Saturday, 17 May 2014

Rockpooling destination: Revisit Seapalling, April 2014

The shore at Seapalling is influenced by a series of artificial sea defences that have changed the dynamics of the shore to produce multiple bays comprised of mobile sands with shingle berms in between.

The hard substrate is characterised by a barnacle community with periwinkles, limpets, dog whelks and beadlet anemones. The lower edges of the breakwater harbour occasional seaweeds, whilst beneath the sea defences are a network of tidal pools.

Since February certain features of the shore have changed, namely reduced strandline, decreased sand height and increased ephemeral algae.

Habitat classifications:

LR (Littoral rock)
LS (Littoral substrate)
HLR (High energy littoral rock)
FLR (Features of littoral rock)
LS.LSa (Littoral sand)
Biotope complex
LR.HLR. MusB (Mussel and/or barnacle communities)
Rkp (Rockpools)
Eph.FLR.Eph (Ephemeral green or red seaweed communities (Shingle and gravel shores)
LS.LSa.MoSa.BarSa (Barren littoral coarse sand)

LR.FLR.Eph.EntPor (Porphyra purpurea and Entomorpha spp. on sand scoured lower eulittoral rock)

Below are images of organisms you may see whilst rock pooling in this location:

The sea defences provide an artificial hard substrate amongst the littoral sediments of the shore. The defences take the brunt of the waves.   Habitat classification: LR.HLR (High energy littoral rock) and LS.LSa (Littoral sand).

The sea defences comprise large rectangular boulders that have relatively shear faces which support rocky shore communities comprised of barnacles, limpets and periwinkles. Habitat classification:  LR.HLR.MusB (Mussels and/or barnacles in high energy littoral rock).
The littoral sediments surrounding the sea defences continually experience the dynamic forces of erosion and deposition.  Since February there has been deposition of finer sediment at the base of the sea defences at this location.

The same location as above but a few months previous shows how the sediment distributions have changed since February.

Other locations have experienced increased erosion reflected in the distribution of the barnacles. Erosion of sediment has provided new areas for settlement, resulting in a distinct barnacle size distribution. With a band of more recently settled and smaller barnacles on the recently available substrate below the more established barnacle community above. 

Variability in barnacle size gives an indication of the changing availability of substrate on the shore. Smaller, younger barnacles mark out those areas previously under sand.

The white tests of dead barnacles mark a previous height of the sand. 

Rocks covered in the dead tests of barnacles indicate that the sand was previously at a higher level, and their distribution suggest that the sand is lower than it had been when they originally colonised the rock.

Spiral wrack (Fucus spiralis) has experienced regrowth since February (see image below).
Spiral wrack (Fucus spiralis) in February.

Ephemeral seaweeds have increased in abundance and cover many of the lower shore rocks. Habitat classification: LR.FLR.Eph.EntPor (Porphyra spp.and Entomorpha spp. on sand scoured lower eulittoral rock)

Porphyra spp. occur on the sand scoured lower shore rocks.

A small coralline rockpool within the sea defences supports a number of seaweeds, limpets, and a serpulid polychaete all of which are subject to the dynamic nature of the shore at Seapalling. Habitat classification:  LR.FLR.Rkp (Rockpools).

This photo from February shows the same rock pool full of sand

A beadlet anemone (Actina equina) within its tentacles out within a rock pool.
A beadlet anemone (Actina equina) within its tentacles withdrawn to conserve water whilst exposed to the drying air.

A common star fish (Asterias rubens)

Thursday, 8 May 2014

Revisit Lands End Peninsular, April 2014

The dynamic nature of the sediment regime at this cove is exemplified by the following images taken four months apart over the winter.

Since September winter storms have eroded the overlying sand at the top of the shore to reveal the boulders beneath.

The shore is still comprised of boulders and now ephemeral green and red seeweeds are covering areas of recently exposed rock. Other fauna  such as limpets and periwnkles remain in their original locations and have not moved to colonise the newly available substrate.

