Isotopic Niche Research Articles

Anthropogenic and Climatic Drivers of Long-Term Changes of Mercury and Feeding Ecology in Arctic Beluga (Delphinapterus leucas) Populations.

We assessed long-term changes in the feeding ecology and mercury (Hg) accumulation in Eastern High Arctic-Baffin Bay beluga (Delphinapterus leucas) using total Hg and stable isotope (δ13C, δ15N) assays in teeth samples from historical (1854-1905) and modern (1985-2000) populations. Mean δ13C values in teeth declined significantly over time, from -13.01 ± 0.55‰ historically to -14.41 ± 0.28‰ in 2000, while no consistent pattern was evident for δ15N due to high individual variability within each period. The temporal shift in isotopic niche is consistent with beluga feeding ecology changing in recent decades to a more pelagic and less isotopically diverse diet or an ecosystem wide change in isotope profiles. Mercury concentrations in modern beluga teeth were 3-5 times higher on average than those in historical beluga. These results are similar to the long-term trends of Hg and feeding ecology reported in other beluga populations and in other Arctic marine predators. Similar feeding ecology shifts across regions and species indicate a consistent increased pelagic diet response to climate change as the Arctic Ocean progressively warmed and lost sea ice. Previously, significant temporal Hg increase in beluga and other Arctic animals was attributed solely to direct inputs of anthropogenic Hg from long-range sources. Recent advances in understanding the Arctic marine Hg cycle suggest an additional, complementary possibility─increased inputs of terrestrial Hg of mixed anthropogenic-natural origin, mobilized from permafrost and other Arctic soils by climate warming. At present, it is not possible to assign relative importance to the two processes in explaining the rise of Hg concentrations in modern Arctic marine predators.

The Effects of Climatic Variability on the Feeding Ecology of the Scalloped Hammerhead Shark (Sphyrna lewini) in the Tropical Eastern Pacific

Climatic variability changes ocean productivity and generates systematic cascading effects in marine food webs. Studying the feeding ecology of top predators, such as sharks, can provide insights into the overall health of marine ecosystems. We conducted a 4-year study to evaluate seasonal and inter-annual trophic variations and their relationship with El Niño Southern Oscillation (ENSO) on the largest aggregation of scalloped hammerhead shark (Sphyrna lewini) in the Tropical Eastern Pacific (TEP). We used δ13C and δ15N signatures to gain a better understanding of hammerheads’ feeding strategies as well as variations of their isotopic niche. Our results suggest that the hammerhead sharks in the Galapagos Marine Reserve respond to climatic fluctuations, with La Niña event potentially benefiting their trophic needs as the overall marine productivity increased in the region. This work is the first of its kind in the TEP and provides insights on how climate variability influences the feeding ecology of this critically endangered species. It also highlights the need to incorporate climate-related conservation strategies into the management of this species since ENSO events become more frequent and intense in the face of climate change.

Ontogeny drives allochthonous trophic support of snappers: Seascape connectivity along the mangrove-seagrass-coral reef continuum of a tropical marine protected area

Ecosystems are connected through the movement of organisms, nutrients, energy, and matter. The connection and dependence between aquatic habitats enhances our capacity to understand the functioning of the seascape. In this paper, we investigated the trophic ecology of two snapper species, Lutjanus analis and Lutjanus alexandrei, along a tropical coastal seascape (inner estuary, outer estuary, marine beach, and coastal reefs). To quantify and compare trophic (isotopic) niches, primary trophic support, and trophic connectivity along the ontogeny, δ13C and δ15N were used to construct isotopic metrics and mixing models for assessing consumers’ isotopic niches and the relative contributions of primary sources supporting them. The isotopic niche was wider for fishes from coastal reefs, but narrower for those from inner estuary, suggesting diversification on trophic support when these species move out from the estuary to the sea. Mixing models showed that smaller individuals generally showed their previous habitat support and as the fish start to feed locally and grow, they change tissues and reflect local sources. Inside the estuary, larger fish started to show marine support while smaller fish from coastal reefs still reflected sources from previous habitats. Specifically, the models revealed that smaller individuals of L. alexandrei retained their mangrove and estuarine particulate organic matter previous support, while the L. analis model was inconclusive but converged with stable isotope niche metrics, which indicated high variability that could be related to periphyton sources from seagrass beds. The allochthonous support seems to occur either by movement or recent migrations of organisms instead of organic matter flow promoted by abiotic vectors. These results suggest the importance of maintaining habitat connections for these valuable commercial species. Future studies should focus on other sites with seagrass beds to fully understand the habitat and resource use, as well as the movements among them, especially for L. analis.

