Abt Associates Inc. WA2-9_T4_Wetland.Fish.productivity.memo_12.24.09 1

Environment and Resources

55 Wheeler Street, Cambridge, MA  Tel: 617 492-7100  www.abtassociates.com

Date December 24, 2009

To Tom Born, Josh Hall, and Erik Helm U.S. Environmental Protection Agency

From David Mitchell

Subject WA2-9 T4_Wetland Fish Production Function memo.

The purpose of this memo is to identify an approximate proportion of total wetland ecosystem function

that is associated with fish production for application of willingness-to-pay (WTP) assessments for the

habitats of interest. There is no generally-recognized default proportion of wetland function associated

with the fish production function since wetlands vary tremendously. Therefore, a number of qualitative

approaches at determining this proportion were investigated and indicated:

 Comparison of fish production on a strictly biomass basis (i.e., trophic transfer) provides a

minimal estimate (<1%) of fish production function. This value is considered an underestimate as

it does not take into account all of habitat services important for fish production.

 HGM wetland functional assessment methods provide examples where fish production function

has been judged by wetland experts to be a major ecosystem function and where it is not. Using

recent HGM examples from Gulf Coast states, a gradient of relative importance from 20% to 0%

could be possible, depending on wetland type.

 Use of a stated preference survey case study in the Northeast provided a public opinion of the

relative importance of fish production relative to overall wetland restoration at 25.6%.

Using this information (discussed below) and best professional judgment, we derived relative values of

the percentage of fish production function for various wetland types and settings:

 For coastal marine and freshwater tidal marsh areas a value of 25% of wetland function is

suggested.

 For Great Lakes freshwater coastal marsh areas a value of 20% of wetland function is suggested.

 For Inland freshwater wetlands systems, a value of 10% of wetland function is suggested.

Further information and detail on these findings and conclusions are contained below.

1 Introduction

Wetlands provide a suite of physical, chemical, and biological interactions that are collectively referred to

as wetland ecosystem functions. With regard to fish, wetlands can provide an important ecosystem

function in their ability to provide critical spawning, nursery, forage and refuge areas for fish species

(collectively termed “fish production function”). The importance of the fish production function of

wetlands is highly significant for many species. It has been estimated that 95% of the finfish and shellfish

that are commercially harvested in the United States are wetland-dependent (Feierabend and Zelazny

1987; cited in Street et al. 2005). Yet not all wetlands are equally effective in producing young fish; some

inland wetlands in headwater areas may have negligible fish production. Clearly, the importance of the

fish production function will vary significantly between wetland habitat types as well as be highly

influenced by the specific properties within the individual wetland. In addition, when wetland restoration

has actually been implemented, the actual size, configuration and hydrological regime that are available

memorandum
Abt Associates Inc. WA2-9_T4_Wetland.Fish.productivity.memo_12.24.09 2

may be constrained by site-specific factors and may or may not be conducive to all wetland ecosystem

functions (Zedler 2000).

Despite this variability, it is useful to identify, if possible, an approximate proportion of total wetland

ecosystem function that is associated with fish production for valuation of the wetland restoration/creation

needed for restoring lost fish biomass from impingement and entrainment (I & E) losses and application

to a public “willingness-to-pay” (WTP) assessment. However, a review of the wetland literature suggests

that there are no generally-recognized quantitative or default values as to what percentage of total wetland

ecosystem functions are directly associated with fish production. This memo summarizes several lines of

evidence that were considered in a first attempt to derive reasonable representative values, based on:

 General Wetland Characteristics

 Biomass Transfer Efficiency

 Wetland Functional Assessment Methods

 Previous WTP work

1.1 General Wetland Characteristics

The regional wetland habitat types (and representative species) that we considered for application in the

HEA approach for restoring lost fish biomass from I&E losses include marine wetlands (tidal salt marshes

(Spartina alterniflora); seagrasses (Zostera marina, Thalassia testudinum); kelp forests (Macrocystis

pyrifera) and freshwater wetlands (tidal freshwater marshes, non-tidal freshwater marshes) (Typha

latifolia). We have discussed these habitat types and their expected levels of primary productivity

previously (Mitchell et al. 2009). There are different sets of ecosystem functions associated with these

different types of wetlands. Some of the typical functions that are common to most emergent wetlands

(Spartina, Typha) include: wave and shoreline protection, surface water storage (including flood control),

subsurface water storage and recharge, nutrient and sediment retention, water quality enhancement,

maintenance of plant and animal communities, and societal values (e.g., aesthetics, biodiversity). For the

seagrasses and kelp, the ecosystem functions are less broad but could include wave protection, nutrient

retention, water quality enhancement, maintenance of plant and animal communities, and societal values.

