CHECKLIST OF THE MARINE ALGAE ON THE OFFSHORE OIL PLATFORMS OF LOUISIANA by Theresa M, Bert and Harold J. Humm ABSTRACT A survey was conducted over a period of a year for the marine algae present on eight oil production platforms located in the offshore waters of Louisiana. A total of 120 species was recorded, bringing the total known for Louisiana to 180. Of the 120 species collected 18% are Cyanophyta, 31070 Rhodophyta, 16% Phaeophyta, and 35070 Chlorophyta. Two floristic provinces were noted with regard to algal occurrences on these platforms: a coastal province characterized by shallow water of reduced salinity with fewer species especially of browns and reds, and an offshore province characterized by deeper, clearer water and a large number of species especially of browns and reds. INTRODUCTION Prior to the initiation of this work, nearly all studies of the marine flora of Louisiana had been limited to bays or near-shore areas. An exception was Kapraun's (1974) collections from submerged offshore reefs. He reported 31 species new to the Louisiana coast and commented on their distribution, habitat, and reproduction. Early reports of the marine algae of Louisiana included a Iist of species from the vicinity of the Gulf Biological Station at Cameron (Cocks 1907), and two lists from the Grand Isle area (Behre 1950; Flint 1951). Taylor (1954) mentioned a few species from Louisiana and in- At the time of this investigation, Theresa Bert and Harold Humm were at the Department of Marine Science, University of South Florida. 438 RICE UNIVERSITY STUDIES CHECKLIST OF MARINE ALGAE 439 cluded these and a few additional species in his 1960 book. Humm and Darnel1 (1959) and Mullahy (1959) published articles on collections from the Chandeleur Islands. Drouet (1968, 1973, 1978) and Drouet and Daily (1956) listed the Cyanophyta that they and others had collected from the state. Earle (1969), in her study of the Phaeophyta of the eastern Gulf of Mexico, included the area east of Grand Isle. The purpose of this paper is to present the results of an algal survey conducted over a period of a year from the offshore petroleum platform pilings. It is hoped that these results will be of use in future in- vestigations to determine whether or not future petroleum activities have any adverse effect on these plant species. Ecological relationships be- tween the algal species and abiotic parameters will be presented elsewhere. MATERIALS AND METHODS Seven field trips were made to eight offshore platform stations in Louisiana from July 17, 1973, to July 23, 1974 (figure 1). Petroleum platforms (stations) were selected to reach the widest possible range of water characteristics. Stations were chosen along two transects, one running in close proximity and perpendicular to the Mississippi River discharge (Stations 30, 73, and 99) and the second running away from the influence of the river discharge (16, 26, 54, and 165). Station 19 was added near shore within the west delta embayment. Samples were taken from the pilings by use of SCUBA. Scrapings of 0.01 m' surface area were taken at regular intervals from the surface to the lowest level of the algal zone usually at about 9.2 m. Samples were generally taken from the southwestern side of the piling where the algal growth was richest and from the shaded northern side. Samples were fixed in 5% sea water formalin and brought to the laboratory for identification. RESULTS A total of 120 species of algae was collected from these platforms, of which 22 (18%) belong to Cyanophyta, 37 (31%) Rhodophyta, 19 (16%) Phaeophyta, and 42 (35%) Chlorophyta (table 1). These species bring the total of known species of marine algae from Louisiana to 180. Station 54, located in 21.6 m water depth, was the richest station, with 76 species present, followed by Station 165, in 27.7 m, with 63 species. The number of species collected from the remaining six stations ranged from 40 to 53. RICE UNIVERSITY STUDIES XXXXX XXX XX XXX XX XXXX XXX XX X X XX XXX X XXX X XXXXX XXX XXX XXXXXXXX X XXX X XXXXXXX X XXX X XXXXXXXX XX XXX X XXXXXX X XX XXXX XXXXX XXX X CHECKLIST OF MARINE ALGAE XXX XX XXX XXXX X XXXX X XXXX XXX X X X XX XXX x x X XX X XX X XX XXXX X X X X XX X X XX X X X X X X x X X TABLE 1 (continued) Station Number of Oil Platforms Species 16 19 26 30 54 73 99 165 Phylum Rhodophyta (continued) Order Ceramiales Antithamiion cruciatwr' Ceramiwn byssoidewn C. fastzgiatwn C. f. E. fZaccida Herposip:wnia secunda Laurelzcia papiZZosa Lophosiphonia eristata L. saccorhiza L. subadunca PoZysiphonia hava?zensis P. hemisphaerica P. howeii P. subtilissinia Spermotbrmion inuestiens Phylum Phaeophyta (19 specles) Order Ectocarpales Ac, netospora el-inita Bachelotia antiZlarwn Cctocarpus eZacI?istaefor~nis C. intermedius