PRATT, M.C.; Bowdoin College, Brunswick, ME: Will an opportunistic invasive bryozoan displace or coexist with other epiphytic bryozoans in the Gulf of Maine?

The bryozoan Membranipora membranacea was introduced into the Gulf of Maine in 1987 and within two years became the dominant epiphyte on kelps. While we know that Membranipora can increase the likelihood of breakage of kelps, we know nothing of competitive interactions between Membranipora and other epiphytic bryozoans. To determine whether Membranipora will outcompete or coexist with other bryozoans, I used field observations and measured feeding, growth, and respiration rates to better understand the life history strategies of Membranipora and another epiphytic bryozoan, Electra pilosa. Membranipora is the dominant epiphyte on kelps from the late summer through the fall, but does not survive the winter well. Electra never dominates on kelps, but it survives the winter better than Membranipora. Membranipora dominates by settling in very high numbers and growing very fast, which allows it to almost completely cover kelp blades. Membranipora grows very fast by having a high feeding rate, maintaining a high metabolic rate, and putting the vast majority of its energy into growth. This strategy has a cost, as Membranipora does not survive poor conditions as well. While Membranipora maintains a high metabolic rate and still puts energy towards growth in low food conditions, Electra lowers its metabolic rate and generally puts more energy into maintaining the colony rather than trying to grow further. Electra may not be able to compete with Membranipora effectively in good conditions, but it may be able to coexist by using spatial and temporal refuges.