Meeting Abstract
95.3 Wednesday, Jan. 7 Crab scent induces thicker skeletons, smaller gonads and size-specific adjustments in growth rate in sea urchins JOHNSON, A.S.*; SELDEN, R; ELLERS, O; Bowdoin College, Maine; Bowdoin College, Maine; Bowdoin College, Maine ajohnson@bowdoin.edu
Indirect predator-induced effects on morphology of marine invertebrates have been studied in snails, mussels, bryozoans, cladocerans and others but not in post-metamorphic sea urchins. We tracked the growth of a size range (0.065-161.385 g) of sea urchins, Strongylocentrotus droebachiensis with or without upstream odor cues from Jonah crabs, Cancer borealis. In an initial experiment, at ambient temperatures (14.9oC average) during one summer month, growth of small urchins (less than 17 mm diameter) was slowed in the presence of crab scent whereas growth of larger urchins was not detectably affected. In a second, longer experiment during 22 weeks over winter (6.0 oC average) we tracked several measures of growth. Similar to the summer results, odor cues induced slower growth in small urchins (less than 7 mm in the winter). However in contrast to the summer results, the growth rates of larger urchins increased slightly in the presence of crab scent. Furthermore, odor cues from crabs induced thicker skeletons and smaller gonads for urchins between 10 and 30 mm diameter, but did not affect spine length or jaw size. These growth responses suggest size-specific shifts in gonadal and somatic investment. Thicker skeletons may be stronger and thereby reduce predation risk. Smaller urchins may have grown more slowly because they foraged less as has been observed in other studies for smaller urchins hiding from predators. Mid-sized urchins may increase their somatic growth rate to outgrow sizes more vulnerable to predation. Higher somatic growth may be achieved at the expense of gonadal production.
