Predation Rates in Discovery Bay – Mike and Nate

Sand Flats Tile 2
A tile baited with a brittle star and a crab. 

Predation is an important interaction within communities that keeps some species from overpopulating and causing shifts in habitats from overgrazing, or resource depletion. We measured the rates of predation in 3 habitats to see how it changes from habitat to habitat within the fringing reef ecosystem in Discovery Bay. These habitats are the mangroves, the turtlegrass beds, and the sand flats. We took two prey species, the reticulated Brittle Star (Opheonereis reticulata) and the Green Clinging Crab (Mithrax sculptus), and used them as bait that was attached to a hook, and approximately 2 feet of 8 or 25 pound test line that was secured to a tile on the bottom. On each tile were 2 lines, one with Mithrax s. and the other with Opheonereis r. to see if there was a preference among the two species. For each habitat we placed five of these tiles approximately 3 meters apart, leaving ten lines per zone. We also measured the night vs. day predation in these zones as well to compare that data to the total predation rates among the habitats. The only significant data we found was that in the mangroves the predation dramatically increased for nocturnal predators, though we could not catch any of them, the mean number of missing prey items was much higher during night trials there.

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