Composition of cetacean communities worldwide shapes their contribution to ocean nutrient cycling

Humpback whale (Megaptera novaeangliae) visual acuity allows silhouette detection but not fine detail discrimination over ecological distances

Few studies have been conducted on the visual capabilities of large cetaceans, such as the humpback whale (Megaptera novaeangliae), and understanding these capabilities provides insights into the natural history and anthropogenic vulnerabilities of these animals, which are otherwise difficult to study in situ. Here, we performed an anatomical and histological study of a subadult humpback whale eye to estimate visual acuity (i.e. spatial resolution of vision) for modelling the perception of relevant visual targets in an open ocean environment. Visual acuity was estimated at 3.95 cycles per degree (CPD)-a value that is an order of magnitude lower than what is predicted by absolute eye size. Perceptual models based on this acuity indicated that low frequency spatial information (e.g. large silhouettes) remains discriminable over ecologically relevant distances, while high frequency spatial information, perhaps critical for target identification, appears lost at 3-4 average humpback whale body lengths away. Models of horizontal sighting distance provided detection-distance thresholds that encompassed the effective range predicted for visual acuity. This study provides new insight into the visual capabilities of humpback whales, suggesting spatial vision that is suited to their open ocean ecology, but challenged by visual targets with more nuanced characteristics unless viewed at close range.

Predator-mediated nutrient transfers and recycling in ecosystems: Fine-scale variation in the contribution of Antarctic fur seals (Arctocephalus gazella) on and around the Kerguelen Islands

Waters on the Kerguelen Plateau are characterised by a high productivity and unique nutrient dynamics compared to the surrounding Southern Ocean. They support large populations of amphibious marine predators such as seabirds and marine mammals, which participate in nutrient recycling at sea and nutrient transfers from sea to land on their colonies. This study investigates the contribution of Antarctic fur seals (Arctocephalus gazella) to the biological recycling of 15 essential and 5 non-essential nutrients on and around the Kerguelen Islands during their four-month breeding season. Nutrient concentrations of 59 fur seal scats from two colonies were examined and used to determine faecal nutrient output from lactating females using a bioenergetic model. We evidenced individual variability in the multi-nutrient composition of fur seal scats, with different types of potential fertilisers. Colony differences in scat compositions resulted in multi-nutrient release levels that did not simply reflect colony abundances. This suggests that estimating predators' nutrient release based on averages (diets, prey or faecal nutrient contents) likely overlooks important fine-scale spatial variability in their contributions. Collectively, fur seals deposit up to 628 kg (95 % CI [548-710]) of phosphorus (limiting on land), 46.4 [39.8-53.2] kg of iron (limiting at sea), and 5.9 [5.2-6.8] g of lead (toxic to most organisms). At sea, fur seal defecation could trigger locally significant enrichment events. On land, fur seal faecal nutrient deposition is spatially concentrated in coastal colonies where phosphorus deposition is in the range of global crop fertiliser use. We argue that the role of marine predators in the local nutrient dynamics of the Kerguelen area should not be overlooked, and that fine-scale variability in the nutrient input by such marine predators is important to consider in any local nutrient dynamic study.

Migrating baleen whales transport high-latitude nutrients to tropical and subtropical ecosystems

Baleen whales migrate from productive high-latitude feeding grounds to usually oligotrophic tropical and subtropical reproductive winter grounds, translocating limiting nutrients across ecosystem boundaries in their bodies. Here, we estimate the latitudinal movement of nutrients through carcasses, placentas, and urea for four species of baleen whales that exhibit clear annual migration, relying on spatial data from publicly available databases, present and past populations, and measurements of protein catabolism and other sources of nitrogen from baleen whales and other marine mammals. Migrating gray, humpback, and North Atlantic and southern right whales convey an estimated 3784 tons N yr-1 and 46,512 tons of biomass yr-1 to winter grounds, a flux also known as the "great whale conveyor belt"; these numbers might have been three times higher before commercial whaling. We discuss how species recovery might help restore nutrient movement by whales in global oceans and increase the resilience and adaptative capacity of recipient ecosystems.

Movement ecology of gelatinous zooplankton: approaches, challenges and future directions

Understanding the movement patterns and behavior of marine organisms is fundamental for numerous ecological, conservation and management applications. Over the past several decades, advancements in tracking technologies and analytical methods have revolutionized our ability to study marine animal movements. Oceanic zooplankton often make up the bulk of the macroscopic animal biomass in the oceans, yet we know very little about the life histories, migrations and long-term behaviors of these ecologically important animals. In this Review, we consider recent developments in marine movement ecology and animal tracking techniques of gelatinous zooplankton, and discuss the challenges, opportunities and future directions in this rapidly evolving field.

