Antarctic Krill Lipid and Fatty acid Content Variability is Associated to Satellite Derived Chlorophyll a and Sea Surface Temperatures

Antarctic krill (Euphausia superba) plays a central role in the Antarctic marine food web and biogeochemical cycles and has been identified as a species that is potentially vulnerable to plastic pollution. While plastic pollution has been acknowledged as a potential threat to Southern Ocean marine ecosystems, the effect of nanoplastics (<1000 nm) is poorly understood. Deleterious impacts of nanoplastic are predicted to be higher than that of larger plastics, due to their small size which enables their permeation of cell membranes and potentially provokes toxicity. Here, we investigated the intergenerational impact of exposing Antarctic krill to nanoplastics. We focused on whether embryonic energy resources were affected when gravid female krill were exposed to nanoplastic by determining lipid and fatty acid compositions of embryos produced in incubation. Embryos were collected from females who had spawned under three different exposure treatments (control, nanoplastic, nanoplastic + algae). Embryos collected from each maternal treatment were incubated for a further 6 days under three nanoplastic exposure treatments (control, low concentration nanoplastic, and high concentration nanoplastic). Nanoplastic additions to seawater did not impact lipid metabolism (total lipid or fatty acid composition) across the maternal or direct embryo treatments, and no interactive effects were observed. The provision of a food source during maternal exposure to nanoplastic had a positive effect on key fatty acids identified as important during embryogenesis, including higher total polyunsaturated fatty acids (PUFA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) when compared to the control and nanoplastic treatments. Whilst the short exposure time was ample for lipids from maternally digested algae to be incorporated into embryos, we discuss why the nanoplastic-fatty acid relationship may be more complex. Our study is the first to scope intergeneration effects of nanoplastic on Antarctic krill lipid and fatty acid reserves. From this, we suggest directions for future research including long term exposures, multi-stressor scenarios and exploring other critical energy reserves such as proteins.

Key factors influencing the occurrence and frequency of ciguatera

Tropical cyclones (TCs) induce intense mixing in the upper ocean, which significantly impacts sea surface temperature (SST) and marine environment. Previous studies have shown that TCs can cause a decrease in sea surface temperature (DSST), while further research is required to elucidate the factors influencing SST changes. This study employs satellite observations and reanalysis data from the western North Pacific during 2002–2020 to investigate the relationship between DSST and the ocean background state (BG). In addition, by incorporating TC characteristics, we construct indices to explore the synergistic effects of TCs and BG on DSST, enabling a more comprehensive understanding of the mechanisms governing DSST variability. The results indicate that DSST exhibits significant monthly variations, with the maximum DSST in September for coastal regions and in August for offshore regions. Regardless of TC characteristics, when the mixed layer depth (MLD) exceeds 60 m or thermocline depth (TD) exceeds 115 m, it is difficult for the DSST to exceed 1 °C. In both coastal and offshore regions, MLD and TD exhibit moderate negative correlations with DSST, with values around −0.3. When TC characteristics are incorporated, these correlations rise to approximately 0.6, highlighting the importance of jointly considering BG and TC effects in characterizing DSST. The findings of this study provide theoretical support for improving the capability to predict DSST changes before the TC approaches the coast.

