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Algal community structure of the East and West Flower Gardens, northwestern Gulf of Mexico.

Abstract.--The Flower Garden Banks are located approximately 200 km south of the border between Texas and Louisiana, on the outer continental shelf, beginning at a depth of approximately 20 m. The algal community has not been comprehensively evaluated and only checklists of a few dominant macroalgal species have been reported. This study utilized both destructive and non-destructive techniques to characterize the algal community structure. Harvest and photogrammetric samples were collected during two trips to the Flower Garden Banks in October 1998 and March 1999. A total of forty 0.25 [m.sup.2] quadrats of standing stock material were randomly collected, curated and stored for further evaluation. Photogrammetric samples (161) were obtained using an underwater camera and were evaluated by a grid of 25 random points. A total of 4,025 points of information were used to calculate percent composition and cover. Harvest sampling was used to characterize the algal composition of the 'red algal mat' which was the dominant feature comprising 38.4% of the photogrammetric samples. A total of 44 species were identified from the samples. The 'red algal mat' was primarily composed of members of the Order Ceramiales (Centroceras, Ceramium, Hypoglossum, Polysiphonia and Anotrichium).

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The Flower Garden Banks are deep-water coral habitats located on the edge of the outer continental shelf in the northwestern Gulf of Mexico and cover an area of 143 [km.sup.2]. The Flower Garden Banks are found at approximately 18-36 m below the water surface and extend down to 100-150 m (Lugo-Fernandez et al. 2001). The Flower Garden Banks are separated into the East Flower Gardens and the West Flower Gardens and are 12-15 km apart. They were designated as a protected National Marine Sanctuary in 1992. The East Flower Garden Bank is located at 27[degrees] 54.5' N latitude and 93[degrees] 36.0' W longitude, approximately 193 km southeast of Galveston, Texas. The West Flower Garden Bank is located approximately 172 km southeast of Galveston, Texas at 27[degrees] 52.4' N latitude and 93[degrees] 48.8' W longitude (Fig. 1).

[FIGURE 1 OMITTED]

Both banks are topographic features created by the uplift of underlying salt domes of Jurassic, Louann origin (Rezak 1981). Bedrock material above the domes is covered with an overgrowth of calcareous marine organisms and represents the largest charted calcareous banks in the northwestern Gulf of Mexico (Bright et al. 1985) and the northernmost coral reefs on the continental shelf of North America (Bright et al. 1984). The Flower Garden Banks are part of a widely dispersed and discontinuous are of reef material located along the outer continental shelf of the Gulf of Mexico (Rezak et al. 1985). The diversity of the coral community at the Flower Garden Banks has been described as depauperate as it supports only 20 species of hermatypic corals (Bright et al. 1984; Lugo-Fernandez et al. 2001). Although low diversity communities exist on neighboring banks, the reefs adjacent to Cabo Rojo, approximately 100 km south of Tampico, Mexico are the closest extensively developed coral reefs in the Gulf of Mexico and make up the Tuxpan Reef System (Universidad Veracruzana 1996; 2003; Tunnell 2007). The Tuxpan Reefs are approximately 644 km south of the Flower Garden Banks and are composed primarily of stony corals; 31 species of scleractinia coral and two hydrocorals (Universidad Veracruzana 1996; 2003; Tunnell 2007).

Monitoring of the Flower Garden Banks began in 1989 (Gittings et al. 1992) for the purposes of: (1) documenting long-term natural changes in reef growth and associated communities, (2) providing information and scientific data on the effect of gas and oil exploration in the vicinity of this sensitive ecosystem, and (3) encouraging and coordinating research efforts with agencies and institutions in order to better evaluate and/or determine causes of environmental change in the vicinity of the Flower Garden Banks (Dokken et al. 2001). Taxonomic lists of benthic marine algae from the Flower Garden Banks were included in investigations by Bright and Pequegnat (1974) and Rezak et al. (1985; 1990). This study characterizes and provides an updated taxonomic assessment of the algae, coral and algae associations and algal distribution of the East and West Flower Garden Banks.

MATERIALS AND METHODS

Ecological field methods followed those described by Littler & Littler (1985) and Brower et al. (1989). A herbarium voucher collection of benthic macroalgae (seaweeds) was completed and is located at the Ruth O'Brien Herbarium at Texas A&M University-Corpus Christi, Corpus Christi, Texas. Voucher specimens of macroalgal samples were also preserved in 2% gluteraldehyde and microscopic material was preserved on microscope slides sealed with Flo-Texx.