We have much less quantitative information on fish production services in seagrasses and kelp forests; so

much of the following discussion pertains mainly to emergent wetlands.

In addition to the distinction between marine/estuarine habitats and freshwater ones, the literature also

distinguishes between the functional significance of wetlands that are directly connected to or bordering a

larger waterbody and those which are isolated or in upper watershed locations (e.g., headwater swamps).

The former generally are considered to have higher ecological functions than the latter. For example, the

North Carolina Coastal Regional Evaluation of Wetlands Significance (NC-CREWS) evaluated thirtyeight wetlands functions for each mapped wetland area within 20 coastal counties (Street et al. 2005).

Wetlands were classified as “exceptional”, “substantial”, or “beneficial” in functional significance. The

evaluation indicated that riparian wetlands (i.e., those wetlands directly connected to or fringing a larger

waterbody) were ranked much higher than non-riparian wetlands; being greater than 50% in the

“exceptional” category and having none ranked lower than “substantial” (Street et al 2005).

1.1.1 Marine Habitats

Based on the historic literature, there is general consensus that marine tidal wetlands and seagrasses

provide good to excellent fish production function for many important commercial, recreational and

forage species (Graff and Middleton 2003, Street et al. 2005). Tidal wetlands are well suited for juveniles

or young-of-year since they provide: good food availability resulting in high growth rates; increased

survivorship due to lowered mortality; and a favorable physico-chemical environment for their

development. Marshes are important refuge habitat for young fish due to the interaction of temperature,

turbidity, and dense vegetative structure in reducing the effectiveness of predators (Deegan, Hughes, and

Rountree 2000). While the precise role of such habitats as nurseries for juvenile fish has been recently

critically re-examined, suggesting the need for better quantification of the precise role of nearshore
Abt Associates Inc. WA2-9_T4_Wetland.Fish.productivity.memo_12.24.09 3

ecosystems in producing more adult fish (Beck et al 2003), the fish production function of tidal wetlands

would be considered high.

1.1.2 Freshwater Habitats

There is more variability in the importance of fish production within freshwater wetlands. This is due to

the greater variety of freshwater wetland environments (freshwater marshes, bottomland flood plain,

headwater swamps, bogs, wet meadows, etc.). While some of these freshwater wetlands may have

important fish production function, there may be little or none associated with others, based on

hydrology, geographic locations, water quality or other factors (Graff and Middleton 2003). In particular,

tidal freshwater marshes along the seacoast and coastal marshes connected to the Great Lakes have been

identified as having important fish production function.

Tidal freshwater wetlands are located at the upper end of estuaries and while they experience tidal

fluctuations they are essentially fresh in water quality and dominant plant composition (e.g., cattails,

bulrushes, etc). These wetlands are commonly used by freshwater, estuarine, marine and migratory fish

since their dense vegetation and rapid detritus cycling provides excellent refuges for juveniles, spawning

areas, and good food availability (Graff and Middleton 2003).

Non-tidal freshwater wetlands which are connected to large bodies of water may also have enhanced fish

production function. For example, it has been estimated that about 75% of the fish species in the Great

Lakes utilize coastal marshes during some part of their life cycle (Stephenson 1990, Jude and Pappas

1992, Meixler 2005). Lake Erie is reported to support the best fishery of the Great Lakes, in terms of

diversity and number, partly because of its extensive system of adjoining coastal marshes (Graff and

Middleton 2003).

The importance of fish production in isolated non-tidal freshwater wetlands, forested wetlands (i.e.,

seasonally flooded areas), swamps, bogs, etc. has not been well-quantified but has the potential to be far

less than that found in either tidal or coastal situations. Small wetlands attached to lakes or fringing

marshes on rivers may be locally productive. However, inland wetlands, such as isolated shallow

depressions, headwater swamps, or seepage-derived wetlands may have poor or non-existent fish

production (Graff and Middleton 2003). Thus the anticipated potential for fish production in non-coastal

inland wetlands would be lower.

1.2 Biomass transfer efficiency

Consideration of the transfer efficiency of biomass production via trophic feeding links is one quantitative

way of estimating the importance of the wetland habitat to fish production. For application of the HEA

trophic transfer approach to estimate necessary habitat size to restore I & E losses, we have assumed that

the rate of biomass transfer from primary producers to secondary consumers (i.e., juvenile fish and

invertebrate production) is fixed at a certain percentage of the primary production. These transfer rates

were obtained from Natural Resource Damage Assessment (NRDA) cases and other restoration projects

(see Stapler et al 2008).

