Tracing biogeochemical subsidies from glacier runoff into Alaska's coastal marine food webs

Nearly half of the freshwater discharge into the Gulf of Alaska originates from landscapes draining glacier runoff, but the influence of the influx of riverine organic matter on the trophodynamics of coastal marine food webs is not well understood. We quantified the ecological impact of riverine organic matter subsidies to glacier‐marine habitats by developing a multi‐trophic level Bayesian three‐isotope mixing model. We utilized large gradients in stable (δ¹³C, δ¹⁵N, δ²H) and radiogenic (Δ¹⁴C) isotopes that trace riverine and marine organic matter sources as they are passed from lower to higher trophic levels in glacial‐marine habitats. We also compared isotope ratios between glacial‐marine and more oceanic habitats. Based on isotopic measurements of potential baseline sources, ambient water and tissues of marine consumers, estimates of the riverine organic matter source contribution to upper trophic‐level species including fish and seabirds ranged from 12% to 44%. Variability in resource use among similar taxa corresponded to variation in species distribution and life histories. For example, riverine organic matter assimilation by the glacier‐nesting seabirds Kittlitz's murrelet (Brachyramphus brevirostris) was greater than that of the forest‐nesting marbled murrelet (B. marmoratus). The particulate and dissolved organic carbon in glacial runoff and near surface coastal waters was aged (12100–1500 years BP ¹⁴C‐age) but dissolved inorganic carbon and biota in coastal waters were young (530 years BP ¹⁴C‐age to modern). Thus terrestrial‐derived subsidies in marine food webs were primarily composed of young organic matter sources released from glacier ecosystems and their surrounding watersheds. Stable isotope compositions also revealed a divergence in food web structure between glacial‐marine and oceanic sites. This work demonstrates linkages between terrestrial and marine ecosystems, and facilitates a greater understanding of how climate‐driven changes in freshwater runoff have the potential to alter food web dynamics within coastal marine ecosystems in Alaska.     

Utilization of invasive tamarisk by salt marsh consumers

Plant invasions of coastal wetlands are rapidly changing the structure and function of these systems globally. Alteration of litter dynamics represents one of the fundamental impacts of an invasive plant on salt marsh ecosystems. Tamarisk species (Tamarix spp.), which extensively invade terrestrial and riparian habitats, have been demonstrated to enter food webs in these ecosystems. However, the trophic impacts of the relatively new invasion of tamarisk into marine ecosystem have not been assessed. We evaluated the trophic consequences of invasion by tamarisk for detrital food chains in the Tijuana River National Estuarine Research Reserve salt marsh using litter dynamics techniques and stable isotope enrichment experiments. The observations of a short residence time for tamarisk combined with relatively low C:N values indicate that tamarisk is a relatively available and labile food source. With an isotopic (¹⁵N) enrichment of tamarisk, we demonstrated that numerous macroinvertebrate taxonomic and trophic groups, both within and on the sediment, utilized ¹⁵N derived from labeled tamarisk detritus. Infaunal invertebrate species that took up no or limited ¹⁵N from labeled tamarisk (A. californica, enchytraeid oligochaetes, coleoptera larvae) occurred in lower abundance in the tamarisk-invaded environment. In contrast, species that utilized significant ¹⁵N from the labeled tamarisk, such as psychodid insects, an exotic amphipod, and an oniscid isopod, either did not change or occurred in higher abundance. Our research supports the hypothesis that invasive species can alter the trophic structure of an environment through addition of detritus and can also potentially impact higher trophic levels by shifting dominance within the invertebrate community to species not widely consumed. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Niche overlap and trophic resource partitioning of two sympatric batoids co‐inhabiting an estuarine system in southeast Australia

