Marine Ecosystem Dynamics Research Articles

Uncertainty and natural variability in the ecological footprint of fisheries: A case study of reduction fisheries for meal and oil

It is well understood that measurements of ecological footprint and many other ecological indicators are associated with varying degrees of uncertainty, yet imprecision in ecological footprint results is rarely assessed or communicated. We calculated the marine portion of the ecological footprint of products derived from five reduction fisheries: Peruvian anchovy ( Engraulis ringens), Atlantic herring ( Clupea harengus), Gulf menhaden ( Brevoortia patronus), blue whiting ( Micromesistius poutassou) and Antarctic krill ( Euphausia superba). Monte Carlo analysis was used to measure the imprecision in marine footprint measurements resulting from multiple sources of uncertainty and natural variability in input parameters, and to determine the degree to which imprecision affects our ability to draw meaningful conclusions when comparing products sourced from different fisheries on the basis of ecological footprint. Gulf menhaden and Antarctic krill were found to have the smallest marine footprints, while blue whiting was found to have the largest. Results show that there is much uncertainty associated with marine footprint calculations and that the most significant drivers of this imprecision are uncertainty and natural variability regarding measurements of trophic level and trophic interactions. Marine footprint is highly correlated with trophic level, and clear differences can be seen when comparing species of very different trophic levels. However, comparisons of products derived from species’ with similar trophic levels are less likely to provide conclusive results. The choice of mass, protein or energy content as the basis of comparison was also considered and was found to influence the results, particularly when comparing species with similar trophic levels. While it is likely that imprecision of marine footprint measurements of fishery-derived products will remain high, technological improvements and a better understanding of marine ecosystem dynamics may make future studies more precise.

Fate of three major rivers in the Bohai Sea: A model study

Huanghe (Yellow River), Haihe and Liaohe are three major rivers flowing into the Bohai Sea and account for more than 80% of the freshwater and land-drained material inputs annually. The fate of three rivers in the seawaters correlates with the transport and distribution of the riverine sediments and nutrients, and further exerts a profound influence on the local marine ecosystem dynamics. Therefore, the evolution of the river plumes under the influence of the freshwater buoyancy, the tidal forcing and the wind stress are examined using a three-dimensional primitive equation ocean circulation model, independently and jointly. It is found that both tide and wind stirring can deteriorate the stabilization of the water column caused by the freshwater buoyancy; however, the processes are different. The tide stirring originates from the seafloor due to the bottom friction as the tidal wave propagates into the shallow waters, and then the turbulent kinetic energy dissipates upward. On the other hand, the wind stirring proceeds in the up–down direction. The influences of different winds on the evolution of the river plumes are also examined. Since the situation of each river mouth is different, the wind influence is also distinct. At last, the fate of three major rivers driven by the combined tidal forcing and climatology winds is reproduced, and the simulated salinity distribution shows a reasonable agreement with that observed, meaning that the river plume evolution plays a crucial role in shaping the salinity distribution in BS.

A statistical dynamics model of the marine ecosystem and its application in Jiaozhou Bay

Models of marine ecosystem dynamics play an important role in revealing the evolution mechanisms of marine ecosystems and in forecasting their future changes. Most traditional ecological dynamics models are established based on basic physical and biological laws, and have obvious dynamic characteristics and ecological significance. However, they are not flexible enough for the variability of environment conditions and ecological processes found in offshore marine areas, where it is often difficult to obtain parameters for the model, and the precision of the model is often low. In this paper, a new modeling method is introduced, which aims to establish an evolution model of marine ecosystems by coupling statistics with differential dynamics. Firstly, we outline the basic concept and method of inverse modeling of marine ecosystems. Then we set up a statistical dynamics model of marine ecosystems evolution according to annual ecological observation data from Jiaozhou Bay. This was done under the forcing conditions of sea surface temperature and surface irradiance and considering the state variables of phytoplankton, zooplankton and nutrients. This model is dynamic, makes the best of field observation data, and the average predicted precision can reach 90% or higher. A simpler model can be easily obtained through eliminating the terms with smaller contributions according to the weight coefficients of model differential items. The method proposed in this paper avoids the difficulties of obtaining and optimizing parameters, which exist in traditional research, and it provides a new path for research of marine ecological dynamics.

