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As we see it. A broader view of ecosystem services related to oyster restoration

Authors:
  • Florida Atlantic University, HBOI, 5775 Old Dixie Hwy Ft. Pierce FL 34946, USA

Abstract

The importance of restoring filter-feeders, such as the Eastern oyster Crassostrea virginica, to mitigate the effects of eutrophication (e.g. in Chesapeake Bay) is currently under debate. The argument that bivalve molluscs alone cannot control phytoplankton blooms and reduce hypoxia oversimplifies a more complex issue, namely that ecosystem engineering species make manifold contributions to ecosystem services. Although further discussion and research leading to a more complete understanding is required, oysters and other molluscs (e.g. mussels) in estuarine ecosystems provide services far beyond the mere top-down control of phytoplankton blooms, such as (1) seston filtration, (2) benthic–pelagic coupling, (3) creation of refugia from predation, (4) creation of feeding habitat for juveniles and adults of mobile species, and for sessile stages of species that attach to molluscan shells, and (5) provision of nesting habitat.
MARINE ECOLOGY PROGRESS SERIES
Mar Ecol Prog Ser
Vol. 341: 303– 307, 2007 Published July 4
INTRODUCTION
Dramatic decreases in eastern oyster Crassostrea
virginica populations have occurred in many estuar-
ies along the USA Atlantic and Gulf coasts (e.g.
Rothschild et al. 1994, Coen & Luckenbach 2000,
French McCay et al. 2003, NRC 2004). Although the
loss of this valuable fishery species is cause for con-
cern, increasing recognition of the many ‘ecosystem
services’ provided by healthy oyster reefs and by
bivalve molluscs in general has led to a broader
appeal for restoration of oyster reefs and other
bivalve-dominated habitats (see ASMFC 2007). One
of these ecosystem services, the grazing of phyto-
plankton populations, was the focus of a recent
review (Pomeroy et al. 2006), which concluded that
filtration by C. virginica in Chesapeake Bay, either at
historical densities or at current restoration target
densities, is insufficient for top-down control of the
spring phytoplankton bloom and for reduction of
© Inter-Research 2007 · www.int-res.com**Email: coenl@dnr.sc.gov
**Authors after Coen in alphabetical order
AS WE SEE IT
Ecosystem services related to oyster restoration
Loren D. Coen1,*, Robert D. Brumbaugh2,**, David Bushek3, Ray Grizzle4,
Mark W. Luckenbach5, Martin H. Posey6, Sean P. Powers7, S. Gregory Tolley8
1South Carolina Department of Natural Resources, Marine Resources Research Institute, 217 Fort Johnson Road,
Charleston, South Carolina 29412, USA
2The Nature Conservancy, University of Rhode Island, Narragansett Bay Campus, South Ferry Road, Narragansett,
Rhode Island 02882-1197, USA
3Haskin Shellfish Research Laboratory, Rutgers University, 6959 Miller Avenue, Port Norris, New Jersey 08349, USA
4Jackson Estuarine Laboratory, University of New Hampshire, 85 Adams Point Road, Durham, New Hampshire 03824, USA
5Virginia Institute of Marine Sciences, College of William and Mary, PO Box 350, Wachapreague, Virginia 23480, USA
6Department of Biology and Marine Biology, University of North Carolina, 601 S. College Road, Wilmington,
North Carolina 28403, USA
7Department of Marine Sciences, University of South Alabama, and Dauphin Island Sea Lab, 101 Bienville Blvd,
Dauphin Island, Alabama 36528, USA
8Florida Gulf Coast University, Coastal Watershed Institute, 10501 FGCU Blvd South, Fort Myers, Florida 33965, USA
ABSTRACT: The importance of restoring filter-feeders, such as the Eastern oyster Crassostrea
virginica, to mitigate the effects of eutrophication (e.g. in Chesapeake Bay) is currently under debate.
The argument that bivalve molluscs alone cannot control phytoplankton blooms and reduce hypoxia
oversimplifies a more complex issue, namely that ecosystem engineering species make manifold
contributions to ecosystem services. Although further discussion and research leading to a more
complete understanding is required, oysters and other molluscs (e.g. mussels) in estuarine eco-
systems provide services far beyond the mere top-down control of phytoplankton blooms, such as
(1) seston filtration, (2) benthic– pelagic coupling, (3) creation of refugia from predation, (4) creation
of feeding habitat for juveniles and adults of mobile species, and for sessile stages of species that
attach to molluscan shells, and (5) provision of nesting habitat.
KEY WORDS: Crassostrea virginica · Restoration · Chesapeake Bay · Filter-feeders · Water quality ·
Ecosystem services
Resale or republication not permitted without written consent of the publisher
Mar Ecol Prog Ser 341: 303–307, 2007
summer hypoxia on a bay-wide scale. This central
premise in Pomeroy et al. (2006) is the subject of a
Comment by Newell et al. (2007, this volume) and is
indirectly addressed by Cerco & Noel (2007) in a
recent modeling paper.
