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Southern Ocean iron fertilization by baleen whales and Antarctic krill
Abstract
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.
... Grazing and predation by fauna, and the subsequent release of waste (faeces and urine) in the euphotic zone, retain nutrients in the surface ocean for extended periods of time, rather than them being lost to depths with sinking materials. Among the SO fauna, air-breathing megafauna such as cetaceans, seals and penguins may contribute significantly to SO productivity by releasing iron-rich waste products in surface waters (Lavery et al. 2010(Lavery et al. , 2014Nicol et al. 2010;Ratnarajah et al. 2014;Wing et al. 2014;Otero et al. 2018;Sparaventi et al. 2021). These diving top predators differ from most marine life in that they are tied to surface waters for breathing. ...
... As top predators, they may impact the structure and the biomass of the SO ecosystem through predation (Krause et al. 2015;Goetz et al. 2017;Staniland et al. 2018). However, their role as vectors of limiting micronutrients has received little attention despite iron concentrations in their faeces (950.8 ± 148.9 mg·Fe·kg −1 dry weight (Wing et al. 2021)) in line with that of whales and seabirds (Nicol et al. 2010;Wing et al. 2021). ...
... We opted for the Sobol method, a variance-based approach where the variance of the output can be decomposed into the contributions imputable to each input factor. We used R package "sensitivity" (version 1.27.0) with function "soboltSalt", and computed Table 2 Data and literature sources (References) used to estimate the energy content (E pg ) and iron (Fe) concentration (x Fe,pg ) of the functional prey groups (pg) used to describe the diet of each pack-ice seal species, and diets as established with percentage of consumption (in weight) of each prey group a Armstrong and Siegfried (1991), Mårtensson et al. (1996), Kiørboe (2013), Ruck et al. (2014) b Palmer Locarnini and Presley (1995), Caroli et al. (1998), Barbante et al. (2000), Nicol et al. (2010), Kim et al. (2014) c Tierney et al. (2002), Chouvelon et al. (2022a, b) d Honda et al. 1987, Goutte et al. 2015, Chouvelon et al. (2022a e Croxall and Prince (1982) first-order (with respect to each input factor individually) and total (inclusive of interactions between input factors) sensitivity indices for all parameters of the model. Code to reproduce the full analysis in R is available on Github (https:// github. ...
The contribution of animals to biological transfers of essential nutrients in ecosystems is increasingly recognised as a significant component of ecosystem functioning. In the Southern Ocean (SO), primary productivity is primarily limited by the availability of iron in the euphotic zone, which makes animals locally releasing iron-rich faeces potential fertilizers of the SO food web. We quantified the amounts of iron released by four species of Antarctic pack-ice seals using a bioenergetic model set up with best available data on species abundance, energetics, diets and prey composition. We estimated that leopard, crabeater, Weddell and Ross seals together release 208 tonnes of iron per year (95% confidence interval [104–378]). This is equivalent to the current contribution of SO humpback whales and four times that of SO sperm whales. At the population level, crabeater seals are the major contributors (73%), followed by Weddell (21%), leopard (4%) and Ross seals (1%). Locally, each species shows different daily individual iron release rates, suggesting the patchy and transient impact of these iron releases on primary producers might differ according to species. Beyond quantitative aspects, pack-ice seals’ contribution to horizontal, vertical and trophic transfers of iron depends on their habitat preferences, on their ecology and behaviours at sea and on the ice. Although their role as iron vectors has been mostly overlooked so far, our results place pack-ice seals alongside whales and penguins as significant components of the SO ecosystem biological iron cycling, thus contributing substantially to its productivity and functioning.
... There is growing interest in assessing the contribution of whales to nutrient recycling in surface waters (e.g. Lavery et al. 2010, Nicol et al. 2010, Roman and McCarthy 2010, Ratnarajah et al. 2014, Ratnarajah et al. 2018, Savoca et al. 2021). However, uncertainties on several model parameters have impeded progress in obtaining robust quantifications of this contribution (Ratnarajah et al., 2016). ...
... Elemental Zn and Fe were the trace elements found at the highest concentrations in minke whale faeces and this is similar to what has been observed in faeces of other large whales in the Southern Ocean (Ratnarajah et al., 2014). However, Fe concentration in our samples (498 ± 119.5 mg kg − 1 ) was approximately-three times larger than the concentration measured in baleen whales in the Southern Ocean (Nicol et al., 2010;Ratnarajah et al., 2014). This might be because the Southern Ocean is an iron-limited ecosystem or because of differences in dietbaleen whales in the Southern Ocean feed mainly on krill while the studied minke whales had foraged on capelin. ...
... Therefore, most studies of nutrient recycling by whale in the Southern Ocean have focused on this element (e.g. Nicol et al. 2010, Ratnarajah et al. 2016, Ratnarajah et al. 2018, Savoca et al. 2021. Similar to whales, other marine taxa may also recycle Fe through excretion and it has been suggested that commercial fish harvesting has removed significant amounts of iron from the ocean (Moreno and Haffa 2014). ...
There is increasing interest in assessing the impact of whales on nutrient and carbon cycling in the ocean. By fertilising surface waters with nutrient-rich faeces, whales may stimulate primary production and thus carbon uptake, but robust assessments of such effects are lacking. Based on the analysis of faeces collected from minke whales (n=31) off Svalbard, Norway, this study quantified the concentration of macro-and micronutrients in whale faeces prior to their release in seawater. Concentrations of the macronutrients nitrogen (N) and phosphorous (P) in minke whale faeces were 50.1 ± 10.3 and 70.9 ± 12.1 g kg⁻¹ dry weight, respectively, while the most important micronutrients were zinc (Zn), iron (Fe), manganese (Mn) and copper (Cu). By combining measured faecal nutrient concentrations with estimated prey-consumption and prey-assimilation rates, we calculate that the current population of approximately 15 000 individuals in the small management area (SMA) of Svalbard defecate daily 7 ± 1.4 tonnes (t) N and 10 ± 1.7 t P during summer. The molar ratio of N:P in minke whale faeces was 1.6:1, meaning that N was proportionally limiting, when compared to average elemental ratios of 16:1 in phytoplankton. In case of no N-limitation in surface waters at that time, the release of elemental P through defecation in surface waters has the potential to stimulate 407 ± 70 t of carbon per day during summer as new or regenerated primary production in the SMA of Svalbard. This amounts to 0.2 to 4 % of daily net primary production to this region. This study provides the first assessment of nutrient concentration in whale faeces prior to their dissolution in sea water. Further research, namely on the amount of N released via urine and seasonal changes in excreted nutrients, is needed to better assess the full potential of whale nutrient additions to dissolved nutrient pools in surface waters at regional and global scales.
... First, thanks to their longevity and high weight, they store large amounts of organic carbon in their body mass throughout their lifetime, that can be up to one century for some species like blue whales (electronic supplementary material, figure S1). Second, whales have been shown to be efficiently recycle nutrients and boost primary production [29][30][31][32]. Indeed, the Southern Ocean is largely considered to be a high-nutrient low-chlorophyll zone, i.e. a zone where macronutrients (nitrogen and phosphorus) concentrations are high but primary productivity is low [33]. ...
... Phytoplankton growth is limited by the availability of trace elements (Fe, Cu, Zn, Co and Cd), especially iron [33] as confirmed by many short-term iron-addition experiments [34,35]. In that context, southern whales play a critical functional role since they feed mostly on krill which is an iron accumulator [31,36]. Thus, they can alleviate the growth limitation of phytoplankton through the supply of iron-rich faeces. ...
... Indeed, whales' faeces are highly concentrated in iron (the iron concentration of whales' faeces was estimated to be 145.9 ± 133.7 mg kg −1 , being approximately 10 million times that of Antarctic seawater [31]). Plus, they are likely highly bioavailable as they are liquid and buoyant, remaining in the euphotic zone where whales defaecate, and iron is also excreted with other nutrients, preventing phytoplankton growth from colimitations and successive limitations. ...
Despite the importance of marine megafauna on ecosystem functioning, their contribution to the oceanic carbon cycle is still poorly known. Here, we explored the role of baleen whales in the biological carbon pump across the southern hemisphere based on the historical and forecasted abundance of five baleen whale species. We modelled whale-mediated carbon sequestration through the sinking of their carcasses after natural death. We provide the first temporal dynamics of this carbon pump from 1890 to 2100, considering both the effects of exploitation and climate change on whale populations. We reveal that at their pre-exploitation abundance, the five species of southern whales could sequester 4.0 × 10 ⁵ tonnes of carbon per year (tC yr ⁻¹ ). This estimate dropped to 0.6 × 10 ⁵ tC yr ⁻¹ by 1972 following commercial whaling. However, with the projected restoration of whale populations under a RCP8.5 climate scenario, the sequestration would reach 1.7 × 10 ⁵ tC yr ⁻¹ by 2100, while without climate change, recovered whale populations could sequester nearly twice as much (3.2 × 10 ⁵ tC yr ⁻¹ ) by 2100. This highlights the persistence of whaling damages on whale populations and associated services as well as the predicted harmful impacts of climate change on whale ecosystem services.
... 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: ...
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.
... In addition, microbial remineralization (Liu et al., 2020;Tagliabue et al., 2012) and pelagic recycling by marine animals (Nicol et al., 2010;Ratnarajah et al., 2018;Tovar-Sanchez et al., 2007) have been suggested as potential mechanisms that sustain surface dFe concentrations. Heterotrophic bacteria have a significant Fe demand (Boyd & Ellwood, 2010;Mazzotta et al., 2020;Tortell et al., 1996), but play an important role in the remineralization of particulate Fe into dFe , and release Fe-binding ligands (Hunter & Boyd, 2007) that maintain the solubility of remineralized Fe in the upper ocean. ...
... In this study, we found dFe along the continental shelf, to be supplied from a combination of upwelled CDW (Section 4.1), shelf sediment resuspension (Section 4.2) and microbial remineralization (Section 4.3). However, previous coastal East Antarctic studies have suggested ice melt (Section 4.4) drives summer productivity (Dinniman et al., 2020), while others propose higher trophic levels such as Antarctic krill, seabirds, and marine mammals (Section 4.5) sustain surface Fe throughout late summer (Nicol et al., 2010;Schmidt et al., 2016;Shatova et al., 2016;Wing et al., 2014). Whilst we cannot quantitatively determine the most important source of Fe, we can explore the potential mechanisms which drive Fe supply in the Mertz Region during late summer, each of which are discussed in detail below. ...
... Copepods have been observed to elevate Fe concentrations and strong Fe-complexing organic ligands present via fecal pellet release, which may be remineralized following sloppy feeding or coprophagy (Laglera et al., , 2020. Other studies have proposed larger animals including seabirds (Shatova et al., 2016), seals (Wing et al., 2014), and baleen whales (Nicol et al., 2010) may have a biogeochemical role, with incubation experiments finding additions of seabird guano and whale fecal material can stimulate phytoplankton photosynthetic performance (Shatova et al., 2016;Smith et al., 2013). ...
