1981 L37.Pdf

This paper not to be eited without referenee to the author. International Couneil for C.M. 1981/L:37 the Exploration of the Sea 8iologieal Oeeanography Committee. Observationson blooms oF Noetiluea of the south eoast of Ireland during summer 1977 by 1 1 Miles Parker , Dan Minehin , p.J. Ga~land2 and Paul Connolly1. 1 Fisheries Research Centre, Abbotstown, Castleknock, Co. Dublin. 2 Sherkin Island ~arlne Station, Sherkin Island, Co. Cork. Abstract Red water assoeiated with blooms of Noetiluea seintillans (MeCartney) Ehrenberg oecurred along the south eoast during Jul~ and August 1977. Small, 10ea1 blooms oeeurred inshore at several points and extensive oFF-shore blooms oeeurred briefly during August. The oeeurrenee of Noetiluea at Lough Hyne (Ine) and Sherkin Island, County Cork, i5 r~ported in more detail. Comparison is made with other reported oeeurrenees. , Resume ./ Des Eaux Rouges, aSSOClees avee des proliFerations anormalles • de Noetiluea seintillans (McCartney) Ehrenberg, se sont produltss sur la eote sud d'Irlande au cours des mois de Juillet et / d'Aout 1977. Des petites proliferations l~cales se sont produites sur 1e littoral en difFerents points et quelques proliF~rations de courte durcie se sont produites au 1arge au cours du mois d'Aout. La pr;sence de Noetiluca ~ Lough Hyne (Ine) et ~ Sherkin Is1and, en County Cork, est decrite en detaIl." . ,,,-; , " -1- ( ... Introduction In 1976, a bloom oF Gyrodinium aureolum Hulbert on the south coast of Ireland caused mortalities oF littoral Fauna and demersal Fish (Ottway ~.~., 1979). Subsequently, it was decided that observations on similar oocurrences should be collected by the Fisheries Research Centre; this paper presents three sets oF observations made on blooms during 1977. Thece are, Firstly, a compilation oF reports From Fishermen and others of the incidence oF 'red tides' and oF the results oF examination oF water sampies sent in by these observers; secondly, data on hydrography and plankton distribution in Lough Hyne (Ine), Co. Cork, where a Fisheries Research Centre project on collection oF Pecten maximus spat had been in progress since 1975; thirdly, similar observations made in the vicinity of Sherkin Island, Co. Cork where a These study on Crassostrea ~igas growth was in progress. observations were gathered by MP, DM & PC, and PJG respectively. • Coastal sightings of discoloured water. Figure 1 shows the south and southwest of Ireland; numbers on the map indicate sightings referred to in the text. Red water was first observed in the vicinity oF Helvick Head, ( 1 ) A patch of rliscoloured south oF Dungarven on 14 Jul y. water was observed which moved to a point about 5 km south oF the head the Following day and was observed further west • -2- on 16 July. ~reshening south westerly winds appear to have dispersed this patch by 17 July. Several patches of discoloured water were observed in Youghal Bay(2) on 15 and 16 July and water in neighbouring Ballycottin (3) Bay was reported to be 'slimy' during this period. Between 15 end 17 July a patch of red water was noted off Aoches Point(4J. There was only one report of red water (from Knockadoon Head(5) on Youghal Bay on 1 August) between 17 July end 8 August. Subsequent reports were from further south end west than the July events. On Band 9 August a very extensive series of offshore dis- colouretiorewas observed by the pilot of a helicopter servicing the Kinsale Head Gas Field Platforms and by an Irish Air Corp pilot on a routine flight. Their flight paths, in the area where they observed red water are marked on Figure 1 together with a point at which a fishing vessel r6il~b,c) off Kinsale noted red water on 8 August • A week later (15 August) two further reports of patches of red water were received from a fishing boat near the Old , (7] Head of Kinsale and the pilot of a commercial aircraft en route from Cork (8] Further west, patches oF discoloured water were observed in Ounmanus Bey(9) on 8 and 9 August; subsequently on 23 August very dense patches of red wa~er occurred in the -3- bays of the north side of Ounmanus. Observations in Lough Hyne and Roaring Water Bay are reported later in this paper. Water sampies were taken at Helvick (14 July), Youghal (1 August), Kinsale [8 and 15 August) and Ounmanus (23 August) in addition to those taken in the Loch Hyne and Sherkin Island Studies. In all cases the dominant organism was noted to be Noctiluca ~cintil13ns (McCartney) Ehrenberg; the state of the sampie from Ounmanus would suggest that the bloom was at that time moribund or decaying in that area. Other organisms in