Intertidal organisms of an industrialized estuary

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population numbers found in the controls, i.e., samples not exposed to oil. These results substantiate earlier observations that petroleum can limit bacterial growth (Walker & Colwell, 1974). In addition, we conclude that there are measurable effects of oil on ecologically important bacterial groups, since the crude and refined oils employed in our work demonstrated a significant limiting effect on total viable numbers and, probably, the activity of these micro-organisms.

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Blumer, M., Sanders, H. L., Grassle, J. F. & Hampson, G. R. (1971). A small oil spill. Environment, 13: 2-12. Cowell, E. B. (1971). The ecological effects of oil pollution on 10 littoral communities, 250 p., Elsevier, London. Mitchell, R., Fogel, S. & Chet, I. (1972). Bacterial chemoreception inhibited by hydrocarbons. Water Res., 6: 1137-1140. i .~ = I t Sizemore,R. K. & Stevenson, L. H. (1970). Method for the iso0 / 14 21 28 lation of proteolytic marine bacteria. Appl. Microbiol., 20: 991-992. Time (days) Walker, J. D. & Colwell, R. R. (1974). Some effects of petroleum on estuarine and marine microorganisms.Jan. Can. Microbiol. (submitted). Walker, J. D. & Colwell, R. R. (1973). Microbial ecology of Fig. 3 Fluctuation in percentage of chitinolytic bacteria: absence petroleumutilization in Chesapeake Bay, pp. 685-690, In: of added substrate (©); with Fuel Oil No. 2 ([-1); and with APZ/EPA/USCG,Conference on Prevention and Control of Louisiana crude oil (A). Oil Spills, American Petroleum Institute, Washington, D. C. D

Intertidal Organisms of an Industrialized Estuary A study of the intertidal organisms of the Clyde Estuary is being undertaken to assess the effects of changing levels of pollution and to relate to these and other changes the distribution of important winter flocks of waders and ducks. The Clyde sea area may be subdivided into the Firth of Clyde, the sea lochs and the Clyde estuary. While the first two categories have in the past received much attention from biologists based at Millport and elsewhere, the last has only recently begun to receive the study it deserves. In this paper the estuary is defined as extending from the tidal weir in Glasgow westwards to a line between Gourock pier and Kilcreggan, and excluding the Gare Loch north of a line from Rhu to Roseneath (Fig. 1). The estuary was one of those described by Porter (1973) in her case studies of polluted estuaries, and much of what is now known about it is the product of work by the Clyde River Purification Board's staff (see for example papers by Mackey et al. 1969, 1971, 1972). The present authors have become concerned with two main aspects of the estuary. The first is the relationship between the distribution of organisms and the pollution load with special reference to changes which are anticipated during the next few years, a study with which the River Purification Board is associated. The second aspect relates to the food and feeding distribution of birds in the estuary, a matter which has acquired special importance recently, as in other estuaries, from pro188

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posals for land reclamation to provide industrial building sites; in this we have collaborated with the Nature Conservancy Council and other interested bodies.

Distributions of intertidal organisms The upper estuary between the tidal weir and Erskine is relatively narrow and enclosed between steep walls. Under conditions of high river flow, low salinites may

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dissolved oxygen content of the water regularly falls to zero (Mackay & Waddington, 1970). The flora in this region is restricted to species of green and blue-green algae and the filamentous diatom Melosira nummuloides, while the larger fauna is limited to a few species of oligochaetes. Below Erskine the estuary widens, banks of tidal sand and mud becoming its most conspicuous feature. Fluctuations of salinity and dissolved oxygen content become less extreme and there is a considerable increase f r o m east to west in the numbers of species of both plants and animals. For most groups a line between D u m b a r t o n Castle and West Ferry appears to be a significant demarcation line (Wilkinson, 1973), perhaps because of the improvement in oxygenation of the water brought about by the inflow of the River Leven (Table I). West of this line fucoid algae predominate on the shores, The tidal banks are the winter feeding ground of large flocks of birds; Fig. 2 shows the distribution of selected species made during the winter of 1972-73 (Gibson, 1973). Of these, the flocks of redshank and shelduck are of particular importance and Prater (1973) notes that the Clyde Estuary, though carrying more than 1% of the total European population of redshank, is regarded by the International Waterfowl Research Bureau as of international importance. He also notes (1974) that with a peak count of 28,432 waders it ranks twentieth among British estuaries, In the lower estuary, attached algae are found on boulders scattered over the sand surface and on various rock and constructed surfaces close to the edge of the shore, where they shelter a variety of animals not found elsewhere. The restricted rocky shores, docks and harbour works between Port Glasgow and Greenock, however, show features associated with heavy pollution, notably the dominance of mat-forming polychaetes, especially Fabricia sabella, and the absence of normal rocky shore species (Smyth, 1968, 1973). To a lesser extent the same is true of rock surfaces at Helensburgh. The distribution of intertidal organisms thus corresponds closely with the areas of different pollution levels distinguished on the basis of other river quality criteria in maps published by the Clyde River Purification Board (1968) and the Scottish Development Department (1972) (Fig. 1).

