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Iron is the limiting micronutrient in the Southern Ocean and experiments have demonstrated that addition of soluble iron to surface waters results in phytoplankton blooms, particularly by large diatoms. Antarctic krill (Euphausia superba) eat diatoms and recycle iron in surface waters when feeding. Baleen whales eat krill, and, historically, defecation by baleen whales could have been a major mechanism for recycling iron, if whale faeces contain significant quantities of iron. We analysed the iron content in 27 samples of faeces from four species of baleen whale. Faecal iron content (145.9 ± 133.7 mg kg−1) is approximately ten million times that of Antarctic seawater, suggesting that it could act as a fertilizer. Furthermore, we analysed the iron content of seven krill species and of muscle tissue of two species of baleen whales; all samples had high iron levels. Using these figures, together with recent estimates of the range and biomass of krill, we calculate that the Antarctic krill population contains ∼24% of the total iron in the surface waters in its range. Thus, krill can act as a long-term reservoir of iron in Antarctic surface waters, by storing the iron in their body tissue. Pre-exploitation populations of whales and krill must have stored larger quantities of iron and would have also recycled more iron in surface waters, enhancing overall ocean productivity through a positive feedback loop. Thus, allowing the great whales to recover might actually increase Southern Ocean productivity through enhancing iron levels in the surface layer.
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... Top predators have direct effects on their prey that translate to indirect effects on ecosystem structure, function and productivity 1,2,14,15 . Understanding the causes and consequences of these effects depends on direct measurements from large vertebrates, which are logistically challenging to collect, particularly for species threatened with extinction 16,17 . ...
... Mysticetes ingest large quantities of prey and egest their remains in the photic zone, thereby facilitating nutrient recycling and retention in Article the epipelagic 21 (Fig. 1). This recycling of limiting nutrients from mysticetes to primary producers has the capacity to boost the intensity and extent of phytoplankton blooms, in both space and time, thus influencing ecosystem dynamics 3,15 . In the Southern Ocean, mysticete abundance declined dramatically from 1910-1970 due to industrial whaling, and the functional extinction of large whales preceded reductions of primary productivity and krill biomass in the region 22,23 . ...
... The exact quantity of egesta that whales produce is unknown; however, there is a growing body of literature on the nutrient content of mysticete feces. In particular, we used published concentrations of iron from Southern Ocean rorquals 15,113 . The equation for iron egested (recycled) is: ...
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Baleen whales influence their ecosystems through immense prey consumption and nutrient recycling1–3. It is difficult to accurately gauge the magnitude of their current or historic ecosystem role without measuring feeding rates and prey consumed. To date, prey consumption of the largest species has been estimated using metabolic models3–9 based on extrapolations that lack empirical validation. Here, we used tags deployed on seven baleen whale (Mysticeti) species (n = 321 tag deployments) in conjunction with acoustic measurements of prey density to calculate prey consumption at daily to annual scales from the Atlantic, Pacific, and Southern Oceans. Our results suggest that previous studies3–9 have underestimated baleen whale prey consumption by threefold or more in some ecosystems. In the Southern Ocean alone, we calculate that pre-whaling populations of mysticetes annually consumed 430 million tonnes of Antarctic krill (Euphausia superba), twice the current estimated total biomass of E. superba10, and more than twice the global catch of marine fisheries today11. Larger whale populations may have supported higher productivity in large marine regions through enhanced nutrient recycling: our findings suggest mysticetes recycled 1.2 × 104 tonnes iron yr−1 in the Southern Ocean before whaling compared to 1.2 × 103 tonnes iron yr−1 recycled by whales today. The recovery of baleen whales and their nutrient recycling services2,3,7 could augment productivity and restore ecosystem function lost during 20th century whaling12,13. A combination of 3D whale locations and acoustic measurements of prey density is used here to show that whales’ consumption of krill is several times larger than often thought.
... These new estimates lend additional support to the concept that whales fertilised their own feeding grounds in the Southern Ocean by feeding on iron-rich krill and discharging iron-rich faecal plumes in the surface www.nature.com/scientificreports/ layer [88][89][90][91] . In a region where primary productivity is largely limited by iron availability, whales would thus have substantially enhanced phytoplankton growth, boosting food availability for krill 91,92 . ...
... The recovery of baleen whales and their nutrient recycling services, known as "the whale-pump" 91 , could thus augment primary productivity and restore ecosystem functions lost during twentieth century whaling 85,86 . A recovering fin whale population may lead to an increase of Southern Ocean productivity through enhancing iron levels in the surface layer 88 . By stimulating primary production, whales act as a carbon sink in the Southern Ocean 85,94 . ...
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Fin whales (Balaenoptera physalus quoyi) of the Southern Hemisphere were brought to near extinction by twentieth century industrial whaling. For decades, they had all but disappeared from previously highly frequented feeding grounds in Antarctic waters. Our dedicated surveys now confirm their return to ancestral feeding grounds, gathering at the Antarctic Peninsula in large aggregations to feed. We report on the results of an abundance survey and present the first scientific documentation of large fin whale feeding aggregations at Elephant Island, Antarctica, including the first ever video documentation. We interpret high densities, re-establishment of historical behaviours and the return to ancestral feeding grounds as signs for a recovering population. Recovery of a large whale population has the potential to augment primary productivity at their feeding grounds through the effects of nutrient recycling, known as 'the whale pump'. The recovery of fin whales in that area could thus restore ecosystem functions crucial for atmospheric carbon regulation in the world's most important ocean region for the uptake of anthropogenic CO2.
