Wednesday, June 4, 2014

Old Dan Bank - Day One, Site Two (Dana Nieuwkerk)


After Koch Cay and before Old Sweat Bank, we snorkeled at Old Dan Bank. Our second site had a lot in store for us with its <0.5m-3.0m range in depth. Though some parts were too shallow to snorkel, we were able to see a range of biodiversity that differed greatly from Koch Cay. The fish of Koch Cay were abundant and many were large, while the fish of Old Dan Bank were small and sparse. Due to the shallow depth of the site, it experiences more current influence. We also noticed that the site is a considerably uniform field, composed of loose sediment, making it an ideal place for macroalgae such as Halimeda incrassata (three finger leaf alga). 
Halimeda incrassata is the dark green macroalga composed of discs stacked atop each other. To the right is Penicillus dumetosus.

The site was dominated by Thalassia testudinum (turtle grass), Halodule wrightii (shoal grass), and Porites difurcata (a branching coral of no common name, lovingly referred to as the Cheeto coral by our group). 
A Chilomycterus schoepfi (striped burrfish) in a bed of Thalassia testudinum with bits of Halodule wrightii throughout
A colony of Porites difurcata
We also saw several Manicinia areolata (rose coral), a coral that is not attached to the benthos but is nestled into the sediment. The coral ­skeleton tapers to an originating point, making it conical; due to its small originating point, the coral grows outward to maximize the amount of photons able to hit it. 
Manicina areolata (rose coral)
The Siderastrea siderea (starlet coral) was present at all three sites of the day, and it is always small and found in shallow, sandy, dynamic habitats; its polyps sit sunk down in the corralite. We noticed that corals existed in higher concentrations in the shallower portions of the site, this is because corals not on the ridge are hit with current (which carries sediment) and are smothered, killing corals at depth. Several of the corals we saw had their polyps out; corals typically extend their polyps at night to feed, however polyps were extended due to the overcast. In addition to a variety of corals, we saw some juvenile white grunts, sergeant majors, striped burrfish, blue crab, and anemone! 
Valonia ventricosa (green bubble weed).
Condylactis gigantea (Caribbean anemone).
Though there was a lesser quantity of fish than Koch Cay, biodiversity was still high. We were able to recognize that fish abundance is driven by structure as opposed to production. The mangrove islands provided a highly structured habitat for organisms; though the grass beds offer plenty of production and nutrients, the organisms are reliant on the benthos for protection/habitat, which offers fewer places to hide for a wide array of organisms.

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