The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. 
The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. 
The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. 
The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

We provide a brief synopsis of the unique physical and ecological attributes of sandy beach ecosystems and review the main anthropogenic pressures acting on the world's single largest type of open shoreline. Threats to beaches arise from a range of stressors which span a spectrum of impact scales from localised effects (e.g. trampling) to a truly global reach (e.g. sea-level rise). These pressures act at multiple temporal and spatial scales, translating into ecological impacts that are manifested across several dimensions in time and space so that today almost every beach on every coastline is threatened by human activities. Press disturbances (whatever the impact source involved) are becoming increasingly common, operating on time scales of years to decades. However, long-term data sets that describe either the natural dynamics of beach systems or the human impacts on beaches are scarce and fragmentary. A top priority is to implement long-term field experiments and monitoring programmes that quantify the dynamics of key ecological attributes on sandy beaches. Because of the inertia associated with global climate change and human population growth, no realistic management scenario will alleviate these threats in the short term. The immediate priority is to avoid further development of coastal areas likely to be directly impacted by retreating shorelines. There is also scope for improvement in experimental design to better distinguish natural variability from anthropogenic impacts. Sea-level rise and other effects of global warming are expected to intensify other anthropogenic pressures, and could cause unprecedented ecological impacts. The definition of the relevant scales of analysis, which will vary according to the magnitude of the impact and the organisational level under analysis, and the recognition of a physical–biological coupling at different scales, should be included in approaches to quantify impacts. Zoning strategies and marine reserves, which have not been widely implemented in sandy beaches, could be a key tool for biodiversity conservation and should also facilitate spillover effects into adjacent beach habitats. Setback and zoning strategies need to be enforced through legislation, and all relevant stakeholders should be included in the design, implementation and institutionalisation of these initiatives. New perspectives for rational management of sandy beaches require paradigm shifts, by including not only basic ecosystem principles, but also incentives for effective governance and sharing of management roles between government and local stakeholders.

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Threats to sandy beach ecosystems: A review

Cold seeps occur in geologically active and passive continental margins, where pore waters enriched in methane are forced upward through the sediments by pressure gradients. The advective supply of methane leads to dense microbial communities with high metabolic rates. Anaerobic methane oxidation presumably coupled to sulphate reduction facilitates formation of carbonates and, in many places, generates extremely high concentrations of hydrogen sulphide in pore waters. Increased food supply, availability of hard substratum and high concentrations of methane and sulphide supplied to free-living and symbiotic bacteria provide the basis for the complex ecosystems found at these sites. This review examines the structures of animal communities in seep sediments and how they are shaped by hydrologic, geochemical and microbial processes. The full size range of biota is addressed but emphasis is on the mid-size sediment-dwelling infauna (foraminiferans, metazoan meiofauna and macrofauna), which have received less attention than megafauna or microbes. Megafaunal biomass at seeps, which far exceeds that of surrounding non-seep sediments, is dominated by bivalves (mytilids, vesicomyids, lucinids and thyasirids) and vestimentiferan tube worms, with pogonophorans, cladorhizid sponges, gastropods and shrimp sometimes abundant. In contrast, seep sediments at shelf and upper slope depths have infaunal densities that often differ very little from those in ambient sediments. At greater depths, seep infauna exhibit enhanced densities, modified composition and reduced diversity relative to background sediments. Dorvilleid, hesionid and ampharetid polychaetes, nematodes, and calcareous foraminiferans are dominant. There is extensive spatial heterogeneity of microbes and higher organisms at seeps. Specialized infaunal communities are associated with different seep habitats (microbial mats, clam beds, mussel beds and tube worms aggregations) and with different vertical zones in the sediment. Whereas fluid flow and associated porewater properties, in particular sulphide concentration, appear to regulate the distribution, physiological adaptations and sometimes behaviour of many seep biota, sometimes the reverse is true. Animal-microbe interactions at seeps are complex and involve symbioses, heterotrophic nutrition, geochemical feedbacks and habitat structure. Nutrition of seep fauna varies, with thiotrophic and methanotrophic symbiotic bacteria fueling most of the megafaunal forms but macrofauna and most meiofauna are mainly heterotrophic. Macrofaunal food sources are largely photosynthesis-based at shallower seeps but reflect carbon fixation by chemosynthesis and considerable incorporation of methane-derived C at deeper seeps. Export of seep carbon appears to be highly localized based on limited studies in the Gulf of Mexico. Seep ecosystems remain one of the ocean's true frontiers. Seep sediments represent some of the most extreme marine conditions and offer unbounded opportunities for discovery in the realms of animal-microbe-geochemical interactions, physiology, trophic ecology, biogeography, system-atics and evolution.

