Positive Relationship between Freshwater Inflow and Oyster Abundance in Galveston Bay, Texas
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
Estuaries and Coasts (2009) 32:206–212
DOI 10.1007/s12237-008-9078-z
TECHNICAL COMMUNICATION
Positive Relationship between Freshwater Inflow
and Oyster Abundance in Galveston Bay, Texas
David Buzan & Wen Lee & Jan Culbertson &
Nathan Kuhn & Lance Robinson
Received: 29 June 2008 / Accepted: 21 July 2008 / Published online: 19 August 2008
# Coastal and Estuarine Research Federation 2008
Abstract Analysis of fisheries-independent data for estuary in order to increase oyster harvest. We have the
Galveston Bay, Texas, USA, since 1985 shows eastern opposite concern that oysters will be harmed by projects
oysters (Crassostrea virginica) frequently demonstrate that reduce flow, increase salinity, and increase the
increased abundance of market-sized oysters 1 to 2 years duration of higher salinity periods in a basin with
after years with increased freshwater inflow and decreased increasing demand for limited freshwater. Turner’s study
salinity. These analyses are compared to Turner’s (Estuaries and our analysis reflect different aspects of the complex,
and Coasts 29:345–352, 2006) study using 3-year running important relationships between freshwater inflow, salin-
averages of oyster commercial harvest since 1950 in ity, and oysters.
Galveston Bay. Turner’s results indicated an inverse
relationship between freshwater inflow and commercial Keywords Freshwater inflow . Oyster productivity .
harvest with low harvest during years of high inflow and Oyster landings . Galveston Bay
increased harvest during low flow years. Oyster popula-
tions may experience mass mortalities during extended
periods of high inflow when low salinities are sustained. Introduction
Conversely, oyster populations may be decimated during
prolonged episodes of low flow when conditions favor The eastern oyster, Crassostrea virginica, contributes
oyster predators, parasites, and diseases with higher ecologically and economically to coastal ecosystems along
salinity optima. Turner’s (Estuaries and Coasts 29:345– United States’ Atlantic and Gulf of Mexico coasts.
352, 2006) analysis was motivated by a proposed project Commercial oyster production in Texas, second to Louisiana,
in a basin with abundant freshwater where the goal of the comprised 20% of the nation’s harvest from 2000 to 2005
project was to substantially increase freshwater flow to the (NOAA 2007). Oyster reefs filter solids from the water
column, influence hydrological patterns, and provide habitat
and refugia for a variety of species (Coen et al. 1999; Meyer
D. Buzan (*) and Townsend 2000; Rodney and Paynter 2006; Zimmerman
PBS&J,
et al. 1989).
6504 Bridge Point Parkway, Suite 200,
Austin, TX 78730, USA Estuaries with substantial freshwater inflows like Ches-
e-mail: dlbuzan@pbsj.com apeake Bay on the Atlantic coast, Apalachicola Bay in
Florida, Mobile Bay in Alabama, the Louisiana coastal
W. Lee : N. Kuhn
zone, and Galveston Bay in Texas support relatively large
Texas Parks and Wildlife Department,
4200 Smith School Road, populations of oysters. In Texas, bays with productive
Austin, TX 78744, USA shellfish industries tend to have relatively high rates of
freshwater inflow (Montagna and Kalke 1995). Galveston
J. Culbertson : L. Robinson
Bay receives the second-highest freshwater inflow of any
Texas Parks and Wildlife Department, Dickinson Marine Lab,
1502 FM 517 East, Texas estuary with an annual average 11.4 million acre-ft/
