Checklist of the marine flora of Nha Trang Bay (Vietnam, South China Sea) and decadal changes in the species diversity composition between 1953 and 2010

The first complete checklist of the intertidal and subtidal marine algae (Rhodophyta, Chlorophyta and Ochrophyta) of Nha Trang Bay (Vietnam) is presented. A brief history of the species records in the bay between 1953 and 2010 is documented. A total of 481 macroalgal taxa and their forms have been found, including 275 red (57%), 121 green (25%) and 85 brown (18%) algal taxa. The data, analyzed in terms of time period, revealed shifts in the number of species in most of the taxonomic families. However, the most interesting differences between the time periods occurred in the overall algal species diversity and in the floristic ratios (red: brown: green algae). The collections sampled in 1953-1968 and those in 1982-1987 did not change significantly in either species diversity or floristic composition, but a comparison of the collections from 1953 to 1987 and from 2002 to 2010 revealed substantial differences. In 2002-2010, the absolute and relative numbers of green algal species increased while those of red and brown algal species decreased. Our background data indicate that this change is likely due to increasing seawater pollution caused by dissolved organic and inorganic substances. The increase in the number of green algal species is due primarily to the greater number of species in the Caulerpaceae, Ulvaceae and Cladophoraceae, all families that thrive in polluted water.