D. Rittschof et al., Movements of anemones symbiotic with hermit crabs: Effects of light, gravity, flow and conspecifics, MAR FRESH B, 32(4), 1999, pp. 193-205
Anemones, Calliactis tricolor (Le Sueur, 1817), are common symbionts associ
ated with several genera of hermit crabs on the South East and Gulf Coasts
of the United States. Anemones are reported to be mutualistic symbionts. Cr
abs protect anemones from anemone predators and anemones protect crabs by s
tinging crab predators. Previous studies show protection afforded by anemon
es is dependent upon their location in relation to the aperture of the shel
l. We conducted studies of anemone responses to physical factors (light, gr
avity, and flow) and conspecifics to assess the role that anemone behavior
plays in determining location on the shell. Anemones collected on crabs fro
m offshore and from crabs in near-shore environments were induced to attach
individually to upright cylinders and to shells positioned as if occupied
by hermit crabs. Movements of individuals were followed for 48 h. Frequency
analysis was performed to determine if anemone movements were random. Anem
ones do not show a locomotory response to simple variations in direction of
light. Most anemones (70-90% of over 200 individuals) display negative geo
taxis in static conditions and move to high points on cylinders and shells.
Most anemones show positive geotaxis in continuous flow conditions compara
ble to those generated by a crab walking. The presence of a second anemone
on a shell results in a more even distribution of anemones because anemones
cannot occupy the same spot and interfere with each others' movements. Ane
mone distribution is dependent upon movement behavior of the anemone in res
ponse to gravity, flow and conspecifics. The anemone collecting and packing
behavior reported for crabs of the genus Dardanus may be adaptive because
a crab that packs its shell with anemones has a better chance of receiving
protection than a crab that hosts only a single anemone.