The regular occurrence of Reophax scottii Chaster, a benthic foraminiferan, in plankton samples from the North Sea

The benthic foraminiferan Reophax scottii Chaster, not previously recorded in suspension, is shown to occur regularly in plankton samples taken at 10m by the Continuous Plankton Recorder in the North Sea. The species’ seasonal and geographical distribution is described. It was found mainly in the winter and spring (November to April).


INTRODUCTION
The presence of benthic foraminifera in samples taken in the water column has been reported on only a few occasions (e.g. Murray, 1965;Murray et al., 1982;Williams & Collins, 1985), although this could be due to lack of sampling, rather than real absence. In the course of routine examination of plankton samples taken with the Continuous Plankton Recorder (CPR) in the North Sea and shelf waters around the British Isles, benthic foraminifera have been noted fairly frequently, the most regular of which is Reophax scottii Chaster. This is an elongate form with a wall composed of detrital mica plates arranged in an overlapping series; it has an average length of 700pm (Murray, 1979). It is the purpose of this short note to demonstrate that R. scottii occurs regularly in small numbers in the surface waters of the North Sea in winter and spring.

MATERIALS AND METHODS
Since 1048 CPRs have been used in synoptic surveys to determine the abundance and distribution of plankton in thc North Sea and the North Atlantic (Edinburgh Oceanographic Laboratory, 1973). They are towed hy merchant ships and weather ships at a depth of IOm over ii number of standard routes at monthly intervals. The plankton is filtered by a continuously moving hand of bolting silk wiith a mesh size of270pm. The prcsence of R. scottii was noted regularly by two observers between 1964-1986 and only occasionally by others.

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The seasonal pattern of occurrence of R. scottii observed in CPR samples from 1964-1986 is shown in Fig. 1. The majority of the records were found in the central and western North Sea between 53"N and 59"N from November to April. The species was also found occasionally in the western English Channel, the Bristol Channel, the Irish Sea, southwest and north of Ireland and north of Scotland. In the western Atlantic, R. scottii was found in two CPR samples taken over the shelf southeast of Newfoundland in March 1969and January 1970. Culver & Buzas (1980, who summarised all published distribution records of foraminifera off the North American Atlantic coast, showed that this species occurred widely between Cape Hatteras and Newfoundland at depths less than 200m. Although R. scottii was found in every month of the year, it was rare between May and August (Fig. I).

DISCUSSION
R. scottii is a characteristic species of muddy sediments on the inner shelf and is described by Murray (1971) as a 'southern' species. All the specimens found in CPR samples were in shelf waters or very close to the shelf edge. The fact that it is commoner in samples taken during the winter and spring is probably linked to the mixing of the water column by winter storms, causing suspension of benthic material. During the summer there is thermal stratification of the water column and benthic foraminifera are absent from water above the thermocline. The only occurrences of R. scottii in the summer months (June to August) were all in the Bristol Channel in 1977; this is probably due to the year-round vertical mixing in this estuary caused by the large tidal range.
Despite its regular appearance in CPR samples taken at 10m, R. scottii has not been reported previously in suspension (J. W. Murray, pers. comm.). It was not one of the benthic foraminifera recorded in the water column of the western English Channel in January 1962 (Murray, 1965) or October 1979 (Murray et al., 1982), nor was it included in the list of benthic foraminifera Fig. 1. The monthly distribution of R. scottii found in CPR samples in the waters around Britain from 1964-86; small circles = 1-2 records per sampled square, large circles = 3 or more records.
found by Murray in plankton samples taken in the Bristol Channel and Severn estuary in September 1974 (Williams & Collins, 1985).
The results from the CPR show R. scottii to occur regularly further north in the North Sea than the northern boundary for southern species given by Murray (1971). Two other recent studies are of interest. Bamber (1984) found R. scottii to be abundant in the sediment off Blyth, on the Northumberland coast. Murray (1985) recorded it as an accessory species in the Ekofisk area (56"32'N, 3'13'E) in both living