How multiple stressors affect habitat and water quality for freshwater pearl mussels. Freshwater Biologists Meeting, Trinity College 4 th March 2016

Transcription

1 How multiple stressors affect habitat and water quality for freshwater pearl mussels Freshwater Biologists Meeting, Trinity College 4 th March 2016

2 Freshwater pearl mussel life strategy is to live long in very low nutrient, clean, fast flowing rivers

3 Good mussel populations have very low intensity land use with low levels of artificial drainage

4 Many have a lake upstream

5 And they have one or more steep mountain streams to replenish river bed gravels and cobbles

6 The adult mussels wedge between protective river bed stones and the juveniles are beneath buried in gravels

7 Negative effects often lethal Negative effects often sub-lethal

8 Freshwater pearl mussel declines Lethal events (documented events toxic and major silt / nutrient pollution events) - RARE Chronic and / or pattern of ongoing repeated or cumulative sub-lethal events drainage, intensification, loss of terrestrial protective habitat - leading to loss of juvenile recruitment and slow loss of adult mussels COMMON Rarely properly assessed Commonly assessed for EIS / NIS

9 Example of sub-lethal adult / lethal juvenile issues Excess mobile sand interfering with filtration

10 Excess nutrients interfering with filtration

11 Decaying organic products interfering with filtration

12 Longer term damage in this case flow issues

13 Stress Death Dead shells

14 Energetics of Bivalve Feeding More straightforward than most animals No predator / prey dynamics to consider - No choice of food to consider - Bivalves are either: highly oxygen demanding, long-lived, slow growing or are tolerant of low oxygen, short-lived, fast growing

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17 Energetics of Bivalve Feeding 1) Power output from pump, frictional heat, kinetic energy 2) Energy consumed by the beating of the lateral cilia, work done by pump 3) Energy consumed by the cells carrying the bands of lateral cilia 4) Energy consumed by the gills, water processing 5) Energy consumed by the water processing by the pump

18 Energy balance in bivalves Rate of synthesis of ATP in the lateral cells Dependent on: ease of feeding / effort of processing inappropriate food / velocity of water / temperature of water V Rate at which the active cilia are hydrolysing ATP Dependent on: ease of feeding / effort of processing inappropriate food / velocity of water / temperature of water

19 Energy balance in bivalves Ratio of synthesis (good food / oxygen in) of ATP to hydrolysis (work done in gaining food / oxygen) In general (Jørgensen, 1990, 1996; Riisgård et al.,2014) Good conditions: 2 ATP molecules hydrolysed per dynein per ciliary beat = approx. 58% rate of synthesis (enough left for gamete production) Poorer conditions: 3 ATP molecules hydrolysed per dynein per ciliary beat = approx. 87% rate of synthesis (metabolism compromised) Ongoing poor or severe conditions: 4 ATP molecules hydrolysed per dynein per ciliary beat = negative rate of synthesis (metabolism compromised, ongoing stress and death)

20 Energy balance in bivalves FPM life strategy to filter clean waters, more in summer (growth and gamete development periods), less in winter (low metabolism, low growth, no gamete development) This life strategy depends on low stress conditions, especially in the growing season

21 High flow, clean river bed, clear water, low temperature: mussels are in naturally low metabolic state and are filtering at low level (high energy cost filtration)

22 Low flow, less clean river bed, clear water, higher temperature: mussels are in naturally high metabolic state and are filtering at low level (not able to take advantage of low energy cost filtration)

23 Good flow, clean river bed, clear water, higher temperature: mussels are in naturally high metabolic state and are filtering well (able to take advantage of low energy cost filtration)

24 Multiple stressors, in-combination Effects lead to Cumulative Impacts P from land during rainfall Inadequate dilution due to low flow Algal growth Drainage increases winter flows Poor redox, No juvenile survival Rain, increase in flow, P released from drape Dead, P laden organic material infiltrates substrate Drainage reduces summer flows Algal die-off Dead algae not dissipated due to low flow

25 Stress testing mussels to gauge ability to clam

26 Conclusions 1) Multiple stressors act to kill juvenile mussels and stress adult mussels 2) Ongoing or chronic stress leads to inefficient uptake of food and oxygen and to muscle decay and death 3) There are no simple levels of silt, nutrient and hydrological change that can be used as a rule of thumb (stop asking please!) 4) More protective catchment management is needed to restore favourable condition, protect mussels from stress and rehabilitate conditions for juvenile survival

27 Example of reversal of decline

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30 Farmer retired, land bought for conservation Just following land acquisition

31 After one growth period

32 Start of recovery in river bed

33 Example of protective terrestrial habitat that needs to remain unimpacted

34 We need to protect low-nutrient wetter land...

35 Connectivity through small natural streams to river

36 Demographic quadrat here

37 % of mussels Demography 10 9 Owenriff 2014 All quadrats (n=208)

38 FPM Ian Killeen Environment Agency, United Utilities, Natural England, Gail Butterill, Jane Atkins, Grace Martin RPS Francis Mackin, Mark Magee NPWS Department of Arts, Culture & Gaeltacht Áine O Connor, Jim Ryan, Liz Sides Kerry LIFE team - Richard O Callaghan Sheila Downes, FPM CEN group Comhairle Chontae Dhún na ngall Donegal County Council THANK YOU