WADA-SD-CAN: DESCRIPTOR 2. Once introduced, alien species are components of ecosystems that can be evaluated by means of condition indicators, but in terms of good environmental status they should be considered as a pressure on native ecosystems. Thus, what will guarantee good environmental status in relation to this descriptor will be the absence of pressure, that is, the absence of alien species. However, given the irreversibility of the great majority of processes of establishment of alignant species, it is not possible to consider the BEA as the absence of alignant species. For this reason, the criteria associated with the descriptor are oriented on the one hand towards maintaining the status quo, that is to say, to reducing the rate of new primary introductions and limiting the expansion of those already established, which reduces the possibility of negative impacts, and on the other hand refers to the direct evaluation of these impacts. For the same reason as mentioned above regarding the irreversibility of the invasions, these impact indicators should give an account of the temporal evolution of the degree of negative impact, and consider that the BEA is achieved by reducing the rate of increase of these impacts.
br />According to what was explained in the previous section, in the sense that alien species are in fact a pressure that threatens the good environmental status of ecosystems, the BEA should not be defined as the result of a particular state of alien species, but rather as a function of the state of native biotas. In fact, the BEA in relation to descriptor 2 consists of the achievement of the BEA with respect to descriptors 1 (biodiversity), 3 (commercial species), 4 (food webs) and 6 (integrity of the bottoms). In addition, taking into account the characteristic of pressure on the marine environment that involves the algae species, a second characteristic of the BEA can be established in reference to the minimization of pressures. Therefore, the Good Environmental Status of descriptor 2 is defined in these two facets
AMA-ES-SD-CAN: DESCRIPTOR 4. Due to the scarcity of information on this descriptor in the Canary Islands Marine Demarcation, it has been decided to define Good Environmental Status in a qualitative way.
AMA-ES-SD-CAN: DESCRIPTOR 5. According to the DMEM, Good Environmental Status (GES) with respect to eutrophication is achieved when “human-induced eutrophication is minimized, especially adverse effects such as loss of biodiversity, ecosystem degradation, massive algae blooms and oxygen deficit in deep waters”. It is clear that minimizing the effects of eutrophication occurs when the impact of nutrients released from ocean sources remains below a threshold that does not produce effects on the marine environment. This maximum threshold will depend on the characteristics of each area (hydrographic conditions, currents, ecosystem structure, etc.). Therefore, it should be defined specifically for each area of study within the Demarcation. In the evaluation presented in the previous section, areas of relatively homogeneous productivity have been defined, which are therefore expected to present a high degree of sensitivity to nutrient enrichment.
In practice, it is not possible to quantitatively define, with the available data, that maximum threshold of nutrient load. Alternatively, we propose to evaluate the eutrophication in the coastal areas of the Demarcation by comparison with the open sea areas. According to this evaluation, it is possible to define a BEA for each of the indicators (or group of indicators) in the terms shown in Table 5.6. As can be seen, the definition includes two complementary criteria for defining the EA for each group of indicators: time trends and reference values.
The indicators of Descriptor 5 are hierarchically structured, so that only if a trend towards an increase in nutrient concentration is detected, not linked to hydrological variability, quantifiable effects on the concentration of chlorophyll or phytoplankton communities attributable to contamination can be expected. However, similarly to what was done for Criterion 3.1, a definition of the BEA can be suggested for Criterion 3.2:
"The BEA corresponds to SSB/SSBMSY being ≥1 for at least 50% of the stocks and not {;0. 6 for no stock."
The value 0.6 is the result of 1/1.6, being 1.6 the value used in the definition of the BEA for Criterion 3. 1.
In an analogous way, the current state in relation to the BEA could be measured in a scale of 0 to 1, with the value 0 corresponding to the worst situation and 1 corresponding to the BEA, by means of the formula:
max[ 0 , 1 – proportion of red stocks – max{0, 0. 5 – proportion of stocks in green} When there is no SSBMSY (or precautionary biomass) reference point, it is not possible to work on the basis of columns 1 & 2 of Table 3.4. In that case, it would be possible to work with columns 3 and 4 of the table, which use the average of the biomass over the whole period,7)-T(T,B, instead of BMSY. The advantages of working with columns 3 and 4 over using columns 1 and 2 are that all stocks with main or secondary indicators are considered in the calculation and that the interpretation is consistent among them. However, it is very important to note that a value of 1 in this case would not necessarily correspond to the BEA, since the analysis is not based on BMSY but on the historical values of the B.
AMA-ES-SD-CAN: DESCRIPTOR 6
In none of the habitats is currently available adequate information on its extent and / or status. The spatial and methodological limitations do not allow to define at this time the BEA (Good Environmental Status) of the habitats as a quantitative value or point. Therefore, the definition of Good Environmental Status should not be the reference level established in the evaluation of the state, but a positive trend towards that level or stability, since in many cases the reference level is impossible to achieve (loss of irreversible habitat, high social costs, long-term time scale of recovery processes, etc.). On the other hand, the concept of Good Environmental Status must take into account the sustainable use of the seas and a level of human activity that is compatible with the conservation of marine ecosystems, in accordance with the ecosystem approach. Therefore, the BEA cannot be assimilated to the reference level, but must take into consideration other factors.

