Seafloor biodiversity of Canada's three oceans: patterns, hotspots and potential drivers

Aim We examined the relationships between bathymetry, latitude and energy and the diversity of marine benthic invertebrates across wide environmental ranges of Canada's three oceans. Location Canadian Pacific, Arctic and Atlantic Oceans from the intertidal zone to upper bathyal depths, encompassing 13 marine ecoregions. Methods We compiled 35 benthic datasets that encompass 3,337 taxa (70% identified to species and 21% to genus) from 13,172 samples spanning 6,117 sites. Partitioning the analyses by different gear types, ecoregions or sites, we used Hill numbers to examine spatial patterns in α‐diversity. We used resampling and extrapolation to standardized sampling effort and examined the effects of depth, latitude, chemical energy (export particulate organic carbon [POC] flux), thermal energy (bottom temperature) and seasonality of primary production on the benthic biodiversity. Results The Canadian Arctic harboured the highest benthic diversity (e.g. epifauna and common and dominant infauna species), whereas the lowest diversity was found in the Atlantic. The Puget Trough (Pacific), Beaufort Sea, Arctic Archipelago, Hudson Bay, Northern Labrador and Southern Grand Bank (Atlantic) were the “hotspots" of diversity among the ecoregions. The infauna and epifauna both exhibited hump‐shaped diversity–depth relationships, with peak diversity near shelf breaks; latitude (positively) predicted infaunal diversity, albeit weakly. Food supply, as inferred from primary production and depth, was more important than thermal energy in controlling diversity patterns. Limitations with respect to calculating POC flux in coastal (e.g. terrestrial runoff) and ice‐covered regions or biological interactions may explain the negative POC flux–infaunal diversity relationship. Main Conclusions We show previously unreported diversity hotspots in the Canadian Arctic and in other ecoregions. Our analyses reveal potential controlling mechanisms of large‐scale benthic biodiversity patterns in Canada's three oceans, which are inconsistent with the prevailing view of seafloor energy–diversity relationships. These results provide insightful information for conservation that can help to implement further MPA networks

The BenBioDen database, a global database for meio-, macro- and megabenthic biomass and densities

Benthic fauna refers to all fauna that live in or on the seafloor, which researchers typically divide into size classes meiobenthos (32/64 µm–0.5/1 mm), macrobenthos (250 µm–1 cm), and megabenthos (>1 cm). Benthic fauna play important roles in bioturbation activity, mineralization of organic matter, and in marine food webs. Evaluating their role in these ecosystem functions requires knowledge of their global distribution and biomass. We therefore established the BenBioDen database, the largest open-access database for marine benthic biomass and density data compiled so far. In total, it includes 11,792 georeferenced benthic biomass and 51,559 benthic density records from 384 and 600 studies, respectively. We selected all references following the procedure for systematic reviews and meta-analyses, and report biomass records as grams of wet mass, dry mass, or ash-free dry mass, or carbon per m2 and as abundance records as individuals per m2. This database provides a point of reference for future studies on the distribution and biomass of benthic fauna

Climate-induced changes in the suitable habitat of cold-water corals and commercially important deep-sea fishes in the North Atlantic

The deep sea plays a critical role in global climate regulation through uptake and storage of heat and carbon dioxide. However, this regulating service causes warming, acidification and deoxygenation of deep waters, leading to decreased food availability at the seafloor. These changes and their projections are likely to affect productivity, biodiversity and distributions of deep-sea fauna, thereby compromising key ecosystem services. Understanding how climate change can lead to shifts in deep-sea species distributions is critically important in developing management measures. We used environmental niche modelling along with the best available species occurrence data and environmental parameters to model habitat suitability for key cold-water coral and commercially important deep-sea fish species under present-day (1951–2000) environmental conditions and to project changes under severe, high emissions future (2081–2100) climate projections (RCP8.5 scenario) for the North Atlantic Ocean. Our models projected a decrease of 28%–100% in suitable habitat for cold-water corals and a shift in suitable habitat for deep-sea fishes of 2.0°–9.9° towards higher latitudes. The largest reductions in suitable habitat were projected for the scleractinian coral Lophelia pertusa and the octocoral Paragorgia arborea, with declines of at least 79% and 99% respectively. We projected the expansion of suitable habitat by 2100 only for the fishes Helicolenus dactylopterus and Sebastes mentella (20%–30%), mostly through northern latitudinal range expansion. Our results projected limited climate refugia locations in the North Atlantic by 2100 for scleractinian corals (30%–42% of present-day suitable habitat), even smaller refugia locations for the octocorals Acanella arbuscula and Acanthogorgia armata (6%–14%), and almost no refugia for P. arborea. Our results emphasize the need to understand how anticipated climate change will affect the distribution of deep-sea species including commercially important fishes and foundation species, and highlight the importance of identifying and preserving climate refugia for a range of area-based planning and management tools.S

