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.     

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.     

Mating system, multiple paternity and effective population size in the endemic flatback turtle (Natator depressus) in Australia

In recent years, genetic studies have been used to investigate mating systems of marine turtles, but to date no such research has been conducted on the flatback turtle (Natator depressus). This study investigates paternity of flatback turtle clutches at two rookeries in Queensland, Australia; Peak Island (Keppel Bay), and Mon Repos (Bundaberg). In the 2004–2005 nesting season, tissue samples were taken from either single or multiple clutches (n = 16) of nesting females (n = 8) representing a sampling effort ranging from 25% to 50% offspring per nest. Determination of the extent of multiple paternity was done using a comparative approach that included initial inferences based on observed alleles, Chi-square tests for deviations from Mendelian expectations, and three software programs (PARENTAGE1.0, GERUD2.0 and MER3.0). Results varied depending on the approach, but by calculating a consensus value of the output from these different methods, the null hypothesis of single paternity could be rejected in at least 11 of the 16 clutches (69%). Multiple paternity was thus observed in the clutches of six of nine females (67%), with two or three fathers being the most likely outcome. Analyses of successive clutches illustrated that paternal contribution to clutch fertilization can vary through time, as observed for two females. This first evidence regarding the mating system of flatback turtles indicates that multiple paternity is common in this species and that the observed frequency of multiple paternity is among the higher values reported in marine turtle species. Application of these results to estimates of effective population size (N _e) suggests that population size may have been relatively stable over long periods. Continued monitoring of population dynamics is recommended to ensure that future changes in the east coast can be detected.     

Non‐marine turtle plays important functional roles in Indonesian ecosystems

The Southeast Asian box turtle (Cuora amboinensis) is numerically the most important turtle exported from Indonesia. Listed as Vulnerable by the IUCN, this turtle is heavily harvested and exported for food and traditional medicine in China and for the pet trade primarily in the United States, Europe, and Japan. Despite its significance in global markets, relatively little is known about the species’ ecology or importance to ecosystems. We conducted our research in a national park in Sulawesi, Indonesia, and our objectives were to quantify trophic breadth, capacity for seed dispersal between aquatic and terrestrial ecosystems, and whether ingestion of seeds by C. amboinensis enhances germination. We obtained diet samples from 200 individual turtles and found that the species is omnivorous, exhibiting an ontogenetic shift from more carnivorous to more omnivorous. Both subadults and adults scavenged on other vertebrates. In a seed passage experiment, turtles passed seeds for 2?9 days after ingestion. Radio‐tracked turtles moved, on average, about 35 m per day, indicating that seeds from ingested fruits, given seed passage durations, could be dispersed 70?313 m from the parent tree and potentially between wetland and upland ecosystems. In a seed germination experiment, we found that ingestion of seeds by turtles enhanced germination, as compared with control seeds, for four of six plant species tested. Of these, two are common in the national park, making up a significant proportion of plant biomass in lowland swamp forest and around ephemeral pools in savanna, and are highly valued outside of the park for their lumber for construction of houses, furniture, and boats. Protection of C. amboinensis populations may be important for maintaining trophic linkages that benefit biodiversity, communities, and local economies.     

Species richness and similarity of metazoan parasite communities in three species of leatherjacket (Oligoplites: Pisces: Carangidae) from the Pacific coast of Mexico

Species richness and similarity in metazoan parasite communities of fishes can be influenced by several biotic (age, body size, vagility, feeding and social behavior, among others), and local abiotic (temperature, salinity, etc.) factors. The parasite communities of three species of Oligoplites, marine fishes from the Pacific coast of Mexico, were quantified and analyzed. Four hundred sixty‐eight leatherjackets (O. altus, n=94; O. saurus, n=260; and O. refulgens, n=114) were collected from February 2016 to June 2017 from five locations. Twenty‐eight species of metazoan parasites were recovered and identified: four species of Monogenea (adults), nine of Digenea (seven adults and two metacercariae); two of Cestoda (larvae); four of Nematoda (two adults and two larvae); four of Acanthocephala (two adults, one juvenile, and one cystacanth); four of Copepoda; and one Pentastomida (larvae). At the component community level, species richness ranged from 9 in O. saurus to 19 in O. altus. Different species of helminth dominated the component communities of each species of host. Community composition and species richness of parasites differed among the three species of host, locations, and sampling years. Host feeding behavior, body size, and vagility had the most influence on these differences.     