Elasmobranchs play an important role within the trophic structure of marine ecosystems, but there are relatively few studies published on the feeding ecology of these species. Reported herein is the feeding ecology and trophic resource partitioning of two sympatric batoid species, Urolophus cruciatus and Narcine tasmaniensis from southeast Australia. The diet of males and females of both species was similar, suggesting no sex‐specific dietary preferences. Ontogenetic changes in diet were observed from the diets of both species: as the body size increased, the proportion consumed of crustacea to polychaeta decreased. A relatively high degree of niche overlap (70%) was detected between the trophic resources of the two species. The way in which the predators partitioned the resources, however, was significantly different. U. cruciatus fed predominately on small benthic crustaceans (amphipods and decapods), while N. tasmaniensis displayed a preference towards Maldanidae polychaetes. Therefore, although U. cruciatus and N. tasmaniensis both feed predominately on benthic invertebrates, they specialise on different taxa. This trophic resource partitioning contributes to the biodiversity of the region by facilitating the coexistence of these sympatric species.     

Climate and fishing drive regime shifts in consumer‐mediated nutrient cycling in kelp forests

Globally, anthropogenic pressures are reducing the abundances of marine species and altering ecosystems through modification of trophic interactions. Yet, consumer declines also disrupt important bottom‐up processes, like nutrient recycling, which are critical for ecosystem functioning. Consumer‐mediated nutrient dynamics (CND) is now considered a major biogeochemical component of most ecosystems, but lacking long‐term studies, it is difficult to predict how CND will respond to accelerating disturbances in the wake of global change. To aid such predictions, we coupled empirical ammonium excretion rates with an 18‐year time series of the standing biomass of common benthic macroinvertebrates in southern California kelp forests. This time series of excretion rates encompassed an extended period of extreme ocean warming, disease outbreaks, and the abolishment of fishing at two of our study sites, allowing us to assess kelp forest CND across a wide range of environmental conditions. At their peak, reef invertebrates supplied an average of 18.3 ± 3.0 µmol NH₄⁺ m^?2 hr^?1 to kelp forests when sea stars were regionally abundant, but dropped to 3.5 ± 1.0 µmol NH₄⁺ m^?2 hr^?1 following their mass mortality due to disease during a prolonged period of extreme warming. However, a coincident increase in the abundance of the California spiny lobster, Palinurus interupptus (Randall, 1840), likely in response to both reduced fishing and a warmer ocean, compensated for much of the recycled ammonium lost to sea star mortality. Both lobsters and sea stars are widely recognized as key predators that can profoundly influence community structure in benthic marine systems. Our study is the first to demonstrate their importance in nutrient cycling, thus expanding their roles in the ecosystem. Climate change is increasing the frequency and severity of warming events, and rising human populations are intensifying fishing pressure in coastal ecosystems worldwide. Our study documents how these projected global changes can drive regime shifts in CND and fundamentally alter a critical ecosystem function.     

Trophic levels of teleost and elasmobranch species in the Persian Gulf and Oman Sea

Knowing the trophic level of marine organisms is essential to understanding their ecological role in the ecosystem and for quantifying the ecosystem effects of fishing to establish effective management of fishing resources. In comparison to other systems, information about the trophic level of marine organisms in the Persian Gulf and Oman Sea is very scarce. Here, the main aim was to estimate trophic level in these areas using all available diet information from different marine species using TrophLab software. The trophic level of 32 fish species was estimated with the available diet data. The trophic level ranged from 2.28 to 4.50. High trophic levels were found for Chorocentrus nudus (TL = 4.7), Saurida tumbil (TL = 4.6), Rhizoprionodon acutus (TL = 4.5), Torpedo sinuspersici (TL=4.5), Gymnura poecilura (TL = 4.5), Sphyraena putnamae (TL = 4.5) and Euthynnus affinis (TL = 4.5). In contrast, lower trophic levels were estimated for Tenualosa ilisha (TL = 2.28) and Sardinella sindensis (TL = 2.92). As expected, a positive correlation was found between the trophic level and body size, indicating changes in the diet due to variations in predatory capacities. The results of this study may be useful in the formulation of trophic indicators and modelling of the ecosystems.     

