The definition of marine habitats as ordinated biological community complexes can allow variations in structure and prevalence of species to be used to show change that may be linked to environmental pressures. To date, the inshore intertidal and subtidal reef has not been the subject of the same degree of focused surveys as the offshore. As a result, Ireland’s knowledge of the communities that occur here is qualitative and patchy. Without these data it is not possible to describe marine community structure for the development of site-specific conservation objectives in Special Areas of Conservation (as required to facilitate compliance with the Habitats Directive) or to classify marine communities in terms of the European Nature Information System (EUNIS) biotopes. Detecting change in these communities and monitoring of conservation status is obviously not possible without baseline marine community data.
Geogenic reef habitat is variable in structure. It includes a broad range of substrates from bedrock to cobble and from flat fields to structures with significant relief above the seabed. Aspect, slope, rugosity and exposure can vary and provide microhabitats for marine fauna and flora. Marine communities in geogenic reef as a result are complex and variable. Characterisation and monitoring of change is difficult and both sampling methods and sampling design need to be carefully considered.
Sampling can be done in situ or remotely but in both cases this involves taking images rather than physical samples of epifauna/flora on the reef. Infauna is only a consideration in cobble fields and where physical samples would need to be extracted. Camera technology continues to improve as does the capacity to operate cameras using remotely operated vehicles such as gliders. High quality images and video can be acquired at points or along transects. Flora and fauna can be identified from images. The resulting data can be at least semi-quantitative (SACFOR scale), providing relative species abundance estimates, or fully quantitative providing data on numbers per unit area of reef surface. The second and potentially bigger issue, however, is how to extrapolate from a point or transect sample to distribution and extent of particular biological communities (defined at, for instance, a given EUNIS level) over an area of interest given that the underlying physical terrain, which influences biological community structure, may be highly variable. Extent and distribution of biological communities cannot be estimated using biological sampling alone given the inherently variable underlying physical habitat which influences their distribution. Defining the association with underlying physical terrain variables, the distribution of which is known exhaustively, is a key process in predicting extent and distribution of biological communities. Extent and distribution are key metrics for reporting under Article 17 of the Habitats Directive. Combinations of GIS, geostatistical, General Additive Modelling (GAMs) and ordination statistical and modelling methods can all be used to derive predictive habitat maps using a combination of exhaustively sampled physical habitat data and less well sampled biological data (e.g. ICES WGMarine Habitat Mapping) to produce baseline habitat maps for setting of conservation objectives and targets.
Monitoring for change and avoidance of and or detection of deterioration in habitats and mitigating these effects is central to the proper implementation of the Habitats Directive (Articles 6, 11 and 17). Change can be estimated by comparing the structure (species composition) of a marine community at one time compared to another time using multi-variate classification and ordination methods and the species contributing to such change can be identified. This information may provide indicators as the to the cause of change given that some species may respond to certain variables such as temperature, acidification or abrasion from fishing gears for instance. Such change also infers that the modelled relationships between physical terrain variables, which are mostly constant in time, and biological communities also changes. Although samples taken at the same approximate point over time may show shifts in biological communities assessing why such changes occur and their spatial extent requires re-sampling. The sampling design required to assess the spatial extent of change would need to consider how or if such areas were exposed to particular pressures and to re-assess some of the underlying physical variables that may vary in time. The statistical power of such monitoring programmes need to be considered against management objectives which would include maximum thresholds for change and the need for mitigation when thresholds are exceeded.
1. Map physical reef habitat from existing multibeam and LIDAR data
2. Extract physical terrain variables for mapped reef habitat and identify sub-categories of reef on which to base future stratified biological sampling programmes. This would also include other modelled spatial variables such as temperature, depth and kinetic energy to inform the categorization
3. Sample biological communities within a number of reef sub-types using state of the art remote quantitative methods.
a. Initial work on this will be done in 2021 in Kilkieran Bay and an exposed reef area in deeper water with a view to expanding biological sampling across sites in the future.
4. Model the relationship between biology and physical/environmental variables within reef sub-types at fine spatial scale
This project began in 2021 and was due to run for 2 years. It is now being extended to complete in 2023
1. Methods developed for quantitative assessment of reef biological communities
2. The extent of Annex I geogenic reef habitat and its sub-categories in coastal waters
3. Modelled extent of biological communities in reef sub-categories
4. A methodology for quantitative sampling and assessing the extent of Annex I habitat
1. A tried and tested methodology to be applied in the National Conservation Status Monitoring of Reefs to be carried out in 2022 and onwards, as part of the Article 17 reporting under the Habitats Directive.
2. Improvement in Ireland’s understanding of its inshore reef habitats, with consequent benefits for the implementation of the Habitats Directive here.