Ecosystem functioning in northeast pacific soft-sedimentary habitats: the roles of species diversity, functional diversity, and environmental variables.

Previous studies indicate a central role for biodiversity and environment in marine ecosystem functioning, raising concerns about the potential consequences of biodiversity alteration. By combining marine biology and biogeochemistry approaches, and field and laboratory-based approaches I provide new information on biodiversity and environmental contributions to important ecosystem functions such as benthic flux variation and organic matter degradation. Using published benthic flux rate measurements and available environmental variables, I created global models and maps to identify predictors of benthic fluxes of oxygen and nutrients. By performing incubations of intact sediment cores and measuring benthic flux rates, I determined that, of the environmental variables examined, bottom water properties, organic matter quality, and sediment characteristics best explained benthic flux variation. By adding functional and species diversity metrics, I demonstrated that biodiversity and environment contribute about equally to these functions, and that functional richness was the most important predictor of benthic flux variation and organic matter degradation. In experimental incubations where I added phytodetritus to intact sediment cores, I determined that higher taxonomic diversity, and densities of detritivores and omnivores explained higher benthic flux rates in enriched sediment cores. These results point to the combined importance of biodiversity and environment in controlling ecosystem functioning and illustrate the need to combine established and novel approaches to evaluate more fully the consequences of anthropogenic impacts, such as biodiversity alteration and environmental change for ecosystem functioning

Effects of hypoxia on benthic macrofauna and bioturbation in the Estuary and Gulf of St. Lawrence, Canada

The bottom water in the 4300 m deep Lower St. Lawrence Estuary (LSLE) is persistently hypoxic in contrast to the normoxic bottom waters in the Gulf of St. Lawrence (GSL). We photographed the seabed at 11 stations in the Estuary and Gulf of St. Lawrence (EGSL) during the summers 2006 and 2007 and analysed the images to identify bioturbation traces (lebensspuren) and benthic macrofauna. The objective was to identify the environmental variables that influence the density and diversity of benthic macrofauna and bioturbation traces, and the differences that exist among regions with high, medium and low oxygen levels in the bottom water. The bottom water oxygen concentration is the variable that best explains the densities of total-traces as well as surface-traces. However, the density of these traces was higher in hypoxic regions than in well-oxygenated regions. The higher density of traces in the hypoxic region of the LSLE is mainly due to the activities of the surface deposit feeder Ophiura sp., which occurs in large numbers in this region. Possible explanations explored are stress behaviour of the organisms in response to hypoxia and different benthic macrofauna community structures between the hypoxic regions of the LSLE and the normoxic regions of the GSL. In the former, surface deposit feeders and low-oxygen tolerant species dominate over suspension feeders and low-oxygen intolerant species

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

Variables environnementales influençant la densité et la diversité de la macrofaune épibenthique et la bioturbation dans l'estuaire et le golfe du Saint-Laurent, Canada

L'estuaire et le golfe du Saint-Laurent (EGSL), Canada, subit présentement un évènement hypoxique qui pourrait être causé par des changements dans la composition de la masse d'eau de fond et une augmentation de l'apport en matière organique. Le fond marin de l'EGSL a été photographié à 11 stations durant les étés 2006 et 2007. Les images ont ensuite été analysées afin d'identifier les traces de bioturbation (Lebensspuren) et les organismes macrobenthiques présents. Les objectifs de cette étude sont: 1) d'identifier les variables environnementales qui influencent la densité et la diversité de la macrofaune épibenthique ainsi que les traces de bioturbation, et 2) de déterminer les différences entre les régions de l'EGSL avec des niveaux d'oxygène élevés, moyens et bas. La concentration d'oxygène dans la couche de fond est la variable environnementale qui explique le mieux les densités de traces totales et de surface : les densités de ces traces augmentent alors que l'oxygène diminue. La densité de traces plus élevée dans la région hypoxique de l'EGSL est principalement due au déposivore de surface Ophiura sp. , qui se retrouve en grande densité dans cette région. Les résultats indiquent que les conditions hypoxiques actuelles n'affectent pas négativement la densité et la diversité des traces de bioturbation ainsi que la richesse spécifique. Cependant, nous avons observé dans la zone hypoxique une augmentation des déposivores de surface (tolérants aux basses concentrations d'oxygène) et une diminution des suspensivores (intolérants aux basses concentrations d'oxygène). Nous émettons l'hypothèse que la diminution de la concentration d'oxygène des eaux de fond au cours des dernières années a causé un changement dans la structure de la communauté macro-épibenthique de l'estuaire maritime du Saint-Laurent (EMSL). Les espèces avec une plus faible tolérance aux basses concentrations d'oxygène, qui sont généralement responsables des traces en relief, sont remplacées par des espèces plus tolérantes, tels que les déposivores de surface Ophiura sp. , qui sont responsables de la majorité des traces de surface

Relative contributions of biodiversity and environment to benthic ecosystem functioning