Our aim here is to address arguments that advo-
cates of oyster restoration have advanced to the
effect that enhancing oyster populations ’is an easy
solution for controlling phytoplankton blooms‘. We
also seek to clarify the positions that researchers in
this field have advanced as the rationale for oyster
restoration, vis-à-vis localized impacts on water
quality and the provision of habitat (i.e. ‘ecosystem
services’). Our intent is to clarify our position as
restoration scientists on the manifold ecosystem ben-
efits of healthy population densities of filter-feeding
bivalves, i.e. to demonstrate the attendant services of
oyster restoration that are sometimes overlooked or
misinterpreted (e.g. Lenihan & Peterson 1998, Coen
et al. 1999, Coen & Luckenbach 2000, Grabowski &
Peterson 2007).
ECOSYSTEM SERVICES PROVIDED BY OYSTERS
We take issue with 2 of the points highlighted
recently by Pomeroy et al. (2006), who state that (1)
native oyster restoration or (2) the introduction of an
exotic (non-native) oyster species have been widely
advocated in the scientific literature as solutions
to eutrophication in Chesapeake Bay. In reviewing
the goals and success criteria for native oyster reef
restoration, Coen & Luckenbach (2000) and others
(reviewed in ASMFC 2007, Coen et al. 2007, Grab-
owski & Peterson 2007) expressly noted that the sys-
tem-level effects of oyster filtration have been poorly
quantified, especially as they might relate to any spe-
cific restoration project (but see Nelson et al. 2004,
Newell 2004, Grizzle et al. 2006). The goals and suc-
cess criteria emphasized by Coen & Luckenbach
(2000) and elaborated upon subsequently by Luck-
enbach et al. (2005), Coen et al. (2007) and S. P. Pow-
ers et al. (unpubl.) have focused, among others, on
the development of: (1) sustainable oyster popula-
tions; (2) enhanced species diversity; (3) trophic com-
plexity; and (4) localized material fluxes to the ben-
thos. Similarly, Grabowski & Peterson (2007) point out
that although effects of oyster restoration on water
quality in large water bodies are difficult to quantify,
localized effects of oyster filtration (e.g. reduced tur-
bidity) have been observed and, together with other
ecosystem services (e.g. Meyer et al. 1997, Allen et al.
2003, French McCay et al. 2003, Peterson et al. 2003)
provided by oyster reefs, constitute a strong case for
restoration.
We are aware of only one peer-reviewed paper that
expressly advocated the introduction of C. gigas to
Chesapeake Bay for the purpose of improving water
quality (Gottlieb & Schweighofer 1996). In advocating
the consideration of introducing C. gigas to Chesa-
peake Bay for fisheries restoration, Mann et al. (1991)
mentioned possible water quality benefits, but ex-
pressly stated that their commentary was directed
towards recovery of a commercial fishery. Ruesink et
al. (2005) were cited by Pomeroy et al. (2006) as sug-
gesting that the Ocean Studies Board of the National
Research Council recommended the introduction of an
exotic species to Chesapeake Bay for controlling
phytoplankton blooms; this is inaccurate (cf. NRC
2004). The potential benefits of filtration by oysters as
stated in the popular press1ignore the realities of the
scale of restoration required to achieve such benefits,
and we concur with Pomeroy et al. (2006) that using
this position to support the introduction of an exotic
oyster species such as Crassostrea ariakensis places
the ecosystem at risk.
We welcome the effort to advance more realistic
expectations for oyster restoration to policy makers,
resource managers and the public, and to dampen the
enthusiasm for the introduction of exotic oyster spe-
cies, which is based on unfounded assumptions (see
Newell et al. 2007, Pomeroy et al. 2007, this volume).
Nevertheless, by attributing to oyster restoration a
goal of system-wide water quality improvement and
then proceeding to argue for the futility of that goal,
while failing to mention the real and more tractable
goals of oyster restoration, critics risk adversely affect-
ing all other oyster restoration efforts in Chesapeake
Bay and elsewhere. Specifically, Grabowski & Peter-
son (2007) have identified 7 categories of ecosystem
services provided by oysters: (1) production of oysters;
(2) water filtration and concentration of biodeposits
(largely as they affect local water quality); (3) provi-
sion of habitat for epibenthic fishes (and other verte-
brates and invertebrates see Coen et al. 1999,
ASMFC 2007); (4) sequestration of carbon; (5) aug-
mentation of fishery resources in general, (6) stabi-
lization of benthic or intertidal habitat (e.g. marsh);
and (7) increase of landscape diversity (see also re-
views by Coen et al. 1999, Coen & Luckenbach 2000,
ASMFC 2007).
In the following section we highlight categories 2, 3,
5, 6 & 7, as summarized in Grabowski & Peterson
(2007).
304
1E.g. Zimmerman T: How to revive the Chesapeake Bay: filter
it with billions and billions of oysters; US News & World
Report, December 29, 1997. Harper S: $2 million approved
for oyster revival efforts in Bay; The Virginian-Pilot, January
24, 2007
Coen et al.: Ecosystem services related to oyster restoration
DISTURBANCE AND RESTORATION
The dramatic decline in oyster abundances in
Chesapeake Bay and other estuaries along the Gulf
and Atlantic coasts of the USA over the 20th century
has led to concomitant reductions in hard substrate
habitat in ecosystems dominated by sedimentary habi-
tats (e.g. Rothschild et al. 1994, NRC 2004). Studies
comparing invertebrate faunal abundance and diver-
sity between restored and non-restored oyster reefs
(e.g. Luckenbach et al. 2005, Rodney & Paynter 2006,
L. D. Coen et al. unpubl.), between oyster reefs or
reef mimics, and soft bottom habitats (e.g. Posey et al.
