Key Ecological Function Peaks at the Land–Ocean Transition Zone When Vertebrate Scavengers Concentrate on Ocean Beaches

Mass Die-Off Events in Swarming Hyperiid Amphipods: Potential Drivers

Beach mass stranding events of marine organisms, widely documented worldwide, are triggered by a range of biotic and abiotic environmental factors, often unexplained. Such occurrences among pelagic crustaceans are less frequent, yet not uncommon. Here we studied mass mortality events of hyperiid amphipods-abundant members of pelagic zooplankton, commonly associated with gelatinous organisms. Our study examined consecutive mass die-off and stranding events of free-living hyperiids in the Red Sea during 2023 and 2024. We investigated three potential causes: semelparous reproduction, thermal stress, and physical oceanographic conditions. To place our findings in a broader context, we further performed a global review of hyperiid swarming and mass mortality events from scientific literature and a citizen science repository. Morphological and molecular analyses confirmed that the hyperiid species in the die-off events at the Red Sea was Anchylomera blossevillei (Phrosinidae). The balanced male: female sex ratio (0.99), combined with the absence of gravid or brooding females, led to the rejection of semelparity as a driving factor. The environmental data did not indicate thermally stressful conditions, and no evidence of parasitic infection was found. Nonetheless, previous studies have shown that under weak wind conditions, as measured during the stranding events, coherent cyclonic eddies with diameters of 5-6 km are developed in the northern Gulf of Aqaba, persisting for about a day. These eddies can exceed velocities of 100 cm s-1 and may have facilitated the hyperiid stranding events. Future research should unveil the impacts of such events on marine ecosystems.

The role of inputs of marine wrack and carrion in sandy-beach ecosystems: a global review

Sandy beaches are iconic interfaces that functionally link the ocean with the land via the flow of organic matter from the sea. These cross-ecosystem fluxes often comprise uprooted seagrass and dislodged macroalgae that can form substantial accumulations of detritus, termed 'wrack', on sandy beaches. In addition, the tissue of the carcasses of marine animals that regularly wash up on beaches form a rich food source ('carrion') for a diversity of scavenging animals. Here, we provide a global review of how wrack and carrion provide spatial subsidies that shape the structure and functioning of sandy-beach ecosystems (sandy beaches and adjacent surf zones), which typically have little in situ primary production. We also examine the spatial scaling of the influence of these processes across the broader land- and seascape, and identify key gaps in our knowledge to guide future research directions and priorities. Large quantities of detrital kelp and seagrass can flow into sandy-beach ecosystems, where microbial decomposers and animals process it. The rates of wrack supply and its retention are influenced by the oceanographic processes that transport it, the geomorphology and landscape context of the recipient beaches, and the condition, life history and morphological characteristics of the macrophyte taxa that are the ultimate source of wrack. When retained in beach ecosystems, wrack often creates hotspots of microbial metabolism, secondary productivity, biodiversity, and nutrient remineralization. Nutrients are produced during wrack breakdown, and these can return to coastal waters in surface flows (swash) and aquifers discharging into the subtidal surf. Beach-cast kelp often plays a key trophic role, being an abundant and preferred food source for mobile, semi-aquatic invertebrates that channel imported algal matter to predatory invertebrates, fish, and birds. The role of beach-cast marine carrion is likely to be underestimated, as it can be consumed rapidly by highly mobile scavengers (e.g. foxes, coyotes, raptors, vultures). These consumers become important vectors in transferring marine productivity inland, thereby linking marine and terrestrial ecosystems. Whilst deposits of organic matter on sandy-beach ecosystems underpin a range of ecosystem functions and services, they can be at variance with aesthetic perceptions resulting in widespread activities, such as 'beach cleaning and grooming'. This practice diminishes the energetic base of food webs, intertidal fauna, and biodiversity. Global declines in seagrass beds and kelp forests (linked to global warming) are predicted to cause substantial reductions in the amounts of marine organic matter reaching many beach ecosystems, likely causing flow-on effects for food webs and biodiversity. Similarly, future sea-level rise and increased storm frequency are likely to alter profoundly the physical attributes of beaches, which in turn can change the rates at which beaches retain and process the influxes of wrack and animal carcasses. Conservation of the multi-faceted ecosystem services that sandy beaches provide will increasingly need to encompass a greater societal appreciation and the safeguarding of ecological functions reliant on beach-cast organic matter on innumerable ocean shores worldwide.

Diet of a threatened endemic fox reveals variation in sandy beach resource use on California Channel Islands

The coastal zone provides foraging opportunities for insular populations of terrestrial mammals, allowing for expanded habitat use, increased dietary breadth, and locally higher population densities. We examined the use of sandy beach resources by the threatened island fox (Urocyon littoralis) on the California Channel Islands using scat analysis, surveys of potential prey, beach habitat attributes, and stable isotope analysis. Consumption of beach invertebrates, primarily intertidal talitrid amphipods (Megalorchestia spp.) by island fox varied with abundance of these prey across sites. Distance-based linear modeling revealed that abundance of giant kelp (Macrocystis pyrifera) wrack, rather than beach physical attributes, explained the largest amount of variation in talitrid amphipod abundance and biomass across beaches. δ¹³C and δ¹⁵N values of fox whisker (vibrissae) segments suggested individualism in diet, with generally low δ¹³C and δ¹⁵N values of some foxes consistent with specializing on primarily terrestrial foods, contrasting with the higher isotope values of other individuals that suggested a sustained use of sandy beach resources, the importance of which varied over time. Abundant allochthonous marine resources on beaches, including inputs of giant kelp, may expand habitat use and diet breadth of the island fox, increasing population resilience during declines in terrestrial resources associated with climate variability and long-term climate change.

Interactions at surface-subterranean ecotones: structure and function of food webs within spring orifices

Spring orifices are ecotones between surface and subterranean aquatic ecosystems. Invertebrates of different origins (e.g., surface, spring obligate, and subterranean) coexist in these spatially restricted environments, potentially competing for resources. However, processes that allow for population coexistence in these presumably low resource environments are not well understood. We examined invertebrate communities at two spring complexes in Texas, USA and assessed resource use and food web structure at spring orifices using stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N). Using bulk δ¹³C and δ¹⁵N of organisms and potential food sources, we elucidated dietary sources and found that invertebrate communities exhibited resource partitioning and contained two main food chains (periphyton versus terrestrial organic matter [OM]). In both spring complexes, several endemic spring orifice associated and subterranean taxa derived most of their diet from terrestrial OM. Analysis of compound-specific stable isotopes (i.e., δ¹³C of essential amino acids, EAAs) from two co-occurring elmid species indicated that the endemic spring orifice-associated species (Heterelmis comalensis) derived > 80% of its EAAs from bacteria, whereas the widespread surface species (Microcylloepus pusillus) derived its EAAs from a more equitable mix of bacteria, fungi, and algae. We additionally calculated niche overlap among of several taxonomically related groups (aquatic beetles and amphipods) that co-occur in spring ecotones and posterior probability estimates indicated little to no niche overlap among related species. Results indicate that invertebrates at subterranean-surface aquatic ecotones are partitioning food resources and highlight the importance of connections to riparian zones for persistence of several endemic invertebrates.