Las condiciones hidrográficas e hidrodinámicas en la demarcación son naturales excepto localmente, en determinadas zonas afectadas por infraestructuras, siendo la extensión de éstas reducida en comparación con las zonas naturales y no causando daños irreversibles en hábitats bioénicos y hábitats protegidos. Los hábitats marinos evolucionan en consonancia con las condiciones climáticas reinantes.

A la hora de establecer un nivel de referencia o de base tenemos dos posibles puntos de partida a considerar, el correspondiente a un estado prístino anterior a que cualquier interferencia humana hubiese tenido lugar y el correspondiente al estado real en la actualidad. El documento AdGES7 indica que el BEA debe en principio identificarse con el estado “normal” conocido, y ser modificado en función de las alteraciones inducidas por el cambio climático que puedan hacer variar las condiciones a escala de la propia demarcación. En el caso del cambio climático los niveles de referencia serán las climatológicas existentes tanto de los campos termohalinos como de los campos de corriente y oleaje (incluyendo su estacionalidad intrínseca). En este sentido, los principales organismos de estudios del clima utilizan períodos de 30 años para definir condiciones de referencia. Para estudios oceánicos en muchos casos no se dispone de series temporales suficientemente largas y detalladas que permitirían construir climatologías robustas sobre períodos tan largos. En lo que se refiere a las afecciones derivadas del impacto causado por obras civiles y vertidos, los niveles de referencia habrán de identificarse con el estado actual, que por tanto se asocia al BEA (es importante insistir que se trata de una valoración general para la demarcación). Sería interesante cuantificar en qué medida se ha distorsionado el estado actual respecto de un hipotético estado prístino, lo cual únicamente puede ser abordado mediante estudios específicos sustentados por modelos hidrodinámicos de vanguardia. De hecho, hoy en día no se realiza un modelado sistemático de regiones costeras al nivel de detalle requerido para proporcionar un mapeado continuo de los parámetros indicados en el anexo III de la Estrategia Marina que pudiera servir como referencia para actuaciones futuras. Existe sin embargo en nuestro país capacidad suficiente para implementar dichos modelos (p. ej. el Grupo de Ingeniería Oceanográfica y de Costas del IH Cantabria o la Unidad de Gestión Integrada de la Zona Costera IMEDEA–Gobierno de Islas Baleares), y de hecho se llevan a cabo estudios y proyectos específicos en este ámbito de forma regular, en ocasiones para dar soporte a declaraciones de impacto ambiental.

Se considera separadamente la gran escala, afectada por cambios graduales debidos a variabilidad natural y cambio climático, de las escalas locales e intermedias donde existe afección por causa de infraestructuras o actividades que generen vertidos o afecten a los vertidos naturales.