Photogrammetric and harvest samples were collected during two trips to the Flower Garden Banks in October 1998 and March 1999. Random quadrats were photographed using a Nikonos V equipped with a 28 mm lens, close-up kit, and Nikonos strobe. Each transparency represented a 0.25 [m.sup.2] quadrat that was evaluated by projecting onto a grid containing 25 random points (modified point quadrat) and evaluated based on (1) Bare Substrate, (2) Cyanobacteria, (3) Green Algal Mat, (4) Red Algal Mat, (5) Coralline Algae, or (6) Live Coral coverage. Values are expressed as the number of 'hits' for each species or feature divided by the total number possible. This number varied with each bank and season measured. A total of 4,025 points of data were identified and used to calculate percent composition, species richness, dominance, diversity and cover. Such samples can be used to generate precisely detailed and highly reproducible quantitative information, including cover, density, frequency and diversity (Littler & Littler 1985). Diversity and other indices were calculated from relative abundance of both, algae and total species observations. Diversity values were determined for each bank and sampling season using the Shannon Index (H', natural log) (Shannon 1948), Richness, Evenness (J') (Pielou 1966) and Simpson's Index of Dominance (Simpson 1948). Relative Community Similarity was determined by species or feature abundance from each bank and season and compared with total percent similarity and Morisita's Index of Community Similarity (Morisita 1959). Morisita's Index is based on Simpson's Index of Dominance and determines the probability that two randomly selected individuals will be the same species. The range of results are 0 (no similarity) to approximately 1 (identical).

Macroalgal mat samples were harvested using paint scrapers and placed into nylon net bags. A total of forty 0.25 [m.sup.2] quadrats of standing stock material were randomly collected, preserved and stored for evaluation. This sampling was used to characterize the algal composition of the 'red algal mat'.

RESULTS

A total of forty 0.25 [m.sup.2] quadrats of standing stock material were randomly collected along with one hundred sixty-one 0.25 [m.sup.2] photo-quadrats from an average depth of 27 m. A systematic list of marine algae from the East and West Flower Garden Banks has been compiled (Table 1). The systematic organization follows that of Wynne (1998). Taylor (1960) and Schneider & Searles (1991) were referenced when species were encountered that were uncommon to the region.
Table 1. Taxonomic list of algae collected from East and West Flower
Garden Banks, northwestern Gulf of Mexico. (E = East, W = West).

 DIVISION CYANOBACTERIA

Order Oscillatoriales
 Family Oscillatoriaceae
 Lyngbya sp. E & W
 Oscillatoria sp. E & W
 Schizothrix calcicola (C. Agardh) Gomont E & W
 Spiridina sp. W
 Unknown (3 species) E & W

 DIVISION RHODOPHYTA

Order Compsopogonales
 Family Erythropeltidaceae
 Erythrocladia sp. E
 Erythrotrichia sp. E

Order Bonnemaisoniales
 Family Bonnemaisoniaceae
 Asparagopsis taxiformis (Delile) Trevisan E & W

Order Corallinales
 Family Corallinaceae
 A mphiroa fragilissima( Linnaeus) Lamouroux E
 Corrallina spp. (3 species) E & W
 Jania adhaerens Lamouroux E & W

Order Ceramiales
 Family Ceramiaceae
 Anotrichium tenue (C. Agardh) Nageli E & W
 Antithamnion sp. E & W
 Antithamionella sp. E
 Callithamiella sp. E & W
 Callithamnion sp. E & W
 Centroceras clavulatum (C. Agardh) Montagne E & W
 Ceramium spp. (2 species) E & W
 Griffithsia globulifera Kutzing W
 Plenosporium flexuosum (C. Agardh) De Toni E & W
 Ptilothammon occidentale Searles W
 Rhododictyon bermudense W. R. Taylor E
 Spyridia spp. (2 species) E & W

 Family Delesseriaceae
 Hypoglossum hypoglossoides (Stackhouse)
 Collins et Hervey E & W
 Hypoglossum sp. W
 Myriogramme sp. W
 E & W

 Family Dasyaceae
 Dasya Sp. E & W

Family Rhodomelaceae
 Chondria sp. E & W
 Herposiphonia sp. W
 Polysiphonia spp. (3 species) E & W

Order Rhodymeniales
 Family Rhodymeniaceae
 Botryocladia occidentalis (Borgesen) Kylin E & W
 Chrysymenia enteromorpha Harvey E & W
 Chrysymenia sp. W
 Rhodymenia divaricata Dawson E