Spatial organization of krill and seabirds in the central California Current

AbstractSantora, J. A., Ralston, S., and Sydeman, W. J. 2011. Spatial organization of krill and seabirds in the central California Current. – ICES Journal of Marine Science, 68: 1391–1402. The hypothesis that krill and krill–predator spatial organization and abundance co-vary interannually was tested by investigating the spatial organization of krill and planktivorous seabirds in the central California Current ecosystem over 5 years of varying oceanographic conditions, 2002–2006. To measure the abundance and distribution of krill, data were integrated from large-scale hydroacoustic surveys and station-based net samples, and these data linked to concurrent shipboard visual surveys of seabirds. Acoustically based estimates of the relative abundance of krill were correlated with net samples of Euphausia pacifica, suggesting that acoustic signals mainly reflected the distribution of this numerically dominant species. The distribution and abundance of krill displayed marked changes over years, but the characteristic spatial scale of krill and seabirds remained similar (1–4 nautical miles), confirming the hypothesis of covariance in spatial structure. Krill and the seabird species investigated showed similar habitat associations, i.e. the outer shelf and shelf–slope region, showing that the at-sea distributions of seabirds can provide information on the presence/absence of krill patches. The results also underscore the importance of measuring spatial organization as well as relative abundance in promoting better understanding of predator–prey and marine ecosystem dynamics.

Genomics, metagenomics, and microbial oceanography—A sea of opportunities

Microbial oceanography is an emerging discipline resulted from the interaction, cross-fertilization and integration of life science and ocean science. Microbial oceanography integrates the principles of marine microbiology, microbial ecology and oceanography to study the role of microorganisms in the biogeochemical dynamics of natural marine ecosystems. The application of genomics tools to study marine microbes is resulting in rapid advancements in microbial oceanography that has important implications in global carbon cycle, climate change, and ecosystem function. Here we review the application of genomics and metagenomics in microbial oceanography and suggest future directions in microbial oceanography research.

Limits to exploitation: dynamic food web models predict the impact of livestock grazing on Ethiopian wolves Canis simensis and their prey

Summary 1. Anticipating the consequences of, and sustainable limits to, human exploitation of ecosystem resources requires a quantitative understanding of food web dynamics. While dynamic food web models are commonly used to investigate the impact of human exploitation on marine ecosystem structure and dynamics, they are less commonly applied to human‐induced disturbances in terrestrial food webs. 2. The intensifying and expanding use of rangelands for domestic livestock production creates a potential conflict with the conservation of extensive populations of wildlife. The Bale Mountains National Park (BMNP) is an example of an area that increasingly has been used as an open‐access resource by pastoralists and their herds. Livestock grazing, through its impact on herbivorous rodents, is suspected to negatively affect the critically endangered Ethiopian wolf Canis simensis, a rodent specialist. 3. We developed a series of simple dynamic food chain models to explore the interactions between these trophic levels and how they might be affected by livestock grazing. We also explored how predictions made about these trophic dynamics are affected by the type of functional response linking the different trophic levels. 4. If rodent and/or wolf populations exhibit extreme type 2 responses to resource availability, they can both remain at densities close to their ungrazed equilibrium as livestock density increases, but will rapidly crash once vegetation biomass collapses as a result of the increased grazing pressure. The model predicts the maximum sustainable livestock density to lie between 32 and 117 TLU·km−2, above which populations of wolves are expected to become locally extinct. 5. Synthesis and applications. We show that dynamic trophic modelling is an informative approach when investigating the response of terrestrial ecosystems to human‐induced disturbance. In particular, the models described in this paper provide a first step towards enabling managers to predict the implications of changing patterns of human impact on rangelands and support the identification of sustainable grazing grounds for livestock. The models also reveal that monitoring primary productivity alone may be a simple and effective way to detect stresses on food chains and predict the impact of increased livestock grazing on higher trophic levels. In the context of the BMNP, the models predict that some areas of high conservation value appear to be exploited unsustainably, thereby possibly affecting long‐term conservation goals for the Park’s flagship species.

