Population-level consequences of seismic surveys on fishes : an interdisciplinary challenge

Offshore activities elevate ambient sound levels at sea, which may affect marine fauna. We reviewed the literature about impact of airgun acoustic exposure on fish in terms of damage, disturbance and detection and explored the nature of impact assessment at population level. We provided a conceptual framework for how to address this interdisciplinary challenge, and we listed potential tools for investigation. We focused on limitations in data currently available, and we stressed the potential benefits from cross‐species comparisons. Well‐replicated and controlled studies do not exist for hearing thresholds and dose–response curves for airgun acoustic exposure. We especially lack insight into behavioural changes for free‐ranging fish to actual seismic surveys and on lasting effects of behavioural changes in terms of time and energy budgets, missed feeding or mating opportunities, decreased performance in predator‐prey interactions, and chronic stress effects on growth, development and reproduction. We also lack insight into whether any of these effects could have population‐level consequences. General “population consequences of acoustic disturbance” (PCAD) models have been developed for marine mammals, but there has been little progress so far in other taxa. The acoustic world of fishes is quite different from human perception and imagination as fish perceive particle motion and sound pressure. Progress is therefore also required in understanding the nature and extent to which fishes extract acoustic information from their environment. We addressed the challenges and opportunities for upscaling individual impact to the population, community and ecosystem level and provided a guide to critical gaps in our knowledge.Publisher PDFPeer reviewe

Importance of mesozooplanckton feeding for the downward flux of biogenetic carbon in the Gulf of St. Lawrence (Canada)

We tested the importance of mesozooplankton feeding and defecation for the downward flux of biogenic carbon (C) in the Gulf of St. Lawrence, a marine coastal environment characterized by high zooplankton abundance. Five stations were sampled over nine cruises between July 1992 and June 1994. The rates of chlorophyll (Chl) ingestion and C defecation were determined for the major copepod species. Free-drifting, short-term (24　h) sediment traps were deployed at the sampled sites at 50 and 150　m, and the trap contents were analyzed for fecal pellets (microscopy), Chl and pheopigments (chromatography). The flux at 50　m of C associated with fecal pellets ranged between 5 and 138　mg C m-2 d-1, while total POC flux varied between 78 and 302　mg C m-2 d-1. Of the total POC found in sediment traps at 50　m, close to 50%, on average, was composed of zooplankton fecal pellets. In contrast, direct algal (Chl) sinking was <10%. The fecal pellet contribution varied seasonally, with a maximum (>73%) in June 1994 at all stations. This maximum did not necessarily coincide with the highest rate of production of fecal pellets in the surface waters, indicating that other factors influenced the sinking of fecal pellets. A shallow mixed-layer depth seemed to favor fast removal from the surface. The average fecal pellet contribution to the total downward POC flux was slightly higher for stations 4 and 5 (52% compared with 39% for the other stations). These stations were characterized by zooplankton communities that differed from those of the other stations, smaller copepods such as Temora longicornis frequently dominated at stations 4 and 5, Calanus spp. dominated at stations 1, 2 and 6. High fluxes of fecal pellets frequently occurred when the index of herbivory (Chl ingestion　:　total C ingestion) was low, transferring downwards carbon of heterotrophic origin. The contribution of C-transformed pheopigments to total POC flux was low (6% on average). It co-varied with the degree of herbivory in the overlying waters. The production of fecal pellets in the top 50　m co-varied with Chl ingestion, but not with the index of herbivory, consistent with an algal food intake representing <50% of total C ingested. Phytoplankton ingestion was highest when primary production (not algal biomass) was maximum. In consequence, mesozooplankton feeding did not exert a strong control over the phytoplankton biomass of the Gulf of St. Lawrence (at most 10%), but it was more closely tied to primary production. Phytoplankton biomass is more likely controlled by physical factors in this region. Mesozooplankton fecal pellets contributed significantly to the downward flux of biogenic C all through the year in this environment, transferring alternatively C of autotrophic and heterotrophic origin

Trophic structure of macrobenthos in the Gulf of St. Laurence and on the Scotian Shelf

The Gulf of St. Lawrence and Scotian Shelf provide a diversity of oceanographic conditions in a continental margin setting. Climate is markedly seasonal, and bathymetry and hydrodynamic conditions cover a broad range, significantly influencing the patterns of organic matter sedimentation and, potentially, benthic community dynamics. Samples for analysis of benthic macrofauna and sediment microorganisms were collected at six stations in the Gulf of St. Lawrence (GSL) and the Scotian Shelf during winter and summer cruises, as part of the Canadian Joint Global Ocean Flux Study. Multivariate analyses indicate significant site-related trends in trophic guilds, benthic assemblages, and microbial activity, some of which are related to geomorphological characteristics (bathymetry, topography, and substratum). Macrofaunal trophic guild data show that the stations with relatively deep settling basins (Cabot Strait and Emerald Basin), dominated by surface deposit feeders, were distinct from stations with sloping bottoms (Anticosti Gyre and Anticosti Channel), where subsurface deposit feeders dominated or surface and subsurface deposit feeders were equally abundant. Deposit feeders (surface and subsurface trophic groups) made up >60% of the benthic communities, except at the Scotian slope station where they represented 44% of the total benthic abundances. Based on the data collected in both the water column and the sediment at three deep stations in the GSL, we hypothesize that the proportion of surface and subsurface deposit feeders, and thus the nature of bioturbation activity, is related to the magnitude and pattern of organic matter supply from the euphotic zone

Decadal weakening of the wind-induced upwelling reduces the impact of nutrient pollution in the Bay of Malaga (western Mediterranean Sea)

Publicado