Friday, 18 March 2016

Characterising species of the littoral fringe rock


The littoral fringe zone occurs between the supralittoral and eulittoral zones and in some cases is considered a terrestrial habitat i.e. within the EUNIS classification it is placed with the coastal habitats and the supralittoral and littoral fringe lichen communities come under the one broad habitat complex, Lichens or small green algae on supralittoral and littoral fringe rock B3.11. 

The littoral fringe receives the salt spray from the waves, as such, those shores experiencing greater exposure and salt spray from waves have larger littoral fringe zones. Rock altitude, angle, shade and local climate also influence the extent of the zone. These factors also effect the distinction between the supralittoral and littoral fringe communities so that sometimes they are distinct or are intermingled.

The littoral fringe zone is often characterised by rocks covered in the black tar lichen (Verrucaria maura), rough periwinkles, channel wrack, ephemeral seaweeds, sparse barnacles and pools with variable salinity and temperatures. 

Other organisms that come under the broad lichen habitat complex (LR.FLR.Lic) that are also characteristic of littoral fringe communities are green seaweeds such as Blidingia sp, Ulothrix sp and Urospora sp that can characterise areas of littoral fringe soft rock or vertical rock where there is fresh water run off. 

The organisms living in this zone are highly specialized to endure variable salinity and extended periods of air exposure.  

The littoral fringe can often be discernible from a distance by the presence of the black tar lichen (Verrucaria maura) that covers the rock, above which the rocks of the supralittoral appear light grey whilst below the rocks of the eulittoral appear beige.

High wave exposure leads to an extended splash zone enabling lichens to colonise further up the cliffs. In the photograph above two distinct bands of differing lichen communities can be seen. At the highest position on the supralittoral are yellow and grey lichens, whilst on the littoral fringe below V. maura covers the bedrock. Habitat classification: LR.FLR.Lic.YG (Yellow and grey lichens on supralittoral rock) EUNIS: B3111 and LR.FLR.Lic.Ver (Verrucaria maura on littoral fringe rock) EUNIS: B3.113.

Variations in rock altitude can lead to a mosaic like distribution of the supralittoral and littoral fringe lichen communities. Also at this altitude on the shore fluctuating temperatures and salinity lead to prolific growth of Ulva spp (formally Entomorpha spp) in some of the rockpools. Habitat classification: LR.FLR.Lic.YG (Yellow and grey lichens on supralittoral rock) EUNIS: B3111, LR.FLR.Lic.Ver (Verrucaria maura on littoral fringe rock) EUNIS: B3.113 and  LR.FLR.Rkp.G (Green seaweeds (Entomorpha spp. and Cladophora spp.) in shallow upper shore rock pools) EUNIS: A1.421. 

The lichen communities are not always present on unstable rock substrates, and this can make the distinction between the the supralittoral and littoral fringe difficult. On the shore above the supralittoral and littoral fringe rock is distinguishable by its 'white colour' as these boulders do not experience daily submergence. The yellow and grey lichens of the supralittoral are able to grow on the boulders of the most upper shore that have been thrown up during storms and are only rolled during the most extreme storms, however the remaining boulders of the supralittoral and littoral fringe are rolled just enough during periodic storms to prevent their growth.

On the shore above the boulders are larger and more stable allowing for a more established and diverse lichen community to develop. The black tar lichen (V. maura) is still absent from many of the boulders that would occupy the altitude of the littoral fringe but does occur on the bedrock of this height. On the boulders where the V. maura is absent the littoral fringe is identified by the presence of other organisms, including rough (Littorina saxatilis) and small periwinkles (Melarhaphe neritoidesand sparse barnacles. The ineffective application of the JNCC and EUNIS habitat classification to the littoral fringe boulder habitat is rectified by the much broader 1993 phase 1 habitat classification which seems to capture these environments under the boulder habitat classification which is in turn listed under the EUNIS website as comparable to the habitat classification supralittoral rock (lichen or splash zone).

On stable bedrock the black lichen, V. maura is one of the most characteristic species of the littoral fringe. Living among this lichen you may also encounter L. saxatilis, ephemeral seaweeds and sparse barnacles. Because of the extended period of exposure the organisms tend to aggregate in crevices or shaded areas in order to reduce desiccation. The rockpools of the littoral fringe are species poor. Fluctuating temperatures and salinity lead to prolific growth of Ulva spp (formally Entomorpha spp) in some of the rockpools whilst others support the occassional amphipod. Habitat classification: LR.FLR.Lic.Ver (Verrucaria maura on littoral fringe rock) EUNIS: B3.113 and  LR.FLR.Rkp.G (Green seaweeds (Entomorpha spp. and Cladophora spp.) in shallow upper shore rock pools) EUNIS: A1.421. 

A characteristic species of the lower littoral fringe rock of some shores is channel wrack (Pelvetia canaliculata) and on moderately exposed shores an accompanying spare barnacle community. Habitat classification: LR.MLR.BF.PelB (Pelvetia canaliculata and barnacles on moderately exposed littoral fringe rock) EUNIS: A1.211.

P. canaliculata cover increases on sheltered shores and the there is no associated barnacle community. Habitat classification: LR.LLR.F.Pel (Pelvetia canaliculata on sheltered littoral fringe rock) EUNIS: A1.321.

Monday, 7 March 2016

Rockpooling destination: Hemsby, March 2016

During the months of February and March the eggcases of a variety of rays, skates and catshark are washed up onto the Norfolk shores. Common eggcases that can be found include the Thornback and Spotted ray and the curly ended eggcases of the catshark. Sometimes you can find the larger Blonde ray eggcases.

A walk along the shore turned up some nice mermaid purses and lots of the bryozoan, Flustra foliacea.