Integrating indicators of water column effects Algal bioassays - ecasa

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Integrating indicators of water column effects Algal bioassays - ecasa

Integrating indicators of watercolumn effectsAlgal bioassays


Integrating indicatorsWhy do we need such indicators?– Very few records of eutrophication around finfishor shellfish farms; usually because the sites arewell-flushed (good site selection)– But ….. a constant flux of nutrients is beingreleased from the cages– The algal bioassay is one way to gauge thewater column effects of aquaculture


Algal bioassay• Algal grazing may obscure algal growth• Seawater in dialysis bags to reducegrazing• Dialysis bags deployed along nutrientgradient away from fish cages• 5-day deployment for algal growth• Chlorophyll a measurements


eference50250Fish farmCurrent-meterDirection ofcurrent


(μg/l)1.510.5average value of Chl adown to 5m water depthKephalonia,GreeceJune 20060FF 25 50 100 200 550chl a4.543.532.521.510.50Cephalonia-6/06Algal bioassay 6/2006initial FF 25m 50m 550mfilteredunfiltered


Conclusions• Bioassay is relatively easy and cheap tocarry out• Provides biological means to estimatezone of influence of aquaculture on waterquality (nutrients, algal production)


Vidlin Voe 7/066chl a (ug/l)54321Scotland*all bioassay bagswere filled with20um pre-filteredseawater0t0 filt t0 unfilt 0m 50m 100m 200m RefLoch Creran, Scotland 8/06In other cases,filtration does not …65chl a (ug/l)43210t0 Filt t0 Unfilt 0m 50m 100m 200m Ref


2,0Chllorophyl a(ug/L)1,51,00,5FSWSWPortoroz,Slovenia0,0CC S50 S100 REFStations2,0Phaeopigments (ug/L)1,51,00,5FSWSW0,0CC S50 S100 REFStations


Tromso, Norway 7/06chl a (ug/l)2.52.01.51.00.5In Tromso, allwater in bags waspre-filtered0.0t0 F t0 U 0m 50m 100m 200m RefEilat 1/07chl a (ug/l)1.61.41.210.80.60.40.20initial FF 25m 50m 550mfilteredunfiltered


Chioggia, Italy - mussel farmJuly 2006all water in bags was prefilteredChl aμg L -114012010080601.5 m6 m40200UnfilteredseawaterPrefilteredseawaterS2G 50 mH 100 mDistance from the mussel farmL 750m


Why pre-filter the water?• Measurable algal growth is a balance between growthand grazing• Dialysis bags provide algae with nutrients (for growth) &refuge from grazers, but if the seawater has sufficientnumbers of grazers, grazing effect will occur inside bags• Prefiltration may eliminate large alga-vores• Prefiltration also eliminates large diatoms & dinos thatmay be key primary producers• 20um filtration may not eliminate the small grazers;removal of large grazers may enhance grazing by smallgrazers (on pico – e.g. Synech, Prochlor, etc.)• Conclusion – need to look at the phytoplankton andgrazer communities (microscopy, FACS)

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