Order Gigartinales
 Family Dumontiaceae
 Dudresnaya sp. W

 Family Hypneaceae
 Hypnea sp. W

Order Gelidiales
 Family Belidiaceae
 Gelidium sp. W

DIVISION OCHROPHYTA
Class Phaeophyceae

Order Dictyotales
 Family Dictyotaceae
 Dictyota dichotoma (Hudson) Lamouroux E&W
 Diciyoia sp. E&W
 Dictyota sp. E&W
 Lobophora variegata (Lamouroux) Womersley E&W
 Spatoglossum schroederi (C. Agardh) Kutzing E&W

DIVISION CHLOROPHYTA

Order Ulotrichales
 Family Ulotrichaceae
 Ulothrix flacca (Dilwyn) Thuret E&W

Order Dasycladales
 Family Polyphysaceae
 Polyphysa polyphysoides
 (P. and H. Crouan in Maze and Schramm) Schnetter E&W

Order Ulvales
 Family Ulvellaceae
 Entocladia viridis Reinke E
 Family Ulvaceae
 Enteromorpha sp. E&W

Order Caulerpales
 Family Bryopsidaceae
 Bryopsis pennata Lamouroux E&W
 Derbesia sp. E&W
 Family Caulerpaceae
 Caulerpa sp. W

Order Cladophorales
 Family Cladophoraceae
 Chaetomorpha sp. E
 Cladophora sp. E&W
 Family Anadyomenaceae
 Anadyomene stellata (Wulfen) C. Agardh W


Photogrammetric sampling.--The feature 'red algal mat' had the greatest coverage comprising 38.4% of all photogrammetric samples followed by Bare Substrate (14.6%), Coralline Algae (9%), Green Algal Mat (8.1%), and Cyanobacteria (4%) (Figure 2). Species richness totaled 25 with both banks combined. The East Bank had the greatest species richness October 1998 with 19 and lowest March 1999 with 14 (Table 2).
Figure 2. Percent algal coverage of photogrammetric samples from 1998,
1999, and both years combined. (TD = total; FG = Flower Gardens)

 TD 98 TD 99 FG TD %

Bare Substrate 11.4 18.8 14.6
Cyanobacteria 4.4 3.4 4
Coralline Algae 7.3 5.3 9
Green Mat 10.7 4.7 8.1
Red Mat 38.7 37.9 38.4

Note: Table made from bar garph.
Table 2. Species richness, diversity, dominance and evenness of the
East and West Flower Gardens Banks, 1998-1999.

Bank/Year Species Shannon's Shannon's Simpson's Simpson's
 Richness Diversity Evenness Dominance Evenness

West 98 15 2.10 0.77 0.15 0.93
East 98 19 1.90 0.65 0.26 0.77
West 99 16 1.94 0.70 0.23 0.82
East 99 14 2.06 0.78 0.18 0.88
Total 25 2.20 0.68 0.19 0.84


Diversity measures using Shannon's Diversity Index and Evenness show little differences in diversity between years and between the East and West Banks (Table 2). The West Bank had the greatest diversity October 1998 (H' = 2.10) and the East Bank had the highest diversity March 1999 (H' = 2.06). Overall, species diversity with both banks combined was H' = 2.20. Morisita's Index of Community Similarity indicated the East and West Banks in 1999 and the total of the East and West Banks from 1998 & 1999 were almost identical (0.94). Percent (Proportional) similarity supported these results (Table 3).
Tables 3. Community similarity using Percent Similarity and Mortisita's
Inbox of the East and West Flower Garden Banks, 1998 & 1999.

Bank/Years Percent Similarity Mortisita's Index

East 98 vs. West 98 53.01 0.72
East 99 vs. West 99 72.26 0.94
East 98 vs. East 99 61.54 0.85
West 98 vs. West 99 58.94 0.79
East vs. West Total 73.59 0.94


Association between corals and algal mat communities were investigated to determine if a particular coral species had a partiality with the red algal mat. Within all quadrats, each time a coral species was encountered, the presence or absence of the red algal mat was assessed. A proportion of coral species to total red algal mat was computed. Montastrea cavernosa was most often associated with the red algal mat at 54.2% with Diploria strigosa following at 27.1%. Additional corals that were also associated with the red algal mat were Diplora clivosa at 11.9% and Montastrea annularis at 10.1%.

Harvest sampling.-Harvest samples were evaluated to characterize the species composition of the algal mat found at the coral/algal interface. The most common species collected were from the Division Rhodophyta. A 'red algal mat' was the dominant algal and non-algal coverage comprising 30.4% of all photogrammetric samples. The mat was composed primarily of members of the Order Ceramiales comprising 37.6% of coverage and was represented by species of Centroceras, Ceramium, and Polysiphonia (Table 3). The Order Ceramiales was also the dominant group at each bank; 38.3% at the East, and 36.9% at the West. The East bank was represented by 13 algal families and the West Bank by 14.

