DIVERPEL – New Diversity Indicators in the Pelagic Habitat: response to the new requirements to define Good Environmental Status proposed in the Marine Strategies Framework Directive
Pleamar program
Description:
The recent Decision of the European Union (2017/848) to specifically include the Pelagic Habitat (HP) as well as certain criteria that must be considered to estimate its quality following the Marine Strategies Framework Directive (MSF; in particular with regard to Descriptor 1: Biodiversity) has revealed the existence of a large methodological and basic knowledge gap. At the moment there is no consensus regarding the definition of Good Environmental Status (GES) for HPs. However, it is essential to determine what qualities a PH must have in order to be considered in GES in order to create indicators that allow the monitoring and management objectives proposed in the DMEM to be met (Dickey-Collas et al. 2017).
One of the conditions that the HP must meet to meet the GES criteria is that all species present in normal environmental conditions must be able to find their HP necessary to complete their life cycle. Another condition that the HP must meet to be in GES is precisely that neither the physical dynamics of the ocean nor the movements of biota and water masses are obstructed (Dickey-Collas et al. 2017). Knowledge of the pelagic environment, hydrographic characteristics and dynamics of water bodies plays a fundamental role in understanding the processes that regulate both the dynamics of populations exploited by fishing (Alvarez-Berastegui et al. 2014) and marine diversity (Hidalgo et al. 2015). Such knowledge is therefore crucial for the evaluation and planning of management measures to ensure the sustainability of pelagic and demersal living resources. Time series of planktonic phases and hydrographic and biogeochemical variables (nutrients and dissolved oxygen) can be a very valuable tool for monitoring marine biodiversity and changes in water bodies. These changes can be used to determine indicators and threshold values that define the GES of a HP and its impact on biodiversity. Many species of fish in the Mediterranean have their laying season in spring-summer.
Spring-summer fish larvae data sets exist for most of the Mediterranean Geographic Sub-Areas (GSAs) described by the General Fisheries Commission of the Mediterranean. For most GSAs, there is also sufficient hydrographic information related to fish larvae to be able to cover the objectives regarding the establishment of ranges and thresholds proposed by EU Decision 2017/848: “The establishment of threshold values should take into account the dynamic nature of marine ecosystems and their elements, which can change in space and time due to hydrological and climatic variations, predator-prey relationships and other environmental factors. Threshold values should also reflect the fact that marine ecosystems can recover, if they are deteriorated, to a state that reflects the prevailing physiographic, geographical, climatic and biological conditions, rather than returning to a particular previous state.”
Line of action:
Marine ecosystemsStatus:
FinalizadoExecution date:
2019General Objective:
Estimate the environmental status of pelagic habitats.
Specific objectives:
- To analyze the impact of environmental variability on pelagic ecosystems through spatial and temporal changes in biodiversity.
- Compile and evaluate existing information on anthropogenic pressures (eutrophication and fishing) in open ocean ecosystems, characterizing and comparing marine pelagic communities in different bioregions.
- To generate scientific tools to assess Good Environmental Status (GES) in the current open ocean pelagic environment and that will serve for the future implementation of the Marine Strategies Framework Directive in relation to the descriptors biodiversity, fisheries and eutrophication.
- Evaluation of the implementation of the scientific tools for the evaluation of the GES in the bioregions identified in the case study.
The IEO Baleares has achieved the general objective, allowing that, for the first time, indicators of diversity and good environmental status in the pelagic habitat that surrounds the Balearic archipelago are identified. Changes in the values of these indicators will allow variations in the pelagic diversity patterns of the area to be observed in the future.
In addition, it is concluded that:
- It has been possible to identify 135 taxa of fish larvae in the superficial layer of the water column around the Balearic Sea in the summer season, based on data collected over five years (2012-2016). Of the 135 taxa, 94 refer to species, 21 to genus and 20 to family, so the specific richness of the pelagic habitat in the area is very high.
- The sum of the abundances of only eight of these species represents 95% of the total abundance of larvae in the area, so diversity indicators should be used in this area to take into account the presence of the least abundant species. The proposed index is Shannon’s.
- Statistically, a change in diversity values is observed along the depth gradient. It is estimated that the change between the communities occurs at a depth of 650 m. This depth is proposed as an indicator of changes in the diversity of the area in future assessments, as no sentinel species of change have been identified.
- The marine dynamics of the area, especially the salinity front that separates two bodies of water that face each other in summer in the area, also represents a barrier of diversity. The diversity change along the salinity gradient is estimated to occur around the value of 37.7. This salinity value is suggested as an indicator of changes in the diversity of the area in future assessments, as no sentinel species of change have been identified.
- The concentrations of nutrients in the area are very low, corresponding to an oligotrophic zone. No influence of these concentrations on diversity values is observed.
- The densities of bluefin tuna larvae are increasing year by year with respect to the larvae of other large pelagics. The diversity of large pelagics near the coast is associated with peaks of Auxis rochei densities, while in more open waters the diversity is driven by the high densities of bluefin tuna larvae.
DIVERPEL – New Diversity Indicators in the Pelagic Habitat: response to the new requirements to define Good Environmental Status proposed in the Marine Strategies Framework Directive
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