Dickinson, TX 77539, USA year (TWDB 2007a) and produces most oysters commer-Estuaries and Coasts (2009) 32:206–212 207 cially harvested in Texas. Galveston Bay reefs grow patterns in the relationships between freshwater inflow, primarily in the middle of the bay and cover more than salinity, and oyster productivity in Galveston Bay. These 10,000 ha of bay bottom (Powell et al. 2003). Monthly broad annual patterns indicate possible value in future, average salinities in Galveston Bay range from 12 to 19 psu more intensive analysis of seasonal salinities or inflows on (Ray 1987; Quast et al. 1988; TPWD 2006a). one or a few reefs in Galveston Bay. Our analysis also Turner (2006) compares oyster harvest to river inflow (as utilizes a shorter period of record, 1985 to 2004, than a proxy for salinity) for five Gulf of Mexico estuaries Turner (2006) and oyster abundance data obtained from a including Galveston Bay. He suggests Gulf of Mexico fisheries-independent monitoring program rather than estuaries with salinity above optimum levels will experi- oyster commercial harvest. ence increased oyster harvest as salinity decreases towards an optimum. He further suggests a continued decline in salinity past some optimal point will lower oyster produc- Materials and Methods tivity. Turner (2006) evaluated a 54-year record of oyster harvest in Galveston Bay. Comparing peaks and troughs in Oysters are monitored by Texas Parks and Wildlife oyster landings to freshwater inflows, Turner (2006) Department’s (TPWD) Coastal Fisheries Resource Moni- concludes “…the annual variability in oyster landings of toring Program according to the “Marine Resource the Gulf of Mexico estuaries are, in general, inversely Monitoring Operations Manual” (TPWD 2002). Samples related to freshwater inflow.” are collected with dredges (Louisiana style nine-tooth, Freshwater inflow is a critical factor influencing oyster 46 cm wide, 25 cm tall with a 36-cm-deep bag) on reefs abundance. Lengthy periods of low freshwater inflow allow where oysters form the bottom and the reefs extend at least salinities to rise and oyster mortality from predation and 0.2 m above the bottom for a continuous distance of 91.4 m parasitism to increase (Ray 1987). Floods may suppress long by 0.5 m wide in any direction. The dredge is towed in salinities long enough to cause mass mortalities of oysters a straight line for 30 s. All live oysters are counted and 19 (Wilber 1992). Powell et al. (2003) describe how changes live individuals are chosen at random and measured. in location of freshwater inflow, inflow amounts, among Salinity is measured with a refractometer or digital other factors interact to determine future oyster abundance. conductivity/salinity meter 0.3 m above the bottom sub- Turner (2006) and Wilber (1992) both studied the strate at the dredge starting point. relationship between harvest and freshwater inflow. Wilber Catch-per-unit-effort (CPUE) of “market-sized” oysters (1992) calculated oyster abundance by dividing the pounds is calculated by multiplying the number of live oysters of oysters harvested by the number of registered oystermen ≥76 mm dredged in 30 s by 120 to convert dredge results to for each year and eliminating harvest years which were CPUE measured per hours. CPUE (market-sized oysters per confounded by hurricanes, drought, and oyster-reef resto- hour) is used to indicate market-sized oyster relative ration. Turner (2006) utilized a 3-year moving average of abundance. The annual value discussed in this report is oyster harvest to deal with the highly variable harvest data the average CPUE for all TPWD samples collected within and influence from occasional rare events. the bay in the same calendar year. Although Turner’s conclusions clearly focus on the Freshwater inflow for Galveston Bay includes all U.S. relationship between oyster harvest and freshwater inflow, Geological Survey (USGS) gaged flows to the estuary plus we are concerned his conclusions will be interpreted by modeled flows from ungaged coastal watersheds dis- some to indicate freshwater inflow events are generally charging to the estuary over the period from 1941 to 2005 detrimental to oyster health. This paper describes a positive, (TWDB 2007b). The Texas Rainfall Runoff model uses 1- to 2-year lagged relationship between freshwater inflow rainfall, flow diversion reports, and reported wastewater and oyster abundance as distinguished from oyster harvest discharges to model flow from ungaged watersheds. Daily in Galveston Bay. Wilber (1992) showed 2- to 3-year time rainfall data are obtained from the National Weather lags between low flow events and subsequent poor oyster Service. Return flow and diversion data are from the Texas harvest and a positive relationship