... While there is a long-established expectation that increased predation negatively impacts krill populations (Laws, 1977), there is also a hypothesized positive feedback between baleen whale and krill populations. This states that preexploitation whale and krill populations may have consumed and recycled larger quantities of iron thereby enhancing overall ocean productivity and the production of krill (Smetacek, 2008;Nicol et al., 2010;Henley et al., 2020). Changes to predator populations as a result of past perturbation are still ongoing (Branch et al., 2007;Branch, 2011;Zerbini et al., 2019) and the full implications of these changes for krill populations remain to be explored. ...
... Model-based projection studies suggest that climate change could delay their recovery due to reduced krill availability (Klein et al., 2018;Tulloch et al., 2019). However, the hypothesized positive feedback loop whereby nutrient recycling by increased whale populations could enhance primary production and support increased krill stocks (Smetacek, 2008;Lavery et al., 2010;Nicol et al., 2010) may counteract this impact. ...
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In the Southern Ocean, several zooplankton taxonomic groups, euphausiids, copepods, salps and pteropods, are notable because of their biomass and abundance and their roles in maintaining food webs and ecosystem structure and function, including the provision of globally important ecosystem services. These groups are consumers of microbes, primary and secondary producers, and are prey for fishes, cephalopods, seabirds, and marine mammals. In providing the link between microbes, primary production, and higher trophic levels these taxa influence energy flows, biological production and biomass, biogeochemical cycles, carbon flux and food web interactions thereby modulating the structure and functioning of ecosystems. Additionally, Antarctic krill (Euphausia superba) and various fish species are harvested by international fisheries. Global and local drivers of change are expected to affect the dynamics of key zooplankton species, which may have potentially profound and wide-ranging implications for Southern Ocean ecosystems and the services they provide. Here we assess the current understanding of the dominant metazoan zooplankton within the Southern Ocean, including Antarctic krill and other key euphausiid, copepod, salp and pteropod species. We provide a systematic overview of observed and potential future responses of these taxa to a changing Southern Ocean and the functional relationships by which drivers may impact them. To support future ecosystem assessments and conservation and management strategies, we also identify priorities for Southern Ocean zooplankton research.
... Great whales (baleen whales and sperm whales) are also known to be marine ecosystem engineers, as they facilitate nutrients transfer from deep waters to the surface, as well as across latitudes via migration from feeding to calving areas (Roman et al., 2014). These whales further sequester large amount of carbon to the deep sea, thus contributing to natural climate-change mitigation (Lavery et al., 2010;Martin et al., 2021;Roman and McCarthy, 2010) and maintain iron levels in the surface layer, which promotes krill abundance (Nicol et al., 2010;Pershing et al., 2010;Roman et al., 2014;Roman and McCarthy, 2010;Willis, 2014). Our results indicate that, in particular at local and regional scales, a further reduction in these services due to whales moving to other, more suitable areas, could affect wider ecosystem functioning and destabilize ecological processes (Roman et al., 2014). ...
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Climate impacts affect marine ecosystems worldwide with island nations such as New Zealand being extremely vulnerable because of their socio-economic and cultural dependence on the marine and costal environment. Cetaceans are ideal indicator species of ecosystem change and ocean health given their extended life span and cosmopolitan distribution, but limited data availability prevents anticipating change in distribution under future climate changes. We projected the range shifts of a key odontocete and mysticete species (Physeter macrocephalus and Balaenoptera musculus) in 2100 relative to present day in New Zealand waters, using an ensemble modelling approach, under three climate change scenarios of different severity. The results show a latitudinal shift in suitable habitat for both whale species, increasing in magnitude with severity of sea surface temperature warming. The most severe climate change scenario tested generated 61% and 42% loss and decrease of currently suitable habitat for sperm and blue whales, respectively, mostly in New Zealand’s northern waters. These predicted changes will have a strong impact on the ecosystem functioning and services in New Zealand’s northern waters but also in coastal areas (critical for the species’ foraging and survival). Not only do these simulated range shifts help to identify future potential climate refugia to mitigate a global warming, they also generate a range of socioeconomic consequences for island nations relying on wildlife tourism, industry, and environmental protection.
... For example, Weddell and harp seals routinely make longer and deeper dives ( Fig. 8a; Weddell 64 . Notably, this is the only species that primarily consumes iron-rich krill (Euphausia superba) 65 and likely has much higher dietary iron intake than other pinnipeds which may explain why crabeater seals have even higher milk iron concentrations than Weddell seals in this study. ...
