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Glider Observations Support Plankton Population Characterization

By Dr. Fraser Dalgleish
Ocean Visibility and Optics Lab

John Reed
Senior Research Scientist and Research Professor
Robertson Coral Reef Program
Harbor Branch Oceanographic Institute
Florida Atlantic University
Fort Pierce, Florida

Dr. Tamara Frank
Associate Professor
Nova Southeastern University
Dania Beach, Florida

Sampling and persistent monitoring of undersea habitats provide baseline information and important data characterizing change related to events (e.g., oil spills) and phenomena (e.g., climate change), which informs scientific discovery and aids efforts to better understand and perhaps mitigate change. Autonomous glider technology has improved researchers' ability to conduct both types of assessment: Rapid site characterization enables cost-effective identification of areas that warrant more detailed assessment, and deployments lasting several months provide previously unavailable temporal and spatial breadth that can reveal trends and illustrate change.

Over the past two years, work conducted by the NOAA Cooperative Institute for Ocean Exploration, Research and Technology, headquartered at Florida Atlantic University's Harbor Branch Oceanographic Institute, has been shaped by the Deepwater Horizon oil spill. The Florida Shelf Edge Exploration (FLOSEE) expedition was launched in July 2010, three months after the spill, to explore and assess mesophotic and shelf-edge reefs, which were deemed at risk via the Gulf of Mexico Loop Current and the Florida Current. Expedition goals included characterizing spill impacts on the ecosystems or, in the absence of such evidence, establishing baselines in advance of potential impacts, as the flow of oil from the well had not been contained when the expedition commenced.

In September 2011, a follow-up expedition, FLOSEE II, was launched to locate and characterize deep reefs, with a focus on coral and commercial fish. It assessed the effectiveness of marine managed areas for restoring coral and fish, monitored the effects of oil contamination and characterized plankton populations above or near reefs.

Mapping and biodiversity assessments were conducted from the NOAA vessel Nancy Foster using multibeam sonar and the University of Connecticut's Kraken II ROV for high-definition video surveys and MOCNESS (Multiple Opening and Closing Net Environmental Sensing System) trawls. To perform water-column measurements, the Harbor Branch Ocean Visibility and Optics Lab at Florida Atlantic University deployed Bluefin Robotics Corp.'s (Quincy, Massachusetts) Spray Glider.

Spray Glider and Pulley Ridge Missions
The Spray Glider, which is rated to 1,500 meters and travels at 25 centimeters per second, is capable of deployments lasting up to six months. For these recent missions the glider, diving to less than 100 meters at a 19-degree angle of attack, covered approximately 20 kilometers per day.

A pumped CTD sensor is standard to combat the biofouling that is typical in shallow-water environments, especially during long deployments. Optional sensors include turbidity, dissolved oxygen, fluorometer, photosynthetically active radiation, acoustic Doppler current profiler and altimeter. For the purpose of phytoplankton distribution and water quality measurements at these mesophotic reefs, the Spray Glider was outfitted with Turner Designs (Sunnyvale, California) C7 sensors to measure chlorophyll-a fluorescence and optical scattering, and a pumped Sea-Bird Electronics Inc. (Bellevue, Washington) CTD.

The FLOSEE II glider missions took place at Pulley Ridge, a shelf-edge mesophotic coral reef on the southern edge of the west Florida shelf, which is more than 60 meters below the surface. Mesophotic reefs, the deepest coral communities that depend on sunlight for survival, are not particularly well studied, as they tend to be beyond the maximum scuba depths of 30 to 40 meters. Pulley Ridge is characterized as hard, flat, gently sloping bottom with rock rubble and cobble. Live coral cover had previously been reported at up to 60 percent in some areas. Macroalgae, sponges and sediment also occupy the benthos, which is shared by shallow- and deepwater fish species and is considered an important breeding habitat. The Loop Current brings clear, warm water to Pulley Ridge, which is also within a thermocline that provides nutrients during upwelling.

Considered in the context of sudden or persistent environmental change, Pulley Ridge reef communities that survive on 1 to 2 percent of available surface light are therefore very vulnerable to persistent elevations in turbidity, which result in reduced available light and benthic productivity. Furthermore, persistent temperature maxima have been associated with bleaching events affecting hard and soft corals and sponges. Corals are also susceptible to persistent salinity depressions, which can result from proximity to the Loop Current and possibly heavy rains or hurricanes. Surprisingly little data exists on the seasonal dynamics of phytoplankton populations and environmental correlates at shelf-edge reef environments. To continue this article please click here.

Dr. Fraser Dalgleish directs the Ocean Visibility and Optics Laboratory at Harbor Branch Oceanographic Institute. His research emphasis is on undersea optical sensor development for remote and in-situ environmental measurements and the improvement of sensing and communications capabilities as an enabling technology for multivehicle surface-to-seabed imaging and sensing operations.

John Reed is a senior research scientist and research professor heading the Robertson Coral Reef Program. He has organized and supervised 60 expeditions worldwide that have resulted in the collection of more than 30,000 marine specimens. His research specializes in the biology of deepwater reefs and taxonomy of reef organisms.

Dr. Tammy Frank is an associate professor at Nova Southeastern University. Her research focuses on how light controls the distribution pattern of midwater animals, functional adaptations of photoreceptors to different light environments, and linkages between pelagic and benthic habitats.

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