Despite widespread iron (Fe) limitation in the Southern Ocean, intense phytoplankton blooms are observed around productive coastal regions such as the Mertz Polynya (off George V Land and Adelie Land, East Antarctica; 140–155°E). Sources of Fe across coastal East Antarctica vary, with limited data available for late summer months. We investigated the sources of dissolved Fe (dFe; <0.2 μm) at 19 oceanographic stations in the Mertz Glacier Region (64–67°S; 138–154°E), between January and March of 2019. Concentrations of dFe ranged from below detection limit (0.03 nM) at the surface, to 0.34 nM above the base of the mixed layer (35 m), reaching 0.59 nM at depth (520 m). Using oceanographic features and trace element ratios (manganese and titanium), we identified Circumpolar Deep Water (CDW) and shelf sediment resuspension in modified CDW as contributors of dFe to the region over this period. Microbial Fe remineralization was evident where nutrient-rich water met highly oxygenated waters over the continental shelf. Reduced Fe concentrations in the mixed layer and euphotic zones suggested rapid biological uptake prior to sampling. Despite proposals for pelagic Fe recycling by marine animals, preliminary investigations reveal no significant spatial relationship between animal presence and surface ocean Fe concentrations over the study area. Further research is required to identify seasonal changes to Fe supply in coastal areas which will strengthen our understanding of the Fe cycle and its influence on microbial and primary productivity in this globally significant region.
... Chinstrap penguin's main food source, the Antarctic krill, which acts like long-term Fe reservoir 25,48 . ...
... As consequence, a decoupling between krill concentrations and distribution and the nonbreeding winter migrations could be responsible for the decreasing Chinstrap penguin numbers 46 . This downtrend of the Chinstrap penguin population could potentially lead to a similar situation as that experienced by baleen whales, in which their Fe recycling is now up to ten times lower than in the pre-whaling period 48 . In this sense, a global decline of >50% in the Chinstrap penguin numbers has been reported since the 1980s 46 , thus suggesting that only four decades ago, Fe recycling by these seabirds had approximately the same magnitude as that produced by baleen whales subjected to current whaling pressure. ...
Iron plays a crucial role in the high-nutrient, low-chlorophyll Southern Ocean regions, promoting phytoplankton growth and enhancing atmospheric carbon sequestration. In this area, iron-rich Antarctic krill (Euphausia superba) and baleen whale species, which are among their main predators, play a large role in the recycling of iron. However, penguins have received limited attention despite their representing the largest seabird biomass in the southern polar region. Here, we use breeding site guano volumes estimated from drone images, deep learning-powered penguin census, and guano chemical composition to assess the iron export to the Antarctic waters from one of the most abundant penguin species, the Chinstrap penguin (Pygoscelis antarcticus). Our results show that these seabirds are a relevant contributor to the iron remobilization pool in the Southern Ocean. With an average guano concentration of 3 mg iron g⁻¹, we estimate that the Chinstrap penguin population is recycling 521 tonnes iron yr⁻¹, representing the current iron contribution half of the amount these penguins were able to recycle four decades ago, as they have declined by more than 50% since then.
... Carbon sequestration, however, extends beyond the time horizon of carbon storage and it often follows from more complex dynamics. For example, great whale excreta are highly enriched in limiting nutrients, including nitrogen, phosphorus, and trace metals (e.g., iron) that baleen whales recycle within the epipelagic (see Whale pump section; Figure 1A) [11,40,[43][44][45][46][47][48]. In the case of sperm whales (Physeter macrocephalus), the transport of these limiting nutrients from the deep ocean can enhance phytoplankton production in the photic zone. ...
... Buoyant fecal plumes released by whales can provide limiting nutrient concentrations three to seven orders of magnitude higher than background seawater concentrations [40,[45][46][47]56] and can persist at the surface, allowing nutrients to leach into the surrounding seawater and become bioavailable to phytoplankton [40,45,46,57]. Nutrient recycling and transport by whales and other top predators may push planktonic food web structure toward systems dominated by large-celled, quickly sinking diatoms and krill that could affect carbon export [44,58]. ...
The great whales (baleen and sperm whales), through their massive size and wide distribution, influence ecosystem and carbon dynamics. Whales directly store carbon in their biomass and contribute to carbon export through sinking carcasses. Whale excreta may stimulate phytoplankton growth and capture atmospheric CO2; such indirect pathways represent the greatest potential for whale-carbon sequestration but are poorly understood. We quantify the carbon values of whales while recognizing the numerous ecosystem, cultural, and moral motivations to protect them. We also propose a framework to quantify the economic value of whale carbon as populations change over time. Finally, we suggest research to address key unknowns (e.g., bioavailability of whale-derived nutrients to phytoplankton, species- and region-specific variability in whale carbon contributions).
... Whales also recycle nutrients, excreting bioavailable iron in surface waters, which plays an important role in fertilising primary productivity (Ratnarajah, et al., 2014) and in particular diatoms, the staple food of krill (Schmidt and Atkinson, 2016). For example, Nicol et al. (2010) calculated that the Antarctic krill population contains ~24% of the total iron in the surface waters in the Southern Ocean and that pre-exploitation populations of whales and krill must have stored and recycled more iron in surface waters, enhancing overall ocean productivity through a positive feedback loop. ...
... Model-based estimates of humpback whales in the Scotia Sea also increased by an order of magnitude from the 2000 survey (Hedley et al., 2001) to 2019 (Baines et al., 2021). The great whales recycle large volumes of nutrients, especially in feeding habitats, excreting nutrients that fertilise oceanic habitats (Lavery et al., 2014;Nicol et al., 2010;Roman et al., 2014) and it is plausible that increased abundance of humpback whales has contributed to the increased biomass of krill in the SSI region. However, while the humpback whale data presented here are consistent with a continuous trend of recovery observed in breeding habitats (Zerbini et al., 2019), the krill data represent two snapshot estimates some 19 years apart, for a species known to display significant inter-annual variability (Fielding et al., 2014;Loeb and Santora 2015;Reiss et al., 2008;Steinberg et al., 2015). ...
Following the cessation of whaling, the southwest Atlantic humpback whale (Megaptera novaeangliae) population is thought to be close to pre-exploitation size, reversing 20th century changes in abundance. Using a model-based approach applied to concurrently collected data on baleen whale abundance and Antarctic krill (Euphausia superba) biomass in the South Sandwich Islands (SSI) region, we explore ecological interactions between these taxa. Krill biomass and baleen whale density were highest to the north and northeast of the SSI, where the Antarctic Circumpolar Current (ACC) is deflected around the island chain. Humpback whale density was elevated at locations of krill biomass density >150 gm⁻². Krill consumption by baleen whales was estimated at 19–29% of the available krill standing stock. We used historic whaling data to confirm the plausibility of these consumption rates and found evidence of rapid weight gain in humpback whales, such that blubber depleted during the breeding season could be restored in a much shorter period than previously assumed. Little is known about krill replenishment rates in the flow of the ACC, or about niche separation between recovering baleen whale populations; both factors may affect species carrying capacities and further monitoring will be required to inform the management of human activities in the region.
... 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 . ...
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. ...
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.
... 67,68 Marine vertebrates that feed at depth and return to the surface to breathe, recover from diving, rest, or warm up provide an opportunity for movement of nutrients from depth to surface waters, which can stimulate primary production. This has been documented for whales, where the term ''whale pump'' describes vertical transport of nutrients from depth to the surface layer, where whales release nutrient-rich fecal plumes, which can stimulate new phytoplankton growth 111,[125][126][127][128][129][130] (Figure 2). Movement patterns of various vertebrates suggests that they may transfer nutrients in this manner. ...
... 9,131-133 However, marine vertebrates that feed and release egesta within the surface layer support total, rather than new, primary production. 20,117,126 Blue whales in the Southern Ocean typically both feed and defecate within the surface layer 125 (Figure 2). Other species that may support C fixation in this manner include Auckland Island shags (Phalacrocorax colensoi), black-backed gulls (Larus dominicanus), brown skuas (Catharacta skua), and northern giant petrels (Macronectes halli) in the sub-Antarctic Auckland Islands, 124 and North Atlantic right whales (E. ...
... Indeed, it is assumed that marine organisms not only remove the available nutrients and TMs from the environment, but they reinsert the digested components in the euphotic zone, through excretion products, recycling and making them bioavailable again (Ratnarajah et al., 2018). Actually, several studies have already demonstrated that Antarctic krill (Euphausia superba), and whales (whose main food source is krill) contribute, via their excretion products, to the recycling of TMs in the surface waters of the SO (e.g., Lavery et al., 2010;Nicol et al., 2010;Ratnarajah et al., 2014;Tovar-Sanchez et al., 2007;Wing et al., 2014;Schmidt et al., 2016). ...
... The average metal contents in the guano (μg g − 1 dry weight) from the three species of penguins studied [i.e., Zn (210 ± 90), Fe (4.1 ± 2.9) x 10 2 , Cu (2.0 ± 1.4) x 10 2 and Mn (30 ± 34) ( Table 1);] were of the same magnitude as those reported in whale feces (μg g − 1 dry weight): Zn (6.2 ± 4.3) x 10 2 , Fe (1.5 ± 1.4) x 10 2 , Cu (2.9 ± 2.4) x 10 2 and Mn (28 ± 17) (Ratnarajah et al., 2014) and one order of magnitude higher than krill (the main prey of whales and penguins) with a metal composition (μg g − 1 dry weight) of Zn (13.5 ± 1.7); Fe (24 ± 29) and Cu (10.2 ± 5.5) (Tovar-Sanchez et al., 2009). Therefore, as suggested for whales (Smetacek, 2008;Nicol et al., 2010), defecation by Antarctic penguins could have a fertilizing effect by releasing essential TMs back into the surface layer, linked from a common source of food represented by krill. ...
Penguins dominate the Antarctic avifauna. As key animals in the Antarctic ecosystem, they are monitored to evaluate the ecological status of this pristine and remote region and specifically, they have been used as effective bioindicators suitable for long-term monitoring of metals in the Antarctic environment. However, studies about the role of this emblematic organism could play in the recycling of trace metals (TMs) in the Antarctic ecosystem are very limited. In this study we evaluate, using the peer review research articles already published and our own findings, the distribution of metals (i.e., Ca, Fe, Al, Na, Zn, Mg, Cu, K, Cd, Mn, Sr, Cr, Ni, Pb, Hg, V, Ba, Co, La, Ag, Rb, Sb, Hf, Sc, Au and Cs) and the metalloid (As), measured in different biotic matrices, with emphasis on guano, of the Chinstrap (Pygoscelis antarcticus), Adélie (Pygoscelis adeliae) and Gentoo (Pygoscelis papua) penguins.
Regarding bioactive metals, the high concentrations (μg g⁻¹ dry weight) of Cu (2.0 ± 1.4) x 10², Fe (4.1 ± 2.9) x 10², Mn (30 ± 34) and Zn (210 ± 90) reported in the guano from all the penguin species studied including our data, are of the same order of magnitude as those reported for whale feces (μg g⁻¹ dry weight): Cu (2.9 ± 2.4) x 10², Fe (1.5 ± 1.4) x 10², Mn (28 ± 17) and Zn (6.2 ± 4.3) x 10², and one order of magnitude higher than the metal contents in krill (μg g⁻¹ dry weight) of Cu (10.2 ± 5.5), Fe (24 ± 29) and Zn (13.5 ± 1.7).
This suggest that penguin's excretion products could be an important source of these essential elements in the surface water, with an estimated annual release on a breeding season for Cu, Fe, Mn, Zn respectively of 28, 56, 4 and 29 tons, for the Chinstrap, Adélie and Gentoo penguins. The results provide evidence on the potential influence of penguins recycling TMs in the surface layer of the water column.