Antarctic krill, known for its abundant reserves and high nutritional content, represents a valuable resource for humanity. The purpose of this study was to explore the feasibility of simultaneous extraction of Antarctic krill oil (AKO), Antarctic krill protein (AKP), and Antarctic krill polysaccharides (AKS) from krill by three‐phase partitioning (TPP) method and the optimal extraction conditions of AKO. The fatty acid composition of AKO and the structural characteristics of AKP and AKS were analyzed and compared with the experimental results obtained by other methods. Response surface optimization results showed that under the conditions of 50% (w/v) (NH 4 ) 2 SO 4 , 1:1 (v/v) ratio of slurry to t ‐butanol, pH 5.10, extraction temperature 50°C, and extraction time 2 h, the optimal extraction yield of AKO (EY AKO ) was 17.65%. Under these conditions, the extraction yields of AKP (EY AKP ) and AKS (EY AKS ) were 9.44% and 0.25%, respectively. Additionally, AKO extracted by TPP method was rich in more polyunsaturated fatty acids (PUFAs) than traditional methods, especially n ‐3 PUFAs. The structure of AKP was analyzed by Fourier transform infrared (FTIR) and sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE), showing that it is not damaged. The FTIR results show that AKS has the characteristic structure of homologous marine sulfated polysaccharides, indicating it is maybe a sulfated polysaccharide. This study shows that it is feasible and efficient to extract AKO, AKP, and AKS simultaneously by TPP methods. Our research provides a new way to extract nutrients from Antarctic krill. Practical Applications : This study facilitates the comprehensive utilization of the substantial Antarctic krill resource, significantly enhancing their economic value and utilization efficiency. The optimized TPP method yields AKO with both high extraction efficiency and a rich content of n ‐3 PUFAs. These two advantages combine to enable its use in high‐end AKO production while simultaneously laying the technical groundwork for valorizing AKP and AKS as main products, thereby providing more options for the Antarctic krill industry. It also serves as a valuable reference for researchers engaged in the comprehensive utilization of other marine biological resources. The preliminary structural analyses (FTIR, SDS–PAGE) of AKP and AKS provide essential preliminary data to support deeper investigation into these molecules and lay a scientific foundation for the subsequent development and application of AKP and AKS.

The schooling Euphausiid, Antarctic krill (Euphausia superba) is considered a keystone species in the Southern Ocean due to its abundance, prominent role in nutrient cycling, and dependency of almost all Antarctic predatory species on this single species. It has often been postulated that polar species may be more sensitive to anthropogenic contaminants on account of their evolutionary isolation from exposure. Despite geographical isolation, anthropogenic contaminants have frequently been detected in the Southern Ocean and Antarctica biota, including, heavy metals, petroleum products, persistent organics pollutants (POPs) as well as microplastic (plastics <5 mm diameter) marine debris. This thesis examined the response of Antarctic krill exposed to two common pollutants; the POP compound para, para-Dichlorodiphenyldichloroethylene (p,p’-DDE), a metabolic by-product of the pesticide Dichlorodiphenyltrichloroethane (DDT); and polyethylene (PE) microplastics. To investigate the fate of microplastics ingested by a grazing crustacean of high dietary plasticity, commercial microplastic PE beads were offered to Antarctic krill as a proportion of their diet. Krill were exposed to either a low (20%) or high (80%) dose plastic diet for four days, after which the faecal pellets and internal body burdens were examined. Antarctic krill were found to mechanically alter ingested microplastic beads into irregular fragments and nanoplastics. The capacity for fragmentation was found to be dependent on the concentration ingested. Further, the krill displayed size dependant depuration of the altered beads. This is the first time pristine microbeads have been noted to be physically altered by ingestion. With regards to the fate of commercial PE beads ingested by Antarctic krill, it appears that larger microplastics are fragmented into pieces that are small enough to cross biological barriers after ingestion, or are egested as a mixture of irregular triturated particles. These findings suggest that the current literature, based on observations from laboratory-based feeding studies, may be oversimplifying the way in which zooplankton interact with microplastics. To investigate the uptake and depuration kinetics, bioaccumulation potential and detrimental health effects of irregular triturated microplastics Antarctic krill were exposed to commercial microplastic PE beads in a range of concentrations (10, 20, 40 and 80% plastic mixed diet). Toxicological endpoints of mortality and weight loss were both found to be non-sensitive for acute exposure in Antarctic krill. The depuration of particles large enough to be detected was found to be extremely fast, with krill eliminating 80% of their accumulated body burden in a matter of hours. Effective depuration was proposed to be the primary mechanism for mitigation of bioaccumulation and toxicity in krill, with bioaccumulation over 10 days of exposure found to be negligible. However, as uptake rates were similarly fast, and organisms in the marine environment are unlikely to experience microplastic free conditions to depurate their accumulated burden, chronic exposure over the lifetime of the organism with a continuous, yet variable, uptake and egestion is suggested to be a more likely scenario. Further, particles small enough to cross biological barriers were not quantified in this study, and the bioaccumulation potential of these particles remains to be evaluated. To investigate sublethal p,p’-DDE exposure and identify potential biomarkers of sub cellular damage Antarctic krill were aqueously exposed to five treatments (1, 5, 10, 15 and 20 μg L-1) of p,p’-DDE. The response of enzymes with known roles in exogenous compound metabolism (glutathione S-transferase, GST and cytochrome P450 2B, CYP2B), neurotoxicity (acetylcholinesterase, AChE) and oxidative stress (glutathione peroxidase GPx) were quantified. CYP2B was not detectable in Antarctic krill. None of the enzymes detected induced linear concentration-dependant responses. GST was elevated at all exposure concentrations compared to the control, however no treatments were significantly different. GPx and GST followed similar trends throughout the treatment responses suggesting that an underlying biological factor may be influencing both enzymes. AChE activity was not correlated with p,p’-DDE exposure concentration, but all concentrations displayed lower activity than the solvent control however no treatment was significantly inhibited by p,p’-DDE in Antarctic krill. These findings did not provide evidence for an activated detoxification response to p,p’-DDE via the targeted biochemical pathways in Antarctic krill. These findings provide an important baseline for future work to establish the mechanisms of organochlorine toxicity and further our understanding of Antarctic krill detoxification capabilities. Overall, the results of the work described in this thesis characterise several key interactions between anthropogenic pollutants and Antarctic krill. This work provides a comprehensive foundation for further investigation on the combined effect of p,p’-DDE and polyethylene microplastic stressors, as well as other microplastics and POPs in isolation and as mixtures, which may better reflect environmental conditions.

