Current Status of Dermo
Disease in Oysters of
Matagorda and Aransas Bay
Systems
By Sammy M. Ray1, Jennifer Pollack2 and Jan Culberston3
1 Professor Emeritus Texas A&M University at Galveston, rays@tamug.edu
2Professional Research Professor, Fisheries and Mariculture Program
Coordinator, Texas A&M University-Corpus Christi
3Fisheries Scientist, Texas Parks and Wildlife
Oyster Reef Restoration
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There is a great interest in restoration of oyster reefs in the Gulf of Mexico
as a result of destruction brought on by three major hurricanes (Katrina,
Rita, Ike) and the more recent BP oil spill
Recent reports suggest that oysters are disappearing worldwide except
the Gulf of Mexico
In most places throughout the world oyster populations are less than 10%
of there former levels
And in many areas natural recruitment is so poor that hatchery production
is relied upon to provide recruitment for oyster reef restoration and
commercial production
The worlds one bright spot for oysters has been dimmed by the BP oil spill
and the ill conceived fresh water diversion from the Mississippi river that
decimated oyster populations along the Louisiana coast
Other than the aforementioned natural and man-made disasters being
responsible for oyster disappearances, “over fishing and pollution” are the
most often cited causes of this marked decline
Except for areas like the East Coast of North America, seldom mention is
made of diseases and predation as significant contributors to this decline
The purpose of this presentation is to highlight the role of these factors as
headwinds to the restoration of oyster reefs in the Gulf of Mexico
Oyster Drill Stramonita (Thais) haemastoma
Oyster Drill Egg Cases, Galveston Bay
Oyster Drill
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Currently there is little information on the population density and damage caused by
the Southern oyster drill
Oyster fisherman reported heavy damages from this predator in Galveston Bay in
2010
This predator is appearing in unexpected abundances in January and February of
2011
The early appearance of this predatory snail in winter bodes ill for the oyster
recruitment and production in the spring and summer of 2011
Drill populations are generally reduced by salinities below 15 ppt and low
temperatures
Due to the colder than usual winter of 2010 and thus far in 2011 I am surprised at the
levels of drill populations
It is my opinion, without data to support it, that the recent widening and deepening of
the Houston Ship Channel is providing a vast refuge for drills, where they can escape
the deleterious low salinity caused by floods
One approach to control may be introducing the predatory snails as specialty seafood
items
Pilot studies by a local seafood provider in this regard are being conducted with
oyster drills as Biganos
The utilization of animals as food is a well known method of population control
This method is also being suggested for the control of cow nose rays (an oyster
predator) on the East Coast.
Perkinsus marinus (Dermo)
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Responsible for millions of dollars in loss of the eastern oyster on
the East and Gulf Coast
Much effort with little results has been expended towards
developing a genetically engineered oyster that is resistant to
dermo
Thus far the only successful remedy is through the reduction of
salinity by adequate freshwater inflow
For twenty years or more Dr. Thomas Soniat and I, with the
cooperation of the Texas Department of Parks and Wildlife, and
The Coastal Management Program of the Texas General Land
Office have monitored the dermo levels in the major oyster reefs of
Texas bays
We also have limited coverage of dermo levels in major oyster
producing areas throughout the Gulf of Mexico
One of the sites proposed for a major restoration of oyster reefs is
Matagorda Bay, Texas
I have a concern about the selection of this site because of
increases in dermo in the area beginning in late summer and
continuing through the winter
Mackin’s 5 point system of weighting
Dermo infection intensity (weighted prevalence) in
live oysters
0.00-0.99
Green
1.00-1.99
Yellow
2.00+
Red
- Generally oysters accumulate heavier infections
of dermo as they age
- Recently, I discovered moderately heavy
infections in small oysters (1-1.5 inch length) in
December from Aransas Bay, Texas
- In high salinity bays oysters survive dermo
disease better in the intertidal zone than subtidally
- During long droughts market oysters practically
disappear sub-tidally with the subsequent
invasion of the horse oyster (Ostera equestris)
Cultured gill x80
Oyster Sentinel
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Oyster Sentinel is a web-based community which uses the eastern oyster, Crassostrea
virginica, as a bioindicator of estuarine health. Oysters are sessile filter feeders which
concentrate toxins, accumulate pathogens and harbor parasites. The distribution of oysters
and their parasites are practical indicators of salinity regimes in estuaries.
