1. CONCEPTS "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." "Sea Floor" includes both the physical structure and biotic composition of the benthic community. "ntegrity"includes the characteristic functioning of atural ecosystem processes and spatial connectedness. There are no points of significant disagreement among experts regarding key terms or what constitutes gradients of degradation in environmental status. However serious problems of sampling and measurement and high scientific uncertainty about aspects of benthic ecology and tolerances of benthic ecosystems to perturbations pose challenges to application of "good environmental status". Sound assessments of GES are possible, but they will have to integrate results from local scales where both natural benthic ecosystems and pressures may be very patchy, to much larger regional and subregional scales. Many common uses of the sea necessarily impact the sea floor and benthic communities. "Good environmental status" of the seafloor requires that diversity and productivity are maintained and the uses do not cause serious adverse impacts to the natural ecosystem structure and functioning in both space and time. The pressures associated with those uses do not hinder the ecosystem components to retain their natural diversity, productivity and dynamic ecological processes. Perturbations due to use should be small enough that recovery is rapid and secure if a use ceases. Many benthic areas do not meet these standards and management must improve status. Scale for assessing GES of the sea floor is particularly challenging for four reasons. First, benthic ecosystem features are patchy on many scales. Second, a wide range of human activities cause pressures on the sea floor, and they usually operate at patchy spatial scales. Third, although initial impacts of human activities are often local and patchy their direct and indirect ecological consequences may be transported widely by physical and biotic processes. Fourth, all monitoring of the seafloor is also patchy and often local. In all evaluations of impacts the scale of the impact relative to the availability of the ecosystem properties being impacted is an important consideration. To deal with these challenges, the measurement of GES for seafloor integrity has three steps. First: identify the ecological structures and functions of particular importance. Second: identify the human pressures known or likely to reach levels that degrade environmental status. Third, for the ecosystem components and pressures identified as being of greatest importance, use a suite of appropriate Attributes and Indicators to assess status relative to pre-identified standards for GES, along gradients reflecting meaningful scales of the seafloor attributes and pressures. The standards for GES on various Indicators must reflect the different sensitivity and resilience of the Indicators and their functions in ecosystem processes. Risk-based approaches to monitoring and assessment are proposed to deal with the local-scale patchiness of seafloor Attributes, pressures, and impacts. 2. ATTRIBUTES Substrate: The physical properties of the seabed such as grain size, porosity, rugosity, solidity, topography and geometric organization (e.g three-dimensional habitats). Substrate is a driver of patterns in diversity, function and integrity of benthic communities. Together with hydrodynamics, it is a main factor structuring benthic habitats. Four types of Substrate are considered separately, both because they contribute differently to ecosystem processes and they are affected differently by diverse pressures: soft sediments, gravels, hard substrates, and biogenic substrates. Indirect Indicators of functions are often more practical to use in assessing GES than Indicators of substrate itself. Bioengineers: Organisms that change the structure of the seafloor environment in ways not done by geophysical processes alone, by reworking the substrate or by providing structures that are used by other species. Bioengineers may serve functions such as providing shelter from predation or substrate for other organisms, reworking of sediments, transporting interstitial porewater, and facilitating material exchange at the sediment-water interface. Bioengineers are sensitive to may pressures, but often prove difficult to monitor directly. Indirect indicators of the functions they serve or indicators from mapping the pressures on bioengineers are often practical alternatives for assessing GES. Oxygen: Concentration of dissolved oxygen in the bottom water and/or in the upper sediment layer of the seafloor. Decreasing oxygen supply of bottom water and/or the upper sediment results in significant changes of the benthic communities and can lead to mass mortality. Oxygen depletion is particularly associated with excessive nutrient and organic enrichment of the seafloor. Important indicators for Oxygen concentration include abundance of organisms sensitive or tolerant to oxygen level and the spatial distribution of oxygen/hydrogen sulphide concentrations conducted in critical regions and in critical seasons. Contaminants and Hazardous Substances: Guidance on including these substances in assessments of GES is presented in the Report of TG-8. Particular attention should be given to applying that guidance for seafloor communities and habitats. Sediments may be repositories for many of the more toxic chemicals that are introduced into water bodies. Contaminated sediments represent a hazard to aquatic life through direct toxicity as well as through bioaccumulation in the food web. Species Composition: The list of species present in an area, their abundances, and/or their evolutionary and ecological relationships, including their pattern of occurrence in space and time. Species composition captures information on the biological diversity, structure, and dynamics of communities. It represents a fundamentally valued feature of ecosystem‘s potential to function well, to resist potential threats, and be resilient. Of the large number of indicators of species composition, those focusing on diversity among samples (space or time) and measures of species/area relationships may be most useful. These must be applied on local scales to account for natural scales of community structure and pressures on them. Size Composition: Abundance or biomass of individuals of different sizes in the community, with "Size" either continuous or as categories. The size composition of a community integrates information of about productivity, mortality rate, and life histories of the full community. Indicators include the proportion of numbers (or biomass) above some specified length, parameters (slope and intercept) of the "size spectrum" of the aggregate size composition data, and shape of a cumulative abundance curve of numbers of individuals by size group. Trophodynamics: A complex attribute with many subcomponents. Key ones include Primary and Secondary Production, Carrying Capacity, Energy Flows, and Food Web Relationships. TG 4, on Food webs deals thoroughly with primary production, energy, flow and food webs. When evaluating Seafloor Integrity it is important to follow the expert guidance from TG 4 in the specific context of the benthic community, its food web relations, and benthic-pelagic relationships. Secondary Production and Carrying Capacity are also important to Seafloor Integrity but at this time there are no practical indicators for their assessment. Life History Traits: Life History Traits are the categorisation of characteristics of the life cycle that species can exhibit, i.e. growth rates, age or size or maturation, fecundity and the seasonality of life history features such as reproduction. Various combinations of these traits lead to species differing in their natural productivity, natural mortality, colonization rates, etc. They are important to GES as they reflect the status of ecosystem functioning. Their changes are direct measures of the condition of the biota, or may uncover problems not apparent with other Attributes, and provide measurements of the progress of restoration efforts. Many synthetic indices based on representation of species with different sensitivities and tolerances for general or species pressures have been used. 3. COMBINING INDICATORS Because of the patchiness of seafloor attributes, pressures and impacts on many scales, the optimal suites of Indicators and their reference levels will differ on all but local scales. This means that monitoring must be adapted to local conditions, and expanded for the seafloor – both in terms of area covered and types of attributes measured. It also means that no single algorithm for combining Indicator values will be appropriate for evaluating GES or providing a meaningful "index" of GES for Seafloor Integrity. It may be possible to conduct such analytical syntheses of Indicators for individual Attributes on local scales. However across Attributes and on even moderate scales expert assessments rather than algorithmic formulae will be needed for evaluation of GES of Seafloor Integrity.