From mice to elephants: overturning the ‘one size fits all’ paradigm in marine plankton food chains

It is widely believed that consumer control is a weak regulator of marine phytoplankton communities. It remains unclear, however, why this should be the case when marine consumers routinely regulate their prey at higher trophic levels. One possibility is that the weak consumer control of phytoplankton communities results from the inability of field researchers to effectively account for consumer–prey trophic relationships operating at the scale of the plankton. We explored this issue by reviewing studies of trophic control in marine plankton. Experimental studies indicate that size is a critical determinant of feeding relationships among plankton. In sharp contrast, of the 51 field studies reviewed, 78% did not distinguish among the sizes or species of phytoplankton and their consumers, but instead assumed a general bulk phytoplankton–zooplankton trophic connection. Such an approach neglects the possibility that several trophic connections may separate the smallest phytoplankton (0.2 μm) from the larger zooplankton (~ 1000 μm), a remarkable size differential exceeding that between a mouse (~10 cm) and an elephant (~2500 cm). The size‐based approach we propose integrates theory, experiments and field observations and has the potential to greatly enhance our understanding of the causes and consequences of recently documented restructuring of plankton communities.     

Effect of nutrition on fatty acid profiles of riverine, lacustrine, and aquaculture-raised salmonids of pre-alpine habitats

We examined trophic positions and fatty acid concentrations of riverine, lacustrine, and aquaculture diet and fish in Austrian pre-alpine aquatic ecosystems. It was hypothesized that dietary fatty acid (FA) profiles largely influence the FA composition of the salmonids Salvelinus alpinus, Salmo trutta, and Oncorhynchus mykiss. We analyzed trophic positions using stable isotopes (δ¹⁵N) and tested for correlations with polyunsaturated fatty acid (PUFA) concentrations. Gut content analysis revealed benthos (rivers), pellets (aquaculture), and zooplankton (lakes) as the predominant diet source. Results of dorsal muscle tissues analysis showed that the omega-3 PUFA, docosahexaenoic acid (DHA; 22:6n − 3), was the mostly retained PUFA in all fish of all ecosystems, yet with the highest concentrations in S. alpinus from aquaculture (mean: 20 mg DHA/g dry weight). Moreover, we found that eicosapentaenoic acid (EPA; 20:5n − 3) in fish of natural habitats (rivers, lakes) was the second most abundant PUFA (3–5 mg/g DW), whereas aquaculture-raised fish had higher concentrations of the omega-6 linoleic acid (18:2n – 6; 9–11 mg/g DW) than EPA. In addition, PUFA patterns showed that higher omega-3/-6 ratios in aquacultures than in both riverine and lacustrine fish. Data of this pilot field study suggest that salmonids did not seem to directly adjust their PUFA to dietary PUFA profiles in either natural habitats or aquaculture and that some alterations of PUFA are plausible. Finally, we suggest that trophic positions of these freshwater salmonids do not predict PUFA concentrations in their dorsal muscle tissues.     

Global Trophic Position Comparison of Two Dominant Mesopelagic Fish Families (Myctophidae,Stomiidae) Using Amino Acid Nitrogen Isotopic Analyses

The δ¹⁵N values of organisms are commonly used across diverse ecosystems to estimate trophic position and infer trophic connectivity. We undertook a novel cross-basin comparison of trophic position in two ecologically well-characterized and different groups of dominant mid-water fish consumers using amino acid nitrogen isotope compositions. We found that trophic positions estimated from the δ¹⁵N values of individual amino acids are nearly uniform within both families of these fishes across five global regions despite great variability in bulk tissue δ¹⁵N values. Regional differences in the δ¹⁵N values of phenylalanine confirmed that bulk tissue δ¹⁵N values reflect region-specific water mass biogeochemistry controlling δ¹⁵N values at the base of the food web. Trophic positions calculated from amino acid isotopic analyses (AA-TP) for lanternfishes (family Myctophidae) (AA-TP ∼2.9) largely align with expectations from stomach content studies (TP ∼3.2), while AA-TPs for dragonfishes (family Stomiidae) (AA-TP ∼3.2) were lower than TPs derived from stomach content studies (TP∼4.1). We demonstrate that amino acid nitrogen isotope analysis can overcome shortcomings of bulk tissue isotope analysis across biogeochemically distinct systems to provide globally comparative information regarding marine food web structure.     

