Sunday, 29 May 2016

Rockpooling destination: Revisit West Penwith, March 2016

The rocky shore is comprised of boulders and bedrock with rockpools, crevices and gullies. Habitat classification: LR.HLR (High energy littoral rock) EUNIS: A1.1 , LR.FLR.Rkp (Rockpools) EUNIS:A1.41 and LR.FLR.Lic.(Lichens on supralittoral and littoral fringe rock) EUNIS: B3.11

The rocky shore is a high energy environment comprised of boulders and bedrock with rock pools, crevices and gullies.

The high energy environment of the shore leads to an extended lichen zone, that descends over much of the boulder field, which apart from Littorinids is relatively barren. Patches of lichens extend further down into the barnacle communities, which dominate from the upper to lower shore, inter-dispersed by shallow coralline rockpools in the mid shore, and deeper cobble filled rockpools on the lower shore. As the low tide mark is reached wave tolerant seaweeds lace the gullies.

Habitat classification:

LR (Littoral rock)
LR.HLR (High energy littoral rock)
LR.FLR (Features of littoral rock)
Biotope complex
LR.HLR. MusB (Mussel and/or barnacle communities)
LR.HLR.FR (Robust fucoid and/or red seaweed communities)
    LR.FLR.Lic.(Lichens on supralittoral and littoral fringe rock).
LR.FLR.Rkp (Rockpools)
LR.HLR.MusB.Cht (Chthamalus sp on exposed upper eulittoral rock)
LR.HLR.MusB.Sem (Semibalanus balanoides on exposed to moderately exposed or vertical sheltered eulittoral rock)

LR.FLR.Lic.Ver (Verrucaria Maura on  littoral fringe rock)
LR.FLR.Lic.YG (Yellow and grey lichens on supralittoral rock)
LR.FLR.Rkp.Cor (Coralline crust dominated shallow eulittoral rockpools)
Below are images of the organisms you may encounter in these habitats:

Among the mobile boulders of the littoral fringe are populations of rough and small periwinkles. In this high energy environment organisms are confined to crevices and nooks, where they are buffeted from the full force of the waves and potential dislodgement. Habitat classification:  LR.FLR.Lic.(Lichens on supralittoral and littoral fringe rock) EUNIS: B3.11

Small and rough periwinkles aggregate in a boulder crevice.

Wave exposure drives the distribution of many organisms on the shore. A larger boulder provides shelter from the waves and resists rolling enabling it to support a community of limpets, periwinkles and barnacles.

Waves pick up and roll boulders that lie within the gullies ‘ grinding’ away much of the epifauna. Those that survive seek refuge within crevices of the bedrock or, occur on larger boulders/bedrock that is not subjected to the same forces.

However, during winter storms even the bedrock fractures and comes away! Demonstrating the strength of the waves hitting these shores and the ability of wave exposure  to modify the environmental conditions experienced by the organisms and/or dislodge the organisms themselves!

Exposed uppershore bedrock is covered in dense barnacles, with crevices jammed by mussels, anemones and coralline seaweeds. Small periwinkles occur among the barnacles, seeking shelter within the dead barnacle tests. The black lichen Lichina pygmaea forms tufts on the upper rock. All these organisms are characteristic of the biotope: LR.HLR.MUSb.CHT (Chthamalus sp on exposed upper eulittoral rock) EUNIS: A1.112.

Mussels (M. edulis) on the edge of a coralline rockpool

At this time of year the ephemeral seaweeds within rockpools, Fucoids and some patches of Lichina pygmaea have died back.

  There is also ‘New life’ as young fucoid fronds defy the elements

On areas of lower lying bedrock and boulders seaweeds, topshells and dog whelks increase in abundance. The lichen V mucosa is characteristic of this biotope, as is an increase in fucoid and red seaweeds, such as Osmundea sp with the relative abundances varying throughout the year. Topshells, dogwhelks, anemones and Patella depressa are also characteristic. Habitat classification: LR.MUSb.Sem (Semibalanus balanoides on exposed to moderately exposed or vertical sheltered eulittoral rock) EUNIS: A1.113.

Patella depressa among barnacles and limpets.

Shallow coralline rockpools of the upper to mod eulittoral. Habitat classification: LR.FLR.Rkp.Cor (Coralline crust dominated shallow eulittoral rockpools) EUNIS:A1.411.

Scytosiphon lomentaria is present in some of the rockpools, as the season goes on this will be one of the most common brown seaweeds in the coralline rockpools of the upper eulittoral.
At this time of year the ephemeral seaweeds within rockpools have died back, whilst the coralline and perennial brown seaweeds are beginning to show new growth. These coralline rockpools of the mid and lower eulittoral support a greater diversity of seaweeds, including Bifurcaria bifurcata, Corallina officinalis, coralinaceae crusts and the early growths of ephemeral green seaweeds, along with beadlet anemones, china limpets, flat topshells and thick topshells.
The snakelocks anemone occurs in the shallow coralline rockpools of the lower eulittoral.

Seaweeds are almost absent from the rockpools of the lower shore at this time of year. Possible due to the ‘grinding’ nature within these pools during this time of year. The only seaweed to persist is an ephemeral green.