Quarterdeck 3.2
Recent Graduate
by Randy J. Runnels
Methods used in studying small, motile invertebrates on reefs are remarkably similar to methods used for analogous terrestrial organisms. For example, many reef-associated species respond to light changes by emerging from their substrates at dusk and resettling near dawn. This enables oceanographers to use emergence traps and light traps, nearly identical to the ones used by entomologists, to attract and capture reef zooplankton. Observations of swarming reef zooplankton indicate that at least some aspects of their behavior are reminiscent of the insect swarms with which we are more familiar.
It is logistically difficult to study the ecology of epizoites on the surfaces of their host organisms. Most studies requiring the microscopic identification and counting of epizoite populations have necessitated the removal and preservation of the corals or other host organisms. Such methods are not only destructive, but the preservation of the entire host organism makes it impossible to study smaller-scale population dispersion patterns. I developed a sampler that can remove the organisms from a well-defined, small area without harming the substrate, and was able to address a variety of ecological questions.
[51K] Randy Runnels uses a sampling device he designed to remove epizoites without destroying the coral on which they live.
My work has benefited from the use of a unique offshore research facility. Through the U.S. Coast Guard and the Florida Keys National Marine Sanctuary, my colleagues and I have been able to work from the Carysfort Reef Lighthouse, ten kilometers off Key Largo. This structure has been useful to a number of Texas A&M scientists over the past few decades. The Coast Guard's plans to renovate Carysfort Lighthouse this summer will ensure its value in future experiments.
One of the clearest and most consistent patterns I saw was the concentration of coral parasites toward the sun. In the morning, parasitic mites and copepods are significantly concentrated on the east sides of heads of the reef-building coral Montastrea annularis. In the evenings, more individuals are found toward the west surfaces. The epizoites may use this behavior to escape nighttime feeding by corals, take advantage of photosynthetic differences in the corals' symbiotic algae, or select microclimates with optimal temperatures for reproduction. My data also indicate that morphological adaptations of parasitic species allow them to remain on the coral heads even during strong currents.
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[9K] Siphonostomatoids, a type of epizoite, appear in larger numbers on the sides of coral heads which face sunlight.
Quantitative analyses of reef epizoites make a number of applications feasible. Our understanding of carbon and nutrient cycling on reefs will benefit from a better understanding of patchiness in small, motile reef animals. In addition, the apparent predictability of finding some species on coral surfaces raises the prospect that we may eventually use these organisms as biological indicators of environmental stress on reefs. While epizoite ecology is only one piece of the entire reef-ecology puzzle, at least we now have a grasp of that piece.
Oceanography, Texas A&M
University
rshatto@ocean.tamu.edu
URL=http://oceanography.tamu.edu/Quarterdeck/QD3.2/Runnels/runnels.html
Updated September 14, 1995
