Polar Biol (2003) 26: 666–671 DOI 10.1007/s00300-003-0540-x ORIGINAL PAPER G. Kattner Æ C. Albers Æ M. Graeve S. B. Schnack-Schiel Fatty acid and alcohol composition of the small polar copepods, Oithona and Oncaea : indication on feeding modes Received: 2 April 2003 / Accepted: 28 July 2003 / Published online: 27 August 2003 Ó Springer-Verlag 2003 Abstract The fatty acid and alcohol compositions of the (Paffenho¨ fer 1993). They occur from the polar seas to Antarctic copepods Oithona similis, Oncaea curvata, tropical regions at both hemispheres. Species of both Oncaea antarctica and the Arctic Oncaea borealis were genera can reach high concentrations, exceeding 5,000 determined to provide the first data on their lipid bio- individuals m)3 (Dagg et al. 1980; Koga 1986; chemistry and to expand the present knowledge on their Paffenho¨ fer 1993; Metz 1996). The high abundance of feeding modes and life-cycle strategies. All these tiny these tiny species compensates for the low biomass and, species contained high amounts of wax esters (on average thus, the populations can reach biomass levels of the 51.4–86.3% of total lipid), except females of Oithona same order as dominant calanoid species (Metz 1996). In similis (15.2%). The fatty-acid composition was clearly the Southern Ocean, Oithonidae and Oncaeidae can dominated by 18:1(n-9), especially in the wax-ester-rich account for between 20 and 24% of the total copepod Oncaea curvata (79.7% of total fatty acids). In all species, biomass (Schnack-Schiel et al. 1998). 16:0 and the polyunsaturated fatty acids 20:5(n-3) and The epipelagic species, Oithona similis, has been de- 22:6(n-3), which are structural components of all mem- scribed as the most numerous and widely distributed branes, occurred in significant proportions. The domi- species in the world (Wilson 1942). It occurs in temperate nant fatty alcohols were 14:0 and 16:0. In Oncaea and tropical regions, but is especially abundant at high antarctica and Oncaea borealis, the 20:1(n-9) and 22:1 latitudes (e.g. Nishida 1985). Oncaea species are likewise (n-11) alcohols and, to a lesser extent, the corresponding plentiful in most of the world’s oceans. In the Antarctic, fatty acids were also found in high proportions. This the cyclopoid O. similis and the endemic poecilostoma- indicates carnivorous feeding, although de novo bio- toids Oncaea curvata and Oncaea antarctica dominate the synthesis cannot be excluded. The variable composition copepod assemblages (Schnack et al. 1985; Hopkins and might be due to a wider range of food items and parasitic Torres 1989; Metz 1996), while in the Arctic, Oithona feeding. Typical trophic marker fatty acids for phyto- similis and Oncaea borealis are the most numerous plankton ingestion occurred only in small amounts, (Richter 1994; Auel and Hagen 2002). The Arctic Oncaea which suggests that the species were feeding on particles borealis appears to be a genuine cold-water species which such as detritus or aggregates and not on living phyto- avoids warmer waters, and is suggested to be the only plankton. From the compositional data of fatty acids true Arctic Oncaea species (Sewell 1947). and alcohols, it can be concluded that feeding behaviour Despite their high abundances, detailed information of all species is omnivorous and/or carnivorous. on their ecology and role within the ecosystems is lim- ited. Both taxa are known to be preyed on by, for example, fish larvae (Hoshiai and Tanimura 1981; Introduction Kellermann 1987), chaetognaths (Øresland 1990), car- nivorous and omnivorous calanoid copepods (Øresland Oithonidae and Oncaeidae are probably the most 1991; Øresland and Ward 1993; Metz and Schnack- abundant metazoans by numbers in the world’s oceans Schiel 1995) and cnidarians (Page` s and Schnack-Schiel 1996). However, only little is known about the feeding of Oithona and Oncaea species themselves, and their feed- G. Kattner (&) Æ C. Albers Æ M. Graeve Æ S. B. Schnack-Schiel ing behaviour is still debated in the literature. Alfred-Wegener-Institut fu¨ r Polar- und Meeresforschung, Only very few lipid studies exist on small-sized Postfach 12 01 62, 27515 Bremerhaven, Germany copepods. Lipid class and fatty-acid compositions E-mail: [email protected] Tel.: +49-471-48311490 have been determined for calanoid species such as Fax: +49-471-48311425 Pseudocalanus acuspes and Acartia longiremis from the 667 northern Norwegian Balsfjorden (Norrbin et al. 1990), reproduction, which is an energy-consuming process. and Temora longicornis, A. clausi, Centropages hamatus The production of spermatophores probably needs less and P. elongatus from temperate regions (Kattner et al. energy expenditure so that wax-ester deposits are still 1981; Cotonnec et al. 2001). However, these species are abundant in males. Such large