Evidence of Recruitment Inhibition of Zebra Mussels (Dreissena polymorpha) by a Freshwater Bryozoan (Lophopodella carteri)

Abstract

Competitive interactions involving macrofouling organisms were virtually unknown in North American freshwater systems prior to the introduction of the Eurasian zebra mussel Dreissena polymorpha. In southern Lake Michigan, the zebra mussel co-occurs on solid surfaces with an exotic bryozoan, Lophopodella carteri. Previously unreported from Lake Michigan, L. carteri was found attached to the shells of adult zebra mussels that were encrusting pier posts (depth 2-4 m) in the Michigan City, Indiana, harbor. This epizoic growth was often so prolific that entire patches of mussels were obscured by gelatinous colonies of L. carteri, thereby reducing shell surface area available to settling mussel larvae. A 4 to 5× difference in densities of newly settled mussels on mussel groups not covered by L. carteri compared to covered groups indicated that recruitment of mussel larvae was inhibited by the presence of bryozoan colonies. Although dense colonies of bryozoans, such as L. carteri at Michigan City, may not be wid...