1999, Tolley & Volety 2005), and among oyster reefs
of varying complexity (e.g. Coen & Luckenbach 2000,
Luckenbach et al. 2005), consistently find higher
abundances, biomass and species richness on the
structurally more complex reef habitats. Densities of
decapods and meiofauna on oyster reefs are similar
to those in other structured habitats (e.g. Glancy et
al. 2003, Hosack et al. 2006).
Abundance, biomass and species richness of finfish
species are higher at oyster reefs than in unstructured
estuarine habitats (reviewed in Coen et al. 1999, ASMFC
2007). Some of these species (e.g. gobies, blennies and
toadfish) are obligate reef residents throughout their
post-larval life, while other species are either facultative
residents or transient associates (discussed in Breitburg
1999, Coen et al. 1999, ASMFC 2007). Though few
studies have yet sought to quantify secondary produc-
tion attributable to oyster reefs, Peterson et al (2003)
estimated that restored oyster reef habitat may yield
0.26 g m–2 yr–1 of fish and large decapod crustacean
biomass in southeastern USA estuaries.
Habitat disturbance and/or loss are ranked worldwide
as the principal threat to biodiversity, and are also re-
sponsible in part for many declines in fisheries (Fogarty
& Murawski 1998, Lenihan & Peterson 1998, Beck et al.
2001, NRC 2007). In the southeastern USA (southern
North Carolina, South Carolina, Georgia, parts of
Florida) and in Virginia and the Gulf of Mexico, oysters
are predominantly intertidal, forming a protective
breakwater that retards shoreline (primarily marsh) ero-
sion (e.g. Meyer et al. 1997, Grizzle et al. 2002, Coen &
Bolton-Warberg 2005, ASMFC 2007, NRC 2007). In
addition to natural erosion, coastal development and
boat traffic have accelerated disturbance of oysters and
of the fringing saltmarsh, e.g. by increasing wave effects
(Grizzle et al. 2002, Coen & Bolton-Warberg 2005, Piazza
et al. 2005, Wall et al. 2005, NRC 2007, L. D. Coen et al.
unpubl, L. J. Walters et al. unpubl). Oyster restoration
can slow down disturbance effects on marshes and
fringing oysters, and constitutes an alternative to the
hard bulk-heading of shorelines (e.g. Meyer et al. 1997,
Coen & Bolton-Warberg 2005, NRC 2007).
There is a need for rigorous establishment and clear
articulation of the goals of oyster restoration, especially
in the context of large public expenditures, as well as
deliberations surrounding the introduction of an exotic
species. Our central tenet is that ecological goals of
oyster restoration are broader than the top-down
control of phytoplankton production on a system-wide
basis. The complex interactions between filter-feeders
and their environment are not completely understood,
but evidence is accumulating that native and intro-
duced bivalves, including those on aquaculture farms,
have significant impacts on seston and overlying
phytoplankton communities on both local and larger
scales (reviewed in Dame 1996, French McCay et al.
2003, NRC 2004, Cerco & Noel 2007, Grant et al. 2007).
For example, Mercenaria mercenaria aquaculture in
lower Chesapeake Bay appears to be enhancing sea-
grass abundance (see Grizzle et al. 2006). In Florida,
seagrass beds often harbor dense American horse
mussel Modiolus americanus populations (up to 2000
ind. m–2; Valentine & Heck 1993), and the activities of
these and other filter-feeders enhance seagrass pro-
duction further via a positive feedback loop (e.g.
Reusch et al. 1994, Peterson & Heck 1999, 2001a,b,
C. C. Wall et al. unpubl.). In their recent modeling
paper, Cerco & Noel (2007) assess the impact of a 10%
increase in oyster biomasss in Chesapeake Bay, on 3
spatial scales, and suggest that the enhancement of
submerged aquatic vegetation would be the greatest
direct beneficiary of oyster restoration through water
clarity.
CONCLUSIONS
Although it is difficult to determine empirically the
system-wide effects of historical abundances of oysters
and of restoration targets (Pomeroy et al. 2006, Newell
et al. 2007), localized influence of oyster reefs on water
quality has been verified. In situ measurements have
demonstrated that oysters reduce the quantity of sus-
pended solids and phytoplankton (chlorophyll aor
other proxies) (e.g. Nelson et al. 2004, Grizzle et al.
2006). At the current oyster abundances in Chesa-
peake Bay, these effects are limited, but significantly
enhanced abundances of filter-feeders can signifi-
cantly improve water quality in shallow, mesohaline
regions of estuaries (e.g. Newell & Koch 2004, Cerco
& Noel 2007).
Acknowledgements. We thank J. Kraueter, R. Dame, J. Levin-
ton, K. Walters, R. Newell, J. Grabowski, B. Peterson, P.
Wilber, and F. Holland for their comments and critiques. A
majority of the authors were part of the Oyster Restoration
Metrics Working Group supported by Grants from NOAA’s
South Carolina Sea Grant Consortium (NOAA# NA16RG-
305
Mar Ecol Prog Ser 341: 303–307, 2007
2250) and the South Carolina Department of Natural
Resources through its Marine Resources Research Institute.
