Seasonal and diel variations of some physico-chemical parameters of Boulder shore habitats

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Abstract
The variations in physico-chemical conditions on a boulder shore on Great Cumbrae Island, Firth of Clyde, were investigated. Two micro-habitat types – dry understone and wet understone environments — were sampled at two positions on the shore, above and below MTL. Temperature, oxygen tension (P02), salinity, pH, Eh and humidity were measured under these stones over two tidal cycles once monthly for a period of a year. Temperature, P02, Eh and salinity showed the greatest diurnal and seasonal variation. High temperatures in the summer, combined with the presence of a large mass of decaying algae on the upper shore, served to deplete the P02 of the incoming tide and resulted in almost continuous hypoxic conditions on the upper shore during both immersion and emersion. Humidity was usually greater than 70 % under the stones. The major difference between the upper and lower shores was the duration of emersion during low tide which generally led to larger variations in most physico-chemical conditions at the upper shore. The habitats described showed a combination of the environmental characteristics expected of rock pool, crevice and sedimentary habitats.