Posted by: carlsafina | Friday, January 16 09

Spotlight on Sponges – Part II

This is Part II of Blue Ocean Research Scientist Dr. Alan Duckworth’s  blog as he oversees a coral reef study in Jamaica.

Days 5 – 8

The past few days have been mostly spent attaching settlement plates to the reef. Each plate, 11 x 11 cm in size, is made of terracotta, which is a good substitute for coral substrate. This will allow us to measure the number and type of sessile organisms (e.g. sponge, coral, and algae) that settle and recruit onto Jamaican reefs.

Deploying sediment traps

Deploying sediment traps

First, two small holes are drilled into the reef using an air drill run off a large SCUBA tank. Next the stainless steel base plate is secured to the reef, using two “xmas tree” bolts. Finally, a numbered settlement plate is bolted onto the base plate. The settlement plate rests about 1 cm off the substrate so organisms can settle on the top and bottom. Most animals settle on the bottom side, away from light and predators.

Drlling holes in coral

Drlling holes in coral

 

Side view of settlement plate

Side view of settlement plate

Although it’s heavy work, drilling holes is a lot of fun. We drill holes into dead coral only so there is minimal impact to the reef. However, some dead coral is so dense that only a few holes can be drilled off one tank, which means that you need to swim back to the boat several times to swap tanks to finish the job. Afterwards, small fish swarm around inspecting the work, trying to find any worms flushed from the dead coral.

Our dive gear

Our dive gear

We have attached settlement plates at 30 and 60 feet in one impact location (next to several resorts), and two control or non-impacted locations. Plates will be photographed, examined and replaced every 6 months for 2 years. This experiment will help determine what effect coastal development has on the recruitment of sessile organisms onto coral reefs.

 At each depth and location we also deploy settlement traps. These will record the amount, type and size of particles (e.g. sand, terrestrial mud) that wash off from the surrounding land. These are left out for one week only.

 

Settlement plate and sediment trap, seen from above

Settlement plate and sediment trap, seen from above

All going well we should knock it off in one more day. The work is very enjoyable but tiring. Generally we leave at 7 am and return at 1 pm. If the weather holds we head out for another dive in the afternoon. In between we clean gear, fill tanks, get equipment organized, brush-up on sponge identifications, plan for the next day, and….eat.

Cheers, Alan

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