Impacts of Reduced Salinity on Seagrasses in Indian River Lagoon

Abstract

AbstractFrom November 1993 to November 1995, a study was conducted in Indian River Lagoon (IRL) to determine relationships of light attenuation, water quality, and seagrass at sites representing a range of water quality conditions. There were considerable interannual differences at the sites. The most striking event occurred at a station in northern Banana River, an area of IRL considered the least anthropogenically impacted. This station had a well‐developed, multispecies seagrass bed (Halodule wrightii and Syringodium filiforme, with small quantities of Halophila englemannii). Throughout the first year, salinity was stable (90% of weekly values ranged from 26 to 32 ppt). Beginning in November 1994, the cover, shoot density, and biomass of all three species declined precipitously due to sharply reduced salinities associated with high rainfall and run‐off. Salinities during the following year varied little and remained low (90% of weekly values ranged from 13.5 to 19.8 ppt). The lack of recovery to earlier salinity levels was due to the long residence time (about 1 year) in that portion of IRL. Seagrass cover, shoot density, and biomass reached minima in May 1995. By August 1995, Halodule began to recover, but nearly 8 years later, Syringodium has not recovered to 1994 levels.