Palatability and chemical defense of eggs, embryos and larvae of shallow-water Antarctic marine invertebrates

The present study examines aspects of palatability and chemical defense in the early life history stages of 7 common species of shallow-water antarctic marine invertebrates with contrasting modes of reproduction. These included the spawned eggs and larvae of a sea urchin and the intraovarian eggs of a sea star, both with planktotrophic larvae, and the lecithotrophic embryos and larvae of 3 sea stars with either brooding or broadcasting modes of reproduction. In addition, a sponge and a nudibranch with brooded lecithotrophic embryos and egg ribbons, respectively, were investigated. Ovaries containing eggs, spawned eggs, and developing embryos or larvae were tested for their palatability against 3 common sympatric predators representing widely disparate feeding patterns: the sea star Odontaster validus (a benthic scavenger), the sea anemone Isotealia antarctica (a benthic filter feeder and opportunistic carnivore) and the amphipod Paramoera walkeri (a benthic and water column scavenger). Alginate feeding pellets containing hydrophilic and lipophilic extracts of spawned eggs of the broadcasting planktotrophic sea urchin Sterechinus neumayeri and ovaries containing developing eggs of the broadcasting planktotrophic sea star O. validus were readily consumed by all 3 predators. Pellets containing hydrophilic and lipophilic extracts of 4-armed echinoplutei larvae of S, neumayeri offered to the sea anemone I. antarctica were also consumed, indicating a lack of chemical defense. In contrast, at least 1 of the 3 predators demonstrated feeding inhibition to eggs, embryos, larvae or their hydrophilic or lipophilic extracts in the remaining 5 lecithotrophic species. In the lecithotrophic sea star Diplasteria brucei we demonstrate that the basis of rejection is chemically mediated. It is likely that rejection among the other 4 lecithotrophic species is also chemically based as eggs, embryos and larvae are conspicuous and high in energy content, lack morphological defenses, and are immobile or sluggish swimmers. Our findings indicate predators display species-specific feeding deterrent responses and support observations that lecithotropkic embryos or larvae may be particularly well suited to chemical defenses. Chemical defense in early life history stages may be especially important in shallow antarctic seas where species with lecithotrophic development patterns are relatively common, and where conspicuous yolky embryos or larvae may spend a considerable period of time developing in benthic or pelagic environments prior to recruitment.