We began our research dives with two spots on the Atlantic side of the St. Kitts and Nevis, seaward of the narrows in a reef system known as Grid Iron. This shallow reef stretches over 10 km from the northeastern end of Nevis to the coastline off St. Kitts. Formerly a flourishing elkhorn coral reef at depths of 5-10 m, most of this coral died 30 years ago and dense interdigitated skeletons remain in growth position. We did find a few survivors, some growing atop old skeletons and others sending branches up from the bottom.
Large fish were notably absent, but there were many smaller herbivores, including juvenile parrotfish and surgeonfish, which were actively grazing on the algae.
The reefs also had a few long-spined black sea urchins, another keystone herbivore known to control algal populations.
Our afternoon dive was off the southwestern tip of St. Kitts at Nags Head. This reef extends from just below the water’s surface to 70-80 feet. Large volcanic boulders that have fallen from the surrounding cliffs form a mini-wall, with small caves, crevices and channels between the rocks. Much of the bottom was covered in fine silt, with a lot of fleshy macroalgae and cyanobacteria, but the coral community was quite unusual and diverse. Corals normally seen in deep water, including large plates of sheet coral (Agaricia lamarcki and A. grahamae) and cactus coral (Mycetophyllia aliciae), carpeted the vertical surfaces of boulders. Other corals that form boulders in shallow water exhibited plating growth forms in response to lower light levels and turbid conditions. Competing for space with the corals, sponges every color of the rainbow grew into barrel shapes, tubes, twisted ropes, and baseball-shaped lobes. What was most interesting was the high numbers of small corals, recruits and juveniles that had colonized the volcanic rocks.
In addition to brain corals, star corals, starlet corals, finger corals and other common species, mountainous star coral (Montastraea faveolata) colonies formed small sheets and volcano-shaped mounds. This coral is one of the most important reef-building corals in the Caribbean, but over the last 15 years it has suffered large die-offs from bleaching and disease. Juvenile colonies are also rarely seen on a reef, as larvae rarely settle and survive.
Our first full day of research was extremely productive. Our core team characterized three reefs, completing several dozen benthic transects, coral transects and fish transects. Simultaneously, our local divers got more experience in coral reef assessments and began to collect meaningful information on the status of their coral reefs.
Written by Andy Bruckner, Chief Scientist, Living Oceans Foundation
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(Images/Photos: 1-5. Andy Bruckner, 6. Amanda Williams)