This is Contribution #616 from the Marine Resources
Research Institute, South Carolina Department of Natural
Resources, Contribution #451 from the Jackson Estuarine
Laboratory, University of New Hampshire, and Contribution
# 2833 from the Virginia Institute of Marine Science.
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Editorial responsibility: Howard Browman (Associate Editor-
in-Chief), Storebø, Norway
Submitted: April 19, 2007; Accepted: May 18, 2007
Proofs received from author(s): June 1, 2007
... Often referred to as ecosystem engineers, reef-forming shellfish, such as mussels and oysters, create habitats through the production of prominent reef or bed structures [1,2]. In such high abundance, shellfish provide a range of ecosystem services for coastal environments and communities, including the provision of habitat and prey communities for fish and crustaceans, the enhancement of biodiversity, and the improvement of water quality through filter feeding [3][4][5][6]. ...
... The environmental, cultural, and societal importance of the Swan-Canning Estuary, along with its historical loss of shellfish habitats and significant, increasing stressors through impacts such as harmful algal blooms, hypoxia, and contaminant loads [9,19], highlight this estuary as an excellent candidate for restoration using nature-based solutions (NbS), and specifically the reconstruction of shellfish reefs. While such habitat restoration is just one part of the broader management approach needed to sustain the health of complex waterways like the Swan-Canning Estuary, global evidence demonstrates the significant benefits restored shellfish reefs can bring to help recover ecosystem functioning, including improved water quality, greater fish productivity, and biodiversity gains [1]. This in turn supports benefits for local communities through enhanced recreational opportunities, support for local fishing and ecotourism industries, cultural reconnection and job opportunities. ...
... However, these suboptimal conditions were less of a concern in winter. The use of mussels for NbS in estuaries should thus be encouraged to recover, not only water quality but also other ecosystem services that bivalves provide, such as habitat provision and biodiversity enhancement [1,2,57]. Table A1. ...
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Restoration ecologists recognize the need for restoring ecosystem servicesin sustainable ways that meet societal needs. In the UK, Ireland, Australia,and some US states the goal is restoring native oyster reefs. In otherstates, failures at restoration due to poor water quality and predation havefocused restoration activities on techniques that work, restoring intertidalreefs and generating living shorelines that reduce or reverse erosion. In theUnited States, restoring water quality and reducing or reversing erosion aresocietally accepted entry points for repairing estuarine ecosystems. Thisstudy is an overview of the current status of oyster reef restoration andprovide a novel approach called “oyster reef in a bag”. Combining oysterreef restoration efforts with existing floating oyster aquaculture technologygenerates novel ecosystems that are a combination of biofouling and oysterreef communities. These novel ecosystems could be a practical beginningto improve water quality, mitigate erosion and restore higher trophic levelecosystem services.
... Our study organism is the eastern oyster (Crassostrea virginica, Gmelin, 1791) because of its keystone role, contributing valuable ecosystem services to estuarine communities such as water filtration, benthic pelagic coupling, and a structurally complex benthic reef habitat used by many commercial fish species (Coen et al. 2007;Beck et al. 2011;Bricker et al. 2020;Rose et al. 2021). The synergistic mix of coastal degradation, overharvesting, disease, eutrophication, and climate change threatens to degrade oyster populations to functional extinction in some regions, if it has not done so already (Beck et al. 2011). ...
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Low salinity can negatively affect reproduction in estuarine bivalves. The spatial and temporal extents of these effects are important to inform models of population dynamics, environmental risk assessments, restoration efforts, and predictions of climate change effects. A hypothesis of delayed gametogenesis for oysters at low salinity sites was tested relative to their higher salinity counterparts in downstream experimental cages. In 2018, the timing of gametogenesis and spawning was observed June–August for 2-year-old oysters from three distinct ancestries (native, hatchery, aquaculture), outplanted at age 1 month along the salinity gradient (3–30 psu) of a temperate estuary. A second season of data was collected in 2019 from a 3-year-old aquaculture line and mixed-age native adult oysters dredged and transplanted 1 year prior. Dermo was tested in 2019 and prevalence was 1.3% ( n = 240). Gametogenesis and spawning were retarded for all ancestries at low salinity relative to higher salinity sites during July and August. The reverse pattern was found in June, with low salinity sites having more advanced gonad index than at a high salinity site. This difference in average gonad index was 2.65 vs 1.46, respectively, for the native line and 2.62 vs 2.08 for aquaculture. Low salinity seemed to not only induce earlier gametogenesis in June, but also extended the reproductive season relative to higher salinity sites. Among oyster ancestries, the aquaculture line stood out as having 30–48% lower gametogenic synchrony within sites, but only in 2018. Because the native oysters used in this study have been restricted to low salinity conditions for many generations, demonstration of their reproductive plasticity across salinities is notable and broadens the range of potential future restoration strategies.
... Subtidal habitats included hard bottom (Jaap and Hallock, 1990;Ash and Runnels, 2005;Kaufman, 2017;CSA Ocean Sciences, 2019), artificial reefs (Dupont, 2008), tidal flats (Moore et al., 1968;Eisma, 1998), seagrasses (Heck et al., 2003;Sherwood et al., 2017), and oyster reefs (Coen et al., 2007;Ermgassen et al., 2013). Intertidal habitats (or emergent tidal wetlands) included mangroves (Odum and McIvor, 1990), salt marshes (Comeaux et al., 2012;Raabe et al., 2012), salt barrens (Bertness, 1985;Hsieh, 2004), tidal tributaries (Sherwood, 2008;Wessel et al., 2022), and living shorelines (National Oceanic and Atmospheric Administration, 2015;Restore America's Estuaries, 2015;Smith et al., 2018). ...
