Effects of intrinsic and extrinsic factors on reproduction of an ecologically significant invasive bryozoan: implications for invasion success.
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.