differences in lipid accu- larger than Oithona and Oncaea. In contrast to this lack mulation between females and males have been observed of knowledge, there is a wealth of interesting lipid visually in smaller copepods but were not found in the studies on larger copepods (reviewed by Sargent and larger dominant Antarctic copepods (e.g. Kattner et al. Henderson 1986) especially from both polar regions (e.g. 1994). Kattner and Hagen 1995). The other dominant small copepod in the Southern Nothing is known about lipids and lipid composition Ocean, Oncaea curvata, was not sorted into sexes. The of Oithona and Oncaea species from polar regions. adults were extremely rich in wax ester, accounting for Therefore, the present study aims to clarify the fatty acid 86.3% on average. Oncaea curvata has been described as and alcohol compositions of the abundant Antarctic and a pre-bloom spawner like Oithona similis (Fransz 1988; Arctic Oithona and Oncaea species, as well as their Metz 1996). The high wax-ester deposits might be due to ability to produce wax esters, as done by most of the the dominance of males in summer, assuming that the larger copepods. The objective is to reveal and discuss wax-ester deposit is similarly high to Oithona similis information on feeding behaviour and life-cycle from the males. Metz (1996) found ratios between males and lipid compositional data. females of 1.1–2.6 and, at one station, even a ratio of 4.8. The females of the larger Oncaea antarctica contained, on average, 55.2% wax esters, varying between 39 and Materials and methods 68%. These moderate to high amounts of wax-ester stores reflect its reproduction strategy, which probably The Antarctic Oithona and Oncaea species were collected in the takes place in autumn (Metz 1996). Thus, lipids may be Antarctic Peninsula region around Elephant and King George Is- utilised in autumn for reproduction and start to be lands during the summer cruise ANT XIV/2 of RV ‘‘Polarstern’’ in December 1996. The Arctic Oncaea borealis specimens were sam- replenished during spring and summer. pled in the Greenland Sea during the expedition ARK XIII/1 in The Arctic Oncaea borealis had wax-ester propor- May/June 1997. The copepods were sampled by vertical bongo-net tions of 51.4% and, hence, resembled that of Oncaea hauls from 200 m depth to the surface. Adult specimens were antarctica. Oncaea borealis is said to breed during immediately sorted in a cooling container to species and sex where summer (Pavshtiks 1975); however, little is known about possible. A single sample usually comprised 176–420 specimens. The samples were stored in dichloromethane:methanol (2:1 by its ecology so far and similar life-cycle strategies as volume) at )30°C until lipid analyses. Oncaea antarctica are assumed. The copepods were homogenised in dichloromethane:methanol The fatty-acid compositions of all copepod species (2:1 by volume) by ultrasonification (10 min), and lipids were ex- were clearly dominated by 18:1(n-9), which was ex- tracted essentially according to the method of Folch et al. (1957). The fatty acid and fatty alcohol compositions were determined by tremely high in the wax-ester-rich specimens. Owing to gas chromatography (for details, refer to Kattner and Fricke 1986). the different amounts of wax esters, 18:1(n-9) was less Briefly, lipid extracts were hydrolysed and fatty acids converted to abundant in Oithona similis females but abundant in methyl esters by transesterification in methanol containing 3% males. The other major fatty acid was 16:0. The poly- concentrated sulphuric acid at 80°C for 4 h. Fatty acid methyl esters and alcohols were extracted with hexane and an aliquot unsaturated fatty acids were almost exclusively com- analysed by gas liquid chromatography (Chrompack 9000) on a posed of 20:5(n-3) and 22:6(n-3). Highest proportions 30 m·0.25 mm i.d. wall-coated open tubular column (film thick- were found in the wax-ester-poor Oithona similis ness: 0.25 lm; liquid phase: DB-FFAP) using temperature pro- females, which supports the notion that these polyun- gramming. Fatty acids and alcohols were identified with standard saturates are dominant in the phospholipids. They are mixtures and, if necessary, additional confirmation was made using GC-MS (Kattner et al. 1998). The proportion of wax esters was structural membrane components in marine organisms estimated from the fatty acid and alcohol compositions. (for copepods, see Albers et al. 1996; Scott et al. 2002). In addition, smaller amounts of 14:0, 16:1(n-7), 18:1(n-7) and 20:1(n-9) were detected. The fatty alcohols were Results and discussion composed predominantly of 14:0 and 16:0, with higher proportions of 20:1(n-9) in Oithona similis and, in All species contained considerable amounts of wax es- addition, 22:1(n-11) in Oncaea borealis.