Chlorination in power station cooling water systems: Effect on biomass, abundance and physiology of natural phytoplankton communities.

Chlorination is a widely used method to prevent biofouling in power station cooling water systems in coastal and estuarine environments. This study evaluated the impact of chlorination together with temperature increase to simulate primary entrainment of a phytoplankton community. Biomass, diversity, and photosynthetic activity were monitored over 72 hours to establish impacts on the phytoplankton community. Biomass was significantly reduced after treatment. The mean cell size of the population significantly increased immediately after treatment highlighting an impact on the smaller cell size species of the community (picophytoplankton). Changes in accessory pigments composition suggest an effect on groups such as Prasinophyceae, Cyanobacteria and Chlorophycea. Species composition, dominated by diatoms, was also affected with Skeletonema marinoi and Asterionellopsis glacialis amongst the most sensitive species. Photosynthetic activity was affected in the short term but recovered after 48 hours. This study shows that by using a combination of measurements (e.g biomass, diversity, and physiology) the effects of entrainment in power station cooling water systems, that may be of longer-term significance for specific functional groups of phytoplankton communities, can be discerned. These changes would not necessarily be seen using individual techniques alone such as cell number counts or biomass assessment which may indicate apparent community recovery.

The effects of marine sand and gravel extraction on the sediment composition and macrofaunal community of a commercial dredging site (15 years post-dredging).

A prediction that faunal recovery of a marine aggregate extraction site subjected to high dredging intensity was likely to take 15-20 years was investigated. Samples were collected at the high dredging intensity site and two reference sites in 2011 (15 years post-dredging). Results indicated that the high site had similar sediment characteristics to the reference sites by 2011. Macrofaunal data analyses showed no difference between the values of all calculated univariate measures (abundance, number of taxa, biomass and evenness) between the high and reference sites. Multivariate analyses found that the macrofaunal community at the high site was comparable to those of the reference sites by 2011. Overall, the results supported the predicted recovery time. The findings of the study suggest that persistent physical impacts prolonged the biological recovery of the high site.

Sampling epifauna, a necessity for a better assessment of benthic ecosystem functioning: an example of the epibenthic aggregated species Ophiothrix fragilis from the Bay of Seine.

Sampling the sea bottom surface remains difficult because of the surface hydraulic shock due to water flowing through the gear (i.e., the bow wave effect) and the loss of epifauna organisms due to the gear's closing mechanism. Slow-moving mobile epifauna, such as the ophiuroid Ophiothrix fragilis, form high-density patches in the English Channel, not only on pebbles like in the Dover Strait or offshore Brittany but also on gravel in the Bay of Seine (>5000 ind m(-2)). Such populations form high biomasses and control the water transfer from the water column to the sediment. Estimating their real density and biomass is essential for the assessment of benthic ecosystem functioning using trophic web modelling. In this paper, we present and discuss the patch patterns and sampling efficiency of the different methods for collecting in the dense beds of O. fragilis in the Bay of Seine. The large Hamon grab (0.25 m(-2)) highly under-estimated the ophiuroid density, while the Smith McIntyre appeared adequate among the tested sampling grabs. Nowadays, diving sampling, underwater photography and videos with remote operated vehicle appear to be the recommended alternatives to estimate the real density of such dense slow-moving mobile epifauna.