Thursday, 19 May 2016

Koch Key (5/16/16) - UNF

The first site we visited at the Keys Marine Laboratory was a site called Koch Key. This key was a mangrove island surrounded by fine silt sediment and sea grass meadows. The average visibility of this site was estimated to be around 6 feet and the depth of the site fluctuated between 1 to 6 feet. The weather at the site on this day was fair; the sky was partly cloudy and the wind was moderate. Northerly currents were flowing around the island, which made it particularly difficult on the south side when we were swimming against the current directly.

Thalassia testudinum (Turtle Grass)
Syringodium filiforme (Manatee grass)
Halodule wrightii (Shoal Grass)
Red and black Mangroves

Sergeant major
Cottonwick (juveniles)
Snapper (mangrove, mutton, schoolmaster)
Barracuda (juvenile)
Sheep's head
Striped burrfish
Grunts (french, tomtate)
Needle fish

Spiny lobster
Tunicates (bubble, mangrove, colonial)
Polychaetes (egg cases)
Spaghetti worms
Mangrove crabs
Blue Crabs
Stone crabs
Mithrax crabs
Mantis shrimp
Brown anemones
Brown anemone (Aiptisia)


The first main observation we had about this site was that there were a lot more juvenile fish here than at other locations we've visited. It is known that mangroves are an important nursery habitat for many different fish species, as mangrove roots provide great protection for juvenile fish. This pattern of high juvenile concentration was also observed at the other mangrove habitat we visited, Zane Grey Creek. A higher biodiversity of species was also observed here than at some of the other sites, particularly the sea grass meadows. We think that this is because there is more 3D structure created by the mangrove roots, resulting in more niches and refuges for species to occupy.

Comparing this mangrove site to Zane Grey Creek further, we also noticed the differences that arose between them due to their locations in the bay. While Koch Key was located in the open water of the bay, ZGC was located closer to land and formed a network of mangroves that provided more seclusion from the water. First, we noticed that the visibility at Koch Key was far worse than at ZGC. We hypothesized that this was due to a difference of sediments, where Koch Key had much finer, muddier sediments that settled slower when upset, and ZGC had sandier sediment that settled quicker; ZGC was more protected from oceanic and bay currents than Koch Key, which would upset the sediment less; Also, we visited ZGC at the apex of low tide, while we visited Koch Key in between the tidal apexes, meaning that the sediment was being mixed by tidal currents.

Koch Key also had an interesting pattern where the sea grass present did not grow right up to the mangroves. Rather, it stopped about 4-5 feet away from the mangrove roots. We hypothesized that this was either due to the mangrove roots out-competing the sea grass for light, or because the herbivorous fish that live in the mangrove roots will only graze so far away from the lights.

Underneath the Red and Black mangroves of Koch Key - Photo Credit: Corey Corrick

Blue Crab nestled in Shoal Grass (Halodule wrightii) - Photo Credit: Corey Corrick

Spiny Lobster in its burrow under mangrove roots - Photo Credit: Corey Corrick

By: Melissa Betters & Katy Fink

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