Yallop Extra reading Flashcards
Peay et al 2009
Signal crayfish introduced late 70s, carriescrayfish plague and alters benthis food webs through predation, competition and modification of habitat.
used chelae to enlarge body, and pres on fish eggs and large inverts.
compete for shelter w atlantic juvenile salmon, displace fish from shelter.
more aggressive in lab trials than white clawed.
study: river w historically only whiteclawed, known point of signal invasion.
fish surveyed by electrofishing, crayfish surveys with traps w funnel entrances, 15 traps per site. Recorded pH, channel characteristics and conductivity.
7 years after, detected 0.65km downstream of point of introduction.
13 yeas after, detected 3.4km downstream and 0,6 upstream. Salmonid pops at 0 abundance.
strong neg correlations betw abundance of signal crayfish and density of trout.
weak neg correlation btw bullhead and salmon.
Pace et al 1999
5 points about trophic cascades
- trophic cascade: stong inverse patterns in abundance or biomass links in a food web - dont represent predictions of equilibrium.
- Alternative states - non linear ecological interactions.
- Enrichment strengthens trophic cascade - eg Pace et al 1999 lake A bass dominated, B minnow donimated. after nutrient enrichment, A increased most in pp.
- Refuges stabilise cascades. allows larger zooplankton to establish. At night migrate out of refuge to clear water.
- Omnivores very important.
Pace et al 1999
examples of trophic cascades.
- Pitcher plant trophic cascade documented - mosquito predation has strong effect on protozoans community composition, shifts predation on bacterial biomass.
- Costa rica - 4 level trophic cascade documented - beetles prey on ants, ants eat herbivores, herbivores graze on piper plants. Tested by comparing 4 forests w different levels of piper plants, enclosure w beetles added - 15% piper plants had petioles whereas control was 50%.
- Brown trout in NZ stream results in 6x difference in annual pp of adjacent stream which has different top predator.
Carpenter et al 1995
threshold of P loading is >0.36-1.5mg/m3/day.
Testeh whether grazer control becomes inneffective at higher levels of P.
measures responses of chl and biomass of blue/green algae - indicators of eutrophication.
Compare 3 small lakes - reference, piscivorous and planktivorous.
Piscivorous lake has largemouth bass, drives planktivores away from pelagic waters.
Test lakes enriched with fertiliser, N.P ratio of 25.
Chl a weekly measure at 6 depths.
Phytoplankton samples collected weekly from 3 depths.
Found herbivore biomass effectively controlled by planktivory, and after enrichment herbivore biomass in piscivorous lake increased after enrichment.
chl conc corresponded to vollenweider model but piscivore lake was only half what was expected - shows large cladocera exert strong top down effect on phytoplankton. algae digested much slower by larger cladocera and consume more, so nutrient level doesn’t increase as much.
Scheffer et al 1993
switching alternative states.
food web manipulation can switch, nutrient reduction not always successful.
vegetation promotes clearness whereas turbidity prevents plant growth by light limitation.
Transition from turbid to clear - induced by forcing switch ‘pushing ball over the hilltop’, so within attraction basin of clear state. Needs temporary reduction in turbidity for recolonisation of macrophytes.
Or - ‘move hill up to other side of ball’.depth and turbidity determine UW light level, so reduce depth to increase light.
Restoration often slowed by internal loading. may require additional shock therapy.
Bottom feeders - carp or bream cause resuspension of material. Removal can give instant clarity.
Robb et al 2003
study of phoslock in 2 enclosed estuaries - FW in Aus.
Phoslock - modified clay, permanently binds P.
lab trials show only 1mm layer needed.
Aims to determine application rate pf phoslock needed, evaluate use of phoslock and see effect on phytoplankton community.
tested historically worse areas for cyanobacterial blooms. weekly sampling at 7 sites in each river, 3 weeks before treatment and 1 week after - to monitor N, TP, silicate, DOC, Chl a and abiotic factors.
sampled phytoplankton after 1st application, 2h, 6h, 1 day and then weekly for 29weeks.
Saw that in treated lake, P decreased from 50-20 µg/l, then below detection rate of 5µg/l in less than an hour after treatment. in untreated river, inreased to 200µg/l.
