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.J. Newman et al. J. Exp. Mar. Biol. Ecol. 255 2000 93 –110
1. Introduction
Overwhelming evidence exists that UVB radiation and the shorter wavelengths of UVA 320–400 nm can penetrate natural waters to biologically significant depths of up
to 20 m Jerlov, 1950; Smith and Baker, 1979; Booth and Morrow, 1997 and cause genetic and physiological damage to aquatic organisms Williamson and Zagarese, 1994;
¨ Worrest and Hader, 1997. Environmental ultraviolet radiation UVR can also affect
organisms indirectly by disrupting trophic-level interactions within aquatic ecosystems Bothwell et al., 1994. Algae are known to respond to UV exposure by synthesising
UV-absorbing compounds Helbling et al., 1996; Riegger and Robinson, 1997 and by repairing DNA damage Karentz et al., 1991a; Scheuerlein et al., 1995; Buma et al.,
1997. Algal taxa also vary widely in their sensitivity to UV Neale et al., 1998, which can affect succession to favour more UV-tolerant species Bothwell et al., 1993, 1994.
In contrast, fewer studies have examined the effects of environmental UVR on algal consumers such as zooplankton.
Zooplankton are a key intermediate in trophic energy transfer and nutrient regenera- tion in marine food chains Banse, 1995. Given this importance, the effects of UV
radiation on zooplankton production were examined in the early to mid-1980s following initial concerns about ozone depletion Damkaer et al., 1980; Karanas et al., 1981;
Hunter et al., 1982; Ringelberg et al., 1984. Following a lull in research activity of nearly a decade, investigation on the effects of increasing UVR on zooplankton has
re-emerged in tropical marine Saito and Taguchi, 1995, freshwater Williamson and Zagarese, 1994; Zagarese et al., 1998, mid-latitude marine Chalker-Scott, 1995;
Naganuma et al., 1997; Kouwenberg et al., 1999 and Antarctic ecosystems Malloy et al., 1997; Newman et al., 1999.
MAAs are geographically and taxonomically widespread in marine species, and MAAs are particularly common in many classes of microalgae Jeffrey et al., 1999 and
algal macrophytes Karentz et al., 1991b; Banaszak and Lesser, 1995. MAAs are produced from a branch of the shikimic acid pathway Favre-Bonvin et al., 1987; Shick
et al., 1999, a biochemical route not available in animals. Evidence is mounting that MAAs in vertebrate and invertebrate marine animals are derived from dietary accumula-
tion Carroll and Shick, 1996; Carefoot et al., 1998, or via translocation from algal symbionts Shick et al., 1999, to provide UV protection reviewed in Dunlap and Shick,
1998. In a survey of 48 species of Antarctic marine invertebrates conducted by Karentz et al. 1991b, Antarctic krill had the third highest body concentration of total MAAs. It
has also been noted that the MAA content of krill closely resembles the diversity of MAAs in the natural phytoplankton assemblage collected at the site of capture Dunlap
et al., 1995, which is consistent with MAAs in krill having a trophic origin.
This study investigates the source of MAAs in primary consumers of Antarctic marine microalgae, by determining whether krill acquire MAAs from ingested algae and
examining the effect of starvation on MAA concentrations. These experiments are also designed to provide the experimental framework for further examination of the
physiological function of MAAs in krill such as protection from UV exposure. The ecological importance of krill in the Southern Ocean ecosystem Quetin and Ross, 1991
makes the study of such mechanisms of UV protection desirable.
S .J. Newman et al. J. Exp. Mar. Biol. Ecol. 255 2000 93 –110
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2. Materials and methods
