How multiple stressors
affect habitat and water
quality for freshwater pearl
mussels
Freshwater Biologists Meeting, Trinity College
4th March 2016
Freshwater pearl mussel life strategy is to live long in
very low nutrient, clean, fast flowing rivers
Good mussel populations have very low intensity
land use with low levels of artificial drainage
Many have a lake upstream
And they have one or more steep mountain streams
to replenish river bed gravels and cobbles
The adult mussels wedge between protective river bed
stones and the juveniles are beneath buried in gravels
Negative effects often lethal
Negative effects often sub-lethal
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
Commonly assessed for EIS / NIS
Rarely properly assessed
Example of sub-lethal adult / lethal juvenile issues
Excess mobile sand interfering with filtration
Excess nutrients interfering with filtration
Decaying organic products interfering with filtration
Longer term damage – in this case flow issues
Stress
Death
Dead shells
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
Energetics of Bivalve Feeding
1) Power output from pump, frictional heat, kinetic
2)
3)
4)
5)
energy
Energy consumed by the beating of the lateral cilia,
work done by pump
Energy consumed by the cells carrying the bands of
lateral cilia
Energy consumed by the gills, water processing
Energy consumed by the water processing by the
pump
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
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)
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
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)
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)
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)
Multiple stressors, in-Combination Effects
lead to Cumulative Impacts
P from land
during rainfall
Inadequate dilution
due to low flow
Algal growth
Algal die-off
Drainage increases
winter flows
Rain, increase in flow,
P released from drape
Poor redox,
No juvenile survival
Dead, P laden organic
material infiltrates
substrate
Drainage reduces
summer flows
Dead algae not
dissipated due
to low flow
Stress testing mussels to gauge ability to clam
Conclusions
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
1)
Example of reversal of decline
Farmer retired, land bought for
conservation
Just following land acquisition
After one growth period
Start of recovery in river bed
Example of protective terrestrial habitat
that needs to remain unimpacted
We need to protect low-nutrient wetter land.....
Connectivity through small natural
streams to river
Demographic quadrat here
Demography
10
Owenriff 2014 All quadrats (n=208)
9
8
% of mussels
7
6
5
4
3
2
1
0
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
THANK YOU
Comhairle Chontae
Dhún na nGall
Donegal County Council
www.donegal.ie