A Multiscale Investigation of Physical/Biological Coupling on the Florida Keys Reef Tract

Mission 2 — A Multiscale Investigation of Physical / Biological Coupling on the Florida Keys Reef Tract.

Principal Investigator: Dr. James Leichter, Scripps Institution of Oceanography
Training: June 7-11
Mission: June 14-23

The goal of this project is to examine the biological consequences of physical forcing at multiple spatial and temporal scales across the Florida Keys reef tract with an emphasis on the effects of nutrient upwelling on benthic macroalgal populations. Recent studies indicate that internal tidal forcing along the reefs appears to be modulated at a regional scale by variability associated with the Florida Current and then further modified at smaller length and time scales by the interaction of these water masses with local topography which then ultimately effect the physical-biological coupling of the entire reef ecosystem.

To examine these interactions, the project is developed around three major objectives.

The first includes broad scale surveys of the abundance and composition of macroalgal communities seaward of the reef tract in depths of 30 to 70 m. Access to some of the sites will utilize NURC resources for deep water access (ROV and Technical SCUBA diving) that have greatly expanded the in situ capabilities for experimentation and exploration at depths previously considered inaccessible. A second objective is the continued study of long-term, high frequency physical data at multiple reef sites using a series of oceanographic sensor moorings along the Florida reef tract. The third objective is a detailed analysis of the interaction between small scale topographic features and mixing on and seaward of the slope of a single reef, Conch Reef, in the Upper Florida Keys. This will include the use of a new sensor technology, BOA, capable of long term, high frequency and high resolution temperature recording in a web of 100 sensor nodes spaced along the reef front. BOA will also allow real-time display and internet monitoring of reef front conditions if connected to the Aquarius Habitat. Organized in this fashion, our work targets spatial and temporal scales ranging from inter-reef comparisons at a 100-km scale and interannual periods, to within-reef mixing processes occurring at length scales less than 1 m and times on the order of seconds.

The project will be carried out over a two-year period:

In Year-1 an Aquarius mission will be conducted during which the BOA II 100-node temperature sensor array, 3 vertical micro-arrays, and 2 acoustic Doppler current meters will be deployed and surveyed at Conch Reef. This deployment will focus upon small scale (order meters to hundreds of meters) physical forcing and mixing associated with the interaction of topography and the run-up of internal tidal bores on the reef slope. Patterns of macroalgal abundance as well as algal tissue carbon and nitrogen content and isotopic composition will be sampled across the reef slope in association with the sensor array. In Year-2 a second detailed quantitative description of macroalgal distributions will be conducted using the combination of ROV and technical diving. Recording temperature sensors will again be deployed at 10, 20, 30 m depth on each of 6 study sites along with vertical temperature sensor strings deployed at 50 m depth. The BOA-II array and associated instruments deployed at Conch Reef in Year-1 will be recovered.