Date of Award

Summer 2009

Document Type


Degree Name

Master of Science (MS)


Biological Sciences



Committee Director

Mark J. Butler, IV

Committee Member

Daniel M. Dauer

Committee Member

John R. Holsinger

Call Number for Print

Special Collections LD4331.B46 O85 2009


Coral reefs worldwide are undergoing dramatic habitat modification from coral to macroalgal dominance due to water pollution, coral diseases, global. warming, and the loss of herbivores. This phase-shift bas been particularly severe on Caribbean reefs due in large measure to the decline of piscine and echinoderm grazers, whose presence appears crucial for stemming the decline of coral reefs and enhancing their resilience. Virtually unknown, however, is the role of other macrograzers in coral reef ecosystems. This is the first study to examine the feeding ecology and grazer effect of the herbivorous West Indian spider crab (Mithrax spinosissimus) on inshore patch reefs in the Florida Keys, Florida (USA). Grazing by M. spinosissimus on coral reef community structure was assessed by: (i) measuring its selectivity and consumption of macroalgae in laboratory and field experiments (ii) estimating its natural density on patch reefs, and (iii) comparing its herbivory on reefs to that of the herbivorous fish guild. My results showed that M. spinosissimus prefers fleshy macroalgae, as do herbivorous fishes, but M. spinosissimus will consume relatively unpalatable calcareous algae in large quantities if no other choice is available. Field estimates of M. spinosissimus grazing effects within cages deployed on reefs show that it can indeed graze macroalgae to levels significantly lower than that of the typical suite of mobile grazers present on Florida patch reefs. Yet, the effect of M. spinosissimus on macroalgal community structure in general is diminished by its low abundance and perhaps by its low mobility in predator-rich environments. Poor recruitment and high post-settlement mortality are obvious hypotheses that might be influencing their natural rarity on coral reefs, but virtually nothing is known of these processes. Moreover, the abundance of this crab in other reef habitats and regions of the Caribbean, hence its true contribution to reef resilience through herbivory, is also unknown.


In Copyright. URI: This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).