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Ecology of cold seep sediments: interactions of fauna with flow, chemistry and microbes

Stelios Katsanevakis*, Inger Wallentinus, Argyro Zenetos, Erkki Leppakoski, Melih Ertan Cinar, Bayram Ozturk, Michal Grabowski, Daniel Golani and Ana Cristina Cardoso European Commission, Joint Research Centre (JRC), Institute for Environment and Sustainability (IES), Ispra, Italy Department of Biological and Environmental Sciences, University of Gothenburg, Sweden Institute of Marine Biological Resources and Inland Waters, Hellenic Centre for Marine Research, Ag. Kosmas, Greece Department of Biosciences, Environmental and Marine Biology, Abo Akademi University, Turku, Finland Ege University, Faculty of Fisheries, Department of Hydrobiology, Bornova, Izmir, Turkey Faculty of Fisheries, Marine Biology Laboratory, University of Istanbul, Istanbul, Turkey Department of Invertebrate Zoology & Hydrobiology, University of Lodz, Poland Department of Ecology, Evolution and Behavior and the National Natural History Collections, The Hebrew University of Jerusalem, Israel

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Impacts of invasive alien marine species on ecosystem services and biodiversity: a pan-European review.

The Humboldt Current System (HCS) is one of the most productive marine ecosystems on earth. It extends along the west coast of South America from southern Chile (∼42°S) up to Ecuador and the Galapagos Islands near the equator. The general oceanography of the HCS is characterised by a predominant northward flow of surface waters of subantarctic origin and by strong upwelling of cool nutrient-rich subsurface waters of equatorial origin. Along the coast of northern and central Chile, upwelling is localised and its occurrence changes from being mostly continuous (aseasonal) in northern Chile to a more seasonal pattern in southern-central Chile. Several important upwelling centres along the Chilean coast are interspersed with long stretches of coast without or with sporadic and less intense upwelling. Large-scale climatic phenomena (El Nino Southern Oscillation, ENSO) are superimposed onto this regional pattern, which results in a high spatiotemporal heterogeneity, complicating the prediction of ecological processes along the Chilean coast. This limited predictability becomes particularly critical in light of increasing human activities during the past decades, at present mainly in the form of exploitation of renewable resources (fish, invertebrates and macroalgae). This review examines current knowledge of ecological processes in the HCS of northern and central Chile, with a particular focus on oceanographic factors and the influence of human activities, and further suggests conservation strategies for this high-priority large marine ecosystem. Along the Chilean coast, the injection of nutrients into surface waters through upwelling events results in extremely high primary production. This fuels zooplankton and fish production over extensive areas, which also supports higher trophic levels, including large populations of seabirds and marine mammals. Pelagic fisheries, typically concentrated near main upwelling centres (20-22°S, 32-34°S, 36-38°S), take an important share of the fish production, thereby affecting trophic interactions in the HCS. Interestingly, El Nino (EN) events in northern Chile do not appear to cause a dramatic decline in primary or zooplankton production but rather a shift in species composition, which affects trophic efficiency of and interactions among higher-level consumers. The low oxygen concentrations in subsurface waters of the HCS (oxygen-minimum zone, OMZ) influence predator-prey interactions in the plankton by preventing some species from migrating to deeper waters. The OMZ also has a strong effect on the bathymetric distribution of sublittoral soft-bottom communities along the Chilean coast. The few long-term studies available from sublittoral soft-bottom communities in northern and central Chile suggest that temporal dynamics in abundance and community composition are driven by interannual phenomena (EN and the extent and intensity of the OMZ) rather than by intra-annual (seasonal) patterns. Macrobenthic communities within the OMZ are often dominated in biomass by sulphide-oxidising, mat-forming bacteria. Though the contribution of these microbial communities to the total primary production of the system and their function in structuring OMZ communities is still scarcely known, they presumably play a key role, also in sustaining large populations of economically valuable crustaceans.