Spatial and temporal variabilities of δ<Superscript>13</Superscript>C and δ<Superscript>15</Superscript>N within lower trophic levels of a large lake: implications for estimating trophic relationships of consumers

Stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) often have unique values among lake habitats (e.g. benthic, littoral, pelagic), providing a widely used tool for measuring the structure and energy flow in aquatic food webs. However, there has been little recognition of the spatial and temporal variabilities of these isotopes within habitats of aquatic ecosystems. To address this, δ¹³C and δ¹⁵N were measured in seston, zebra mussels (Dreissena polymorpha) and young-of-year (YOY) yellow (Perca flavescens), and white perch (Morone americana) collected from four sites across the offshore habitat of the western basin of Lake Erie during June–September 2009. Values of δ¹³C and δ¹⁵N showed significant spatial and temporal variations, with month accounting for >50% of the variation, for both stable isotopes and all the species except seston. Such variation in isotope values has the potential to significantly influence or confound interpretation of stable isotopes in measures, such as trophic position (TP) which use lower trophic level organisms as their baseline. For example, TP was found to vary up to 0.7 for yellow and white perch (TP = δ¹⁵N_fish − δ¹⁵N_{zebra mussel}/diet-tissue fractionation factor) depending on the zebra mussel data used (e.g., from a different location or a different collection month). As the use of stable isotopes continues to move from qualitative to more quantitative measures of trophic structure, food web research must recognize the importance of stable isotopes' variability in lower trophic level organisms, especially in large lake systems.     

Investigation of mercury concentrations in fur of phocid seals using stable isotopes as tracers of trophic levels and geographical regions

Recent studies have shown that the complementary analysis of mercury (Hg) concentrations and stable isotopic ratios of nitrogen (δ¹⁵N) and carbon (δ¹³C) can be useful for investigating the trophic influence on the Hg exposure and accumulation in marine top predators. In this study, we propose to evaluate the interspecies variability of Hg concentrations in phocids from polar areas and to compare Hg bioaccumulation between both hemispheres. Mercury concentrations, δ¹⁵N and δ¹³C were measured in fur from 85 individuals representing 7 phocidae species, a Ross seal (Ommatophoca rossii), Weddell seals (Leptonychotes weddellii), crabeater seals (Lobodon carcinophagus), harbour seals (Phoca vitulina), grey seals (Halichoerus grypus), ringed seals (Pusa hispida) and a bearded seal (Erignathus barbatus), from Greenland, Denmark and Antarctica. Our results showed a positive correlation between Hg concentrations and δ¹⁵N values among all individuals. Seals from the Northern ecosystems displayed greater Hg concentrations, δ¹⁵N and δ¹³C values than those from the Southern waters. Those geographical differences in Hg and stable isotopes values were likely due to higher environmental Hg concentrations and somewhat greater number of steps in Arctic food webs. Moreover, dissimilarities in feeding habits among species were shown through δ¹⁵N and δ¹³C analysis, resulting in an important interspecific variation in fur Hg concentrations. A trophic segregation was observed between crabeater seals and the other species, resulting from the very specific diet of krill of this species and leading to the lowest observed Hg concentrations.     

Experimental test of the ecosystem impacts of the keystone predator Triops cancriformis (Branchiopoda: Notostraca) in temporary ponds

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Quantitative evaluation of marine protein contribution in ancient diets based on nitrogen isotope ratios of individual amino acids in bone collagen: An investigation at the Kitakogane Jomon site

