Date of Award

Fall 2004

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

Program/Concentration

Biology

Committee Director

Mark J. Butler, IV

Committee Member

Kent E. Carpenter

Committee Member

William J. Resetarits, Jr.

Call Number for Print

Special Collections LD4331.B46 L391 2004

Abstract

Coexisting species may simultaneously compete for resources and interact as predator and prey, creating a strong interaction that can alter the structure of animal communities. This type of interaction potentially occurs between juvenile Caribbean spiny lobster (Panulirus argus) and Caribbean reef octopus (Octopus briareus) within hard-bottom habitats in the Florida Keys, FL (USA), where octopuses may consume juvenile lobsters and also compete with them for limited crevice shelters. I conducted a series of field and mesocosm studies to investigate the nature of octopus-lobster interactions and their implications for the structure of their populations in the wild. Six surveys (summer 2001, spring, summer, and fall 2002, and spring and summer 2003) of juvenile lobsters and octopuses occupying artificial shelters at 19 hard-bottom sites in the Florida Keys confirmed that lobsters do not cohabitate with octopuses. The number of juvenile lobsters on a site was negatively correlated with octopus abundance, although the frequency of injuries to lobsters was unrelated to the abundance of shelters, octopus, or conspecifics. Tethering of lobsters at seven sites that varied in octopus abundance revealed that significantly more juvenile lobsters were consumed on sites with more octopus. In contrast, the density of natural crevice shelters had no effect on the abundance of either species. Results from mesocosm experiments indicated that juvenile lobsters do not attain a size refuge from octopus predation and that octopus do not select dens in response to the chemical cues of lobster or other octopus. A separate set of mesocosm studies showed that the presence of alternative prey and lobster conspecifics reduced predation on lobster. Although lobsters were often displaced from dens by octopus, octopuses were never displaced from shelters by lobster. Thus, the negative association between lobster and octopus is driven largely by predation, not competition. Avoidance of octopus by lobster is of particular importance; direct predation probably plays a lesser role. The risk of predation by octopus on lobster depends strongly on the availability of alternative prey for octopus and the presence of lobster conspecifics that enhance group defense. Crevice shelters suitable for juvenile lobster are limited in many hard-bottom areas in the Florida Keys, so areas with abundant octopuses may further limit the local abundance and shelter use of juvenile spiny lobsters.

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DOI

10.25777/eq6f-rz18

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