Isotopic niche size variability in an ecosystem engineer along a disturbance gradient in a South African lagoon

A key challenge for natural resource management is how to detect effects of environmental stress on individuals and populations before declines in abundance occur. Variability in carbon and nitrogen isotope composition (δ13C and δ15N) among consumers can provide information on the population trophic niche and how it may change in response to environmental stress. We measured δ13C and δ15N values in primary producers and in an ecosystem engineer, the bioturbating sandprawn Kraussillichirus kraussi, in Langebaan Lagoon, South Africa, along a human disturbance gradient. Diet partitioning mixing models were coupled with isotope niche analyses and individual body condition data to investigate shifts in resource utilisation and diet plasticity from minimally to highly disturbed sites. The δ15N values of seagrass, Zostera capensis indicated a nutrient gradient, with the highest δ15N values at highly disturbed sites indicating either anthropogenic or marine nitrogen inputs. A decreasing δ15N signal with distance from human disturbance/mouth of lagoon was however not evident for sandprawns nor their presumed dietary sources (phytoplankton, microphytobenthos or sediment organic matter), likely because of faster isotope turnover time compared to seagrass and/or differential fractionation for sandprawns among the sites. Sandprawn isotope niche sizes varied among sites, with no trend along the disturbance gradient. The smallest niche coincided with uniform feeding on microphytobenthos according to mixing models. On an individual level, deviating isotope values from population means were correlated to better body condition, suggesting that a divergent feeding strategy is beneficial. Our results support a generalist feeding behavior of the sandprawns with no evidence of reduced physiological status at the site with most human disturbance.

Panthera onca (Linnaeus, 1758) from the late Pleistocene of Brazilian Intertropical Region: taxonomy, habitat, isotopic diet composition, and isotopic niche overlap with extinct faunivores

This paper focuses in the description, radiocarbon dating and isotopic analyses (δ13C, δ18O) of new fossils of Panthera onca from the late Pleistocene of the Brazilian Intertropical Region. This paper focuses on the paleoecology of this large cat and is of major importance to understand ecological niches in evolutionary time. Radiocarbon datings and stable isotope compositions (carbon and oxygen) were determined from the structural carbonate of enamel for two fossils of Panthera onca found in two caves in Bahia, Brazil. Isotopic data available of large faunivores and other extinct and extant herbivorous taxa from the late Pleistocene of the Brazilian Intertropical Region were used for paleoecological interpretations. Carbon and oxygen isotopic values from P. onca allow us to suggest that these individuals lived in arboreal savanna habitat between 26 and 33 kyr BP, could reach 209 kg and feed mainly on Nothrotherium maquinense, Tapirus terrestris and Alouatta sp., being a specialist. The isotopic niche overlap with Smilodon populator and Arctotherium wingei was high, while with Protocyon troglodytes was low. In the late Pleistocene P. onca probably suffer high ecological pressure by S. populator, while with A. wingei this could not occur, as this species could be mainly herbivorous.

Reconstructing the diet, trophic level and migration pattern of mysticete whales based on baleen isotopic composition.

