesopelagic layers, Rhizaria are biomineralizing protists, mixotrophs or flux-feeders, often reaching gigantic sizes. In situ imaging showed their contribution to oceanic carbon stock, but left their contribution to element cycling unquantified. Here, we compile a global dataset of 167,551 Underwater Vision Profiler 5 Rhizaria images, and apply machine learning models to predict their organic carbon and biogenic silica biomasses in the uppermost 1000 m. We estimate that Rhizaria represent up to 1.7% of mesozooplankton carbon biomass in the top 500 m. Rhizaria biomass, dominated by Phaeodaria, is more than twice as high in the mesopelagic than in the epipelagic layer. Globally, the carbon demand of mesopelagic, flux-feeding Phaeodaria reaches 0.46 Pg C y⁻¹, representing 3.8 to 9.2% of gravitational carbon export. Furthermore, we show that Rhizaria are a unique source of biogenic silica production in the mesopelagic layer, where no other silicifiers are present. Our global census further highlights the importance of Rhizaria for ocean biogeochemistry.
The North Scotia Ridge is the offshore morphostructural expression of the left-lateral transcurrent South America-Scotia Plate Boundary. Several blocks compose the ridge, including the scarcely studied Namuncurá Bank (NB, also known as Burdwood). We present the first detailed study of active structures on the seafloor of the western NB from a database of 3D and 2D seismic data, multibeam bathymetry, and sub-bottom profiles. This work assesses the architecture, style of deformation and Cenozoic evolution of NB, where several groups of faults, and en echelon folding, affects the seabed and shallow sub-bottom. These features compound the northernmost structures associated with a releasing bend, fitting well with a left-lateral Riedel shear model oriented at N74°E, slightly rotated with respect to the present-day plate boundary stress regime. The current tectonic scenario started with a main deformational phase in the Neogene, partially distributed by the Malvinas Fold-Thrust Belt, while modern deformation continues to be conditioned by pre-existing structures. This study allows for a better understanding of the tectonics of the North Scotia Ridge, a morphostructure that influences the circulation of the Antarctic Circumpolar Current thus impacting the global climate.
Perfluoroalkyl acids (PFAAs) are highly persistent anthropogenic pollutants that have been detected in the global oceans. Our previous laboratory studies demonstrated that PFAAs in seawater are remobilized to the air in sea spray aerosols (SSAs). Here, we conducted field experiments along a north-south transect of the Atlantic Ocean to study the enrichment of PFAAs in SSA. We show that in some cases PFAAs were enriched >100,000 times in the SSA relative to seawater concentrations. On the basis of the results of the field experiments, we estimate that the secondary emission of certain PFAAs from the global oceans via SSA emission is comparable to or greater than estimates for the other known global sources of PFAAs to the atmosphere from manufacturing emissions and precursor degradation.
Considering habitat use throughout the whole range of a highly mobile marine species is necessary to understand life history, identify vulnerabilities, and inform effective management. We used satellite tagging data from 128 adult female salmon sharks Lamna ditropis to identify seasonal hotspots of activity in an extended California Current region (ECCR; encompassing the California Current Large Marine Ecosystem), an area far away from their well-described primary habitat in the Alaska Downwelling Region where they have been documented, but whose utility has been poorly understood. Tag track durations had a mean of 447.7 ± 381 d, and 88 sharks (68.8%) visited the ECCR, comprising 33.6% of 28019 total daily Argos detections. Tracking data revealed that the timing and duration of migrations to the ECCR varied, but salmon shark distribution within the ECCR displayed consistent latitudinal shifts in accordance with regional oceanographic seasons. High site fidelity across multi-year tracks to high-productivity features, such as sea banks, and previously published knowledge of salmon shark life history suggest that the ECCR provides important foraging habitat which may be linked to reproductive success. The data reveal high overlap of salmon shark distribution with cumulative fishing effort collected by Global Fishing Watch for 2012-2019, particularly around seasonal hotspots, suggesting that female salmon sharks might be at risk of fisheries encounters. Collectively, our findings emphasize the importance of the ECCR in salmon shark life history and demonstrate the influence of spatial and temporal scale on interpretation of large movement data sets and identification of critical habitat outside of well-studied regions.
The subtropical North Atlantic is a key region for understanding climate impact in the ocean. Plankton studies in this region have been generally framed in biogeographic provinces or focused on latitudinal gradients. In this study, we demonstrate the benefits of using empirically constructed continuous gradients versus the use of average values for biogeographical provinces to characterize plankton assemblages along a longitudinal transect at 24.5° N using an unprecedented array of stations including hydrographic observations, abundance of phytoplankton and zooplankton, and plankton size spectra in the epipelagic layer (0–200 m). In addition, the variability of zooplankton assemblages was analyzed using detailed taxonomic identification at selected stations. We found significant gradients in most hydrographic and plankton variables. The former, including surface temperature and salinity, the depth of the upper mixing layer, and the depth of the chlorophyll maximum, displayed non-linear gradients with maximum or minimum values near the center of the transect. In contrast, most plankton variables showed linear zonal gradients. Phytoplankton, microzooplankton (<100 µm), and the slope and the intercept of the size spectra increased (and Trichodesmium decreased) to the west. Total mesozooplankton (>200 µm) did not show any significant zonal pattern, but the taxonomic assemblages were characterized by a gradual replacement of large Calanoids by small-bodied Cyclopoid copepods from east to west. The use of continuous gradients provides more detailed information on the zonal structure of subtropical plankton than the classical approach using discrete areas.
The “ACCOBAMS Survey Initiative” (ASI) is a pilot programme aimed at
establishing an integrated and coordinated monitoring system for cetaceans
across the Agreement on the Conservation of Cetaceans of the Black Sea,
Mediterranean Sea and contiguous Atlantic (hereafter “ACCOBAMS”) area.
Conducted in coordination with Mediterranean coastal countries, it supports
the implementation of European and regional policies, in particular the EU Marine
Strategy Framework Directive and the Ecosystem Approach process. In summer
2018, a synoptic survey was conducted across the Mediterranean Sea and
contiguous Atlantic area, combining visual monitoring from aircrafts with visual
and passive acoustic monitoring from vessels. Species density and abundance
were estimated through design-based approach in a line-transect sampling
framework. Based on data arising from the aerial survey only, uncorrected
design-based abundance was obtained for striped (N=426,744, CV=0.13),
common (N=65,359, CV=0.4), bottlenose (N=63,333, CV=0.17), and Risso´s
dolphins (N=26,006, CV=0.3), Cuvier’s beaked whales (N=2,929, CV=0.4) and
long-finned pilot whales (N=5,540 CV=0.4). A merged category of either striped
or common dolphins resulted in 212,483 individuals (CV=0.26). Fin whales
abundance of 1,749 animals (CV=0.3) was corrected for both availability and
perception biases and resulted in 3,282 (CV=0.31). The ASI survey offers an
overall picture of the distribution and abundance of cetaceans throughout the
Mediterranean basin, providing robust estimates to be considered as a baseline
for future regional systematic monitoring programmes. The ASI survey is the first step towards establishing a long-term monitoring program across the entire
ACCOBAMS area, and, as such, it sets the basis for further future basin-wide
monitoring efforts using systematic, shared, coordinated and comparable
methods. The information gathered will further enhance knowledge on
cetacean status, facilitating the development of informed conservation and
mitigation measures, as well as supporting the implementation of international
obligations. Furthermore, the outcomes of this survey will support both placeand
threat-based conservation efforts in the ACCOBAMS area, through the
identification of Important Marine Mammal Areas and Cetacean Critical
Habitats. Here the results of the ASI survey are presented and discussed
alongside proposed management and conservation actions aimed at ensuring
the persistence of cetacean populations in the region.