E. variabzlis Giffordia conifera G. indiea G. mitchel liae G. raZZsiae iferponenia tortugense Phaeostronia pusiZZwn Spongonema tomentosvni CHECKLIST OF MARINE ALGAE XX XXX X XX XX XX X XX XX X X X X XX X XXX X X X X X XXX XXX x X X XXX X x X xx TABLE 1 (continued) Station Number of Oil Platforms Species 16 19 2 6 30 54 7 3 99 165 Phylum Chlorophyta (continued) Order Cladophorales Chaetomorpha brachygona C. graciZis C. Zinwn C. minima CZadophora aLbida C. brachyczona C. catenata C. constricta C. dalmatica C. deZicatuZa C. flexuosa C. graciZis C. repens C. sericea C. vagabunda RhizocZoniwn hookeri R. kochianwn R. riparwn Order Siphonocladales CZadophoropsis membranacea Order Dasycladales Batophora oerstedii Order Siphonales Bryopsis hypnoides B. pennata Derbesia Zamourouxii D. vaucher~aeformls Ostreob~uinquekellu Number of Species 52 43 49 40 76 50 53 63 CHECKLIST OF MARINE ALGAE 445 Analysis of the species composition indicated two groups, based primarily on water depth: the coastal stations 16, 19, 26, and 30, which were located in water depths of 11.6 to 16.0 m, and an offshore group of four stations, 54, 73, 99, and 165, which were located in water depths of 21.6 to 58.0 m. The offshore province averaged 60 species as compared to 46 from the coastal province; this difference was largely the result of an increase in the number of species of reds and browns at the offshore stations. DISCUSSION Comparisons of the algal species composition with pre-oil production activity is impossible because of the near absence of suitable solid substrate for algal attachment in this area before the platforms were constructed. The pilings, supporting hundreds of oil platforms, constitute a substrate of major importance to the occurrence and distribution of marine algae. In addition to benthic algae, these pilings also support large populations of sessile and free-living invertebrates and serve as a base of the food sources for herbivorous and carnivorous fish. The influence of the run-off of the Mississippi River is evident from the smaller species total of those shallow water stations located within the plume. The lower species totals are probably the result of lowered surface salinities and increased turbidity, which decreases the light penetration. The presence of a nepheloid area near the bottom limited algal growth at this depth (Oetking et al. 1974). The knowledge of the species composition of marine algae on these pilings may be of value in assessing the effects of an oil spill or blowout in the event that one should occur within this area. ACKNOWLEDGMENTS This study was supported by research grant OB 70 HJM from the Gulf Universities Re- search Consortium. We are grateful to Curtis Kruer, Bruce DeGroot, and Bob Ernest for asssting in the field work, and to the Exxon Corporation for provid~ngtransportation and lodging while we conducted the field work. REFERENCES CITED Behre, E. H. 1950. Annotated list of the fauna of the Grand Isle Reg~on,1928-1946. Occas~onalPapers of the Marine Laboratory, Louls~anaState Univers~ty6:l-66. 446 RICE UNIVERSITY STUDIES Cocks, R. S. 1907. Flora of the Gulf biologic station. Bulletin of the Louisiana Gulf B~ologicStation (Cameron) 7: 1-42. Drouet, F. 1968. Revision of the Classification of the Oscillatoriaceae. Monograph 15. Philadelphia, Academy of Natural Sciences. 1973. Revision of the Nostocaceae with Cylindrical Trichomes. New York: Hafner Publishing Co. 1978. Revision of the Nostocaceae with Constricted Trichomes. Vaduz, Liechten- stein: J. Cramer. and W. A. Daily. 1956. Revision of the Coccoid Myxophyceae. Butler University Botan~calStudles 12:l-222. Earle, S. A. 1969, Phaeophyta of the eastern Gulf of Mexico. Phycologia 7:71-254. Flint, L. H. 1951. Some winter red algae of Louisiana. Proceedings of the Louisiana Academy of Sciences 14:34-36 Humrn, H. J. and R. M. Darnell. 1959. A collection of marine algae from the Chandeleur Islands. Publications of the lnst~tuteof Marine Science, The University of Texas 6:265-276. Kapraun, D. F. 1974. Seasonal per~odicityand spatial distribution of benthic marine algae In Louisiana. Contribut~onsin Marine Science, The University of Texas 18:140-167. Mullahy, J. H. 1959. Prelimtnary survey of the algal flora of the Chandeleur Islands. Proceedings of the Lou~sianaAcademy of Sciences 23:62-68. Oetking, P., R. Back, R. Watson, and C. Merks. 1974. Hydrography on the nearshore continental shelf of South Central Louisiana. Gulf Universities Research Con- sortium. Appendix to Report No. 138. Taylor, W, R. 1954. Sketch of the character of the marlne algal vegetation of the shores of the Gulf of Mexico. In P. S. Galtsoff, ed., Gulf of Mexico, its Origin, Waters, and Marine Life, Fishery Bulletln 89, U.S. Fish and Wildl~feService 55:177-192.