Male Control Conditions (10

ppt Salinity, 20oC)Female Control Conditions Fall

& Spring (10ppt Salinity, 20oC)

Male High Salinity (35 ppt, 20oC)

Male High Temperature

(10 ppt Salinity, 30oC)

The blue crab fishery is the largest fishery in the Chesapeake Bay and now accounts for $50 million a year in revenue for Chesapeake Crabbers. However, this fishery has slowly been declining and has dropped by 70% since 1990, mostly due to overfishing (Lee et al 2004).

Previous research had been done on cannibalism in blue crabs, but only in juveniles. Little has been done to observe cannibalism and its effects in adult blue crabs. No previous work was found that showed a difference in cannibalism between the sexes.

Reproduction and migration both require large energy expenditures by females. Females should thus require a higher food intake to fulfill these energy needs.

Studies have shown that blue crabs are sensitive to high salinities. This is especially true in males (Ryer et al. 1997). No studies have been done to see how environmental stressors may effect blue crab behavior, including their cannibalistic tendencies.

Pilot studies performed in conjuncture with this experiment in the fall of 2008 did show an overall higher aggressiveness in the female populations under normal conditions.

Introduction

Ho - There will be no difference in the rates of cannibalism between the sexes

H1 – The females will show a higher rate of cannibalism compared to the males

Ho – There will be no difference in rates of cannibalism upon induction of stress

H1 – Males will show a higher rate of cannibalism in high stress situations

Hypotheses

Cannibalism in blue crabs, Callinectes sapidus: with emphasis in varying

stressors and differences between sexesBy: Alex Crouse

Mentor: Dr. NolanMethods

48-hour isolation in tanks

Weighed, measured, marked, and initial

limb loss noted

5 Crabs in a tank. Tanks had the

following treatments:

Dead crabs removed daily and weighed, limb loss recorded

Cannibalism evaluated as limb

loss or total cannibalism.

Statistical analysis was done using

either 2-way ANOVA and Bonferroni Post test or a one way

ANOVA, significance was p<0.05.

Results

Figure 1. Male and female limb loss under control conditions. No significance was found between males and females or over the course of the experiment. Error bars in this graph and in the following graphs are representative of the standard error.

Figure 2. Male limb loss over a seven day period under stressful conditions. Significant difference was seen between high salinity and high temperature at days 3 & 4, p<0.05.

AcknowledgementsFigure 3. Data shows cannibalism in control conditions for male and females. No significant difference was seen between treatments

Figure 4. Data shows cannibalism in male control and stressful experimental conditions. No significant difference was seen between treatments.

The data showed no significant difference in cannibalistic tendencies either between the sexes under controlled conditions or in males under experimental conditions.

Time may have played a critical factor in the lack of results found in this experiment.

This experiment should be repeated on a shorter time interval without separation to observe initial stress. When running the pilot studies in the Fall of 2008 we did not isolate the crabs and saw increased levels of cannibalism (data not shown). This being said we believe the immediate stress of being moved could cause cannibalism. The separation in the current experiment was done to acclimate the crabs to the new environment and eliminate the weaker crabs.

This experiment should also be repeated on a longer time scale to see if long term exposure to environmental stressors will cause an increase energy demand and thus an increase in cannibalism.

Conclusion

R.F. Lee, M.E. Frischer. Ecology and the decline of the Blue Crab. American Scientist 2004 92:548

Ryer, C. H., J. vanMontfrans,K. E. Moody. 1997. Cannibalism, refugia and the molting blue crab. Marine Ecology-Progress Series 147(1-3):77-85.

Literature Cited

I would like to thank Dr. Jessica Nolan and Dr. Karl Kleiner for their help and continued support in this project.