Littoral zones can be characterized with temporal exposure of algae to diurnal desiccation at low tides. Combinations of diverse freshwater, marine, and brackish diatoms dominate exposed mud samples. With enlargement of the delta of the Savannah River, Georgia and other anthropogenic influences, changes in the rich epipelic community will not be estimated accurately without baseline data. In the current study, mud samples were taken from the Savannah River estuary along with physicochemical characteristics every two months throughout 2011. Live algal communities were assessed in every sample and live to dead diatom proportions in the communities were calculated. Cleaned diatoms were analyzed following standard protocols. Community indices were compared between sampling events and with literature reports from similar habitats in the Southeastern USA diverse diatom community of 241 species was documented and 39 of those species should be described as new to science. Decrease in species richness and diversity was due to dominance of representatives of the genera Cymatosira and Minidiscus during the summer months.
Widening and deepening of river deltas, as proposed for the Savannah River with the Savannah Harbor Expansion Project [
Algal communities within estuaries consist of a mixed flora containing freshwater, brackish, and marine species that can be potentially influenced by change in water quantity and chemical composition. Mud samples found within littoral zones contain both epipelic and epipsammic diatom dominated communities [
Few studies have been dedicated to the littoral zones found throughout brackish waters in the Southeastern United States. In 1956 Friedrich Hustedt examined two mud samples that were taken from Beaufort, North Carolina [
The objectives of this study were to: identify algal communities present within mud samples taken during low tide periods, and create a baseline information for comparison and evaluation of magnitude effect with future changes within the epipelic community. Second, calculate community indices and infer changes in biodiversity through seasons. Lastly to compare epipelic communities found 50 years ago by Hustedt with the current study [
Mud samples were taken from the Savannah River estuary through 2011, with an attempt to follow significant changes in temperature through the seasons (Savannah River USGS site 2198920, location Lat 32˚09'57" Long 81˚09'14"). Sampling events took place during the months of January, March, June, October, and December 2011. All sample collections followed standard protocols for sampling methods and processing [
Physicochemical measurements: temperature, pH, conductivity, turbidity, and dissolved oxygen content were measured during each event for both the seasonal and observational study, using a YSI 556 Multiprobe System (YSI Inc., Yellow Springs, Ohio) at the time of collection. In addition, chemical data was obtained from the USGS website so that long term monitoring analyses gathered within the field could be verified with a second set of readings. Nutrient data such as N and P concentrations were also obtained from the USGS site (http://waterdata.usgs.gov/nwis). All samples were preserved within an hour of collection with formaldehyde (3% final concentration).
Enumeration followed standard methods [
For SEM studies, aliquots of processed material were air dried onto 15 cm2 pieces of aluminum foil. The foil was trimmed into smaller pieces and mounted on aluminum stubs with double-sided tape. The stubs were then coated with gold-palladium using a Polaron Sputter Coater for ca. 1.5 min at 1.8 kV. A Leo-Zeiss 982-DSM electron microscope was used for SEM analysis. Digital images were captured and plates were assembled using Adobe Photoshop CS4. Morphological terminology follows [22,23].
All community attributes were calculated based upon valve counts as well as species abundance. Dominant taxa with relative abundance of 5% or more in at least 1 sample. Species within the list were then designated as freshwater if the taxon appeared in the North American Water Quality Assessment most current list maintained by the Academy of Natural sciences of Philadelphia for the last 20 years in both rivers and lakes. All the other taxa were then classified as marine unless the original description designated it as being brackish.
Standard community indices including species richness (SR), species evenness (J’, [
Temperature for the year followed seasonal changes. The average air temperature for the sample site was 22.8˚C ranging from 8.2˚C to 35.9˚C. Average water temperature was 18.9˚C and ranged from 8.7˚C to 29.3˚C. Dissolved oxygen had an average value of 6.8 mg/L, with a range of 4.5 mg/L to 9.7 mg/L. The average pH was 7.5 and remained neutral throughout the year. Turbidity was 49.6 NTU on average and ranged from 26 NTU to 90 NTU. Average conductivity throughout the year was 11,294 µS/cm and had a range of 4570 µS/cm to 17,400 µS/cm. Nutrient concentrations throughout the year were 0.46 mg to 1.6 mg of total nitrogen/L with an average concentration of 0.92 mg of TN/L. Total phosphate was 0.14 mg to 0.49 mg of TP/L with an average 0.24 mg of TP/L.
