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Silica-scaled Chrysophytes and Synurophytes from east Texas.

Article Excerpt
Abstract.--A total of 27 scale-bearing species of the algal classes Chrysophyceae and Synurophyceae, referred to herein as scaled chrysophytes, were recorded in 35 water bodies from 11 eastern Texas counties using transmission electron microscopy. These were distributed between the Chrysophyceae (one Chrysosphaerella sp., one Paraphysomonas sp. and two Spiniferomonas sp.) and Synurophyceae (14 Mallomonas sp. and nine Synura sp.). The number of taxa per collection varied from zero to six. Twenty-three taxa are new records for Texas. Mallomonas multisetigera is reported for the first time from North America. Scales of the colorless free-living flagellate Gyrornitus disomatus, an organism of uncertain taxonomic affinity, were also observed.

Surveys of the freshwater algal flora of Texas were initiated through a series of investigations by H. C. Bold and his students (Deason & Bold 1960; Chantanachat & Bold 1962; Bisehoff & Bold 1963; Brown & Bold 1964; Cox & Bold 1966; Smith & Bold 1966; Groover & Bold 1969; Archibold & Bold 1970; Baker & Bold 1970. Other studies have included Texas collections, but were not directed specifically on the Texas flora (Flint 1955; Nicholls 1964; Hoffman 1967; Ott 1976; Carty 1989; Carty & Cox 1985; 1986; Sheath et al. 1993a; 1993b; Swamikannu & Hoagland 1990; Vis & Sheath 1996). All of these reports are based on light microscopy.

Silica-scaled chrysophytes are taxonomically placed in the division Chrysophyta, classes Chrysophyceae and Synurophyceae, based on ultrastructural and biochemical characteristics (Andersen 1987). The majority of chrysophyte genera lack a covering of siliceous scales and exhibit a great plasticity in regard to both morphology and nutrition (Hoek et al. 1995). Most of the common chrysophytes are flagellated, occurring as single cells or are colonial.

The first electron micrographs of silica-scaled chrysophytes from Texas are in the unpublished report of Marquis (1977) based on collections made in the Edwards Plateau located at the southern most end of the High Plains province (Cole 1966). The chrysophyte flora of neighboring Louisiana (Wee et al. 1993), the nearby state of Arizona (Gretz et al. 1979; 1983; 1985), and the country of Mexico (Kristiansen & Tong 1995) also have been studied previously using electron microscopy. Adjacent states, such as New Mexico and Oklahoma remain to be investigated.

In this study, the silica-scaled algal flora from 11 counties representing 35 eastern Texas locations in the western Coastal Plain physio-graphic province (Cole 1966) were examined using transmission electron microscopy (TEM).

MATERIALS AND METHODS

Phytoplankton samples were collected with a plankton net (10[mu]m mesh size) in mid-March of 1996 from 35 ponds and lakes in 11 Texas counties (Table 1). Samples were fixed in acid Lugol's (Wee 1983). For TEM, subsamples were placed on Formvar-coated, carbon-stabilized grids, air dried and examined with a Philips 300 transmission electron microscope. All identifications were based on TEM. Percentages were based on the number of samples in which a taxon was observed divided by the total number of samples. Physical/chemical parameters taken in the field were surface water temperature, pH (Markson model 85), and specific conductance (Oakton WD-60). In an attempt to identify coordinated variation between physical/chemical parameters and species composition of the samples, the data were subject to multivariate analyses, including Detrended Correspondence Analysis (DCA, Hill 1979) and Canonical Correspondence Analysis, (CCA, ter Braak 1992). Species occurring in only one sample were eliminated prior to analysis, re sulting in a...