Rockpool surveys


This page is dedicated to rockpool survey results carried out for ‘Pembrokshire Scientific Rockpools Surveys’, and ‘The Rockpool Project’ ( ). The purpose of these surveys is to monitor fluctuations and possible longer term changes in variety and abundance of species.

Photo-mosaics are used to record the rockpool at the time of each survey. The variety and abundance data were obtained using these photo-mosaic images rather than directly in the field (this is an experimental approach). The complete high resolution photo-mosaics can be viewed by clicking on the individual images in ‘Monthly photo-mosaics’ section below. (Further examples illustrating this technique are available on this website here. )

The specific type of rockpool selected for these surveys is described below.

The rock pool

The rockpool lies in Pwllaelod bay on the north Pembrokeshire coast. It is typical of a lot of pools in this area insofar as it is an striking pink colour. This colouration is due to a pink covering on the rocks below the water line and the presence of pink-red seaweeds within the pool itself.

Different types of rock pool provide distinct habitats and many of those around the coast of the UK and Ireland, have been classified by the Joint Nature Conservation Council (JNCC).

Under the JNCC scheme these characteristically pink rockpools are classified as;

Coralline crusts and Corallina officinalis in shallow eulittoral rock pools

This name is also designated, using the JNCC hierachical nomenclature, as LR.FLR.Rkp.Cor.Cor, which means; a habitat defined by Coralline crusts and Corallina officinalis (Cor.Cor) which appear as Features of Littoral Rock (FLR) in Rockpools (Rkp) in Littoral Rock (LR) (littoral rock includes bedrock, boulders and cobbles).

The key to this designation is therefore the presense of the two pink-red elements ‘Coralline crust’ and ‘Corallina officinalis’. Coralline crust is an encrusting red algae and Corallina officinalis’ a calcareous red seaweed. Both these elements are shown in Figure 2.

This type of rockpool is typically shallow and sunlit. The table below, which was taken from the JNCC website, lists some of the flaura and fauna typical of these rockpools and their relative abundances.

TaxonRelative importance of taxon for defining this community (%)Typical abundance – SACFOR scale% of core records where taxon was recorded
Corallina officinalis24Common81-100%
Ceramium nodulosum7Frequent41-60%
Littorina littorea7Common41-60%
Patella vulgata7Frequent41-60%
Actinia equina4Occasional41-60%
Mytilus edulis3Occasional21-40%
Mastocarpus stellatus2Occasional21-40%
Ulva lactuca2Occasional21-40%
Semibalanus balanoides1Occasional21-40%
Chondrus crispus1Occasional21-40%
Nucella lapillus1Occasional21-40%
Table 1. Species summary for “Coralline crusts and Corallina officinalis in shallow eulittoral rock pools

Rockpool N1

The specific rockpool, designated N1 (North 1), lies at the mid-shore level of the north of the bay. It is the larger of a cluster of similar pools as shown in shown in figure 3 below.


Species counts from monthly survey are presented in Table 2 below along with corresponding image mosaics and more general observations and notes.


Littorina littorea7043364820212431
Patella vulgata5049484044414242
Actinia equina158788779
Gibbula umbilicalis35930210
Corallina officinalis
Ceramium nodulosum
Mytilus edulis
Mastocarpus stellatus
Ulva lactuca
Semibalanus balanoides
Chondrus crispus
Nucella lapillus
Aulactinia verrucosa
Cereus pedunculatus
Table 2. Monthly species count for rockpool N1.

Monthly photo-mosaics



  1. Mosaic processing error – additional photographs used for counts.
  2. Storm or rough weather since previous survey – rockpool cleaned and scoured of epiphytic growth on, e.g. coral weed. Colonies of daisy anemones visible again.
  3. Lots of red seaweed and laminaria strewn along beach and in rockpool. Large areas of bryzoan.
  4. Reduction in limpets seems to be real (e.g. reduced numbers along bottom shore)
  5. Questions:
    • Is the scouring action of rough weather a requirement of the eco-system, i.e. like fire ir strong winds in forest habitats?
    • Ho do daisy anemones attach to the rockpool bottom when covered in gravel?

September 2022