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In 1954, H. W. Graham stated, “Despite the importance of these organisms, the Gulf of Mexico is almost a terra incognita in respect to our knowledge of the dinoflagellate plankton.” In the same article, he gave a historic presentation on what dinoflagellate studies had been conducted , basic ecological considerations, and mentioned some common and oceanic species. It wasn’t until 1972 that a checklist of dinoflagellates (406 taxa) of the Gulf of Mexico was published by Steidinger, who used literature published up to 1971 as well as her own observations. The reference list in that paper contained many of the earlier works. Although records were scattered, and were principally in response to harmful algal blooms caused by dinoflagellates , there were studies that increased the number of taxa from less than 100 to 400 (Balech 1967a, b, c, Steidinger, Davis, and Williams 1967). Since 1967, the dinoflagellate taxa list has increased to 644 (this contribution and references herein; taxon summary). Dinoflagellate studies were most extensive in continental shelf waters, particularly off Mexico and Florida. The Gulf of Mexico is a tropical/warm temperate body of water that covers more than 8 degrees of latitude and has a corresponding biological diversity that is reflected in its dinoflagellate assemblages. There are several comprehensive works listing dinoflagellates within regions of the Gulf; all were consulted to compose the current checklist. These major contributions start with Balech (1967b). The 30 most common taxa of Balech (1967b) were Ceratium furca, C. massilense , C. trichoceros, C. fusus, Diplopelta asymmetrica, Dinopysis caudata, Ceratium tripos, Goniodoma polyedricum , Protoperidinium brochii, Ceratocorys horrida, Blepharocysta splendor-maris, Ceratium teres, Gonyaulax polygramma, Pyrophacus horologium, Ceratium extensum , Ceratium macroceros var. galicum, Protoperidinium conicum, P. depressum, Pyrocystis pseudonoctiluca, Podolampas palmipes, Ceratium contortum, Protoperidinium divergens, Ceratium trichoceros var. contrarium (= C. con131 7 Dinoflagellates (Dinoflagellata) of the Gulf of Mexico Karen A. Steidinger, Maria A. Faust, and David U. Hernández-Becerril  Dinoflagellata. After Lauterborn 1895. 132 ~ Dinoflagellates (Dinoflagellata) teres, C. breve var. breve, C. macroceros var. macroceros, C. massiliense, C. pentagonum var. pentagonum, Protoperidinium divergens, Podolampas palmipes, Ceratium tripos var. tripos, Dinophysis caudata var. caudata, Ornithocercus magnificus, Prorocentrum compressum, P. gracile , Ceratium furca var. furca, C. contortum var. contortum, C. horridum var. horridum, Prorocentrum micans, Ceratium kofoidii, Ceratocorys horrida, Pyrophacus steinii, Gonyaulax polygramma, Ceratium extensum, Gyrodinium fusiforme, Oxytoxum gracile, Protoperidinium mediterraneum , Amphisolenia bidentata, and Protoperidinium grande. This study, as well as most other studies of planktonic dinoflagellates, does include some benthic species that have become tychoplanktonic (Steidinger 1983). Of the 30 common taxa, Dinophysis caudata is known to produce toxins. As in many other studies on dinoflagellate diversity, this one relied on preserved specimens (Lugol’s solution) because of the length of the cruises. Lugol’s solution is a good fixative and specimens can be destained to observe finer structures. We have found that unacidified Lugol’s solution preserves refrigerated phytoplankton samples successfully for several years for dinoflagellates. If not refrigerated, samples will deteriorate. Samples fixed in 2% buffered gluteraldehyde and refrigerated provide well-preserved specimens for light microscopy and scanning electron microscopy. The current checklist has resulted from expanded studies as well as new technologies and methods. For example , scanning electron microscopic techniques, particularly in processing, have allowed identification of trarium), Ornithocercus magnificus, Ceratium hexacanthum , Amphisolenia bidentata, Protoperidinium crassipes, Podolampas palmipes, Ceratium contortum var. karstenii (= C. karstenii), and C. carriense. Only two of these species are toxic—Protoperidinium crassipes and Dinophysis caudata. Ceratium, Dinophysis, and Protoperidinium contain the most armored species among the dinoflagellate genera and therefore their representation would be expected to be high in any study. The reason armored species are represented more than unarmored dinoflagellates is because most of studies recording dinoflagellates from Gulf of Mexico and contiguous waters relied on preserved samples and light microscopy for detection of specimens. Unarmored species can round out when fixed and preserved , and although cells may be recognizable as unarmored , species determination may not be possible. One notable exception was the Hourglass Cruise phytoplankton study that used live material (Steidinger and Williams 1970) and was conducted on the West Florida Shelf over a 28-month period out to 170.5 km from shore. Six stations were occupied monthly. The majority of species were photosynthetic, armored, neritic and oceanic, and present throughout the year. A total of 232 taxa were identified. A more recent study (Licea et al. 2004) listed 252 dinoflagellate taxa from the southern Gulf of Mexico off Mexico . Again in this list, Ceratium, Dinophysis, and Protoperidinium had the...

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