Algae, sea urchins, introduced pathogens

Here's a story of small things making big differences.

First, we have the long-spined sea urchin, Diadema antillarum. These little guys look like pincushions stuck full of porcupine spines. They are echinoderms, like starfish, distinguished by radial symmetry and a marine lifestyle. Their ancestors first appeared in the Cambrian period, 541 to 485 million years ago. They have no heads, and just a single hole on their undersides that serves as a mouth. They move around the ocean floor on little tube feet, which can propel them with astonishing speed when they feel threatened. They eat algae, vast amounts of algae.

Now, algae. Algae are not plants, though they are autotrophs that conduct photosynthesis. They are at least eukaryotes, organisms with membrane-bound organelles. The algae aren't really a true taxonomic grouping, because there are many different types and not all of them share a common ancestor. (Like slime molds and water molds, algae are now taxa without a kingdom. They just get a domain, Eukarya.) Green algaes do look like plants, and so we sometimes call them seaweed.

Algae are ubiquitous in the seas around the Bahamas. So are coral. For millenia (eons?), algae populations on coral reefs by animals that ate them. Parrotfish eat some algae off the coral, along with some of the coral, but sea urchins are the real stars. They're little vegetarian (algaetarian?) vacuum cleaners that spend their nights gorging on new algal growth on coral reefs, and their days hiding in cavities within the coral. It keeps the urchins happy and the coral clean and beautiful.

(Parrotfish start off life as females and then turn into males. Scientists call them sequential hermaphrodites.)

Third character: a pathogen. No one knows what kind, bacteria or virus or fungus. In any case, a pathogen is a disease-causing organism.  In 1983 a pathogen entered the Atlantic through the Panama Canal, perhaps in the ballast water of a cargo ship. It was deadly to sea urchins and spread rapidly through the water. Within a year, some 97 percent of the Diadema from South America to the Bahamas had died. 

The resulting algae growth on the coral was entirely predictable and unstoppable. Today Caribbean reefs look like shaggy green monsters.

Various organizations have been working to correct this situation. Some have been breeding sea urchins and restoring them to habitats. Others have been collecting urchins from the few places they still live and moving them to algae-covered reefs.

Blackbeard's Cruises and the Cat Ppalu have been conducting Diadema restoration trips for around a decade. I went on one of these trips with the Cat Ppalu back in 2005. It was hard work! We went out every night to free dive for urchins, brought them back to the boat, and then delivered them to their new homes that day. Urchins hide in daylight, which makes them nearly impossible to catch without seriously damaging them, so it has to be done by darkness, when they walk around the sandy bottom. The idea is to create a critical mass of adult urchins so that they're close enough to one another to breed successfully - they do that echinoderm thing of everyone spawning at once one very special night each year.

Reportedly these efforts have been paying off, and some reefs with restored urchins are looking cleaner. I'll get to see next week because I'm heading off to do another urchin restoration week on the Cat Ppalu.

Living Fossils Everywhere

The ginkgo is often described as a "living fossil." But what the heck does that mean?

Charles Darwin coined the term in On the Origin of Species in reference to the platypus. Discover Online suggests that living fossils are animals (sic) that have remained relatively unchanged since they first evolved - like the platypus. The coelacanth is famously called a living fossil, though Smithsonian notes that it's more living than fossil.

Darwin suggested that these archaic forms somehow are immune to the ravages of natural selection, surviving when their compatriots go extinct due to inhabiting a protected niche without much competition. Without pressures that affect survival, there is little incentive to evolve much.

I like Darwin, and think he had great ideas. I think the term "living fossil," though, is overused and a little silly, because fossils aren't living and the experience of living long after an evolutionary starting date is hardly rare or unique. Brian Switek has a great blog posting at Wired on this very topic, entitled "Unless they're zombies, fossils don't live."

Organisms that meet the definition of living fossil are absolutely everywhere. Almost every single plant species should qualify. The various plant families originated in the antedeluvian past, some long before dinosaurs. See a moss or fern lately? A magnolia? A crazy sago palm?

The ginkgo gets star billing because it had faded out of human view for millennia, only to be revived by adventurous botanists in the 1700s and then discovered for what it was by a Japanese botanist with a microscope in 1896. Lo and behold, it was found to have exceedingly archaic sperm, characteristic of very primitive plants. Turns out that our current landscape species, Ginkgo biloba, first hit the scene about 56 million years ago. Its genus appeared 170 million years ago, in the Jurassic - dinosaur central. Its order appeared in the Permian, before the horrendous end-Permian extinction - ginkgoes made it through that bottleneck.

So the ginkgo is a special case. But plants everywhere have been around for ages and ages, way more than our paltry 200,000 years. Even the most recently evolved families, such as the Asteraceae and Fabaceae and Poaceae, are millions and millions of years old. You can look at any landscape and view snapshots from the history of life on earth. So what's a living fossil? Either all of them, or none of them.