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Native habitats in Florida face dual pressures at the land-sea interface from urban development and sea-level rise. To address these pressures, restoration practitioners require robust tools that identify reasonable goals given historical land use trends, current status of native habitats, and anticipated future impacts from coastal stressors. A restoration framework for native habitats was created for the Tampa Bay watershed that identifies current opportunities and establishes short-term (2030) targets and long-term (2050) goals. The approach was informed through a three-decade habitat change analysis and over 40 years of habitat restoration projects in the region. Although significant gains in subtidal habitats have been observed, expansion of mangroves into salt marshes and loss of native upland habitats to development highlights the need to target these locations for restoration. The long-term loss of potentially restorable lands to both coastal and upland development further underscores the diminishing restoration opportunities in the watershed. The established targets and goals identified habitats to maintain at their present level (e.g., mangroves) and those that require additional progress (e.g., oyster bars) based on past trends and an expected level of effort given the restoration history of the region. The new approach also accounts for the future effects of sea-level rise, climate change, and watershed development by prioritizing native coastal habitats relative to subtidal or upland areas. Maps were created to identify the restoration opportunities where practitioners could focus efforts to achieve the targets and goals, with methods for repeatable analyses also available using an open source workflow.
... The eastern oyster Crassostrea virginica is native to the northwestern Atlantic coast, ranging from the Gulf of St. Lawrence in Canada to the Gulf of Mexico and West Indies in the south (Galtsoff 1964). As a reef-builder and filter-feeder, the eastern oyster provides critical ecological services to coastal and estuarine ecosystems (Loren et al. 2007;Beck et al. 2011;Grabowski et al. 2012). The eastern oyster also is economically important. ...
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The eastern oyster Crassostrea virginica is a major aquaculture species for the USA. The sustainable development of eastern oyster aquaculture depends upon the continued improvement of cultured stocks through advanced breeding technologies. The Eastern Oyster Breeding Consortium (EOBC) was formed to advance the genetics and breeding of the eastern oyster. To facilitate efficient genotyping needed for genomic studies and selection, the consortium developed two single-nucleotide polymorphism (SNP) arrays for the eastern oyster: one screening array with 566K SNPs and one breeders’ array with 66K SNPs. The 566K screening array was developed based on whole-genome resequencing data from 292 oysters from Atlantic and Gulf of Mexico populations; it contains 566,262 SNPs including 47K from protein-coding genes with a marker conversion rate of 48.34%. The 66K array was developed using best-performing SNPs from the screening array, which contained 65,893 oyster SNPs including 22,984 genic markers with a calling rate of 99.34%, a concordance rate of 99.81%, and a much-improved marker conversion rate of 92.04%. Null alleles attributable to large indels were found in 13.1% of the SNPs, suggesting that copy number variation is pervasive. Both arrays provided easy identification and separation of selected stocks from wild progenitor populations. The arrays contain 31 mitochondrial SNPs that allowed unambiguous identification of Gulf mitochondrial genotypes in some Atlantic populations. The arrays also contain 756 probes from 13 oyster and human pathogens for possible detection. Our results show that marker conversion rate is low in high polymorphism species and that the two-step process of array development can greatly improve array performance. The two arrays will advance genomic research and accelerate genetic improvement of the eastern oyster by delineating genetic architecture of production traits and enabling genomic selection. The arrays also may be used to monitor pedigree and inbreeding, identify selected stocks and their introgression into wild populations, and assess the success of oyster restoration.
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The quantification of ecosystem services (ES) remains challenging and can result in biases towards data-rich ES in management. For infaunal bivalves, little quantitative in situ data are available on the ES they provide, and differences between functionally similar species in different habitats are rarely considered. Here, we aimed to measure and compare the ecosystem functions (primary production, nutrient processing, water clearance rates) underpinning water quality regulation in an estuarine intertidal and subtidal bivalve habitat (dominated by Austrovenus stutchburyi and Paphies australis respectively). In situ benthic chambers were used to measure sediment–water column solute fluxes (NH4⁺, N2, O2) and clearance rates which were scaled up (accounting for habitat differences; e.g. inundation period) to daily estimates of ES potential. Higher hourly microphytobenthic productivity, nitrogen recycling and water filtration were observed for the intertidal bivalve habitat. These differences were attributed to environmental differences rather than differences in bivalve biomass. However, scaling these rates to daily ES estimates showed that inundation period will restrict water quality regulating services in the intertidal. Measuring multiple ecosystem functions in situ provides an important step forward in ES quantification and accounts for ecological complexity, feedbacks and highlights habitat-specific differences in how functionally similar species contribute to ES.
