For each SAC the Member State concerned must establish the necessary conservation measures corresponding to the ecological requirements of the natural habitat types in Annex I and the species in Annex II present on the site. Such measures should, if need be, involve appropriate management plans. More specifically, Member States are obliged to take appropriate steps to avoid, in the SACs, the deterioration of natural habitats and the habitats of species, as well as disturbance of the species for which the areas have been designated, in so far as such disturbance could be significant in relation to the objectives of the Directive.38 (Art 6.)
In order to find a breach of this obligation there is no need to prove a cause- and-effect relationship between an activity and significant disturbance to a species for which the area has been designated. The existence of a probability or risk that an operation might cause significant disturbances for such a species is sufficient if the Member State has authorised the activity or at least failed to take measures for bringing it to an end.39
Of particular practical significance is the assessment requirement pertaining to any plan or project not directly connected with or necessary to the management of the site but likely to have a significant effect on an SAC, either individually or in combination with other plans or projects. Any such plan or project must be subject to appropriate assessment of its implications for the site in view of its conservation objectives.         A pressing question is, obviously, how one is to know whether a plan or a project is likely to have a significant effect on an SAC, and therefore require an impact assessment? The Court of Justice has found that, in the light of the precautionary principle, a plan or project requires an assessment unless it can be ‘excluded, on the basis of objective information’, that it will have a significant effect on the site concerned.41 The Court has also held that although the Habitats Directive does not define any particular method for carrying out an ‘appropriate assessment’, such an assessment must identify all the aspects of the plan or project which can, either individually or in combination with other plans or projects, affect the site’s conservation objectives in the light of the best scientific knowledge in the field.42 An assessment is not appropriate if it contains gaps and lacks complete, precise, and definitive findings and conclusions ‘capable of removing all reasonable scientific doubt’ as to the effects of the works proposed on the site concerned.43 Categories of projects cannot be exempted from assessment unless that is done on the basis of criteria which adequately ensure that those projects will not have a significant effect on the protected sites.44
The competent national authorities, taking account of the conclusions of the appropriate assessment, may only agree to the plan or project after having ascertained that it will not adversely affect the integrity of the site concerned and, if appropriate, after having obtained the opinion of the general public (Art 6). This applies also when a plan or a project is approved by a legislative authority.45
In order for the integrity of a site not to be adversely affected, the site needs to be preserved at a favourable conservation status. This entails the lasting preservation of the constitutive characteristics of the site concerned that are connected to the presence of a natural habitat type whose preservation was the objective justifying the designation of that site in the list of SCIs.4fi Only where ‘no reasonable scientific doubt remains’ as to the absence of adverse effects on the integrity of the site may the national authorities authorise the activity.47
Where the development consent given to a project is annulled because reliable and updated data concerning the species concerned was missing when the decision was taken, the Court of Justice has opened the possibility to gather a posteriori reliable and updated data and appraise, on the basis of that data, whether the project adversely affects the integrity of the site.4®
Compensatory measures that are not aimed either at avoiding or reducing the significant adverse effects for a habitat type, but rather tend to compensate after the fact for those effects, may not be taken into account in the assessment of the implications of the project.     
Under certain circumstances plans or projects may be authorised even if they do negatively affect the integrity of a protected site. This is the case if there are no alternative solutions and the plan or project must be carried out for imperative reasons of overriding public interest, including those of a social or economic nature. In such a case the Member State must take, and inform the Commission of, all compensatory measures necessary to ensure that the overall coherence of Natura 2000 is protected. If the site concerned hosts a priority natural habitat type and/or a priority species, the only considerations which may be raised are those relating to human health or public safety, to beneficial consequences of primary importance for the environment, or, after the Commission has issued an opinion, to other imperative reasons of overriding public interest. (Art 6.)
