Today we are exploring the coral reefs of Saba. Saba is the top of an old volcano that rose up out of the sea thousands of years ago. Steep volcanic cliffs drop straight into the sea. So, unlike other Caribbean islands, Saba has no beaches. On our dives here we saw that the corals appear to be healthy, but they are not very large. We’ve seen only small patches or clumps of corals growing on the reef, which probably means it’s a young reef. Corals grow very slowly and these corals have not had time to get very large. The growth of coral is affected by other things, as well. The visibility (how far one can see underwater) here is about 80 feet. The visibility on some healthy coral reefs can be over 200 feet! Corals need water that is clear and clean. Even though the water here is not polluted, we do see some sediment (tiny particles of dirt) in the water. Part of that sediment is from the strong waves that delayed our departure from St. Maarten. These waves stirred up sediment underwater near the shore, much like dust is stirred up on land on a windy day. The rains we had could also have washed sediment from the island into the sea. A little sediment cuts down on the sunlight the corals need to grow. A lot of sediment can choke corals and prevent them from feeding. During our dive, we see many colorful fish that use the reef as a home. As we descend to the sea floor, we find some curious reef squid. They are about eight inches long and swim toward us to take a look at these strange sea creatures – us! We stop. They stop. We swim toward them and they slowly swim backward with their tentacles bunched together. It’s funny to watch them swim since they don’t have tails like fish. Squid have what looks like a clear skirt on the sides of their bodies. They flutter this "skirt" like wings to swim. The squid are also pretty to watch since they quickly change colors while swimming. They transform from pale brown with brown bars, to brown spots, then greenish spots, then no spots, then white and back to the start. The squid are mainly hanging out, trying to keep from being eaten. If they are attacked, they’ll squirt a glob of ink at their predator and swim away. When sun sets, the squid will jet around to hunt for small fish they can eat. Karen swims up to me and makes a rapid swimming movement with her arms. She motions for me to follow her and I know she has found something really cool. She points under a ledge of coral on the sea floor. It’s a shark! We aren’t scared. This is just a little two-foot nurse shark. (Nurse sharks can grow up to 14 feet long!) I reach out to pet it. Its skin feels rough like sandpaper. Sharks don’t have scales like other fish. Instead they have tiny teeth on their skin called dermal denticles. This nurse shark is sleeping under the ledge to hide until sunset, when it will come out to look for crabs, lobster and octopuses to eat at night. |
The island of Saba is an old volcano, rising up out of the Caribbean Sea.
Pillar coral is a fast growing coral. It can grow over one inch per year. It grows pillars about as big around as your arm and up to 10 feet tall!
Reef squid hovering above the reef.
A nurse shark sleeping under the reef overhang.
Head of the nurse shark. The two long white points hanging down at the front of the nurse shark’s mouth are not teeth. They are feelers called "barbels." |
|||||||||||||||||||||
December 18, 2000
|
||||||