the samples were not identified but none were noticeably abundant. It seems Iikely that Noctiluca was the organism dominating all the observed blooms. They were all described as being orange to red in colour and as occurring in patches or long slicks. One report, from salmon netsmen suggested that the visible effects did not extend further than about 1 metre depth. • Weather data for this per iod from the three south coast weather statiorlS [Rosslare, Roches Point rCo~~j Rnd Valentia Island) was examined. That From Roches Foint is presented in Figure 2; the data from the other two stations does not differ greatly and indicates the same pattern of events. Wind strength was variable, beirg close to the 30 year average in July but lower in August. However, blooms occurred _4_ during, or just aFter, periods oF low wind speed, and dis- pers~cl as wind speed rose. The apparent exception to this rule is the appearance oF red watp.r in Ounmanus Bay on 23 August; however, in this case it seems possible that relatively strong southerly and south-westerly winds caused inFluxes of moribund blooms to the north side oF the bay. On most oF the other occasions, the winds were onshore or along-shore, From an easterly quadrant. RainFall throughout the period was very low until aFter the last bloom. There was no obvicus correlation between the • Few showers that did occur and the appearance oF red water. On the other hand, there was generally rather more sunshine than the 30-year average during this period. Air temperature was close to normal For this time oF year. Tidal height data For Cobh, Co. Cork, is given as being indicative oF the occurrence oF spring and neap tides and hence oF the strength oF the tidal stream. It may be noted that, while the inshore blooms occurred at or beFore spring tides, the extensive ofFshore bloom occurred at the • lowest neap tides of this per iod. The occurrence oF Noctiluca in Lough Hyne Oiscoloured water was observed between the end of July and mid August, ~ostly on the northern shore of the lough (Fig.5). Ouring this time observations on plankton and hydrography were being regularly müde at a single station (station C oF Bassindale et al., 1957) in the northern basin of the lough, -5- though discolouration was not observed at the sampling point. Methods Oally vertical plankton hau's were made From 20m to the surFace and the sampies were examined under binocular microscope; order-of-magnitude counts (as tensthundreds, thousands, greater than thousands per cubic metre) were made. On the night oF 10 11 August, these were supplemented by pumped sampies taken at depths oF 0.1m, 5m, 10m, 15m and 20m at 1800hrs BST, 2100 hrs, Midnigh~ and 0300hrs • • Water temperature was measured daily to 0.05o'C with calibrated reversing thermometers mounted on a Nansen bottle. Water transparency was estimated with a white 32cm diameter Secchi disco RainFall measurements (in mm) ware taken near the north-west shore oF the Lo~gh From a rain guage; insolation was estimated in terms oF sunshine hours/day and wind strength was visually estimated From water surFace conditions according to the BeauFort scale. Observations • Weather data is present~d in Figure 3, together with estimat- ions oF Noctiluca abundance From the vertical hauls. Noctiluca was First observed on 29 JulYi numbers at the sampling station ex~eeded one thousand per cubic metre between 6 and 14 August. Wind speeds were low during the First halF oF August and insolation was high: the Lopgh was thermally stratiFied (Fig. 4). Secchi depth decreased From 22 July to 3 August but thereaFter increased agaln. -6- From mid August numbers oF Noctiluca declined though there was a slight increase around 28 August which persisted for about a week. Noctiluca ceased to be recorded in the plankton on September 14. At the sampling station, Noctiluca was most concentrated between the surFace end ten metres at night with little or none occurring below 15m (Tab1 e 1). TABLE 1 Numbers oF Noctiluca at diFFerent depths during the night of 10 / 11 August. • 3 Numbers oF ~octiluca in 1000s/m (% total) Time Oepth (m) 1800 2100 2400 0300 0.1 14.4(20.3) 19.8(21.7) 26.0(36.5) 24.3(22.5) 5 29.0(40.9) 43.5(47.6) 23.1(32.4) 17.0(22.5) 10 15.7( 22 .1 ) 20.4(22.3) 22.1 (31 .0) 40.5(37.5) 15 11.8(16.6) 7.6( 8.3) O.O( 0 ) 20.3(18.8) 20 O.O( 0 ) O.O( 0 ) 0.2( 0.3) 5.9( 5.5 • 70.9 91.3 71 .3 108.0 From late July to mid August, orange discolouration oF th. water was noticeable at the north shore, especially on the rising tide; brilliant luminescence was noted at night.

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