To clarify potential trans-oceanic connectivity and variation in the natal origin of albacore tuna (Thunnus alalunga) from the southwest Indian Ocean (SWI) and the southeast Atlantic (SA), lifetime otolith elemental signatures were assessed from 46 adults sampled from Reunion Island, and 26 juveniles(group 2+) sampled from two locations along the Atlantic coast of South Africa. LA-ICP-MS analysis was used to assess the multi-elemental composition in B, Ba, Mg, P, Sr, and Zn along the otolith edge (chemical signatures of the capture area), but also near the otolith primordium (spawning origin) and in an area located at 1400–1600 µm from it (nursery origin). Two groups of distinct near-primordium multi-elemental signatures, denoting potentially discrete spawning origins (SpO), were identified using hierarchical clustering. Each of the two SpO was found to contribute to the albacore stocks from all the areas sampled, suggesting a common spawning origin in some fish from the SWI and from the SA, and complex migrations between the two oceans. Three potentially discrete primary nursery sites were identified, each contributing to SA juvenile and SWI adult capture sites differently. The timing for the trans-oceanic movements observed for each albacore capture zone and its implications for local stock management are discussed.
The water column of the deep ocean is dark, cold, low in food, and under crushing pressures, yet it is full of diverse life. Due to its enormous volume, this mesopelagic zone is home to some of the most abundant animals on the planet. Rather than struggling to survive, they thrive—owing to a broad set of adaptations for feeding, behavior, and physiology. Our understanding of these adaptations is constrained by the tools available for exploring the deep sea, but this tool kit is expanding along with technological advances. Each time we apply a new method to the depths, we gain surprising insights about genetics, ecology, behavior, physiology, diversity, and the dynamics of change. These discoveries show structure within the seemingly uniform habitat, limits to the seemingly inexhaustible resources, and vulnerability in the seemingly impervious environment. To understand midwater ecology, we need to reimagine the rules that govern terrestrial ecosystems. By spending more time at depth—with whatever tools are available—we can fill the knowledge gaps and better link ecology to the environment throughout the water column.
The southern African subcontinent and its surrounding oceans accommodate globally unique ecoregions, characterized by exceptional biodiversity and endemism. This diversity is shaped by extended and steep physical gradients or environmental discontinuities found in both ocean and terrestrial biomes. The region’s biodiversity has historically been the basis of life for indigenous cultures and continues to support countless economic activities, many of them unsustainable, ranging from natural resource exploitation, an extensive fisheries industry and various forms of land use to nature-based tourism.
Being at the continent’s southern tip, terrestrial species have limited opportunities for adaptive range shifts under climate change, while warming is occurring at an unprecedented rate. Marine climate change effects are complex, as warming may strengthen thermal stratification, while shifts in regional wind regimes influence ocean currents and the intensity of nutrient-enriching upwelling.
The flora and fauna of marine and terrestrial southern African biomes are of vital importance for global biodiversity conservation and carbon sequestration. They thus deserve special attention in further research on the impacts of anthropogenic pressures including climate change. Excellent preconditions exist in the form of long-term data sets of high quality to support scientific advice for future sustainable management of these vulnerable biomes.
The element silicon (Si) is required for the growth of silicified organisms in marine environments, such as di-atoms. These organisms consume vast amounts of Si together with N, P, and C, connecting the biogeochemical cycles of these elements. Thus, understanding the Si cycle in the ocean is critical for understanding wider issues such as carbon sequestration by the ocean's biological pump. In this review, we show that recent advances in process studies indicate that total Si inputs and outputs, to and from the world ocean, are 57 % and 37 % higher, respectively, than previous estimates. We also update the total ocean silicic acid inventory value, which is about 24 % higher than previously estimated. These changes are significant, modifying factors such as the geochemical residence time of Si, which is now about 8000 years, 2 times faster than previously assumed. In addition, we present an updated value of the global an-Published by Copernicus Publications on behalf of the European Geosciences Union. 1270 P. J. Tréguer et al.: Reviews and syntheses: The biogeochemical cycle of silicon in the modern ocean nual pelagic biogenic silica production (255 Tmol Si yr −1) based on new data from 49 field studies and 18 model outputs, and we provide a first estimate of the global annual benthic biogenic silica production due to sponges (6 Tmol Si yr −1). Given these important modifications, we hypothesize that the modern ocean Si cycle is at approximately steady state with inputs = 14.8(±2.6) Tmol Si yr −1 and outputs = 15.6(±2.4) Tmol Si yr −1. Potential impacts of global change on the marine Si cycle are discussed.
Earth system models suggest that anthropogenic climate change will influence marine phytoplankton over the coming century with light-limited regions becoming more productive and nutrient-limited regions less productive. Anthropogenic climate change can influence not only the mean state but also the internal variability around the mean state, yet little is known about how internal variability in marine phytoplankton will change with time. Here, we quantify the influence of anthropogenic climate change on internal variability in marine phytoplankton biomass from 1920 to 2100 using the Community Earth System Model 1 Large Ensemble (CESM1-LE). We find a significant decrease in the internal variability of global phytoplankton carbon biomass under a high emission (RCP8.5) scenario and heterogeneous regional trends. Decreasing internal variability in biomass is most apparent in the subpolar North Atlantic and North Pacific. In these high-latitude regions, bottom-up controls (e.g., nutrient supply, temperature) influence changes in biomass internal variability. In the biogeochemically critical regions of the Southern Ocean and the equatorial Pacific, bottom-up controls (e.g., light, nutrients) and top-down controls (e.g., grazer biomass) affect changes in phytoplankton carbon internal variability, respectively. Our results suggest that climate mitigation and adaptation efforts that account for marine phytoplankton changes (e.g., fisheries, marine carbon cycling) should also consider changes in phytoplankton internal variability driven by anthropogenic warming, particularly on regional scales.
Tiny ocean plankton (picoplankton) are fundamental for the functioning of the biosphere, but the ecological mechanisms shaping their biogeography were partially understood. Comprehending whether these microorganisms are structured by niche versus neutral processes is relevant in the context of global change. We investigate the ecological processes (selection, dispersal, and drift) structuring global-ocean picoplanktonic communities inhabiting the epipelagic (0 to 200 meters), mesopelagic (200 to 1000 meters), and bathypelagic (1000 to 4000 meters) zones. We found that selection decreased, while dispersal limitation increased with depth, possibly due to differences in habitat heterogeneity and dispersal barriers such as water masses and bottom topography. Picoplankton β-diversity positively correlated with environmental heterogeneity and water mass variability, but this relationship tended to be weaker for eukaryotes than for prokaryotes. Community patterns were more pronounced in the Mediterranean Sea, probably because of its cross-basin environmental heterogeneity and deep-water isolation. We conclude that different combinations of ecological mechanisms shape the biogeography of the ocean microbiome across depths.
Due to historical under‐sampling of the deep ocean, the distributional ranges of mesopelagic zooplankton are not well documented, leading to uncertainty about the mechanisms that shape midwater zooplankton community composition. Using a combination of DNA metabarcoding (18S‐V4 and mtCOI) and trait‐based analysis, we characterized zooplankton diversity and community composition in the upper 1000 m of the northeast Pacific Ocean. We tested whether the North Pacific Transition Zone is a biogeographic boundary region for mesopelagic zooplankton. We also tested whether zooplankton taxa occupying different vertical habitats and exhibiting different ecological traits differed in the ranges of temperature, Chl‐ a , and dissolved oxygen conditions inhabited. The depth of the maximum taxonomic richness deepened with increasing latitude in the North Pacific. Community similarity in the mesopelagic zone also increased in comparison with the epipelagic zone, and no evidence was found for a biogeographic boundary between previously delineated mesopelagic biogeochemical provinces. Epipelagic zooplankton exhibited broader temperature and Chl‐ a ranges than mesopelagic taxa. Within the epipelagic, taxa with broader temperature and Chl‐ a ranges also had broader distributional ranges. However, mesopelagic taxa were distributed across wider dissolved oxygen ranges, and within the mesopelagic, only oxygen ranges covaried with distributional ranges. Environmental and distributional ranges also varied among traits, both for epipelagic taxa and mesopelagic taxa. The strongest differences in both environmental and distributional ranges were observed for taxa with or without diel vertical migration behavior. Our results suggest that species traits can influence the differential effects of physical dispersal and environmental selection in shaping biogeographic distributions.
