Studies on the macroinvertebrate community of the Loch of Strathbeg, Aberdeenshire

• Main Author: Forteath, G. N. R.
• Published: University of Aberdeen 1977
• Subjects: 592.09412
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.455774

(i) The Loch of Strathbeg lies in a very exposed part of N.E. Scotland and is only 0.5 km. from the sea. Its shallow depth (< 2m.) and sandy substrate combine with the effects of wind to provide a relatively uniform habitat. (ii) The wind causes a great amount of water turbulence which in turn prevents any stratification in the summer and aids in maintaining high levels of dissolved oxygen throughout the year which is supplemented by oxygen released by Chara during the summer months often resulting in super-saturation. Wind driven sea spray results in a high sodium content in the water. (iii) The turbulence of the water restricts the emergent vegetation to a narrow belt around the shores. A Chara meadow develops in the summer but is destroyed by wave action during the autumn and winter with autochthonous debris being deposited along the margins of the loch. (iv) One hundred and twenty three species of macroinvertebrates were identified to the specific level some of which were considered rare and some associated with brackish conditions. (v) Fager's method of species grouping was applied to six out of the twelve monthly samples taken at random from all over the loch, February to January, 1975/76. Intergroup and interspecific analyses were carried out on each of the monthly groups. (vi) The total number of species and their abundances in each of the twelve monthly samples were fitted to the log-series model and the parameter-JL used as an index of diversity. (vii) Monthly samples were taken along k transects permanently sited in the loch during 1976 (March to November). The quantitative results from this study were used to supplement the community analysis and to obtain life-history data on the more common species, in particular Caenis horaria and Potamopyrgus jenkinsi. (viii) The intergroup analysis showed the community to be integrated and the biota to be best described by the concept of a 'continuum'. The degree of integration was dependent on the time of year with the greatest integration taking place in mid-summer (July) and midwinter (January) corresponding with the periods of greatest overall uniformity in the environment. (ix) Many species changed their 'position' in the community depending on seasons. By mid-winter, species most affected by water turbulence were more abundant in the more sheltered areas along the western shores while those less affected were more widely dispersed amongst the emergent vegetation around the shores. Only animals adapted to living in the substrate were abundant in areas of open-water. In the summer, species moved out into areas of open-water but were transported .back to the edges with the Chara in the autumn/winter. (x) The study shows how the community reacts to changes brought about in the loch through the seasons and stresses the roles played by the wind and the growth of Chara. (xi) The study is considered a useful baseline for: (1) further quantitative analyses in which specific environmental parameters can be correlated with species abundances; (2) monitoring the effects of pollution in the face of increasing industrialization and urbanization in the vicinity of the loch. (3) understanding patterns in the feeding behaviour of the trout. (xii) It is concluded that a sustained increase in eutrophication will cause the death of the Ghara meadow which will prove detrimental to the macroinvertebrate community, the water fowl and the fishery.