... 67,68 Marine vertebrates that feed at depth and return to the surface to breathe, recover from diving, rest, or warm up provide an opportunity for movement of nutrients from depth to surface waters, which can stimulate primary production. This has been documented for whales, where the term ''whale pump'' describes vertical transport of nutrients from depth to the surface layer, where whales release nutrient-rich fecal plumes, which can stimulate new phytoplankton growth 111,[125][126][127][128][129][130] (Figure 2). Movement patterns of various vertebrates suggests that they may transfer nutrients in this manner. ...
... 9,131-133 However, marine vertebrates that feed and release egesta within the surface layer support total, rather than new, primary production. 20,117,126 Blue whales in the Southern Ocean typically both feed and defecate within the surface layer 125 (Figure 2). Other species that may support C fixation in this manner include Auckland Island shags (Phalacrocorax colensoi), black-backed gulls (Larus dominicanus), brown skuas (Catharacta skua), and northern giant petrels (Macronectes halli) in the sub-Antarctic Auckland Islands, 124 and North Atlantic right whales (E. ...
In the last decade, the ocean has absorbed a quarter of the Earth's greenhouse gas emissions through the carbon (C) cycle, a naturally occurring process. Aspects of the ocean C cycle are now being incorporated into climate change mitigation and adaptation plans. Currently, too little is known about marine vertebrate C functions for their inclusion in policies. Fortunately, marine vertebrate biology, behavior, and ecology through the lens of C and nutrient cycling and flux is an emerging area of research that is rich in existing data. This review uses literature and trusted data sources to describe marine vertebrate C interactions, provides quantification where possible, and highlights knowledge gaps. Implications of better understanding the integral functions of marine vertebrates in the ocean C cycle include the need for consideration of these functions both in policies on nature-based climate change mitigation and adaptation, and in management of marine vertebrate populations.
... Euphausiids are a pelagic crustacean taxa with high grazing rates and lipid contents and with active behaviour, often involving horizontal and vertical migration. They are a pivotal prey item for many higher predators and are also key to biogeochemical cycling and carbon export in marine ecosystems (Everson, 2000;Pakhomov et al., 2002;Nicol et al., 2010;Hill et al., 2012;Siegel and Watkins, 2016b;Cavan et al., 2019). This is exemplified by the case of the euphausiid species Euphausia superba (Antarctic krill) in the Southern Ocean. ...
... Their importance in the diets of vertebrate predators is well documented (Grantham, 1977) with populations of penguins, whales, seals, and albatrosses all exhibiting a dependence on krill (Croxall et al., 1999;Reid et al., 2005;Trivelpiece et al., 2011;Braithwaite et al., 2015). Krill also play an important role in iron cycling (Nicol et al., 2010; and carbon export (Pakhomov et al., 2002) and support a commercial fishery, managed by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) (Everson, 2000;Siegel, 2016). ...
Antarctic krill are a key component of the Southern Ocean ecosystem and support a variety of predators as well as an expanding commercial fishery. Yet, despite the ecological and economic importance of krill, crucial aspects of their recruitment are not understood. We need greater understanding of these processes in order to predict and model their population dynamics in the light of growing anthropogenic pressures. This thesis identifies three knowledge gaps in krill reproduction and, through mapping, modelling and laboratory experimentation, provides new insights into these research areas. The area of study is the south-west Atlantic sector as it contains the highest densities of krill, key krill spawning grounds and has supported the entire krill fishery since the mid 2000’s. By generating distribution maps of six life stages of Antarctic krill, I identified key hotspots of egg production and nursery areas for larval krill along the Southern Scotia Arc. These maps showed that, although adult krill are widely distributed, the location of eggs, nauplii and metanauplii are mainly restricted to shelf and shelf-slope regions, partitioned spatially from the oceanic distributions of calyptopes and furcilia. By conducting a series of laboratory experiments, I identified the point at which temperature induces hatch failure and nauplii malformations in krill embryos. Hatching success decreased markedly above 3.0 °C, and the percentage of malformed nauplii reached 50 % at 5.0 °C. Furthermore, hatching success was variable and low (mean 27 %) between females. To further understand the whereabouts of spawning at the Antarctic Peninsula, and to test the hypothesis that krill migrate off-shelf to spawn, I conducted a seasonal analysis of adult krill size classes in relation to environmental variables. Contrary to the current paradigm, I found the adult krill population does not migrate on mass to off-shelf waters (>1000 m depth) to spawn their eggs. Instead all length categories of adult krill appear in reliably high concentrations ~ 75 km before the shelf break throughout the spawning season, where temperatures are lower and food availability is higher, potentially increasing growth and spawning potential. This information provides a more holistic view of krill spawning, reproduction and recruitment within the south-west Atlantic sector and provides policy makers with better information on which to base future krill fishery management decisions.
... [18][19][20][21]. Cetaceans are singular nutrient vectors in the oceans as (i) their waste products are greatly concentrated in nutrients compared to surface waters 7,8,22,23 , (ii) they are highly mobile, and can transfer nutrients against physical forces and between habitats of different nutrient regimes 24,25 , (iii) deep diving species can transfer nutrients from the ocean depths, where they feed, to the surface, mediating a nutrient pump known as the "whale pump" 7,26 , (iv) some species can form large aggregations and create "hotspots" and "hot moments" of nutrient biological cycling 24,27 , and, finally, (v) they are tied to the euphotic zone for breathing, where they release their wastes. On a large spatiotemporal scale, the gross nutrient enrichment caused by cetacean waste release is likely minor compared to that caused by physical processes (e.g. ...
Defecation by large whales is known to fertilise oceans with nutrients, stimulating phytoplankton and ecosystem productivity. However, our current understanding of these processes is limited to a few species, nutrients and ecosystems. Here, we investigate the role of cetacean communities in the worldwide biological cycling of two major nutrients and six trace nutrients. We show that cetaceans release more nutrients in mesotrophic to eutrophic temperate waters than in oligotrophic tropical waters, mirroring patterns of ecosystem productivity. The released nutrient cocktails also vary geographically, driven by the composition of cetacean communities. The roles of small cetaceans, deep diving cetaceans and baleen whales differ quantitatively and functionally, with contributions of small cetaceans and deep divers exceeding those of large whales in some areas. The functional diversity of cetacean communities expands beyond their role as top predators to include their role as active nutrient vectors, which might be equally important to local ecosystem dynamics.
... However, indicator coverage is assessed as partially adequate, mainly because of lack of seasonally-resolved long time-series on phytoplankton and ice algal biomass and species composition and in situ primary production measurements. (Nicol et al., 2010). Upper trophic levels (marine mammals, seabirds) show limited or substantial deviation from reference conditions. ...
... Polyunsaturated fatty acids (PUFA) have a fundamental role, among others, in the human nervous system development. Krill is the largest world biomass estimated around 300,000 million metric tons in the Atlantic ocean and it is the major food for baleen whales (Nicol et al., 2010). In 2009, the European Union allowed the introduction in the market of the lipid extract from Krill (Regulation EU 2009/752/EC, 2009 followed by the commission implementing regulation 2019/108). ...
Sustainable sources of dietary proteins are making their way into the market to reduce the impact of food production on the environment. Considerations from several standpoints are to be made when supporting the dietary shift toward these alternative sources, particularly regarding their nutritional and safety quality. Research is making enormous steps forwards by producing highly valuable proteins with little environmental impact or by turning by-products and wastes into sources of valuable proteins. The chapter will summarize the environmental, nutritional, and safety aspects related to novel foods, including microalgae, plants, insects, microbial, and synthetic-based ingredients. Consumer acceptability is taken into central consideration throughout the chapter being the final user of the novel food ingredients.
... 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). ...
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. ...
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 . ...
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. ...
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. ...
By transferring energy and nutrients from plankton to top predators, forage species play a major ecological role in marine food webs. While large differences in energy densities have been demonstrated among these species, other determinants of their quality remain poorly explored. We analysed 78 forage species from the Bay of Biscay, NE Atlantic, for their concentrations in various chemical elements with a documented biological role (i.e. micro‐nutrients). Species encompassed jellyfish, crustaceans, cephalopods, cartilaginous and bony fish. Elements included two essential macro‐minerals (nitrogen and phosphorous) and nine trace elements (arsenic (As), cobalt, copper (Cu), chromium, iron, manganese, nickel, selenium (Se), zinc). We showed a broad range of elemental composition values across forage species, partly driven by taxonomy (fish versus crustaceans/cephalopods) or their habitat (coastal versus oceanic, pelagic versus benthic). Some elements (As, Cu or Se) were more variable than others, especially in fish for Cu and Se. The 78 forage species were then classified by hierarchical clustering analysis (HCA) into different nutritional groups, based on their composition in eleven elements. Mean concentrations of each element in the diet of eight cetacean species was finally calculated, as well as the importance of each nutritional group (as defined by HCA including all elements) for each predator species. We revealed contrasting diets in terms of exposure to elements. Neritic common dolphins and harbour porpoises but also minke whales were thus mainly supplied by the Se‐enriched nutritional group composed of small (pelagic) schooling fish (including sandeels, (horse) mackerel and also some Clupeids), while the diets of pilot whales or Risso's dolphins that mostly consume benthic cephalopods were clearly Cu‐enriched. This study raises the issue of essential element composition as another determinant of food quality, and the risk associated with changes in forage species' availability for the proper functioning of marine food webs and ecosystems.
... Whales can also aid iron availability by mixing ocean waters through their vigorous tail movements. thus boosting the availability of food for krill 6,7 . ...
Reaching a deeper understanding of the ocean ecosystems that maintain whales might aid conservation efforts. Measurements of the animals’ krill intake indicate that previous figures were substantial underestimates. Whales in the ocean consume unexpectedly high levels of krill.
... Many vertebrates in the SO, including the great whales, are highly dependent on Antarctic krill (13)(14)(15). Apparently paradoxically, whales also seem to support krill populations by stimulating primary productivity via iron recycling, a feedback mechanism known as the "krill paradox" (16,17). The El Niño-Southern Oscillation (ENSO) is a well-known climate driver affecting the SO by producing interannual changes in sea ice and atmospheric effects (18,19). ...
Whales contribute to marine ecosystem functioning, and they may play a role in mitigating climate change and supporting the Antarctic krill (Euphausia superba) population, a keystone prey species that sustains the entire Southern Ocean (SO) ecosystem. By analyzing a five-decade (1971–2017) data series of individual southern right whales (SRWs; Eubalaena australis) photo-identified at Península Valdés, Argentina, we found a marked increase in whale mortality rates following El Niño events. By modeling how the population responds to changes in the frequency and intensity of El Niño events, we found that such events are likely to impede SRW population recovery and could even cause population decline. Such outcomes have the potential to disrupt food-web interactions in the SO, weakening that ecosystem’s contribution to the mitigation of climate change at a global scale.
... Therefore, systematic data on their (yearround) presence, abundance, and spatial distribution are missing for the ASSO. Insights on distribution are however vital for understanding their present and future role as large predators in structuring the Southern Ocean ecosystem 3,4 . A long-term autonomous passive acoustic monitoring (PAM) network was installed in 2010 to record humpback whales in their natural Antarctic environment year-round. ...