Energyscapes pinpoint marine megafauna feeding hotspots in the Mediterranean

Ocean giants shape the structure and functioning of marine food webs via trophic top-down controls, landscapes of fear, vertical and horizontal redistribution of nutrients, energy, and matter. Yet, they face threats from overfishing, pollution, habitat degradation, and climate change, and one-third of marine megafauna species are at risk of extinction, ultimately endangering the resilience of entire ecosystems. In such a context, knowing when and where megafauna find resources to balance their substantial energy requirements is critical for their management. Through an energyscape approach integrating abundance censuses, diet, and energy requirements, we investigated the prey consumption patterns of Mediterranean marine megafauna during the summer. We thereby shed light on a diverse guild of species composed of fishes, mammals, reptiles, and birds and estimated that 4.1 million individuals consume 1.6 million tons of prey each summer, pelagic cephalopods being the primary food resource and cetaceans and tunas being key players in the community. Spatial patterns in prey consumption reflected the diverse distribution and needs of the megafauna species and underlined the critical importance of the western Mediterranean for the megafauna community. Conservation strategies should prioritize spatial and biological diversity to safeguard megafauna and ecosystem functions across the Mediterranean basin.

Unlocking Topological Effects in Covalent Organic Frameworks for High-Performance Photosynthesis of Hydrogen Peroxide

Covalent organic frameworks (COFs) offer a compelling platform for the efficient photosynthesis of hydrogen peroxide (H2O2). Constructed with diverse topologies from various molecular building units, COFs can exhibit unique photocatalytic properties. In this study, three π-conjugated 2D sp2 carbon-linked COFs with distinctly different topologies (hcb, sql, and hxl) are designed to investigate the topological effect on the overall photosynthesis of H2O2 from water and oxygen. Despite their similar chemical and band structures, the QP-HPTP-COF with hxl topology outperformed other COFs in the photosynthesis of H2O2, demonstrating a remarkable solar-to-chemical conversion efficiency of 1.41%. Comprehensive characterizations confirmed that the hxl topology can substantially improve charge separation and transfer, thereby significantly enhancing photocatalytic performance. This study not only unravels the topology-directed charge carrier dynamics in COFs but also establishes a molecular engineering framework for developing high-performance photocatalysts for sustainable H2O2 production.

Marine mammals as indicators of Anthropocene Ocean Health

The current state of marine mammal populations reflects increasing anthropogenic impacts on the global Ocean. Adopting a holistic approach towards marine mammal health, incorporating healthy individuals and healthy populations, these taxa present indicators of the health of the overall Ocean system. Their present deterioration at the animal, population and ecosystem level has implications for human health and the global system. In the Anthropocene, multiple planetary boundaries have already been exceeded, and quiet tipping points in the Ocean may present further uncertainties. Long and short-term monitoring of marine mammal health in the holistic sense is urgently required to assist in evaluating and reversing the impact on Ocean Health and aid in climate change mitigation.

Identifying prey capture events of a free-ranging marine predator using bio-logger data and deep learning

Marine predators are integral to the functioning of marine ecosystems, and their consumption requirements should be integrated into ecosystem-based management policies. However, estimating prey consumption in diving marine predators requires innovative methods as predator-prey interactions are rarely observable. We developed a novel method, validated by animal-borne video, that uses tri-axial acceleration and depth data to quantify prey capture rates in chinstrap penguins (Pygoscelis antarctica). These penguins are important consumers of Antarctic krill (Euphausia superba), a commercially harvested crustacean central to the Southern Ocean food web. We collected a large data set (n = 41 individuals) comprising overlapping video, accelerometer and depth data from foraging penguins. Prey captures were manually identified in videos, and those observations were used in supervised training of two deep learning neural networks (convolutional neural network (CNN) and V-Net). Although the CNN and V-Net architectures and input data pipelines differed, both trained models were able to predict prey captures from new acceleration and depth data (linear regression slope of predictions against video-observed prey captures = 1.13; R 2 ≈ 0.86). Our results illustrate that deep learning algorithms offer a means to process the large quantities of data generated by contemporary bio-logging sensors to robustly estimate prey capture events in diving marine predators.

The illusion of balance in the history of the biosphere

Earth's surface has been irreversibly altered by the activity of organisms, a process that has accelerated as the power of the biosphere (the rate at which life extracts and deploys energy) has increased over time. This trend is incompatible with the expectation that the inputs to Earth's surface of life's materials from the crust and mantle be matched by export from Earth's surface to long-term reservoirs. Here, I suggest that the collective activity of organisms has always violated this balance. The biosphere's ability to extract, retain, recycle, and accumulate materials has allowed living biomass to increase and for exports to decrease over very long timescales. This collective metabolism implies a net transfer of materials from the planet's interior to its surface. The combination of metabolic innovations, competition, adaptive evolution, and the establishment of collaborative economic feedback in ecosystems created dynamic ecological stability despite great spatial and temporal heterogeneity in physical and biological inputs and export of nutrients into and out of the biosphere. Models of geochemical cycling must take the fundamental role of living organisms and the evolutionary changes in these roles into account to explain past and future conditions.