Transplanted Oyster (Crassostrea virginica) Beds as Self-Sustaining Mechanisms for Water Quality Improvements in Small Tidal Creeks: A Pilot Study Kimberly A. Nelson

OYSTER FILTRATION  Oysters filter up to 120 L of H 2 O daily.  In flume studies, oysters may remove up to 50% of the seston from the overlying water column.  Oysters may decrease the risk of eutrophic conditions, thereby improving light penetration and water clarity.  Oysters filter up to 120 L of H 2 O daily.  In flume studies, oysters may remove up to 50% of the seston from the overlying water column.  Oysters may decrease the risk of eutrophic conditions, thereby improving light penetration and water clarity.

HYDRODYNAMICS Flow Low Velocity “Shadow Zone” REEF Increased turbulence at reef crest Increased flow velocities at reef crest Low velocity “shadow zones” downcurrent and on reef edges Increased turbulence at reef crest Increased flow velocities at reef crest Low velocity “shadow zones” downcurrent and on reef edges

OYSTER RESTORATION Current Methods Large subtidal reefs of high- relief, to improve reef health and survival. Current Methods Large subtidal reefs of high- relief, to improve reef health and survival. PROBLEMS 1.Subtidal reefs may not allow the majority of the water column to reach the benthos for filtration. 2.High velocities may decrease filtration capabilities. PROBLEMS 1.Subtidal reefs may not allow the majority of the water column to reach the benthos for filtration. 2.High velocities may decrease filtration capabilities. Piankatank River, Virginia

Establish self-sustaining oyster reefs in two small tidal creeks. Examine hydrodynamic changes associated with the placement and subsequent growth of the oyster reefs. Investigate downstream changes in suspended particulate matter, chlorophyll a and ammonium as function of reef placement and growth. Establish self-sustaining oyster reefs in two small tidal creeks. Examine hydrodynamic changes associated with the placement and subsequent growth of the oyster reefs. Investigate downstream changes in suspended particulate matter, chlorophyll a and ammonium as function of reef placement and growth. OBJECTIVES

STUDY AREA UPLAND LOWER CREEK

REEF PLACEMENT: September m X 3 m PVC frame with hardware cloth Mature oysters (3”) 125 live oysters per m 2 REEF PLACEMENT: September m X 3 m PVC frame with hardware cloth Mature oysters (3”) 125 live oysters per m 2 METHODS

WATER QUALITY ANALYSIS Monthly Samples Total Suspended Solids (TSS) Chlorophyll a Ammonium Ebbing Tide 1 m 3 m REEF 4-6 cm 5 cm

SAMPLING SCHEME – Upland Flow Measurements Reef Channel Profile Sediment Analysis Reef Characteristics Density Growth Mortality Flow Measurements Reef Channel Profile Sediment Analysis Reef Characteristics Density Growth Mortality

OYSTER PARAMETERS Aug - 00Dec - 00Jun - 01 Mean size (mm) length width Total mortality % survivorship DEC - 00 JUN % 43.8 % 79.7% 56.1 %

Mean TSS - Lower Creek Reef Control TSS mg L -1 Above Below TSS mg L -1 * Reef & Control Channels Above & Below Reef

Mean TSS – Upland Reef Control TSS mg L -1 ** Above Below Reef & Control Channels Above & Below Reef

CHLOROPHYLL a Phytoplankton is the preferred food source of Crassostrea virginica. Oysters may deplete 20 to >75% of chlorophyll a concentrations from the particulate supply over oyster beds in flume studies. By active filtration of phytoplankton and nutrients (phosphate, nitrogen, silica), oysters may decrease the potential for eutrophication in estuaries.

Mean Chlorophyll a – Lower Creek Chl a µg L -1 Reef & Control Channels Above & Below Reef Reef Control Above Below

Mean Chlorophyll a - Upland Chl a µg L -1 Reef Control Chl a µg L -1 Above Below Reef & Control Channels Above & Below Reef

FLOW DYNAMICS Velocity Discharge Max impact

Reef Control Hour 3 Hour 3 Chlorophyll a - Lower Creek Reef to Control Channels Chl a µg L -1

Hour 3 Chlorophyll a - Lower Creek Above to Below Reef Chl a µg L -1 Above Below

Reef Control Hour 3 Hour 3 Chlorophyll a - Upland Reef to Control Channels Chl a µg L -1 *

Hour 3 Chlorophyll a - Upland Above to Below Reef Chl a µg L -1 Above Below * * *

AMMONIUM (NH 4 + ) After consumption and processing, seston is deposited as feces or pseudofeces. Oysters may contribute 15 to 40% of the dissolved organic nitrogen within in situ domes. After consumption and processing, seston is deposited as feces or pseudofeces. Oysters may contribute 15 to 40% of the dissolved organic nitrogen within in situ domes.

Ammonium - Lower Creek Reef to Control Channels Ammonium µg L -1 Reef Control

Ammonium - Lower Creek Above to Below Reef Ammonium µg L -1 Above Below

Ammonium - Upland Reef to Control Channels Ammonium µg L -1 Reef Control

Ammonium - Upland Above to Below Reef Ammonium µg L -1 Above Below

Hour 3 Hour 3 Ammonium - Lower Creek Reef to Control Channels Ammonium µg L -1 Reef Control

Hour 3 Ammonium - Upland Above to Below Reef Ammonium µg L -1 Above Below

Hour 3 Hour 3 Ammonium - Upland Reef to Control Channels Ammonium µg L -1 Reef Control

GRAIN SIZE ANALYSIS Particle Diameter (  m) Volume (%) Particle Diameter (  m) Volume (%) Reef Matrix Downstream Upstream Control Reef Matrix Downstream Upstream Control Mode(µm)Mean(µm)

LAST THOUGHTS Small, viable oyster reefs can be established and maintained over periods of at least ten months duration in small upland tidal creeks. An optimal ratio of reef size to flow discharge exists whereby filtration is maximum. Additional studies are needed to determine the volume of reef ratio and the reef geometry that would achieve desired results utilizing maximum resources. Small, viable oyster reefs can be established and maintained over periods of at least ten months duration in small upland tidal creeks. An optimal ratio of reef size to flow discharge exists whereby filtration is maximum. Additional studies are needed to determine the volume of reef ratio and the reef geometry that would achieve desired results utilizing maximum resources.