Effects of salinity changes on growth of Ruppia maritima L.

Abstract

The ability of Ruppia maritima L. to tolerate moderate salinity changes was determined in a greenhouse study. While R. maritima has been shown to survive in salinities from 0 to 70 ppt, it has been suggested that changes in salinity alone may be detrimental. We tested the hypothesis that along the northern shore of the Gulf of Mexico, R. maritima may be limited not by salinity averages, but by salinity changes which occur. In a 9-week experiment, in summer 2001, relative growth rate of R. maritima was compared between salinity treatments which included constant salinity (10 g l −1), one salinity change (±10 g l −1), and two salinity changes (±10 g l −1). Relative growth rate was highest under constant salinity, and significantly lower than the control (constant salinity) when salinity was reduced by 10 g l −1 over 48 h at week 3, and increased by 10 g l −1 at week 6 suggesting that short-term freshening events may negatively impact R. maritima growth. Relative growth rate was also significantly lower when salinity was raised twice, once at week 3, and again at week 6 to reach 30 g l −1. Pulsed salinity changes may limit R. maritima growth and distribution in this region.