[Coral-List] algae vs. herbivory and the RDM

[thaddeus nicholls]

Hello all, my name is Thaddeus Nicholls and I am finishing up my MS thesis on the reefs in Quintana Roo, Mexico, specifically Akumal and Chemuyil.  I did not have the means to collect nutrient data from the water column, or the time to collect herbivory rates while I was collecting data on the reefs, and have been trying to find the best ways to interpret my results.  Data shows that there is an overall increase in filamentous and turf algae accompanied by an increase in crustose coralline algae.  Macroalgae rises in some areas but decreases in others.  I came across the Relative Dominance Model constructed by Littler (et al. 2006) and was wondering about the strength of its interpretations... According to the RDM, rises in crustose coralline algae indicate eutrophication, rises in turf algae indicates reduced herbivory, and combination of reduced herbivory and eutrophication results in frondose macroalgae.  Is the RDM an acceptable tool to use in my
 interpretation? There are a fair number of fish on the reefs at Akumal and Chemuyil, so it seems that reduced herbivory wouldn't be as large a factor as my data shows... Plus, the Yucatan Platform is all karst limestone with no surface draining, so any nutrient-rich water from the inland flows directly to the coast through the cenotes with ease... Taking all factors into account, it seems that eutrophication would be the main culprit in these changes, but the RDM interprets herbivory as the most significant malefactor.  I would like to get this figured out soon for the sake of finishing my thesis, but also since I will be presenting at the ICRS in July--I would rather not get torn apart after my presenation!!!!  Thanks!

Thaddeus