The effect of Orconectes rusticus on the mortality and habitat selection of Orconectes propinquus.

Abstract

The effect of Orconectes rusticus on the mortality and habitat selection of Orconectes propinquus was examined at the University of Michigan Biological Station. Substrate preference was determined by placing O. propinquus, and O. propinquus and O. rusticus in aquaria with different sequences of substrates: sand, gravel, pebble, rock. The substrate occupied by the crayfish was recorded. Chi-aquared analysis indicated that in in the presence of O. rusticus, there was a significant shift in habitat occupation by O. propinquus (0.025>p>0.01). The effect of O. rusticus on O. propinquus mortality was determined by constructing enclosures containing O. propinquus, and O. rusticus and O. propinquus (sex and size matched to 1 mm, and sex matched with a carapace length difference of >5 mm). The enclosures were placed in Douglas Lake for 10 days. At the time of removal, the crayfish were measured to examine the growth of O. propinquus with and without the presence of O. rusticus. The results indicated that the direct mortality of O. propinquus caused by O. rusticus occurred only when O. rusticus had a carapace length of 5 mm greater than O. propinquus. The effect of O. rusticus on the growth of O. propinquus was not significant (t-test, p=0.247), although there was a trend towards showing an effect.