The humboldt current system of northern and central chile : Oceanographic processes, ecological interactions and socioeconomic feedback

Temporal and spatial patterns of growth in mussels Mytilus edulis on an offshore platform: relationships to water temperature and food availability

Allochthonous subsidies of organic material can profoundly influence population and community structure; however, the role of consumers in the processing of these inputs is less understood but may be closely linked to community and ecosystem function. Inputs of drift macrophytes subsidize sandy beach communities and food webs in many regions. We estimated feeding rates of dominant sandy beach consumers, the talitrid amphipods (Megalorchestia corniculata, in southern California, USA, and Talitrus saltator, in southern Galicia, Spain), and their impacts on drift macrophyte subsidies in field and laboratory experiments. Feeding rate varied with macrophyte type and, for T. saltator, air temperature. Size-specific feeding rates of talitrid amphipods were greatest on brown macroalgae (Macrocystis, Egregia, Saccorhiza and Fucus). Rates for large individuals of both species ranged from ∼40 mg wet wt individual−112 h−1 on brown macroalgae to negligible feeding by M. corniculata on a vascular plant (surfgrass). Amphipod growth rates were also greatest on Macrocystis and lowest on surfgrass, Phyllospadix. For a Californian beach with substantial inputs of macrophyte wrack (>70 kg wet wt m−1 month−1 in summer), we estimated that the population of talitrid amphipods could process an average of 55% of the palatable Macrocystis input. Our results indicate that talitrid amphipod populations can have a significant impact on drift macrophyte processing and fate and that the quantity and composition of drift macrophytes could, in turn, limit populations of beach consumers.

Processing of allochthonous macrophyte subsidies by sandy beach consumers: estimates of feeding rates and impacts on food resources

We investigated the role of sandy beaches in nearshore nutrient cycling by quantifying macrophyte wrack inputs and examining relationships between wrack accumulation and pore water nutrients during the summer dry season. Macrophyte inputs, primarily giant kelp Macrocystis pyrifera, exceeded 2.3 kg m−1 day−1. Mean wrack biomass varied 100-fold among beaches (range = 0.41 to 46.43 kg m−1). Mean concentrations of dissolved inorganic nitrogen (DIN), primarily NO
 x
 −
 -N, and dissolved organic nitrogen (DON) in intertidal pore water varied significantly among beaches (ranges = 1 to 6,553 μM and 7 to 2,006 μM, respectively). Intertidal DIN and DON concentrations were significantly correlated with wrack biomass. Surf zone concentrations of DIN were also strongly correlated with wrack biomass and with intertidal DIN, suggesting export of nutrients from re-mineralized wrack. Our results suggest beach ecosystems can process and re-mineralize substantial organic inputs and accumulate dissolved nutrients, which are subsequently available to nearshore waters and primary producers.

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Marine Macrophyte Wrack Inputs and Dissolved Nutrients in Beach Sands

We used natural abundance measurements of stable carbon and nitrogen isotopes and a short-term 15N-enrichment experiment to explore the importance of river-derived and autochthonous sources to the diet of intertidal suspension-feeding bivalves in the Ria de Arosa, an oceanic-dominated system in northwest Spain. Highly seasonal and intense phytoplankton "bloom" events occur in this estuary. However, relatively low phytoplankton standing crop and productivity are present during much of the year, suggesting that food sources other than phytoplankton must support bivalves during these periods. Bivalves (Cerastoderma edule, Tapes decussatus, Mytilus galloprovincialis) were sampled quarterly at four intertidal stations along the length of the estuary with increasing distance from the Ulla River. Muscle tissue was consistently enriched in 13C and 15N relative to stomach contents. The stable C isotope values of bivalves indicated that river-derived inputs were, at most, a minor component of diet. These values suggested the potential importance of benthic microalgae to bivalve diet much of the year and the incorporation of 15N label applied to the sediment surface into stomach contents and muscle tissue in a field experiment supported this conclusion. Other labeled components of the microbenthos such as bacteria could also have been ingested. 13C-depleted values of bivalves in May coincided with elevated offshore chlorophyll a concentrations, suggesting the increased use of a phytoplankton source during the spring. We propose that intertidal suspension-feeding bivalves in this estuary use primarily resuspended microbenthos during periods of low phytoplankton concentration, but that phytoplankton increases in relative dietary importance during bloom events.

Henry M. Page

Papers

Temporal and spatial patterns of growth in mussels Mytilus edulis on an offshore platform: relationships to water temperature and food availability

Processing of allochthonous macrophyte subsidies by sandy beach consumers: estimates of feeding rates and impacts on food resources

Marine Macrophyte Wrack Inputs and Dissolved Nutrients in Beach Sands

Diet of intertidal bivalves in the Ría de Arosa (NW Spain): evidence from stable C and N isotope analysis

Experimental evidence for filter-feeding by the hydrothermal vent mussel, Bathymodiolus thermophilus