Sponges in the marine desert

One of the things I think is most awesome about science is when people identify or otherwise figure out the awesome adaptations animals have that allow them to live in places you simply wouldn't expect them to live. This week's Science Sunday is featuring an article out of Science magazine that reports why coral reefs are able to exist in parts of the ocean that would otherwise be considered marine deserts.

Mostly a thriving, productive ecosystem is only possible in places where nutrients are abundant. In the oceans that means near upwelling regions, like the coast of California and South America, the west coast of Africa, parts of the coast of Antarctica, and the equatorial Pacific ocean. All of those places have significant upwelling and, consequently, an intense blooming of life.

Those regions are far from the only productive parts of the ocean. Indeed, some of the highest diversity and highest productivity in the ocean occurs at coral reefs, which occur primarily in areas lacking significant upwelling or other nutrient inputs. In fact, coral reefs occur in regions that are so nutrient poor they're considered marine deserts. The question is, how does that happen? We know that corals have photosynthetic symbiotes, but are they productive enough to overcome the nutrient scarcity of the local environment?

In a word, no. But sponges are. Sponges, which are really heterotrophs turn out to be major producers of biomass on reefs. They filter out dissolved organic matter (DOM--basically any carbon-containing molecule or larger particle in the water) and turn it into their cells. Filter cells then get spewed out into the larger ecosystem and consumed by everything else, supporting much of the food chain. The cool thing about the de Gooj, et al. article is that it suggests the amount of waste produced by the sponges is close to the amount of gross primary production required by the coral reef ecosystem.

How does that work into fiction? Well, imagine you need to create an ecosystem on a desert planet and need to come up with some way to support that ecosystem. Sponges (or some analog) are very simple, easily overlooked creatures, and might be one way to support your ecosystem. If, say, you wanted to give your story a relatively hard science feel to it.