Large‐scale introduction of the Indo‐Pacific damselfish Abudefduf vaigiensis into Hawai'i promotes genetic swamping of the endemic congener A. abdominalis

Hybridization in the ocean was once considered rare, a process prohibited by the rapid evolution of intrinsic reproductive barriers in a high‐dispersal medium. However, recent genetic surveys have prompted a reappraisal of marine hybridization as an important demographic and evolutionary process. The Hawaiian Archipelago offers an unusual case history in this arena, due to the recent arrival of the widely distributed Indo‐Pacific sergeant (Abudefduf vaigiensis), which is hybridizing with the endemic congener, A. abdominalis. Surveys of mtDNA and three nuclear loci across Hawai'i (N = 396, Abudefduf abdominalis and N = 314, A. vaigiensis) reveal that hybridization is significantly higher in the human‐perturbed southeast archipelago (19.8%), tapering off to 5.9% in the pristine northwest archipelago. While densities of the two species varied throughout Hawai'i, hybridization was highest in regions with similar species densities, contradicting the generalization that the rarity of one species promotes interspecific mating. Our finding of later generation hybrids throughout the archipelago invokes the possibility of genetic swamping of the endemic species. Exaptation, an adaptation with unintended consequences, may explain these findings: the endemic species has transient yellow coloration during reproduction, whereas the introduced species has yellow coloration continuously as adults, in effect a permanent signal of reproductive receptivity. Haplotype diversity is higher in Hawaiian A. vaigiensis than in our samples from the native range, indicating large‐scale colonization almost certainly facilitated by the historically recent surge of marine debris. In this chain of events, marine debris promotes colonization, exaptation promotes hybridization, and introgression invokes the possible collapse of an endemic species.     

Spatial patterns and predictors of trophic control in marine ecosystems

A key question in ecology is under which conditions ecosystem structure tends to be controlled by resource availability vs. consumer pressure. Several hypotheses derived from theory, experiments and observational field studies have been advanced, yet a unified explanation remains elusive. Here, we identify common predictors of trophic control in a synthetic analysis of 52 observational field studies conducted within marine ecosystems across the Northern Hemisphere and published between 1951 and 2014. Spatial regression analysis of 45 candidate variables revealed temperature to be the dominant predictor, with unimodal effects on trophic control operating both directly (r² = 0.32; P < 0.0001) and indirectly through influences on turnover rate and quality of primary production, biodiversity and omnivory. These findings indicate that temperature is an overarching determinant of the trophic dynamics of marine ecosystems, and that variation in ocean temperature will affect the trophic structure of marine ecosystems through both direct and indirect mechanisms.     

Trophic role of demersal mesopredators on rocky reefs in an equatorial Atlantic Ocean island

The decrease in the number of sharks around Saint Peter and Saint Paul Archipelago (SPSPA) may impact food web structure. We investigated trophic relationships in the shallow rocky reefs of the SPSPA using stable isotopes and stomach contents with a particular focus on three abundant mesopredators: Caranx lugubris, Enchelycore nigricans and Muraena pavonina. Food web structure was described using samples of the most abundant basal resources, fishes and invertebrates, which were collected in April and October 2012. Individuals of the three focal species (n = 138: C. lugubris, n = 56; E. nigricans, n = 18; M. pavonina, n = 64) were collected during four expeditions to SPSPA (April and October of 2011 and 2012). Results suggest that this shallow water food web is supported by trophic pathways originating from benthic resources. Stable isotope data suggest potential competitive interactions between the whitespot moray and the other two mesopredators. Conversely, stomach content data suggest little niche overlap in the three focal species, but these data must be interpreted carefully because of the small sample sizes and restricted temporal sampling windows. All three mesopredators have a significant, albeit weak, relationship between body size and δ¹⁵N, suggesting ontogenetic diet shifts. These data contribute baseline information to assess shifts in food web structure that may stem from top predator decline in this unique ecosystem.     

