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Most research on biological invasions to date has focused on the population dynamics of very successful and disruptive introduced species; however, additional knowledge of the biology of the native species is essential for understanding interactions between the two and may reveal factors that limit invasion success. The invasive bryozoan Membranipora membranacea interacts with native Electra pilosa on two substrates in northwest Atlantic subtidal habitats: highly dynamic and fast-growing kelps; and smaller, more stable, and slow-growing fucoid algae. We quantified the relative abundance and evaluated encounter outcomes in different seasons of these two bryozoans on kelp and Fucus at four sites in Nova Scotia. We also examined the effects of substrate (kelp, Fucus), temperature (7, 10, 13°C), and food (limited, unlimited) on growth rates of E.pilosa in laboratory experiments and using field manipulations. We compared our findings on factors affecting the growth of E. pilosa to those on M. membranacea obtained in similar and thus directly comparable experiments from a previous study. The proportional abundance of M.membranacea was greater than that of E. pilosa on kelps, but the opposite was observed on Fucus. Competitive standoffs between the two bryozoans were more frequent than expected, with no differences recorded between substrates; most encounters were won by M. membranacea. Growth of E.pilosa was faster on Fucus than kelp, decreased with increasing temperature only on Fucus, and was not affected by food. Growth rate of E. pilosa in all treatments was slower than that previously measured for M.membranacea. Faster growth and strong overgrowth abilities likely interact on kelps to ensure success of the invasive bryozoan. Success can be limited by low space availability, which in turn restricts growth rate, and consequently, colony size, such as on fucoid substrates. The incorporation of alternative contexts into invasion research can reveal factors involved in the resilience of native communities., Author(s): Alana F. Yorke [sup.1] , Anna Metaxas [sup.2] Author Affiliations: (1) grid.55602.34, 0000000419368200, Department of Biology, Dalhousie University, , B3H 4R2, Halifax, NS, Canada (2) grid.55602.34, 0000000419368200, Department of [...]

The capacity to predict changes in the distribution and abundance of sessile marine invertebrates depends on quantifying factors that affect spatial and temporal variation in propagule production. This is particularly important for invasive species, since both the timing and abundance of introduced propagules can determine invasion success. This study examines the role of reproductive dynamics in contributing to the invasion success of the highly invasive bryozoan Membranipora membranacea by quantifying temporal patterns in the sexual stage and potential fecundity of colonies and examining the effects of intrinsic (colony size) and extrinsic (temperature, host substrate) factors on the reproductive potential of invasive populations. Colonies were collected on the 4 most abundant algal substrates in Nova Scotia at 2-3 sites approximately monthly from 2012 to 2015. Individual zooids within each collected colony were classified by sexual stage (immature, producing sperm only, producing sperm and oocytes, producing oocytes only), and the number of oocytes per colony was counted as a measure of potential colony fecundity (reproductive potential). There were significant seasonal patterns in colony fecundity; however, temperature and colony size accounted for only 12 and 7% of the observed variation, respectively. Instead, consistent differences in reproductive potential were observed among colonies on different algal substrates. Our results indicate how critical demographic processes can differ for invasive species outside of their native range. Our study underscores the need to quantify population dynamics of non-indigenous species within the invaded community to more accurately predict the long-term consequences for invaded ecosystems., Author(s): Danielle Denley [sup.1] , Anna Metaxas [sup.1] Author Affiliations: (1) Department of Oceanography, Dalhousie University, 0000 0004 1936 8200, grid.55602.34, , B3H 4R2, Halifax, NS, Canada Introduction For benthic [...]