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Fig. 2 Monthly counts made in the estuary from July 1972 to May 1973 of Redshank Tringa totanus, Dunlin Calidris alpina, Oystercatcher Haematopus ostralegus, Lapwing Vanellus vanellus, Shelduck Tadorna tadorna, Mallard Anas platyrhynchos and Black-headed Gull Larus ridibundus (from Gibson, 1973).

Fauna of the mud-flats Clearly the sand and m u d banks are the largest intertidal habitat in the estuary, and in addition carry the winter food supply for important bird flocks. A preliminary survey of the mud-fiat invertebrates was carried out during the summer of 1972 by a postgraduate student of Paisley College, J. W. West, on the basis of eleven transects. He suggested that the area might be subdivided according to the relative dominance of three organisims--Corophium volutator, Hydrobia ulvae or Mytilus edulis. In summer 1973 a second survey was carried out by M. Minto and W. Scott, based this time on 40 sites selected at random from intersections of lines in a grid superimposed on charts of the area. Samples were taken by cores of internal diameter 10.16 cm, to a depth of 20 cm, five were taken at each site, calculated to be the minimum number acceptable. Samples were sieved through a 1 m m mesh. Of some twenty species of larger invertebrates occurring in the samples, three were outstandingly numerous and widely distributed: Corophium volutator, Nereis diversicolor and Hydrobia ulvae. Very few of the sampling sites were in places where Mytilus was present so this survey gave no further information about its distribution. Correlation coefficients were calculated which made it clear that C. volutator and N. diversicolor formed a faunal group (r = 0.56) distinct from H. ulvae, the correlation between the two groups being r = --0.23, confirming the impressions formed in the 1972 survey. F o r comparisons of the distribution of these species, the mud-fiats were divided into five areas (labelled A-E in Fig. 4), and various procedures carried out, a fuller 189

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Fig. 3 Principal components plot for the five areas examined in the Clyde Estuary, in terms of the larger invertebrates found there. The envelopes enclose regions in which fall the sites from each area A-E (Fig. 4). Abscissa-principal component I, ordinate-principal component II. Most variation in areas B and C is due to Corophium;in areas D and E Hydrobiamakes most contribution.

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relative to Corophium. Areas B-E were richer than A, while B and D, on the south bank, included sites yielding more animals than sites in areas C and E on the north bank. These conclusions were confirmed by multiple discriminant analysis and the differences between the areas were shown to be significant. Studies of the invertebrates are continuing. Large populations of smaller polychaetes and oligochaetes were recorded during the summer surveys but not analysed, and an investigation of these has now commenced. They include Manayunkia aestuarina, Fabricia sabella, Pygospio elegans, Streblospio sp., Capitella capitata, Tubifex costatus, Peloscolex benedeni and others. Harpacticoid copepods and ostracods are also being studied. Measurements were made of organic carbon and nitrogen and of particle size distributions of the sediments, but have so far yielded few significant correlations with the distribution of the animals studied.

Bird feeding areas account of which will be published separately. In a principal components analysis the three dominant species accounted f or nearly all of the variation, making most contribution to the first three components which took up 99.82 % of the total variance. The principal components analysis showed a relatively clear separation of the five areas. Areas B and C, east of D u m b a r t o n and the mouth of the River Leven (Fig. 3) showed higher relative values for Corophium, while areas D and E to the west showed increasing numbers of Hydrobia 190

The bird counts upon which Fig. 2 is based were carried out as part of the BTO/RSPB Birds of Estuaries enquiry, and compiled by Gibson (1973). They were largely of roosting birds; thus while the birds concerned depend on the mud-flats for food throughout the winter (e.g. redshank) or in hard weather (e.g. lapwing), information about their fedding patterns is based largely on numerous subjective observations rather than on systematic counts. As a first step to establishing relationships between these observations

