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Deep-water corals and sponges provide habitat complexity and shelter for many fauna, contributing to the health of deep-sea ecosystems. However, these taxa are vulnerable to anthropogenic disturbances such as fishing and climate change because they grow slowly and have long life spans. This vulnerability has led to the protection of several deep-water coral and sponge aggregations globally, as Vulnerable Marine Ecosystems. On the continental shelf and slope in Atlantic Canada protection targets the gorgonian corals Paragorgia arborea and Primnoa resedaeformis, and the sponge Vazella pourtalesi. Populations of these three species are discontinuous and spatially fragmented, making self-recruitment and population connectivity important factors in regulating population persistence. However, measures of recruitment are lacking. We used a Remotely Operated Vehicle to collect high resolution video of coral and sponge distribution and size frequency at three locations in the Corsair and Georges Canyons Coral Conservation Area and Northeast Channel Coral Conservation Area on 18–24 June 2019. Analysis revealed evidence of high coral recruitment at two locations on the continental slope off Nova Scotia, and high sponge recruitment at one location. To our knowledge, such high natural recruitment of deep-water corals and sponges has not been recorded elsewhere in the deep sea. Size frequency distributions varied with depth, likely because of differences in larval supply, or post-settlement disturbance due to faunal movement and unstable substrate. The results from this study can be incorporated into high resolution hydrodynamic modeling to assess population connectivity between populations of P. arborea, P. resedaeformis and V. pourtalesi and help identify potentially significant larval sources on the Scotian continental margin. Our results also can also inform ecological risk assessments, leading to more effective design of a network of Marine Protected Areas. [ABSTRACT FROM AUTHOR]

A mechanistic understanding of the factors that influence establishment and secondary spread of introduced species is critical for predicting the spatial extent and magnitude of negative impacts of species invasions. In the northwest Atlantic, an ecologically significant invasive bryozoan (Membranipora membranacea) has expanded its range northwards over the last 30 years. Warm ocean temperature has been linked to population outbreaks of M. membranacea within its established invasive range in southwestern Nova Scotia; however, rates of spread and the physical and biological factors affecting establishment of founding populations have not been explicitly quantified. Here, we use unique baseline data on presence/absence and abundance of this bryozoan near its current northern range limit to quantify rates of spread and identify factors influencing its establishment in three regions in the Gulf of St. Lawrence. Except for one potential incident of human-facilitated long-distance dispersal, the rate of spread of M. membranacea in the northwest Atlantic was comparable to that of other invasive marine invertebrates. Contrary to our predictions based on long-established populations in Nova Scotia, the abundance of M. membranacea was not strongly related to regional differences in ocean temperature at its northern range limit. Our results suggest that colder temperatures are not limiting the northward spread of this bryozoan in the northwest Atlantic. Instead, relationships between temperature and abundance of M. membranacea in the Gulf of St. Lawrence may be moderated by a lack of available kelp substrate. Our findings, therefore, have important implications regarding the potential for M. membranacea to impact vulnerable Arctic ecosystems where laminarian kelps are widespread. [ABSTRACT FROM AUTHOR]

This study quantified the fine- scale (0.5 km) of variability in the horizontal distributions of benthic invertebrate larvae and related this variability to that in physical and biological variables, such as density, temperature, salinity, fluorescence and current velocity. Larvae were sampled in contiguous 500-m transects along two perpendicular 10-km transects with a 200-µm plankton ring net (0.75-m diameter) in St. George’s Bay, Nova Scotia, Canada, in Aug 2009. Temperature, conductivity, pressure and fluorescence were measured with a CTD cast at each station, and currents were measured with an Acoustic Doppler Current Profiler moored at the intersection of the 2 transects. Gastropod, bivalve and, to a lesser extent, bryozoan larvae had very similar spatial distributions, but the distribution of decapod larvae had a different pattern. These findings suggest that taxonomic groups with functionally similar larvae have similar dispersive properties such as distribution and spatial variability, while the opposite is true for groups with functionally dissimilar larvae. The spatial variability in larval distributions was anisotropic and matched the temporal/spatial variability in the current velocity. We postulate that in a system with no strong oceanographic features, the scale of spatially coherent physical forcing (e.g. tidal periodicity) can regulate the formation or maintenance of larval patches; however, swimming ability may modulate it. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The article analyzes the distribution and abundance of introduced and native bryozoan cyphonautes larvae in relation to variations in the stratification of the water column in a coastal embayment of Saint Margarets Bay in Nova Scotia, Canada. Information on the sea level, mean horizontal circulation, temperature and shoreline geology of the bay is presented. The bathymetric and temporal variation in abundance of Membranipora membranacea and Electra pilosa species throughout the study period is observed.