Humpback whales are thought to undertake annual migrations between their low latitude breeding grounds and high latitude feeding grounds. However, under specific conditions, humpback whales sometimes change their migratory destination or skip migration overall. Here we document the surprising persistent presence of humpback whales in the Atlantic sector of the Southern Ocean during five years (2011, 2012, 2013, 2017, and 2018) using passive acoustic data. However, in the El Niño years 2015 and 2016, humpback whales were virtually absent. Our data show that humpback whales are systematically present in the Atlantic sector of the Southern Ocean and suggest that these whales are particularly sensitive to climate oscillations which have profound effects on winds, sea ice extent, primary production, and especially krill productivity. Schall et al. use passive acoustic recordings of humpback whale calls to report the presence of humpback whales in the Atlantic sector of the Southern Ocean between 2011 and 2018. This serves as the first long-term report of humpback whales on a Southern Ocean feeding ground, and their notable absence during the El Niño years of 2015 and 2016 indicates that the inter-annual variability in their acoustic presence is driven by large-scale climate variability.
... Moreover, the statistical power needed to determine ecological change points may not be available (CCAMLR, 2003;Reid et al., 2007). Translation will also be made complex should the ecosystem become more productive as whales recover (Dewar et al., 2006;Nicol et al., 2010), which they now are within the Scotia Sea (Zerbini et al., 2019;Calderan et al., 2020). The approach reported in Supplementary Material SB, could be enhanced with additional monitoring data, including from krill-eating fish (Main et al., 2009;Hollyman et al., In Review) and cetaceans (Zerbini et al., 2019). ...
The objective of the ecosystem approach to fisheries management is to sustain healthy marine ecosystems and the fisheries they support. One of the earliest implementations was in the Southern Ocean, where decision rules and stock reference points were developed for managing the Antarctic krill fishery, together with an ecosystem-monitoring programme intended to aid management decisions. This latter component has not been incorporated directly into management, so here, we consider variability in the krill fishery at South Georgia, relating it to physical and biological monitoring indices, finding sea surface temperature to be a key correlate with both annual catch and long-term biological indices. Some indices from krill predators showed significant positive relationships with krill harvesting in the preceding winter, presumably indicative of the importance of winter foraging conditions. We explore how ecological structure affects results, examining two monitoring sites 100 km apart. Results suggest different biological conditions at the two sites, probably reflecting different scales of ecosystem operation, emphasizing that an appreciation of scale will enhance krill fishery management. Finally, in reviewing different drivers of ecological change, we identify important additional monitoring that would help better reflect ecosystem status, improve the utility of CEMP, providing information necessary for the ecosystem approach at South Georgia.
... The 2019 Scientific Committee of the Commission (SC-CAMLR) report also notes the fundamental role played by Antarctic krill in sequestering carbon, observing that 'this is highly significant as it could amplify the ecosystem feedback loops and thus accelerate effects of climate changes' [90,10,69]. ...
Human activities in the Southern Ocean are managed through the international consensus-based Convention on the Conservation of Antarctic Marine Living Resources. In recent years, rapid environmental changes likely associated with the impact of global anthropogenic climate change have been reported in parts of the Antarctic region, and research suggests ongoing and increasing changes can be expected. The observed and projected changes reflected in Antarctic climate change research are likely to affect the efforts of the Convention’s Commission to deliver the objective of the Convention – the conservation of Antarctic marine living resources – and will also influence the role of the Southern Ocean in delivering ecosystems services, including globally significant contributions to carbon capture and biodiversity. An analysis of the annual reports of the meetings of the Commission and its Scientific Committee finds that the Commission’s considerations of climate change thus far are inadequate. The paper concludes that without prompt action to address the issue, the effects of climate change in the Convention area are highly likely to significantly impact the effective implementation of the Convention’s objective. The possible implications of CCAMLR’s failure to act going forward are explored, and some suggested management response actions are provided.
... Αντίστοιχα, στο Νότιο Ωκεανό όπου ο σίδηρος (Fe) αποτελεί θρεπτικό περιοριστικό παράγοντα, οι φάλαινες αποβάλλουν σημαντικές ποσότητές του μέσω των κοπράνων στα επιφανειακά νερά, καθώς τρέφονται με το κριλλ της Ανταρκτικής (Euphausia superba), το οποίο τρέφεται με διάτομα. Η περιεκτικότητα των κοπράνων σε σίδηρο (Fe) είναι μεγάλη και έτσι εκτιμάται ότι η ανάκαμψη των φαλαινών θα μπορούσε να αυξήσει την παραγωγικότητα στο Νότιο Ωκεανό, μέσω αυτής της θετικής ανατροφοδότησης (feedback) σιδήρου (Nicol et al., 2010). Επιπλέον, μυστακοκήτη όπως οι μεγάπτερες φάλαινες (Megaptera novaeangliae) μέσω της ετήσιας μετανάστευσης, μεταφέρουν θρεπτικά στοιχεία και άλλα σημαντικά υλικά από τις περιοχές σίτισης των μεγάλων γεωγραφικών πλατών στις ολιγότροφες περιοχές αναπαραγωγής και ανατροφής κοντά στον Ισημερινό. ...
Η παρούσα εργασία καταγράφει και περιγράφει τις τεχνικές παρακολούθησης που εφαρμόζονται στην σύγχρονη επιστημονική έρευνα για τα κητώδη, με ειδίκευση τη συλλογή δεδομένων για την εκτίμηση των πληθυσμών και της κατανομής των ειδών. Βασική μεθοδολογία για τη συγγραφή της αποτέλεσε η διεξοδική μελέτη της πρόσφατης βιβλιογραφίας στο πεδίο της επιστήμης των θαλάσσιων θηλαστικών.
Η εργασία χωρίζεται σε τέσσερα κεφάλαια.
Στο πρώτο κεφάλαιο αποτυπώνονται τα γενικά στοιχεία γύρω από τα κητώδη. Περιγράφονται βασικά βιολογικά και οικολογικά χαρακτηριστικά των κητωδών και γίνεται λόγος για την συμβολή τους στα οικοσυστήματα και την αξία τους γενικότερα. Το κεφάλαιο κλείνει με μια αναδρομή στη σχέση του ανθρώπου με τα κητώδη από την εποχή της φαλαινοθηρίας στις σημερινές προσπάθειες προστασίας.
Το δεύτερο κεφάλαιο περιγράφει τις σημαντικότερες τεχνικές παρακολούθησης της αφθονίας και της κατανομής των κητωδών. Με βάση τα τεχνικά μέσα και τον τρόπο που χρησιμοποιούνται για τη δειγματοληψία των δεδομένων, διακρίνονται πέντε τεχνικές και επεξηγούνται τα βασικά χαρακτηριστικά, τα πλεονεκτήματα, τα μειονεκτήματα και η μελλοντική τους βελτίωση.
Στο τρίτο κεφάλαιο παρουσιάζεται η σημερινή γνώση της αφθονίας και της κατανομής των ειδών στη Μεσόγειο και τη Μαύρη θάλασσα, με βάση τα αποτελέσματα των επιστημονικών ερευνών τις τελευταίες δεκαετίες. Αναφέρονται παραδείγματα από τις έρευνες για κάθε είδος ξεχωριστά και οι συγκεκριμένες τεχνικές που εφαρμόστηκαν.
Τέλος, στο τέταρτο κεφάλαιο παρατίθενται τα συμπεράσματα που προκύπτουν από το σύνολο της εργασίας και η συζήτηση για την αποτελεσματική προστασία και διατήρηση των κητωδών που παραμένει ανοικτή.
... Ce mécanisme est maintenu par le recyclage du fer par le zooplancton et les bactéries dans les eaux de sub-surface. Enfin, via leurs pelotes fécales, la migration verticale dans la colonne d'eau de certains organismes et animaux tels que le krill ou encore les baleines peut contribuer à l'apport de fer particulaire et dissous (Tovar-Sanchez et al., 2007 ;Nicol et al., 2010 ;Schmidt et al., 2011 ;Ratnarajah et al., 2015). ...
Il existe encore des incertitudes importantes concernant le cycle biogéochimique du fer, sa nature et la quantification de ses sources. Ce fer dissous (dFe) est considéré comme étant la forme la plus biodisponible ce qui a induit la sous-évaluation du rôle du fer particulaire (pFe) comme une source potentielle de dFe. Pourtant, la remise en suspension des sédiments libère davantage de pFe que de dFe. Dans ce contexte, ma thèse remet en question la vision traditionnelle du rôle du fer particulaire inorganique sédimentaire (pFeinorg) et propose la première modélisation de ce dernier comme source externe de dFe. Le modèle numérique PISCES a donc été adapté pour tenir compte d’un flux supplémentaire de fer en s’appuyant sur une climatologie de la dynamique à partir de la configuration NEMOPISCES globale à 2 degrés de résolution. Les simulations mettent en exergue la sensibilité de la biomasse phytoplanctonique à la forme de fer provenant des sédiments ; les limitations en macronutriments et celles en fer sont considérablement modifiées, ainsi que les gradients côte–large de chlorophylle. Le transport plus efficace du fer en tant que pFeinorg permet d’atteindre des régions éloignées de sa source. Son accumulation et sa dissolution dans les zones de convergences induisent via downwelling l’enrichissement de la surbsurface ; à ceci s’ajoute le processus de chute de la particule. Cependant, ces processus demeurent peu étudiés. Les tests de sensibilité ont montré que le gain (absence de chute) ou la perte (chute rapide) en fer dans l’océan, ou encore la prépondérance du pFe sur le dFe seraient modulés par le taux de dissolution. En revanche, la distribution de la chlorophylle est mieux représentée dans la mesure où les processus qui régissent la distribution du PFeinorg et du dFe qui en dérive sont, de concert, pris en compte. Une manière de mieux représenter les répercussions du fer sur les cycles biogéochimiques marins, serait de mieux contraindre les processus liés au PFeinorg.
... The close association of the historical sperm whale distribution and elevated ocean productivity featured in the upwelling zone is unlikely accidental (Jaquet, 1996), though efforts to map out the missing causative links via measuring sperm whale prey dynamics in the deep scattering layer using shipboards acoustic tools are difficult but ongoing (Hazen and Johnston, 2010). The relationship between surface ocean productivity and presence of whales may be even more complicated, as whales foraging at depth and defecating at the surface have been shown to be a locally significant pathway of iron fertilization in iron limited waters such as the Equatorial Pacific (Lavery et al., 2010;Nicol et al., 2010). If this is the case, the role of whales in the ecology and the nutrient dynamics in the protected areas would have to be re-evaluated and future studies of these systems would have to consider that instead of being solely consumers of the carbon produced in the equatorial upwelling, the presence of whales might be contributing to the elevated primary production of the area. ...
The Phoenix Archipelago in the Central Pacific is situated in what was once one of the most productive areas for capturing sperm whales (Physeter macrocephalus). These whales were the focal targets of American offshore whalers in the mid-19th century along the equator, an area known as the “on-the-line” whaling grounds. Now, as large-scale Marine Protected Areas (MPAs) have provided protection for marine mammals and their food sources, it is important to have a solid understanding of historical baselines so recovery distributions can be compared with pre-whaling distributions. The Phoenix Islands archipelago contains two large MPAs: the Phoenix Islands Protected Area (PIPA), established by Kiribati in 2008, and the Howland/Baker unit of the Pacific Remote Islands Marine National Monument (PRIMNM), established by the United States in 2009. Using historic whaling records from American whaling vessels operated through the wider Phoenix Archipelago region, we reconstructed information about the presence and distribution of P. microcephalus throughout the 1800s within and around PIPA and the Howland/Baker units of the PRIMNM. Historical data analyzed using ArcGIS showed that sperm whales were present year-round within the study area, which is consistent with 20th century records from the Ocean Biogeographic Information System (OBIS). A Getis Ord Gi∗ hotspot analysis also revealed sighting hotspots within PIPA and near Howland and Baker, suggesting that these two areas may be of long-term ecological importance to sperm whales in the central Pacific. The New England whaling fleet ceased whaling effort in the central Pacific in the late 1800s, and publicly available records since that time are scarce. There has been no modern systematic whale survey ever conducted within the Phoenix Archipelago, though anecdotal accounts and sightings have been compiled over the years. These intermittent accounts suggest that though whale populations have not recovered to pre-whaling baselines, large-scale MPAs may play a role in helping to foster a resurgence of marine mammal populations. As the network of large-scale MPAs continue to grow as part of the commitment to ocean conservation set forth by UNESCO, IUCN, and the UN Decade for Ocean Science, historical baselines will be critical as a “yardstick” to measure population resurgence success for each MPA, and for populations overall.