Fronts are ubiquitous discrete features of the global ocean often associated with enhanced vertical velocities, in turn boosting primary production. Fronts thus form dynamical and ephemeral ecosystems where numerous species meet across all trophic levels. Fronts are also targeted by fisheries. Capturing ocean fronts and studying their long-term variability in relation with climate change is thus key for marine resource management and spatial planning. The Mediterranean Sea and the Southwest Indian Ocean are natural laboratories to study front-marine life interactions due to their energetic flow at sub-to-mesoscales, high biodiversity (including endemic and endangered species) and numerous conservation initiatives. Based on remotely-sensed Sea Surface Temperature and Height, we compute thermal fronts (2003–2020) and attracting Lagrangian coherent structures (1994–2020), in both regions over several decades. We advocate for the combined use of both thermal fronts and attracting Lagrangian coherent structures to study front-marine life interactions. The resulting front dataset differs from other alternatives by its high spatio-temporal resolution, long time coverage, and relevant thresholds defined for ecological provinces.
The combination of iron limitation and microzooplankton grazing controls phytoplankton productivity and taxonomic composition in high‐nutrient low‐chlorophyll (HNLC) regions. While increased productivity and diatom contribution triggered by iron enrichment support this view, direct measurements of underpinning group‐specific growth and grazing rates are scarce for the Southern Ocean. To assess these rates, we conducted dilution experiments coupled to high‐performance liquid chromatography and flow‐cytometry in sub‐Antarctic waters on and off Campbell Plateau, southeast of Aotearoa‐New Zealand. Off the plateau, growth and grazing were closely balanced for all groups despite a two‐fold difference between slow‐ and fast‐growing groups. On Campbell Plateau, where HNLC conditions were alleviated, the balance was disrupted, mainly by the preferential growth of diatoms and green algae, which was stimulated beyond grazing. Our results expand the recognized ability of diatoms to escape grazing control to picoplanktonic green algae that also avoid grazing and contribute significantly to phytoplankton productivity and biomass accumulation.
Traditional interpretations of marine plankton ecology, such as that in the Indian Ocean, mirror the plant-animal dichotomy of terrestrial ecology. Thus, single-celled phytoplankton produce food consumed by single-celled zooplankton, and these are in turn consumed by larger zooplankton through to higher trophic levels. Our routine monitoring surveys, research, models, and water management protocols all reflect this interpretation. The last decade has witnessed the development of an important revision of that traditional vision. We now know that the phytoplankton-zooplankton dichotomy represents, at best, a gross simplification. A significant proportion of the protist plankton at the base of the oceanic food-web can photosynthesise (make food ‘like plants’) and ingest food (eat ‘like animals’), thus contributing to both primary and secondary production simultaneously in the same cell. These protists are termed ‘mixoplankton’, and include many species traditionally labelled as ‘phytoplankton’ (a term now reserved for phototrophic microbes that are incapable of phagocytosis) or labelled as ‘protist zooplankton’ (now reserved for protist plankton incapable of phototrophy). Mixoplankton include various harmful algal species, most likely all the phototrophic dinoflagellates, and even iconic exemplar ‘phytoplankton’ such as coccolithophorids (which can consume bacteria). Like all significant revisions to ecology, the mixoplankton paradigm will take time to mature but to ignore it means that we fail to properly represent plankton ecology in teaching, science, management, and policy. This chapter introduces the mixoplankton functional groups and provides the first insight into the biogeography of these organisms in the Indian Ocean. A first attempt to consider the implications of the mixoplankton paradigm on marine primary productivity and ecology in the Indian Ocean is also given.
The gravitational sinking of organic debris from ocean ecosystems is a dominant mechanism of the biological carbon pump (BCP) that regulates the global climate. The fraction of primary production exported downward, the e‐ratio, is an important but poorly constrained BCP metric. In mid‐ and high‐latitude oceans, seasonal and local variations of sinking particle fluxes strongly modulate the e‐ratio. These locally specific e‐ratio variations and their ecological foundations are here encapsulated in the term “export systems” (ES). ES have been partly characterized for a few ocean locations but remain largely ignored over most of the ocean surface. Here, in a fully conceptual approach and with the primary aim to understand rather than to estimate ocean carbon export, we combine biogeochemical (BGC) modeling with satellite observations to map ES at fine spatio‐temporal scales. We identify four plausible ES with distinct e‐ratio seasonalities across mid‐ and high‐latitude oceans. The ES map confirms the outlines of traditional BGC provinces and unveils new boundaries indicating where (and how) the annual relationship between carbon export and production changes markedly. At six sites where ES features can be partially inferred from in situ data, we test our approach and propose key ecological processes driving carbon export. In the light of our findings, a re‐examination of 1,841 field‐based e‐ratios could challenge the conventional wisdom that e‐ratios change strongly with latitude, suggesting a possible seasonal artifact caused by the timing of observations. By deciphering carbon export mechanistically, our conceptual ES map provides timely directions to emergent ocean robotic explorations of the BCP.
Global biogeochemical ocean models are invaluable tools to examine how physical, chemical, and biological processes interact in the ocean. Satellite-derived ocean color properties, on the other hand, provide observations of the surface ocean, with unprecedented coverage and resolution. Advances in our understanding of marine ecosystems and biogeochemistry are strengthened by the combined use of these resources, together with sparse in situ data. Recent modeling advances allow the simulation of the spectral properties of phytoplankton and remote sensing reflectances, bringing model outputs closer to the kind of data that ocean color satellites can provide. However, comparisons between model outputs and analogous satellite products (e.g., chlorophyll a) remain problematic. Most evaluations are based on point-by-point comparisons in space and time, where spuriously large errors can occur from small spatial and temporal mismatches, whereas global statistics provide no information on how well a model resolves processes at regional scales. Here, we employ a unique suite of methodologies, the Probability Density Functions to Evaluate Models (PDFEM), which generate a robust comparison of these resources. The probability density functions of physical and biological properties of Longhurst's provinces are compared to evaluate how well a model resolves related processes. Differences in the distributions of chlorophyll a concentration (mg m−3) provide information on matches and mismatches between models and observations. In particular, mismatches help isolate regional sources of discrepancy, which can lead to improving both simulations and satellite algorithms. Furthermore, the use of radiative transfer in the model to mimic remotely sensed products facilitates model–observation comparisons of optical properties of the ocean.
The Asian green mussel (AGM), Perna viridis , is a mussel of ecological and economic importance throughout much of the tropical and subtropical regions of Asia, from China and Korea in the east to Oman on the Arabian Peninsula in the west. We collated published DNA sequence data and then analysed 467 bp of cytochrome c oxidase I gene (COI) sequence variation from 649 mussels (576 from SE Asia and 73 from India) to test for regional differentiation. Analysis of molecular variation, a haplotype network and a neighbour-joining tree all revealed significant differentiation between mussels from India and those from SE Asia. We observed a greater number of segregating sites (haplotypes) and private haplotypes than expected for Indian mussels compared to SE Asian mussels, based on the respective sample sizes. Tests of neutrality revealed population expansion or a recent selective sweep for only the mussels from India. We suggest that the differentiation of the Indian from the SE Asian mussels is explained by the pronounced seasonal input of freshwater into the northern Bay of Bengal area, which acts as a (semi-permeable) barrier to gene flow between the two regions (i.e., east versus west of the Bay). This suggestion is based on the oceanography of the region and is consistent with the biogeography and reports of genetic breaks in a range of taxa in this region. Further targetted sampling of AGMs from the east coast of India, Bangladesh and Myanmar is required to test this hypothesis, and additional sampling of AGMs from west of India (e.g., Pakistan, Iran, the Arabian Peninsula) will also be informative. Finally, this study is based on the analysis of a single marker (COI) because this is all that is presently available from published sources but we note that the application of new molecular markers such as single nucleotide polymorphisms to newly collected mussel samples will greatly advance our understanding of the AGM genetic discontinuity and its age, and help test its geographical location and its nature (e.g., a steep/shallow cline or a stepped cline).