Functional diversity in amphipods revealed by stable isotopes in an eelgrass ecosystem

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 420:277-281 (2010) - DOI: https://doi.org/10.3354/meps08873 NOTE Functional diversity in amphipods revealed by stable isotopes in an eelgrass ecosystem J. P. Farlin1,*, L. S. Lewis1,2, T. W. Anderson1, C. T. Lai1 1 Department of Biology and Coastal & Marine Institute, San Diego State University, 5500 Campanile Drive, San Diego, California 92182-4614, USA 2Present address: Center for Marine Biodiversity and Conservation, Scripps Institution of Oceanography, 9500 Gilman Drive, La Jolla, California 92083-0202, USA *Email: nilraf@gmail.com ABSTRACT: Amphipods are often dominant components of benthic marine communities and may exhibit taxon-specific differences in feeding behavior. As a result, variation in the composition of amphipod communities is an important metric for the interpretation of trophic dynamics in benthic marine ecosystems. Though previous studies of amphipod diets indicate functional diversity among taxa, few studies have examined whether these differences are detectible using time-integrated natural tracers of in situ feeding habits. We used stable isotope ratios of nitrogen (δ15N) and carbon (δ13C) to examine trophic structure among amphipod taxa belonging to 5 families in an eelgrass (Zostera marina) ecosystem in San Diego Bay, California. The relative contribution of sources of primary production to amphipod diets was further analyzed using a mixing model bracketed by 2 dominant sources of primary production in the system: eelgrass and algae. We detected significant differences in both δ13C and δ15N among amphipod taxa, indicating family-specific differences in feeding habits that generally agree with previous studies of amphipod diets. Hyalids fed almost exclusively on eelgrass, ischyrocerids and ampithoids tended to feed more on algae and eelgrass, respectively, and caprellids exhibited heterogeneous feeding on both algae and eelgrass. The relatively high δ15N value of oedicerotids suggested that this group was likely carnivorous. Our findings are in general agreement with previous descriptions of family-specific amphipod feeding behaviors, suggesting that stable isotopes are a useful tool for describing the functional roles of mesograzers in eelgrass ecosystems. KEY WORDS: Functional diversity · Stable isotopes · Eelgrass food web · Amphipods · Amphipod feeding Full text in pdf format PreviousNextCite this article as: Farlin JP, Lewis LS, Anderson TW, Lai CT (2010) Functional diversity in amphipods revealed by stable isotopes in an eelgrass ecosystem. Mar Ecol Prog Ser 420:277-281. https://doi.org/10.3354/meps08873 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 420. Online publication date: December 16, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

The northeast US application of ATLANTIS: A full system model exploring marine ecosystem dynamics in a living marine resource management context