(oystersentinel.com 2011)
Half moon
Reef
Half Moon Reef
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Changes wrought by building of dams, waterways, pipeline
corridors, flood and erosion control projects, etc. in most cases
have reduced and/or changed the timing of freshwater flows
into estuaries
Man’s alteration of the environment resulted in average
increases in bay salinities which in turn exacerbates the
ravages of oyster enemies
The philosophy of providing undisturbed sanctuaries to restore
oyster reefs to their former productivity may be misleading
Such approach permits the accumulation of silt along with reef
subsidence which often occurs that may render the substrate
unsuitable for spat set
This condition can be alleviated by working reefs with dredges
sans the netting to loosen the silt and turn over the substrate
and oysters (rolling oysters)
The periodic removal of oysters for the market may reduce the
reservoir of disease organisms
The infective dermo cells survive decomposition in dead tissue
and the digestive processes when devoured by scavengers
Current restoration goals appear to be based on yesterday’s
rather than today’s conditions
Sammy’s Reef (2010-2011)
Date Collected
T
S
Juvenile Infection
Percent Infection
Commercial Infection
Infection
Intensity
Weighted
Prevalence
Percent Infection
Infection
Intensity
Weighted
Prevalence
1/19/2011
12.6
23.8
80
1.5
1.2
12/13/2010
11.1
23.7
80
2.29
1.83
11/9/2010
19.2
24.9
43.8
0.9
0.4
100
1.93
1.93
10/19/2010
25.7
20
21.4
1.67
0.36
92.3
1.78
1.64
9/21/2010
26.4
26
40
1.83
0.73
100
2.73
2.73
8/17/2010
31.4
25
25
1.34
0.33
88.9
2.38
2.11
7/20/2010
30.3
17.6
100
1.77
1.77
6/23/2010
31.2
25
70
2.48
1.73
5/26/2010
27.2
25.1
70
2.14
1.5
4/19/2010
21.9
29
60
1.67
1
84.6
1.76
1.49
3/16/2010
18.1
18
12.5
0.67
0.08
30
0.67
0.2
2/17/2010
10.8
20.4
30
0.33
0.1
10
0.33
0.03
1/20/2010
15.7
9.9
60
0.61
0.37
Mad Island Reef (2010-2011)
Date Collected
T
Juvenile
Infection
S
Commercial Infection
Percent
Infection
Weighted
Percent
Infection
Weighted
Infection
Intensity
Prevalence
Infection
Intensity
Prevalence
3/24/2011
23.5
30
90
2.15
1.93
2/22/2011
19.7
21.7
80
0.84
0.67
1/19/2011
12.6
23.8
80
1.5
1.2
12/13/2010
11.1
23.7
80
2.29
1.83
11/9/2010
19.2
24.9
43.8
0.9
0.4
100
1.93
1.93
10/19/2010
25.7
20
21.4
1.67
0.36
92.3
1.78
1.64
9/21/2010
26.4
26
40
1.83
0.73
100
2.73
2.73
8/17/2010
31.4
25
25
1.34
0.33
88.9
2.38
2.11
7/20/2010
30.3
17.6
100
1.77
1.77
6/23/2010
31.2
25
70
2.48
1.73
5/26/2010
27.2
25.1
70
2.14
1.5
4/19/2010
21.9
29
60
1.67
1
84.6
1.76
1.49
3/16/2010
18.1
18
12.5
0.67
0.08
30
0.67
0.2
2/17/2010
10.8
20.4
30
0.33
0.1
10
0.33
0.03
1/20/2010
15.7
9.9
60
0.61
0.37
Shell Island Reef 2010-2011
Date
Collected
T
Juvenile
Infection
S
Commercial
Infection
Percent