between fall inflows and Commission on Environmental Quality. Turner’s (2006) oyster harvest 2 years later. Hofstetter (1988) described a analysis used Trinity River inflow measured at a USGS lagged relationship between inflow and oyster harvest in gage upstream of the bay. Annual trends in Trinity River Galveston Bay for the 1980 year class following severe flow into Galveston Bay are generally comparable to flooding in 1979 which supported record harvests in the annual trends in freshwater inflow. Approximately 69% of 1982–1983 season. Most recently, Bergquist et al. (2006) the freshwater inflow to the bay has been gaged flow over demonstrated positive relationships between four indicators the period from 1941 to 2005. of oyster community health and changes in salinity 1 to This report focuses on changes in oyster abundance 2 years earlier. Our analysis simply compares broad annual when compared to freshwater inflow and salinity 1 to 2 years
208 Estuaries and Coasts (2009) 32:206–212
earlier. Increases and decreases in oyster abundance are 2 years after years of increased freshwater inflow and
utilized, not for their magnitude but for the direction of the experiences lows 1 to 3 years after declines in freshwater
response they indicate to changing freshwater inflow and inflow. Three years, 1988, 2000, and 2001, illustrated a
salinity conditions. pattern similar to that recognized by Turner (2006) where a
peak in inflow or oyster productivity was matched by a low
Study Site in the other variable in the same year. As mentioned earlier,
each of these years was also preceded by an increase or
Galveston Bay is located along the upper Texas coast decrease in inflow 1 to 2 years earlier.
(Fig. 1) in the northwestern Gulf of Mexico. The Trinity When Turner’s analytical approach is applied to oyster
River contributes 54% of the annual average flow to the CPUE and total annual freshwater inflow to the bay, it
bay while the San Jacinto River/Buffalo Bayou watersheds illustrates increasing oyster relative abundance from 1989
contribute 38% of the total annual average inflow to the bay until 1993 which is preceded by increasing freshwater
(TWDB 2007b). Peak flows to the estuary typically occur inflow from 1988 until 1992 (Fig. 3). The high oyster
in May and June and low inflows occur August through CPUE in 1999 follows an increasing trend from 1996
October. which was paralleled by increasing to stable inflow from
1995 to 1998. Similarly, as inflow decreased over the
period from 1992 to 1995, it was followed by decreasing
Results oyster CPUE from 1993 to 1996.
Oyster Abundance and Freshwater Inflow Oyster Abundance and Salinity
Freshwater inflow to Galveston Bay increased in 1986, Increases in oyster CPUE in 1988, 1993, 2000, and 2002
1992, 1998, and 2001 and upward trends in oyster CPUE were preceded by lows in salinity 2 or 3 years earlier, in
occurred in 1988, 1993, 2000, and 2002, 1 to 2 years 1986, 1991, 1997, and 2001 (Fig. 4).
afterwards (Fig. 2). Declines in market-sized oyster abundance occurred
Conversely, lows in oyster CPUE occurred in 1987, from 1988 to 1990, a period when salinity was also
1990, 1996, 2001, and 2004 following lows in freshwater declining from year to year. CPUE rose from 1990 to
inflow that occurred in 1988, 1996, 2000, and 2003. 1993 and 1994 when salinities remained relatively low and
Annual freshwater inflow and oyster CPUE declined for stable. Slightly increasing salinity from 1993 to a sharp
three consecutive years prior to the 1996 low in oyster peak in 1996 occurred at the same time oyster CPUE was
abundance. Oyster abundance appears to increase 1 to declining. From 1997 to 2004, salinity and oyster CPUE
Fig. 1 Galveston Bay, Texas
with major oyster reefs (shaded
areas in bay) illustrated (Texas
General Land Office 2006)Estuaries and Coasts (2009) 32:206–212 209
Fig. 2 Galveston Bay annual
average oyster CPUE compared
to annual total freshwater
inflow to the estuary
exhibited similar patterns, both increasing from 1997 to genic factors like oyster harvesting techniques and regu-
2000 and dropping in 2001. lations have varied relatively little since the early 1980s.