... The Southern Ocean includes the most important feeding areas for baleen whales in the Southern Hemisphere [12], but knowledge on the year-round distribution of baleen whales in many regions of the Southern Ocean is still limited due to the restricted accessibility of these areas outside the summer months. Baseline information on baleen whale distribution and ecology is key for understanding their role as large predators in structuring the Southern Ocean ecosystem [13]. ...
Southern Hemisphere humpback whales ( Megaptera novaeangliae ) inhabit a wide variety of ecosystems including both low- and high-latitude areas. Understanding the habitat selection of humpback whale populations is key for humpback whale stock management and general ecosystem management. In the Atlantic sector of the Southern Ocean ( ASSO ), the investigation of baleen whale distribution by sighting surveys is temporally restricted to the austral summer. The implementation of autonomous passive acoustic monitoring, in turn, allows the study of vocal baleen whales year-round. This study describes the results of analysing passive acoustic data spanning 12 recording positions throughout the ASSO applying a combination of automatic and manual analysis methods to register humpback whale acoustic activity. Humpback whales were present at nine recording positions with higher acoustic activities towards lower latitudes and the eastern and western edges of the ASSO . During all months, except December (the month with the fewest recordings), humpback whale acoustic activity was registered in the ASSO . The acoustic presence of humpback whales at various locations in the ASSO confirms previous observations that part of the population remains in high-latitude waters beyond austral summer, presumably to feed. The spatial and temporal extent of humpback whale presence in the ASSO suggests that this area may be used by multiple humpback whale breeding populations as a feeding ground.
... plankton 3,4 and has a key role in biogeochemical cycles, such as carbon export 5 and iron-recycling 6,7 . ...
Antarctic krill, Euphausia superba, supports a valuable commercial fishery in the Southwest Atlantic, which holds the highest krill densities and is warming rapidly. The krill catch is increasing, is concentrated in a small area, and has shifted seasonally from summer to autumn/winter. The fishery is managed by the Commission for the Conservation of Antarctic Marine Living Resources, with the main goal of safeguarding the large populations of krill-dependent predators. Here we show that, because of the restricted distribution of successfully spawning krill and high inter-annual variability in their biomass, the risk of direct fishery impacts on the krill stock itself might be higher than previously thought. We show how management benefits could be achieved by incorporating uncertainty surrounding key aspects of krill ecology into management decisions, and how knowledge can be improved in these key areas. This improved information may be supplied, in part, by the fishery itself. A ntarctic krill (Euphausia superba, hereafter referred as krill) is a key dietary item for vertebrate predators, such as whales, seals, seabirds, and fish, as well as for invertebrates 1. At between 300 and 500 million tonnes 2 its biomass is the largest of any multicellular wild animal species on the planet 3. Krill is an important grazer of autotrophic and heterotrophic
... Animals can act as powerful biological pumps and transfer nutrients, trace elements and environmental contaminants between ecosystems [1][2][3][4][5] . Seabirds are arguably the most pertinent present-day vectors of compounds from marine to terrestrial ecosystems 6,7 and have been demonstrated to enhance production and alter dynamics of local ecosystems adjacent to breeding colonies [8][9][10] . ...
Seabirds redistribute nutrients between different ecosystem compartments and over vast geographical areas. This nutrient transfer may impact both local ecosystems on seabird breeding islands and regional biogeochemical cycling, but these processes are seldom considered in local conservation plans or biogeochemical models. The island of Stora Karlsö in the Baltic Sea hosts the largest concentration of piscivorous seabirds in the region, and also hosts a large colony of insectivorous House martins Delichon urbicum adjacent to the breeding seabirds. We show that a previously reported unusually high insectivore abundance was explained by large amounts of chironomids-highly enriched in δ 15 N-that feed on seabird residues as larvae along rocky shores to eventually emerge as flying adults. Benthic ammonium and phosphate fluxes were up to 163% and 153% higher close to the colony (1,300 m distance) than further away (2,700 m) and the estimated nutrient release from the seabirds at were in the same order of magnitude as the loads from the largest waste-water treatment plants in the region. The trophic cascade impacting insectivorous passerines and the substantial redistribution of nutrients suggest that seabird nutrient transfer should be increasingly considered in local conservation plans and regional nutrient cycling models.
The ecosystem approach to fisheries has been discussed since the 1980s. It aims to reduce risks from fisheries to whole, or components of, ecosystems, not just to target species. Precautionary approaches further aim to keep the risk of damage to a low level. Here, we provide a dynamic framework for spreading the ecosystems risk of fisheries in space and time, a method that can be used from the outset of developing fisheries and continually updated as new knowledge becomes available. Importantly, this method integrates qualitative and quantitative approaches to assess risk and provides mechanisms to both spread the risk, including enabling closed areas to help offset risk, and adjust catch limits to keep regional risk to a baseline level. Also, the framework does not require uniform data standards across a region but can incorporate spatially and temporally heterogeneous data and knowledge. The approach can be coupled with the conservation of biodiversity in marine protected areas, addressing potential overlap of fisheries with areas of high conservation value. It accounts for spatial and temporal heterogeneity in ecosystems, including the different spatial and temporal scales at which organisms function. We develop the framework in the first section of the paper, including a simple illustration of its application. In the framework we include methods for using closed areas to offset risk or for conserving biodiversity of high conservation value. We also present methods that could be used to account for uncertainties in input data and knowledge. In the second section, we present a real-world illustration of the application of the framework to managing risks of food web effects of fishing for Antarctic krill in the Southern Ocean. Last, we comment on the wider application and development of the framework as information improves.
Since 1970, there has been an overall decline in wildlife populations in the order of 52%. Freshwater species populations have declined by 76%; species populations in Central and South America have declined by 83%; and in the Indo-Pacific by 67%. These are often not complete extinctions, but large declines in the numbers of animals in each species, as well as habitat loss. This presents us with a tremendous opportunity, before it is too late to rescue many species. This book documents the present state of wildlife on a global scale, using a taxonomic approach, and serving as a one stop place for people involved in conservation to be able to find out what is in decline, and the success stories that have occurred to bring back species from the brink of extinction - primarily due to conservation management techniques - as models for what we might achieve in the future.
The growth of diatoms in the Southern Ocean, especially the region surrounding the West Antarctic Peninsula, is frequently constrained by low dissolved iron and other trace metal concentrations. This challenge may be overcome by mutualisms between diatoms and co-occurring associated bacteria, in which diatoms produce organic carbon as a substrate for bacterial growth, and bacteria produce siderophores, metal-binding ligands that can supply diatoms with metals upon uptake as well as other useful secondary compounds for diatom growth like vitamins. To examine the relationships between diatoms and bacteria in the plankton (diatom) size class (> 3 µm), we sampled both bacterial and diatom community composition with accompanying environmental metadata across a naturally occurring concentration gradient of macronutrients, trace metals and siderophores at 21 stations near the West Antarctic Peninsula (WAP). Offshore Drake Passage stations had low dissolved iron (0.33 ± 0.15 nM), while the stations closer to the continental margin had higher dissolved iron (5.05 ± 1.83 nM). A similar geographic pattern was observed for macronutrients and most other trace metals measured, but there was not a clear inshore-offshore gradient in siderophore concentrations. The diatom and bacteria assemblages, determined using 18S and 16S rDNA sequencing respectively, were similar by location sampled, and variance in both assemblages was driven in part by concentrations of soluble reactive phosphorous, dissolved manganese, and dissolved copper, which were all higher near the continent. Some of the most common diatom sequence types observed were Thalassiosira and Fragilariopsis , and bacteria in the plankton size fraction were most commonly Bacteroidetes and Gammaproteobacteria. Network analysis showed positive associations between diatoms and bacteria, indicating possible in situ mutualisms through strategies such as siderophore and vitamin biosynthesis and exchange. This work furthers the understanding of how naturally occurring gradients of metals and nutrients influence diatom-bacteria interactions. Our data suggest that distinct groups of diatoms and associated bacteria are interacting under different trace metal regimes in the WAP, and that diatoms with different bacterial partners may have different modes of biologically supplied trace metals.
Mysticetes (baleen whales) include the largest animals on Earth and are renowned for their songs and long-distance communication. Even so, the scope and origins of their hearing abilities remain poorly understood. Recent work on their sister clade, the toothed whales (odontocetes), has revealed notably convergent trends in the evolution of their inner ear. Here, we test whether the same applies to baleen whales via SURFACE, a phylogenetic method that fits Ornstein-Uhlenbeck models with stepwise Akaike Information Criterion to identify instances of convergent evolution. We identify a single convergent regime, including minke (Balaenoptera acutorostrata) and Bryde’s (Balaenoptera edeni) whales, which, however, is not statistically significant. We discuss potential reasons for the overall absence of convergence and suggest improvements for future work.
The present paper is a review of the available literature on the significance of forage fish, the plethora of services they provide, and the threats faced by them. Forage fish are pelagic planktivorous species that operate as conduits of energy between the lower trophic level (plankton) and the upper trophic level (predators). A variety of ecosystem services are provided by them, from serving as prey for higher trophic levels to producing fish meal and oil. Forage fish have a consumption value for humans and cultural importance to many societies. Forage fish have faced constant natural and anthropogenic threats in the past, resulting in numerous fish collapses which subsequently impacted their predators. The economic benefit provided by forage fish has been estimated to be approximately $ 18.7 billion per annum. An introspection of the data on ecosystem services revealed lack of data on regulating and cultural services, eventually leading to a monetary underestimation and their commercial prioritization over the wider benefits they provide.
Changes in habitat availability and prey abundance are predicted to adversely influence survival and reproduction of wildlife in the Southern Ocean. Some populations of southern right whale (SRW; Eubalaena australis) are showing dramatic changes in habitat use. Surveys were undertaken in the austral winters of 2020 and 2021 at the key nursery and socialising ground for New Zealand SRWs: Port Ross, Auckland Islands, with 548 encounters and 599 skin biopsy samples collected. Data from these two surveys spanned peak periods of use and were used to test the hypothesis there have been shifts in the phenology, demographic composition and behaviour of SRWs using the Auckland Islands over the past three decades. The behavioural phenology and demographic composition of SRW resembles that observed in the 1990s. In contrast, the proportion of groups containing cow-calf pairs increased from 20% in the 1998 survey to 50% in 2020/21. These changes are consistent with a growing population undergoing strong recruitment, not limited by food resources. Continued use of Port Ross by all SRW demographic classes confirms this as key habitat for SRW in New Zealand waters, and we support increased enforcement of existing management measures to reduce whale-vessel interactions in this remote subantarctic archipelago.