Infection
Weighted
Percent
Infection
Weighted
Infection
Intensity
Prevalence
Infection
Intensity
Prevalence
3/24/2011
23.8
30
100
1.73
1.73
2/22/2011
20.3
19.7
90
1.19
1.07
1/19/2011
13.4
23
100
1.13
1.13
12/13/2010
10.8
20.2
90
1.37
1.23
11/9/2010
20.1
23
16.7
1.34
0.22
100
1.7
1.7
10/19/2010
25.5
17
71.4
0.93
0.67
90
2.04
1.83
9/21/2010
26.7
25
90
3.19
2.87
8/17/2010
31
24
80
2.58
2.07
7/20/2010
30.1
15.2
90
2.3
2.07
6/23/2010
31.1
24
70
1.76
1.23
5/26/2010
27.3
25.1
100
1.83
1.83
70
2.38
1.67
4/19/2010
21.8
26.5
33.3
0.5
0.17
78.6
1.61
1.26
3/16/2010
18.4
17.6
10
0.33
0.03
0
0
0
2/17/2010
9.9
12.8
20
0.33
0.07
40
0.33
0.13
1/20/2010
16.5
2.3
20
0.5
0.1
50
2.67
1.33
Oyster Lake 3-14-11
Temp
Salinity
20.6
26.4
Weighted
Prevalence Prevalence
90
1.54
Freshwater
inflow
Aransas/Copano Bays
Station
Date Collected
T
Juvenile
Infection
S
Commercial
Infection
Percent
Infection
Weighted
Percent
Infection
Weighted
Infection
Intensity
Prevalence
Infection
Intensity
Prevalence
Lap Reef
12/16/2010
16.7
8.5
10
0.33
0.03
20
1
0.2
Shell Bank Reef
12/16/2010
15.9
6.9
0
0
0
0
0
0
SW Causeway Reef
12/16/2010
16.9
10
70
1.57
1.1
70
1.14
0.8
Grass Islands Reef
12/16/2010
15.8
10
50
0.47
0.23
60
1.78
1.07
Half-Moon Reef
12/16/2010
15.4
12
40
0.83
0.33
20
0.33
0.07
NW Causeway Reef
12/16/2010
16.3
9.3
50
1.8
0.9
Long Reef
12/16/2010
16.2
12.4
90
1.93
1.73
100
1.67
1.67
Grass Islands Reef
4/12/2011
23.5
21.5
70
1.09
0.77
90
1.78
1.6
Half-Moon Reef
4/12/2011
23.1
24.4
40
1.25
0.5
40
1.41
0.57
Long Reef
4/12/2011
22.5
25.7
90
2.15
1.93
90
2
1.8
NW Causeway Reef
4/12/2011
25.4
19.5
90.9
1.7
1.55
90
1.56
1.4
Discussion
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As a conclusion: It is my opinion that disregarding the
potential damage by diseases and predators to oyster
reef restoration is a mistake
It is my opinion with the prospects of climate change and
sea level rise that care should be taken in selecting
restoration sites and efforts should be made to select sites
nearest fresh water inflow to reduce the adverse effect of
high salinities in promoting oyster enemies.
In a recent report there was the prediction that the sea
level would rise up to 3 feet along the Eastern and Gulf
Shores within the next 90+ years
When choosing potential reef sites go towards the
freshwater
In keeping with my interest in hunting, I think of salinity
and temperature conditions for best oyster culture in
terms of rifle caliber 20-20 is good, 30-30 is bad
Acknowledgments
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Perley G. and Kathreen Parr Gift Account for
financial support
Texas Parks and Wildlife for providing oysters
from Matagorda Bay
Rachel Dean (Lousby, Maryland) for providing
oysters from Maryland
Elizabeth Silvy for technical assistance