Phenology and Floristics of Seaweeds from the Offshore Waters of Georgia

Seaweeds were studied from rock outcrops in two areas on the Georgia continental shelf, Gray's Reef National Marine Sanctuary on the inner shelf and an area known as the "Snapper Banks" on the outer shelf. The seaweeds observed are seasonal; only a few plant persist through the winter. In this study a gradual increase in number and size of plants and number of species was observed through June; by July-early August, when all 68 species reported were present, the quantity of plants also appeared maximal. Of the 68 species, 43 are species not previously reported from Georgia; eight additional taxa are identified only to genus, but are also new to the region. Sixty-five of the species were col· lected at Gray' Reef and 22 at the Snapper Banks; three of the latter did not occur at Gray's Reef. In late August and September, wh1m water temperatures were still near the seasonal high, there was a rapid decline in number of species and algal cover. Establishment of the Gray's Reef National Marine Sanctuary off Sapelo Island, Georgia has been an impetus for investigation of the flora of these offshore waters. For seaweeds, the waters along the southeastern seaboard from Cape Hatteras, North Carolina to Cape Canaveral, Florida appear to constitute a phytogeographically distinct warmtemperate region (Searles, 1984), with Georgia in the least studied, southern half of the region. Seaweeds are generally restricted to hard, rocky substrates and Gray's Reef is an area of rock outcrops on the inner continental shelf 32 km off the Georgia coast (Fig. 1), which supports an interesting algal flora in depths of 17-22 m. It was the site of most of the collections reported here. A few collections were made further offshore on rock outcrops known locally as the "Snapper Banks" (Fig. 1), in depths of 30-35 m, but those sites have yet to be studied in detail. Prior to the study reported here, a total of 93 seaweeds identified to species had been reported from Georgia, (Chapman, 1971, 1973; Blair and Hall, 1981; Searles, 1981, 1983; Searles and 99 Ballantine, 1986; Richardson, 1987); 21 of these were listed from offshore waters. The following account provides seasonal information on the flora and increases the known flora for the offshore waters to 73 taxa including eight currently identified only to genus; many of the eight are probably undescribed, new species. Five species previously reported from Georgia's offshore waters were not observed in this study: Peyssonnelia rubra (Grev.) J. Ag. (Blair & Hall, 1981), plus Chaetomorpha minima Collins & Harvey, Pterocladia americana Taylor, Gracilaria foliifera (Forssk.) Boerg. ( = Graci/aria tikvihiae McLachlan), and Ceramium leptozonum Howe (Chapman, 1971). Richardson (1987) has recently enlarged upon the earlier records (Chapman, 1971, 1973) of the seaweed in nearshore, coastal environments; he lists 65 species, not including the 8 Cyanophyta reported by Chapman. Six of the coastal species reported are also reported from offshore waters. The seaweed flora known for the state of Georgia thus total 145 species, including the 8 taxa identified only to genus in this report. 1 Searles: Phenology and Floristics of Seaweeds from the Offshore Waters of Published by The Aquila Digital Community, 1987