The Atlantic sector of the Southern Ocean (ASSO) has one of the highest densities of Antarctic krill ( Euphausia superba ) compared to other polar and subpolar regions, which attracts migratory baleen whale species to aggregate in this area for feeding. Humpback whales ( Megaptera novaeangliae ) also sing extensively while on the Southern Ocean feeding grounds which allows for the exploration of song similarity between feeding grounds and breeding populations which helps to understand population mixing. The results of comparative song analyses between the ASSO and the Ecuadorian and Brazilian breeding populations and recordings from the Chilean, South African and Namibian migration routes/mid-latitude feeding grounds revealed that individuals from at least three humpback whale breeding populations most likely migrate to shared feeding grounds in the ASSO. Humpback whales from different populations potentially mix at different times (i.e., years) at feeding hotspots in variable locations. The ASSO seems to provide sufficient prey resources and seems to present an important area for both cultural and maybe even genetic exchange between populations supporting the maintenance of large gene pools. Assuming that multi-population feeding hotspots are also suitable habitat for krill and other krill-dependent predators, these areas in the ASSO should be carefully managed integrating population, ecosystem and fisheries management.
Primary producers are the foundation of marine food webs and require reliable nutrient sources to maintain their important role with ecosystems. While marine mammals and seabirds can play critical roles in marine nutrient cycling, their contributions are often overlooked. Southeast Alaska’s marine environment supports abundant marine mammal and seabird populations in addition to valuable fisheries. Nonetheless, there is still relatively little known about nutrient sources and fluxes in this region which is a critical component of fisheries management. The goal of our study was to advance knowledge of the role of mammals and seabirds in marine nutrient cycling and to understand how changing marine mammal and seabird populations may alter ecosystem dynamics. We utilized qualitative network models (QNMs) to examine how a simulated Southeast Alaska ecosystem would respond to an increase in marine mammals, seabirds, and nutrients. Researchers are increasingly utilizing QNMs as a first step in the development of ecosystem-based fisheries management plans as their adaptable nature is well suited to address rapidly changing climatic conditions. Our results indicate that marine mammals and seabirds make important contributions to marine nutrient concentrations in the region and that these valuable ecosystem services should not be overlooked.
The highly productive waters off Iceland are an important feeding ground for baleen whales. Five balaenopterid species coexist there during the summer feeding season: the blue whale, the fin whale, the sei whale, the humpback whale and the common minke whale. For capital breeders such as baleen whales, niche partitioning and reduced interspecific competition during their stay in the feeding grounds may be critical for the completion of their annual cycles and the long-term stability of populations. Coexistence often entails spatio-temporal or trophic segregation to avoid competitive exclusion. With the aim of studying how these species share habitat and trophic resources, we analyzed the δ¹³C, δ¹⁵N and δ³⁴S values in skin samples. Bayesian stable isotope mixing models to calculate compositional mixture of food sources showed that most species segregate by resourcing on different prey. Segregation was further enhanced by some degree of spatio-temporal exclusion. Overall, clear ecological niche partitioning was apparent between all species except between blue and fin whales. All the species consumed krill and, except for the common minke whale, this was the dominant prey. Among baleen whales, common minke whales and humpback whales were the major predators of sand eel, capelin and herring. In humpback whales, a strong reliance on krill may explain the apparently low rates of local entanglement in fishing nets that the species shows in other areas. Except for the blue whale, all species have shown evidence of adapting to shifts in prey availability and thus suggested capacity to cope with variability. However, in a scenario of increasing environmental variability associated to global warming, the overlap between ecological niches may have to decrease to allow long-term coexistence.
Nontrophic interactions can contribute to negative and positive feedbacks within a community, thus affecting likelihood of regime shifts; however, assessing the nature and importance of these effects in a network remains challenging, especially for pelagic ecosystems. Here, we present a qualitative modeling approach for assessing the importance of different effects and resultant feedbacks for community stability, using a Southern Ocean example. A potentially important positive feedback in the Southern Ocean ecosystem involves production of a chemical cue, dimethyl sulfide (DMS), by some phytoplankton. Production of DMS can promote phytoplankton growth by attracting predators of phytoplankton‐grazers, and nutrients released as feces from those predators help fertilize the water column. We explored how uncertainties in the nature of this feedback affect community stability in a set of small, community models. We found that stability varied substantially depending on how the community was modeled, but that the interactions most important for determining stability were consistent across all models. Model stability was sensitive to the strength of phytoplankton competition, controls on phytoplankton, DMS production and release, and predator attraction to DMS, suggesting that the community could be destabilized by perturbation affecting these interactions. Incorporating DMS‐mediated feedbacks into a larger Southern Ocean network had a moderate impact on stability characteristics and altered the trophic level at which the system would be most vulnerable to perturbation.
Aim
The global decline of megafauna is believed to have had significant and widespread ecological impacts. One such extinction of likely important consequence is the 18th century extinction of the Steller’s sea cow ( Hydrodamalis gigas ); however, little has been written about how the loss of this megaherbivore may have impacted coastal ecosystem dynamics. Drawing on historical evidence, sea cow biology, kelp forest ecology, and the ecology of extant sirenians, we propose several discrete hypotheses about the effects Steller’s sea cows may have had on kelp forest dynamics of the North Pacific.
Location
North Pacific Ocean.
Time period
Pre‐1760s.
Major taxa studied
Steller’s sea cow ( Hydrodamalis gigas ).
Results & conclusions
The evidence we review suggests that Steller’s sea cows exerted substantial direct and indirect influences on kelp forests, likely affecting the physical ecosystem structure, productivity, nutrient cycling, species interactions, and export of nutrients to surrounding ecosystems. This suggests that kelp forest dynamics and resilience were already significantly altered prior to the influence of more recent and well‐known stressors, such as industrial fishing and climate change, and illustrates the important ecological roles that are lost with megafaunal extinction.
Climatic changes have had significant impacts on marine ecosystems, including apex predators such as cetaceans. A more complete understanding of the potential impacts of climate change on cetaceans is necessary to ensure their conservation. Here we present a review of the literature on the impacts of climate change on cetacean distribution, habitat and migrations and highlight research gaps. Our results indicate that due to rising sea surface temperatures (SSTs) and/or reducing sea ice extent, a variety of impacts on the distribution, habitat and migration of cetaceans have been observed to date and several more are predicted to occur over the next century. Many species have demonstrated a poleward shift, following their preferred SSTs to higher latitudes, and some have altered the timing of their migrations, while others appear not to be affected. These changes may benefit certain species, while others will be placed under extreme pressure and may face increased risk of extinction. Broader implications may include increased inter-specific competition, genetic alterations, ecosystem-level changes and conservation challenges. Existing research on the topic is both extremely limited and unevenly distributed (geographically and phylogenetically). Further research is necessary to determine which species and populations are most vulnerable and require the earliest conservation action.
Large animals such as sea birds and marine mammals can transport limiting nutrients between different regions of the ocean, thereby stimulating and enhancing productivity. In Antarctica this process is influenced by formation and breakup of sea ice and its influence on the feeding behaviour of predators and their prey. We used analyses of bioactive metals (for example, Fe, Co, Mn), macronutrients (for example, N) and stable isotopes (δ¹³C and δ¹⁵N) in the excreta of Adélie (Pygoscelis adeliae) and emperor penguins (Aptenodytes forsteri) as well as Weddell seals (Leptonychotes weddellii) from multiple sites, among multiple years (2012–2014) to resolve how changes in sea ice dynamics, as indicated by MODIS satellite images, were coincident with prey switching and likely changes in nutrient fluxes between the offshore pelagic and coastal zones. We also sampled excreta of the south polar skua (Stercorarius maccormicki), which preys on penguins and scavenges the remains of both penguins and seals. We found strong coincidence of isotopic evidence for prey switching, between euphausiids (Euphausia superba and E. crystallorophias) and pelagic/cryopelagic fishes (for example, Pleuragramma antarcticum) in penguins, and between pelagic/cryopelagic fishes and Antarctic toothfish (Dissostichus mawsoni) in Weddell seals, with changes in sea ice cover among years. Further, prey switching was strongly linked to changes in the concentrations of nutrients (Fe and N) deposited in coastal environments by both penguins and seals. Our findings have important implications for understanding how the roles of large animals in supporting coastal productivity may shift with environmental conditions in polar ecosystems.
Limiting climate warming below 2°C requires both reducing anthropic greenhouse gas emissions and sequestering more atmospheric carbon. Natural Climate Solutions (NCS) rely on the ability of ecosystems to capture and store carbon. Despite the important role of marine megafauna on the ocean carbon cycle, its potential as a NCS has not yet been explored. Here, we quantify the amount of carbon potentially sequestered by five baleen whale species across the Southern Hemisphere between 1890 and 2100 through both the sinking of carcasses after natural death and the fertilisation of phytoplankton by nutrients in faeces. At their pre-exploitation abundances, the five whales could sequester 10.6 106 tonnes of carbon per year (tC.yr-1) but this natural carbon sink was reduced at 2 106 tC.yr-1 in 1965 due to commercial whaling. However, the restoration of whale populations could sequester 8.7 106 tC.yr-1 at the end of the 21st century suggesting an efficient but neglected NCS that remains to be estimated globally including all marine vertebrates.
Analysis of data on the hydrodynamics of swimming by 100 species, ranging in body mass (M) from bacteria to blue whales, leads to a model of animal-induced turbulence in the ocean. Swimming speeds and Reynolds number (Re) are strongly correlated with body mass, both at typical cruising speeds and at escape speeds associated with predator-prey interactions. We find that animals operating at Re > 1000 typically form schools that are concentrated by many orders of magnitude above their average abundance. We calculate the rate of kinetic energy production by 11 representative species of schooling animals ranging in size from euphausiids to whales, and find it to be of the order of 10(-5) W kg(-1), regardless of animal size. Animal-induced turbulence is comparable in magnitude to rates of turbulent energy dissipation (epsilon) that result from major storms. The horizontal length scale (10 to 1000 m) of energy production rate by animal schools is comparable to the observed fine-scale variability in epsilon. We present detailed case studies of 4 species -Atlantic bluefin tuna, Norwegian herring, northern anchovy and Antarctic krill -all of which have schooling behavior that places them within the zone of maximum seasonal stratification where their energy production rate would be 3 to 4 orders of magnitude greater than the background average rate of turbulent energy dissipation. We conclude that schooling animals are an important source of fine-scale turbulent mixing in the ocean, especially in coastal regions during summer.
Magnetic sector ICP-MS was used to measure the first row transition metals Sc, V, Cr, Mn, Fe, Co, Ni, Cu and Zn in certified reference materials, viz., NIST SRM 1643d Water, NIST SRM 1573a Tomato Leaves, NIST SRM 1566a Oyster Tissue, Bio-Rad Level 1 Urine, and in geological standard rocks BHVO-1, BCR-1 and AGV-1. Solid samples were prepared for ICP-MS analysis via high temperature and pressure digestion, followed by simple dilution (1 + 99 or 1 + 999). The water sample was analysed without further treatment, while the urine sample was diluted 1 + 9. With the exception of Zn in the urine matrix, indium was found to be a suitable internal standard for most of the isotopes of interest in the samples considered. All samples were analysed using both low (300) and medium (3000) resolutions (m/Δm at 10% peak height). The transition metals are well known often to suffer major interference from polyatomic species, and the extent of this interference was clearly evident when using spectral resolution 300. Depending on the sample type and matrix, accurate results could not be guaranteed for all isotopes when using low resolution. Without mathematical correction, extra sample preparation measures, or modified instrument operation, the same problems would be encountered in quadrupole ICP-MS studies. However, magnetic sector ICP-MS using medium resolution mode was found to overcome adequately polyatomic interferences associated with the transition metal isotopes considered, for all sample types. To a general approximation, measured elemental concentrations agreed to within ±5–10%, or better, of certified values when a spectral resolution of 3000 was employed [the accuracy found for individual elements varies depending on sample type, analyte concentration, isotope considered, and the relative success of the sample digestion procedure (if required)]. Results are presented taking into consideration both instrumental and method detection limits.
