Assessing Ecosystem Functional Equivalence between Constructed and Natural Oyster

Reefs

Kevin S. Dillon and Mark S. Peterson

Increase marsh habitat & complexity Stabilize marsh edge Trophic mediators Metrics of restoration have been measured

relative to cultch, design, & depth Most studies focus on larger, subtidal

reefs Little attention to small, intertidal reefs

particularly in the Northern Gulf Coast

Why small, intertidal oyster reefs?

Research Objectives Assess the ecological equivalency

of natural vs. constructed reefs Measure the trajectory of colonization and

ecological functions on natural vs. constructed oyster reefs over 2 years

Assess changes in faunal assemblages Quantify food-web dynamics using stable

isotope analysis – Restore the isotopes, restore the function

Study Site Grand Bay National Estuarine Research Reserve

Retrograding delta Freshwater inputs small Microtidal

Methods Natural reefs were

assessed pre-deployment Determine and quantify

faunal assemblage Quantify oyster density

Construct oyster reefs & designate natural reefs Deployed randomly assigned

sampling units, interspersed in constructed reefs

Construct reefs with 30-35% coverage

Establish upland and lowland stakes

Methods

Artificial reef cultch deployed in August 2006

Natural and constructed reefs sampled every 6 months for 2 years

3 sample trays from each reef harvested

Samples washed through 500 µm sieve

ID & quantify oyster spat, seed, adults and other fauna

Samples were freeze dried, acid washed, rinsed, dried and ground to a fine powder for SI analysis.

Samples analyzed for δ13C and δ15N values with a Thermo Delta V Advantage stable isotope ratio mass spectrometer coupled to a Costech elemental analyzer

RESULTS

15008

Summary of Total Macrofauna Collected Over Two Years

Stable Isotopes in Ecology Stable C and N isotopes can be traced through food webs with predictable fractionation and mixing at various trophic levels

13C show very little enrichment (~1 ‰) in tissues with trophic transfer and is useful in tracing C sources through the food web

15N shows an enrichment of 2-4‰ with each trophic transfer and can be used to determine an organisms trophic level Isotope ratios are expressed as parts per thousand differences from a standard material:

δX = [(Rsample / Rstandard) – 1] x 1000 where X is the stable isotope (13C, 15N), R is the corresponding ratio of heavy to light isotopes (13C/12C or 15N/14N)

Primary Producers and Plankton 13C vs. 15N

November 2006

May 2007

0

5

10

15

20

25

30

35Sa

linity

Date

Salinity - Bayou Cumbest Grand Bay SWMP data

December 2007

May 2008

BC CR NR Balanus sp. x Crassostrea virginica spat x x x Crassostrea virginica seedling x x Ischidium recurvum x Melita sp. x x Panopeus herbstii x Xanthid crabs x x Capitellidae x Eunicidae x

List of unbiqitous taxa used in the cluster analysis and SIMPROF tests by bayou pooled by reef type and Spring 2007 and 2008 periods.

BC-Nat 2007 BC-Con 2007 BC-Nat 2008 BC-Nat 2008

CR-Nat 2007 CR-Con 2008 CR-Nat 2008 CR-Con 2007

NR-Nat 2007 NR-Con 2007 NR-Nat 2008 NR-Con 2008

SIMPROF test, p < 0.05

SIMPROF test, p < 0.05

SIMPROF test, p < 0.05

Cluster analysis similarity profiles 13C

CONCLUSIONS Density of oyster spat and seed are greater in constructed reefs. Taxa richness is greater in all constructed reefs Increases over time Assemblages vary between subsystems Artificial constructed reefs at long term site were had similar community structure and stable isotope values after 15 months Reef trophic structure: Amphipods < Crabs/Mussels < Oysters/Polycheates < Shrimps < Barnacles < Large Polycheates and Fish (Gobies/Toadfish) Spatial and temporal variability in 13C (and 34S) values with salinity