The impacts of non-indigenous oysters on biodiversity and

ecosystem functioning

Dannielle Green

Supervisor: Tasman Crowe (UCD)Collaborators: Carlos Rocha (TCD), Bas Boots (UCD)

www.ucd.ie/marbee

Potential impacts of invasive species

Invasivespecies

Ecosystem functioningBiodiversity

Ecosystem services

Physical structure of oystersHard substratum new habitat for colonisation

Complex shell structure biodiversity

Biological activities of oysters

Biodeposits

Oxicsediment

Anoxic sediment

Buried N and C

Mineralisation Nitrification

Denitrification

NH4+ NO‐

2 NO‐3

NO‐3 NO‐

2 N2

OM loading

PhytoplanktonFiltering

N2  or N2O

CH4

CO2Organic Matter

Environmental context

Sedimentshores

Rocky shores

Impacts of

Oysters

Ecosystem functioningBiodiversity

Ecosystemservices

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

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.

Experiment 1• Effects of oysters on boulder-field communities

especially the honeycomb worm, Sabellaria alveolata

Experiment 1• Increasing cover of alive and dead oysters were

added onto boulders

Reduction of S. alveolata with oysters on boulders

Alive oysters Dead oysters

0

100

200

300

400

0 5 50 100 0 5 50 100

Num

ber o

f S. a

lveo

lata

tube

s pe

r m2

Oyster cover (%)

0

5

10

15

0 5 50 100 0 5 50 100

Num

ber o

f spe

cies

Oyster cover (%)

Impacts on biodiversity in boulder-fields

Alive oysters Dead oysters

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.

Experiment 2• Effects of oysters were also assessed in mud-

flat and mussel beds habitats

Measures of biodiversity

• Epifauna

• Infauna

Measures of ecosystem functioning

Functional measures: • Porewater nutrient profiles

– Sediment – water interface flux– Nutrient turnover rates

• Gas – Flux rates of CO2 , CH4 and N2 O

0

7

14

21

0 5 50 100 0 5 50 100

Num

ber o

f spe

cies

Oyster cover (%)

Impacts on biodiversity at L. Swilly

Mussel-beds Mud-flats

Consistent facilitation of an invasive barnacle, macroalgae and a key grazer in all habitats

0

15

30

45

0 5 50 100

Num

ber o

f ind

ivid

uals

Oyster cover (%)

Impacts on pore-water ammonium fluxes

Similar result for silicate

Mussel-beds Mud-flats

0

0.4

0.8

1.2

0 5 50 100 0 5 50 100

Am

mon

ium

(mm

ol-1

m-2

d-1 )

Oyster cover (%)

Impacts on community respiration

Mussel-beds Mud-flats

0

50

100

150

0 5 50 100 0 5 50 100

Car

bon

diox

ide

(mg-

1m

-2h-

1 )

Oyster cover (%)

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)

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.

HELP and ADVICE• Ciarán McGonigle, Loughs Agency• Carlos Rocha, TCD• Bas Boots, UCD

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

Acknowledgements

www.ucd.ie/marbee

Any questions?