This study investigates the influence of along‐front wind forcing on chlorophyll‐a (Chl‐a) at the Otago Shelf Break (OSB) in southeast Aotearoa/New Zealand using remotely‐sensed and in situ data. Summer wind stress over the OSB was shelf‐aligned, oscillating between upfront and downfront. Surface Chl‐a concentrations along the OSB were shown to increase episodically (≤10 days duration) following upfront wind stress. This response occurred over most of the 350 km long shelf break, and was most intense north of the Otago Peninsula. Peak Chl‐a enhancement at the shelf break occurred following periods of upfront winds, exhibiting a lagged response of approximately 5 days. Moored thermistor data indicated that upfront wind events were followed by increased thermal stratification over the mid‐shelf, whereas downfront wind events were followed by a well‐mixed water column. In situ temperature, salinity, and nutrient measurements suggested an offshore movement of the surface expression of the front following upfront winds, and a reduction in nitrate over the shelf break. From these observations a model of Ekman restratification driven by upfront winds is proposed for this system, wherein off‐shelf Ekman transport converts strong horizontal isopycnal gradients at the shelf break front into vertical stratification. This stratification holds phytoplankton in the upper water column, allowing increased access to light, which is marked by the increased drawdown of nitrate at the shelf break. Downfront winds break down this stratification, move the shelf break front onshore, and mix phytoplankton through the water column, reducing the surface expression of chlorophyll.
Zooplankton is crucial for transmitting energy from primary producers to higher trophic levels. A study was done in a Bangladesh eutrophic fish pond to know zooplankton's seasonal dynamics in relation to environmental factors. There were 11 different zooplankton genera, which belong to three major classes: Copepoda, Rotifera, and Cladocera. Peak abundance of zooplankton was found in the spring and winter, respectively. Cluster analysis clearly indicated zooplankton abundance during the spring and winter. Rotifera was the main dominant group in the total zooplankton population. Copepoda and Cladocera had a lower abundance than those of Rotifera. During the study period, environmental factors were observed monthly. The total zooplankton abundance showed a positive correlation only with pH and a negative correlation with transparency, dissolved oxygen, phosphates, nitrates, and temperature during Pearson’s correlation coefficient analysis. The canonical correspondence analysis also indicated that pH, transparency, and temperature significantly affect the abundance of zooplankton groups. Therefore, further research on the influence of environmental factors on different species of zooplankton is strongly suggested for achieving sustainable fish production from eutrophic fish ponds.
The northwest Atlantic Ocean is an important sink for carbon dioxide produced by anthropogenic activities. However the strong seasonal variability in the surface waters paired with the sparse and summer biased observations of ocean carbon makes it difficult to capture a full picture of its temporal variations throughout the water column. We aim to improve the estimation of temporal trends of dissolved inorganic carbon (DIC) due to anthropogenic sources using a new statistical approach: a time series generalization of the extended multiple linear regression (eMLR) method. Anthropogenic increase of northwest Atlantic DIC in the surface waters is hard to quantify due to the strong, natural seasonal variations of DIC. We address this by separating DIC into its seasonal, natural and anthropogenic components. Ocean carbon data is often collected in the summer, creating a summer bias, however using monthly averaged data made our results less susceptible to the strong summer bias in the available data. Variations in waters below 1000m have usually been analyzed on decadal time scales, but our monthly analysis showed the anthropogenic carbon component had a sudden change in 2000 from stationary to an increasing trend at the same rate as the waters above. All depths layers had similar rates of anthropogenic increase of ∼0.57µmol kg⁻¹ year⁻¹, and our uncertainty levels are smaller than with eMLR results. Integration throughout the water column (0–3,500 m) gives an anthropogenic carbon storage rate of 1.37 ± 0.57 mol m⁻² year⁻¹, which is consistent with other published estimates.
Fronts affect phytoplankton growth and phenology by locally reducing stratification and increasing nutrient supplies. Biomass peaks at fronts have been observed in situ and linked to local nutrient upwelling and/or lateral transport, while reduced stratification over fronts has been shown to induce earlier blooms in numerical models. Satellite imagery offers the opportunity to quantify these induced changes in phytoplankton over a large number of fronts and at synoptic scales. Here we used 20 years of sea surface temperature (SST) and chlorophyll a (Chl a) satellite data in a large region surrounding the Gulf Stream to quantify the impact of fronts on surface Chl a (used as a proxy for phytoplankton) in three contrasting bioregions, from oligotrophic to blooming ones, and throughout the year. We computed an heterogeneity index (HI) from SST to detect fronts and used it to sort fronts into weak and strong ones based on HI thresholds. We observed that the location of strong fronts corresponded to the persistent western boundary current fronts and weak fronts to more ephemeral submesoscale fronts. We compared Chl a distributions over strong fronts, over weak fronts, and outside of fronts in the three bioregions. We assessed three metrics: the Chl a excess over fronts at the local scale of fronts, the surplus in Chl a induced at the bioregional scale, and the lag in spring bloom onset over fronts. We found that weak fronts are associated with a local Chl a excess weaker than strong fronts, but because they are also more frequent, they contribute equally to the regional Chl a surplus. We also found that the local excess of Chl a was 2 to 3 times larger in the bioregion with a spring bloom than in the oligotrophic bioregion, which can be partly explained by the transport of nutrients by the Gulf Stream. We found strong seasonal variations in the amplitude of the Chl a excess over fronts, and we show periods of Chl a deficit over fronts north of 45∘ N that we attribute to subduction. Finally we provide observational evidence that blooms start earlier over fronts by 1 to 2 weeks. Our results suggest that the spectacular impact of fronts at the local scale of fronts (up to +60 %) is more limited when considered at the regional scale of bioregions (less than +5 %) but may nevertheless have implications for the region's overall ecosystem.
Environmental controls of species diversity represent a central research focus in evolutionary biology. In the marine realm, sharks are widely distributed, occupying mainly higher trophic levels and varied dietary preferences, mirrored by several morphological traits and behaviours. Recent comparative phylogenetic studies revealed that sharks present a fairly uneven diversification across habitats, from reefs to deep-water. We show preliminary evidence that morphological diversification (disparity) in the feeding system (mandibles) follows these patterns, and we tested hypotheses linking these patterns to morphological specialisation. We conducted a 3D geometric morphometric analysis and phylogenetic comparative methods on 145 specimens representing 90 extant shark species using computed tomo-graphy models. We explored how rates of morphological evolution in the jaw correlate with habitat, size, diet, trophic level, and taxonomic order. Our findings show a relationship between disparity and environment, with higher rates of morphological evolution in reef and deep-water habitats. Deep-water species display highly divergent morphologies compared to other sharks. Strikingly, evolutionary rates of jaw disparity are associated with diversification in deep water, but not in reefs. The environmental heterogeneity of the offshore water column exposes the importance of this parameter as a driver of diversification at least in the early part of clade history.