Spawning period of Mediterranean marine fishes

We collected all available information (i.e. international and local journals, conference proceedings, theses, technical reports) on the spawning season (n = 511 stocks, 168 species), gonadosomatic index (n = 237 stocks, 81 species) and sex ratio (n = 97 stocks, 68 species) of Mediterranean marine fish. The 511 stocks represented 20 orders (most were Perciformes, 283 stocks) and 65 families (most were Sparidae: 17 species and 63 stocks). Overall, 346 stocks (128 species) spawned between April and August, 139 stocks (60 species) between September and March, while the remaining 26 stocks (13 species) were all-year-round spawners. In addition, 174 stocks (34.1%) were characterised by an extended (>4 months) spawning season, but, for most stocks (332 stocks, 64.4%), spawning duration ranged from 2 to 4 months inclusive. Regardless of the onset and the duration of spawning, the spawning period of 284 and 287 stocks included June and July, respectively, indicating that most Mediterranean species are summer spawners. Female gonadosomatic index ranged between 0.06 and 37 (mean ± SE = 8.55 ± 0.647, n = 95) and was significantly higher (t-test: t = 5.58, P < 0.001) than the corresponding male one, which ranged between 0.06 and 30 (mean ± SE = 4.21 ± 0.431, n = 95). Congeneric species that occupied the same area and share the same requirements exhibited successive and non-overlapping spawning (e.g. Sparidae in the Adriatic Sea, Mugilidae in the Ionian Sea and Tunisian waters). The knowledge of the spawning period coupled with information on spawning and nursery grounds and detailed knowledge of mating systems, social interactions, maturity and fecundity may be very useful for fisheries management.     

Insights into marine otter (Lontra felina) distribution along the Peru coastline

The marine otter (Lontra felina) has a patchy distribution associated with rocky coastlines along the Pacific coast of South America. In Peru marine otters are found from La Libertad (8°04′S) to Tacna (18°09′S), however, few studies have assessed its population and conservation status. To assess marine otters' current distribution along the Peru coastline, we conducted visual surveys and collected environmental characteristics such as human presence and habitat type. We surveyed 20 locations from five regions where otter presence was based on signs of detection (spraints, food leftovers, tracks, or direct observations). In addition, data on human presence, habitat type, and geographic location were also collected. Across the 20 locations, 268 sections were scanned, and marine otters were detected in 90% (n = 18) of locations and in 19% (n = 52) of sections. Spraints were the most frequent sign detected while direct observations occurred only in seven locations. Our analysis indicates habitat features play an important role in marine otter presence, with habitats with large rocks providing preferred conditions. Our study provides information on marine otter distribution along the Peru coastline that can assist in the identification of locations for focused conservation initiatives and strategies, which should be coordinated among regions to strengthen their design and implementation.     

Resilience of marine turtle regional management units to climate change

Enhancing species resilience to changing environmental conditions is often suggested as a climate change adaptation strategy. To effectively achieve this, it is necessary first to understand the factors that determine species resilience, and their relative importance in shaping the ability of species to adjust to the complexities of environmental change. This is an extremely challenging task because it requires comprehensive information on species traits. We explored the resilience of 58 marine turtle regional management units (RMUs) to climate change, encompassing all seven species of marine turtles worldwide. We used expert opinion from the IUCN‐SSC Marine Turtle Specialist Group (n = 33 respondents) to develop a Resilience Index, which considered qualitative characteristics of each RMU (relative population size, rookery vulnerability, and genetic diversity) and non climate‐related threats (fisheries, take, coastal development, and pollution/pathogens). Our expert panel perceived rookery vulnerability (the likelihood of functional rookeries becoming extirpated) and non climate‐related threats as having the greatest influence on resilience of RMUs to climate change. We identified the world's 13 least resilient marine turtle RMUs to climate change, which are distributed within all three major ocean basins and include six of the world's seven species of marine turtle. Our study provides the first look at inter‐ and intra‐species variation in resilience to climate change and highlights the need to devise metrics that measure resilience directly. We suggest that this approach can be widely used to help prioritize future actions that increase species resilience to climate change.     