Understanding marine ecosystem dynamics is a key challenge and opportunity facing us. One of the ways we can continue to unravel and understand marine ecosystem dynamics is via ecosystem modeling. We used one such model, ATLANTIS, to help explore the dynamics of the Northeast United States (NEUS) Continental Shelf Large Marine Ecosystem (LME). We have parameterized ATLANTIS for the NEUS LME by including major functional groups across a range of biota, the physiographic dynamics of the ecosystem, and the major fishing fleets. The objectives of this work were to describe the application of this ATLANTIS NEUS model; briefly highlight modeling skill; note areas for further improvement, data gaps, major lessons learned, and how our understanding of the ecosystem was enhanced as we executed the modeling process; and note how these model outputs could inform living marine resource management in this region. The preliminary results we show here describe outputs from a multivariate, multispecies, multifactorial modeling approach. Our modeling skill is reasonable, as determined by the fact that over 90% of our fleet effort estimates, nearly 80% of our functional group catches, and 100% of our main functional group biomasses were within limits of tolerance. Moreover, the general patterns and phenology of major events were replicated consistently, both in space and time across a broad suite of physical, chemical, biological and human factors. These include several taxa groups such as primary producers, zooplankton, benthos, fishes, marine mammals, as well as nutrients, landings, and fishing effort. Conversely, as expected, there were some groups or fleets that did exceed levels of tolerance. These were mostly invertebrate groups such as shrimp, squid or gelatinous zooplankton, groups which are notorious for being difficult to model. Yet the major taxa groups and main fishing fleets were all well within levels of tolerance. Thus, we assert that with the majority of all main processes and state variables simulated, this ATLANTIS model can indeed reasonably approximate observations for the NEUS LME across a range of factors, and more importantly can be used to evaluate the relative prominence across a range of factors that contribute to the dynamics of this marine ecosystem.

Halogenated compounds from marine algae.

Marine algae produce a cocktail of halogenated metabolites with potential commercial value. Structures exhibited by these compounds go from acyclic entities with a linear chain to complex polycyclic molecules. Their medical and pharmaceutical application has been investigated for a few decades, however other properties, such as antifouling, are not to be discarded. Many compounds were discovered in the last years, although the need for new drugs keeps this field open as many algal species are poorly screened. The ecological role of marine algal halogenated metabolites has somehow been overlooked. This new research field will provide valuable and novel insight into the marine ecosystem dynamics as well as a new approach to comprehending biodiversity. Furthermore, understanding interactions between halogenated compound production by algae and the environment, including anthropogenic or global climate changes, is a challenging target for the coming years. Research of halogenated metabolites has been more focused on macroalgae than on phytoplankton. However, phytoplankton could be a very promising material since it is the base of the marine food chain with quick adaptation to environmental changes, which undoubtedly has consequences on secondary metabolism. This paper reviews recent progress on this field and presents trends on the role of marine algae as producers of halogenated compounds.

Clearance rates of ephyrae and small medusae of the common jellyfish Aurelia aurita offered different types of prey

Prey selection and knowledge of the amounts of water processed by the early stages of the common jellyfish Aurelia aurita may at certain times of the year be crucial for understanding the plankton dynamics in marine ecosystems with mass occurrences of this jellyfish. In the present study we used two different methods (“clearance method” and “ingestion-rate method”) to estimate the amount of water cleared per unit of time of different types and sizes of prey organisms offered to A. aurita ephyrae and small medusae. The mean clearance rates of medusae, estimated with Artemia sp. nauplii as prey by both methods, agreed well, namely 3.8 ± 1.4 l h − 1 by the clearance method and 3.2 ± 1.1 l h − 1 by the ingestion-rate method. Both methods showed that copepods (nauplii and adults) and mussel veligers are captured with considerably lower efficiency, 22 to 37% and 14 to 30%, respectively, than Artemia salina nauplii. By contrast, the water processing rates of ephyrae measured by the clearance method with A. salina nauplii as prey were 3 to 5 times lower than those measured by the ingestion-rate method. This indicates that the prerequisite of full mixing for using the clearance method may not have been fulfilled in the ephyrae experiments. The study demonstrates that the predation impact of the young stages of A. aurita is strongly dependent on its developmental stage (ephyra versus medusa), and the types and sizes of prey organisms. The estimated prey-digestion time of 1.3 h in a steady-state feeding experiment with constant prey concentration supports the reliability of the ingestion-rate method, which eliminates the negative “container effects” of the clearance method, and it seems to be useful in future jellyfish studies, especially on small species/younger stages in which both type and number of prey can be easily and precisely assessed.