Nitrogen stable isotopes analysis of individual bone collagen amino acids was applied to archeological samples as a new tool for assessing the composition of ancient human diets and calibrating radiocarbon dates. We used this technique to investigate human and faunal samples from the Kitakogane shell midden in Hokkaido, Japan (5,300–6,000 cal BP). Using compound‐specific nitrogen isotope analysis of individual amino acids, we aimed to estimate i) the quantitative contribution of marine and terrestrial protein to the human diet, and ii) the mean trophic level (TL) from which dietary protein was derived from marine ecosystems. Data were interpreted with reference to the amino acid trophic level (TL_AA) model, which uses empirical amino acid δ¹⁵N from modern marine fauna to construct mathematical equations that predict the trophic position of organisms. The TL_AA model produced realistic TL estimates for the Kitakogane marine animals. However, this model was not appropriate for the interpretation of human amino acid δ¹⁵N, as dietary protein is derived from both marine and terrestrial environments. Hence, we developed a series of relevant equations that considered the consumption of dietary resources from both ecosystems. Using these equations, the mean percentage of marine protein in the Kitakogane human diet was estimated to be 74%. Although this study is one of the first systematic investigations of amino acid δ¹⁵N in archeological bone collagen, we believe that this technique is extremely useful for TL reconstruction, palaeodietary interpretation, and the correction of marine reservoir effects for radiocarbon dating. Am J Phys Anthropol 143:31–40, 2010. © 2010 Wiley‐Liss, Inc.     

Interpopulation trophic niches and ontogenetic shifts of a mangrove fish predator

Fish trophic niches reflect important ecological interactions and provide insight into the structure of mangrove food webs. Few studies have been conducted in mangrove fish predators to investigate interpopulation trophic niches and ontogenetic shifts. Using stable isotope analysis and two complementary approaches, the authors investigated trophic niche patterns within and between two ontogenetic groups (juveniles and sub-adults) of a generalist predator (Acentrogobius viridipunctatus) in four mangroves with heterogeneous environmental conditions (e.g., tidal regimes, salinity fluctuations and mangrove tree community). The authors hypothesized that the trophic niche between populations would vary regionally and trophic position would increase consistently from juvenile to sub-adult stages. The results revealed that both δ¹³C and δ¹⁵N values varied greatly across populations and between ontogenetic groups, and complex spatio-ontogenetic variations were expressed by Layman's metrics. They also found some niche separation in space, which is most likely related to resource availability in spatially diverse ecosystems. In addition, trophic niche position increased consistently from juveniles to sub-adults, indicating ontogenetic feeding shifts. The isotopic plasticity index and Fulton's condition index also showed significant spatial-ontogenetic variation, which is consistent with optimal foraging theory. The findings highlight that trophic plasticity has a high adaptive value for mangrove fish predators in dynamic ecosystems.     

Disciplinary reporting affects the interpretation of climate change impacts in global oceans

Climate change is affecting marine ecosystems, but different investigative approaches in physical, chemical, and biological disciplines may influence interpretations of climate‐driven changes in the ocean. Here, we review the ocean change literature from 2007 to 2012 based on 461 of the most highly cited studies in physical and chemical oceanography and three biological subdisciplines. Using highly cited studies, we focus on research that has shaped recent discourse on climate‐driven ocean change. Our review identified significant differences in spatial and temporal scales of investigation among disciplines. Physical/chemical studies had a median duration of 29 years (n = 150) and covered the greatest study areas (median 1.41 × 10⁷ km², n = 148). Few biological studies were conducted over similar spatial and temporal scales (median 8 years, n = 215; median 302 km², n = 196), suggesting a more limited ability to separate climate‐related responses from natural variability. We linked physical/chemical and biological disciplines by tracking studies examining biological responses to changing ocean conditions. Of the 545 biological responses recorded, a single physical or chemical stressor was usually implicated as the cause (59%), with temperature as the most common primary stressor (44%). The most frequently studied biological responses were changes in physiology (31%) and population abundance (30%). Differences in disciplinary studies, as identified in this review, can ultimately influence how researchers interpret climate‐related impacts in marine systems. We identified research gaps and the need for more discourse in (1) the Indian and other Southern Hemisphere ocean basins; (2) research themes such as archaea, bacteria, viruses, mangroves, turtles, and ocean acidification; (3) physical and chemical stressors such as dissolved oxygen, salinity, and upwelling; and (4) adaptive responses of marine organisms to climate‐driven ocean change. Our findings reveal that highly cited biological studies are rarely conducted on scales that match those of physical and chemical studies. Rather, we suggest a need for measuring responses at biologically relevant scales.     