and invertebrate distribution, two observers with long experience of bird counts were asked to name the three species of waders and the three species of duck they would most expect to find feeding at each o f the invertebrate sampling sites, placing each of the three in order of importance. Fig. 4 shows the sites at which redshank and shelduck were rated most likely to predominate a m o n g feeding birds. The distribution of redshank showed a marked relationship to the sites dominated by Corophium and Nereis. This method of assessment did not, of course, take into account relative numbers of feeding birds: by far the largest number of feeding redshank is found on the south side of the estuary and it would be tempting but premature to associate this entirely with the probable greater richness of the fauna there, referred to above. Another factor which probably influences their preference is the lesser degree of h u m a n disturbance to which they are subjected on the south bank. The main feeding grounds of shelduek are on the western part of the mud-banks much of which was not covered by the sampling programme, but those included on the north side of the lower estuary were in sites relatively rich in Hydrobia. Some birds move to the sites shown upstream late in the winter as part of a wider dispersal associated with breeding. In some winters, however, the move to sheltered areas m a y also occur earlier, possibly in response to bad weather. At these sites the food supply m a y include a greater variety of organisms. W o r k is continuing on the distributions of algae and invertebrates and the factors affecting them, and on the feeding movements of bird species, from which it is hoped a clearer picture will emerge of the intricate pattern of relationships between the organism of the mud-flats, the bird flocks and the industrialized h u m a n population surrounding them.

Clyde River Purification Board (1968). Thirteenth Annual Report, Glasgow. Curtis, D. J., Minto, M., Scott, W. & Wilkinson, M. (in prep.). Multivariate analysis of the distribution of littoral macroinvertebrates in the Clyde Estuary. Gibson, I. (1973). B.T.O./R.S.P.B. Birds of Estuaries Enquiry: Inner Clyde Report for 1972]73. 21 pp. Mackay, D. W. & Fleming, G. (1969). Correlation of dissolved oxygen levels, freshwater flows and temperatures in a polluted estuary. Water Research, 3: 121-128. Mackay, D. W. & Gilligan, J. (1972). The relative importance of freshwater input, temperature and tidal range in determining levels of dissolved oxygen in a polluted estuary. Water Research,6: 183-190. Mackay, D. W. & Waddington, J. I. (1971). Quality predictions in a polluted estuary. Prec. Fifth Int. Conf. Water Pollut. Res., San Francisco, 1970. Porter, E. (1973). Pollution in four industrialised estuaries: four case studies undertaken for the Royal Commission on Environmental Pollution. London, H.M.S.O. Prater, A. J. (1973). The 1972 midwinter census of waders in Scotland. Scottish Birds, 7 (8): 391-398. Prater, A. J. (1974). Estuary birds survey 1972/73. B.T.O. News, 66:2, Scottish Development Department (1972). Towards cleaner water: Rivers pollution survey of Scotland. Edinburgh, H.M.S.O. Smyth, J. C. (1968). The fauna of a polluted shore in the Firth of Forth. Helgoliinder wiss. Meeresunters., 17: 216-223. Smyth, J. C. (1973). The fauna of some rocky shores in the Clyde Estuary. Western Naturalist, 2: 53-58. Wilkinson, M. (1973). A preliminary survey of the intertidal benthic algae of the Clyde Estuary. Western Naturalist, 2: 59-69.

We are indebted to many people who have assisted with collection and preparation of the data on which this paper is based and whose help is being acknowledged in the more detailed accounts of the work. We are grateful to Mr. J. Gray for preparing the illustrations.

Department of Brewing and Biological Sciences, Heriot- Watt University, Edinburgh, Scotland.

J . C . SMYTH D . J . CURTIS

Department o f Biology, Paisley College o f Technology, I. GmSON 41B Mossvale Street, Paisley, Scotland M. WmKINSON

Pollution, Prevention and Clean-Up Oil Spills and the Marine Environment. Papers prepared for the Energy Policy Project of the Ford Foundation by Boesch, D. F., Hershner, C. H. & Milgram, J. H., Ballinger Publishing C o m p a n y : Cambridge, Mass. xv -q- 144 pp. (1974). Price $7.00 (Paperback $2.50). These papers are published as one of the special group of reports dealing with part of the Energy Policy Project. The object is to bring together, in one place, a critical review of current knowledge about the effects of oil spills and the efficiency of preventative safeguards, This seems an admirable project and it is a pity that neither of these papers carries it out at all. Dealing first with the effects of oil in the marine environment. This seems at first sight to be a well

written, and well documented paper (there are 123 references). There are three reasonably well documented oil spills, these are the Torrey Canyon, the Santa Barbara blow-out and the West Falmouth spill; all three are referred to almost continuously in this paper, particulady the last one. Unfortunately, the papers describing the effects are assumed to be the present state of the art. Thus m a n y of the effects observed immediately after the Torrey Canyon spill and admirably reported were transient. This fact is not commented upon. In particular, the m a n y references to the West Falmouth spill claiming to show the high mortality produced by the oil and the bio-aeeummulation in the species do not take account of the m a n y faults in experimental methods and reporting. 191