"The European Water Framework Directive (WFD; 2000/60/EC) aims at achieving ‘good’ ecological and chemical quality status for all water types, by 2015. The quality status of a water body can be determined based on the evaluation of biological quality elements, which are phytoplankton, macroalgae, macro-invertebrates and fish (the latter only in transitional waters), which are supported by chemical, physico-chemical (e.g. transparency, thermal and oxygen conditions, salinity and nutrients) and hydromorphological (e.g. depth variation, quantity structure and substrate of the sub-tidal and intertidal zone, tidal regime) quality elements. GES is defined as ‘the values of the biological quality elements for the surface water body type show low levels of distortion resulting from human activity, but deviate only slightly from those normally associated with the surface water body type under undisturbed conditions’. The evaluation of GES is based on the integration of well defined quality criteria per quality element. Each of these quality criteria supports a classification (bad, poor, moderate, good and high) to measure the ‘health’ of the system compared to reference conditions. For the biological quality element macro-invertebrates, the composition and abundance of the fauna has to be identified. Within a WFD context, many benthic indicators were developed and intercalibrated, which combine some benthic variables such as abundance, biomass, diversity (e.g. Shannon Wiener, Margalef, Simpson indexes), Bray-Curtis similarity, species sensitivity/tolerance classifications (e.g. AMBI, ES500.05 species values) in a multivariate or multimetric way (Borja et al., 2007)"

"The main objective of the Marine Strategy Framework Directive (MSFD; 2008/56/EC) is to achieve good environmental status (GEnS), by 2020. GEnS is defined as ‘the environmental status of marine waters where these provide ecologically diverse and dynamic oceans and seas which are clean, healthy and productive within their intrinsic conditions, and the use of the marine environment is at a level that is sustainable, thus safeguarding the potential for uses and activities by current and future generations’. Therefore, the MSFD established a framework for the development of strategies designed to achieve GEnS, which takes into account the structure, function and processes of the marine ecosystems together with natural physiographic, geographic and climatic factors, as well as physical and chemical conditions including those resulting from human activities in the area concerned. This is reflected in the development of 11 quality descriptors for determining good environmental status, for which a set of criteria and associated indicators were proposed by expert groups. Based on the expert group reports, an EU Commission Decision document on the criteria and methodological standards on GEnS of marine waters were defined (2010/477/EU). Based on this document, macro-invertebrates were taken into account in four descriptors:"
"• ‘Biological diversity is maintained. The quality and occurrence of habitats and the distribution and abundance of species are in line with prevailing physiographic, geographic and climatic conditions.’ Proposed criteria are species distribution, population size, population condition, habitat distribution, extent and condition for the benthic community among other fauna groups (Table 1 of Annex III of MSFD)."
"• ‘Non-indigenous species introduced by human activities are at levels that do not adversely alter the ecosystem.’ In case benthic species were identified as non-indigenous, in particular invasive, this descriptor has to be taken into account by GEnS evaluation."
"• ‘All elements of the marine food webs, to the extent that they are known, occur at normal abundance and diversity and levels capable of ensuring the long-term abundance of the species and the retention of their full reproductive capacity.’ A proposed indicator for the criterion ‘abundance/distribution of key groups/species’ are abundance trends of functionally important selected groups/species (e.g. biological groups with high turnover rate, habitat defining groups/species, …)."
"• ‘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.’ For the criterion on the condition of benthic community, the following indicators are proposed: presence of particularly sensitive/tolerant species, multi-metric indexes assessing benthic community condition and functionality (species diversity and richness, proportion of opportunistic to sensitive species), proportion of biomass of number or individuals above some specified length/size class and parameters (slope and intercept) of the size spectrum of the aggregate size composition data."
"For a number of criteria and related indicators, the need for further development and additional information was identified in the document. Member States need to consider each of the criteria and related indicators in order to identify those which are to be used to determine the GEnS. Methodological standards still need to be developed."

Principles,,Water Framework Directive,Marine Strategy Framework Directive
2. Use of the Ecosystem approach,Realization,"• Biological quality elements with supporting chemical, physico-chemical and hydromorphological variables","• Eleven descriptors, with several indicators covering ecological, physical, chemical and anthropogenic components of the ecosystem"
,Challenge,"• Integration of the elements based on one out - all out principle’, which is not always appropriate",• Selection of the appropriate indicators and the integration of the several indicators per descriptor
,Way to go,"• Scientific selection of elements/indicators in relation to their sensitivity, robustness and confidence.• Integration of indicators based on a decision tree process, with a clear transparency of the integration acts at indicator and descriptor level."

3.1 Benthic Indicators,Realization,"• National approaches, which require intercalibration• Multi-metric benthic indicators","• Regional approach, with common indicators• Mainly univariate indicators per descriptor"
,Challenge,• Comparability of the national approaches,"• No comparability tests on indicator level needed, but still on other aspects of the Directive (e.g. GEnS thresholds)• Sensitivity of single univariate benthic indicators less clear!"
,Way to go,"• The selection of appropriate indicators, with complementary properties and related to the Directive objectives.• Integration of single univariate indicators required to detect the complex response of benthos"

3.2 From pristine conditions to sustainably functioning ecosystems,Realization,"• Reference = ‘undisturbed (pristine) condition’, to be determined based on reference sites or benchmarking","• Reference = ‘sustainable functioning ecosystems’, but no methodology for determining thresholds for GEnS"
,Challenge,"• No benthic reference sites, poor historical data• Expert judgment good first step, but needs funding",• What is good or sustainable?• No single GEnS thresholds for any indicator will be appropriate within a region
,Way to go,• The use of clear stressor-response data• Defining the ‘naturalness’ of the system

3.3.1 Anthropogenic pressure types,Realization,• Indicators have to prove their pressure type dependency,"• Indicators have to be selected based on pressure type (most appropriate, measurable)"
,Challenge,• Multi-pressure environments• Large scale pressures• No impact free areas
,Way to go,• Marine Protected Areas (MPAs)• Accurate and detailed quantification of the pressure types in the marine systems

3.3.2 Natural versus anthropogenic response,Realization,• Indicators not or less sensitive to natural variability
,Challenge,• Currently less investigations regarding sensitivity of indicators to natural variability and scoping the natural variability in defining reference conditions,• Availability of detailed data on large temporal and spatial scale
,Way to go,• Integration of all available temporal and spatial data information• The use of spatially well designed monitoring systems

3.3.3 Alien species or non-indigenous species,Realization,• Alien species were considered as a pressure,• Non-indigenous species is a descriptor
,Challenge,• May not be present at high status.• Measures to remove or reduce the impact are scarce,• Measures to remove or reduce the impact are scarce
,Way to go,"• Research has to focus on the effect of alien species (function, niche) on the ecosystem• Prevention of further invasions by early warning systems (precautionary principle)"

4. Monitoring requirements for environmental assessment,Realization,• Monitoring programs on national level,• National monitoring programs to be integrated on regional sea or sub-sea level
,Challenge,• Influence of sampling strategy type on assessment results• Diversity of national approaches in sampling strategy
,Way to go,"• Use of the habitat approach (stratified sampling strategy) in benthos monitoring• Incorporation of statistical power, effect size and variance determination in determining number of samples• Setting of an adequate time scaling of the monitoring in relation to the indicator type• Use of standard benthic quality assurance guidelines• Adaptation of national monitoring programs towards cost-effective, integrative strategies• A switch from ‘station oriented monitoring’ towards a ‘basin or system oriented monitoring’"