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

Methods

• Identification• Light Intensity Test• Activity Levels Procedure• Statistical Analysis

Identification

• Five hermits crabs labelled with different nail polish colours

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

Results

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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

Questions or comments?