Zooplankton play a crucial role in marine ecosystems as the link between the primary producers and higher trophic levels, and as such they are key components of global biogeochemical and ecosystem models. While phytoplankton spatial-temporal dynamics can be tracked using satellite remote sensing, no analogous data product is available to validate zooplankton model output. We develop a procedure for linking irregular and sparse observations of mesozooplankton biomass with model output to assess regional seasonality of mesozooplankton. We use output from a global biogeochemical/ecosystem model to partition the ocean according to seasonal patterns of modeled mesozooplankton biomass. We compare the magnitude and temporal dynamics of the model biomass with in situ observations averaged within each partition. Our analysis shows strong correlations and little bias between model and data in temperate, strongly seasonally variable regions. Substantial discrepancies exist between model and observations within the tropical partitions. Correlations between model and data in the tropical partitions were not significant and in some cases negative. Seasonal changes in tropical mesozooplankton biomass were weak, driven primarily by local perturbations in the velocity and extent of currents. Microzooplankton composed a larger fraction of total zooplankton biomass in these regionsWe also examined the ability of the model to represent several dominant taxonomic groups. We identified several Calanus species in the North Atlantic partitions and Euphausiacea in the Southern Ocean partitions that were well represented by the model. This partition-scale comparison captures biogeochemically important matches and mismatches between data and models, suggesting that elaborating models by adding trait differences in larger zooplankton and mixotrophy may improve model-data comparisons. We propose that where model and data compare well, sparse observations can be averaged within partitions defined from model output to quantify zooplankton spatio-temporal dynamics.
Twelve pairs of sister taxa in the speciose rockfish genus, Sebastes, overlap coastal distributions but are bathymetrically segregated. These pairs are ideal for comparative studies to understand how life-history traits, historical events, and environment interact to produce population genetic structure. Black rockfish, Sebastes melanops, forms one such pair. Its sister species, yellowtail rockfish (Sebastes flavidus), shows a genetic cline likely influenced by a dispersal barrier at Cape Mendocino, CA and northward range expansion. Due to geographic overlap and close systematic relationship, we predicted black rockfish was influenced by similar evolutionary processes and thus would show genetic pattern concordance with yellowtail rockfish. We analyzed ~ 1000 black rockfish from 22 sites spanning the species’ range to test the null hypothesis of no structure, using the same markers that characterized yellowtail rockfish (i.e., 812 bp of the mitochondrial cytochrome b gene and six microsatellite loci). We reject the null hypothesis based on existence of at least three populations and microsatellite genetic divergence that separates the Alaskan and Continental U.S. populations (FCT = 0.021, p << 0.001), and a mitochondrial genetic cline near Cape Mendocino (FCT = 0.132, p < 0.01). We also found single collections genetically divergent from neighboring collections. Like yellowtail rockfish, oceanographic dispersal barriers and northern range expansion were inferred to influence black rockfish, however, unlike yellowtail rockfish, Cape Mendocino did not split the range into two stocks and was, therefore, inferred to be a less severe barrier. We hypothesize a higher frequency of extinction/recolonization events in black rockfish populations may have led to more complex genetic structure.
Context Identifying trophic guilds, i.e. species groups having similar trophic niches, is a first step in effective stock and fisheries management with consideration of multiple species interactions or ecosystems. Aims We evaluated isotopic niches by using stable isotope values (δ13C and δ15N) for 53 species, including commercially important demersal fishes, squids and crustaceans, from the continental shelf to the slope of the East China Sea (ECS), to segregate these species into guilds. Methods We inferred the isotopic niche space of each species and community metrics for guilds using Bayesian statistics. Key results Values of δ13C and δ15N showed different isotopic niches among species, reflecting a range of trophic positions and baseline food sources. The 53 species were segregated into 12 guilds on the basis of isotopic niche overlaps. Niche size and evenness differed among guilds; half of the guilds had smaller and less diverse niches than did the others. Conclusions The guilds identified for ECS demersal biota reflected similarities of taxonomy, behaviour, habitat and feeding type; niche size and evenness within each guild might have been influenced by the degree of species interaction. Implications These results provide important ecological information for considering effective multi-species management.
Changes in coccolithophore productivity in response to climate-driven ocean warming are likely to have cascading biogeochemical effects that feed back to the changing climate. This paper investigates the role (and interplay) of large- scale oceanographic and atmospheric processes across the North- and Equatorial Atlantic, including Saharan dust deposition, on the distribution of coccolithophore communities. The study is based on biological and hydrological data collected across the photic zone of the ocean, and aerosol data collected from the lower atmosphere, across 50°N–1°S during the Atlantic Meridional Transect in boreal Autumn of 2018 (AMT28), in synergy with Earth Observations. Results confirm existing understanding of the distribution of coccolithophore communities which are related to major meridional hydrological gradients across the North Atlantic. Dynamic, oxygenated and microphytoplankton- enriched waters at higher-latitudes were characterized by less diverse coccolithophore populations, dominated by placolith-bearing r-selected coccolithophores. In contrast, the heavily stratified and picoplankton-enriched waters of the subtropical gyre revealed more diverse populations, dominated by umbelliform coccolithophores and holococcolithophores at the surface, and by floriform taxa in the lower photic zone. Mean concentrations of 14.4×103 cells/L present in the North Atlantic Tropical Gyre Province (30–12°N), only slightly lower compared to 17.7×103 cells/L produced in the North Atlantic Drift province (50–40°N), provide a snapshot perspective on the importance of coccolithophore production in heavily stratified gyre conditions. Higher concentrations of 19’-Hexanoyloxyfucoxanthin (HexFuco) in regions of enhanced production of r-selected placolith-bearing species suggest that this pigment should not be generalized as a proxy for the entire coccolithophore community. Enhanced abundances of fast-blooming Emiliania huxleyi and Gephyrocapsa oceanica, and of cyanobacteria (including both picoplankton and N2-fixing Trichodesmium spp.) at the surface of the region of more persistent Saharan dust deposition (at ~12-10°N) appeared to result from dust- born nutrient input. Underneath this stratified surface layer, enhanced productivity in the deep chlorophyll maximum (DCM) appeared decoupled from that on the surface, fueled by geostrophic eastward shoaling of the nutricline across the tropical North Atlantic. As this was the region of highest macronutrient concentrations measured along and below the nutricline, our data suggest that the NE tropical Atlantic may act as a permanent dust-born nutrient depocenter as previously hypothesized.
Zooplankton are the primary energy pathway from phytoplankton to fish. Yet, there is limited understanding about how climate change will modify zooplankton communities and the implications for marine food webs globally. Using a trait-based marine ecosystem model resolving key zooplankton groups, we find that future oceans, particularly in tropical regions, favour food webs increasingly dominated by carnivorous (chaetognaths, jellyfish and carnivorous copepods) and gelatinous filter-feeding zooplankton (larvaceans and salps) at the expense of omnivorous copepods and euphausiids. By providing a direct energetic pathway from small phytoplankton to fish, the rise of gelatinous filter feeders partially offsets the increase in trophic steps between primary producers and fish from declining phytoplankton biomass and increases in carnivorous zooplankton. However, future fish communities experience reduced carrying capacity from falling phytoplankton biomass and less nutritious food as environmental conditions increasingly favour gelatinous zooplankton, slightly exacerbating projected declines in small pelagic fish biomass in tropical regions by 2100.
Marine Spatial Planning (MSP) has become a priority for many states wanting to develop national blue economy plans and meet international obligations in response to the increasing cumulative impacts of human activities and climate change. In areas beyond national jurisdiction (ABNJ), MSP is proposed as part of a package of solutions for multi-sectoral management at the ocean basin scale. To facilitate planning, maps showing the spatial distribution of marine biological diversity are required. In areas lacking data, like the South Atlantic, environmental proxies can be used to predict these distributions. We undertook broad-scale benthic habitat classification of the South Atlantic, employing two top-down approaches spanning from national waters to ABNJ. The first was non-hierarchical and clustered groups of environmental variables prior to combination; the second was hierarchical and clustered Principal Components of environmental variables. Areas of agreement between the two approaches were identified and results compared with existing national and global classifications and published biodiversity patterns. We highlight several habitat classes we can be cautiously confident represent variation in biological diversity, such as topographic features, frontal systems and some abyssal basins. We also identify critical gaps in our knowledge of regional biogeography and advocate for collaborative effort to compile benthic species records and promote further exploration of the region to address these gaps. These insights into the distribution of habitats have the potential to support sustainable use and conservation of biodiversity beyond national jurisdiction, enable transboundary and ocean basin scale management, and empower nations to make progress towards achieving Sustainable Development Goals.