DNA metabarcoding assays reveal a diverse prey assemblage for Mobula rays in the Bohol Sea,Philippines

Diet studies provide base understanding of trophic structure and are a valuable initial step for many fields of marine ecology, including conservation and fisheries biology. Considerable complexity in marine trophic structure can exist due to the presence of highly mobile species with long life spans. Mobula rays are highly mobile, large, planktivorous elasmobranchs that are frequently caught either directly or as bycatch in fisheries, which, combined with their conservative life history strategy, makes their populations susceptible to decline in intensely fished regions. Effective management of these iconic and vulnerable species requires an understanding of the diets that sustain them, which can be difficult to determine using conventional sampling methods. We use three DNA metabarcode assays to identify 44 distinct taxa from the stomachs (n = 101) of four sympatric Mobula ray species (Mobula birostris, Mobula tarapacana, Mobula japanica, and Mobula thurstoni) caught over 3 years (2013–2015) in a direct fishery off Bohol in the Philippines. The diversity and incidence of bony fishes observed in ray diets were unprecedented. Nevertheless, rays showed dietary overlap, with krill (Euphausia) dominating their diet. Our results provide a more detailed assessment of sympatric ray diets than was previously described and reveal the complexity that can exist in food webs at critical foraging habitats.     

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.     

Length‐weight relationships for three species of common scorpaenoids from Singapore

This study provides length‐weight relationships (LWR) for three common marine species collected from Singapore, a small tropical island country in southeast Asia, where monthly collections using seine netting and fish trapping were performed at six sites from January to December 2010. The LWRs of these three species were BW = 0.0348 SL^3.002 (n = 305, r² = .9747) for Paracentropogon longispinis, BW = 0.0315 SL^3.039 (n = 104, r  = .9798) for Trachicephalus uranoscopus and BW = 0.0651 SL^3.021 (n = 70, r² = .9601) for Synanceja horrida respectively.     

Using the otolith sulcus to aid in prey identification and improve estimates of prey size in diet studies of a piscivorous predator

Diet studies are fundamental for understanding trophic connections in marine ecosystems. In the southeastern US, the common bottlenose dolphin Tursiops truncatus is the predominant marine mammal in coastal waters, but its role as a top predator has received little attention. Diet studies of piscivorous predators, like bottlenose dolphins, start with assessing prey otoliths recovered from stomachs or feces, but digestive erosion hampers species identification and underestimates fish weight (FW). To compensate, FW is often estimated from the least affected otoliths and scaled to other otoliths, which also introduces bias. The sulcus, an otolith surface feature, has a species‐specific shape of its ostium and caudal extents, which is within the otolith edge for some species. We explored whether the sulcus could improve species identification and estimation of prey size using a case study of four sciaenid species targeted by fisheries and bottlenose dolphins in North Carolina. Methods were assessed first on otoliths from a reference collection (n = 421) and applied to prey otoliths (n = 5,308) recovered from 120 stomachs of dead stranded dolphins. We demonstrated in reference‐collection otoliths that cauda to sulcus length (CL:SL) could discriminate between spotted seatrout (Cynoscion nebulosus) and weakfish (Cynoscion regalis) (classification accuracy = 0.98). This method confirmed for the first time predation of spotted seatrout by bottlenose dolphins in North Carolina. Using predictive models developed from reference‐collection otoliths, we provided evidence that digestion affects otolith length more than sulcus or cauda length, making the latter better predictors. Lastly, we explored scenarios of calculating total consumed biomass across degrees of digestion. A suggested approach was for the least digested otoliths to be scaled to other otoliths iteratively from within the same stomach, month, or season as samples allow. Using the otolith sulcus helped overcome challenges of species identification and fish size estimation, indicating their potential use in other diet studies.     

Extreme rainfall events and cooling of sea turtle clutches: Implications in the face of climate warming

Understanding how climate change impacts species and ecosystems is integral to conservation. When studying impacts of climate change, warming temperatures are a research focus, with much less attention given to extreme weather events and their impacts. Here, we show how localized, extreme rainfall events can have a major impact on a species that is endangered in many parts of its range. We report incubation temperatures from the world's largest green sea turtle rookery, during a breeding season when two extreme rainfall events occurred. Rainfall caused nest temperatures to drop suddenly and the maximum drop in temperature for each rain‐induced cooling averaged 3.6°C (n = 79 nests, min = 1.0°C, max = 7.4°C). Since green sea turtles have temperature‐dependent sex determination, with low incubation temperatures producing males, such major rainfall events may have a masculinization effect on primary sex ratios. Therefore, in some cases, extreme rainfall events may provide a “get‐out‐of‐jail‐free card” to avoid complete feminization of turtle populations as climate warming continues.     

