Aquarius is an underwater ocean laboratory located in the Florida Keys National Marine Sanctuary. The laboratory is deployed three and half miles offshore, at a depth of 60 feet, next to spectacular coral reefs. Scientists live in Aquarius during ten-day missions using saturation diving to study and explore our coastal ocean. Aquarius is owned by NOAA and is operated by the National Undersea Research Center at the University of North Carolina at Wilmington.
Last September, Aquarius was utilized by a crew of six aquanauts that spent nine days living underwater to study coral reef sponges - an important feature of coral reefs in Florida and throughout the world. This mission is part of a larger research effort to understand the feeding biology of sponges in the Florida Keys, from nearshore (including Florida Bay) to the offshore coral reefs. Sponges are an important part of the coral reef ecosystem, yet surprisingly little is known about their biology and ecology. A major focus of this work is to understand how sponges secure carbon and nitrogen to meet their basic needs of metabolism and growth. In other words, what and how do they eat?
Sponges are animals that make their living on the reef by filtering massive amounts of water to extract bacteria and other fine particles for food. Importantly, recent discoveries have shown that large populations of bacteria live inside some sponge species. The bacteria are hypothesized to have the ability to take dissolved nitrogen gas in seawater and convert it to forms of nitrogen that can be used to help support sponge nutrition. The consequences of these different feeding strategies - filtering or using the products of bacteria - are significant for individual species and for the nutrient budget of the larger reef system.
Since tracking and measuring ammonium was of critical importance to the study, the researchers evaluated the different options available before deciding on the fluorometric method of ammonium measurement utilizing the Turner Designs 10AU Field Fluorometer. This choice was made over the phenol hypochlorite method that the researchers had used in the past. After the study concluded, the researchers were extremely pleased with the quality of the data generated by the 10AU, along with it's relative ease of use. Here is some of the data that they gathered from the 10AU, relating two different sponge species (Aplysina cauliformis and Niphates erecta):
Overall, the researchers on this mission were successful in learning more about the biology and ecology of sponges, especially as it pertains to their role in nitrogen cycling in the oceans. The data gathered shows that certain species can act as nitrogen sources, whereas others can act as nitrogen sinks, and these findings will most likely bring more attention to them in future environmental research.
Author: Dr. Chris Martens
Institution: Aquarius, Florida Keys, USA