Antarctic krill (Euphausia superba Dana), one of the resources which have never been fished before, is full of development potential. The data of the ocean environment, generated from remote sensing, is the important parameter in analyzing the spatial and temporal distribution, the state of resource and the fishery work environment of Antarctic krill fishery. After downloading, extracting, clipping, registration, projection and calculation, we have got the information about the sea area and state data of Antarctic Krill fishery. Then we make the thematic map according to the data characteristic. From the distribution map of the 3 fishing areas in 2011, it is indicated that chlorophyll-a density is maximum in December and minimum in February. The sea surface temperature is maximum in February, and minimum in August. And the sea ice density is maximum in September and minimum in February. There are some differences in different season.

As a key species in the Antarctic food web, Antarctic krill (Euphausia superba) is a potentially healthy source of lipids, containing two of the most important omega 3 fatty acids. However, the degree of unsaturation of long-chain polyunsaturated fatty acids, especially those from the omega 3 family, makes dry samples of the species vulnerable to oxidative degradation during long-term storage. The ontogenetic and temporal variation in fatty acids of dry krill tissues preserved under ambient temperature is unclear. To investigate the effects of long-term storage at ambient temperatures on degradation of fatty acids in krill, variation in the fatty acid composition of dried tissues at 0, 4, and 8 months was investigated. The results showed that storage time had a significant effect on fatty acid composition. When preserved for up to 4 months, the fatty acid content of krill changed dramatically, after which the proportion of fatty acids stabilized. Sensitivity to oxidation varied with the type of fatty acid, and krill size had an effect on the antioxidant capacity of fatty acids. Novelty impact statement The ontogenetic and temporal variation in fatty acids of dry Antarctic krill (Euphausia superba) tissues preserved under ambient temperature was investigated. Storage time had a significant effect on fatty acid composition for long-term storage of dried krill tissue preserved at a constant temperature. Krill size affected the degree of fatty acid oxidation and larger individuals lost more polyunsaturated fatty acids in the long term (8 months). Four months is a valuable reference for studying the effects of storage time on fatty acid degradation of krill tissue to maximize its nutritional value.

We hypothesized that the polyunsaturated fatty acids of the butterfly were probably derived from the diet and that there might be a great loss of body fat during metamorphosis. To substantiate these hypotheses, we analyzed the fatty acid composition and content of the diet, the larva, and the butterfly Morpho peleides. Both the diet and the tissues of the larva and butterfly had a high concentration of polyunsaturated fatty acids. In the diet, linolenic acid accounted for 19% and linoleic acid for 8% of total fatty acids. In the larva, almost 60% of the total fatty acids were polyunsaturated: linolenic acid predominated at 42% of total fatty acids, and linoleic acid was at 17%. In the butterfly, linolenic acid represented 36% and linoleic acid represented 11% of total fatty acids. The larva had a much higher total fatty acid content than the butterfly (20.2 vs. 6.9 mg). Our data indicate that the transformation from larva to butterfly during metamorphosis drastically decreased the total fatty acid content. There was bioenhancement of polyunsaturated fatty acids from the diet to the larva and butterfly. This polyunsaturation of membranes may have functional importance in providing membrane fluidity useful in flight.

