Variation in the population dynamics of the invasive bryozoan Membranipora membranacea along a 450-km latitudinal gradient in Newfoundland and Labrador, Canada

Caines, Scott Clifford Peter (2012) Variation in the population dynamics of the invasive bryozoan Membranipora membranacea along a 450-km latitudinal gradient in Newfoundland and Labrador, Canada. Masters thesis, Memorial University of Newfoundland.

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Abstract

The overall objective of this study was to quantify and compare seasonal (June to November) and inter-annual (2008 and 2009) variation in settlement, recruitment, and colony cover of the invasive bryozoan Membranipora membranacea on the kelp Saccharina longicruris across eight sites spanning a 450-km latitudinal gradient between the southwestern tip of Newfoundland and southeastern tip of Labrador. Thermal histories were calculated for each site to determine the extent that the observed variation was explained by sea temperature. Analysis of settlement data (Chapter II) indicated that (1) settler abundance varied both seasonally and annually with a sharp increase between August and September at warmer sites, and spatially with differences of up to three orders of magnitude between sites, (2) settler abundance and sea temperature were strongly correlated (r(2)=0.577), with maxima at mid-latitudes and minima at the northernmost and southernmost sites, and (3) exposure to waves, degree of kelp blade corrugations, and surface area of colonies of M. membranacea on kelp had little explanatory power on settler abundance across the study sites compared to sea temperature. Analysis of recruitment and colony cover data (Chapter III) indicated that (4) recruitment and colony cover varied seasonally, though variation generally decreased with increasing latitude, (5) temperature in the 76 days preceding measurements explained most [>60%] of the variation in recruitment within each month from late summer [September] to late fall [November] with the highest predictive capability (97%) in late fall, and (6) colony cover was strongly correlated (r(2)=0.524) to recruit abundance from late summer to late fall. Consistently low abundances of settlers, recruits, and colonies at the two northernmost sites suggested that M. membranacea is nearing its northern distribution limit in the northwest Atlantic. This study provides the first quantitative analysis of spatial and temporal variation in the abundance of M. membranacea in Newfoundland and Labrador since its introduction in the early 2000s. It strongly supports the general hypothesis that temperature is a key factor in regulating the population dynamics of this species, while suggesting that oceanographic phenomena such as upwelling and downwelling, which act on larval transport, also affect the dynamics at different spatial and temporal scales. A few inconsistencies both within the system studied and between the system studied and that of Nova Scotia indicate additional long-term observational and experimental studies are required to elucidate factors that regulate local and regional variation in the abundance of M. membranacea in cold temperate and subarctic environments.

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