Sharing the results of a high-resolution ocean general circulation model under a multi-discipline framework—a review of OFES activities

Quasi-global, eddy-resolving ocean general circulation model experiments, so-called OFES (ocean general circulation model for the Earth Simulator) project, have been conducted with a basic concept of sharing results among scientists in a multi-discipline framework. Studies using such OFES results extend widely from the physical aspects of ocean circulations and energy considerations to biogeochemical tracer distributions and marine ecosystem dynamics. This article reviews the OFES activities during a period from 2004 to 2009 and highlights some interesting scientific results that emerged from the OFES project. Future plans of the project are also presented.

Mollusks and Mass Harvesting in the Middle Holocene

Archaeological excavations at California Channel Island sites have produced a history of roughly 12,000 years of maritime subsistence, technological change, human-environmental interactions, and cultural evolution. These excavations provide valuable data on the dynamics of Channel Island nearshore marine ecosystems and the adaptive strategies of maritime hunter-gatherers who foraged, fished, and hunted in them for millennia. In this article, we summarize the context, chronology, and implications of two Middle Holocene sites on San Miguel Island, where black turban snails (<i>Tegula funebralis</i>) dominate the faunal assemblages. We discuss the dominance of small shellfish in relation to optimal foraging theory and the general belief that larger-bodied animals were more attractive to ancient coastal foragers.

Climate-forced seasonal mismatch between the hatching of rhinoceros auklets and the availability of anchovy

Predator-prey relationships are key to understanding complex marine ecosystem dynamics. The match-mismatch hypothesis posits that predators time energy-intensive activities, such as reproduction, to periods of high food availability. However, predators may be constrained by various ecological or physiological processes, leading to mistimed activities relative to prey availabil- ity. We investigated inter-annual variation in the timing of breeding for a piscivorous seabird (rhinoc- eros auklet Cerorhinca monocerata) in relation to availability of a preferred prey item, Japanese anchovy Engraulis japonicus, using data collected over 18 yr between 1984 and 2006 at Teuri Island in the northern Japan Sea. Our primary goals were (1) to identify the climatic factors that affect the seabirds' timing of breeding, proxied by hatching date, and anchovy seasonal availability, and (2) to quantify the fitness effects of predator-prey matches and mismatches relative to climate variability. Hatching date was later in years with lower spring air temperatures. Auklets switched their feeding from sandlance and juvenile greenling to anchovy when it was transported into the birds' foraging range with the seasonal northern expansion of 13°C warm water from the south. The mismatch between hatching date and the period of high anchovy availability was most pronounced when spring air temperatures were warm, and there was a weak Tsushima (warm) Current. Spring air tem- perature was influenced by spring atmospheric pressure gradients in the Arctic and northern Eur- asia, which drive the east Asian winter monsoon, whereas timing of the Tsushima warm water expan- sion was influenced by winter surface pressures over the western North Pacific. Chick growth rates, mass at fledging, and overall fledging success (fitness) were lower during mismatch years when the auklets fed less on anchovy. The auklets were constrained to adjust hatching date because the sea- sonal mismatch appeared to be driven by independent and unpredictable surface pressure patterns.

Bridging biogeochemical and food web models for an End-to-End representation of marine ecosystem dynamics: The Venice lagoon case study

The simultaneous accounting of effects of natural and anthropogenic changes within a common framework calls for the development of new comprehensive tools capable of integrating biological processes that span a huge range of scales, from viruses to fishes, in addition to their interactions with physical–chemical environmental properties, i.e. End-to-End models. Here we propose an approach to model integration in which two models are not coupled by using the output of first model as a forcing of the second model and vice versa, but an approach in which the two models work separately and the output of one model is used to constrain the trajectory of the other, as in Data Assimilation methodology. This methodology is employed for integrating the biogeochemical processes as described in a coupled transport–biogeochemical model into an Ecopath with Ecosim food web model, using the Lagoon of Venice as a case study. The integrated End-to-End model reproduces the multi-annual time dynamics of the lower trophic levels as obtained by the biogeochemical model and, when run in a 2D grid, produces steady state distributions of high trophic level groups that agree with observed gradients. The research highlights the important contribution of higher trophic level dynamic to the flows related to organic non-living pools as well as the great influence inorganic nutrients in shaping the time-space patterns of higher trophic level organisms, thereby confirming the importance of pursuing an integrated End-to-End approach to marine ecosystem study. We argue that modular approach to End-to-End modelling is efficient but that model closure terms should be modified before integration. The quasi-modular approach proposed here meets these requirements while maintaining the advantages of using existing models.