The response of sea surface temperature (SST) before and after the passage of Typhoon-18 Songda in the vicinity of Chjeu Island in the southern sea of Korea was investigated using satellite-derived GOES-MCSST (SST), GOES infrared cloud image and a three dimensional WRF-3.0 model with FNL initial meteorological data on September 5 to 8, 2004. On September 4, before the typhoon passed by Cheju Island, the SST extending southwards and eastwards of the island was 27°C. However, after the typhoon passed by the island at 2100 LST, September 7, the SST decreased by 2°C to 25°C. Asymmetrical-cyclonic surface wind generated by the combination of the movement of the typhoon and the cyclonic winds of the typhoon itself, caused divergence of wind driven currents, which induced upwelling of deep sea colder water to the sea surface and outward spreading of cold waters near the island. This resulted in the decrease of SST and a negative maximum geopotential tendency of 500 hPa for 24 hours (∂Φ/∂t; m/day) was detected in the center of the typhoon eye, where the thinner atmospheric layer existed. This induced a decrease in the sea surface height and in the downwelling of surface waters. A positive maximum geopotential tendency was detected behind the typhoon center along its track, where maximum expansion of the atmospheric depth caused the level of the sea surface to rise and upwelling of deep sea cold waters to the surface. Thus, the slope height ranging from 422 to 639 m/day between two maxima of geopotential tendencies could strongly influence the sea surface elevation, thereby inducing a very strong upwelling and outward spreading of deep sea colder waters toward the inclined sea surface, resulting in a decrease of SST in the wake of the typhoon track.

In situ, satellite and model analyses data in April–July 2006 are used to investigate the links between sea surface temperature (SST) and the marine atmospheric boundary layer (MABL) in the Gulf of Guinea. The study region between 10°W and 6°E is divided into three areas with different characteristics: the North Area (4.5°N to 1°N) with the wettest atmosphere and the warmest SST, the Upwelling Area (1°N to 4°S) with the strongest SST decrease, and the South Area (4°S to 8°S) with a drier atmosphere and a more slowly decreasing SST than in the Upwelling Area. The key zone of the air‐sea interactions in this region seems to be the SST front between North and Upwelling Areas. On the one hand, the study of the MABL on either side of the front shows a well‐mixed layer between the surface and about 500 m high, sensitive to surface variations, which gets shallower (deeper) when the SST decreases (increases). The MABL height (about 1500 m) follows the same variations but is not exactly collocated with the SST variations. On the other hand, the observation of the MABL across the SST front shows a strengthening of southeasterlies in the South Area coinciding with a strong SST decrease in the Upwelling Area. In the latter, the wind weakens above the colder SST. Besides, in the North Area, the wind strengthens above the warmer SST. However, the wind acceleration spans from the equator to 2°N in April and as far as 4°N in June. A convergence zone is observed in the vicinity of 2°N in April, suggesting a convection activity there, favoured by the SST front. Copyright © 2011 Royal Meteorological Society

The variability of Sea Surface Temperature (SST) and chlorophyll-a distribution in the southern waters of East Java is heavily influenced by the Indian Ocean Dipole (IOD) phenomenon. This study examines oceanographic parameter variability, their relationship with the IOD from 2003 to 2014, and fishing dynamics in the southern waters of East Java, particularly at PPN Prigi. Data utilized include SST and chlorophyll-a from Aqua-MODIS satellites, the Dipole Mode Index (DMI), and 12 years of fish production records. The analysis reveals significant fluctuations in SST and chlorophyll-a, with a strong inverse relationship (correlation: –0.677), where chlorophyll-a concentrations rise as SST decreases. Positive IOD events reduce SST, while negative IOD events increase SST, with correlations of –0.591 for SST and IOD and 0.601 for chlorophyll-a and IOD. During the positive IOD events of 2006–2008, SST decreased, leading to increased fish production. Conversely, the negative IOD in 2010 raised SST, contributing to a decline in fish stocks. Over the 12-year period, a notable increase in Bali Sardinella and skipjack production was observed, despite a sharp decrease in 2010 caused by higher SST levels. This study highlights the importance of understanding the interactions between SST, chlorophyll-a, and IOD in developing sustainable fisheries management strategies. These insights can support efforts to optimize fish resource utilization, mitigate the impacts of climate variability, and ensure long-term fisheries productivity in the southern waters of East Java, particularly for strengthening adaptive resource planning within climate-sensitive pelagic ecosystems and supporting informed decision-making for regional fisheries policies and sustainable blue-growth initiatives.

