Fig 1 - uploaded by Valerie Loeb
Content may be subject to copyright.
Shelled (thecosome) pteropod species (a) Limacina helicina f. antarctica (shedding eggs) and (b) Clio pyramidata f. sulcata; naked (gymnosome) species (c) Clione limacina antarctica and (d) Spongiobranchaea australis. (Photographs by V. Loeb and K. Dietrich.)
Source publication
Contexts in source publication
Context 1
... of the Polar Front in the Southern Ocean the most common thecosome pteropods are Limacina helicina antarctica f. antarctica and Clio pyramidata f. sulcata ( Fig. 1a and b). These two shelled species are reported to be the sole prey items for their gymnosome relatives Clione limacina antarctica and Spongiobranchaea australis (van der Spoel and Dadon, 1999;Hunt et al., 2008); thecosome pteropods are also important food sources for other carnivorous zooplankton taxa and fish (Hopkins, 1987;Hopkins and ...
Context 2
... were associated with a climate regime shift off the Antarctic Peninsula evidenced by increased ACC vs. Weddell Sea water influence after 1998 Loeb et al., 2010). Limacina helicina was significantly more abundant after the regime shift due to increased concentrations during both early-and late-summer surveys (nested ANOVA, P < 0.01; Table 5, Fig. 10). Overall abundance changes of C. pyr. sulcata and C. antarctica between the 2 regimes were not significant but suggest trends of decreased concentrations of C. pyr. sulcata during early-summer and increased concentrations of C. antarctica during late-summer after 1998. Significantly greater concentrations of S. australis after 1998 ...
Similar publications
We review the history of how research directed towards marine ornithology has led to an appreciation of seabirds as highly specialized marine organisms. Beginning with R. C. Murphy (Pacific), V. C. Wynne-Edwards (Atlantic), and associates in the early 1900s, the research approach grew from an emphasis on seabird single-species ecology to an appreci...
Antarctic krill (Euphausia superba) has a circumpolar distribution and is central to the food chain of the Southern Ocean. The current annual catch (ca. 120,000 tonnes) is well below the precautionary catch limits set by CCAMLR of 4,000,000 tonnes in Statistical Area 48 and 890,000 tonnes in Statistical Area 58. In this paper, a brief review of the...
Antarctic krill is a vital part of the food web and supports a significant fishery in the Southern Ocean. Shifts in historical fishing grounds and spatial distribution of catches have occurred as a result of recent changes in fishery practices. To understand these shifts, fishery spatial dynamics and fishing fleet behavior evaluated on different sp...
Copepods are present in numerous aquatic environments, playing key roles in food webs, and are thought to be useful indicators of environmental change. Boeckella is a calanoid copepod genus distributed mainly in the Southern Hemisphere, with 14 species reported at higher southern latitudes in South America and Antarctica. We present an updated data...
Sea ice algae represent a key energy source for many organisms in polar food webs, but estimating their biomass at ecologically appropriate spatiotemporal scales remains a challenge. Attempts to extend ice-core derived biomass to broader scales using remote sensing approaches has largely focused on the use of under-ice spectral irradiance. Normaliz...
Citations
... In that regard, sediment traps have been proven as a reliable tool to document the composition and seasonality of different zooplankton groups (Boltovskoy et al., 1996;Willis et al., 2008;Sampei et al., 2012;Matsuno et al., 2014). For pteropods phenology and population dynamics, net sampling or plankton tows are more widely used Beare et al., 2013;Loeb and Santora, 2013) than sediment traps (Oakes and Sessa, 2020); as these organisms might actively swim into the cups and can be considered an artefact generated by the presence of sediment traps that may bias total mass calculations (Buesseler et al., 2007). However, comparisons between net and sediment traps have demonstrated a close correlation between the assemblages collected by these two methods (Almogi-Labin et al., 1988;Makabe et al., 2016;Weldrick et al., 2021). ...