Oyster relative abundance is not significantly related Texas Department of State Health Services (TDSHS)
(rs =−0.418, p=0.0823, n=18) to annual average salinity regulations affect landings when suspending oyster harvest
2 years earlier (Fig. 5a). The analysis suggests the to protect human health from pathogens and red tide toxins.
relationship between salinity and oyster CPUE may be The current system for closing oyster harvest areas has been
negative. Market-sized oyster abundance and annual fresh- in place since the early 1980s (Kirk Wiles, personal com-
water inflow to the bay 2 years earlier exhibit a significant munication). Harvest areas are frequently closed following
(rs =0.541, p=0.0137, n=20) positive relationship (Fig. 5b). rainfall events because of elevated bacterial levels in the
water. Consequently, oyster harvest tends to decline as the
number of harvest area closure days increase.
Discussion TPWD implemented a probability-based, fishery-
independent monitoring program for oysters in October
We analyzed the period from 1985 through 2004 because 1984 in Galveston Bay. This program combined with
fishery-independent monitoring of oysters and anthropo- improvements in data management creates a relatively
Fig. 3 Comparison of a 3-year
moving average of annual aver-
age oyster CPUE to a 3-year
moving average of annual total
freshwater inflow. The values
have been normalized by divid-
ing the 3-year moving average
of annual average total freshwa-
ter inflow and CPUE by the
annual average freshwater
inflow for the period from 1985
to 2005 and the annual average
CPUE for the period from 1985
to 2002, respectively210 Estuaries and Coasts (2009) 32:206–212
Fig. 4 Galveston Bay annual
average oyster CPUE compared
to annual average salinity
in the estuary
comparable, objective data set from 1985 to 2004 for corresponded with increases in surface water inflow 2 years
analysis of relationships between oyster abundance, earlier while two other highs were preceded by increases
salinity, and freshwater inflow (TPWD 2006a). in surface flow a year earlier. Hofstetter (1977) noted
Figure 2 illustrates four periods of increase in Galveston Galveston Bay spat were usually abundant in years of
Bay oyster relative abundance. Two of the periods of above-average freshwater inflow. He stated that oyster
increase, including the year of greatest CPUE in 2000, mortality from flooding was more than offset by increased
spat set. Low salinities enhanced survival in central
Galveston Bay, the area historically with the greatest amount
of oyster substrate (Hofstetter 1977; TPWD 2006b).
Floods of sufficient magnitude may reduce oyster
harvest during the years in which they occur by both
killing oysters in parts of the bay and increasing the amount
of time the bay is closed to harvest. Conversely, the same
floods ensure long-term survival of oyster populations by
reducing oyster predators and parasites such as the oyster
drill, Stramonita haemastoma, and Perkinsus marinus.
Floods that kill oysters may also aid in the long-term
control of Perkinsus epizootics by periodically, temporarily
eliminating the oyster host (Ray 1987; Hofstetter 1977;
Powell et al. 2003). Analysis of P. marinus in oysters
showed infection increased with increasing salinity (TPWD
2006b). Oysters colonize formerly flooded areas, particu-
larly dead oyster shell, beginning a new cycle of growth
with reduced numbers of predators and parasites. Fresh
dead oysters release a pheromone from tissues that attracts
larval oysters resulting in increased spat set on the inside of
these shells and increased spat survival (Keck et al. 1971).
During periods of low rainfall, the number of days oyster
harvest areas are closed is reduced and harvest may
increase as a result of increased oystering days. On the
other hand, as salinity increases during periods of drought,
oyster reefs may become heavily infested with predators
and parasites resulting in increased oyster mortality.
Fig. 5 Correlation a between annual average oyster CPUE and lagged
Pierce and Conover (1954) suggested oysters in systems
(2 years) annual mean salinity (psu) and b between annual average
oyster CPUE and lagged (2 years) freshwater inflow (million acre- with fluctuating salinities grew better than those under
feet) to Galveston Bay 1985 to 2004 relatively constant conditions. La Peyre et al. (2003) foundEstuaries and Coasts (2009) 32:206–212 211
numerous freshwater releases to the Caloosahatchee River are a key factor to the health and survival of oyster
kept P. marinus infection intensities low, resulting in low populations.
