Friday, 27 May 2016

KML: Alligator Reef

Alligator Reef
Alligator Reef is a small bank reef within the Florida Keys National Marine Sanctuary. It is considered a Sanctuary Protected Area (S.P.A.) for the protection of the species as well as to sustain the diving industry. This reef was the most seaward location that we had visited within the first two days, because of this the visibility in the water was approximately 50ft.
Figure 1: Photo credit NOAA
Alligator Reef was a mixed hard bottom with sand, mostly dominated by soft corals and sponges such as the tube sponge and barrel sponge. The most abundant species of corals we found were Acropora cervicornis, Siderastrea siderea, Dichocoenia stokesi, and Meandrina meandrites.   At one time, hard corals were more abundant at this site but due to disease most of the corals died off.  The water in this region was also deeper than at some of the other locations, the water was at some points 24 feet deep.
School of Bermuda Sea Chub.
Photo Credit: Dr. Voss
At this location there was a greater abundance of fish but with less species richness. This decrease of species richness is likely due to the lack of hard corals and sea grasses. Alligator reef was a more open water habitat, so a majority of the fish species we observed in the water column were larger. Because of this open water habitat the smaller species were found in and around the corals to avoid the larger predators.The smaller species living among the corals consisted of Spiny lobsters, and different species of Butterfly fish and Damsels. Species higher in the water column included: Green Sea Turtles, Great Barracuda, Bermuda sea chubs different species of parrotfish, grunts, and snappers.
Green Sea Turtle.
                     Photo Credit: Dr. Voss
As we swam into deeper water there was a rapid decrease in water temperature. This thermocline was much more apparent compared to the other locations. A thermocline is normally created when the shallow surface water is heated by the sun, resulting in warm, less dense, water that remains at the surface and the cold, dense water sinks to the bottom.  Other than sunlight, this rapid change in temperature as depth increased can also be influenced by changes in salinity, wind, currents, and tides. Saltwater, having more dissolved solutes, is more dense than freshwater and will sink due to having a greater density. The higher salinity of the water deeper in the water column will also change the heat capacity in such a way that it keeps that water temperature cooler than that higher in the water column.

Expertly written by Rachel Urbaniak and Austin Cavanaugh

No comments:

Post a Comment