Van de Bund and van Donk, 2002
Van Donk and Gulati - 1995
Zwemlust - Diuron herbicide 1968 caused shift to turbidity
1987, started electrofishing and seine nets, removed bream - quick switch to clear and macrophyte growth.
High nutrient loading meant unstable in long term.
Similar in 1999 removal of rudd.
Found that short term, fish removal was sufficient, but not sustainable long term.
shift in size of herbivores in very important, big effect.
Transition period - allowed high density of zooplanton before macrophytes grew. low productivity due to heterotrophic activity.
Massive variation btw years in bottom up and top down controls making long term clarity hard.
Monitored Zwemlust by secchi depth, chemical parameters and phyto and zooplankton density sampling. Also fish biomass by mark recapture method. Consumption of macrophytes estimated by ‘bird days’.
Macrophyte change:
1989 Elodea nuttallii, selective herbivory by rudd and coot decreased E. nuttallii.
1991 Ceratophyllum demersum. coot decline. allelopathic chemicals can reduce epiphyte cover.
1992 3 years of potamogeton.
Also potamogeton overwinter structures promote algal blooms.
Switches in macrophyte caused by selective herbivory of rudd and coot.
6 years after manipulation, turbid again.
Sondergaaurd et al 2007
long term data only available for a few lakes but return to turbidity after 10 years normally. Often due to internal P loading, can continue for 10-15 years after reducing external loading.
in Denmark and Netherlands - after 1970 chemical treatment started in sewage works, decrease TP and TN by 73% 1978-1993.
methods of manipulation include stocking piscivores eg pike fingerlings at high densities.
Lake Hald - hyperlimnetic oxygenation for 20 years, Positive results
Lake Sonder - First alum treatment, improvements for 3 years, then reversal.
Lake Braband - sediment dredging, removed 0.5 millionm3 P rich sediment but no improvement as continually high loading.
Sondergaaurd et al 2007
Reasons for manipulation failure
Gulati et al 2008
- Fish removal: not enough removed, rapid return of cohorts of zooplanktivores. Invert predators eg Chaoborus.
Internal P loading and high resuspension of sediment. Instability due to low macrophyte coverage. - Pike stocking: low survival, low consumption of fish, bad timing - relative to cyprinid hatching. not reccomended as lowest success rate.
- Sediment removal - low P sorption capacity of new sediment surface. incomplete dredging.
- P-fixation: aging of alum, reduced retention capacity.
- oxygenation - no permanent effect achieved
- inability of daphnids to eat poor filamentous and colonialcyanobacteria.
- foraging by fish and birds - prevents macrophyte coverage.
- insufficient reduction of allochthonous P and increase in autochthonous P.
Gulati et al 2008
New ecotechnological measures include: reduction of sediment resuspension (by creating islands to minimise wind fetch and reduce wave amplitude);
water-level management (allow more fluctuations in water level, to increase quality and biodiversity);
Zebra mussel, Dreissena polymorpha as effective grazers on lake seston.
Criteria for successful manipulation: sustained increase in secchi depth, sig reduction in cyanobacterial blooms, increase in densities of large bodied grazers, increase macrophyte cover.
N control is more difficult as cyanobacteria can fix N in heterocysts.
Unsure how to retain low pop offish after big reduction, unless repeated, no success documented.
Phyto promote accumulation of fine sediment which is resuspended by wind fetch, problem in coastal countries.
high water levels reduce light availability, whereas low increases damage from ice and wave action and dessication in summer.
Use of Zebra mussels
Lake Erie - dreissena abundand but thought daphnids control phyto. Other studies say water above driessena beds depleted in Chl a, and relocate energy from pelagic to benthic system in sinking pseudofaeces.
Lake Huron - dreissena selectively remove cryptomonas and cyclotella but not microcystis, whereas in Hudson river, they have strongest clearance of microcystis.
Pires et al 2005 showed they can feed on both microcystin producing strain of cyanobacteria and microcystin free strain.
Macrophyted can serve as attachment substrate which may sink them. also injure swimmers and neg impact native fauna