The molecular diversity of marine picocyanobacterial populations, an important component of phytoplankton communities, is better characterized using high-resolution marker genes than the 16S rRNA gene as they have greater sequence divergence to differentiate between closely related picocyanobacteria groups. Although specific ribosomal primers have been developed, another general disadvantage of bacterial ribosome-based diversity analyses is the variable number of rRNA gene copies. To overcome these issues, the single-copy petB gene, encoding the cytochrome b6 subunit of the cytochrome b6f complex, has been used as a high-resolution marker gene to characterize Synechococcus diversity. We have designed new primers targeting the petB gene and proposed a nested PCR method (termed Ong_2022) for metabarcoding of marine Synechococcus populations obtained by flow cytometry cell sorting. We evaluated the specificity and sensitivity of Ong_2022 against the standard amplification protocol (termed Mazard_2012) using filtered seawater samples. The Ong_2022 approach was also tested on flow cytometry-sorted Synechococcus populations. Samples (filtered and sorted) were obtained in the Southwest Pacific Ocean, from subtropical (ST) and subantarctic (SA) water masses. The two PCR approaches using filtered samples recovered the same dominant subclades, Ia, Ib, IVa, and IVb, with small differences in relative abundance across the distinct samples. For example, subclade IVa was dominant in ST samples with the Mazard_2012 approach, while the same samples processed with Ong_2022 showed similar contributions of subclades IVa and Ib to the total community. The Ong_2022 approach generally captured a higher genetic diversity of Synechococcus subcluster 5.1 than the Mazard_2012 approach while having a lower proportion of incorrectly assigned amplicon sequence variants (ASVs). All flow cytometry-sorted Synechococcus samples could be amplified only by our nested approach. The taxonomic diversity obtained with our primers on both sample types was in agreement with the clade distribution observed by previous studies that applied other marker genes or PCR-free metagenomic approaches under similar environmental conditions. IMPORTANCE The petB gene has been proposed as a high-resolution marker gene to access the diversity of marine Synechococcus populations. A systematic metabarcoding approach based on the petB gene would improve the characterization/assessment of the Synechococcus community structure in marine planktonic ecosystems. We have designed and tested specific primers to be applied in a nested PCR protocol (Ong_2022) for metabarcoding the petB gene. The Ong_2022 protocol can be applied to samples with low DNA content, such as those obtained by flow cytometry cell sorting, allowing the simultaneous assessment of the genetic diversity of Synechococcus populations and cellular properties and activities (e.g., nutrient cell ratios or carbon uptake rates). Our approach will allow future studies using flow cytometry to investigate the link between ecological traits and taxonomic diversity of marine Synechococcus.
Marine plankton have different biogeographical distribution patterns. However, it is not clear how the entire plankton assemblage is composed of these species with distinct biogeographical patterns. Tintinnina (tintinnids) is single-celled planktonic protozoa commonly used as model organisms in planktonic studies. In this research, we investigated the organization of Tintinnina assemblages along the Atlantic Meridional Transect (AMT) spanning over 90 degrees of latitude during the 29th AMT cruise (2019). Tintinnina with high frequency of occurrence was classified into four biogeographic distribution patterns (equatorial, gyre, frontal, and deep Chl a maximum) according to their vertical and horizontal distribution. All species falling within each distribution pattern formed a sub-assemblage. Equatorial sub-assemblage dominated in upper waters of the equatorial zone and gyre centres. Equatorial and frontal sub-assemblages co-dominated in upper waters of the frontal zones. Deep Chlorophyll a maximum Layer (DCM) sub-assemblage dominated in the DCM waters. Some Tintinnina species with high abundance could be used as indicator species of sub-assemblages. The Tintinnina assemblages in the northern and southern hemispheres exhibited asymmetry in terms of species composition. The latitudinal gradient of Tintinnina species richness was bimodal, which was shaped by the superposition of the species number of the four sub-assemblages with latitude. The result of this study contributes to the understanding of Tintinnina assemblage in the equatorial zone and subtropical gyres of the Pacific and Indian Ocean. It is also valuable for predicting the influence of global warming on changes in Tintinnina distribution and species richness.
Partial migration occurs when only a fraction of a population migrates instead of all individuals. Considered an evolutionary precursor to full migration, understanding why some individuals choose to undertake migration while others do not may serve to inform general migratory theory. While several hypotheses currently exist for explaining the maintenance of partial migration, empirical support for many is limited. To address this gap, we analyzed GPS data acquired from brown pelicans (Pelecanus occidentalis; n = 74), a partially migratory seabird, nesting on six colonies in the South Atlantic Bight over the course of four autumn migrations. We estimated that approximately 74% of pelicans nesting within the study area may be migratory on an annual basis, with the remainder staying within the surrounding marine ecoregion year‐round. Mean date of migration initiation was 9 November, although movements occurred from September to December. Results from Cox's proportional hazards modeling indicated significant positive and negative effects of sea surface temperatures and body condition on migration rate, respectively. We suggest that the ontogenetic migration of the primary forage species of brown pelicans from estuarine to pelagic environments causes a seasonal reduction in prey and that pelicans in poor body condition are unable to meet the energetic demands potentially associated with this decrease in prey availability (i.e., the fasting endurance hypothesis of partial migration). Although we did not find evidence for a density‐dependent migratory response, the effects of intraspecific competition on migration in pelicans also appear to warrant consideration.
Introduction
Mesopelagic fishes play a central role in the transfer of energy through open-ocean food webs, particularly in the Southern Ocean where they are both important predators of zooplankton and a key prey group for many higher predators. However, they are notoriously difficult to sample, which has limited our understanding of the bio-physical predictors of their abundance and spatiotemporal variability. Species distribution models can be used to help understand species’ ecological requirements by relating records of their presence or abundance to environmental data.
Methods
Here, we used data from Myctobase – a new circumpolar database of mesopelagic fishes – to model patterns in abundance of eight key myctophid species (family Myctophidae) and the genus Bathylagus in the Southern Ocean south of 45°S. We developed species-specific boosted regression tree models to obtain circumpolar predictions of abundance. Average daytime and night-time summer predictions for the period 1997 to 2011 at 0 to 200m depths were generated for each species.
Results
Depth and solar position were important predictors and species were stratified in their depth distribution. For all species, except for G. nicholsi , there was an interaction between depth of capture and solar position, reflecting diel vertical migration. Other important variables included sea surface temperature, dissolved oxygen at 200 m, chlorophyll a , and sea surface height, indicating an association with water mass properties. Circumpolar patterns of abundance varied between species with some displaying affinities for oceanic regions at Antarctic latitudes (e.g., E. antarctica and Bathylagus spp.) or sub-Antarctic latitudes (e.g., K. anderssoni and P. tenisoni ); and affinities for shelf regions (e.g., P. bolini and G. nicholsi ).
Discussion
Our findings suggest that the abundance of mesopelagic fish is influenced by diel vertical migration and meso- and sub-mesoscale oceanographic features, with the Polar Front being a major delimiting feature. Our study showed contrasting patterns in community composition with higher species diversity north of the Polar Front that might be indicative of latitudinal variability in food web structure. Our spatial analysis is an important step toward resolving what determines important habitat for mesopelagic fishes, providing foundational information for understanding shifting food web dynamics into the future.