A total of 44 species were identified from harvested samples collected from the East and West Flower Gardens Banks (Table 4). Bryopsis pennata and Derbesia, both in the Order Caulerpales, composed 12.0% of the 'green algal mat' on the East Flower Gardens and 11.0% on the West Flower Gardens. The Rhodophyta, Jania adhaerens, was the most common coralline alga found at both Banks with coverage of 6.1% at the West and 7.1% at the East Bank.
Table 4. Total percentage of each algal species from the East and West
Flower Garden Banks 1998-1999 contributing to total coverage.

Species East Bank West Bank

Amphiroa fragilissima 3.4 0
Anotrichium tenue 0 2.3
Antithamnionella sp. 1.5 0.4
Asparagopsis taxiformis 4.1 2.7
Botryocladia occidentalis 1.1 1.1
Bryopsis pennata 6 6.5
Callithamnion sp. 1.5 2.3
Caulerpa sp. 0 1.1
Centroceras clavulatum 7.5 2.7
Ceramium sp. 6.4 3.8
Chaetomorpha sp. 0.8 0
Chondria sp. 3.8 2.7
Chrysymenia enteromorpha 1.5 2.3
Cladophora sp. 4.9 3.4
Corallina sp. 0.4 0
Dasya sp. 1.1 1.5
Derbesia sp. 6 3.4
Diatom mat 0 0.4
Dictyopteris membranaceae 0 1.1
Dictyota sp. 3.8 3
Dudresnaya sp. 0 1.9
Enterocladaia virdis 0.8 0
Enteromorpha sp. 0.8 2.7
Erythrocladia sp. 0.4 0
Erythrotrichia sp. 1.5 0
Gelidium sp. 0 1.1
Griffithsia globulifera 0 2.7
Herposiphonia sp. 0 1.5
Hypnea sp, 0 0.8
Hypoglossum hypoglosoides 1.9 2.7
Jania adhaerens 7.1 6.1
Lobophora variegata 4.5 1.5
Lyngbya sp. 7.5 5.7
Myriogramme sp. 0 0.4
Oscillatoria sp. 0 6.8
Plenosporium flexuosum 3 3.8
Polyphysa polyphysoides 1.5 0
Polysiphonia sp. 4.9 5.3
Ptilothamnion occidentale 0 0.4
Rhodymenia divaricata 0.8 0
Spatoglossum schroederi 1.9 0.4
Spirulina sp. 0 0.8
Spyridia sp. 3.4 4.9
Ulothrix flacca 2.6 3.4
Unknown 3.8 6.5


Cyanobacteria; primarily Oscillatoriales, were common in samples, representing 7.5% at the East Flower Gardens, and 11.0% at the West Flower Gardens. Oscillatoriales was represented by only a few taxa with Lyngbya as the most common genus at both banks.

DISCUSSION

It is difficult to determine causes or effects of algal populations affecting the health of particular coral species of the Flower Garden Banks because the limited opportunity of sampling during this study. When given the opportunity to collect algal material from the Flower Garden Banks, especially at the interface of coral, algal material should be photographed in situ and samples collected, preserved in 2% gluteraldehyde, and returned to the laboratory for identification and evaluation. Coral species, depth, temperature and other environmental factors at the site should be recorded.

Ceramiales is an Order composed mainly of annual species that dominate as opportunists at sites with irregularly fluctuating conditions (i.e., temperature) (Luning 1990). These opportunists are quick growing algae that, after bacteria and diatoms, are the first multicellular algae to appear on bare, nonliving or damaged substrates. These algae exhibit variability in biomass depending upon herbivorous grazing or changes in environmental and seasonal conditions. Guimaraens & Coutinho (1996) evaluated the effect of an upwelling region near Rio de Janeiro, Brazil on the spatial and temporal variation of benthic marine algae. The survey of benthic algae yielded groups including the Ceramiales with temperature affinities occurring in sites directly influenced by upwelling waters. Their data showed water temperature affects distribution and abundance of algae enabling warm temperate species (18-20[degrees] C) to survive under otherwise tropical conditions.