Baleen from mysticete whales is a well-preserved proteinaceous material that can be used to identify migrations and feeding habits for species whose migration pathways are unknown. Analysis of δ13C and δ15N values from bulk baleen have been used to infer migration patterns for individuals. However, this approach has fallen short of identifying migrations between regions as it is difficult to determine variations in isotopic shifts without temporal sampling of prey items. Here, we apply analysis of δ15N values of amino acids to five baleen plates belonging to three species, revealing novel insights on trophic position, metabolic state and migration between regions. Humpback and minke whales had higher reconstructed trophic levels than fin whales (3.7–3.8 versus 3–3.2, respectively) as expected due to different feeding specialization. Isotopic niche areas between baleen minima and maxima were well separated, indicating regional resource use for individuals during migration that aligned with isotopic gradients in Atlantic Ocean particulate organic matter. Phenylanine δ15N values confirmed regional separation between the niche areas for two fin whales as migrations occurred and elevated glycine and threonine δ15N values suggested physiological changes due to fasting. Simultaneous resolution of trophic level and physiological changes allow for identification of regional migrations in mysticetes.

Extreme bill dimorphism leads to different but overlapping isotopic niches and similar trophic positions in sexes of the charismatic extinct huia

The New Zealand huia (Heteralocha acutirostris) had the most extreme bill sexual dimorphism among modern birds. Given the quick extinction of the species, the cause of the dimorphism could only be hypothesised to reflect different trophic niches and reduce male/female competition. We tested that hypothesis by combining museum specimens, geometric morphometrics, and isotopic analyses. We used geometric morphometrics to describe bill shape; measured bulk (δ15Nbulk) and (δ13Cbulk) values from feather as proxies of the birds’ foraging habitat and diet; and compared compound-specific stable isotopes analyses (CSIA) of nitrogen in amino acids (δ15NAA) in male–female pairs to estimate their trophic position. Sexes had significantly different, but overlapping feather δ15Nbulk and δ13Cbulk values, but δ15NAA indicated identical trophic positions and δ15Nbulk was not related to bill shape. Trophic position was less variable among females, consistent with a specialised foraging behaviour and, thus, supporting a partial male/female foraging segregation.

Mercury exposure driven by geographic and trophic factors in Magellanic penguins from Tierra del Fuego

Penguins accumulate mercury due to their long-life span together with their high trophic position. We sampled adult and juveniles' feathers from three colonies of Spheniscus magellanicus from Tierra del Fuego along an inshore-offshore corridor. We integrated toxicological information (mercury concentrations) and foraging biomarkers (δ13C, δ15N) into a common data analysis framework (isotopic niche analysis) to evaluate the influence of age, location, and foraging behaviors on mercury concentrations. Adults had higher feather mercury concentrations, δ13C, and δ15N values compared to juveniles. Also, adult and juvenile feather mercury concentrations differed between colonies, with lower mercury concentrations at the nearest inshore colony relative to the farther offshore colonies. Trophic position and the isotopic niche analyses suggest that this geographic gradient in mercury concentrations is due to differences in colonies' foraging areas. Understanding penguins' exposure to mercury derived from local food webs is a crucial first step in evaluating the impacts of this heavy metal on their conservation status.

Trophic adaptability shapes isotopic niche of the resident fish Aphanius fasciatus across lagoon habitats

Coastal lagoons are characterized by high habitat heterogeneity where natural habitats coexist with artificial ones, historically set up to support human activities. Increasing anthropogenic pressure may lead to progressive degradation of the most vulnerable lagoonal habitats and the associated biological communities. One of the strictly estuarine-dependent fish species that may be affected by the degradation of lagoon habitats is the South European toothcarp Aphanius fasciatus, archetype of Mediterranean lagoon residents.Carbon and nitrogen stable isotopes were used to disentangle the influence of habitat types (natural vs artificial) and fish community (multi-trophic context) on the trophic niche features of A. fasciatus. Fish communities and organic matter sources were sampled in two Mediterranean lagoons located at the northernmost (Lagoon of Venice) and at the mid-latitude (Stagnone di Marsala, Trapani) of A. fasciatus distribution.Results showed evidence of high trophic adaptability of A. fasciatus, whose omnivorous feeding habit resulted in seasonal changes in isotopic niche width and niche partitioning with co-occurring species, constituting an advantage in habitats characterized by high seasonal variation of resources availability. Furthermore, while macrophytes drove the main trophic pathways leading to A. fasciatus in natural habitats, artificial habitats were mainly based on sedimentary organic matter routes. These outcomes broaden our knowledge on how natural and artificial habitats trophically support A. fasciatus populations and results are discussed in light of the ecological implications for environmental management of coastal lagoons.