Pteropods are a group of cosmopolitan holoplanktic gastropods that produce an aragonite shell and play an important role in both marine ecosystems and geochemical cycles. In addition to being affected by anthropogenic impacts that include warming and changes in carbonate system parameters, the Mediterranean Sea is considered to be understudied concerning pteropods dynamics and abundances. This work aims to document the modern spatial and temporal distributions of pteropods populations in the Northwestern and Central Mediterranean Sea (Gulf of Lions and Strait of Sicily), respectively. We present data from two sediment-trap records that cover the timeframe between early 1996 and early 2004 for the Gulf of Lions and late 2013 to late 2014 for the Sicily Strait. A total of 843 pteropod shells and 18 different species were identified. Limacina inflata, Creseis virgula and Creseis clava were the most abundant species in the Gulf of Lions, while in the Sicily Strait, C. conica replaced C. clava as the most abundant species. These taxons represented around 70% of the total individuals identified in both sites. Overall, our results suggest a greater pteropod abundance in the Gulf of Lions than in the Sicily Strait, most likely due to enhanced food conditions. In the Gulf of Lions, maximum fluxes occurred in autumn (32.5% of the annual pteropod fluxes registered in October), while in the Sicily Strait peak fluxes occurred in winter (30.5% of the annual pteropod fluxes registered in January). Comparison of temporal changes pteropod fluxes with satellite sea surface temperature (SST), and chlorophyll-a concentration suggest a possible positive effect of high algal accumulation and cool water conditions in the Strait of Sicily on the main pteropod groups. In turn, no clear relationships between pteropod groups, SST and chlorophyll-a were identified in the Gulf of Lions, highlighting the effect of salinity and carbonate system parameters. Overall, and despite the limitations associated with the use of sediment traps for pteropod population monitoring, the consistency of our results with the literature supports the use of sediment traps as useful tools for documenting the diversity and temporal distribution of pteropods.
... Gymnosome abundance tracks thecosome abundance, reflecting their trophic dependency. Similar trends in pteropod abundance were observed by the U.S. AMLR Program time series in the northern Antarctic Peninsula region (Loeb and Santora, 2013). The other significant pteropod time series comes from the SO-CPR surveys (1997 to present), which has mainly focused on the Pacific sectors thus far (McLeod et al., 2010). ...
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.
... In addition to these long-term trends, the ecosystem is modulated by climatic oscillations including the El Niño Southern Oscillation and the Southern Annular Mode. These mechanisms are thought to drive the interannual variability in the marine ecosystem productivity and dynamics (e.g., Loeb et al., 2009;Loeb & Santora, 2013;Saba et al., 2014;Trathan & Murphy, 2002). It is possible that top-down pressures including increased competition for krill from recovering whale and finfish populations, recovered fur seal populations and commercial fisheries, combined with bottom-up, climate-driven environmental changes could result in reduced krill availability for penguins and other krill predators (Ballance et al., 2006;Hofman, 2017;Trathan et al., 2012;Trivelpiece et al., 2011). ...
Abstract Ecosystem dynamics at the northwest Antarctic Peninsula are driven by interactions between physical and biological processes. For example, baleen whale populations are recovering from commercial harvesting against the backdrop of rapid climate change, including reduced sea ice extent and changing ecosystem composition. Concurrently, the commercial harvesting of Antarctic krill is increasing, with the potential to increase the likelihood for competition with and between krill predators and the fishery. However, understanding the ecology, abundance, and spatial distribution of krill predators is often limited, outdated, or at spatial scales that do not match those desired for effective fisheries management. We update current knowledge of predator dependence on krill by integrating telemetry‐based data, at‐sea observational surveys, estimates of predator abundance, and physiological data to estimate the spatial distribution of krill consumption during the austral summer by three species of Pygoscelis penguin, 11 species of flying seabirds, one species of pinniped, and two species of baleen whale. Our models show that the majority of important areas for krill predator foraging are close to penguin breeding colonies in nearshore areas where humpback whales also regularly feed, and along the shelf‐break, though we caution that not all known krill predators are included in these analyses. We show that krill consumption is highly variable across the region, and often concentrated at fine spatial scales, emphasizing the need for the management of the local krill fishery at relevant temporal and spatial scales. We also note that krill consumption by recovering populations of krill predators provides further evidence in support of the krill surplus hypothesis, and highlight that despite less than comprehensive data, cetaceans are likely to consume a significant proportion of the krill consumed by natural predators but are not currently considered directly in the management of the krill fishery. If management of the krill fishery is to be precautionary and operate in a way that minimizes the risks to krill predator populations, it will be necessary in future analyses, to include up‐to‐date and precise abundance and consumption estimates for pack‐ice seals, finfish, squid, and other baleen whale species not currently considered.