A seven year mean of water temperature recorded at a depth of 24 m at the West Flower Garden Banks resulted in a range of 18-30[degrees]C with low temperatures occurring in February (18-20[degrees]C) and highs in July-August (29-30[degrees]C) (Lugo-Fernandez 1998). This temperature range at the Flower Garden Banks is optimum for the growth of the 'red algal mat' composed primarily of members from the Order Ceramiales (Guimaraens & Coutinho 1996). The increased growth of these algae may become an environmental problem, possibly global, that would be practically impossible to mediate. The best action is to monitor changes over time to determine the magnitude and effect to the reef resulting from competition of the 'red algal mat'. Little is known about the community dynamics of benthic marine algae and their effect on the character of biotic reefs. Information on the role of interspecific and intra-specific competition, recruitment, natality and mortality phenomena is lacking and it is difficult to make definitive statements concerning the role of algae and their effect on other organisms.

ACKNOWLEDGMENTS

Thanks are extended to the Flower Garden Banks National Marine Sanctuary for their support, interest and permission to conduct this ancillary project in conjunction with the MMS/NOAA funded project "Long-term monitoring at the East and West Flower Garden Banks, 1998-1999." Thanks to Dr. Quenton Dokken, Dr. Carl Beaver, Susan Childs and Suzanne Bates, Center for Coastal Studies, Texas A&M University-Corpus Christi for their support in this project. We appreciate Lee Lehman for his help in sample collection and Amy Nunez for coral identification, Texas A&M University-Corpus Christi, and the crew of the M/V Spree for their assistance.

LITERATURE CITED

Brower, J. E., J. Zar & C. N vonEnde. 1997. Field and laboratory methods for general ecology. WCB/McGraw-Hill, St. Louis, Missouri, 273 pp.

Guimaraens, M. & R. Coutinho. 1996. Spatial and temporal variation of benthic marine algae at the Cabo Frio upwelling region, Rio de Janeiro, Brazil. Aquat. Bot., 52:283-299.

Littler D. S., M. M. Littler, K. E. Bucher & J. N. Norris. 1989. Marine plants of the Caribbean: A field guide from Florida to Brazil. Smithsonian Institution Press, Washington, D.C., 249 pp.

Lugo-Fernandez, A. 1998. Ecological implications of hydrogeography and circulation to the Flower Gardens and Stetson Banks, northwest Gulf of Mexico. Gulf Mex. Sci., 2:144-160.

Lugo-Fernandez, A., K. J. P. Deslarzes, J. M. Price, G. S. Boland & M. V. Morin. 2001. Inferring probable dispersal of Flower Garden Banks coral larvae (Gulf of Mexico) using observed and simulated drifter trajectories. Cont. Shelf Res., 21:47-67.

Luning, K. 1990. Seaweeds. Their environment, biogeography, and ecophysiology. John Wily & Sons, Inc., New York, 527 pp.

Morisita, M. 1959. Measuring of interspecific association and similarity between communities. Mem. Fac. Sci. Kyushu Univ., Ser. E (Biol.), 3:65-80.

Pielou, E. C. 1966. The measurement of diversity in different types of biological collections. J. Theoret. Biol., 13:131-144.

Schneider, C. W. & R. B. Searles. 1991. Seaweeds of the Southeast United States, Cape Hatteras to Cape Canaveral. Duke University Press, Durham, NC, 553 pp.

Shannon, C. E. 1948. A mathematical theory of communication. Bell System Tech. J., 27:379-423, 623-656.

Simpson, E. H. 1949. Measurement of diversity. Nature, 163:688.

Taylor, W. R. 1960 Marine algae of the eastern tropical and subtropical coasts of the Americas. University of Michigan Press, Ann Arbor, MI, 870 pp.

Tunnell, J. W., Jr. 2007. Reef distribution (chapter 2). In Tunnell, J. W. Jr., Chavez, E.O. and Withers, K. (eds) Coral reefs of the southern Gulf of Mexico. Texas A&M University Press, College Station, TX, 216 pp.

Universidad Veracruzana. 2003. Documento tecnico justificativo para la creaction de un area natural protegida en el sistema arrecifal Lobos-Tuxpan. University Press, College Station, TX, 216 pp.

Universidad Veracruzana. 1996. Ecobuceo en la Costa Norveracruzana. Facultad de ciencias biologicas y agropecuarias grupo de ecologia arrecifal.

Wynne, M. J. 1998. A checklist of benthic marine algae of the tropical and subtropical western Atlantic: First Revision. Gebruder Borntraeger. Berlin, Germany, 155 pp.

EMH at: Erin.Hill@tamucc.edu

Erin M. Hill and Roy L. Lehman

Center for Coastal Studies, Texas A&M University-Corpus Christi 6300 Ocean Drive, Corpus Christi, Texas 78412
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Author:Hill, Erin M.; Lehman, Roy L.
Publication:The Texas Journal of Science
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Date:Aug 1, 2008
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