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Wetlands and Aquatic Research Center - Florida
Cruise Log: 12/04/2009
Situating deep-coral communities in larger environmental patterns: use of benthic landers to elucidate global patterns
Furu Mienis, NIOZ
Working for the Royal Netherlands Institute for Sea Research (NIOZ), we have been using our NIOZ benthic landers to study cold-water coral areas on the European margins of the Atlantic Ocean. About a year ago, we deployed our landers in cold water coral communities in the Gulf of Mexico. After retrieving these landers from the Gulf two months ago, we are now back at sea in the Atlantic, this time on the American continental margins. Our goal is to redeploy the landers on the deep coral mounds off of Cape Lookout, North Carolina.
The landers are free falling aluminium frames which can be deployed for a year to measure daily, seasonal and annual variability close to the seafloor. They are equipped with instruments that measure the near bottom current speed and direction, salinity, temperature and the amount of (fresh) particles in the water column. The data we retrieve from the landers will document the environmental conditions cold water corals thrive in. The landers are also excellent platforms for carrying new equipment and experiments. For the current deployment, both landers carried mesocosms made by US colleagues containing living corals that will provide insight into coral growth rates over the deployment period. Sandra Brooke blogged about these coral growth experiments earlier in the cruise.
The water mass that flows through the Gulf of Mexico and along the US margin, known as the Gulfstream, crosses the Atlantic Ocean and continues along the European margin. In other words, cold-water corals on both sides of the North Atlantic Ocean are growing in the same water mass. However, local processes like hydrodynamic regime, tectonic movements and the amount of sediment supply influence the cold water corals. By deploying the landers in different areas we attempt to measure these regional scale processes and define their importance.
At the European margin cold-water corals form large mound structures, several kilometres long and wide and up to 360 m (~1200 ft) high. There, the corals are growing in a confined depth zone between 600-1000 m (~1950-3300 ft) deep and live in temperatures between 6-10 oC (~43-50 oF). The current speed in the area is high and driven by a tidal regime. So, one of our research questions is...how do these conditions compare with deep coral reefs in other parts of the world? As it turns out, the data that we obtained from the previous lander deployment at the Viosca Knoll in the Gulf of Mexico offer some intriguing contrasts. In those coral communities, current speeds were relatively low and bottom water was filled with muddy aggregates. This may be related to the outflow of the nearby Mississippi River. In addition, the dimensions of the Viosca Knoll reef structures are smaller than those on the European margin. Mounds on the North Carolina margin look much more similar to the European ones, albeit not as large and high. Because the North Carolina coral mounds are in close proximity to the Gulfstream, we expect that current speeds over the coral structures will probably be high, and there is likely to be a high deposition of particles.
These are some of the differences we hope to compare and contrast when the landers are recovered in mid-2010. We’ll revisit the spot with the NIOZ research vessel Pelagia, and use the data recorded by the landers to compare the environmental conditions on the NC margin to those in Europe and the Gulf of Mexico. By comparing these conditions in different cold-water coral habitats we hope to define the limiting conditions for coral growth.
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