Linking killer whale survival and prey abundance: food limitation in the oceans' apex predator?

Killer whales (Orcinus orca) are large predators that occupy the top trophic position in the world's oceans and as such may have important roles in marine ecosystem dynamics. Although the possible top-down effects of killer whale predation on populations of their prey have received much recent attention, little is known of how the abundance of these predators may be limited by bottom-up processes. Here we show, using 25 years of demographic data from two populations of fish-eating killer whales in the northeastern Pacific Ocean, that population trends are driven largely by changes in survival, and that survival rates are strongly correlated with the availability of their principal prey species, Chinook salmon (Oncorhynchus tshawytscha). Our results suggest that, although these killer whales may consume a variety of fish species, they are highly specialized and dependent on this single salmonid species to an extent that it is a limiting factor in their population dynamics. Other ecologically specialized killer whale populations may be similarly constrained to a narrow range of prey species by culturally inherited foraging strategies, and thus are limited in their ability to adapt rapidly to changing prey availability.

Food preferences of the common tern, &lt;i&gt;sterna hirundo&lt;/i&gt; (Linnaeus, 1758) at the Densu floodplains, Accra

Seabirds are important in the dynamics of marine ecosystems because they recycle important biomass of lower trophic level organisms. Their faeces and carcasses provide important food sources for terrestrial and benthic scavengers. As a result of the abundance of food resources along the coast of Ghana, common terns (Sterna hirundo) are found in large numbers in productive brackish or saltwater wetlands, and are notable for indicating location of rich fish stocks at sea and in lagoons. The study aimed to determine the variety of food available, and any food preferences exhibited by S. hirundo at the Densu floodplains near Accra. While earlier studies of food habits of seabirds worldwide used examination of regurgitates and telescopic observations, the study quantitatively analyzed guts of common tern for their food content using standardized methods. The utilization by common terns of the Panbros lagoon fish resource during roosting in the night was quantified. Results showed that food available to the birds included marine and fresh or brackish water fish, crustaceans and worms. During caging, only one bird fed on 15 individuals of Hemichromis fasciatus. Prey items such as exoskeleton of crab zoea larvae, capitellid worms, fish otolith, pieces of fish bones and vertebrae, detrital materials and sand grains were found in the guts. The presence of capitellid worms in the guts, a known indicator of excess nutrient enrichment, showed that S. hirundo utilized the Panbros lagoon fish resource in feeding, and the roosting ground was under much stress. The study stressed the importance of complementing conservation efforts for common terns with attempts to manage the fish resources in the Densu floodplains.

Why compare marine ecosystems?

Abstract Murawski, S. A., Steele, J. H., Taylor, P., Fogarty, M. J., Sissenwine, M. P., Ford, M., and Suchman, C. 2010. Why compare marine ecosystems? – ICES Journal of Marine Science, 67: 1–9. Effective marine ecosystem-based management (EBM) requires understanding the key processes and relationships controlling the aspects of biodiversity, productivity, and resilience to perturbations. Unfortunately, the scales, complexity, and non-linear dynamics that characterize marine ecosystems often confound managing for these properties. Nevertheless, scientifically derived decision-support tools (DSTs) are needed to account for impacts resulting from a variety of simultaneous human activities. Three possible methodologies for revealing mechanisms necessary to develop DSTs for EBM are: (i) controlled experimentation, (ii) iterative programmes of observation and modelling (“learning by doing”), and (iii) comparative ecosystem analysis. We have seen that controlled experiments are limited in capturing the complexity necessary to develop models of marine ecosystem dynamics with sufficient realism at appropriate scales. Iterative programmes of observation, model building, and assessment are useful for specific ecosystem issues but rarely lead to generally transferable products. Comparative ecosystem analyses may be the most effective, building on the first two by inferring ecosystem processes based on comparisons and contrasts of ecosystem response to human-induced factors. We propose a hierarchical system of ecosystem comparisons to include within-ecosystem comparisons (utilizing temporal and spatial changes in relation to human activities), within-ecosystem-type comparisons (e.g. coral reefs, temperate continental shelves, upwelling areas), and cross-ecosystem-type comparisons (e.g. coral reefs vs. boreal, terrestrial vs. marine ecosystems). Such a hierarchical comparative approach should lead to better understanding of the processes controlling biodiversity, productivity, and the resilience of marine ecosystems. In turn, better understanding of these processes will lead to the development of increasingly general laws, hypotheses, functional forms, governing equations, and broad interpretations of ecosystem responses to human activities, ultimately improving DSTs in support of EBM.