prevalence of infection, low oyster mortality, and good
growth. They speculated that repetitive and well-timed Acknowledgements We thank Dr. Sammy Ray with Texas A & M
University-Galveston for his critical review of this report. This
freshet events can maintain P. marinus infections at non- analysis was supported by many of the coastal ecologists at Texas
lethal levels in oyster populations. Bergquist et al. (2006) Parks and Wildlife Department including Brenda Bowling, Fernando
noted disappearance of reefs in the lower intertidal reaches Martinez-Andrade, Page Campbell, and Lynne Hamlin. Thanks to
of the Suwannee estuary during a prolonged dry spell while Kirk Wiles and Gary Heideman with the Texas Department of State
Health Services for the support. Finally, we recognize the inspired
new reefs appeared higher in the estuary closer to efforts of Robert Hofstetter who passed away in the spring of 2007
freshwater sources. Modeling of total oyster abundance in and whose 30 years of study of Galveston Bay oysters will continue to
Galveston Bay and possible changes in hydrology predicted contribute to our understanding of oyster and estuarine ecology far
lower adult oyster abundance resulting from P. marinus into the future.
infections associated with lowered freshwater inflows and
increased salinities (Powell et al. 2003). Hofstetter (1977)
advises that for Galveston Bay, we should not conclude that
References
reduced freshwater inflow “…will necessarily be beneficial
to oysters or other estuarine species.”
Bergquist, D.C., J.A. Hale, P. Baker, and S.M. Baker. 2006.
The State Water Plan for Texas (TWDB 2006) concludes Development of ecosystem indicators for the Suwannee River
Texas will not have enough water to meet future demand estuary: Oyster reef habitat quality along a salinity gradient.
during drought unless new water supply projects or Estuaries and Coasts 29: 353–360.
management strategies are implemented. Turner’s (2006) Coen, L.D., M.W. Luckenbach, and D.L. Breitburg. 1999. The role of
oyster reefs as essential fish habitat: a review of current
conclusion that higher oyster harvests are associated with knowledge and some new perspectives. American Fisheries
higher average salinities in Gulf of Mexico estuaries may Society Symposium 22: 438–454.
be misinterpreted as valid rationale to reduce freshwater Hofstetter, R.P. 1977. Trends in population levels of the American
inflows to other estuaries. Wilber (1992), after review of a oyster Crassostrea virginica Gmelin on public reefs in Galveston
Bay, Texas. Texas Parks and Wildlife Department Coastal
number of studies, concluded that relationships between Fisheries Division Technical Series No. 24, 90 pages.
flow and oyster production vary among different estuarine Hofstetter, R.P. 1988. Trends in the Galveston Bay oyster fishery,
ecosystems. Water managers may focus on the inverse 1979–1984. Texas Parks and Wildlife Department Coastal
relationship between oyster harvest and freshwater inflow Fisheries Division Management Data Series Number 125. 36 pp.
Keck, R.D., D. Mauer, J.C. Kaver, and W.A. Sheppard. 1971.
without considering the complex, important role high fresh- Chemical stimulants affecting larval settlement in the American
water inflow events play in ensuring long-term oyster oyster. Proceedings of the National Shellfish Association 61:
health. 24–28.
We concur with Turner’s (2006) caution that sustainable La Peyre, M.K., A.D. Nickens, A.K. Volety, G.S. Tolley, and J.F. La
Peyre. 2003. Environmental significance of freshets in reducing
and healthy ecosystems are based on a wide variety of Perkinsus marinus infections in eastern oysters Crassostrea
factors, natural and anthropogenic. Estuarine management virginica: Potential management applications. Marine Ecology
should be done in “…the context of the whole estuary and Progress Series 248: 165–176. doi:10.3354/meps248165.
not just part of the estuary.” In order to maintain healthy Meyer, D.L., and E.C. Townsend. 2000. Faunal utilization of created
intertidal eastern oyster (Crassostrea virginica) reefs in the
estuaries, oyster communities, and the coastal communities southeastern United States. Estuaries 23: 34–45. doi:10.2307/
that rely on them, we must understand the unique relation- 1353223.
ship between freshwater inflow and estuary health for Montagna, P., and Kalke. 1995. Ecology of infaunal mollusca in South
each estuary (Wilber 1992; Bergquist et al. 2006). Society’s Texas estuaries. American Malacological Bulletin 11: 163–175.
