By Venetia Butler
Gray's Reef National Marine Sanctuary Advisory Council
K-12 Education Representative
Multibeam technician Missy Partyka prepares the CTD for deployment.
The morning broke bright and clear. The waves had calmed sometime during the night. Very shortly after the 8:00 a.m. shift began, we took another CTD (conductivity, temperature, depth) reading. Salinity and temperature can change the density of the water which can affect the speed and direction by which sound travels.
A transducer produces sound that travels through the water column to the sea floor, back to a receiver, and then processed through the computer system. This provides a profile to calibrate the multibeam system so that the processor can accurately calculate the depth of the sea floor, thus providing the means for mapping the sea floor.
As data is entered, it is constantly monitored and cleaned up. One of the tasks is to watch for outlier bits of data that are removed from the picture to provide a cleaner image.
Venetia Butler (author, on left) and Fran Warren, Teacher-at-Sea, demonstrate their successful application of pantyhose on the floats.
Another task for this day is to prepare some of the equipment to be deployed during Leg II of the cruise. Fish tracking devices will be anchored on the sea floor during Leg II. The receivers had to be prepared for underwater use. Each of the receivers will be attached to buoys and left in the water. The growth of algae and other organisms is always a problem for any object left in the water for any length of time. This can alter the accuracy of the data being collected. To keep from having to use toxic antifouling paint, Sarah and Dave used their skills in resourcefulness and decided to cover the buoys with another “high tech” material pantyhose nylon. Our task this afternoon is to cover the buoys with the nylon material. The nylon will have to be routinely replaced, thereby slowing down the cumulative growth of interfering fauna.
We used some of our down time to learn more about the jellyfish we observe on Monday. In the calm, clear waters we observed an abundance of Sea Nettles Chrysaora quinquecirrha (Cnidaria)and Comb Jellies Mnemiopsis mccradyi (Ctenophora).
Sea nettles feed on the comb jelly, small fishes and zooplankton. The southern harvestfish, Oeorukys akeouditys, are often found darting in and around the long marginal tentacles and 4 long oral arms of the sea nettles. The harvestfish is a small, laterally flattened, silverfish. Its young are commensals (symbiotic relationship in which neither organism is harmed) but become predators feeding on the jelly. A small specie of shrimp, blue crabs, and larvae of spiny lobster have been observed riding on the upper surface of the bell.
Ctenophora or comb jellies are delicate, transparent, non-stinging jellies. They are mostly pelagic carnivores feeding on plankton. The comb jellies observed are made of eight radially symmetrical rows of comblike paddles (combs). Each comb consists of thousands of cilia bound together in a single plan.The combs beat like flippers enabling the Ctenophore to swim. They change direction by altering the rate of beat. They are also beautifully bioluminescent.