Indirect impacts of invasive crayfish ecosystem engineering - Poster for the British Hydrological Society meeting on Urban Aquatic Ecosystems

1. Indirect impacts of invasive crayfish ecosystem engineering
Edward Willis-Jones1, C Quezada1, G Harvey1, M Trimmer1, J England2 & J Grey1
g.e.willis-jones@se12.qmul.ac.uk
1 - Queen Mary University of London; 2 – Environment Agency
1 Introduction & Rationale 2 Objectives & Methods
• Some crayfish species are globally renowned as • We use 24 artificial pond mesocosms to test the effects of
destructive invaders due to severe direct impacts on crayfish (Fig 2) density on various parameters below
native aquatic biota
• Ponds contain sediment enriched with leaf
detritus, macrophytes and invertebrate communities
• Their relatively large size and omnivorous feeding derived from the original sediment sample plus subsequent
habits mean that invasive crayfish can outcompete natural colonization. Three density treatments (0, 2 & 4
native species and directly affect all trophic levels crayfish per pond) are replicated 8x
• Turbidity & Dissolved Oxygen: Dedicated probes Fig 2: Red swamp
• Crayfish can also act as ‘ecosystem engineers’ by
suspended in the water column for 24h for diurnal patterns crayfish, Procambarus clarkii
reducing macrophyte abundance and through
activities such as swimming and burrowing which are Fig 1: Burrows and turbid water due to signal • Dissolved Methane: Water extracted from centre of each pond using a gas-tight syringe, discharged
known to disturb fine sediments, thereby altering the crayfish in the River Windrush, Oxfordshire
(Harvey et al 2011) into gas-tight vial, overflowed & capped. Analysed using GC/FID
physical structure of river beds (Fig 1)
• Methane Efflux: Gas tight cylindrical chamber containing 300ml air positioned at water surface with an
• This bioturbation can increase the concentration of organic matter, nutrients and reactive chemical open base to allow free water circulation and capture ebullition from sediment. 3ml air extracted using
species in the water column. However, the knock-on effects of this are yet to be studied gas-tight syringe every 15mins for 1hr into gas-tight vial. Analysed using GC/FID
• Methane Oxidation: Collection identical to dissolved methane. Vials then have CH4-enriched
• We hypothesise that microbial stimulation due to elevated organic matter, together with the increase in headspace introduced and are incubated with CH4 measured at 24hr intervals using GC/FID
reactive chemical species, will reduce the oxygen available for other biota. In addition, this reduced
oxygen environment may enhance methane (CH4) production, and bioturbation may increase ebullition • Chlorophyll a: biofilm collected from 45mm2 ceramic tiles and 500ml water samples collected using a
from the sediments, resulting in elevated CH4 efflux to the air column sampler. All samples filtered, re-suspended in acetone and assessed spectrophotometrically
• Zooplankton Community: All ponds seeded with identical communities of zooplankton prior to
• We also hypothesise that the change in the light, nutrient and chemical regimes will affect algal addition of crayfish. Six weeks after crayfish addition samples will be collected using a column sampler
biomass and alter the zooplankton community and identified to determine community composition
3 Preliminary Results
25 16.00 5.0
4.5
14.00 Control
20 2 Crayfish 4.0
12.00 4 Crayfish
CH4 Concentration (µmol L-1)
3.5
Suspended Solids (mg L-1)
Dissolved Oxygen (mg L-1)
10.00
15 3.0
4 Crayfish 8.00 2.5
2 Crayfish
Control
10 2.0
6.00
1.5
4.00
5 1.0
2.00
0.5
20 Mar 27 Mar 03 Apr 20 Mar 27 Mar 03 Apr 20 Mar 27 Mar 03 Apr
0 0.00 0.0
17:00 21:00 01:00 05:00 09:00 13:00 17:00 10:00 14:00 18:00 22:00 02:00 06:00 10:00 14:00 4 Crayfish 2 Crayfish Control
Time Time Treatment
Fig 3: Mean turbidity per treatments over 24h in March 2013. Fig 4: Dissolved oxygen in 1 pond from each treatment in August 2012 (data Fig 5: Mean (±1SE) dissolved methane concentration of per treatment at
Water temperature ~4°C from Claudio Quezada) 1200 for three dates in early Spring 2013. Water temperature ~4°C
• Ponds containing crayfish are more turbid than the control • The presence of crayfish significantly altered the 24h oxygen • The presence of crayfish may reduce the concentration of
ponds even when the crayfish are somewhat inactive due to low profile in the ponds (Fig 4) dissolved methane in the water, although the variability in the
temperatures (Fig 3) results from the control ponds was very large (Fig 5)
• In particular, a large oxygen deficit arose during daylight hours
• It also indicates a possible diurnal pattern with turbidity in the 4 crayfish pond, suggesting that photosynthetic • If further replication supports this pattern, it might indicate that
increasing during the daylight hours production could not match that in the control pond crayfish bioturbation of the sediments disrupts the anoxic
conditions required for methanogenesis
• The lack of replication to date prevents further speculation.
• The lack of difference between the two crayfish treatments may
However, provides initial evidence for a knock-on effect of • Alternatively, this pattern could indicate that crayfish cause an
be due to their relative inactivity at low temperatures
crayfish bioturbation increase in methane efflux, probably through ebullition, thereby
• Confirms that the crayfish are indeed stirring up the sediment in reducing the dissolved methane concentration
a similar fashion to that documented in a natural river by Harvey • We speculate that the pattern may change during periods of
et al (2011) higher crayfish activity, ie when the water temperature is higher
4 Future Work
• Work on this project has only just begun. It will continue until September as an EA-funded MSc • If differences in methane metabolism are substantiated, then a further avenue to investigate would be
project, after which it will be undertaken as a NERC CASE funded PhD studentship with the EA the potential contribution of methane derived carbon to the food web at different crayfish densities
• The results presented above are preliminary; more data will be collected to confirm the consistency of • This could be determined using the stable carbon isotope composition of zooplankton (sensu Jones
the patterns that have been observed to date et al 1999); more 13C-depleted zooplankton in any of the crayfish treatments would indicate a greater
contribution of methane derived carbon to their biomass
• In addition, data are yet to be collected/analysed on methane efflux, methane oxidation, algal biomass
and the zooplankton community • If evidence is found for the presence of prolonged oxygen deficits, then further work will be done to
determine what effect this might have on other aquatic biota
• All these data will be collected in two blocks this year, once in early spring (Mar-Apr), and again in early
summer (May-Jun) to account for any effect of seasonality • In particular, the effect of such a deficit on young fish development will be investigated as this could
have both an environmental and an economic impact
• This year, only red-swamp crayfish, Procambarus clakii, are being studied; however, since different
species have different daily/seasonal activity patterns and different behavioural traits, other invasive • Finally, field studies in rivers and lakes of known crayfish density will be undertaken to corroborate
crayfish species will also be investigated in the future any significant effect found in the mesocosm studies
Acknowledgements: This work is part funded by the Environment Agency awarded to JG. EWJ is currently undertaking the work as part of his MSc in Aquatic Ecology by Research at QMUL and will continue it next year in a NERC CASE funded PhD at QMUL
References: Harvey et al (2011) Evaluating the role of invasive aquatic species as drivers of fine sediment-related river management problems: The case of the signal crayfish (Pacifastacus leniusculus). Progress in Physical Geography 35(4) p517-533; Jones et al (1999) Stable isotope analysis of zooplankton carbon nutrition in humic lakes. Oikos 86(4) p97-104