Technical Summary :
MMS Publication 92-0006
Long-Term Monitoring at the East and West Flower Garden Banks, Final Report
BACKGROUND:
Environmental threats posed by substantial hydrocarbon
development and other human activities on the outer continental shelf (OCS) in the
northwest Gulf of Mexico, and the sensitivity of coral reefs to unfamiliar environmental
change, prompted the Minerals Management Service to initiate a long-term monitoring
program at the Flower Garden Banks, two OCS banks harboring coral reefs. The East (EFG)
and West (WFG) Flower Garden Banks are located on the edge of the continental shelf,
slightly over 175 km SSE of Galveston, Texas. The banks are topographic expressions of
uplift caused by underlying salt domes originating from Jurassic, Louann evaporite
deposits 15 km below the seafloor. The crests of these isolated banks, which are 19 km
apart, are occupied by submerged coral reefs which rise to within 15 m of the surface.
Together the bank zones containing high diversity coral reefs cover over 450 acres.
A monitoring program was designed to address concerns regarding the potential for both
gradual and catastrophic deterioration. This is important in light of the November 1991
Flower Garden Banks National Marine Sanctuary designation. Recreational use of underwater
areas has historically increased following the establishment of areas as marine parks,
preserves, or sanctuaries. A long-term data base and standardized data collection and
analysis techniques may allow for the identification of impacts caused by the expected
increase in recreational use as well as those caused by escalating industrial activity in
the vicinity.
OBJECTIVES:
(1) To provide relevant and timely environmental data to
those charged with developing policies concerning oil and gas exploration and development
in the vicinity of these sensitive ecosystems; (2) to document long-term changes in coral
and associated communities at the Flower Garden Banks caused either by impacts of
petroleum exploration and development or other human activities; and (3) to document
long-term natural variation in reef-building and associated communities on the banks.
DESCRIPTION:
The establishment of monitoring stations at the East
Flower Bank involved first delimiting a 100 m by 100 m area containing reef communities
considered representative of those inhabiting the high diversity zone of the bank. This
was followed by implanting and mapping one hundred twenty (120) permanent stations for
monitoring encrusting (lateral) growth of Montastraea annularis (mountainous star coral)
and Diploria strigosa (brain coral; 60 stations for each species), forty (40) permanent
posts to mark 8 m2 repetitive sampling station for monitoring individual coral colonies,
and thirty (30) permanent accretionary growth spikes in coral colonies. This resulted in a
study site comparable to that established by Continental Shelf Associates, Inc. in the
West Flower Garden Bank in the summer of 1988 during monitoring efforts conducted for
Union Oil Co. Photographic and video field work was conducted at both banks semi-annually.
During each sampling effort, twenty, 10-meter stratified random transects were
photographed at each study site. Percent cover data were acquired planimetrically for all
coral species, leafy algae, sponges and reefrock on the photographs. Also calculated was
the number of colonies of each species, relative dominance of each coral species (percent
cover relative to total coral cover), species diversity, and evenness.
At each site thirty spikes implatedin the tops of cologines of M. annularis were
repeatedly measured to monitor accretionary growth. In addition, sclerochronology was used
to determine accretionary growth rates in four M. annularis colonies (two from each bank).
Core samples were also analyzed for their trace metal content by Instrumental Neutron
Activation Analysis. A preliminary study of barium incorporation rates in coral skeletons
was conducted to assess the possibility of using barium to document long-term water
quality changes resulting from oil and gas exploration.
Each permanent station for monitoring the encrusting growth of M annularis or D.
strigosa was established by implanting two nails 23 cm apart near colony borders. A
diopter framer attached to an underwater camera and placed directly over the nails allowed
photography of a repeatable 13.3 by 19.7 cm area. Growth and retreat were analyzed by
projecting sequential margins onto the same surface, and by planimetric measurement of
areas of growth and retreat, and border lengths over which the changes occurred.
Permanent posts were installed to mark repetitively photographed 8 m2 areas for
monitoring changes in individual colonies. Single slides were produced for each station
during each sampling effort using a 2 m tall, T-shaped camera frame equipped with a
down-looking camera, wide angle lens, two strobes, a compass, and a bubble level. The
photos were taken at a compass heading of 0000 with the bubble level centered above the
station post. Laboratory tests indicated high repeatability and precision. Growth,
disease, bleaching, algae-mediated or algae/sediment mat-mediated retreat, unexplained
mortality, and mechanical damage were quantified, as were their effect (mortality,
recovery, or no effect).
Two videotaped transects of 100 m length were acquired at each study site during each
cruise to record the general conditions of the coral community at the sites. The video was
taken form approximately two meters above the bottom at an angle of 450. Video transects
were taken along 100 m lines tautly strung along two sides of each survey area.
Ancillary measurements included dissolved oxygen, salinity, temperature, and light.
Samples and measurements were made at one meter depth and one meter above the bottom.
Light was also measured above the surface. Sea surface temperature data between 1979 and
1990 were collected from records of AVHRR satellite transits. In addition, thermographs
were installed in 1990 on the banks on the banks to record bottom temperature every two
hours.