Sand in September 2013 has now been eroded to reveal a cobble and boulder beach (below). (September habitat classification: LS. Sa (Littoral sand)

Cobbles and boulders now characterise the upper shore. (January and April habitat classification LR (Littoral rock).
Sand in September 2013 has now been eroded to reveal a cobble and boulder beach (below)

Cobbles and boulders now characterise the upper shore.
Where once there was sand, now there are rock pools. Habitat classification in September LS.Sa (littoral sand), now LR.FLR.Rkp (Rockpools).

A seasonal explosion of ephemeral green seaweeds covers expanses of the recently available stable rock, which in January was still bear (see images below). Habitat classification: LR.FLR.Eph (Ephemeral green and red algae - fresh water or sand influenced)

Lower on the shore Porphyra sp also colonises the boulders.
Habitat classification: LR.FLR.Eph (Ephemeral green and red algae - fresh water or sand influenced)

Images of the shore previously this year:

September 2013                    January 2014
The overlaying sand has been eroded to reveal the boulders beneath.

September 2013                    January 2014
The overlaying sand has been eroded to reveal the boulders beneath.

Tuesday, 6 May 2014

Additional factors that affect the distribution of habitats:

Many environmental factors interact to determine the distribution of habitats across the shore.

Exposure to air, whilst the tide is out also influences the distribution of organisms and hence the distribution of communities and habitats on the shore. Many organisms show behavioural adaptations to reduce drying out whist exposed to the air and will become inactive in a shady location such as a crevice with other individuals, and clamp down their shells or, reduce their surface area by curling up, so that they can conserve as much water as possible.

Anemones close up to conserve water

Crabs bury in the damp sand.

The longer the period of air exposure the more specialised to with stand the physiological stresses an organism has to be, so that only those specific organisms with the advantages adaptions to with stand being out of the water for prolonged period of the time will occur at the top of the beach. That isn’t to mean that these organisms can’t occur lower down, in deed in many cases they do. It’s just that lower down other organisms who didn’t cash in on the ability to with stand drying out developed abilities which made them competitively superior to and more abundant than the upper shore organisms once conditions became more gentile.

Small and rough periwinkles are characteristic higher shore species.
So the nearer the low tide mark you get, the less physiological stress organisms experience due to exposure to air, and instead increased competition for space is experienced. Therefore anything that increases the available space increases the number of species that can co- occur. Seaweeds, boulders, gullies and rock pools all increase space and species diversity.

Under-boulder environments increase the surface area and complexity enabling more species to be supported.

Of all of these rock pools provide the greatest refuge from the reseeding tide as it provides constant emersion, allowing species less adapt at withstanding desiccation to flourish on the shore and it is because of this and the unique communities that rock pools support that they have their own habitat classifications associated with them. As rockpools can occur across a range of wave exposures these habitats are broadly known as features of littoral rock habitats.
Rockpools can act as refuges from dessication.

Salinity and sand scour can also influences the communities found, with areas experiencing reduced salinity characterised by seaweeds such as estuary wrack or in areas of reduced salinity or sand scour, ephemeral green and red seaweeds. 

A ephemeral seaweed habitat influenced by sand scour.

Monday, 5 May 2014

Examples of features of littoral rock habitats:

Wave exposure can be a major driver in determining the communities and hence habitats present on a shore. However, there are some factors that influence communities that can occur across the spectrum of wave exposures and are classified as features of littoral rock.

Below are example images of these habitat types:

LR.FLR.Lic (lichens and small green algae of littoral rock)

LR.Rkp (Rockpools)

LR.FLR.CvOv (Littoral caves and overhangs)

 LR.FLR.Eph (Ephemeral green or red seaweed communities - fresh water or sand influenced). Here the red seaweed Porphyra sp occurs on the shore where there is sand scour.

 LR.FLR.Eph (Ephemeral green or red seaweed communities - fresh water or sand influenced). Here green ephemeral seaweed occurs where there is fresh water run off.