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The European Marine Strategy Framework Directive (MSFD) requires European states to maintain their marine waters in "Good Environmental Status". The MSFD includes 11 descriptors of "Good Environmental Status" (GES), including "Sea-floor Integrity". This descriptor is defined as: "Sea-floor integrity is at a level that ensures that the structure and functions of the ecosystems are safeguarded and benthic ecosystems, in particular, are not adversely affected." This contribution briefly summarizes the main conclusions of an international expert group established to review the scientific basis for making this concept operational. The experts concluded that consideration of 8 attributes of the seabed system would provide adequate information to meet requirements of the MSFD: (i) substratum, (ii) bioengineers, (iii) oxygen concentration, (iv) contaminants and hazardous substances, (v) species composition, (vi) size distribution, (vii) trophodynamics and (viii) energy flow and life history traits. The experts further concluded that "Good Environmental Status" cannot be defined exclusively as "pristine Environmental Status", but rather status when impacts of all uses were sustainable. Uses are sustainable if two conditions are met:

Sustainable exploitation of marine populations is a challenging task relying on information about their current and past abundance. Fisheries‐related data can be scarce and unreliable making them unsuitable for quantitative modelling. One fishery independent method that has attracted attention in this context consists in estimating the effective population size (Ne), a concept founded in population genetics. We reviewed recent empirical studies on Ne and carried out a simulation study to evaluate the feasibility of estimating Ne in large fish populations with the currently available methods. The detailed review of 26 studies found that published empirical Ne values were very similar despite differences in species and total population sizes (N). Genetic simulations for an age‐structured fish population were carried out for a range of population and samples sizes, and Ne was estimated using the Linkage Disequilibrium method. The results showed that already for medium‐sized populations (1 million individuals) and common sample sizes (50 individuals), negative estimates were likely to occur which for real applications is commonly interpreted as indicating very large (infinite) Ne. Moreover, on average, Ne estimates were negatively biased. The simulations further indicated that around 1% of the total number of individuals might have to be sampled to ensure sufficiently precise estimates of Ne. For large marine populations, this implies rather large samples (several thousands to millions of individuals). If however such large samples were to be collected, many more population parameters than only Ne could be estimated.

This study assesses the impact species ecology, fish reactions, and natural behaviour have on visual strip transect counts of deepwater fish carried out with an ROV (remotely operated vehicle). Two terraces and one canyon were visited on the continental slope of the Bay of Biscay. Species such as rabbit fish (Chimaeridae) and North Atlantic codling (Lepidion eques) appear to have avoided the ROV. The vertical distance off the bottom provided evidence that some individuals, in particular slickheads (Alepocephalidae) might have been missed by being above the ROV. GLM modelling showed the importance of depth, current speed, and relative surveying direction on transect counts. Natural and reaction behaviour of deep-sea fish will lead to variable and biased population density estimates.

In contrast to generally sparse biological communities in open-ocean settings, seamounts and ridges are perceived as areas of elevated productivity and biodiversity capable of supporting commercial fisheries. We investigated the origin of this apparent biological enhancement over a segment of the North Mid-Atlantic Ridge (MAR) using sonar, corers, trawls, traps, and a remotely operated vehicle to survey habitat, biomass, and biodiversity. Satellite remote sensing provided information on flow patterns, thermal fronts, and primary production, while sediment traps measured export flux during 2007–2010. The MAR, 3,704,404 km2 in area, accounts for 44.7% lower bathyal habitat (800–3500 m depth) in the North Atlantic and is dominated by fine soft sediment substrate (95% of area) on a series of flat terraces with intervening slopes either side of the ridge axis contributing to habitat heterogeneity. The MAR fauna comprises mainly species known from continental margins with no evidence of greater biodiversity. Primary production and export flux over the MAR were not enhanced compared with a nearby reference station over the Porcupine Abyssal Plain. Biomasses of benthic macrofauna and megafauna were similar to global averages at the same depths totalling an estimated 258.9 kt C over the entire lower bathyal north MAR. A hypothetical flat plain at 3500 m depth in place of the MAR would contain 85.6 kt C, implying an increase of 173.3 kt C attributable to the presence of the Ridge. This is approximately equal to 167 kt C of estimated pelagic biomass displaced by the volume of the MAR. There is no enhancement of biological productivity over the MAR; oceanic bathypelagic species are replaced by benthic fauna otherwise unable to survive in the mid ocean. We propose that globally sea floor elevation has no effect on deep sea biomass; pelagic plus benthic biomass is constant within a given surface productivity regime.