Calcium-bearing objects elicit shell selection behavior in a hermit crab

Hermit crabs explore empty gastropod shells by touching, rolling, and probing them before choosing one for a home. This component of shell selection behavior was examined in Pagurus hirsutiusculus hirsutiusculus (Dana) with binary choice tests between natural shells and accurate replicas of the shells with different chemical compositions. The results show that calcium emanating from the surface of shells is responsible for the behavior. Sensitivity to calcium may be a factor that enables the hermit crab to locate partially buried shells and discriminate empty shells from ones housing living gastropods or from small pebbles.     

Cyanobacterial blooms: carbon and nitrogen limitation have opposite effects on the buoyancy of oscillatoria

Gas vacuolation in Oscillatoria rubescens decreased with increased nitrogen limitation and increased with transitions from nitrogen to inorganic carbon limitation. Gas vacuoles consist of protein vesicles that can accumulate in carbon- limited but not in unenriched nitrogen-limited cells. Nitrogen limitation is a factor in the formation of deep population maxima; carbon limitation can promote surface blooms.