A total of 241 diatoms were documented during this study, 203 of those taxa were identified to the species level. The remaining 16% of all documented taxa were identified as unknown or c.f. based on size not conforming to available literature or potentially as new to science. Ten taxa were observed as dominant species (
Centric diatoms like Minidiscus sp.1 (
sistent. There was an increase in the overall abundances of chain forming centrics like Skeletonema costatum (
An araphid pennate diatom Cymatosira belgica (Figures 2(6)-(10);
The highest numbers of other pennate diatoms able to move up and down the mud layers, Cylindrotheca gracilis (
ure 3(2)), Tabularia fasciculata (
A diverse naviculoid diatom like Biremis circumtexta (
Several biraphid diatoms with canal raphe like Nitzschia sigma (
Species richness was highest during the colder months and lowest during the warmer seasons. Species richness was 34.8 on average, with the highest in January (42), and the lowest in June (26). Shannon Wiener diversity values were relatively high throughout the seasonal study, on average 2.4. Diversity values ranged from 2.7 (found during both January and December) and lowest at 1.6, during the month of June.
The highest diversity measurements were found in both January and December sampling events with values
of 2.7. During both March and October sampling events diversity values were still high at 2.5. Species evenness for the seasonal study followed the same trend found in diversity values. Average evenness was 0.68, and ranged from 0.74 to 0.49 (lowest found in June). Values between January, March, October, and December remained relatively similar (0.72, 0.74, 0.7, and 0.73 respectively).
Low community indices values found within June’s sample can be attributed to the large percentage of C. belgica (51%) and Minidiscus sp.1 (27%) that occurred during this time. Sorenson similarity values remained low throughout the year. Similarity was highest in October and December (36%) and lowest between January and June samples (6%,
For the current study 44% of the species found in the Savannah River mud samples were classified as freshwater.
Diversity recorded in this study is comparable only to the report by Hustedt [
January.
Cymatosira belgica was observed as the dominant taxon in all samples taken and contributed more than >20% of the total abundance in each sample taken during the seasonal study. Its highest relative abundance (51%) was found in the warmest temperature. Cymatosira belgica is a small diatom, characterized by few morphological characters. Valves are lanceolate and slightly attenuated at the ends, which are subacute, with sparse coarse puncta, 12 in 10 μm, generally leaving a pseudoraphe of greater or less breadth. According to literature C. belgica ranges in length from 10 - 30 µm and 3 - 4.5 µm broad, striae up to 12 in 10 µm [
Within all samples taken throughout the study Minidiscus sp.1 occurred at a relative abundance of >10%. Under LM microscopy Minidiscus spp. are hard to detect due to the inability to see labiate and strutted processes needed for species characterization [
This diatom has complicated taxonomy, originally classified as Coscinodiscus trioculatus Taylor [
Unlike the marginal circlet of fultoportulae, which are present within most other members of the thalassiosiroid lineage, the fultoportulae are irregularly dispersed around the center of the valve face. A single rimoportula is located near the center of the valve. A wide hyaline flange is found marginally along the valve face of the generitype, Minidiscus trioculatus (Taylor) Hasle, however this character is not found within all species. Currently, the genus Minidiscus is comprised of seven species [32,34- 37]. Due to their extremely small size, it is believed that the amount of diversity could be vastly underestimated [
After SEM images were analyzed, two species of Minidiscus were found occurring within the samples, Minidiscus chilensis (
Considering that the community similarity between our samples was never above 30% it is not surprising that overall similarity with taxa from this study and Hustedt’s report was even lower. Spotted abundance information was provided by Hustedt and no information of time of collection at the Buford, N. Carolina. About 44% of the genera reported by Hustedt [
In conclusion high biodiversity of the riverine epipelic community in the Savannah River delta requires consideration and preservation. There is a great potential for additional new to science discoveries of species. In addition preservation of the freshwater component of the estuarine mud community is important for stability of the sediment layer as potential food source for grazers and oxygenation of the top layer. Those properties are contributed by raphe bearing diatoms and not from centric and araphid diatoms dominating marine plankton.
Marká Smith and Robert Moseley helped with field collection. Mary Ann Tiffany helped with SEM images. This work was part of the second author’s Masters graduate research at the Department of Biological and Environmental Sciences at Georgia College and State University. This work was supported by EPD Environmental protection division contract #751-100039.