Photosynthetic picoeukaryotes (PPEs) are characterized by a reduction in cell and genome size but are free living, in contrast to many other organisms that have undergone such reductions. The relative abundance of PPEs in the oceans remains to be determined, as do the evolutionary imperatives behind their cell and genome reduction. Their enigmatic nature may be deciphered through metagenomics approaches; consequently, we utilized shotgun data from the Tara Oceans database to better understand both their ecological and genomic features. The clustering of meta-metabolomic networks constructed from shotgun data from 10 different sampling sites was influenced by the proportion of PPEs in the data sets. This, along with the relative abundance of RUBISCO sequences belonging to PPEs, indicates that they have a significant effect on oceanic meta-metabolism, emphasizing the evolutionary success of the streamlining strategy. Using rRNA sequences extracted from the shotgun data, a global oceanic distribution of PPEs showed little variation, including those lineages with reduced genome sizes. This indicates that genome and cellular streamlining is not an adaptation to environmental parameters but may rather be a community-driven effect. Lastly, and surprisingly given their role as primary producers, PPEs were found to comprise only 2 to 49% (17% on average) of all picoeukaryotes across 93 metagenomes. We show that contamination of the data set by eukaryotes with larger cell sizes is not responsible for the anomaly, and so the observation remains to be explained. The approaches described here allow us to draw a direct link between taxonomic composition and meta-metabolomic capacity, with implications for better understanding carbon fixation, biogeochemical cycling, and planetary self-regulation.
Abstract: The Arctic climate strongly affects phytoplankton production and biomass through several mechanisms, including warming, sea ice retreat, and global atmospheric processes. In order to detect the climatic changes in phytoplankton biomass, long-term variability of chlorophyll a (Chl-a) was estimated in situ with the changes in the surface sea temperature (SST) and salinity (SSS) in the Barents Sea and adjacent waters during the period of 1984-2021. Spatial differences were detected in SST, SSS, and Chl-a. Chl-a increased parallel to SST in the summer-autumn and spring periods, respectively. Chl-a peaks were found near the ice edge and frontal zones in the spring season, while the highest measures were observed in the coastal regions during the summer seasons. SST and Chl-a demonstrated increasing trends with greater values during 2010-2020. Generalized additive models (GAMs) revealed that SST and Chl-a were positively related with year. Climatic and oceanographic variables explained significant proportions of the Chl-a fluctuations , with six predictors (SST, annual North Atlantic Oscillation index, temperature/salinity anomalies at the Kola Section, and sea ice extent in April and September) being the most important. GAMs showed close associations between increasing Chl-a and a decline in sea ice extent and rising water temperature. Our data may be useful for monitoring the Arctic regions during the era of global changes and provide a basis for future research on factors driving phytoplankton assemblages and primary productivity in the Barents Sea.
Coastal climate impact studies make increasing use of multi-source and multi-dimensional atmospheric and environmental datasets to investigate relationships between climate signals and the ecological response. The large quantity of numerically simulated data may, however, include redundancy, multi-colinearity and excess information not relevant to the studied processes. In such cases techniques for feature extraction and identification of latent processes prove useful. Using dimensionality reduction techniques this research provides a statistical underpinning of variable selection to study the impacts of atmospheric processes on coastal chlorophyll-a concentrations, taking the Dutch Wadden Sea as case study. Dimension reduction techniques are applied to environmental data simulated by the Delft3D coastal water quality model, the HIRLAM numerical weather prediction model and the Euro-CORDEX climate modelling experiment. The dimension reduction techniques were selected for their ability to incorporate (1) spatial correlation via multi-way methods (2), temporal correlation through Dynamic Factor Analysis, and (3) functional variability using Functional Data Analysis. The data reduction potential and explanatory value of these methods are showcased and important atmospheric variables affecting the chlorophyll-a concentration are identified. Our results indicate room for dimensionality reduction in the atmospheric variables (2 principle components can explain the majority of variance instead of 7 variables), in the chlorophyll-a time series at different locations (two characteristic patterns can describe the 10 locations), and in the climate projection scenarios of solar radiation and air temperature variables (a single principle component function explains 77% of the variation for solar radiation and 57% of the variation for air temperature). It was also found that solar radiation followed by air temperature are the most important atmospheric variables related to coastal chlorophyll-a concentration, noting that regional differences exist, for instance the importance of air temperature is greater in the Eastern Dutch Wadden Sea at Dantziggat than in the Western Dutch Wadden Sea at Marsdiep Noord. Common trends and different regional system characteristics have also been identified through dynamic factor analysis between the deeper channels and the shallower intertidal zones, where the onset of spring blooms occurs earlier. The functional analysis of climate data showed clusters of atmospheric variables with similar functional features. Moreover, functional components of Euro-CORDEX climate scenarios have been identified for radiation and temperature variables, which provide information on the dominant mode (pattern) of variation and its uncertainties. The findings suggest that radiation and temperature projections of different Euro-CORDEX scenarios share similar characteristics and mainly differ in their amplitudes and seasonal patterns, offering opportunities to construct statistical models that do not assume independence between climate scenarios but instead borrow information (“borrow strength”) from the larger pool of climate scenarios. The presented results were used in follow up studies to construct a Bayesian stochastic generator to complement existing Euro-CORDEX climate change scenarios and to quantify climate change induced trends and uncertainties in phytoplankton spring bloom dynamics in the Dutch Wadden Sea.
Microbial communities in the world ocean are affected strongly by oceanic circulation, creating characteristic marine biomes. The high connectivity of most of the ocean makes it difficult to disentangle selective retention of colonizing genotypes (with traits suited to biome specific conditions) from evolutionary selection, which would act on founder genotypes over time. The Arctic Ocean is exceptional with limited exchange with other oceans and ice covered since the last ice age. To test whether Arctic microalgal lineages evolved apart from algae in the global ocean, we sequenced four lineages of microalgae isolated from Arctic waters and sea ice. Here we show convergent evolution and highlight geographically limited HGT as an ecological adaptive force in the form of PFAM complements and horizontal acquisition of key adaptive genes. Notably, ice-binding proteins were acquired and horizontally transferred among Arctic strains. A comparison with Tara Oceans metagenomes and metatranscriptomes confirmed mostly Arctic distributions of these IBPs. The phylogeny of Arctic-specific genes indicated that these events were independent of bacterial-sourced HGTs in Antarctic Southern Ocean microalgae.
Observations on the Physical and Biological Features of the Inshore Sea Bottom along the Malabar Coast
[Annales Biologique, Copenhagen 1975, Vol. 30 60-62}
In this note we examine 81 upwelling events recorded in the Sicily Channel, south of Sicily, observable as cold patches in NOAA 7 satellite thermographs. Statistical analysis shows that these cold patches are mostly wind-generated events, occurring three days after a strong alongshore wind has blown over the area. These satellite images are compared with historical data and in situ hydrographic measurements. -Authors
Ice-edge zones have been hypothesized to be major sites of primary production and energy transfer within the Southern Ocean, and large biomass accumulations of upper-trophic-level organisms (birds and mammals) occur in these zones. However, few data exist to determine if these ice-edge regions support elevated levels of phytoplankton and enhanced rates of primary production. During 2 cruises on the USCGC Glacier in January-February, 1983, the chlorophyll distribution was measured in different areas of the Ross Sea. Our primary study area was located off the coast of southern Victorialand (76° 30′ S) in a region of receding pack-ice. We occupied 34 stations in a 100 × 300 km area of variable ice concentration. In comparison to control stations and previous data, chlorophyll levels were high, averaging 4.08 ± 1.46 mg chl-a m−3 at the depth of the chlorophyll maximum in the water column, and 128.2 ± 91.7 mg m−2 when integrated from the surface to 150 m. High surface chlorophyll levels appeared to be highly correlated with a stable surface layer at the edge of the receding ice-pack. At stations outside of the ice-edge bloom, stability at the surface was reduced and chlorophyll concentrations were markedly lower. Water column stability appeared to be a major factor in the initiation and maintenance of ice-edge phytoplankton blooms, and the roles of these blooms in the overall estimates of biogenic production and energy flux of the Southern Ocean need to be re-evaluated.
