SynopsisThe Moray Firth forms part of the north British coastal area of the North Sea and is distinguished by its depth, hydrography and plankton from the offshore northern North Sea. The 35·0 or 35·1 × 103 isohaline can be taken as the boundary between the two areas.Geographical and seasonal variations in temperature and salinity are described in terms of a belt of low salinity coastal water in the inner firth and along its southern shore and of “mixed” water to the north and east. During the winter the “mixed” water is warmer than the coastal water, during the summer it is colder. Tidal streams are dominantly semi-diurnal, relatively weak in the inner firth and relatively strong in the outer firth. Residual currents are largely wind driven, and some are caused by tidal effects.Geographical variation in the seasonal changes in the phytoplankton standing stock is related to water column stratification. The early spring standing stocks are highest in the inner firth and off the southern shore. During the summer and early autumn, phytoplankton is most abundant below the pycnocline. Average zooplankton standing stocks increase from 0·2–0·6 g dry weight (100m3) 1 in winter to 1.0 g (100m3) 1 exceptionally 4·5 g (100m3) 1. in summer. Standing stocks in November–December range from 0·3 to 1·8 g (100m3) 1.
Dead and dying fish were reported from the Moray Firth during a period of 15 days in September 1963. The initial mortalities were in the inner Firth, but they later spread outwards, especially eastwards along the southern shores of the Firth. Mass mortalities of the lugworm (Arenicola marina) also occurred in Scottish waters in 1962 and 1963, and at Balintorein Easter Ross fish and lugworm mortalities were contemporary.
SynopsisZooplankton investigations in the Firth of Clyde can be considered as starting in 1885, when the Fishery Board for Scotland built a laboratory at Tarbert and the Granton based Scottish Marine Station extended its studies to the west coast. The work of both groups, and their successors, waxed and waned, with a particularly active period starting in the early 1920s, when the Millport Station received government aid.Although the euphausiids Meganyctiphanes norvegica and Thysanoessa raschii are important in the deep waters around Arran and in Loch Fyne, in general, copepods are the most important pelagic
crustaceans. Of these Calaims occurs in enormous numbers in surface waters in May and June. Thereafter it is found mainly in deep waters such as those of Loch Fyne. Other abundant copepods are Pseudocalanus elongatus, Acarlia clausi and Oithona similis which are particularly characteristic of the area extending from Kilbrannan Sound via the east of Arran to the upper Firth of Clyde. In these latter areas the peak standing stock of the larger zooplankters (as caught by a 250μm mesh net) is about 5, occasionally 8, g dry weight per 100cum, occurring from April to July. The smaller zooplankters (as caught by a 68μm mesh net) add a further 1.3g dry weight per 100 cu m.
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