... Climatic oscillations that may affect the duration and extent of winter sea-ice and short-term ecosystem dynamics include the El Niño Southern Oscillation (ENSO) and the Southern Annular Mode (SAM) (e.g. Trathan and Murphy 2002;Loeb et al. 2009;Loeb and Santora 2013;Saba et al. 2014). Long-term increases in the frequency of years with reduced sea-ice duration, as a result of positive trends in air and sea surface temperatures (SST), have also been observed (Vaughan et al. 2003;Meredith and King 2005;Stammerjohn et al. 2008). ...
This study was performed to aid the management of the fishery for Antarctic krill Euphausia superba. Krill are an important component of the Antarctic marine ecosystem, providing a key food source for many marine predators. Additionally, krill are the target of the largest commercial fishery in the Southern Ocean, for which annual catches have been increasing and concentrating in recent years. The krill fishery is managed by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), which has endorsed a new management framework that requires information about the spatial distribution and biomass of krill. Here, we use krill density estimates from acoustic surveys and a GAMM framework to model habitat properties associated with high krill biomass during summer and winter in the northern Antarctic Peninsula region, an area important to the commercial fishery. Our models show elevated krill density associated with the shelf break, increased sea surface temperature, moderate chlorophyll-a concentration and increased salinity. During winter, our models show associations with shallow waters (< 1500 m) with low sea-ice concentration, medium sea-level anomaly and medium current speed. Our models predict temporal averages of the distribution and density of krill, which can be used to aid CCAMLR's revised ecosystem approach to fisheries management. Our models have the potential to help in the spatial and temporal design of future acoustic surveys that would preclude the need for modelled extrapolations. We highlight that the ecosystem approach to fisheries management of krill critically depends upon such field observations at relevant spatial and temporal scales.
Supplementary information:
The online version contains supplementary material available at 10.1007/s00300-022-03039-y.
... Summertime assessments of macrozooplankton have laid the foundation for understanding connections between ocean-climate conditions, such as El Niño-Southern Oscillation (ENSO), on the recruitment variability of Antarctic krill (Euphausia superba) (Loeb et al., 2009b;Lee et al., 2010;Loeb and Santora, 2015), the numerical dominance of either euphausiids or gelatinous salps (Loeb et al., 1997;Loeb and Santora, 2012), as well as the spatial organization of macrozooplankton species composition (Siegel and Piatkowski, 1990;Steinberg et al., 2015). Specifically, distribution of summer macrozooplankton assemblages reflects differences in bathymetry and source water inputs from the Weddell, Scotia and Bellingshausen Seas, and through coastal currents within Bransfield Strait ( Fig. 1; Jazdzewski et al., 1982;Rakusa-Suszcewski, 1983;Witek et al., 1985;Piatkowski, 1989;Siegel and Piatkowski, 1990;Loeb et al., 2010;Loeb and Santora, 2013;Loeb and Santora, 2015). Climate-driven change in sea-ice conditions is also hypothesized to have impacted Antarctic krill populations, reducing recruitment strength and causing population declines and an apparent poleward distribution shift or contraction of this species (Ross et al., 2014;Atkinson et al., 2019). ...
... We also found a slight shift of L. helicina to the north in winter, although this could also be due to higher Chl a at lower latitudes, a function of different 'age' classes encountered among seasons, or a combination of both. Furthermore, Loeb and Santora (2013) examined the long-term variability of summer abundance and distribution of L. helicina and determined that temporal fluctuation of this species may relate to the ESNO variability and shifts in the position of sACCf. ...
