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Puerto Rico Cruise Day 7
Damage done by manatees
Data photos and figures provided
by Jud Kenworthy
Based on past observations of aerial surveys and data from tracking Antillean Manatees by satellite and radio, it was believed that Pelican Cove, Puerto Rico was an important feeding area for manatees. Recently, as part of the Sirenia Project, the U.S. Geological Survey has been tracking individual manatees by tagging them with GPS receivers. Data from these tracks indicate a heavy use of Pelican Cove. The light colored area in the center of the photo is where manatees are intensively grazing seagrass. The areas around the grazing site (darker signature) are dominated by Thalassia testudinum, the tropical climax seagrass species.
Pelican Cove was one of our primary sites for seagrass core sampling on this cruise. We completed sampling there on the second day. We’ve been able to examine a portion of our data and have found that the grazed area is almost exclusively composed of Halodule wrightii, a smaller, faster growing, opportunistic seagrass species. It appears that by continuously grazing Pelican Cove, the manatees have altered the local seagrass species composition by disturbing the climax species and promoting conditions more suitable for H.wrightii. Learn more about the manatee tracking project.
Photo: Amy V. Uhrin
Ciguatera poisoning is a tropical disorder caused by bioaccumulation of ciguatoxins in human tissues from ingestion of fish tissue that is highly concentrated with the toxins. The most common symptoms are gastrointestinal, including nausea, stomach cramps and severe diarrhea. Neurological symptoms often include numbness in the lips and extremities, hot and cold reversal (hot things feels cold and vice versa), severe headache, dizziness, and low blood pressure. Ciguatera poisoning is often marked by an extensive itchy or burning rash or strange tingling or crawling feelings on the skin. A group at our lab is examining the occurrence of ciguatera-related toxins within Atlantic and Caribbean fishes as well as the dinoflagellates (microscopic, photosynthetic organisms that live in the water column) that may produce the toxins.
removes the hook from a smaller barracuda
in order to release it. Photo: Amy V. Uhrin)
Typically, higher trophic level predator reef fishes such as moray eels, hogfish, and groupers, as well as more pelagic fish such as barracudas, jacks and amberjacks, tend to accumulate ciguatoxins. This group’s goal is to extract and purify ciguatoxins from muscle tissue and viscera of reef fishes to use as standards in their research. So, in addition to hunting down white grunts, we have been asked to collect great barracuda (Sphyraena barracuda). Colleagues often help each other out by collecting samples or gathering other data for teams who do not have the opportunity to conduct a field excursion in a particular locale due to time, budget, and/or personnel constraints. In this case, our “great white hunters” are happy to oblige.
While Nancy Foster is in transit between sites, the whir of rod and reel can be heard from the fantail. The water’s surface becomes dappled with colorful lures, like miniature windsocks straining in the breeze. Today the fishermen were taunted by a small barracuda that kept chomping on the lures. But persistence paid off, and Bob Ellis (Junior Engineer) landed a larger fish that could be kept for analysis.