As a derogation from the criterion for authorisation, the provision allowing a plan or project to be carried out for imperative reasons of overriding public interest is to be interpreted strictly.5° More specifically, the Court of Justice has held that works intended for the location or expansion of an undertaking may be considered to be of both ‘public’ and ‘overriding’ interest only in exceptional circumstances.51
A guidance document on the assessment of plans and projects significantly affecting Natura 2000 sites has been published by the Commission. 52 The Court of Justice has stressed that in order to determine the nature of any compensatory measures, the damage to the site must be precisely identified.53
The restrictions imposed on plans and projects that may adversely affect the integrity of protected sites have, particularly in some Member States, been criticised for being inflexible and not only restricting environmentally harmful activities but also hindering those that could, viewed in a broader perspective or over a longer period of time, contribute to a more sustainable long-term preservation of ecosystems and other environmental values. The level of flexibility seems, however, at least partly to depend on choices made in the national implementation of the Directive.54 Although there is always a risk that overly rigid rules become counterproductive and limit the room for a holistic approach to complex conservation challenges, this must be balanced against the risk that the cumulative effect of many instances of apparently harmless flexibility amount to considerable impairment to the objectives of the protection regime.
The Directive provides, under certain circumstances, for EU co-financing which the Member States consider necessary to allow them to establish the necessary conservation measures (Art 8).
Also with respect to unprotected areas, the Member States shall endeavour, in their land-use planning and development policies, to encourage the management of features of the landscape which are of major importance for wild fauna and flora (Art 10).
Member States must undertake surveillance of the conservation status of the natural habitats and species covered by the Directive with particular regard to priority natural habitat types and priority species. In this context an SAC may be considered for declassification where this is warranted by natural developments. (Arts 9 and 11.)
Annex 4 to the Directive lists animal and plant species of Community interest in need of strict protection. The Member States must establish a system of strict protection for the animal species listed in Annex IV(a) in their natural range. All forms of deliberate capture or killing55 of specimens of these species in the wild; any deliberate disturbance, deliberate destruction, or taking of eggs from the wild; or deterioration or destruction of breeding sites or resting places of these species shall be prohibited. The Court of Justice has made clear that there is an obligation not merely to adopt a comprehensive legislative framework but also to implement ‘concrete and specific protection measures’^6 The Court has also focused on the effectiveness of any measures taken. It has found that the system of strict protection presupposes the adoption of coherent and coordinated measures of a preventive nature.57 Furthermore, the system must
enable the effective avoidance of all forms of deliberate capture or killing of specimens of animal species listed in Annex IV(a) in the wild, deliberate disturbance of the species, particularly during the period of breeding, rearing, hibernation and migration, deliberate destruction or taking of eggs from the wild as well as deterioration or destruction of breeding sites or resting places of those species.5®
The keeping, transport, and sale or exchange, and offering for sale or exchange, of specimens taken from the wild, except for those taken legally before the Habitats Directive was implemented, shall also be prohibited. Member States must establish a system to monitor the incidental capture and killing of the animal species listed in    
Annex IV(a). A similar system of strict protection is to be established for the plant species listed in Annex IV(b). Among the things that shall be prohibited are the deliberate picking, uprooting, or destruction of such plants in their natural range in the wild. (Arts 12 and 13.)
With respect to the capture or killing of species of wild fauna listed in Annex V, the Member States shall prohibit the use of all indiscriminate means capable of causing local disappearance of, or serious disturbance to, populations of such species. This includes prohibiting, inter alia, the use of explosives and poisons and poisoned or anaesthetic bait as well as the use of aircraft or moving motor vehicles. (Art 15.)
Derogations from the prohibition on the capturing and killing of species may be granted, inter alia, in the interest of protecting wild fauna and flora and conserving natural habitats; to prevent serious damage, in particular to crops, livestock, forests, fisheries and water, and other types of property; or for imperative reasons of overriding public interest. Derogations are only allowed if there is no satisfactory alternative and the derogation is not detrimental to the maintenance of the populations of the species concerned at a favourable conservation status in their natural range. The Court of Justice has made clear that derogations may not be contrary to the ‘spirit and purpose’ of the Directive.59 Every second year the Member States shall submit a report to the Commission on any derogations applied.   (Art 16.)
Every six years the Member States shall submit a report on the implementation of the measures taken under the Directive. Based on these reports the Commission shall prepare and publish a composite report (Art 22).
Protection of species and habitats is an area where the Commission, aided by the Court of Justice, has held the Member States to increasingly strict standards. However, so far this has not managed to bring about a clear reversal of the negative trends for biodiversity. Perhaps the best hope for that lies in the strengthened role of NGOs and the legal remedies available to them for the enforcement of EU nature protection law.61