Climate forcing is impacting polar marine ecosystems through increased variability of winter sea-ice dynamics, which likely influences the distribution, abundance and structure of zooplankton assemblages, and thereby trophodynamics of marine food webs. Due to the challenges of working in polar marine ecosystems, most knowledge on polar zooplankton community structure is derived from summer surveys. Here we examine the spatial distribution, abundance and community structure of macrozooplankton in relation to sea-ice and ocean-climate dynamics within the Antarctic Peninsula marine ecosystem over five consecutive winters. We compare the patterns revealed during winter with historical data collected in the same region during austral summer. Hydrographic and macrozooplankton data were collected from >100 standard stations off the northern Antarctic Peninsula during summer (2003-2011) and winter (2012-2016). Using multivariate methods, the environmental drivers and geographic structuring of the macrozooplankton community during winter and summer were investigated.
Eight taxa made up 90% of total macrozooplankton abundance in winter including Metridia species, post-larval and larval Euphausia superba, post-larval Thysanoessa macrura, Limacina helicina, Chaetognatha, Ostracoda and Radiozoa. Eight slightly different taxa including Calanoides acutus, Salpa thompsoni, T. macrura (post-larvae and larvae), Metridia spp., E. superba larvae, Chaetognatha, and Rhincalanus spp. made up 87% of the total abundance in summer. Macrozooplankton clustered into five groups in winter and seven groups in summer. Winter macrozooplankton structure was more spatially consistent among years compared to summer regardless of sea-ice conditions. Salinity, chlorophyll a biomass, upper mixed layer depth and time of day were most strongly correlated with the multivariate ordination in winter whereas salinity, phaeopigment biomass and year had the highest correlations for summer, indicating the importance of similar physical features in both seasons. However, the importance of time scales differed among seasons.
Although environmental determinants of summer and winter macrozooplankton community structure indicate that community structure and occurrence were strongly tied to regional variability of salinity and primary productivity gradients, macrozooplankton community structure is likely much more complex than only a few hydrographic variables can explain. Cluster boundaries are likely driven by dynamic locations of currents, fronts and localized eddies in any given season or year.
... antarctica is the third most abundant macrozooplankton in the WAP (Steinberg et al., 2015). Long-term, time-series analyses of pteropods along the WAP show higher pteropod abundance is associated with warm sea surface temperatures and ice-free waters (Ross et al., 2008;Loeb and Santora, 2013;Steinberg et al., 2015;Thibodeau et al., 2019), suggesting temperature and ice may be important controls on pteropod physiology. However, only Suprenand et al. (2015) has examined environmental controls on pteropod physiology in the WAP, and notably few measures of excretion exist for most pteropod species in the Southern Ocean. ...
Pteropods (pelagic snails) are abundant zooplankton in the Southern Ocean where they are important grazers of phytoplankton, prey for higher trophic levels, and sensitive to environmental change. The Western Antarctic Peninsula (WAP) is a highly dynamic and productive region that has undergone rapid warming, but little is known about how environmental changes there will affect pteropod physiology. In this study, the effects of warming seawater temperatures and shifting food availability on Limacina helicina antarctica metabolism (respiration and excretion) were determined by conducting shipboard experiments that exposed pteropods to a range of temperatures and phytoplankton (food) concentrations. Highest respiration (up to 69 μmol O2 gDW⁻¹ h⁻¹) and usually highest excretion rates occurred under higher temperature with more limited metabolic response to food concentration, indicating these factors do not always have an additive effect on pteropod metabolism. The proportion of dissolved organic matter (DOM) to total organic and inorganic dissolved constituents was high and was also significantly affected by shifts in temperature and food. Dissolved organic carbon, nitrogen, and phosphorus (DOC, DON, and DOP) were on average 27, 51, and 11.5% of the total C, N, and P metabolized, respectively. The proportion of total N excreted as DON and the proportion of total P excreted as DOP were significantly affected by a combination of shifting temperature and food concentrations. There were no effects of temperature or food on DOC excretion (mean 8.79 μmol C gDW⁻¹ h⁻¹; range 0.44 to 44) as a proportion of total C metabolized. Metabolic O2:N ratio ranged from 2 to 9 and decreased significantly with increasing temperature and food, indicating a shift toward increased protein catabolism. Metabolic ratios of C, N, and P were all below the canonical Redfield ratio, which has implications for phytoplankton nutrient uptake and bacterial production. Respiration rates at ambient conditions of other WAP pteropods, and excretion rates for Clio pyramidata, were also measured, with respiration rates ranging from 24.39 (Spongiobranchaea australis) to 28.86 (L. h. antarctica) μmol O2 gDW⁻¹ h⁻¹. Finally, a CO2 perturbation experiment measuring L. h. antarctica metabolism under pre-industrial and elevated dissolved pCO2 conditions showed no significant change in mean L. h. antarctica respiration or excretion rates with higher pCO2. These insights into the metabolic response of pteropods to ocean variability increase our understanding of the role of zooplankton in biogeochemical cycles and help predict future responses to climate change.
