Extreme morphologies are often found in extreme conditions. Many commonalities exist in the morphology of deep and shallow-water sea urchins, but different evolutionary histories and adaptations to living at great depths have created peculiar and divergent morphologies within deep-sea sea urchins. These are highlighted alongside a list of families prevalent and charismatic in the deep sea. Following this brief introduction, life-history traits (growth and reproduction) and nutrition, including food sources, trophic positioning, nutrient partitioning, seasonal dietary shifts, and bioerosion of deep-sea corals are discussed in detail. The majority of deep-sea sea urchins appears to be deposit feeders and scavengers, but some exceptions indicate more sophisticated diets comprised of predation on living coral and highly mobile invertebrates. Our understanding of adaptations to cope with food restrictions and competitive interactions in the deep sea is still limited. However, we do know that growth and reproduction may be coupled to the influx of surface-derived phytodetritus, which heavily influences growth of all taxa and reproduction of seasonal breeders. Known patterns in distribution, abundance, and habitat associations, as well as deep-sea sea urchin interaction with predators, competitors, and symbionts are outlined. The chapter concludes with the evolutionary history of deep-sea fauna, focusing on sea urchin diversity. |