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Introduction As suspension-feeders, bivalves play a key role in maintaining regulatory functions of coastal ecosystems, which are linked to important ecosystem services. The functions attributed to bivalves depend on the life habits of a species (epi- or infauna) and their abundance and biomass. To properly quantify and assess these functions, detailed information the distribution, abundance and biomass at the ecosystem scale is critical. Amongst others, this requires an understanding on how environmental conditions shape special patterns in distribution. In this study we investigate this fundamental information on the Swedish west coast, an area where this information is lacking. Methods A survey which was designed to representatively sample both epi- and infaunal bivalves from randomized locations in various habitat types was conducted. Specifically, abundance and biomass of all species were recorded in the intertidal (0-0.5 m) and the shallow subtidal zone (0.5-2 m). The sites were distributed over an offshore gradient and at two exposure levels. This sampling structure allowed to extrapolate the results to an ecosystem level though information on the areal extent of these habitats using GIS layers. Results It was found that even though there exist a great variability among sites, in general epifaunal bivalves outweigh infaunal bivalves approximately 3 to 1. In terms of abundance, the ratio is more or less reversed and infaunal species occur in greater numbers. Most bivalves were found at an intermediate level of exposure, but due to the areal extend of the sheltered inner-archipelago this was the most important habitat for bivalve abundance and biomass. It was also found that invasive epifaunal oyster Magallana gigas and the invasive infaunal clam Ensis leei both dominated their respective groups in terms of biomass. Discussion Though the survey was relatively small, these results serve as a valuable insight of the relative importance of epi- and infaunal bivalves in this region. This gives understanding on which species and habitats are particularly important for ecosystem functions and services related to bivalves. This also provide a starting baseline for attempts to quantify ecosystem services provided by certain species or groups of bivalves in the future.
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Low salinity can negatively affect reproduction in estuarine bivalves. The spatial and temporal extent of these effects are important to inform models of population dynamics, environmental risk assessments, restoration efforts, and predictions of climate change effects. We hypothesized that oysters at low salinity sites would have delayed gametogenesis compared to their higher salinity counterparts in downstream experimental cages. The timing of gametogenesis and spawning was observed June-August for 2-year-old oysters from three distinct ancestries (Native, Hatchery, Aquaculture), outplanted at age 1 month along the salinity gradient (3-30 psu) of a temperate estuary. A second season of data was collected from 3-year-old Aquaculture oysters (comparable to year 1 data) and Native adult oysters transplanted one year prior. Dermo was very low both years. A delay in gametogenesis and spawning was observed for all ancestries at low salinity relative to higher salinity sites during July and August of the first year but not the second year. In contrast, June showed the reverse pattern with northern low salinity sites having more advanced gonad index (2.65) than a high salinity site (1.46). This difference in average gonad index was 2.65 vs 1.46, respectively, for the Native line and 2.62 vs 2.08 for Aquaculture. Low salinity seemed to not only induce earlier gametogenesis in June, but also extended the reproductive season relative to higher salinity sites. Among oyster ancestries, the Aquaculture line stood out as having 30 — 48% lower gametogenic synchrony within sites, but only in 2018. Despite some dependence of reproductive phenology on salinity variation, the Native low salinity population demonstrates notable reproductive plasticity in the completion of a reproductive cycle across a wide range of salinities, an encouraging result for potential future restoration strategies.
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We reviewed studies providing quantitative measurements of abundance of fishes and large mobile crustaceans on oyster reefs and on nearby sedimentary habitat in the southeast United States. For each species, we compared density by size (age) class on oyster reefs and sedimentary bottom as a means of estimating the degree to which restoration of oyster reef on sedimentary bottom could augment abundances. By applying published information on growth rates of each species and a combination of empirical data and published information on age-specific survivorship, we calculated the per-unit-area enhancement of production of fishes and large mobile crustaceans expected from the addition of oyster reef habitat. For this calculation, we gave the reef habitat full credit for the expected lifetime production of species whose recruitment was judged to be limited by the area of oyster reefs based on nearly exclusive association of recruits to reefs. For species that were only modestly enhanced in abundance by oyster reefs, we gave the reef credit for the fraction of production that is derived from consumption of reef-associated prey, using a combination of gut content data and natural history information. This combination of analyses and calculations revealed that 10 m(2) Of restored oyster reef in the southeast United States is expected to yield an additional 2.6 kg yr(-1) of production of fish and large mobile crustaceans for the functional lifetime of the reef. Because the reef is biogenic and self-sustaining, the lifetime of a reef protected from bottom-disturbing fishing gear is limited by intense storms or sedimentation. A reef lasting 20 to 30 yr would be expected to augment fish and large mobile crustacean production by a cumulative amount of 38 to 50 kg 10 m(-2), discounted to present-day value. This set of calculations assumes that oyster reef habitat now limits production of reef-associated fish and crustaceans in the southeast United States. This assumption seems reasonable based on the tight associations of so many fishes with reef-dependent prey, and the depletion of reef habitat over the past century.
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Restoration of the oyster Crassostrea virginica population in Chesapeake Bay is often advocated as an easy solution for controlling phytoplankton blooms. Even at their pre-colonial densities, oysters are unlikely to have controlled blooms, despite the fact that sediment cores suggest that pre-colonial spring blooms were smaller than at present. Lack of access to all bay water and low springtime filtration rates would make it impossible for oysters to control the spring bloom and the resulting summer hypoxia. Previous studies have overestimated potential oyster filtration rates, because they extrapolated summer rates to spring conditions that are 20 degrees C cooler. Previous studies have also assumed that oysters have access to all phytoplankton, without considering the spatial separation. In Chesapeake Bay, oysters and the spring bloom are separated horizontally owing to the size of the bay and its small tidal amplitude. Indeed, a multi-species guild of suspension feeders now present in the bay should have a filtration capacity approaching that of pre-colonial oysters, but it does not control the bloom. Actual oyster filtration potential must be lower than many advocates of oyster restoration assume, and replenishing the bay with oysters is not the means of controlling blooms and hypoxia.
