The purpose of this study is to produce a series of Conceptual Ecological Models (CEMs)
that represent sublittoral rock habitats in the UK. CEMs are diagrammatic representations of
the influences and processes that occur within an ecosystem. They can be used to identify
critical aspects of an ecosystem that may be studied further, or serve as the basis for the
selection of indicators for environmental monitoring purposes. The models produced by this
project are control diagrams, representing the unimpacted state of the environment free from
anthropogenic pressures.
It is intended that the models produced by this project will be used to guide indicator
selection for the monitoring of this habitat in UK waters. CEMs may eventually be produced
for a range of habitat types defined under the UK Marine Biodiversity Monitoring R&D
Programme (UKMBMP), which, along with stressor models, are designed to show the
interactions within impacted habitats, would form the basis of a robust method for indicator
selection. This project builds on the work to develop CEMs for shallow sublittoral coarse
sediment habitats (Alexander et al 2014).
The project scope included those habitats defined as ‘sublittoral rock’. This definition
includes those habitats that fall into the EUNIS Level 3 classifications A3.1 Atlantic and
Mediterranean high energy infralittoral rock, A3.2 Atlantic and Mediterranean moderate
energy infralittoral rock, A3.3 Atlantic and Mediterranean low energy infralittoral rock, A4.1
Atlantic and Mediterranean high energy circalittoral rock, A4.2 Atlantic and Mediterranean
moderate energy circalittoral rock, and A4.3 Atlantic and Mediterranean low energy
circalittoral rock as well as the constituent Level 4 and 5 biotopes that are relevant to UK
waters. A species list of characterising fauna to be included within the scope of the models
was identified using an iterative process to refine the full list of species found within the
relevant Level 5 biotopes.
A literature review was conducted using a pragmatic and iterative approach to gather
evidence regarding species traits and information that would be used to inform the models
and characterise the interactions that occur within the sublittoral rock habitat. All information
gathered during the literature review was entered into a data logging pro-forma spreadsheet
that accompanies this report. Wherever possible, attempts were made to collect information
from UK-specific peer-reviewed studies, although other sources were used where
necessary. All data gathered was subject to a detailed confidence assessment. Expert
judgement by the project team was utilised to provide information for aspects of the models
for which references could not be sourced within the project timeframe.
A multivariate analysis approach was adopted to assess ecologically similar groups (based
on ecological and life history traits) of fauna from the identified species to form the basis of
the models. A model hierarchy was developed based on these ecological groups. One
general control model was produced that indicated the high-level drivers, inputs, biological
assemblages, ecosystem processes and outputs that occur in sublittoral rock habitats. In
addition to this, seven detailed sub-models were produced, which each focussed on a
particular ecological group of fauna within the habitat: ‘macroalgae’, ‘temporarily or
permanently attached active filter feeders’, ‘temporarily or permanently attached passive
filter feeders’, ‘bivalves, brachiopods and other encrusting filter feeders’, ‘tube building
fauna’, ‘scavengers and predatory fauna’, and ‘non-predatory mobile fauna’. Each sub-model
is accompanied by an associated confidence model that presents confidence in the links
between each model component. The models are split into seven levels and take spatial and
temporal scale into account through their design, as well as magnitude and direction of
influence. The seven levels include regional to global drivers, water column processes, local
inputs/processes at the seabed, habitat and biological assemblage, output processes, local
ecosystem functions, and regional to global ecosystem functions.
The models indicate that whilst the high level drivers that affect each ecological group are
largely similar, the output processes performed by the biota and the resulting ecosystem
functions vary both in number and importance between groups. Confidence within the
models as a whole is generally high, reflecting the level of information gathered during the
literature review.
Physical drivers which influence the ecosystem were found to be of high importance for the
sublittoral rock habitat, with factors such as wave exposure, water depth and water currents
noted to be crucial in defining the biological assemblages. Other important factors such as
recruitment/propagule supply, and those which affect primary production, such as
suspended sediments, light attenuation and water chemistry and temperature, were also
noted to be key and act to influence the food sources consumed by the biological
assemblages of the habitat, and the biological assemblages themselves.
Output processes performed by the biological assemblages are variable between ecological
groups depending on the specific flora and fauna present and the role they perform within
the ecosystem. Of particular importance are the outputs performed by the macroalgae
group, which are diverse in nature and exert influence over other ecological groups in the
habitat. Important output processes from the habitat as a whole include primary and
secondary production, bioengineering, biodeposition (in mixed sediment habitats) and the
supply of propagules; these in turn influence ecosystem functions at the local scale such as
nutrient and biogeochemical cycling, supply of food resources, sediment stability (in mixed
sediment habitats), habitat provision and population and algae control. The export of
biodiversity and organic matter, biodiversity enhancement and biotope stability are the
resulting ecosystem functions that occur at the regional to global scale.
Features within the models that are most useful for monitoring habitat status and change
due to natural variation have been identified, as have those that may be useful for monitoring
to identify anthropogenic causes of change within the ecosystem. Biological, physical and
chemical features of the ecosystem have been identified as potential indicators to monitor
natural variation, whereas biological factors and those physical /chemical factors most likely
to affect primary production have predominantly been identified as most likely to indicate
change due to anthropogenic pressures