Human insulinotropic response to oral ingestion of native and hydrolysed whey protein

The insulinotropic response to the ingestion of whey protein and whey protein hydrolysate, independent of carbohydrate, is not known. This study examined the effect of protein hydrolysis on the insulinotropic response to the ingestion of whey protein. Sixteen healthy males ingested a 500 mL solution containing either 45 g of whey protein (WPI) or whey protein hydrolysate (WPH). The estimated rate of gastric empting was not altered by hydrolysis of the protein [18 (3) vs. 23 (3) min, n = 16; P = 0.15]. Maximum plasma insulin concentration (C _max) occurred later (40 vs. 60 min) and was 28% [234 (26) vs. 299 (31) mM, P = 0.018] greater following ingestion of the WPH compared to the WPI leading to a 43% increase [7.6 (0.9) vs. 10.8 (2.6) nM, P = 0.21] in the AUC of insulin for the WPH. Of the amino acids with known insulinotropic properties only Phe demonstrated a significantly greater maximal concentration [C _max; 65 (2) vs. 72 (3) μM, n = 16; P = 0.01] and increase (+22%) in AUC following ingestion of the WPH. In conclusion, ingestion of whey protein is an effective insulin secretagogue. Hydrolysis of whey protein prior to ingestion augments the maximal insulin concentration by a mechanism that is unrelated to gastric emptying of the peptide solution.     

Evidence of anthropogenic trauma in marine mammals stranded along the central California coast, 2003–2015

A total of 11,162 stranded marine mammals was admitted to a rehabilitation center on the central California coast between January 2003 and September 2015. Six hundred seventeen animals (6%) had evidence of anthropogenic trauma (AT). California sea lions comprised the majority (83%) of AT cases, particularly by entanglement in marine debris (n = 277) and gunshot injuries (n = 165). Guadalupe fur seals had the highest prevalence of entanglement in marine debris. Cetaceans were primarily affected by boat collisions (n = 19). The highest numbers of overall strandings were recorded in 2009 (n = 1,690) and 2015 (n = 1,666); 2009 also had the highest total number (n = 137) and prevalence (8%) of AT cases. Prevalence of fishing tackle cases increased compared to similar data from 1986 to 1998 while prevalence of gunshot cases decreased, and other causes remained static. Cases of fisheries interactions were further examined and characterized, and when direct fisheries interactions were separated from other causes of AT, fisheries interactions accounted for 50% (n = 310) of all AT cases during the study period. Direct fisheries interactions were the most common type of AT observed among stranded marine mammals in central California. Tracking AT trends is important to further understand possible causes and inform mitigation efforts.     

Asymmetric oceanographic processes mediate connectivity and population genetic structure,as revealed by RADseq,in a highly dispersive marine invertebrate (Parastichopus californicus)

Marine populations are typically characterized by weak genetic differentiation due to the potential for long‐distance dispersal favouring high levels of gene flow. However, strong directional advection of water masses or retentive hydrodynamic forces can influence the degree of genetic exchange among marine populations. To determine the oceanographic drivers of genetic structure in a highly dispersive marine invertebrate, the giant California sea cucumber (Parastichopus californicus), we first tested for the presence of genetic discontinuities along the coast of North America in the northeastern Pacific Ocean. Then, we tested two hypotheses regarding spatial processes influencing population structure: (i) isolation by distance (IBD: genetic structure is explained by geographic distance) and (ii) isolation by resistance (IBR: genetic structure is driven by ocean circulation). Using RADseq, we genotyped 717 individuals from 24 sampling locations across 2,719 neutral SNPs to assess the degree of population differentiation and integrated estimates of genetic variation with inferred connectivity probabilities from a biophysical model of larval dispersal mediated by ocean currents. We identified two clusters separating north and south regions, as well as significant, albeit weak, substructure within regions (F_ST = 0.002, p = .001). After modelling the asymmetric nature of ocean currents, we demonstrated that local oceanography (IBR) was a better predictor of genetic variation (R² = .49) than geographic distance (IBD) (R² = .18), and directional processes played an important role in shaping fine‐scale structure. Our study contributes to the growing body of literature identifying significant population structure in marine systems and has important implications for the spatial management of P. californicus and other exploited marine species.     

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.