... The relationship between pteropod phenology and climate indices known to influence the pelagic Antarctic Peninsula region was analyzed (Ross et al., 2008;Stammerjohn et al., 2008b;Loeb and Santora, 2013;Saba et al., 2014;Steinberg et al., 2015, Thibodeau et al., 2019. These indices include the El Niño/Southern Oscillation (ENSO) indicator based on sea surface temperature (referred to as the Multivariate ENSO Index (MEI) (http://www.esrl.noaa.gov/psd/people/klaus.wolterlter/MEI/) ...
... Water column sampling of pteropods with nets along the WAP also indicates sub-decadal climate oscillations are important controls on pteropod abundance, with higher abundance following warmer conditions and subsequently low sea ice (Ross et al., 2008;Loeb and Santora, 2013;Steinberg et al., 2015;Thibodeau et al., 2019). While no long-term changes in L. h. ...
Shifts in phenology – annually occurring life history events – have been observed among many marine organisms due to global warming. We examined if phenological changes in the pteropod (pelagic snail) Limacina helicina antarctica have occurred along the Western Antarctic Peninsula, one of the most intensely warming regions on Earth, which would have important implications for regional food web dynamics. Pteropod shell diameters were analyzed from samples collected in the Palmer, Antarctica Long-Term Ecological Research (PAL LTER) program year-round sediment trap from 2004 to 2018. There was considerable interannual variability in the time of appearance of a new pteropod cohort, which ranged from day of year 22–255, but no long-term, directional change. Mean L. h. antarctica growth rate for the time series was 0.009 mm day⁻¹ and there was no significant long-term change in growth rate. This study represents the first in the Southern Ocean to illustrate that pteropods actively grow throughout the winter season. Sea ice was the dominant driver of pteropod phenology, with earlier sea ice retreat the year prior, lower winter sea surface temperature (SST) the year prior, and higher primary productivity in the same year leading to earlier pteropod time of appearance. Similarly, more open water with higher autumn SST, both the year prior, and elevated chlorophyll a the same year, promoted faster pteropod growth. These results indicate that while pteropods are responsive to considerable environmental variability, their phenology has remained relatively stable. The identified responses of pteropod phenology to environmental shifts are key for determining future effects of climate change on biogeochemical cycling and plankton trophic interactions in the region.
... F I G U R E 8 Bayesian estimates of trophic position created from 20,000 Markov Chain Monte Carlo iterations for each pteropod species TA B L E 1 Bulk stable isotopes (δ 13 C and δ 15 N) signatures (± SD) averaged over all sampling sites and species, as well as results from the same Southern Ocean species from other studies The pteropod species sampled from the southern extent of the Kerguelen Plateau are among the four common species regularly found south of the PF (Loeb & Santora, 2013 ing a 50% to 75% reduction in phytoplankton biomass and high sea ice cover which resulted in nutrient stress-related decreases in metabolic rates in both L. helicina antarctica and its monophagous predator C. antarctica (Seibel & Dierssen, 2003). In 1989, low densities were also recorded in the East Antarctic and may be attributed to low chlorophyll a biomass resulting from late winter sea-ice retreat (Hunt et al., 2008). ...