Dynamics of wind‐forced coherent anticyclones in the open ocean

We numerically study the dynamics of coherent anticyclonic eddies in the ocean interior. For the hydrostatic, rotating, stably stratified turbulence we use a high‐resolution primitive equation model forced by small‐scale winds in an idealized configuration. Many properties of the horizontal motions are found to be similar to those of two‐dimensional and quasi‐geostrophic turbulence. Major differences are a strong cyclone‐anticyclone asymmetry linked to the straining field exerted by vortex Rossby waves, which is also found in shallow water flows, and the complex structure of the vertical velocity field, which we analyze in detail. Locally, the motion can become strongly ageostrophic, and vertical velocities associated with vortices can reach magnitudes and levels of spatial complexity akin to those reported for frontal regions. Transport and mixing properties of the flow field are further investigated by analyzing Lagrangian trajectories. Particles released in the pycnocline undergo large vertical excursions because of the vertical velocities associated to the vortices, with potentially important consequences for marine ecosystem dynamics.

Separate and interactive effects of eutrophication and climate variables on the ecosystem elements of the Gulf of Riga

There is currently a critical knowledge gap in how eutrophication and climate variables separately and interactively impact the dynamics of marine ecosystems. Based on long-term monitoring data we quantified the separate and combined impacts of nutrient loading, temperature, salinity, and wind conditions on zooplankton, zoobenthos and fish inhabiting a brackish water ecosystem in the Gulf of Riga. Changes in zoobenthos communities and herring stock were largely explained by climate variables. Zooplankton species were related to both eutrophication and climate variables, and models combining all environmental variables explained additional variation in zooplankton data compared to the separate models of climate and eutrophication. This suggests that zoobenthos communities and herring stock are largely driven by weather conditions, whereas the combined effect of weather and nutrient loads are likely the cause for dynamic zooplankton communities in the Gulf of Riga.

Nutrient and salinity decadal variations in the central and eastern North Pacific

Long‐term timeseries of upper ocean salinity and nutrients collected in the Alaskan Gyre along Line P exhibit significant decadal variations that are shown to be in phase with variations recorded in the Southern California Current System by the California Cooperative Oceanic Fisheries Investigation (CalCOFI). We present evidence that these variations are linked to the North Pacific Gyre Oscillation (NPGO)—a climate mode of variability that tracks changes in strength of the central and eastern branches of the North Pacific gyres and of the Kuroshio‐Oyashio Extension (KOE). The NPGO emerges as the leading mode of low‐frequency variability for salinity and nutrients. We reconstruct the spatial expressions of the salinity and nutrient modes over the northeast Pacific using a regional ocean model hindcast from 1963‐2004. These modes exhibit a large‐scale coherent pattern that predicts the in‐phase relationship between the Alaskan Gyre and California Current timeseries. The fact that large‐amplitude, low‐frequency fluctuations in salinity and nutrients are spatially phase‐locked and correlated with a measurable climate index (the NPGO) open new avenues for exploring and predicting the effects of long‐term climate change on marine ecosystem dynamics.