A comparison of the effects of Orconectes rusticus and Orconectes virilis on the growth of two species of macrophytes.

Abstract

The effects of equal densities of Orconectes virilis and Orconectes rusticus on the growth of two species of macrophytes (Najas flexilis and Myriophyllum heterophyllum) were examined at Carp Creek, MI (Emmet County). In each of 3 replicates, 55 cm by 55 cm wire enclosures contained either O. rusticus, O. virilis, or no crayfish. Macrophytes were measured before crayfish introduction and after one week. ANOVA of the results indicated that no significant changes in plant size existed between any of the conditions for M. heterophyllum. Significant changes in N. flexilis size were found between the control and O. virilis (p=.001) and for the control and O. rusticus (p=.009), but there was no significant difference between the effects of O. virilis and O. rusticus (p=.082). This study concludes: 1) O. rusticus and O. virilis have similar effects on macrophytes at equal densities; 2) crayfish feed selectively; 3) high densities of crayfish can reduce macrophyte abundance.