Diet reveals potential for competition and coexistence among coyotes (Canis latrans), red foxes (Vulpes vulpes), and gray foxes (Urocyon cinereoargenteus)

Species can alleviate competition by reducing diet overlap. Non-native coyotes (Canis latrans Say, 1823) and historically native gray foxes (Urocyon cinereoargenteus (Schreber, 1775)) have expanded their ranges and may compete with native red foxes (Vulpes vulpes (Linnaeus, 1758)). To examine potential competition among canids in Maine, USA, we compared δ13C and δ15N from muscle and hair samples to assess relative resource use, and we compared frequency of occurrence of prey items from stomach contents to assess diets. For these species, red foxes consumed anthropogenically based foods the most in fall and early winter, gray foxes consumed anthropogenically based foods the most in summer, and coyotes consumed anthropogenically based foods the least in all seasons. Coyotes held the highest relative trophic position in fall and early winter, red foxes held the highest relative trophic position in summer, and gray foxes held the lowest relative trophic position. Based on stomach contents, gray foxes had the broadest diet and consumed the most plants, and coyotes had the narrowest diet. Red foxes were the only species to show isotopic niche overlap with both potential competitors across seasons. Thus, they may be most susceptible to competitive exclusion among these canids, with implications for community dynamics as ranges shift due to human activity.

Social, spatial and isotopic niche partitioning identify an estuarine community of bottlenose dolphins as a discrete management unit

Abstract Investigations of population structure across multiple niche dimensions can identify discrete management units within populations. This study examined social, spatial and isotopic niche partitioning in Indo‐Pacific bottlenose dolphins (Tursiops aduncus) across ca. 600 km2 of coastal and estuarine waters in south‐western Australia, to evaluate whether estuarine dolphins should be treated as a discrete management unit. Photo‐identification data and tissue samples were collected in 2016 and 2017 in a study area covering the Peel‐Harvey Estuary (PHE) and adjacent coastal waters. A total of 1,038 dolphin groups were encountered, and 481 individuals were identified. Tissue samples for stable isotope (δ13C and δ15N) analyses were collected from 96 individuals. Social structure and complexity analyses were conducted, full and core activity spaces were identified, and their size estimated for identified social communities. Differences in stable isotope composition among individuals and communities were examined. A socially, spatially and isotopically distinct dolphin community occurred in the PHE. The coastal waters contained four socially and spatially, but not isotopically, distinct communities as well as a substantial number of dolphins (n = 185) that were sighted infrequently and therefore were not assigned to any community. Individuals formed three levels of relationships; the majority (78%) were weak association relationships (mean half‐weight index 0.006). The estuarine community had significantly higher mean δ13C and significantly lower mean δ15N values than any of the coastal communities. There is a strong scientific basis for treating the PHE dolphin community as a discrete management unit. The estuarine and coastal communities occupied different social environments, with coastal individuals sharing space with more transient individuals. This study shows the value of integrating information from multiple niche dimensions when identifying management units, and the need to consider all encountered individuals in management planning.

Trophic structure of benthic communities in a Chilean fjord (45°S) influenced by salmon aquaculture: Insights from stable isotopic signatures

Benthic marine food webs, which recycle organic matter and sustain unique biodiversity, are an important component of estuarine Patagonian fjords; however, these may be heavily influenced by salmon farming activities. Under the above conditions, this study collected several food sources (sediment organic matter, suspended particulate organic matter, macroalgae) and 26 benthic invertebrate species, and analyzed them using a Bayesian mixing model. Briefly, carbon and nitrogen stable isotopes analyses revealed that the highly variable isotopic niche widths respond to food supplies from marine and terrestrial organic matter. In addition, particulate and dissolved waste from salmon farming activities were found to modify isotopic composition ratios in many suspension feeders. Particularly, our results indicate high δ15N values in the sponge Cliona chilensis and the encrusting coral Incrustatus comauensis, which appear to be potential ecological indicators for evaluating stoichiometry imbalances and trace organic pollution sources in fjord environments.