Abstract: Deep-water corals form unique ecosystems, yet very little is known about factors that regulate their distribution and growth. The abundance and size of two deep-water gorgonian coral species, Paragorgia arborea and Primnoa resedaeformis, and their relationship with depth and substratum cover, were investigated at Northeast Channel, off Nova Scotia, in July 2006. This is the first study to measure abundance and size of these two coral species at depths >500m in the Canadian Atlantic region. A total of 5 transects between 500 and 1000m depth were examined using video collected by the remotely operated vehicle ROPOS. Abundance of both species was patchy, but higher at these deeper depths than at <500m. Abundance generally declined with depth, and was moderately correlated with cover of hard substratum (cobble, boulder, bedrock). These relationships were stronger and less variable for P. resedaeformis than for P. arborea, suggesting that factors such as topographic relief may play an additional role in regulating distributions of P. arborea. Maximum colony height was 125 and 240cm for P. resedaeformis and P. arborea, respectively, and much greater than recorded for depths <500m. Overall, colony height and depth relationships were strong for both species, but variable among transects. P. resedaeformis showed a negative relationship with depth, while the opposite was observed for P. arborea, suggesting that the two species are affected differently by factors that vary with depth (e.g. temperature, fishing disturbance). Relationships between colony size and size of attachment stone were stronger for P. arborea, especially for overturned colonies, than for P. resedaeformis, suggesting that availability of suitably coarse substrate may be more important for the long-term persistence of P. arborea colonies. [Copyright &y& Elsevier]

The European green crab, Carcinus maenas, is an extremely successful species worldwide. C. maenas was first recorded in Nova Scotia in 1953, and by the 1990s it was found in the Bras d'Or Lakes in Cape Breton. Adults of C. maenas can tolerate salinities as low as 4. However, their larvae are not known to survive in salinities below 20 in their native range. High abundances of adult and juvenile C. maenas, as well as zoea-1 larvae and megalopae, are recorded in the Bras d'Or Lakes, where surface salinity may rarely exceed 20. It is possible that the early zoeal stages are more tolerant of lower salinities than those from their native habitat. Alternatively, they may have developed a tolerance for short-term exposure to low salinities. To examine the long-term tolerance of early zoeal stages (zoea-1 and zoea-2) of C. maenas to different salinities, newly released larvae from females from the Bras d'Or Lakes were individually reared in the laboratory at four practical salinities (14, 17, 20, 26). Larval survival decreased sharply and larvae did not develop past zoea-1 in salinities of 14 and 17, while larvae reared at a salinity of 20 did not survive past zoea-2 and larvae reared at a salinity of 26 completed development to the megalopa stage. Variation in larval survival among females was greatest at 26 and decreased with decreasing salinity. To examine the short-term tolerance of early zoeae, newly released zoeae were initially placed in a salinity of 14 for 1 day or 20 for 3 days, before being transferred to a salinity of 26. Larval survival did not increase and development did not resume after larvae were transferred to the higher salinity. These results suggest that early larval stages of C. maenas from the Bras d'Or Lakes are not adapted to either long, or short-term exposures to the low salinities typical of the surface waters of the Lakes. It is possible that these larvae may be able to tolerate exposure to low salinity water for shorter periods than those examined, or that they are behaviourally avoiding waters of low salinity in order to survive in this invaded habitat. [ABSTRACT FROM AUTHOR]