Rock Pooling Destination: Porth Seal, Isles of Scilly, UK. April 2013

The rock pools at Porth Seal vary with those in the upper shore characterized by the green seaweeds Cladophora and Ulva spp; whilst mid shore pools are dominated by encrusting coralline algae and a variety of red and brown seaweeds; further down the shore brown seaweeds, such as Bifurcaria bifurcata and Himanthalia elongata, become more prolific within the coralline pools with red seaweeds occupying the understory. Above the pools is a mosaic of fucoids, osmundea, grazing molluscs and barnacles.


Spring storms had washed large quantities of seaweed up onto the shore where it formed mounds marking the successive strand lines and filled many of the higher to mid shore pools. The presence of the decomposing seaweed in the pools caused the water to become de-oxygenation and stagnant. The spring storms also deposited sand into many of the higher and mid shore pools that formed a thick layer over the pre-existing coralline algae and facilitated the growth of ephemeral green seaweeds such as Cladophora spp. In comparison to April 2012 these pools appeared to contain less mobile fauna (fewer gastropods and no sea hares were observed).

Below are photographs of some of the organisms in these pools:


                                        

Spring storms had washed large quantities of seaweed on the shore.

The washed up seaweed filled many of the higher to mid shore pools.

 The presence of the decomposing seaweed in the pools caused the water to become de-oxygenation and stagnant.

The rocky shore is comprised of bed rock and boulders interspersed with rockpools and gullies. Biotope classification:  LR.MLR (Moderate energy littoral rock).

 The mid and upper shore is charecterised by mosaics of barnacles and fucoids.

Barnacles

The shallow rock pools of the upper and mid shore that have not been smothered by sand or seaweed are charecterised by corallinacea crusts. Biotope classification:   

LR.FLR.Rkp.Cor (Coralline crust-dominated shallow eulittoral rockpools).

A corallinacea crust dominated rock pool with Coral weed (Corallina officinalis), Beadlet anemone (Actinia equina), Topshell (Gibbula umbilicus) and a blenny. 

A beadlet anemone (Actinia equina)

A mussel (Mytilus edulis)

A coralline pool dominated by ephemeral green seaweeds; coralline crusts can still be seen beneath the sand.

Sand covers the Corallinacea crust and the pool is dominated by ephemeral green seaweeds.

Mid shore pools are less effected by the deposition of seaweed and contain more seaweed species.

Coral weed (Corallina officinalis) 

Ceramium Spp 

Codium fragile 

Codium fragile on the mid shore.

 Bushy rainbow wrack (Cystoseira tamariscifolia).

Cladophora rupestris

Calliblepharis jubata

Polychaetes

Daisy anemone (Cereus pedunculatus)



Gem anemone (Aulactinia verrucosa)

  Bifurcaria bifurcate dominates certain pools of the lower shore. Biotope classification: LR.FLR.Rkp.Cor.Bif Bifurcaria bifurcata in shallow eulittoral rockpools.

Serrated wrack (Fucus serratus) dominates the lower shore with red seaweeds beneath its understory. Biotope claasification: LR.MLR.BF.Fser.R (Fucus serratus and red seaweeds on moderately exposed lower eulittoral rock).

Red seaweeds form mosaics amongst the serrated wrack (Fucus serratus). Sand binder (Rhodothamniella floridula) forms a truf whilst Osmundea spp occurs within crevices and cracks of the boulders.

Osmundea spp

A limpet (Patella vulgata) and barnacles

Grape pip weed (Mastocarpus stellatus)

Corallinacea crust, Corallina officinalis , Bifurcaria bifurcata, The limpet Patella vulgata and snakelocks anemone (Anemonia viridis) occur on a boulder amongst Serrated wrack (Fucus serratus).

Corallinacea crust occurring on the lower shore.

Coral weeds (Corallina spp ) form dense turfs on the lower shore.

Dahlia anemone (Urticina felina)

Purse sponge (Grantia compressa)

Further down the shore Thong weed (Himanthalia elongata) occurs amongst red seaweeds.

Common Seaweeds of the shore - Wracks (Part 1)

Seaweeds are often the most conspicuous organisms of the rocky shore and are vital to the intertidal ecosystem, providing food, shelter and a substrate upon which to grow.

There are hundreds of species of seaweed in the UK and these are broadly divided into groups depending on their colour: reds (Rhodophyta), greens (Chloropyhta) and browns (phaeophyta).

The most familiar of the brown seaweeds are the wracks. Wracks can dominate the shore and are often used as the characterising species of a habitat.  For example LR.LLR.F Fucoids on sheltered marine shores.  Wracks can exhibit zonation where horizontal bands of the shore are characterized by a particular species of wrack, these patterns can be useful in inferring the hydrodynamic regimes of a shore and extent of exposure during low tide.

Below are images of wracks you may encounter whilst rock pooling in the UK.

Channel wrack (Pelvetia canaliculata), named after the furrow or, channel that forms as a result of the rolled fronds. Channel wrack is found in the upper shore of sheltered to exposed rocky shores.

Channel wrack (Pelvetia canaliculata)

Channel wrack (Pelvetia canaliculata)

Spiraled wrack (Fucus spiralis), is twisted as it hangs and has a midrib running down each frond. Spiraled wrack occurs in the upper shore below the band of channel wrack

Spiraled wrack (Fucus spiralis)

Bladder wrack (Fucus vesiculosus) has lots of swollen sacks formong pairs either side of its frond. Bladder wrack is found on exposed and sheltered coasts on the mid to lower shore.



Egg wrack (Ascophyllum nodosum) is long with a more rubbery texture than bladder wrack with oval to egg shapped bladders within its fronds. Egg wrack occurs on the mid shore and in sheltered locations can form huge expances.

Egg wrack (Ascophyllum nodosum)

Serrated wrack (Fucus serratus) has a toothed edge to its frond which is also hairy, it has no bladders and is found in the mid to lower shore where it can dominate.

Serrated wrack (Fucus serratus) dominates the lower shore

Serrated wrack (Fucus serratus), close up showing the hairy frond