National Oceanic and Atmospheric Administration. 2007. Fisheries
growing ability to capture and manage water in watersheds Statistics. Commercial Fisheries. Annual Commercial Landing
with limited water supplies may potentially reduce the Statistics for Eastern Oyster for the Chesapeake Region.
frequency and magnitude of freshwater inflow events, http://www.st.nmfs.noaa.gov/st1/commercial/landings/annual_
causing salinities to gradually increase for longer times to landings.html.
Pierce, M.E., and J.T. Conover. 1954. A study of the growth of oysters
unhealthy levels for oyster populations. under different ecological conditions in Great Pond. Abstracts of
Paradoxically, floods may have short-term negative Papers Presented at the Marine Biological Laboratory. The
consequences for oyster harvest but play a vital role in Biological Bulletin, Woods Hole 1072: 318.
ensuring the long-term health of oyster populations and Powell, E.N., J.M. Klinck, E.E. Hofmann, and M.A. McManus. 2003.
Influence of water allocation and freshwater inflow on oyster
consequently the long-term sustainability of oyster harvest. production: A hydrodynamic-oyster population model for
We believe variations in freshwater inflow to an estuary Galveston Bay, Texas, USA. Environmental Management 31:
(particularly associated with moderate floods and freshets) 100–121. doi:10.1007/s00267-002-2695-6.212 Estuaries and Coasts (2009) 32:206–212
Quast, W.D., M.A. Johns, D.E. Pitts, Jr., G.C. Matlock, and J.E. Clark. Texas Parks and Wildlife Department. 2006a. Marine resource
1988. Texas Oyster Fishery Management Plan. Fishery Manage- monitoring program: Coastal fisheries database. Austin, Texas
ment Plan Series Number 1. Source Document. Texas Parks and Texas Parks and Wildlife Department. 2006b. Unpublished data on
Wildlife Department, Austin, TX. 178 pp. commercial oyster landings.
Ray, S. M. 1987. Salinity requirements of the American oyster, Texas Water Development Board. 2007a. In Trinity-San Jacinto
Crassostrea virginica. In: Freshwater Inflow Needs of the Estuary Freshwater Inflows (Galveston Bay). http://hyper20.
Matagorda Bay System with Focus on Penaeid Shrimp. NOAA twdb.state.tx.us/data/bays_estuaries/TxEmp/galv_index.htm
Technical Memorandum, NMFS-SEFC-189, Galveston, Texas. Texas Water Development Board. 2007b. In Coastal Hydrology, Basin
Rodney, W.S., and K.T. Paynter. 2006. Comparisons of macrofaunal Wide Inflow Summary for Galveston Bay. http://hyper20.twdb.
assemblages on restored and non-restored oyster reefs in state.tx.us/data/bays_estuaries/hydrology/galvestonsum.txt
mesohaline regions of Chesapeake Bay in Maryland. Journal of Turner, R.E. 2006. Will lowering estuarine salinity increase Gulf of
Experimental Marine Biology and Ecology 335: 39–51. Mexico oyster landings. Estuaries and Coasts 29: 345–352.
doi:10.1016/j.jembe.2006.02.017. Wilber, D.H. 1992. Associations between freshwater inflows and
Texas General Land Office. 2006. Internet. Available from www.glo. oyster productivity in Apalachicola Bay, Florida. Estuarine,
state.tx.us http://www.glo.state.tx.us. Accessed September 1, 2006. Coastal and Shelf Science 35: 179–190. doi:10.1016/S0272-
Texas Parks and Wildlife Department. 2002. Marine resource 7714(05)80112-X.
monitoring operations manual. 104. Austin: Texas Parks and Zimmerman, R., T. Minello, T. Baumer, and M. Castiglione. 1989.
Wildlife Department. Oyster reef as habitat for estuarine macrofauna. National Oceanic
Texas Water Development Board. 2006. Water for Texas 2007. and Atmospheric Association Technical Memorandum NMFS-
Volume I. Austin, TX. SEFC-249.You can also read