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The profound impacts that maternal provisioning of finite energy resources has on offspring survival have been extensively studied across mammals. This study shows that in addition to calories, high hemoprotein concentrations in diving mammals necessitates exceptional female-to-pup iron transfer. Numerous indices of iron mobilization (ferritin, serum iron, total-iron-binding-capacity, transferrin saturation) were significantly elevated during lactation in adult female Weddell seals (Leptonychotes weddellii), but not in skip-breeders. Iron was mobilized from endogenous stores for incorporation into the Weddell seal’s milk at concentrations up to 100× higher than terrestrial mammals. Such high rates of iron offload to offspring drew from the female’s own heme stores and led to compromised physiologic dive capacities (hemoglobin, myoglobin, and total body oxygen stores) after weaning their pups, which was further reflected in shorter dive durations. We demonstrate that lactational iron transfer shapes physiologic dive thresholds, identifying a cost of reproduction to a marine mammal.
... Entanglements not only threaten individual whales or species but also have broader ecological consequences in regions with diminishing whale populations. Whales are nutrient recyclers in marine ecosystems, supporting primary productivity (Roman et al., 2016), fisheries (Lavery et al., 2014), and mitigating climate change (Nicol et al., 2010;Pershing et al., 2010). Thus, if worldwide fisheries-related entanglements of large whales continue unabated, the resilience and productivity of marine ecosystems could be permanently altered . ...
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North Atlantic right whales frequently become entangled in fishing gear, which can negatively affect their reproductive output and probability of survival. We estimated individual whale health from a hierarchical Bayesian model fit to photographic indices of health. We reviewed 696 whales sighted from 1980 to 2011 and assigned 1196 entanglement events to 573 individuals in six categories of increasing injury severity and estimated monthly median health scores (0–100 scale) for the duration of their life within the study period. We then quantified the relationship between entanglement injury events and their severity with survival, reproduction, and population health. Severe entanglements resulted in worse health for all whales—males and females with severe injuries were eight times more likely to die than males with minor injuries. Females with severe injuries that survived had the lowest birth rates. Though the relationship between entanglement and fecundity was complex, we found that as the health of reproductively active females declined, their calving intervals increased. Unimpacted whale health scores declined significantly over three decades, 1980s, 1990s, and 2000s, suggesting food limitations may be contributing to population‐wide health declines. Decadal health scores of entangled whales showed a more notable reduction in health suggesting a clear and perhaps synergistic effect.
... A. Upstream movement: Many empirical studies show animal movement of P against gravity (see Table 1). Whales transport nutrients vertically from the nutrient-rich deep ocean to surface waters via fecal plumes and urine, where it becomes available for use by phytoplankton in the photic zone (Roman et al., 2014;Nicol et al., 2010;Ratnarajah et al., 2014). P assimilated by phytoplankton travels through the food chain and is eventually consumed by upper-trophic level organisms. ...
Article
Phosphorus (P) is essential for all life on Earth and sustains food production. Yet, the easily accessible deposits of phosphate-rich rock, which underpin the green revolution are becoming rarer. Here we propose a mechanism to help alleviate the problem of “peak phosphorus”. In the past, wild animals played a large role in returning P from ocean depths back to the continental interiors. In doing so, they collectively retained and redistributed P within the biosphere, supporting a more fertile planet. However, species extinctions and population reductions have reduced animal-mediated P transport >90% over the past 12,000 years. Recently a 5R strategy was developed to Realign P inputs, Reduce P losses, Recycle P in bio-resources, Recover P in wastes, and Redefine P in food systems. Here, we suggest a sixth R, to Revitalize the Natural Phosphorus Pump (RNPP). Countries are starting to mandate P recycling and we propose a P-trading scheme based on REDD+, where a country could partially achieve its recycling goals by restoring past animal-mediated P pathways. Accrued money from this scheme could be used to restore or conserve wild animal populations, while increasing natural P recycling.
... For instance, some metals such as iron (Fe) are locally limiting in oceans (Sunda and Huntsman 1995), but large vertebrates can counter the lack of such micro-nutrients in these areas by defecating. Iron intake from prey can exceed nutritional requirements for some whales and consequently, faecal Fe content has been identified as a fertilizer enhancing ecosystem productivity (Nicol et al. 2010). A decrease of Fe content in available prey, as well as other essential elements, could thus have impacts on local nutrients recycling and ultimately on ecosystem dynamics. ...
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The main changes in the distribution and abundance of marine top predators in the Antarctic in the last two centuries were caused by human over-exploitation. Hypotheses that increases in populations of krill-eating penguins and seals represent recovery from exploitation, accelerated by removal of krill-eating whales, are being re-evaluated in the light of correlations between population size and reproductive success of seabirds and seals and various features of the biological and physical environment. These correlations involve phocid and otariid seals, penguins and flying birds and sites ranging from the Antarctic continent to sub-Antarctic islands. Although the nature of, and balance between, physical and biological influences differ between sites, regions and different types of predator, processes (including potentially important links with the Southern Oscillation) involving sea-ice extent and distribution play a key role. Major uncertainties over the nature of the links between physical and biological processes and the responses of marine populations preclude any confident prediction of the potential effects of future environmental change. However, certain taxa, especially those of specialist ecology, extreme demography and restricted distribution (especially in high latitudes) are especially vulnerable to at least some of the likely environmental changes.