Rockpooling Destination: Happisburgh, Artificial sea defences, August 2015

The shore at Happisburgh is comprised of mobile sands and shingle, due to high rates of coastal erosion, artificial sea defences have been erected to protect the cliffs. The defences change the dynamics of the shore and provide a hard substrate for organisms to colonise.

The hard substrate of the wooden sea defences is characterised by lichen, barnacle, gastropod and seaweeds that comprise littoral fringe and sand scour tolerant communities.

The wooden sea defences provide a stable hard substrate in an otherwise mobile sand and shingle shore. Habitat classification: LR (Littoral rock) and LS.LSa.Sh (Shingle and gravel shores) EUNIS: A2.11.

The wooden sea defences support an assemblage akin to a 'rocky shore' community that exhibits zonation in altitude. A black lichen and  small periwinkles (Melarhaphe neritoides) mark the upper vertical extent of the intertidal communities that colonise the wooden sea defences. Habitat classification: Similar to LR.FLR.Lic (Lichens or small green algae on supralittoral and littoral fringe rock) EUNIS: B3.11.

Small periwinkles (M. neritoides) aggregate in wood crevices. 

On the leeward side of the wooden defences, about 1m from their base, barnacles (Elminius modestus and Semibalanus balanoides), periwinkles (Littorina spp and M. neritoides) and occasional Fucus spiralis occur amongst a wider distributed covering of ephemeral green and red (Porphyra spp) seaweeds. Habitat classification: LR.FLR.Eph.EntPor (Porphyra purpurea and Entomorpha spp. on sand scoured mid and lower eulittoral rock) EUNIS: A1.452.

Organisms that have colonised the wooden sea defences demonstrate an aggregated distribution in accordance to their tolerance to wave exposure and sand abrasion.  Sand scour tolerant ephemeral seaweeds cover large areas of the wooden defences and extend lower than the barnacles due to their opportunistic nature, fast growth and ability to withstand the sand abrasion. Above in the leeward side of the defences F. spiralis and barnacles occur and among the barnacles and within crevices periwinkles (Littorina spp and M. neritoides) and limpets. The organisms do not extend to the lower base of the sea defences due to variability in sand movement, abrasion and potential smothering.