Impacts of otter trawling on infaunal bivalves living in sandy bottom habitats on the Grand Banks

Otter trawling has been the prevalent method of ground fishing in Atlantic Canada. Despite this, little is known about associated impacts to benthic habitat and communities. This thesis examines the impacts of otter trawling on bivalves living in sand, a bottom type occurring widely over the Grand Banks. Bivalves are dominant members of sandy bottoms on continental shelves and are good indicators of physical disturbance. Two broad categories of impacts to benthos from mobile fishing gear are direct harvest and incidental damage. Bivalves have low susceptibility to capture by groundfish otter trawls; trawl capture efficiency is on the order of 10⁻⁵. In order to investigate incidental impacts, a three-year otter trawling experiment was conducted on a fine to medium sand bottom on the northeastern Grand Bank. Each year a total of 12 trawl passes were made along the centre line of two 13 km by 200 m experimental corridors. Sampling was conducted inside experimental and adjacent reference corridors with a 0.5 m² hydraulic grab. No significant effects of trawling were detected on bivalve populations in any year. Shallow burrowing species showed no significant changes in density or biomass and recruitment of juveniles ≤3 mm was apparent inside trawled corridors. The size structure of populations from trawled and reference areas were similar. Mean (± sd) percent major shell damage immediately after trawling was low, ranging from 2.8 ± 6.1% to 13.5 + 9.4%. Trawl doors are the most destructive gear component of otter trawls. A physical trawl door model was towed through an artificial sand testbed, constructed to resemble an offshore seabed. Although bivalves within the scour path were displaced, levels of damage were low (c. 5%), similar to levels of damage from the combined effects of all gear components recorded in the field experiment. The anomaly of displacement, accompanied by few instances of damage, is explained by sediment mechanics associated with scouring and size and life position of infaunal bivalves. Compared to natural sediment-mediated disturbances, otter trawling can be manipulated over a wide range of frequencies. Individual and population-level adaptive traits probably confer considerable stability to sandy bottom bivalve populations exposed to typical patterns of trawling activity on the Grand Banks

Growth and reproduction of Mytilus edulis (Linnaeus) on the two sides of the Strait of Belle Isle

A comparative growth study of Strait of Belle Isle Mytilus edulis populations was undertaken, with the hypothesis that the surface water temperature difference between the two sides of the Strait (4-8 C) results in differences in growth rates. Results of the study show that Mytilus edulis collected at four sites, (two on each side of the Strait) from the high, low, and subtidal zones, displays the type of spawning, growth, and population structure, typical of north-temperate, exposed-coast mussel populations. Linear shell growth rates were similar between the two sides of the Strait. Growth rates were low (maximum of 6-8 mm per year) and were highly variable within populations (average range in length of 10 mm per year class). -- Winter growth was negligible as evidenced by pronounced, external shell check-marks, and despite the large spring-summer water temperature difference between sides of the Strait of Belle Isle, the annual spring start of linear shell growth was similar between mussels on the two sides. The seasonal progression of the internal growth line in M. edulis was relatively synchronous within populations, and timing of deposition was similar between sides of the Strait. -- Spawning was synchronized and occurred later (July-August) than at more southern latitudes. Subsequent settlement in 1981 resulted in large numbers of post-larvae over-wintering on algae and adult mussel beds at sizes < 2 mm in shell length. There were large differences in fecundity between sites, however, the range in fecundity was similar on both sides of the Strait. Age-specific fecundity was higher in the low intertidal than in the high intertidal (e.g. 160 and 115 mg gamete dry weight respectively, at Pte. Amour). -- Mussels < 15 mm in shell length dominated the intertidal zone while contributing little to meat weight biomass. At the sampling scale used in this study (200 cm¹), meat dry weight biomass and reproductive output were similar between high and low intertidal zones. Individual meat weight values were similar between the two sides of the Strait and Pte. Amour meat weight values were highest of those in the intertidal zones while similar to values at other sites subtidally

TOBB: Canada's three oceans of benthic biodiversity database

This dataset contain abundance data from Canadian Pacific, Arctic, and Atlantic Oceans from the intertidal zone to upper bathyal depths, encompassing 13 marine ecoregions. 35 benthic datasets that encompass 3,337 taxa (70% identified to species and 21% to genus) from 13,172 samples spanning 6,117 sites. Abiotic data from these ecoregions includes lat long, depth, latitude, chemical energy (export particulate organic carbon [POC] flux), thermal energy (bottom temperature), and seasonality of primary production on the benthic biodiversity