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Journal of Experimental Marine Biology and Ecology 246 2000 103–123
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Elemental composition of Mysis mixta Crustacea, Mysidacea and energy costs of reproduction and
embryogenesis under laboratory conditions
Elena Gorokhova , Sture Hansson
Department of Systems Ecology , Stockholm University, 106 91 Stockholm, Sweden
Received 2 May 1999; received in revised form 3 September 1999; accepted 30 November 1999
Abstract
Mysis mixta were reared under laboratory conditions temperature: 9–10 8C; salinity: 7‰, ad
libitum food. Dry weight, ash, total carbon and nitrogen content of mysids muscle tissue, eggs, and embryos of different developmental stages have been analyzed. We found significant
variations in ash content and elemental composition during growth and maturation for both sexes. The proportion of carbon in abdominal muscle decreased gradually from juveniles with body
weight of 3–4 mg 42.9 to males and gravid females | 40.0. The nitrogen content was relatively constant 11.4 in average with significant differences only between juveniles 11.3
and mature females 11.6. In embryos, carbon and nitrogen content were highest in early stages 58.6 and 14.3, respectively. By the end of the marsupial development, carbon had decreased to
51.4 and nitrogen to 12.6. The C:N ratio reflected the change in somatic carbon content, and the ratio decreased 6.2 from juveniles to gravid females, indicating lipids to be an energy source
during maturation and reproduction. The weight-specific female investment in reproduction increases with body size. In gravid females, intersegmental growth during brooding period was
observed, while males appear to store energy only for copulation and die after mating. Ontogenetic variation in body composition has implications for elemental budgets of M
. mixta, its value as prey for fish and in modeling energy and nutrient cycling.
2000 Elsevier Science B.V. All rights
reserved.
Keywords : Mysis mixta; Energy costs; Reproduction; Embryogenesis
1. Introduction
The changes that accompany development and reproduction in crustaceans are related
Corresponding author. Tel.: 1 46-8-164-256; fax: 1 46-8-158-417.
E-mail address : elenagsystem.ecology.su.se E. Gorokhova
0022-0981 00 – see front matter
2000 Elsevier Science B.V. All rights reserved. P I I : S 0 0 2 2 - 0 9 8 1 9 9 0 0 1 7 3 - 2
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. Gorokhova, S. Hansson J. Exp. Mar. Biol. Ecol. 246 2000 103 –123
to considerable energetic losses and variations in elemental ratios Nicol et al., 1995. Information on the chemical and biochemical composition of animals at different
developmental stages is needed to describe these changes, to understand ecological and life history traits, and to evaluate how these patterns are further affected by environmen-
tal factors. Some aspects of elemental composition and fluctuations associated with maturation and egg production have been reported for both macro- and microinverteb-
rates e.g. for copepods, Arashkevich and Drits, 1997; krill, Ikeda, 1984, 1985; Falk-Petersen, 1981; cephalopods, Bouchaud, 1991; decapod larvae, Anger and Schun,
1992; Minagawa et al., 1993.
In the Baltic Sea, mysids play an important role as major forage species for herring and smelt Aneer, 1980; Arrhenius and Hansson, 1993 and are important zooplankton
predators Hansson et al. 1990; Rudstam et al., 1992. Among the mysids, Mysis mixta Lilljeborg, 1852 is the numerically dominant pelagic species Rudstam et al., 1986,
but very little direct information on its elemental composition is available, and in general this kind of data exists mainly for freshwater species Salonen et al., 1976; Hakala,
1979.
Mysis mixta is a boreal relict species of North-Atlantic origin, which inhabits Eastern Atlantic regions from the White Sea, Spitsbergen, Scandinavia and central and southern
part of the Baltic Sea and westward to Iceland. In the Western Atlantic, it has been found in Greenland coastal waters and the eastern United States down to Cape Cod Wigley
and Burns, 1971, Blaxter et al., 1980. Generally, it is considered an annual species, although some individuals survive a second year Grabe and Hatch, 1982; Salemaa et
al., 1986; Shvetsova and Shvetsov, 1990. The species is semelparous and a cold-season breeder. In December, the population consists of mating mature males and females, and
the males die shortly after copulation. The overwintering population is almost entirely composed of gravid females Shvetsova, 1980, Rudstam et al., 1986. The young
offspring are released in early spring through the beginning of summer, with a peak presumably in March, although protracted spawning periods to July–August have been
observed Shvetsova, 1980; Salemaa et al., 1986. Spawned females gradually disappear from the population and by the end of June, very few individuals of the previous year’s
generation are normally found Simm and Kotta, 1992. Newly released juveniles grow slowly and start to develop secondary sexual characters in June–September and
complete maturation by November–December Simm and Kotta, 1992.
Like in other mysids, the embryonic and post-embryonic development of M . mixta
takes place in the marsupium of the female. No information, so far, has been available on the energy investment in reproduction or about the intermediary metabolism in the
developing embryos. A first step towards understanding these life history trade-offs is to observe the variations in reproductive effort in population under controlled conditions.
Thus, knowledge of the reproductive life history traits and lifetime variations of biomass and body composition in terms of carbon and nitrogen in laboratory reared M
. mixta is likely to provide important information about the biology and ecology of this species.
The present laboratory study considers 1 the costs of reproduction and the energy losses associated with sexual differentiation and gonad development, and 2 energy
expenditure for metabolic activity during egg development from early embryo to hatching. To calculate energetic equivalents, we analyzed the biomass composition in
E . Gorokhova, S. Hansson J. Exp. Mar. Biol. Ecol. 246 2000 103 –123
105
terms of dry weight, carbon, nitrogen and ash content of eggs, embryos at different developmental stages, juvenile, subadults, and adult individuals of M
. mixta.
2. Materials and methods