Compound-specific isotope analyses of harp seal teeth: tools for trophic ecology reconstruction

As sentinels of ecosystem health, high trophic level predators integrate information through all levels of the food web. Their tissues can be used to investigate spatiotemporal variability in foraging behaviour, and with the appropriate analytical methods and tools, archived samples can be used to reconstruct past trophic interactions. Harp seal Pagophilus groenlandicus teeth collected in the 1990s from the Northwest Atlantic were analysed for bulk stable carbon and nitrogen isotopes (δ13Cbulk and δ15Nbulk), and compound-specific stable nitrogen isotopes of amino acids (δ15NAA) for the first time. We developed a fine-scale, annual growth layer group (GLG) dentine sub-sampling method corresponding to the second and third year of life. In accordance with previous diet studies, while there was individual variability in δ15Nbulk, δ13Cbulk and δ15NAA measurements, we did not detect significant differences in isotopic niche widths between males and females, or between GLGs. Relative trophic position was calculated as the baseline-corrected δ15NAA values using trophic (glutamic acid) and source (phenylalanine and glycine) amino acids. Variability was measured between individuals in their relative trophic position, but within-individual variability was low, suggesting that they fed at the same trophic level over these 2 yr of life. These novel δ15NAA data may therefore suggest individual, specialist harp seal foraging behaviour in sub-adults. Our findings show that compound-specific stable isotope signatures of archived, inert predator tissues can be used as tools for the retrospective reconstruction of trophic interactions on broad spatiotemporal scales.

Decade changes of the food web structure in tropical seagrass meadow: Implication of eutrophication effects

Seagrass meadows are experiencing worldwide declines mainly because of nutrient enrichment. However, knowledge about how eutrophication affects its food web structure is still limited. Based on decade-scale observations in a tropical seagrass meadow, we analysed primary producer structures, isotopic niche, and the diets of consumers respond to the decade nutrient enrichment. Through decades of nutrient enrichment, the biomass of epiphytes, particulate organic matter (POM), and macroalgae significantly increased. Correspondingly, the contribution of seagrass to the entire food web decreased significantly. Meanwhile, the isotopic niches of consumers have also become more shrinking, which reflects a more concentrated diet and higher predation pressure for consumers. These findings suggest that eutrophication leads to a significant shift in the structure of primary producers, which has changed food source availability and increased predation pressure, leading to a dietary shift in consumers and a simplified food web structure.

Trophic inferences of the gray triggerfish Balistes capriscus based on stable isotopes analyses, in the Colombian Caribbean

The demersal fish are a commercial resource of small-scale fisheries of northern Colombian Caribbean. Balistes capriscus is frequently and important in fishing landings, but this species has not economic value and its trophic ecology is unknown. Due to this, the diet was examined using the stomach contents and stable isotopes analysis. The individuals were collected with fish pots during two seasonal research expeditions in May and August of 2018. The δ15N and δ13C values were significantly different between size classes, indicating ontogenetic shifts in habitat use and consumption of prey. The δ13C shows that the triggerfish tends to feed in areas closer to the coast and his source of its origin can possibly change from the pelagic zone when they are juveniles, to the benthic trophic networks in his adulthood. The trophic position mean according to Bayesian inferences and Post's estimates was 2.98 and 3.03 and increased with size. Likewise, isotopic niche width corroborates the ontogenetic shift related with the maturity groups.

