Wednesday, October 15, 2008

Fishes in the Sea Part 2: Surgeons, Territorial Gardeners, and the Sand Between Your Toes

There are many niches on the reef for fish to fill and various forms of feeding occur in these niches. Some fish eat other fish (see Dead Eels for example) some specialize in invertebrates (see Fishes in the Sea Part 1) and some are herbivores. Within the herbivores various strategies have evolved.
Let's start with parrotfish. You probably love to play in parrotfish poop. I bet you like the feel of it between your toes. You may even roll around in it and enjoy laying on it. It's what gives rise to most of the tropical beaches around the world. Much of the world's sand is broken down coral skeletons (and coralline algae) that has passed through the intestines of parrotfish. With jaws modified to crush coral, parrotfish are usually seen chomping into dead coral for the algae that are on the coral. When diving or snorkeling you'll hear the crunch, crunch sounds of parrotfish feeding around you.

There are other herbivorous strategies in reef fish. Surgeonfish, for example, typically graze on algae on top of the coral. Sometimes you'll see large schools of sugeonfish moving along in an algae-feeding frenzy (often a mixture of blue tang, ocean surgeonfish and doctorfish -- they all have a sharp spine on the base of their tail----like a scalpel). Unlike the trunkfish and many daytime invert eaters, these fish are often found in schools. Why go to school? A number of functions of schooling (or flock behavior) have been proposedl. For one, there are more eyes to look out for predators (more total vigilance). Plus, when individuals move together it is harder for a predator to keep track of any one individual to strike (confusion). Then there's the increased chance that your schoolmate will get chomped instead of you (bonus!). But schooling in surgeonfish seems to be about overcoming the feisty gardeners that inhabit the reefs. The fearsome damselfish. Perhaps you've heard of them? They're vicious. No, they don't have a damselfish week on the Discovery Channel, but they're more prone to attack than any shark you're likely to run into. And if an individual surgeonfish wanders into a damselfish gardent, it gets its butt (figuratively) kicked. By joinging a gang, surgeonfish can overwhelm and bully the little damselfish. Not that the damselfish stop trying. Watch these two videos and keep an eye out of for small black fish dashing around attacking the schooling fish in vain.

That's a damselfish for you. Feisty "gardeners" of the sea. Really, really feisty gardeners. Damselfish have a different herbivorous strategy, they tend small algae gardens, defending them against everything. Watch yourself, they'll attack fish, fins, and just about anything else that passes by. They regularly feign attacks on me and when I'm not looking they'll bite my fins. I even had one try to kill the lead-core line that I use when doing surveys. It was trying to pick the line up and get it away from its garden. Overall, being a grumpy gardener must be a successful strategy, the reef is covered with little damselfish. These little fish effectively keep most fish away from their scrumptious little patch of algae. Thus, surgeonfish have to stick together to take on the runts a quarter of their size.
That's it for this lesson on reef fish.
(If you're having trouble with the videos try a couple of things 1) use Firefox instead of Internet Explorer; 2) Send me an email and let me know. I may be able to change the HTML code to make it work. Plus, I'll know if anybody I know is reading!)

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