A. Ricciardi et al., LETHAL AND SUBLETHAL EFFECTS OF SPONGE OVERGROWTH ON INTRODUCED DREISSENID MUSSELS IN THE GREAT-LAKES ST-LAWRENCE-RIVER SYSTEM, Canadian journal of fisheries and aquatic sciences, 52(12), 1995, pp. 2695-2703
Freshwater sponges in the Great Lakes - St. Lawrence River system over
grow and kill introduced zebra (Dreissena polymorpha) and quagga musse
ls (Dreissena bugensis) on solid substrates. Sponges overgrow and smot
her mussel siphons, thereby interfering with normal feeding and respir
ation. We tested the significance of sponge-enhanced mussel mortality
by repeated sampling at several sites where both organisms were abunda
nt in the upper St. Lawrence River and on an artificial reef in centra
l Lake Erie. A small proportion (<10%) of the dreissenid population at
each site was overgrown by sponge. Mussel colonies that were complete
ly overgrown for 1 or more months invariably contained a significantly
greater proportion of dead mussels than local uncovered populations.
Mussels that survived prolonged periods (4-6 months) of overgrowth suf
fered significant tissue weight losses. Laboratory experiments and fie
ld observations suggest that dreissenids are not able to colonize spon
ges; therefore, sponges should always dominate competitive overgrowth
situations. The overall impact of sponges on dreissenid populations in
the Great Lakes - St. Lawrence River system will probably be negligib
le because of the high rate of mussel recruitment and the environmenta
l constraints on sponge growth; however, our results suggest that spon
ges may control mussel abundance locally.