Endangered Marine Invertebrate

A physicist friend recently sent me a link to 20 strange and exotic endangered species, saying that the list was "sufficiently yucky and biological" to appeal to me, and it got me thinking about endangered marine invertebrates. The white abalone is the only marine invertebrate that's been listed as endangered under the Endangered Species Act. "Only one? Those marine inverts must be in pretty good shape," you might be tempted to surmise. But you're more sophisticated than that, so you probably wouldn't. There is a long list of assaults on marine invertebrate species: habitat loss, overharvesting, invasive species, disease outbreaks, pollution, global climate change, and more. Most marine invertebrates just haven't been studied in sufficient depth to be listed as endangered, and there are only a handful that are considered to be "threatened" or "species of concern," which are lesser categories than "endangered." To read more about threatened and endangered marine species, you can find plenty here.
White abalone have suffered dramatically from overharvesting. Here's the somewhat oversimplified ecological tale: Usually as population size goes down, individuals enjoy enhanced rates of growth and reproduction, because competition between individuals decreases as populations shrink. But there's a limit. When populations get extremely small (and what's extreme will vary with the ecology of each species), individuals may suffer reduced rates of growth and reproduction. If you do better with some neighbors around, the benefits of reduced competition that come with a shrinking population ultimately lead to other challenges, the most obvious being finding a mate. The general phenomenon of individuals doing worse as population size gets even smaller is called the Allee effect. This is what happened to white abalones. Mating in abalones is not a particularly touchy-feely process. Males and females shed gametes directly into the ocean where fertilization and subsequent embryonic and larval development occur. Fertilization cannot happen if spawning partners are too far away from each other; even a few meters can result dilution of gametes that is severe enough to eliminate the possibility of fertilization. Moving adult abalone closer to each other in the field, as well as spawning them in the lab to produce offspring are management measures that are being taken to rescue this species from the threat of extinction. There's plenty to read about regarding sustainable seafood (white abalone clearly not included) at this month's Carnival of the Blue.