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The effect of light wavelength on hermit crab activity levels
Brendan Phillips, Adele Doucet, Andrew Mosher
BIOL 3401Mount Allison Unversity
Background information
• Coenobita sp.– Terrestrial species
• Crustaceans that inhabit empty snail shells
• Possess compound eyes that vary in visual abilities– Can detect different light intensities and
light wavelengths
Previous Research
• Cronin and Forward 1988– Photoreceptors typically absorbed
wavelengths between 473 nm (blue light) and 515 nm (green light)
• Shaw and Stowe 1982– Photoreceptors that are primarily tuned
to red wavelengths
Purpose
• Examine whether different light wavelengths will affect activity levels in hermit crabs
• Light treatment groups– No Light–White Light– Blue Light– Red Light
Hypotheses
• Ho: Different light wavelengths will not affect hermit crab activity
• Ha: Different light wavelengths will affect hermit crab activity
Predictions
• Activity levels rise in the late afternoon (Ball 1968) and then peak during evening and night (Turra and Denadai 2003)
• Sunset and sunrise – sun’s rays pass through more atmosphere =
red-orange light rays
• We predict hermit crabs will be most active under no visible light and least active under white light
Light intensity
• Light intensity of each colour was measured in candle/feet with light intensity measuring instrument
Activity Level Procedure
• 30 second acclimation period in new tank
• Counted lines crossed for 5 minutes and noted behaviour
• Each crab was subjected to each light treatment (No light, white light, blue light and red light)
Statistical Analysis
• Tested for normality and homogeneity of variances
• Student’s T-test – Comparison of white and low light
• One-Way ANOVA– Activity levels at different lights
• Chi-Square Test– Behaviours
Discussion
• Do not reject our null hypothesis• Overall trend was consistent with
previous studies (Shaw and Stowe 1982, Frank et al. 2002)– slightly higher activity levels at blue and red
light
• Tendency for hermit crabs to walk around perimeter – Inconsistent with previous research (Szabo
2011)
Limitations
• Small sample size• Introduction to novel environment– Increase in anxiety = influence activity
levels
Implications
• Different cues to regulate activity levels (Turra and Denadai 2003)– Tidal rhythms, temperature, circadian
rhythm, and air humidity
• Reduce cost of owning a hermit crab– Lower activity = lower metabolism – Save on food expenses