The distribution of lipid in the tissues of Antarctic krill, Euphausia superba

649

548

Zooplankton storage lipids play an important role during reproduction, food scarcity, ontogeny and diapause, as shown by studies in various oceanic regions. While triacylglycerols, the primary storage lipid of terrestrial animals, are found in almost all zooplankton species, wax esters are the dominant storage lipid in many deep-living and polar zooplankton taxa. Phospholipids and diacylglycerol ethers are the unique storage lipids used by polar euphausiids and pteropods, respectively. In zooplankton with large stores of wax esters, triacylglycerols are more rapidly turned over and used for short-term energy needs, while wax esters serve as long-term energy deposits. Zooplankton groups found in polar, westerlies, upwelling and coastal biomes are characterized by accumulation of large lipid stores. In contrast, zooplankton from the trades/tropical biomes is mainly composed of omnivorous species with only small lipid reserves. Diapausing copepods, which enter deep water after feeding on phytoplankton during spring/summer blooms or at the end of upwelling periods, are characterized by large oil sacs filled with wax esters. The thermal expansion and compressibility of wax esters may allow diapausing copepods and other deep-water zooplankton to be neutrally buoyant in cold deep waters, and they can thus avoid spending energy to remain at these depths. Lipid droplets are often noted in zooplankton ovaries, and a portion of these droplets can be transferred to developing oocytes. In addition to lipid droplets, zooplankton eggs have yolks with lipovitellin, a lipoprotein with approximately equal amounts of protein and lipid. The lipovitellin lipid is predominantly phosphatidylcholine, so during reproduction females must convert a portion of their storage lipid into this phospholipid. Developing embryos use their lipovitellin and lipid droplets for energy and materials until feeding begins. The various functions storage lipids serve during the different life history stages of zooplankton are very complex and still not fully understood and hence offer a multitude of fascinating research perspectives.

“…5a) (Saether et al 1983, Blades-Eckelbarger 1991. Oil sacs, when present, are often in close proximity to developing oocytes (Fig.…”

Section: Ovarymentioning

confidence: 97%

Section: Hepatopancreas and Fat Bodiesmentioning

confidence: 99%

Lipid storage in marine zooplankton

Lee

Hagen²,

Kattner³

2006

649

548

“…Therefore, material converted into the storage component neutral lipid does not result in an increase in krill length in the model. This approach has been used for simplicity although it has been hypothesised that Euphausia superba may accumulate phosphoglycerides as storage lipids (Saether et al 1985, Hagen 1988, which indicates that it is difficult to strictly separate polar and neutral lipids of krill into structural and storage components.…”

Section: Model Descriptionmentioning

confidence: 99%

“…Polar lipid is only depleted in the model when krill is shrinking. This approach was used for simplicity although it has been shown that Euphausia superba may accumulate certain polar lipids as storage lipids as well (Saether et al 1985, Hagen 1988. Nevertheless, the model accounts for polar lipid to neutral lipid ratios within the range of observations (Hagen 1988) and minimum total lipid values in winter that match observations (Hagen et al , 2001.…”

Section: Model Performancementioning

confidence: 99%

Biochemically based modeling study of Antarctic krill Euphausia superba growth and development

Fach¹,

Meyer²,

Wolf-Gladrow³

et al. 2008

A biochemical model of Antarctic krill Euphausia superba was developed to investigate the physiological mechanisms which enable krill to survive winter, when food is scarce. In this modeling approach data sets on the biochemical composition of krill and its food sources are combined into a model that takes food quality into account rather than just food availability during different seasons. Krill is defined in terms of protein, neutral lipid, polar lipid, carbohydrate, chitin, and ash content, and the model tracks krill neutral lipid content separately from weight. The model includes parameterizations of filtration, ingestion, and metabolic processes which determine krill growth rate. Initial ratios of protein, neutral lipid, polar lipid, carbohydrate and ash change in chitin response to the biochemical composition of food as krill grows. Model results show that a diet of phytoplankton food alone may be sufficient for krill to grow to observed sizes but may not be sufficient to provide the summer lipid resources that are observed in the field and that are necessary for krill to reproduce and survive winter. The inclusion of sea ice algae as an additional food is beneficial for krill at the end of winter but does not significantly change summer krill lipid content. However, the amount of lipids accumulated within krill increases significantly when krill feeds on lipid-rich heterotrophic food, which points to the importance of carnivory, even in times when phytoplankton food is available. The strategy of combusting body components to produce energy (shrinking) is found to provide the greatest source of energy for krill of all sizes during times of prolonged starvation.

“…Mayzaud 1997) and internal processes such as gonad maturation , Saether et al 1985, Virtue et al 1996, Mayzaud et al 1998, CuzinRoudy et al 1999. Because krill are pelagic crustaceans, it is difficult to maintain them in in vitro experimental systems, and it is thus difficult to study the ability of euphausiids to acclimate to a variable environment.…”

mentioning

confidence: 99%

Influence of tropho-climatic environment and reproduction on lipid composition of the euphausiid Meganyctiphanes norvegica in the Ligurian Sea, the Clyde Sea and the Kattegat

Albessard¹,

Mayzaud²

2003

Lipid content and lipid-class distribution in the northern krill Meganyctiphanes norvegica (M. Sars, 1857) was investigated in 3 contrasting (in terms of climatic and trophic conditions) areas: the Ligurian Sea, the Clyde Sea and the Kattegat. Seasonal differences in the lipid content of krill were closely related to food supply coupled with the krill reproductive state in both the Ligurian Sea and in the Clyde Sea. In the Kattegat, the lipid reserves of reproductive krill were low and probably used continuously over a longer reproduction period and successive spawning cycles. In the Ligurian and Clyde Seas, female krill lost 55 and 33% of their cephalothorax (CT) lipids through spawning. The content of triacylglycerol (TAG) and phosphatidylcholine (PC), both major lipids in the CT, were higher when food conditions were optimal at the 3 sites, and were correlated to chlorophyll a (chl a) concentration in the Ligurian and Clyde Seas. The influence of reproduction on lipid-class distribution in the Clyde and Ligurian Seas was expressed by a large decrease in PC and TAG throughout spawning, while in the Kattegat PC and TAG levels were low irrespective of the reproductive state. The relative influence of environmental and physiological factors on the lipid distribution of krill in the CT and abdomen (AB) among the 3 locations was evaluated using principal components analysis. In the CT, TAG and PC along with minor lipids were major discriminating factors and were strongly correlated to total lipid content and chl a concentrations. For reproducive krill, marked differences in the CT and AB indicated covariation between reproduction and trophic conditions. The influence of the physical environment on M. norvegica at sexual rest found expression in variation in the membrane lipids in the AB across the different temperature and salinity regimes at the 3 sites. The results are discussed in terms of adaptive mechanisms involving lipid distribution and metabolism developed by the species.