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Abundant suspension-feeding bivalves have a dominant organizing role in shallow aquatic systems by filtering overlying waters, affecting biogeochemical processing, and diverting production from the water column to the benthos. In degraded aquatic systems where bivalve populations have been reduced, successful restoration of ecosystem functions may be achieved by targeting the revival of bivalve populations. The 'North Cape' oil spill on the coast of Rhode Island (USA) provides an opportunity to demonstrate the feasibility of scaling bivalve restoration to meet quantitative goals of enhanced production. After this oil spill, mortalities of bivalves were estimated by impact assessment modeling of acute toxicity, and results were confirmed by comparisons with counts of dead and moribund animals on local beaches. Computation of lost bivalve production included future production expected from affected animals, had they lived out their expected life spans. This calculation of production forgone required a demographic model that combined age-specific mortality with individual growth. Application of this modeling approach to surf clams Spisula solidissima, the species that comprised 97 % of the total loss of bivalve production from the spill, illustrates the detailed implementation of scaling restoration to match estimates of losses. We consider the factors known to limit abundance and production of surf clams and other marine bivalves (hard clams, American oysters and bay scallops) and review the advantages of hatchery stocking, transplantation, habitat restoration, and reduction of fishing pressure in selecting a reliable and efficient restoration action. Age-specific estimates of the scale of population enhancement required to restore production showed that fewer additional animals were needed when larger (older) animals were added, but at the expense of greater grow-out requirements. Relaxation of fishing was most effective for hard clams. Accurate scaling of restoration was most sensitive to mortality rate, and the most efficient restoration involving seeding of small bivalves would be accomplished using surf clams. Monitoring of the restoration option chosen to compensate for the bivalve loss following the 'North Cape' oil spill can serve to test the underlying demographic assumptions and accuracy of the restoration scaling.
Article
Oyster cultch was added to the lower intertidal fringe of three created Spartina alterniflora marshes to examine its value in protecting the marsh from erosion. Twelve 5-m-wide plots were established at each site, with six randomly selected plots unaltered (noncultched) and cultch added to the remaining (cultched) plots. Within each cultched plot, cultch was placed along the low tide fringe of the marsh during July 1992, in a band 1.5 m wide by 0.25 m deep. Marsh-edge vegetation stability and sediment erosion were measured for each plot from September 1992 to April 1994. Significant differences (p < 0.05) in marsh-edge vegetation change were detected at the only south-facing site after a major southwester storm. Significantly different rates of sediment erosion and accretion also were observed at this same site. Areas upland of the marsh edge in the cultched areas showed an average accretion of 6.3 cm, while noncultched treatment areas showed an average loss of 3.2 cm. A second site, with a northern orientation, also experienced differential sediment accretion and erosion between treatment type, caused instead by boat wakes that were magnified by the abutment of a dredge effluent pipe across the entire front fringe of the site. During this period we observed significant differences in sediment accumulation, with the areas upland of the marsh edge in the cultched treatment having an average accretion of 2.9 cm and the noncultched an average loss of 1.3 cm.
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Along the east coast of central Florida in the Indian River Lagoon system, intense recreational boating activity occurs year-round, and intertidal reefs of the eastern oyster Crassostrea virginica (Gmelin) with dead margins (mounds of disarticulated shells) on their seaward edges are commonly found adjacent to major boating channels. These dead margins are caused, at least in part, by boat wakes and extend significantly higher above the high water line than reefs lacking dead margins (pristine reefs). To determine if these "impacted" oyster reefs alter recruitment and subsequent survival of C. virginica, three 8-wk field trials were run between May 2001 and April 2002 in Mosquito Lagoon. During each trial, data were also collected on total sediment loads, silt/clay fractions and relative water motion. Although recruitment did not differ between impacted and pristine reefs, juvenile survival was significantly reduced on impacted reefs. Additionally, larval recruitment and subsequent mortality were greatest during our summer trial. Total sediment loads, percent silt/clay, and relative water motion were significantly higher on impacted reefs. For these three variables, the largest values were consistently found at the bases of exposed (seaward) regions of impacted reefs. By documenting a positive relationship between reduced success of C. virginica and dead margins, and knowing that boat wakes contribute to the development of dead margins, we have provided the first cause and effect mechanism between intense recreational boating activity and increased oyster morality.
Article
Suspension-feeding bivalves serve to couple pelagic and benthic processes because they filter suspended particles from the water column and the undigested remains, ejected as mucus-bound feces and pseudofeces, sink to the sediment surface. This biodeposition can be extremely important in regulating water column processes where bivalves are abundant in coastal waters and in seasons when water temperatures are warm enough to promote active feeding. Bivalves under these conditions can exert "top-down" grazer control on phytoplankton and in the process reduce turbidity, thereby increasing the amount of light reaching the sediment surface. This has the effect of reducing the dominance of phytoplankton production and extending the depth to which ecologically important benthic plants, such as seagrasses and benthic microalgae, can grow. Nitrogen and phosphorus, excreted by the bivalves and regenerated from their biodeposits, are recycled back to the water column and support further phytoplankton production. In some situations, however, bivalves can also exert "bottom-up" nutrient control on phytoplankton production by changing nutrient regeneration processes within the sediment. Some of the N and P that was originally incorporated in phytoplankton, but was not digested by the bivalves, can become buried in the accumulating sediments. Where biodeposits are incorporated in aerobic surficial sediments that overlay deeper anaerobic sediments, microbially mediated, coupled nitrification- denitrification can permanently remove N from the sediments as N2 gas. Consequently, natural and aquaculture-reared stocks of bivalves are potentially a useful supplement to watershed management activities intended to reduce phytoplankton production by curbing anthropogenic N and P inputs to eutrophied aquatic systems. Environmental conditions at bivalve aquaculture sites should be carefully monitored, however, because biodeposition at very high bivalve densities may be so intense that the resulting microbial respiration reduces the oxygen content of the surrounding sediments. Reduction in sediment oxygen content can inhibit coupled nitrification-denitrification, cause P to become unbound and released to the water column, and the resulting buildup of H2S can be toxic to the benthos.