For example, the coastal wetland restoration project conducted by PSEG in New Jersey used a net transfer

rate of 0.0088 from primary production to fish and invertebrates (this value included an adjustment for

carbon export of 45% out of marsh). For the Lake Barre oil spill restoration, Penn and Tomasi (2002)

used a slightly lower net biomass transfer from marsh primary producers to fish and invertebrates of

0.008.

The small magnitude of the biomass transfer rates should not be used as indicative of the proportion of

total wetland function that is associated with fish production. This is because this biomass transfer only

considers the trophic feeding aspect of fish production, while it has been shown that favorable growth

conditions and protection from predators may be an equally important function of the wetland habitat

(Deegan et al., 2000). Thus, it is not only the production of detritus going into the food chain that is
Abt Associates Inc. WA2-9_T4_Wetland.Fish.productivity.memo_12.24.09 4

critical, but the physical structure, reduced energy environment, and diversity of sub-habitats that are

necessary to have successful fish production.

1.3 Wetland functional assessment methods

Wetland functional assessments were developed as tools to quantify the level of applicable functions of a

particular wetland. One of the more commonly used methods is the hydrogeomorphic (HGM) functional

assessment (Smith et al.1995). The HGM fundamentals have been incorporated into most current wetland

functional assessments and, as of 2008, the U.S. Army Corps of Engineers (USACE) had developed and

approved 18 regional guidebooks compiled by wetland experts for application at the local level (NRCS

2008).

Recent regional HGM documents were reviewed to see how fish production functions are translated into

this method (if at all) and what was the relative importance of the fish production function compared to

other wetland functions. We examined three recent regional guidebooks pertaining to wetlands in the

same geographic region (Alabama and Mississippi, West Gulf Coastal Plain) and which dealt with coastal

tidal fringe wetlands (Shafer et al. 2007), forested wetlands (Klimas et al. 2005), and inland headwater

slope wetlands (Noble et al 2007).

For the coastal tidal wetlands, the five major wetland functions were: (1) wave energy alteration; (2)

biochemical cycling; (3) nekton utilization potential; (4) provide habitat for marsh-dependent wildlife;

and (5) characteristic plant community structure and composition (Shafer et al 2007). Fish production was

represented by nekton utilization potential, which was a composite functional capacity index (FCI)

derived as an average of three wetland attributes – aquatic edge, hydrology and nekton habitat diversity

(NHD). These wetland attributes are of interest, because they indicate the wetland features that are more

critical to fish and shellfish production.

Aquatic edge is a composite measure of the amount of tidal drainage network, the percentage of the

wetland perimeter exposed to tide, and percentage of shoreline relative to total wetland area. The

hydrology index is based on the amount of site open to free exchange of tidal energy, the amount of

inundation of the lower marsh area, and amount of hydrologic alteration. The NHD rates the presence of

a number of sub-habitats that typically support fish and invertebrate production including: low marsh,

high marsh, intertidal creeks/channels, sub-tidal creeks/channels, ponds or depression (temporary or

permanent), shallow (<1 m) sand or mudflats, submerged aquatic vegetation (SAV) and oyster reef. For

the highest possible NHD rating, a wetland needs to have 5 of these sub-habitats present (Shafer 2007).

For the inland forested wetlands, a different set of six major wetland functions were used: (1) detain

floodwater; (2) detain precipitation; (3) cycle nutrients; (4) export organic carbon; (5) maintain plant

communities; and (6) provide habitat for fish and wildlife (Klimas et al 2005). Emphasis on habitat value

includes both fish and higher animals. In contrast, the regional guidebook for evaluating functions in

slope headwater swamps (i.e., groundwater seepage derived wetlands) does not include a provision for

fish production, indicating that this is not an important wetland function in that types of system (Noble et

al 2007). Review of this guidebook indicates that these wetland habitats are considered more critical as

habitats for amphibians or birds than for fish.