Although world oceans have been warming over the past 50 years, the impact on biotic components is poorly understood because of the difficulty of obtaining long-term datasets on marine organisms. The Southern Ocean plays a critical role in global climate and there is growing evidence of climate warming. We show that air temperatures measured by meteorological stations have steadily increased over the past 50 years in the southern Indian Ocean, the increase starting in mid 1960s and stabilizing in mid 1980s, being particularly important in the sub-Antarctic sector. At the same time, with a time lag of 2–9 years with temperatures, the population size of most seabirds and seals monitored on several breeding sites have decreased severely, whilst two species have increased at the same time. These changes, together with indications of a simultaneous decrease in secondary production in sub-Antarctic waters and the reduction of sea-ice extent further south, indicate that a major system shift has occurred in the Indian Ocean part of the Southern Ocean. This shift illustrates the high sensitivity of marine ecosystems, and especially upper trophic level predators, to climatic changes.
A central tenet of Antarctic ecology suggests that increases in Chinstrap Penguin (Pygoscelis antarctica) populations during the last four decades resulted from an increase in prey availability brought on by the decrease in baleen whale stocks. We question this tenet and present evidence to support the hypothesis that these increases are due to a gradual decrease in the frequency of cold years with extensive winter sea ice cover resulting from environmental warming. Supporting data were derived from one of the first, major multidisciplinary winter expedition to the Scotia and Weddell seas; recent satellite images of ocean ice cover; and the analysis of long-term surface temperature records and penguin demography. Our observations indicate there is a need to pay close attention to environmental data in the management of Southern Ocean resources given the complexity of relating biological changes to ecological perturbations.
Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 23 (2009): GB4034, doi:10.1029/2009GB003500. Climate change is projected to significantly alter the delivery (stratification, boundary currents, aridification of landmasses, glacial melt) of iron to the Southern Ocean. We report the most comprehensive suite of biogeochemical iron budgets to date for three contrasting sites in subantarctic and polar frontal waters south of Australia. Distinct regional environments were responsible for differences in the mode and strength of iron supply mechanisms, with higher iron stocks and fluxes observed in surface northern subantarctic waters, where atmospheric iron fluxes were greater. Subsurface waters southeast of Tasmania were also enriched with particulate iron, manganese and aluminum, indicative of a strong advective source from shelf sediments. Subantarctic phytoplankton blooms are thus driven by both seasonal iron supply from southward advection of subtropical waters and by wind-blown dust deposition, resulting in a strong decoupling of iron and nutrient cycles. We discuss the broader global significance our iron budgets for other ocean regions sensitive to climate-driven changes in iron supply. T.W. was supported by a BDI grant from CNRS and Région PACA, by CNRS PICS project 3604, and by the “Soutien à la mer” CSOA CNRS-INSU. P.W.B. was supported by the New Zealand FRST Coasts and Oceans OBI. This research was supported by the Australian Government Cooperative Research Centres Programme through the Antarctic Climate and Ecosystems CRC (ACE CRC) and Australian Antarctic Science project 2720.
Recent observations of biologically generated turbulence in the ocean have led to conflicting conclusions regarding the significance of the contribution of animal swimming to ocean mixing. Measurements indicate elevated turbulent dissipation--comparable with levels caused by winds and tides--in the vicinity of large populations of planktonic animals swimming together. However, it has also been noted that elevated turbulent dissipation is by itself insufficient proof of substantial biogenic mixing, because much of the turbulent kinetic energy of small animals is injected below the Ozmidov buoyancy length scale, where it is primarily dissipated as heat by the fluid viscosity before it can affect ocean mixing. Ongoing debate regarding biogenic mixing has focused on comparisons between animal wake turbulence and ocean turbulence. Here, we show that a second, previously neglected mechanism of fluid mixing--first described over 50 years ago by Charles Darwin--is the dominant mechanism of mixing by swimming animals. The efficiency of mixing by Darwin's mechanism is dependent on animal shape rather than fluid length scale and, unlike turbulent wake mixing, is enhanced by fluid viscosity. Therefore, it provides a means of biogenic mixing that can be equally effective in small zooplankton and large mammals. A theoretical model for the relative contributions of Darwinian mixing and turbulent wake mixing is created and validated by in situ field measurements of swimming jellyfish using a newly developed scuba-based laser velocimetry device. Extrapolation of these results to other animals is straightforward given knowledge of the animal shape and orientation during vertical migration. On the basis of calculations of a broad range of aquatic animal species, we conclude that biogenic mixing via Darwin's mechanism can be a significant contributor to ocean mixing and nutrient transport.
Oceanic production of calcium carbonate is conventionally attributed to marine plankton (coccolithophores and foraminifera).
Here we report that marine fish produce precipitated carbonates within their intestines and excrete these at high rates. When
combined with estimates of global fish biomass, this suggests that marine fish contribute 3 to 15% of total oceanic carbonate
production. Fish carbonates have a higher magnesium content and solubility than traditional sources, yielding faster dissolution
with depth. This may explain up to a quarter of the increase in titratable alkalinity within 1000 meters of the ocean surface,
a controversial phenomenon that has puzzled oceanographers for decades. We also predict that fish carbonate production may
rise in response to future environmental changes in carbon dioxide, and thus become an increasingly important component of
the inorganic carbon cycle.
Unique DNA sequences are present in all species and can be used as biomarkers for the detection of cells from that species. These DNA sequences can most easily be detected using the polymerase chain reaction (PCR), which allows very small quantities of target DNA sequence to be amplified even when the target is mixed with large amounts of nontarget DNA. PCR amplification of DNA markers that are present in a wide range of species has proven very useful for studies of species diversity in environmental samples. The taxonomic range of species to be identified from environmental samples may often need to be restricted to simplify downstream analyses and to ensure that less abundant sequences are amplified. Group-specific PCR primer sets are one means of specifying the range of taxa that produce an amplicon in a PCR. We have developed a range of group-specific PCR primers for studying the prey diversity found in predator stomach contents and scats. These primers, their design and their application to studying prey diversity and identity in predator diet are described.
Antarctic krill (Euphausia superba) and salps (mainly Salpa thompsoni) are major grazers in the Southern Ocean, and krill support commercial fisheries. Their density distributions have been described in the period 1926-51, while recent localized studies suggest short-term changes. To examine spatial and temporal changes over larger scales, we have combined all available scientific net sampling data from 1926 to 2003. This database shows that the productive southwest Atlantic sector contains >50% of Southern Ocean krill stocks, but here their density has declined since the 1970s. Spatially, within their habitat, summer krill density correlates positively with chlorophyll concentrations. Temporally, within the southwest Atlantic, summer krill densities correlate positively with sea-ice extent the previous winter. Summer food and the extent of winter sea ice are thus key factors in the high krill densities observed in the southwest Atlantic Ocean. Krill need the summer phytoplankton blooms of this sector, where winters of extensive sea ice mean plentiful winter food from ice algae, promoting larval recruitment and replenishing the stock. Salps, by contrast, occupy the extensive lower-productivity regions of the Southern Ocean and tolerate warmer water than krill. As krill densities decreased last century, salps appear to have increased in the southern part of their range. These changes have had profound effects within the Southern Ocean food web.
The mass extinction at the Permian-Triassic boundary, 251 million years (Myr) ago, is accepted as the most profound loss of life on record. Global data compilations indicate a loss of 50% of families or more, both in the sea and on land, and these figures scale to a loss of 80-96% of species, based on rarefaction analyses. This level of loss is confirmed by local and regional-scale studies of marine sections, but the terrestrial record has been harder to analyse in such close detail. Here we document the nature of the event in Russia in a comprehensive survey of 675 specimens of amphibians and reptiles from 289 localities spanning 13 successive geological time zones in the South Urals basin. These changes in diversity and turnover cannot be explained simply by sampling effects. There was a profound loss of genera and families, and simplification of ecosystems, with the loss of small fish-eaters and insect-eaters, medium and large herbivores and large carnivores. Faunal dynamics also changed, from high rates of turnover through the Late Permian period to greater stability at low diversity through the Early Triassic period. Even after 15 Myr of ecosystem rebuilding, some guilds were apparently still absent-small fish-eaters, small insect-eaters, large herbivores and top carnivores.
Measurements in a coastal inlet revealed turbulence that was three to four orders of magnitude larger during the dusk ascent
of a dense acoustic-scattering layer of krill than during the day, elevating daily-averaged mixing in the inlet by a factor
of 100. Because vertically migrating layers of swimming organisms are found in much of the ocean, biologically generated turbulence
may affect (i) the transport of inorganic nutrients to the often nutrient-depleted surface layer from underlying nutrient-rich
stratified waters to affect biological productivity and (ii) the exchange of atmospheric gases such as CO2 with the stratified ocean interior, which has no direct communication with the atmosphere.
Since the mid-1980s, our understanding of nutrient limitation of oceanic primary production has radically changed. Mesoscale iron addition experiments (FeAXs) have unequivocally shown that iron supply limits production in one-third of the world ocean, where surface macronutrient concentrations are perennially high. The findings of these 12 FeAXs also reveal that iron supply exerts controls on the dynamics of plankton blooms, which in turn affect the biogeochemical cycles of carbon, nitrogen, silicon, and sulfur and ultimately influence the Earth climate system. However, extrapolation of the key results of FeAXs to regional and seasonal scales in some cases is limited because of differing modes of iron supply in FeAXs and in the modern and paleo-oceans. New research directions include quantification of the coupling of oceanic iron and carbon biogeochemistry.
Standard metabolism is estimated for the fin whale, Balaenoptera physalus, from the energy yield of lipid stores consumed while in regions of limited prey availability. The metabolic rate appears better described by a surface rather than a volumetric rule. The larger body size of some Antarctic Balaenoptera compared with those of the Northern Hemisphere is attributed to selection for body proportions that reduce the specific metabolic rate and establish an optimal surface area for deposition of a lipid cache. Such proportions allow short-term forays into areas where prey is extremely dense but of restricted seasonal availability, and permit extended use of lipid stores during exclusion to warmer but less productive waters. Thus, adult body size within species is inversely correlated with the length of the feeding season and directly correlated with prey availability during that period. As differences in diversity of prey and/or their year-round availability become less marked between hemispheres, so do the body-size differences of the lesser rorquals. This is also applied to odontocetes. Thermal homeostasis is considered to be equally dependent upon morphology and behavior. Minimal densities of prey necessary for the maintenance of rorquals could be estimated from certain known parameters.