Competition drives the evolution of emergent neutrality in the dietary niches of mammalian herbivores

The coexistence of multiple species competing for a finite set of resources is a widely debated topic in community ecology. Species with strongly overlapping niches are expected to drive each other towards exclusion, but such species may also coexist if they have similar competitive abilities. This compromise can lead to a peculiar pattern of clumped coexistence, where multiple species share similar niches, leaving gaps open in the theoretically available niche space. Large mammal herbivores may be a good example of this, where species' dietary niches clump as either grazers, browsers, or intermediate-feeders, rather than being continuously distributed over the resource gradient. Here, we develop a model of such emergent neutrality amongst species competing for a set of predefined resources each distributed along a finite niche axis. The model is commensurate with stable isotope niches, thus allowing us to compare its predictions with empirical evidence for changes in community niche structure over evolutionary time. We present stable carbon and oxygen isotope evidence for six discontinuous Late Quaternary assemblages from the central interior of South Africa, demonstrating the emergence of a clumped niche structure from an initial pattern of strongly overlapping diets. We show that species tend to cluster on parts of the niche axis where resource availability is highest, mirroring the proliferation of grazer species as landscapes became more grass-dominated. However, the presence of competition means that species’ niches continue to differentiate, explaining the persistence of browser and intermediate-feeder species even in these open, predominantly treeless landscapes. These results highlight that species interactions are a necessary factor for robust inferences about the evolutionary dynamics of palaeocommunities.

Trophic Ecology of Juvenile Southern King Crab Associated with Kelp Forest: Evidence of Cannibalism

The southern king crab, Lithodes santolla, is a well-known predator/scavenger species during its adult phase but its feeding strategy in early stages is less studied. This information is important to understand their role in ecosystems and to improve fishery management (i.e., stock enhancement). Based on stomach contents and stable isotope analysis, we determined variation in the composition of diet and niche overlap in vagile and cryptic phase collected within and outside a kelp forest, Macrocystis pyrifera, of Aguila Bay at the Magellan Strait in Patagonia, Chile. Results of juvenile stomach content analysis showed 60% dissimilarity between cryptic and vagile juvenile phases. Algae dominated the volumetric contribution in cryptic juveniles while crustacean dominated the diet in vagile phase. Exoskeleton of other king crabs occurred in 43% of juveniles with crustaceans in their stomach. This fact confirms cannibalistic behavior in the wild in this species, which is consistent with findings in massive laboratory cultures. There was no evidence of isotopic niche shift between cryptic and vagile juvenile phases. Overlapping isotopic niches of different-sized juveniles suggest that they exploit similar food resources. However, vagile individuals occupy a higher trophic position than cryptic individuals, which could suggest a switch in dietary preference, from detritivorous/herbivory within kelp forests to omnivory outside of kelp forests, and an increase in the level of cannibalism in vagile juveniles.

Trophic niche overlap between round sardinella (Sardinella aurita) and sympatric pelagic fish species in the Western Mediterranean.

The northward expansion of round sardinella (Sardinella aurita) in the Mediterranean Sea, together with declines and fluctuations in biomass and landings of European sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) observed in recent decades, may suggest potential inter‐specific competition in the pelagic domain. The coexistence of sympatric zooplanktivorous fish species might therefore be exposed in part to trophic niche overlap and competition for food. Combining visual diet characterization under the microscope with DNA metabarcoding from stomach contents of fish collected in spring results show that predation on relatively large krill is equally important for sardinella than for the other two niche overlapping species. Furthermore, an important overlap is found in their isotopic niche, especially with anchovy, using nitrogen (δ15N) and carbon (δ13C) stable isotopes in muscle tissue. In fact, the three fish species are able to feed effectively in the whole prey size spectrum available during the sampled season, from the smallest diatoms and copepods to the larger prey (i.e., decapods and euphausiids), including fish larvae. Moreover, effective predation upon other large prey like siphonophores, which is observed only when multi‐proxy analyses in stomach contents are applied, might also be relevant in the diet of sardinella. The overlapping diet composition in spring, together with the effective use of food resource by sardinella, can be of special interest in potential future scenarios with warmer water temperature leading to lower zooplankton and/or higher jellyfish availability, where sardinella may take advantage over other species due to its feeding plasticity.

