1. www.ucd.ie/marbee
The impacts of non-indigenous
oysters on biodiversity and
ecosystem functioning
Dannielle Green
Supervisor: Tasman Crowe (UCD)
Collaborators: Carlos Rocha (TCD), Bas Boots (UCD)

2. Potential impacts of invasive species
Invasive
species
Ecosystem
Biodiversity functioning
Ecosystem
services

3. Physical structure of oysters
Hard substratum  new habitat for colonisation
Complex shell structure  biodiversity

4. Biological activities of oysters
OM loading N2 or N2O
Filtering
Phytoplankton
Biodeposits
Oxic Mineralisation Nitrification
sediment CO2 NH4+  NO-2  NO-3
Organic Matter
Anoxic CH4 Denitrification
sediment NO-3  NO-2  N2
Buried N and C

5. Environmental context
Impacts
of
Oysters
Sediment Rocky
shores shores
Ecosystem
Biodiversity functioning
Ecosystem
services

6. My objectives
1. Characterise potential impacts of Pacific oysters
on:
(a) Biodiversity
(b) Ecosystem functioning
2. Test whether impacts vary under different
environmental contexts and at different oyster
abundances

7. Experiments
Objectives have been addressed using field
experiments:
• Expt. 1: Biodiversity and the establishment of a
protected biogenic habitat in boulder-fields.
• Expt. 2: Biodiversity and ecosystem functioning
of mud-flat and mussel bed habitats.
• Expt. 3: Microbial diversity and functioning in
mud-flat habitats.

8. Experiment 1
• Effects of oysters on boulder-field communities
especially the honeycomb worm, Sabellaria
alveolata

9. Experiment 1
• Increasing cover of alive and dead oysters were
added onto boulders

10. Reduction of S. alveolata with oysters on boulders
400
Alive oysters Dead oysters
Number of S. alveolata tubes per m2
300
200
100
0
0 5 50 100 0 5 50 100
Oyster cover (%)

11. Impacts on biodiversity in boulder-fields
15
Alive oysters Dead oysters
Number of species
10
5
0
0 5 50 100 0 5 50 100
Oyster cover (%)

12. Key impacts on boulder-field biota
• The honeycomb worm, Sabellaria alveolata was
negatively impacted by oysters.
– Not due to competition for space
• Biodiversity was enhanced at the lowest cover of
living oysters but peaked at greater cover.
• Fucus vesiculosus and Littorina littorea were
facilitated by oysters and may have indirectly
reduced S. alveolata establishment.
• Effects were due to both the physical structure
and the biological activities of oysters.

13. Experiment 2
• Effects of oysters were also assessed in mud-
flat and mussel beds habitats

14. Measures of biodiversity
• Epifauna
• Infauna

15. Measures of ecosystem functioning
Functional measures:
• Porewater nutrient profiles
– Sediment – water interface flux
– Nutrient turnover rates
• Gas
– Flux rates of CO2, CH4 and N2O

16. Impacts on biodiversity at L. Swilly
21
Mussel-beds Mud-flats
Number of species
14
7
0
0 5 50 100 0 5 50 100
Oyster cover (%)

17. Consistent facilitation of a an invasive
barnacle, macroalgae and a key grazer in all habitats
45
30
Number of individuals
15
0
0 5 50 100
Oyster cover (%)

18. Impacts on pore-water ammonium fluxes
1.2
Mussel-beds Mud-flats
Ammonium (mmol-1 m-2 d-1)
Similar result for silicate
0.8
0.4
0
0 5 50 100 0 5 50 100
Oyster cover (%)

19. Impacts on community respiration
150
Mussel-beds Mud-flats
Carbon dioxide (mg-1 m-2 h-1)
100
50
0
0 5 50 100 0 5 50 100
Oyster cover (%)

20. Summary of impacts
• Biodiversity generally increased.
– but in some cases peaked or declined at greater cover
– Several taxa were consistently facilitated in all habitats
• Physical structure decreased establishment of a
protected biogenic habitat.
• Pore-water nutrient fluxes were altered.
• Community respiration increased with the
greatest cover of oysters.
– Likely due to microbial activity (Expt. 3)

21. Conclusions
• Alteration of nutrient cycling and decomposition
rates may lead to nutrient retention and changes
in primary productivity.
• These changes may have consequences for
ecosystem services, e.g. reduced carrying
capacity for aquaculture.
• Some impacts were context dependent.
• Further research is needed to accurately scale
these impacts up and predict their effects on
ecosystems.

22. Acknowledgements
HELP and ADVICE
• Ciarán McGonigle, Loughs Agency
• Carlos Rocha, TCD
• Bas Boots, UCD
www.ucd.ie/marbee
FIELD and LAB WORK
• Bas Boots, Mark Browne, Amy Haughton, Robert Fitzpatrick, Laila Higgins, Erin
Gleeson, Kelly Dunagan, Eoin O’Gorman, Juan Severino, Julien Chopelet, Myriam
Callier, Paul Brooks, Angela Gallagher, Jesko Zimmermann, David Blockley, Ciarán
McGonigle & colleagues, Francis O’Beirn
FUNDING AGENCIES and SIMBIOSYS coordinators
• Environmental Protection Agency, NDP, SSTI, IRCSET & IRCHSS (via UCD Graduate
Research Education Programme in Sustainable Development)
• Jane Stout , Jens Dauber and David Bourke TCD

23. Any questions?

24. Impacts on microbial activity
• Oxic sediment
440
TPF (ug-1 d-1 dry sediment)
330
220
110
0
O L M H
Cover of oysters

25. Impacts on microbial community structure
• Ammonia oxidising microbes in oxic sediment