Over the past 100 years, changes in the food supply in Western nations have resulted in alterations in dietary fatty acid consumption, leading to a dramatic increase in the ratio of omega-6 (omega6) to omega3 polyunsaturated fatty acids (PUFA) in circulation and in tissues. Increased omega6/omega3 ratios are hypothesized to increase inflammatory mediator production, leading to higher incidence of inflammatory diseases, and may impact inflammatory gene expression. To determine the effect of reducing the omega6/omega3 ratio on expression of inflammatory pathway genes in mononuclear cells, healthy humans were placed on a controlled diet for 1 week, then given fish oil and borage oil for an additional 4 weeks. Serum and neutrophil fatty acid composition and ex vivo leukotriene B(4) production from stimulated neutrophils were measured at the start and end of the supplementation period and after a 2-week washout. RNA was isolated from mononuclear cells and expression of PI3K, Akt, NFkappaB, and inflammatory cytokines was measured by real-time PCR. A marked increase was seen in serum and neutrophil levels of long-chain omega3 PUFA concomitant with a reduction in the omega6/omega3 PUFA ratio (40%). The ex vivo capacity of stimulated neutrophils to produce leukotriene B(4) was decreased by 31%. Expression of PI3Kalpha and PI3Kgamma and the quantity of PI3Kalpha protein in mononuclear cells was reduced after supplementation, as was the expression of several proinflammatory cytokines. These data reveal that PUFA may exert their clinical effects via their capacity to regulate the expression of signal transduction genes and genes for proinflammatory cytokines.

Lipids as markers of nutritional condition and diet in the Antarctic krill Euphausia superba and Euphausia crystallorophias during austral winter

ENSO and IOD are oceanographic phenomena that occur in the tropical Pacific Ocean and Indian Ocean, due to the interaction between the sea and the atmosphere. The study aims to determine the impact of ENSO and IOD on the abundance of Sea Surface Chlorophyll (SSC) and Sea Surface Temperature (SST) in the Bali Strait. The data used are Ocean Nino Index (ONI), Dipole Mode Index (DMI), Sea Surface Chlorophyll (SSC) and Sea Surface Temperature (SST). The method applied the SSC and SST anomaly analysis during the ENSO and IOD periods from March 2000 to July 2020. The results showed that during the ENSO and IOD periods in the eastern monsoon, there was an increase in SSC concentrations and a decrease in SST in the Bali Strait. In the ENSO period, there were La Nina and El Nino phases, while IOD had positive and negative phases. During the observation, it was known that the mean range of SSC was 0.49 - 1.91 mg m-3 and 25.32 - 29.30 °C for SST. SSC anomaly during the observation period was between -0.04 - 0.62 and SST was -0.66 - 1.47. Therefore, it was known that the period that causes an increase in high SSC and a decrease in SST in the waters of the Bali Strait was during the El Niño period along with positive IOD phases in 2006, 2015, 2018, and 2019.

In a previous study at South Georgia, carnivory was invoked as a cause of high polyunsaturated fatty acid (PUFA) content of Antarctic krill, Euphausia superba. To examine this, krill were sampled and fed for 16 days exclusively on the locally abundant copepod Drepanopus forcipatus. After 16 days, the krill had increased their PUFA content from 28 to 54% of the total fatty acids. Concurrently, monounsaturated fatty acids (MUFAs) and saturated fatty acids (SFAs) decreased from 41 to 27%. Thus, the krill appeared to accumulate PUFAs as reflected in their diet of D. forcipatus, which also had a relatively high PUFA content (50%). Overall, the results support omnivorous feeding by krill at South Georgia during nonbloom periods. We propose that the ratio of PUFA to SFA content may be used to detect carnivory in the recent feeding history of krill and suggest that this may be an index which could be applied to other zooplankton.