On May 22nd 2017, we visited the Old Dan Bank site. Old Dan Bank is located in a shallow open water area, with depths of 3ft-4ft. As you approached a prop scar found within the location, the water became very shallow. On the outskirts of the reef, sea grass was abundant. However, there was less sea grass at this location compared to the other locations overall. It was partly cloudy with a high of 85 degrees Fahrenheit and a low of 79 degrees Fahrenheit*. At this site, several species of green algae dominated the bank. However, compared to Koch Key there was a higher green algal diversity, a lower fish diversity, and a higher coral diversity at Old Dan Bank. This was due to the lack of mangroves at Old Dan Bank. The lack of mangroves also meant that there was less structure in this ecosystem. This site was shallower, less turbid, and had better light penetration compared to both Koch Key and Old Sweat Bay. A similarity between every location was that they all suffered from human impacts.
Many algae dominated Old Dan Bank. The species observed included: Caulerpa sertularioides, Halodule wrightii, Syrogodium filiforme, Thalassi testudinium, Aurainuillea spp., Caulerpa prolifera, Anadyomene, Halimeda incrassata, Caulerpa paspaloides, Penicillus dumetosus, Penicillus pyriformis, Udotea spp., Dictyosphaeria spp., and Halimeda tuna. Aside from the green algae listed, there was brown alga present as well. The species of brown alga was Sargassum fluitans. The diversity of algae at Old Dan Bank could have been due to the decreased turbidity. Decreased turbidity and lack of mangroves allows for more light penetration and therefore, more photosynthesis can occur. Also, there was less structure at Old Dan Bank because of the absence of mangroves.
|Green alga specimen found on Old Dan Bank.|
Human impacts varied at each location visited on May 22nd, 2017. At Koch Key, the main human impact was fishing and littering. Many abandoned fishing lines were seen in the mangrove branches and roots. In addition to the lines, there were many sunken glass bottles and metal cans due to reckless behavior. As for Old Sweat Bay, the only human impact observed on a large scale, was the dredging of the channel. At our location, Old Dan Bank, the human impact was more severe than the other locations. Our site was damaged by a large, recent prop scar. This prop scar caused a loss of several coral and alga species.
At this location we were able to observe many different species. One that was very interesting was the upside down jellyfish (Cassiopeia cassiopeia). Although there was very few of these species present, it is common for Cassiopeia cassiopeia to be found in sandy bays. However, they were more abundant in mangrove forests such as, Zane Grey Creek. This species of jellyfish obtains its food from a symbiotic relationship with photosynthetic zooxanthellae. The upside down jellyfish feeds off of the sugars provided by the zooxanthellae.
|Cassiopeia cassiopeia photographed at Old Dan Bank by Kayli!|
Even though Old Dan Bank was dominated by green algae, we were able to observe some diversity of invertebrates, fishes, and corals as well. Some of the invertebrates included: orange icing sponge, reticulated brittle star, reticulated hermit crab, turbo snail, queen conch, conical spined sea star, Tripneustes, mantis shrimp, and loggerhead sponges. Some of the fishes included: blue striped lizard fish, slippery dick, bandtail puffer, and bicolored damselfish. As for the corals, there was Manicina areolata, Porites furcata, Cladocora arbuscula, and Siderastrea siderea.