Conference Paper
Restoration of the Chesapeake Bay ecosystem has been a priority for residents and governments of the bay watershed for the past decade. One obstacle in the efforts to 'save the bay' has been continuing nutrient enrichment from agricultural and sewer runoff. The attainability of a mandated 40% nutrient reduction goal has yet to be seen. Furthermore, disappearance of certain organisms may have had an adverse effect on the resilience of the ecosystem. The Eastern oyster (Crassostrea virginica), once abundant in Chesapeake Bay, was a vital part of the food web, processing excess phytoplankton and depositing materials on the bottom. Over harvesting and disease have decimated the native oyster population. The introduction of an exotic species, the Japanese oyster (Crassostrea gigas), may be a way to reestablish a robust oyster community in the bay. The literature on the role of bivalve molluscs in estuarine ecosystems shows that they are an essential part of healthy estuaries around the world. A comparison of C. virginica and C. gigas in terms of temperature and salinity tolerance and resistance to disease shows that C. virginica is ideally adapted to conditions in Chesapeake Bay, but it is unable to stave off the endemic diseases, whereas C. gigas is adapted to conditions in the lower bay only but is much less susceptible to the same diseases. We conclude that the potential introduction of C. gigas to Chesapeake Bay would be limited by the Japanese species' physiological requirements but that the revitalization of a bivalve population is imperative to the restoration of ecosystem function.
Article
Research in the late 1990s showed that some intertidal eastern oyster (Crassostrea virginica, Gmelin) reefs in Mosquito Lagoon within the Canaveral National Seashore, Florida had dead margins consisting of mounded up, disarticulated shells. It was hypothesized that boating activities were the cause of the damage because all the reefs were adjacent to major navigation channels. To investigate this, we characterized the history of the appearance of dead margins and other reef changes using aerial photographs taken between 1943 and 2000. Imagery analyzed included prints (black & white, color, or color infrared) from 1943, 1951, 1963, 1975, 1988, and 1995, and digital imagery from 2000 (USGS 1:12,000 digital ortho-quarterquads), at scales from 1:6,000 to 1:24,000. Prints were scanned at a resolution sufficient to yield 1-m pixels. After scanning, each set of images was georeferenced to the year 2000 imagery using ArcView and ArcInfo GIS software. All reefs found to have dead margins based on 1995 and 2000 aerials were visited in 2001 and 2002 to confirm the presence and extent of dead areas. This provided ground-truthing for the "signature" (a highly reflective, light-colored area adjacent to darker-colored live reef) to be used to detect the appearance of dead margins in the historical aerials. The earliest appearance of dead margins was in the 1943 aerials on one reef adjacent to the Intracoastal Waterway (ICW), a major navigation channel. The total number of reefs affected and areal extent of dead margins steadily increased from 1943 through 2000. In 2000, 60 reefs (of a total of ~400 in the Park) had dead margins, representing 9.1% of the total areal coverage by oyster reefs in the Park. Along the ICW, some reefs migrated away from the channel as much as 50 m and in 2000 consisted mainly of empty shells mounded up a meter above the high water mark. In contrast, many reefs in areas away from navigation channels showed little change over the 57-yr period. This historical analysis provides strong (although correlative) evidence that boating activity has had dramatically detrimental effects on some oyster reefs in the study area. Ongoing studies are aimed at further testing this hypothesis and elucidating the causal mechanisms involved.
Article
Blue mussels Mytilus edulis L. and eelgrass Zostera marina L. commonly co-occur in mixed stands at sheltered sites of the Western Baltic. The effects of mussels on density, vegetative propagation and growth of eelgrass were tested experimentally. Mussels were either added to Z. marina patches or removed from existing Zostera/Mytilus associations. We found no effect of these experimental manipulations on the shoot density of Z. marina from April to October. Likewise, observations on a series of permanent plots over 1 growth period showed that adjacent mussel patches did not impede the vegetative propagation of eelgrass patches. Instead of damaging eelgrass by interference competition, mussels enhance eelgrass growth. At the end of August, plants in the M. edulis addition treatment had a 36% higher leaf area than the controls, whereas mussel removal led to an area decrease of 16% compared to the controls. Since, at the same time, the sediment porewater concentrations of ammonium and phosphate doubled in presence of M. edulis, we infer that Z. marina is nutrient-limited in the sandy, organically poor sediments of the shallow subtidal zone. M. edulis facilitates Z. marina by the biodeposition of organic material via faeces and pseudofaeces. A correlation between porewater ammonium concentration and plant size supports the contention that nitrogen is growth limiting. In contrast, no relationship was found between porewater phosphate concentration and plant size.