Just back from my happy place — I’ve been floating around in the warm tropical waters of coral reefs watching the wildlife going about their daily activities. This time we went to the atolls off the coast of Belize, a remote enough location for the reefs to be as healthy as coral reef ecosystems can be these days. To be sure we did see some signs of stress, but with relative isolation and active protection measures (to which scuba divers contribute by Belizean law), on the outer islands you get a chance to see some of the amazing biodiversity of this special world, the most diverse and threatened ecosystem in the world.
One feature of that diversity is the variety of niches since a lot of creatures are packed together in a limited three dimensional setting, interact in highly complex relationships, and must have functional ways avoid too much competition for food. Amongst the fish, one consequence is a surprising range of shapes.
Typically fish have a fusiform shape, ie wide in the middle and tapering at both ends, an effective shape for fast hydrodynamic swimming. Such fish mostly swim using their whole body, as these do in the video below, an assemblage of many kinds congregating on a coral knob, a common sight for divers.
(Note: I took only videos on my dives, since what interests me most is watching what creatures do using their particular set of physical features. And in any case I don’t have the camera setup to take National Geographic level still photos.)
31 second video:
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In contrast to the general fusiform fish shape, here are a variety of other, more oddly shaped fish, who are actually very well suited for how they make a living on the reef.
Boxfish are (relatively) slow-moving box-shaped fishes that graze algae and invertebrates. They are protected from predation by a heavy-duty bony skeleton, and often a toxic skin secretion. In the video below are a Scrawled cowfish, a Smooth trunkfish, a Spotted trunkfish and a baby Smooth.
53 second video:
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Filefish and Triggerfish have a more fusiform shape but they don’t swim like most fish do. In fact they have a rigid bony skeleton like the boxfishes, and so like them use their fins for locomotion. And like boxfish, these relatives aren’t very speedy (though of course they can outswim a person easily). Like several other kinds of fish on the reef, filefish and triggerfish have sharp collapsible spikes that can impale a predator chomping down on them.
This video shows typical swimming behavior by these fish.
29 second video:
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Some fish are flattened vertically, others horizontally, for various reasons. One of the most beautiful and iconic fish in the Caribbean is the Spotted Eagle ray, which is a cartilaginous fish related to sharks. While they feed by digging in the sand for mollusks and crustaceans, they are more commonly seen soaring and gliding gracefully through open water. Once I saw one swim into a strong current and park itself facing upstream for quite a while before turning to glide away. I have to wonder what it was thinking. In the video below, an eagle ray cruised along the edge of the reef wall past Mr O.
36 second video:
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A couple of bony flat fish include flounder and remora. Flounders usually hang out on the sand; this one was not well camouflaged on the coral. Another diver spooked it, and it swam off. Remoras are flattened on the top of their head so they can attach to the bottom of another swimming creature, usually a shark, turtle, manatee or other mammal. A remora and its host have
a mutualistic arrangement as the remora can move around on the host, removing ectoparasites and loose flakes of skin, while benefiting from the protection provided by the host and the constant flow of water across its gills.[7] Although it was initially believed that remoras fed off particulate matter from the host's meals, this has been shown to be false; in reality, their diets are composed primarily of host feces.[8]
29 second video:
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Then there are the swirly fish. My favorites of these are the Spotted drum fish. The younger they are, the longer their dorsal fin is, which acts like a streamer. The babies are almost all streamer. By the time they are adults they look more like typical fish. Here’s a Spotted drum midway through development. I suspect their swirly shape and constant movement confuses predators.
23 second video:
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Some swimmers on the reef are long and skinny. Eels are one of those. Usually they hide in crevices, but some of the Green morays were out cruising in the open. You can get a really good look with this one below how they slip through holes and cracks in the reef. An odd shaped swimmer indeed.
32 second video:
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The most charming long skinny swimmer (to me) is the Yellow headed Jawfish. These translucent little guys with intense black eyes create vertical burrows in the sand, into which they retreat tail-first, after darting out to feed on passing plankton if they feel threatened by a predator from above. They are territorial, so their neighbors’ dens won’t be too close. If a diver gets low to the sand, and waits patiently without moving, the Jawfish will emerge. The video shows a couple of them cautiously swimming straight up and down, fluttering their fins, looking over at me from time to time. I spend quite a while watching Jawfish.
54 second video:
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There are many other swimmers on the reef, odd shaped and not. But these give an idea of the variety of fish found in coral reef waters, the most biodiverse ecosystem on earth. Sadly, with global sea temperatures annd ocean acidification increasing, overfishing, invasive species spreading, development and other human population pressures, who knows how much longer the world will know this richness.
I had lots more encounters and observations underwater on this trip. I’ll share some in a future bucket or two.
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Back here at home in the Pacific Northwest islands, temps are in the 60s with light breeze today. I’m getting reacclimatized to Pacific Northwest weather!
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