On the control of HAB species using low biosurfactant concentrations

Biosurfactants have been suggested as a method to control harmful algal blooms (HABs), but warrant further and more in-depth investigation. Here we have investigated the algicidal effect of a biosurfactant produced by the bacterium Pseudomonas aeruginosa on five diverse marine and freshwater HAB species that have not been tested previously. These include Alexandrium minutum (Dinophycaee), Karenia brevis (Dinophyceae), Pseudonitzschia sp. (Bacillariophyceae), in marine ecosystems, and Gonyostomum semen (Raphidophyceae) and Microcystis aeruginosa (Cyanophyecae) in freshwater. We examined not only lethal but also sub-lethal effects of the biosurfactant. In addition, the effect of the biosurfactant on Daphnia was tested. Our conclusions were that very low biosurfactant concentrations (5 μg mL⁻¹) decreased both the photosynthesis efficiency and the cell viability and that higher concentrations (50 μg mL⁻¹) had lethal effects in four of the five HAB species tested. The low concentrations employed in this study and the diversity of HAB genera tested suggest that biosurfactants may be used to either control initial algal blooms without causing negative side effect to the ecosystem, or to provoke lethal effects when necessary.     

Predicting the contributions of novel marine prey resources from angling and anadromy to the diet of a freshwater apex predator

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Evidence of rapid shifts in the trophic base of lotic predators using experimental dietary manipulations and assimilation-based analyses

Assimilation-based techniques such as stoichiometric analysis, bulk tissue stable isotope analysis (SIA), fatty acid (FA) profiling and compound-specific SIA of FAs can be used to resolve ambiguities in consumer-resource relationships, but comparisons of their effectiveness are lacking. Feeding trials and concurrent application of these techniques were used to investigate the trophic base of two shrimps from Hong Kong streams: the atyid Caridina cantonensis, which is a primary consumer, and predatory Macrobrachium hainanense (Palaemonidae). Leaf litter and periphyton were fed to C. cantonensis (CC-LF and CC-PF, respectively) reared in the laboratory for 2 months, when C. cantonensis, that had fed on a mixed diet (CC-WC), were collected from the field. Atyids from each group (CC-LF, CC-PF and CC-WC) were fed to M. hainanense (MH-L, MH-P and MH-W, respectively) during a further 2-month trial, at the end of which M. hainanense were also collected from the field (MH-R). FA biomarkers present in CC-WC and CC-PF indicated that C. cantonensis depended primarily on autochthonous foods, and FA profiles of CC-WC were distinct from those of CC-LF. Differences in C/N ratios and isotope signatures of leaf litter and periphyton were not reflected in tissues of atyids or palaemonid predators. FA profiles of M. hainanense groups were similar, but FA stable C isotope ratio (δ¹³C) signatures of MH-R and MH-W were distinct from those of MH-L and leaf litter. FA δ¹³C signatures of MH-R were similar to those of MH-P and MH-W, indicating that autochthonous resources constituted the trophic base of production for this predator. This is the first study using compound-specific SIA to study stream food chains. Compound-specific SIA and FA profiling allowed accurate elucidation of consumer-resource relationships that were not revealed by stoichiometry or bulk tissue SIA. Compound-specific SIA was particularly sensitive for detecting rapid shifts in the predator trophic base. This tool will have wide applicability for investigating food webs in a range of ecosystems. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Trophic ecology of three stingrays (Myliobatoidei: Dasyatidae) off the Brazilian north-eastern coast: Habitat use and resource partitioning