The HGM does not result in an overall summary score or index but is used, in conjunction with the arealweighting of the various wetland areas, to compare overall functional units to reference wetlands or to

gauge the level of impact of a proposed project. Nonetheless, all major wetland functions are equally

scored and considered under HGM, so for coastal wetlands, a relative proportion of 20% of overall

wetland function theoretically would be attributed to fish production while a similar consideration for the

forested wetland would be 16% with a negligible value (0%) for the headwater swamp. Given the nature

of the HGM protocol, these values should not be used directly, but in the selection of important wetland

functions for particular wetlands, the guidebooks document some degree of de facto best professional

judgment (BPJ) of wetland experts that clearly distinguish a gradient of relative importance of fish

production from coastal to inland upland settings.
Abt Associates Inc. WA2-9_T4_Wetland.Fish.productivity.memo_12.24.09 5

Another common wetland assessment method, based on an index of biological integrity (IBI), was

examined for identification of fish production importance. An IBI-based method evaluates a wetland’s

ability to maintain a balanced community, having a species composition, diversity and functional

organization comparable with that of minimally disturbed (i.e., reference) wetlands within a region

(USEPA 1998). However, the IBI uses the condition of selected biota (e.g., vascular plants, periphyton,

macroinvertebrates, fish, amphibians, birds) to arrive at a summary score (index) to evaluate whether the

wetland is potentially being degraded by chemical, physical or biological stressors. While IBI methods

supports this type of decision-making they do not provide direct information regarding the status and

importance of individual functions.

1.4 Previous WTP work

Another independent approach to the relative valuation of ecosystem services is based on the public WTP

to restore a wetland habitat and its perceptions about the importance of various functions of that habitat.

Accordingly, it was possible to identify, based on a stated preference survey, public opinion regarding the

approximate proportion of total wetland ecosystem value that is associated with fish production functions.

The Narragansett Bay Wetland Restoration Study allowed an opportunity for public input on a survey to

judge the importance of the proportion of a restored wetland’s value attributable to fish habitat services

(Johnson et al 2002). Under various restoration scenarios, this value ranged from 20.4 to 32.3%, with an

overall mean of 25.6% (USEPA, 2004).

2 General Findings

The purpose of this memo was to identify an approximate proportion of total wetland ecosystem function

that is associated with fish production; for application of WTP assessments for the habitats of interest. A

number of qualitative approaches at determining this proportion were investigated and indicated:

 Habitat fish production function refers to the collective ecosystem characteristics which provide

critical spawning, nursery, forage and refuge areas for juvenile or young-of-year fish species.

 There is no generally-recognized default proportion of wetland function associated with the fish

production function since wetlands vary tremendously. Less in known regarding the fish

production function in seagrasses and kelp forests than emergent wetlands.

 There is general recognition in the literature that the following wetland habitats have potentially

high fish production significance: coastal tidal wetlands, freshwater tidal wetlands, and Great

Lakes coastal wetlands.

 Non-coastal inland wetlands are more likely to have a lower fish production function.

 Comparison of fish production on a strictly biomass basis (i.e., trophic transfer) provides a

minimal estimate (<1%) of fish production function. This value is considered an underestimate as

it does not take into account all of habitat services important for fish production.

 HGM wetland functional assessment methods provide examples where fish production function

has been judged by wetland experts to be a major ecosystem function and where it is not. Using

recent HGM examples from Gulf Coast states, a gradient of relative importance from 20% to 0%

could be possible, depending on wetland type.

 Use of a stated preference survey case study in the Northeast provided a public opinion of the

relative importance of fish production relative to overall wetland restoration at 25.6%.

3 Conclusions

As discussed above, there are no generally-recognized quantitative or default values as to what percentage

of the total wetland ecosystem functions are directly associated with fish production for the habitats of

interest. We also recognize the great variability possible within the same habitat type based on the

presence or absence of features conducive to fish production. Nonetheless, using the information
Abt Associates Inc. WA2-9_T4_Wetland.Fish.productivity.memo_12.24.09 6

discussed above and BPJ, there is sufficient qualitative consensus to suggest the following relative values

of the percentage of fish production function to aid in the WTP estimates:

 For coastal marine and freshwater tidal marsh areas a value of 25% of wetland function is

suggested; based on the generally-recognized qualitative importance of this habitat to coastal

fisheries. This value is comparable to the stated preference value of 25.6%.

 For Great Lakes freshwater coastal marsh areas a value of 20% of wetland function is suggested,

based on the generally-recognized importance of this habitat to Great Lakes fisheries. The slightly

lower value compared to marine systems reflects the absence of the regular tidal cycle which

provides more sub-habitat diversity within the system.

 For Inland freshwater wetlands systems, a value of 10% of wetland function is suggested. This

intermediate value reflects the diversity of wetland types as well as the lower fish production

potential of some isolated inland wetlands included in this category.

These values should be considered a first approximation that could be refined through additional data

collection and investigation of site-specific factors.
Abt Associates Inc. WA2-9_T4_Wetland.Fish.productivity.memo_12.24.09 7

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