| The area chosen | Sources for records | Fieldwork for the Atlas |
The area chosen for MARINE MOLLUSCA OF WEST SCOTLAND AND THE NORTH COAST OF IRELAND - CHECKLIST AND ATLAS extends from 58°50'N, approximately on a line from Cape Wrath to the Butt of Lewis, to 55°00'N, from Stranraer to north of Larne, including those parts of Loch Ryan, Lough Swilly and Mulroy Bay which lie to the south of this. From the highest reaches of salt water into the mainland of Scotland, it extends westwards to 09°24'W (MAP below). This is an arbitrary limit, which includes some very deep water, allowing inclusion of deepwater species and the representation of fuller depth ranges for others. The incorporation of the north coast of Ireland has proven to be of considerable benefit in demonstrating the geographical range of those southern species which extend into Scotland, and of those which reach Donegal but apparently no further.
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Most of the Scottish shore survey for this Checklist and Atlas has been carried out by Smith, of which much was under contract in the years between 1977 and 1985 to the then Nature Conservancy Council (now Natural England & Joint Nature Conservation Council, Scottish Natural Heritage and various other organisations). However, in addition, she has privately surveyed many areas since 1966 and in more recent times to fill in gaps, and re-survey others to check on quality of earlier methodology and to discover if there had been any changes. For example, work in the Ullapool area in 1998 confirmed that the 1978 methodology had been up to standard, and that there have been no significant changes.The Irish shore work has been carried out mostly by the authors.
Shallow inshore work has been by divers associated with the Ulster Museum (National Museums Northern Ireland), the then Nature Conservancy Council and its successors such as the Joint Nature Conservation Committee and the Marine Conservation Society with many surveys, latterly under Seasearch, a number of the earlier expeditions being organised by Smith. Records obtained through the Conchological Society of Great Britain and Ireland's marine recording scheme are conspicuous by their scarcity as few members (apart from Smith) have visited the region except during a very useful week in the Oban area in 1993 (Smith, 1996). Nunn has been largely responsible for obtaining the Irish records.
Records from further offshore are patchy. Many have been by David W McKay, obtained during his employment by the Marine Laboratory, Aberdeen. We have also been fortunate to have been able to do such extensive dredging off Oban (largely between 1991 and 1992 and 1998, courtesy of the Scottish Association for Marine Science), that a reasonably detailed knowledge of one small part of the sea bed has been established. Access has been granted to numerous grab samples taken by the British Geological Survey. As the result of the National Museums of Scotland being gifted a very large amount of material taken by the BABS programme and subsequently curated by Smith, records from the Hebridean shelf edge and upper slope could be incorporated (although the bulk of this material came from stations outside the present area in deeper water).
Unfortunately, at the present time it is not been possible to incorporate data from research by the Atlantic Frontier Environment Network because this has as yet not been worked up to a useful standard. Specimens, will, it is hoped, be lodged in the National Museums of Scotland. In Ireland, there has been the BioMar project, where littoral and sublittoral recording of species and habitats around the Republic of Ireland has been carried out by Trinity College, Dublin, as part of the European Life Programme.
Where records are of particular interest, reference has been made to the appropriate publication. For unpublished records of rarer species, reference is to the finder concerned. Our own unpublished records are unacknowledged in the text, but our published work is referred to.
Unfortunately some literature records which cannot be checked must be regarded with some scepticism - this is noted in the text where appropriate. We have had particular problems in assessing records in Nature Conservancy Council (or its successors) Reports where we have had no input. In part due to the remit of some surveys aimed at the environment rather that recording of species per se, and in part due to the hasty manner in which much of the work was of necessity undertaken due to underfunding, and to an understandable lack of molluscan expertise, there has proved to be a rate of misidentification of species which we found worrying and a level of finding/recording of species well below the target which we set for ourselves.
It is also particularly disappointing to discover from experts' appraisal of material still extant in museums, that Chaster's identifications of rare species (mostly from off Northern Ireland) were not always accurate, and thus all his work should be re-assessed. We have not yet been able to appraise his material which is in the National Museum of Ireland in Dublin. Similarly, Marshall's identifications occasionally leave something to be desired. Thus his Additions to British Conchology have had to have been treated with caution, especially regarding the rare species and those more difficult to identify. On the other hand, none may be dismissed out of hand since some of his improbable records are backed by voucher specimens. His collection in the National Museum of Wales has been examined.
As the aim of the research was to compile an Atlas, work was directed to mapping on the grid chosen, this being 6' of latitude by 12' of longitude. The rectangles thus devised have been the basis for choice of sites investigated, to include as many habitats as possible. Thus for each area targeted, advance planning would suggest the locations to be visited, subject to accessibility. For complex areas, this may mean several sites to be investigated; for simple areas such as those at the heads of sea lochs, one visit would suffice. Some offshore work has been undertaken on the same grid basis, but most of this has been ad hoc.
Shore work carried out by Smith and Nunn has followed a basic pattern devised by Smith (1979). Each habitat from the upper shore to the lowest available, usually the top of the Laminaria zone, was investigated. This included crevices and the undersides of boulders, stones and boulders under boulders overhangs and gravel. On sediment shores, an assessment of the likely mollusc diversity and biomass could be quickly ascertained from the dead shells at the surface, and where suitable, digging and sieving was done. This was qualitative rather than quantitative; thus a trowel and small sieve were found to be adequate.
Gravel and maerl beds required more careful analysis and complete samples were taken for study in the laboratory. In addition, the most useful part of the survey was to take samples of algae: small algae from rock pools and lower on the shore, as many common species as available; fucoids especially Fucus serratus, especially that with epifauna of spirorbids or hydroids or ascidians. Also samples of Laminaria holdfasts were taken. This material was soaked in fresh water so that the Mollusca fell off and could be preserved for subsequent laboratory identification and counting. Although these samples were random, they were more or less of the same size, and the information, which included data collected, is the basis for comparative research not relevant to the current work. Nunn has also adapted the technique for her diving research. This detailed survey technique has not been used to any great extent by other workers.
Our own dredging has been similarly careful, as we, especially Smith, have been fortunate in having unlimited time at our disposal in which to sort samples. Thus as much material as possible, certainly much more than is normally the case, was brought ashore for careful sorting, identification and counting of specimens. There was of necessity some sieving on board, but this was kept to a minimum.
Copyright © Shelagh Smith & Julia Nunn