pteropod trophic levels and stable isotopes
... Variability in Salpa thompsoni over the shelf is influenced by both ENSO (Loeb and Santora, 2012) and SAM ( Fig. 13; Steinberg et al., 2015), whilst long-term increases throughout the southwest Atlantic sector have accompanied the declines in krill (Atkinson et al., 2004). Variability in abundance of the pteropod Limacina helicina along the WAP is also linked to ENSO cycles ( Fig. 13; Loeb et al., 2009;Loeb and Santora, 2013;Ross et al., 2008;Steinberg et al., 2015). Shifts in phytoplankton community structure can also affect the abundance of krill relative to other major zooplankton taxa, because the grazing efficiency of E. superba is reduced significantly on particles < 20 μm, such that diatom-dominated communities are likely to favour krill, whilst communities dominated by cryptophytes and/or haptophytes are likely to favour salps and other taxa (Haberman et al., 2003;Meyer and El-Sayed, 1983;Moline et al., 2004). ...
The west Antarctic Peninsula (WAP) region has undergone significant changes in temperature and seasonal ice dynamics since the mid-twentieth century, with strong impacts on the regional ecosystem, ocean chemistry and hydrographic properties. Changes to these long-term trends of warming and sea ice decline have been observed in the 21st century, but their consequences for ocean physics, chemistry and the ecology of the high-productivity shelf ecosystem are yet to be fully established. The WAP shelf is important for regional krill stocks and higher trophic levels, whilst the degree of variability and change in the physical environment and documented biological and biogeochemical responses make this a model system for how climate and sea ice changes might restructure high-latitude ecosystems. Although this region is arguably the best-measured and best-understood shelf region around Antarctica, significant gaps remain in spatial and temporal data capable of resolving the atmosphere-ice-ocean-ecosystem feedbacks that control the dynamics and evolution of this complex polar system. Here we summarise the current state of knowledge regarding the key mechanisms and interactions regulating the physical, biogeochemical and biological processes at work, the ways in which the shelf environment is changing, and the ecosystem response to the changes underway. We outline the overarching cross-disciplinary priorities for future research, as well as the most important discipline-specific objectives. Underpinning these priorities and objectives is the need to better define the causes, magnitude and timescales of variability and change at all levels of the system. A combination of traditional and innovative approaches will be critical to addressing these priorities and developing a co-ordinated observing system for the WAP shelf, which is required to detect and elucidate change into the future.
... Prior studies in the Antarctic and elsewhere indicate a variety of climate and environmental controls on pteropod regional abundance and distribution (Beaugrand et al. 2012;Mackas and Galbraith 2012;Loeb and Santora 2013;Howes et al. 2015;Steinberg et al. 2015;Burridge et al. 2017). In the WAP, strong La Niña years combined with a positive SAM lead to warmer, ice-free waters as described above and favor higher abundances of the thecosome pteropod L. antarctica (Ross et al. 2008;Steinberg et al. 2015). ...
... The relationship between pteropod taxon abundance and climate indices known to influence the pelagic Antarctic Peninsula region was analyzed (Ross et al. 2008;Stammerjohn et al. 2008b;Loeb and Santora 2013;Saba et al. 2014;Steinberg et al. 2015). These indices include the ENSO indicator based on SST (referred to as the multivariate ENSO index [MEI]; http://www.esrl.noaa.gov/psd/people/klaus.wolterlter/ ...
... Climate indices (MEI and SAM) and sea ice parameters were chosen as covariates in models because Steinberg et al. (2015) found strong La Niña years, in combination with increasingly ice-free regions of the WAP, corresponded with long-term increases in L. antarctica abundance in the southern WAP. Chl a and PP were used in model building because Loeb and Santora (2013) suggest higher L. antarctica abundance in the North Peninsula region resulted from increased PP. Carbonate chemistry parameters were used to develop models because many studies have indicated pteropods are particularly susceptible to OA conditions leading to shell dissolution and metabolism suppression (Bednaršek et al. 2012b;Maas et al. 2012). ...