The history of human harvests of seals, whales, fish and krill in the Antarctic is summarised briefly, and the central role played by krill emphasised. The background to the hypothesis of a krill surplus in the mid-20th century is described, and the information on population and trend levels that has become available since the postulate was first advanced is discussed. The objective of the study is to determine whether predator-prey interactions alone can broadly explain observed population trends without the need for recourse to environmental change hypotheses. A model is developed including krill, four baleen whale (blue, fin, humpback and minke) and two seal (Antarctic fur and crabeater) species. The model commences in 1780 (the onset of fur seal harvests) and distinguishes the Atlantic/Indian and Pacific Ocean sectors of the Southern Ocean in view of the much larger past harvests in the former. A reference case and six sensitivities are fitted to available data on predator abundances and trends, and the plausibility of the results and the assumptions on which they are based is discussed, together with suggested further areas for investigation. Amongst the key inferences of the study are that: (i) species interaction effects alone can explain observed predator abundance trends, though not without some difficulty; (ii) it is necessary to consider other species, in addition to baleen whales and krill, to explain observed trends - crabeater seals seemingly play an important role and constitute a particular priority for improved abundance and trend information; (iii) the Atlantic/Indian Ocean sector shows major changes in species abundances, in contrast to the Pacific Ocean sector, which is much more stable; (iv) baleen whales have to be able to achieve relatively high growth rates to explain observed trends; and (v) Laws' (1977) estimate of some 150 million tonnes for the krill surplus may be appreciably too high as a result of his calculations omitting consideration of density-dependent effects in feeding rates.
This chapter discusses some of what is known about adaptations to breath holding and overcoming the crushing effects of pressure. When marine mammals descend below the sea's surface they leave behind the thin skin of the earth's atmosphere with one of its essential ingredients to all vertebrate life--oxygen. They begin a journey that is incredible in diverse ways. The magnitude of incredulity varies according to the species, but for all, even the most humble of marine mammals such as the sea otter (. Enhydra lutris), much if not most of the experience is beyond our imagination. Unlike flying, in which our technology now enables us to fly faster, higher, and farther than any bird, bat, or pterosaur ever did, marine mammals, particularly those that dive to great depths, explore and exploit a realm that overwhelms much of our technology and that enables us to gain only fleeting glimpses of what their environment is like. Recently we have enlisted the animals themselves to help us discover more about this cold, dark world without oxygen, where awesome hydrostatic pressures always prevail. However, "crittercams" will only give us fleeting glimpses, under very special conditions, with those few species that lend themselves to the attachment of these cameras. Life in the deep blue remains a mystery. So too do the means that enable diving mammals to exploit this habitat.
Despite much research on Euphausia superba, estimates of their total biomass and production are still very uncertain. Recently, circumpolar krill databases, combined with growth models and revisions in acoustics have made it possible to refine previous estimates. Net-based databases of density and length frequency (KRILLBASE) yield a summer distributional range of ∼19×106km2 and a mean total abundance of 8×1014 post-larvae with biomass of 379 million tonnes (Mt). These values are based on a standardised net sampling method but they average over the period 1926–2004, during which krill abundance has fluctuated. To estimate krill biomass at the end of last century we combined the KRILLBASE map of relative krill density around Antarctica with an acoustics-derived biomass estimate of 37.3Mt derived for the Scotia Sea area in 2000 by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR). Thus the CCAMLR 2000 survey area contains 28% of the total stock, with total biomass of ∼133Mt in January–February 2000. Gross postlarval production is estimated conservatively at 342–536Mtyr−1, based on three independent methods. These are high values, within the upper range of recent estimates, but consistent with the concept of high energy throughput for a species of this size. The similarity between the three production estimates reflects a broad agreement between the three growth models used, plus the fact that, for a given population size, production is relatively insensitive to the size distribution of krill at the start of the growth season. These production values lie within the envelope of what can be supported from the Southern Ocean primary production system and what is required to support an estimated predator consumption of 128–470Mtyr−1. Given the range of recent acoustics estimates, plus the need for precautionary management of the developing krill fishery, our net-based data provide an alternative estimate of total krill biomass.
In order to establish the potential role of Antarctic krill (Euphausia superba) in the recycling of bioactive elements, we have quantified the release of iron, phosphate, and ammonia by these organisms along the Antarctic Peninsula sector of the Southern Ocean. The experimental results suggested that the presence of krill has a significant impact on ambient iron concentrations, as large amounts of this trace element were released by the krill (22-689 nmol Fe g Dry Weight-1 h-1, equivalent to 0.2 to 4.3 nmol Fe L-1 d-1). Half of this iron release occurred within the first hour of the experiment, and differences in iron and phosphate release rates (3.1 to 14.0 mumol PO4 3- g DW-1 h-1) seemed to reflect differences in food availability. These results identify krill as a major node in iron cycling in the Southern Ocean, potentially influencing iron residence time in the upper water column of this region.
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.
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.
There are fewer species of marine mammals in the Antarctic than in the
Arctic, probably because of the wide deep ocean with no geographical
barriers to promote speciation. The stocks are substantially larger in
the Antarctic and the body sizes of individual species are larger,
probably owing to a more abundant food supply. Seasonal changes in the
environment in the Southern Ocean are marked and food available to
baleen whales is very much greater in summer. Ecological interactions of
the consumers, principally in relation to krill Euphausia superba, are
discussed and attention drawn to some of the ways in which ecological
separation is achieved, both within and between species. Estimates of
abundances, biomasses and food requirements are given for the seals and
large whales. The original numbers of whales in the Antarctic were far
greater than in other oceans, but the stocks have been severely reduced
by whaling. This may have increased the availability of krill to other
consumers by as much as 150 million tonnes annually. Increased growth
rates, earlier maturity and higher pregnancy rates have been
demonstrated for baleen whale species, and earlier maturity for the
crabeater seal. While it has not been possible to demonstrate increases
in the populations of any of these species, the stocks of fur seals and
penguins have been monitored and show significant population increases.
A key question is whether the original balance of this ecosystem can be
regained with appropriate management.
Heavy metal concentrations in Antarctic surface seawaters and some marine organisms were determined, and their distributions and bioaccumulations were discussed in comparison with other marine ecosystems. Locational difference of the heavy metal concentrations in Antarctic seawater was negligible, and their concentrations were in the order of Zn - Fe> Mn> Cu>Pb - Ni> Cd> Hg. When compared to the western North Pacific, Japan Sea and Bering Sea, the concentra- tions of Fe, Zn, and Hg in Antarctic seawater were relatively low, which provides evidence that atmospheric transport of these metals from continents, either from natural or anthropogenic sources to the Antarctic water is much less. The Cd level was relatively high compared with those in the western North Pacific and Japan Sea waters, which might be due to the upwelling of Cd-enriched deep waters to the surface. In general, the heavy metal concentrations in Antarctic marine organisms were affected by the metal concentrations in the seawater. Also, it was found that bioaccumulations of metals in Antarctic marine ecosystem were characterized by a high accumulation of Cd and low accumulation of Hg, based on the short food chain with krill as key species, and also by a low accumulation of Fe in fishes as an adaptation to the cold water condition.
Concentrations of water, ash, protein, chitin, lipid, calcium, magnesium, sodium, potassium, strontium and copper were measured in individuals from a laboratory population of Antarctic krill, Euphausia superba Dana, over the course of a moult cycle. Significant changes in all variables were encountered. Total ash, lipid, calcium, magnesium and strontium all increased in concentration following moulting. Water, protein and copper concentrations all decreased following ecdysis and increased again towards the end of the moult cycle. The major ions sodium and potassium fluctuated around mean levels. Cast moults of E. superba were shown to be a drain on the ionic load of the krill, and the losses inherent in exuviation could account for much of the variation observed during the moult cycle.
Dissolved (< 0.4 μm) iron has been measured in 354 samples at 30 stations in the North and South Pacific, Southern Ocean and North Atlantic by the Trace Metals Laboratory at Moss Landing Marine Laboratories. These stations are all more than 50 km from a continental margin. The global distribution of dissolved iron, which is derived from these profiles, is remarkable for several reasons. The dissolved iron profiles have a uniform shape with a nutrient-like profile at each station. Concentrations at the surface are all < 0.2 nmol kg−1 and average 0.07 nmol kg−1. Below 500 m, the average concentration is 0.76 nmol kg−1. The largest value in the data set is 1.38 nmol kg−1. There is no inter-ocean fractionation, which is unique for an element with a nutrient-like profile. Published estimates of the iron residence time are on the order of 100 to 200 yr, indicative of rapid removal. Other elements with such short residence times are characterized by vertical profiles that decrease with depth and deep concentrations that decrease with age as water passes from the Atlantic to the Pacific. This is not the case for iron. The largest horizontal changes in dissolved iron are observed in gradients from the continental margin. There is only a factor of three difference between the minimum (0.4 nmol kg−1) and maximum (1.3 nmol kg−1) value in the data set at a depth near 750 m, where variability is at a maximum. The minimum concentrations are found at stations in the remote central Pacific and the maximum values occur at stations adjacent to the continental margin. The major source of iron in the deep sea is generally aeolian deposition. Integrated (surface to 500 m) concentrations of iron at each station are only weakly correlated with the aeolian iron deposition flux, however. This contrasts with other elements such as lead that also have strong atmospheric sources. These observations lead us to conclude that the nutrient-like profile is maintained by a mechanism that reduces the scavenging rate of dissolved iron at concentrations less than 0.6 nmol kg−1. This mechanism may be complexation by strong iron binding ligands, which have been found in both the Atlantic and Pacific at concentrations near 0.6 nM. This apparent solubility would act to diminish inter-ocean fractionation. It would allow a nutrient-like profile to develop before scavenging began to remove iron. In order to test the concept, we developed a numerical model to make quantitative predictions of dissolved iron concentrations from place to place. The dissolved iron source in the ocean interior is remineralization from sinking particulate organic matter. Scavenging removes dissolved iron only at concentrations greater than the apparent solubility. The only geographically variable parameter in the model is the export flux of carbon from the surface layer, which carries iron with it. The model generated dissolved iron profiles, based on measured or estimated values of the carbon export flux, are in remarkable agreement with the observed profiles at all stations from the North Atlantic through the Southern Ocean to the North Pacific.
The oceanic biogeochemical cycles of many trace elements are dominated by their association with the growth, death, consumption and sinking of phytoplankton. The trace element content of marine phytoplankton reflects nutritional status, species composition, surface area to volume ratios, and interactions with bioactive and toxic elements in the ambient seawater. Despite the ecological and environmental importance of trace element assimilation by autotrophs, there are few modern measurements of trace elements in phytoplankton assemblages from the natural environment. Here we introduce a new method for collection and analysis of size-fractionated particulate samples from practical seawater volumes. We pay particular attention to accurate determination of trace element filter blanks which are typically the limiting factor for analysis of such samples. Metals were determined at very low detection limits by high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) for 11 elements (Ag, Al, Cd, Co, Cr, Cu, Fe, Mn, U, Zn and P, which is used as a biomass normalizer) in three types of polymer filters (0.45, 5.0, and 53 μm pore size) and a quartz fiber filter (0.8 μm pore size). To place these new determinations in a practical context, results are presented for a vertical profile of samples filtered from 1–4 l of coastal seawater (0.3–1.0 mg total solid dry weight) at a station off central California. The results demonstrate that the blanks of the evaluated filter types, precleaned appropriately, are sufficiently low to allow accurate determination of the trace metal content of three size-classes of phytoplankton. At the Pacific station, measured phytoplankton Zn content (as Zn/P) agrees with values predicted from single-species culture studies growing at seawater Zn concentrations expected for coastal waters. The new method has utility as a generally applicable and simple size fractionation technique, and allows determination of natural and pollutant elements in small samples of phytoplankton and particles in coastal, estuarine and offshore marine regimes.