Trophic structure of fish communities in mangrove systems subject to different levels of anthropogenic intervention, Tropical Eastern Pacific, Colombia.

Mangroves are important ecosystems of tropical and subtropical shorelines. Anthropogenic activity decreases their habitat quality, affecting structural and functional trophic features. We hypothesized that higher levels of anthropogenic intervention generate diversity loss and modify the trophic structure of tropical mangrove fish communities. We compared the taxonomic and isotopic (δ13C/δ15N) composition, abundance, trophic position, and isotopic niche of fish communities from three mangrove systems with different anthropogenic intervention levels in the Colombian Pacific. Non-parametric statistical tests and a Bayesian approach were used to analyze data. A total of 1254 specimens belonging to 23 families, 25 genera, and 30 species were identified, presenting higher abundance (821) in moderate anthropogenic intervention level mangrove (Moderate-AIL), with high dominance of one species (Lilestolifera). The low anthropogenic intervention level mangrove (Low-AIL) was the second in abundance (291) but exhibited a greater number of species (23), while the high anthropogenic intervention level mangrove (High-AIL) presented the least abundance (142) and species number (17). The isotopic composition ​​reveals that Moderate and High-AIL mangroves presented enriched 13C and 15N compared to Low-AIL (~ 2 to 4 ‰). Mean trophic position (TP) of communities was slightly higher in the more intervened systems (~ 1 to 2 orders of magnitude), as well as in specific species (Centropomus spp.). Isotopic niche width (TA and SEAc) was greater in High-AIL (41.1 and 9.2), more than doubled compared to Moderate-AIL (33.0 and 4.1). In High-AIL isotopic niche width increased, indicating lesser availability of prey and basal resources. The results obtained in this study support the proposed hypothesis and, suggest that anthropogenic intervention modifies diversity and food webs dynamics, affecting the transfer of matter and energy from macrotidal tropical mangroves to coastal ecosystems. However, it is recommended to be careful concluding differences based exclusively on the anthropogenic intervention level, since it is widely documented that mangrove settings also influence the analyzed trophic parameters.

The response of coastal macrobenthic food-web structure to seasonal and regional variability in organic matter properties

The quantity and quality of organic matter (OM) available for macrobenthos vary on temporal and spatial scale, especially in coastal areas, where the seafloor is supplied by both seasonal pulses of primary production and terrestrial carbon transported by rivers. Human-induced environmental changes will alter OM transport to the seafloor, thus, it is of crucial importance to recognize the impacts of spatio-temporal OM variability on macrobenthic food webs. In this study, the seasonal variability of quantity and quality of OM and its effect on benthic food-web structure were studied at four locations along the southern coast of the Baltic Sea, characterized by similar species pools but different environmental settings and various scales of anthropogenic and riverine influence. Our study shows that temporal changes in the isotopic niche (δ13C and δ15N) of benthic invertebrates follow the patterns of quantity and quality of OM related to seasonal changes of pelagic primary production, riverine discharge of terrestrial OM and the input of anthropogenically enriched sources. In the semi-enclosed bay, exposed to intensive summer blooms, all feeding groups expressed lower δ15N values in autumn, suggesting the incorporation of δ15N-depleted cyanobacteria. At a location supplied by a higher proportion of OM from allochthonous sources (riverine discharge), omnivores occupied higher trophic levels, probably due to a higher abundance of meiobenthic prey. In contrast, at the open Polish coast, where the main food supply occurs during diatom spring bloom, the isotopic niche of omnivorous species showed much higher seasonal variability, underlining the importance of food availability for food-web diversity. Quick adaptation of benthic food-web structure to seasonal variations in OM properties and its modification by local conditions may indicate high plasticity of species feeding behavior that suggests a high capacity of benthic communities to mitigate ongoing changes in the marine environment, at least within the range observed today. Our results confirm that combination of spatial and temporal scales in sampling of the food-web structure is a good indicator of the ecosystem stability and function.