Underwater Christmas Trees!
Location: Alice's Backside - Ginger Island, BVI
by Wayne & Karen Brown
Today is Christmas day! We had our Christmas and presents with our parents before we left California, so for us today is another day to explore the reefs.
Today Corri takes us to Ginger Island. Cori tells us that Ginger was named for the pirate Blackbeard's wife. Off Ginger Island place where we will be diving is called Alice's Backside. Corri shows us how this place got its name. Behind our dive site are two round hills, right next to each other. They kind of look like somebody's rear end!
We enter the water and set our DVs for their slowest speed, so we can slowly cruise over the reef. The bottom is about 20 feet underwater. The reef slopes slowly off into deeper water, down to the sand about 50 feet underwater. The boulder corals and brain corals look healthy here, but the many of the large elkhorn corals are dead. (Boulder corals are rounded and look like big and small boulders. Brain corals look like big and small brains. Elkhorn corals have wide branches that reach up to the surface and look like elks' horns.)
Elkhorn corals are one of the fastest growing corals on the reef. Most corals growth about 1/8 - 1/4 inch per year. Elkhorn corals can grow over 2 inches each year!...More than twice as much as other corals! Because they grow so much faster elkhorn corals need more food and sunlight than other corals. Elkhorn corals need strong currents to bring them lots of food. Any changes in currents, nutrients, sunlight, water temperature, and salinity can hurt or kill elkhorn corals before it affects the other corals. There are also underwater diseases that can hurt or kill corals. Elkhorn corals are what are called indicator species, because they indicate if something is wrong. Even though the other corals look healthy we can see that there are changes happening here that may hurt the other corals in the future.
Fortunately we notice that there are some smaller, younger elkhorn corals that look quite healthy. Are these elkhorn corals more fit and less affected by changes than the other elkhorn corals? Maybe these corals started growing after what killed off the other corals changed back to normal? It is too late to change what happened to these dead elkhorn corals, but maybe these new elkhorn corals can multiply and the elkhorn corals will once again spread their branches all around the reef.
As we look closer we see that fish use the corals as their homes. Big fish live under overhangs and in cracks and caves under the big corals. Tiny fish live in crevasses and holes on the top of the corals.
Looking closely at the corals we see other animals using the corals as home. White, earthworm-sized worms live in tubes covered by the coral. Only a small hole is visible in the coral which is their entrance and exit to their tube. We can't see the worms' bodies hidden in their holes. The only thing we see sticking out of their holes are their gills, which they use like our lungs, to breathe. They also use their gills like a fishing net to catch food (plankton) floating by. What is cool about the gills is that they look like tiny Christmas trees! It looks like the worms have decorated their trees for Christmas, too! The tiny "trees" we see are in different colors, red and white, yellow and blue, and other colors. Of course, these worms didn't decorate for the holidays, they are normally in these pretty colors, adding splashes of colors, like drops of paint on the corals.
We see we have just about run out of time with our air supply, so we turn-up the speed on our diver vehicles and zoom back to the boat.
We had a great Christmas dive today. We hope all you had the best Christmas ever!
Best Christmas Fishes,
Wayne & Karen
Alice's Backside, Ginger Island
Position: 18º 23' N / 64º 29' W
Air Temp: 85ºF
Weather: light breeze, sunny with scattered clouds.
Sea Conditions: slightly choppy seas, slight current
Dive Time: 1 hour 8minutes
Maximum Depth: 54 feet.
Water Temp: 81ºF
Underwater Visibility: 60 feet
Most of the reef we see is boulder and brain corals. The large mound in the center is a huge brain coral about 6 feet across! You can see a small rounded brain coral behind. Surrounding the brain corals are mostly knobby boulder corals.
This healthy elkhorn coral is about 4 feet wide and about 3 feet high.
Sticking out of a small boulder coral we counted 8 Christmas tree worms. (Enlarge the picture and see how many you can find. Hint: Each worm has one pair of "Christmas trees". Also look closely for a tiny fish, called a secretary fish, sticking its head out of a small hole on the front left side of the coral.)
A Christmas tree worm's pair of feathery gills sticks out of a brain coral. Notice how the center stalk is striped like a candy cane. The gills work as lungs. They capture the oxygen that is dissolved in the seawater. They also work as fishing nets. They catch tiny plankton floating by.