SIGNIFICANT CONCLUSIONS:
Virtually no significant long-term changes
have been detected in coral reef populations, cover, or diversity at the Flower Garden
Banks since quantative surveys of the reefs began. Those differences that have been
identified are not considered to represent trends or evidence of deterioration of habitat
quality. Conditions for accretionary and encrusting growth on the banks appeared to be
favorable for both montastraea annularis and Diploria strigosa. Data indicate limited
effects from factors other than those which naturally control coral growth. Monitoring of
the occurrence and effects of coral bleaching (the expulsion of symbiotic algae essential
to vigorous growth) and diseases suggests that disease was the more important cause of
coral mortality even though more coral cover was affected by bleaching than by disease.
The observations of mass spawning by three coral species on the East Bank in 1991, as well
as the studies of recruitment, and observations of reef corals on petroleum platforms
imply that the Flower Garden Banks harbor wholly functional coral communities. This
suggests that the reefs are capable of self-seeding, and may not required gene flow from
outside sources for recovery following natural or human-induced disturbance. Parrotfish
abundances appeared to have increased since the early 1980s. This may be a result of the
1983-1984 mass mortality of the long-spine sea urchin. Diadema antillarum, and consequent
changes in benthic algae availability on the banks. A review of the potential effects of
industrial activities on the reefs indicated that tanker spills and spills resulting from
platform accidents, as well as the application of dispersants during clean-up operations,
pose the most realistic threats to reef corals at the Flower Gardens. Discharges of
produced waters and drilling fluids were not considered to pose substantial threats
because of existing regulations in the vicinity of the banks and dilution by intervening
water masses.
STUDY RESULTS:
Coral cover, relatived dominance, diversity, evenness,
and accretionary and encrusting growth rates were monitored form 1989 through 1991.
Several differences existed between study sites, particularly with respect to diversity
and evenness, but these do not necessarily imply differences between the banks. No
significant trends were observed in any parameters during the study. Comparison with data
from population and growth studies conducted between 1978 and 1982 suggested no
significant long-term trends. However, research plans include reanalysis of archived
transect photographs using current methodologies to reduce variability of historic data.
Coral bleaching was observed every summer during the study, but mortality was seldom
associated with bleaching. Only 7% of bleached colonies exhibited any tissue loss; where
it did occur, loss was limited to small portions of the bleached colonies. Diseases
occurred on less then 2% of all corals analyzed, but relatively high levels of tissue
mortality occurred; 69% of diseased colonies exhibited tissue loss. Late summer bleaching
followed temperature maxima that exceeded 300C. Coral growth on the banks was
characterized by relatively high growth rates, net tissue gain over the study period, and
a high proportion of advancing margins on Montastaea annularis and Diploria strigosa, the
two dominant corals on the banks. Mass spawning (synchronous gamete release) by three
coral species, M. annularis, M. cavernosa, and D. Strigosa was observed in 1990 and fully
documented in 1991. Both events occurred eight evening after August full moons, and were
limited to two to three hour periods.
STUDY PRODUCTS:
Gittings, S.R., G.S. Boland, K.J.P. Deslarzes, D.K.
Hagman, and B.S. Holland. 1992. Long-term monitoring at the East and West Flower Garden
Banks. OCS Study MMS 92-0006. U.S. Department of the Interior, Minerals Management
Service, Gulf of Mexico OCS Regional Office, New Orleans. 206 pp.
ADDITIONAL PRODUCTS:
13 quarterly progress reports, 12 cruise reports,
three project presentations, two presentation summaries, three presentation slide sets,
project video.
CONTRACT NUMBER(S):
14-12-0001-30452.
SPONSORING OCS REGION:
Gulf of Mexico.
APPLICABLE PLANNING AREA(S):
Western Gulf of Mexico.
FISCAL YEAR(S) OF PROJECT FUNDING:
1988.
COMPLETION DATE OF REPORT:
June 1992.
COST(S): FY 1988:
$345,896.
CUMULATIVE PROJECT COST:
$345,896.
PROJECT MANAGER(S):
Stephen R. Gittings.
AFFILIATION:
Geochemical and Environmental Research Group, Texas
A&M University.
ADDRESS:
Geochemical and Environment Research Group, Texas A&M
University, 833 Graham Road, College Station, Texas 77845.
PRINCIPAL INVESTIGATOR(S):
Stephen R. Gittings.
KEY WORDS:
Western Gulf, continental shelf, coral reefs, monitoring,
biology, cover, relative dominance, species diversity, evenness, encrusting growth,
accetionary growth, sclerochronology, disease, bleaching, temperature, salinity, light,
oxygen, barium, random, photography, repetive photography, videography, fish, mass
spawning, reproduction, industrial impacts.
Report Availability and ESPIS
Copies of the technical report for this study are available through the:
Minerals Management Service
Public Information Office
1201 Elmwood Park Boulevard
New Orleans, Louisiana 70123-2394
(504) 736-2519 (local) or 1-800-200-GULF
Copies of many of the Environmental Studies Program reports and pertinent Technical
Summaries are available through the Environmental
Studies Program Information System (ESPIS)
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