Current concern about biodiversity change associated with human impacts has raised scientific interest in the role of biodiversity in ecosystem functioning. However, studies on this topic face the challenge of evaluating and separating the relative contributions of biodiversity and environment to ecosystem functioning in natural environments. To investigate this problem, we collected sediment cores at different seafloor locations in Saanich Inlet and the Strait of Georgia, British Columbia, Canada, and measured benthic fluxes of oxygen and five nutrients (ammonium, nitrate, nitrite, phosphate and silicate). We also measured 18 environmental variables at each location, identified macrofauna, and calculated a suite of species and functional diversity indices. Our results indicated that, examined separately, macrobenthic functional richness (FRic) predicted benthic flux better than species richness, explaining ~ 20% of the benthic flux variation at our sites. Environmental variables and functional diversity indices collectively explained 62.9% of benthic flux variation, with similar explanatory contributions from environmental variables (21.4%) and functional diversity indices (18.5%). The 22.9% shared variation between environmental variables and functional diversity indices demonstrate close linkages between species and environment. Finally, we also identified funnel feeding as a key functional group represented by a small number of species and individuals of maldanid and pectinariid polychaetes, which disproportionately affected benthic flux rates relative to their abundance. Our results indicate the primary importance of environment and functional diversity in controlling ecosystem functioning. Furthermore, these results illustrate the consequences of anthropogenic impacts, such as biodiversity loss and environmental changes, for ecosystem functioning

Morphometrics and processing yield of Cucumaria frondosa (Holothuroidea) from the St. Lawrence Estuary, Canada.

Sea cucumber Cucumaria frondosa have highly variable whole body mass and length, and are usually sold to Asian markets as dried gutted body wall. Understanding the relation between size and yield of dry product is essential for resource conservation and for economic purposes. In this study, stock-specific mass and length recovery rates were estimated for C. frondosa captured by dredging or diving at various depths and seasons on the South shore of the St. Lawrence Estuary, along Gaspé Peninsula, and processed in a commercial plant. The processing yield in dry product mass per sea cucumber was more than 1.5 times larger for sea cucumbers collected at 26-47 m depth compared to those collected at 9-16 m depth. Within each strata, there was little variation in the processed body mass, seasonally or spatially. Recovery rates based on gutted mass for this stock (13.4─14.5%) varied little among depths and seasons, despite observed seasonal and bathymetric variation in reproductive status. In contrast, recovery rates based on whole body mass and length were highly variable both seasonally and spatially. Stress related to dredging or post-capture handling induced important variable body contraction and water content, leading to variation in body length, mass and shape of sea cucumbers having the same processed body mass. Gutted mass was the best metric to predict processed body mass and to estimate size whereas whole body length was the least reliable. New stock-specific information on variability of body mass, length, and recovery rates induced by capture, and on seasonal and bathymetric variation in reproductive status and processing yields will be used for the design of future stock assessment surveys, and for stock conservation

Environmental Drivers of Benthic Flux Variation and Ecosystem Functioning in Salish Sea and Northeast Pacific Sediments.

The upwelling of deep waters from the oxygen minimum zone in the Northeast Pacific from the continental slope to the shelf and into the Salish Sea during spring and summer offers a unique opportunity to study ecosystem functioning in the form of benthic fluxes along natural gradients. Using the ROV ROPOS we collected sediment cores from 10 sites in May and July 2011, and September 2013 to perform shipboard incubations and flux measurements. Specifically, we measured benthic fluxes of oxygen and nutrients to evaluate potential environmental drivers of benthic flux variation and ecosystem functioning along natural gradients of temperature and bottom water dissolved oxygen concentrations. The range of temperature and dissolved oxygen encountered across our study sites allowed us to apply a suite of multivariate analyses rarely used in flux studies to identify bottom water temperature as the primary environmental driver of benthic flux variation and organic matter remineralization. Redundancy analysis revealed that bottom water characteristics (temperature and dissolved oxygen), quality of organic matter (chl a:phaeo and C:N ratios) and sediment characteristics (mean grain size and porosity) explained 51.5% of benthic flux variation. Multivariate analyses identified significant spatial and temporal variation in benthic fluxes, demonstrating key differences between the Northeast Pacific and Salish Sea. Moreover, Northeast Pacific slope fluxes were generally lower than shelf fluxes. Spatial and temporal variation in benthic fluxes in the Salish Sea were driven primarily by differences in temperature and quality of organic matter on the seafloor following phytoplankton blooms. These results demonstrate the utility of multivariate approaches in differentiating among potential drivers of seafloor ecosystem functioning, and indicate that current and future predictive models of organic matter remineralization and ecosystem functioning of soft-muddy shelf and slope seafloor habitats should consider bottom water temperature variation. Bottom temperature has important implications for estimates of seasonal and spatial benthic flux variation, benthic-pelagic coupling, and impacts of predicted ocean warming at high latitudes

Permutational analysis of variance (PERMANOVA) results testing the effect of sampling date and location on benthic fluxes based on Euclidean similarity matrices performed on normalized data.

<p>Permutational analysis of variance (PERMANOVA) results testing the effect of sampling date and location on benthic fluxes based on Euclidean similarity matrices performed on normalized data.</p

Distance-based linear model (DistLM) of benthic fluxes against environmental drivers measured in the Salish Sea and NE Pacific in May/July 2011, and September 2013.

<p>Distance-based linear model (DistLM) of benthic fluxes against environmental drivers measured in the Salish Sea and NE Pacific in May/July 2011, and September 2013.</p