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Day 5, August 5, 2005 TER daily cruise report
Another five stations are scheduled for sampling today. Our goal in monitoring the fishes and habitats at the interface of bank and shelf in the Tortugas is to document the response of both the bank and shelf communities to the establishment of the Tortugas Ecological Reserve.
The study's design focuses on the transition zone (ecotone) between the bank and surrounding shelf in recognition of the ecological linkage of these habitats. One way that energy passes between the two systems is through abundant reef species that shelter on the bank during the day and forage on the shelf at night. Our analysis of the tissue of these species indicates that the benthic micro and macroalgae common to the shelf provides the base of the food web for these reef species. We suspect that an increase in predator populations caused by the establishment of the Tortugas Ecological Reserve (TER) will affect shelf communities through increased predator pressure and an increase in flow of energy from shelf to bank. By monitoring changes in both the bank and shelf communities at their interface we can monitor the larger ecological impact of this marine protected areas (MPA).
One manifestation of the ecological linkage between the bank and shelf habitats
is the maintenance of a vegetation-free halo, by foraging reef dwellers,
on the shelf immediately adjacent to the banks. We are measuring the amount
of grazing activity by herbivorous fishes using Grazing Pressure Assessment
Units (aka 'GPAU's'). GPAU's are made by attaching 5cm 2 strips of the seagrass
Thalassia testudinum ('turtlegrass') to a wire mesh-covered brick. We are
deploying GPAU's at interface stations both in and outside the reserve at
distances of 0m, 5m, 15m, and 30m from the reef. Collection of the units
will proceed 3-4 days after deployment. Any remaining seagrass will be measured
to determine how much plant matter was consumed by herbivorous fishes.
Placing the GPAU's at different distances from the reef will help us understand herbivore feeding patterns and their grazing impact on shelf. By comparing herbivore feeding patterns and intensity in reserve and non-reserve areas we can determine if grazing pressure of herbivores is higher outside the reserve where their predators, fishes such as snappers and groupers, are exposed to fishing.
Night ops. Night operations consisted of drift video and beam trawl sampling
around the north central boundary of the Ecological Reserve. Depth was 20
fathoms (120 ft or about 40 meters). Moving north the bottom grades from
a calcium carbonate rock plain with a veneer of coarse sand to fine sand,
riddled with burrows and landscaped with the mounds and pits of its' benthic
fauna. Notable catches included jack knife fish, tattler bass and brotulids
with their extravagant pelvic fins.