Progress and Plans for the Incorporation of Oysters and Menhaden in the Water

Quality Model

Oysters

• At present, a uniform mortality rate is employed, which represents baywide biomass

• Representation of local biomass requires spatially and temporally varying mortality to represent harvest and disease

• Will be incorporated in 2008

Coupling Ecological with Eutrophication Models

Basic Issues

• How to process spatially and temporally detailed ICM information for use with Ecopath?

• What are the commonalities between the two models?

• How to interface?

An Ecopath Model of ICM

Preliminary Investigation of Increased Predation by Menhaden

• 2002 ICM kinetics installed on 1992 4,000-cell grid

• Ecopath model constructed by Jim Hagy

• Proof of Concept Stage

The ICM Predation Term

RMsz = microzooplankton maximum ration (g algal C g-1 zoo C d-1)SZ = microzooplankton biomass (g C m-3)KHsz = half saturation concentration for carbon uptake by microzooplankton (g C m-3)RMlz = mesozooplankton maximum ration (g algal C g-1 zoo C d-1)LZ = mesozooplankton biomass (g C m-3)KHlz = half saturation concentration for carbon uptake by mesozooplankton (g C m-3)Phtl = rate of predation by other planktivores (m3 g-1 C d-1)

Simulate more menhaden by increasing Phtl by 20% !!!!!

Effects of Increased Predation on ICM Organic Carbon Pools

Effects of Increased Predation on ICM Phytoplankon

Effects of Increased Predation in Ecopath on Organic Carbon Pools

Ecopath Base

Ecopath with 20% Increase in Menhaden

EcopathBase

IncreasedMenhaden

Phytoplankton Ecotrophic Efficiency 0.45 0.467

Free Bacteria, g C m-2 2415 2294

Benthic Bacteria, g C m-2 298 283

Proposed Approach

• Substitute ICM primary producers and rates into Hagy’s Ecopath model. Adjust as necessary.

• Substitute ICM primary producers and rates with 20% increase in predation into above. Adjust as necessary.

• Examine differences

Effects of Increased Predation on Organic Carbon Pools Common to ICM and Ecopath

ICM Base ICM Increased Predation

Meiofauna diet fraction from benthic algae 0.175 0.125

Meiofauna diet fraction from sediment POC 0.425 0.475

Mid-Bay

Conclusions du Jour

• Ecopath alone is not suited for this investigation.– Requires input of algal biomass, growth rate

– Does not incorporate effects such as enhanced nutrient recycling

• We have explored a way in which ICM and Ecopath can be used together. ICM for primary producers, Ecopath to carry effects to higher trophic levels

Conclusions du Jour

• Small predation increases in ICM do not affect production due to enhanced nutrient recycling. This may be a model artifact and requires additional investigation.

• Increased menhaden biomass represented in Ecopath does not have major impacts on higher trophic levels.