On the basis of long-term data (1978-1992), monthly averaged profiles of vertical distribution of primary production (Pp) and chlorophyll a concentration (Ca) were calculated for deep-water (>1000 m) regions of the Black Sea. During late autumn and the winter-spring bloom, the main concentration of Ca occurred within the upper mixed layer. From April to October, a deep-water maximum of Ca occurred between the upper boundaries of the seasonal and main pycnoclines. During the winter-spring bloom, the depth of the photosynthetic layer (Hph) was 25-50 m, and during the other months, it was 50-75 m. The lower boundary of Hph was usually located at the levels with the intensity of irradiation within the photosynthetically active range equal to 0.1-0.3% of the subsurface one. Monthly averaged values Pp ranged within 400-700 mg C m-2 day-1 from November to March and within 200-400 mg C m-2 day-1 from April to October. The bulk annual value of production was 140 g C m-2. Simple algorithms are given for estimation of total Pp values based on Ca in the surface layer and insolation level.
The role of the Loop Current on the fronts of the Gulf of Mexico is studied using the results of the Monreal-Gómez and Salas de León (1985) Gulf of Mexico numerical model. The horizontal thermal structure can be depicted with the pycnocline anomaly. Assuming that biological processes take place in the frontal areas, the thermal boundaries at the cyclonic and anticyclonic eddies, as well as the Loop Current have an effect on the chlorophyll-a concentration in the Gulf of Mexico.
The first results of a multi-year campaign designed to collect a data set suitable for testing theoretical models of the development of the plankton bloom and transition to the oligotrophic regime at mid-latitudes are reported. The data were collected with a towed ‘batfish’ undulating through the euphotic zone along a section running 2000 km north from the Azores through Ocean Weather Ship “C” and into the cyclonic sub-Arctic gyre. The data were analysed to give profiles of temperature, salinity, density, solar irradiance (at 500 nm) and chlorophyll concentration. They permit the first experimental tests of theoretical relationships between horizontal structure of the physics and biology, on both gyre-scale and mesoscale, during the heating season. It is shown that those results could not have been obtained by satellite remote sensing of ocean colour because the latter underestimates the chlorophyll concentration in the seasonal thermocline. The in situ measurements document the following features of the horizontal and vertical structures of the chlorophyll-a concentration, Chl:
(1)
A poleward migration of the near-surface Chl maximum during the heating season. This migration does not keep pace with the propagation of the mixed layer shallowing; rather, it follows the slow propagation of the 12°C-isotherm outcrop.
(2)
A poleward migration of the oligotrophic regime located south of the near-surface Chl maximum. The deep Chl maximum in the oligotrophic regime descends through the seasonal pycnocline during the heating season, and slopes down from north to south.
(3)
Mesoscale variations of Chi are associated with (a) horizontal differences of vertical stability in spring, (b) horizontal gradients of isopycnal spacing and indicators of frontal upwelling in the oligotrophic summer regime.
In December, 1975, an upwelling study was conducted at Punta Curaumilla near Valparaiso, Chile. Previous work had indicated a zone of relatively intense upwelling around this point of land. In the present study, a bathythermograph survey confirmed the presence of the intensification, identified as a tongue of cool water extending seaward and equatorward of the point. It is suggested that the acceleration of relative vorticity past the point of land is responsible for intensification. From current measurements within the coolwater tongue, a double-cell cross shelf circulation was found similar to the model of C. N. K. Mooers, C. A. Collins and R. L. Smith. During a later stage of the experiment, the upwelling-favorable wind stress decreased, accompanied by an increase in the nearshore poleward undercurrent and an increased seaward flow across the shelf. Such pulsations may lead to patchiness of upwelled water. Refs.
Between 1980 and 1994, thirteen marine transects off the Romanian coast were sampled at monthly intervals from February to October at 5, 10 and 20 m depths, together with control sites situated 10, 20 and 30 miles from the coast. The present paper is based on 2,864 phytoplankton and 1,588 pigment samples. In this long data set, consistent patterns of phytoplanktonic community structure were identified: 1) The community maintained the capacity to produce huge biomasses (max. 20,163-205,084 or even 422,140 x 103 cell l-1), but an increased tendency to develop in 'patches' became much more evident; 2) The frequency and cell density of nannoplanktonic species increased up to bloom phenomena: Apedinella (21.5), Mantoniella (5.97), Hyalobrion (13.25), and Coccolithus (30.72), all Figures in cell no x 106 l-1; 3) Ultraplanktonic organisms represented by phytoplanktonic bacteria bloomed between 1990-1994 (103.68 and 63.57 x 106 cell l-1); 4) Chlorophyll a had maximum values of 35-427 and phaeophytin 37.73-65.82 μg l-1. Correlations with nutrients and light are discussed.
Alongshore and cross-shelf patterns of Zooplankton species richness and diversity around southern Africa are summarized for the first time. They are discussed in relation to physical and biological structuring processes. Diversity decreases in an east-west direction around the coast of South Africa, as subtropical communities give way to ones with temperate affinity. A peak in Zooplankton diversity occurs in the transitional area between capes Agulhas and Columbine, where waters of Atlantic, Indian and Southern Ocean origin interact. Diversity appears to be unrelated to productivity in any clear way, but does seem to be correlated with environmental stability and food web structure. Holozooplankton in the Benguela ecosystem is characterized by low species diversity and an absence of endemism, which is largely attributable to the dynamic and pulsed nature of upwelling. Phytoplankton and Zooplank-ton biomass and productivity exhibit significant spatial and temporal variability, and a large proportion of the biomass is concentrated in a small fraction of the area. As there is also a generally poor correlation between phytoplankton and Zooplankton biomass, it can be argued that the system is far from a trophic steady state, and that physical processes dictate community structure. Structuring processes within the areas of low biomass may differ from those outside, and evidence to suggest that biological interactions may be important is presented. Finally, the problems of looking at, and interpreting, patterns of diversity in the marine pelagial are discussed.
The Leeuwin Current is a surface stream of warm, low-salinity tropical water that flows poleward (southward), against the climatological mean equatorward winds, from northwestern Australia to Cape Leeuwin and then eastward towards the Great Australian Bight. It flows principally, but not exclusively, in autumn and winter. In the north, it is broad and shallow (200 km by 50 m), tapering and deepening in the south to a relatively narrow current (less than 100 km wide), with a top speed of 1.8 ms−1 and strong vertical and horizontal shears. There is an equatorward undercurrent below. The warm, low-salinity Leeuwin Current water intrudes between the continent and the southgoing high-salinity flow described by Andrews (1977). As the current approaches Cape Leeuwin, it extends down to about 200 m and is most commonly centered at the shelf edge. After rounding Cape Leeuwin, it spreads onto the shelf and develops seaward offshoots that result in cyclone/anticyclone eddy pairs. A strong poleward geopotential gradient is thought to drive the Leeuwin Current.
Measurements of currents from over the continental margin off Oregon (45°N), northwest Africa (22°N) and Peru (15°S) are used to examine the circulation pattern in coastal upwelling regions. The three regions differ in latitude, in stratification, in the bathymetry of the shelf and slope, and in the strength and variability of the wind that drives the coastal upwelling. The mean wind during the observation periods (each about 50 days) was favorable for upwelling and the mean Ekman transport computed from the wind agrees, within a factor of two, with the mean offshore transport measured in the surface layer. However, the onshore flow in the lower layer does not balance the offshore flow in the surface layer on either the mean or “event” time scale. One concludes that the upwelling process is essentially three dimensional, and upwelling ‘centers’ may develop.
