Assynt’s seashores are a perpetual source of delight. Whether sandy or rocky, sheltered or exposed, there is always something new to see and wonder about.
Such was the case on 15th June, when we paid a brief visit to Balchladich Bay (NC0328) on a very low tide (0.9m asl). The beach here is very exposed and, as a result, an ever-changing mix of rock, shingle and sand, nearly always with huge banks of cast-up kelp and wrack.
There are spectacular views southwards towards the hills of Torridon and Skye (photos 1-2), but on this occasion our attention was drawn to a dense scatter of smooth-topped boulders exposed by the low tide in the northern half of the beach (photo 3).
Boulders
They were a range of banded, usually grey, but sometimes pinkish, Lewisian gneisses and reddish-brown Torridonian sandstones.
The first boulder (photo 4) was pinkish gneiss, with shallow crevices providing cover for young barnacles, probably the northern rock barnacle Semibalanus balanoides. Clustered at its base was a mass of grey periwinkles, probably edible periwinkles Littorina littorea.
The second (photo 5) was banded gneiss, with patchy, mostly young, barnacles, and clusters of periwinkles, mostly edible, but with a few stripy rough periwinkles L. saxatilis.
The third (photo 6) was definitely sandstone, and plastered with barnacles. Closer inspection revealed that these were in two age classes, with older examples almost all empty, surrounded by smaller greyish spat. A few limpets Patella vulgaris were present in open areas, and, clustered around the base were paler dog whelks Nucella lapillus, and more periwinkles.
The fourth (photo 7) was also sandstone, the barnacle spat roughly in rows, corresponding to the strata in the rock, with a few empty older examples. There were again a few limpets, surrounded in this case by barnacles, with dog whelks and periwinkles at the base.
These few observations posed a number of questions. Gneiss is much harder than sandstone; does this consistently affect the patterns of colonisation? Barnacles are stationary filter feeders, selectively predated by highly mobile dog whelks; are the swathes of empty old shells the result of 100% predation or just age?
Edible and rough periwinkles are quite mobile grazers and we need to sharpen up our identification skills to tell them apart; are they found at different levels on the shore, where do they graze and why are they present in such numbers around the base of the boulders?
Limpets are less mobile grazers, famously returning to their resting spots as the sea recedes; how can they graze areas so dominated by barnacle spat?
Rock pools
We had not previously explored the rocks at the north end of this beach, but they proved to house some rich sandy pools, probably exposed only on low tides. These contained a range of ‘seaweeds’ (photos 8-9).
Green algae were represented by the tufted filaments of green branched weeds Cladophora spp. Brown algae included numerous blobby, inflated plants of punctured ball weed Leathesia difformis, a species we had not before noticed.
Elsewhere in the pools there were long, twisted, slightly inflated ribbons of a brownish-red species, that we tried to find amongst the brown algae in the very useful Seaweeds of Britain and Ireland (Bunker et al. 2012). Failing to do so, we turned to the red algae, finally running them down as Dumont’s Tubular Weed Dumontia contorta, again one we had not come across. This group was also represented by the ‘chalky’ tufts of common coral weed Corallina officinalis.
Not a bad haul for a brief unplanned visit!
Ian M. Evans and Gwen Richards
All photos by Gwen Richards