Understanding the ecological role of species with overlapping distributions is central to inform ecosystem management. Here we describe the diet, trophic level and habitat use of three sympatric stingrays, Hypanus guttatus, H. marianae and H. berthalutzae, through combined stomach content and stable isotope (δ¹³C and δ¹⁵N) analyses. Our integrated approach revealed that H. guttatus is a mesopredator that feeds on a diverse diet of benthic and epibenthic marine and estuarine organisms, principally bivalve molluscs, Alpheus shrimp and teleost fishes. Isotopic data supported movement of this species between marine and estuarine environments. H. berthalutzae is also a marine generalist feeder, but feeds primarily on teleost fishes and cephalopods, and consequently occupies a higher trophic level. In contrast, H. marianae is a mesopredator specialized on shrimps and polychaetas occurring only in the marine environment and occupying a low niche breadth. While niche overlap occurred, the three stingrays utilized the same prey resources at different rates and occupied distinct trophic niches, potentially limiting competition for resources and promoting coexistence. These combined data demonstrate that these three mesopredators perform different ecological roles in the ecosystems they occupy, limiting functional redundancy.     

Unchartered waters: Climate change likely to intensify infectious disease outbreaks causing mass mortality events in marine mammals

Infectious disease emergence has increased significantly over the last 30 years, with mass mortality events (MMEs) associated with epizootics becoming increasingly common. Factors influencing these events have been widely studied in terrestrial systems, but remain relatively unexplored in marine mammals. Infectious disease‐induced MMEs (ID MMEs) have not been reported ubiquitously among marine mammal species, indicating that intrinsic (host) and/or extrinsic (environmental) ecological factors may influence this heterogeneity. We assess the occurrence of ID MMEs (1955–2018) across extant marine mammals (n = 129) in relation to key life‐history characteristics (sociality, trophic level, habitat breadth) and environmental variables (season, sea surface temperature [SST] anomalies, El Niño occurrence). Our results show that ID MMEs have been reported in 14% of marine mammal species (95% CI 9%–21%), with 72% (n = 36; 95% CI 56%–84%) of these events caused predominantly by viruses, primarily morbillivirus and influenza A. Bacterial pathogens caused 25% (95% CI 14%–41%) of MMEs, with only one being the result of a protozoan pathogen. Overall, virus‐induced MMEs involved a greater number of fatalities per event compared to other pathogens. No association was detected between the occurrence of ID MMEs and host characteristics, such as sociality or trophic level, but ID MMEs did occur more frequently in semiaquatic species (pinnipeds) compared to obligate ocean dwellers (cetaceans; χ² = 9.6, p = .002). In contrast, extrinsic factors significantly influenced ID MMEs, with seasonality linked to frequency (χ² = 19.85, p = .0002) and severity of these events, and global yearly SST anomalies positively correlated with their temporal occurrence (Z = 3.43, p = 2.7e‐04). No significant association was identified between El Niño and ID MME occurrence (Z = 0.28, p = .81). With climate change forecasted to increase SSTs and the frequency of extreme seasonal weather events, epizootics causing MMEs are likely to intensify with significant consequences for marine mammal survival.     

Phylogeography and genetic population structure of Caribbean sharpnose shark <Emphasis Type="Italic">Rhizoprionodon porosus</Emphasis>

Sharks of the genus Rhizoprionodon are among the most important predators along the coastal marine ecosystems, and they represent an important economic resource for the small-scale fisheries. To properly manage and conserve exploited shark species, detailed analyses of their population structure are needed. To evaluate the gene flow and levels of the genetic diversity among populations of the Caribbean sharpnose shark R. porosus, we identified the nucleotide sequence based on collections (n = 321 specimens) from 10 different areas, including the Caribbean Sea and several locations along the entire Brazilian coast. The analysis of 802 nucleotides from the mitochondrial DNA control region revealed 53 distinct haplotypes. The majority of these haplotypes were restricted to their collection locales with a significant genetic structure detected among the overall populations (Φ _ST  = 0.237, P < 0.0001). The data suggest a population division with two distinct management units in the western Atlantic. These management units are likely separated by the Equatorial Current. The strong population structure in R. porosus indicates that regional populations, if depleted, will not recover swiftly through immigration.