Salinity plays a vital role in the distribution of species, their productivity and growth of mangrove forests (Twilley & Chen, 1998). Mangroves generally tolerate higher salinity than do nonmangrove plants, but tolerance also varies among the mangroves. For example, Rhizophora mucronata seedlings do better in salinities of 30 %, but R. apiculata do better at 15 % (Kathiresan & Thangam, 1990; Kathiresan et al., 1996b). Sonneratia alba grows in waters between 2 % and 18 % , but S. lanceolata only tolerates salinities up to 2 % (Ball and Pidsley, 1995).
In general, mangrove vegetation is more luxuriant in lower salinities (Kathiresan et al., 1996). Experimental evidences indicate that at high salinity, mangroves spend more energy to maintain water balance and ion concentration rather than for primary production and growth (Clough, 1984). On the Pacific coast of Central America, freshwater availability (largely from rainfall and land runoff) controls reproductive phenology, growth and mortality of Avicennia bicolor (Jimenez, 1990). However, low salinity, associated with long periods of flooding, contributes to mangrove degradation through reduced cell turgidity and decreased respiration.
Salinity at high levels also affects mangroves. For instance, high salinity reduces the biomass in hydroponically grown Bruguiera gymnorrhiza (Naidoo, 1990), and causes denaturing of terminal buds in Rhizophora mangle seedlings (Koch & Snedaker, 1997). Saline interstitial water is known to reduce the leaf area, increases the osmotic pressure leaf sap, increases the leaf area/weight ratio, and decreases the total N, K, and P minerals (Medina et al., 1995). Simple salinity fluctuations also have significant negative effects on the photosynthesis and growth of plants (Lin & Sternberg, 1993).
Ball, M.C. and Pidsley, S.M. (1995). Growth responses to salinity in relation to distribution of two mangrove species, Sonneratia alba and S. lanceolata, in northern Australia. Functional Ecology, 9 (1) : 77‐85.
Clough, B.F. (1984). Growth and salt balance in the mangroves Avicennia marina (Forsk.)Vierh. and Rhizophora stylosa Griff. in relation to salinity. Australian Journal of Plant Physiology, 11, 419‐430.
Jiménez, J.A. (1990). The structure and function of dry weather mangroves on the Pacific coast of Central America, with emphasis on Avicennia bicolor forests. Estuaries, 13 (2) :182‐192.
Kathiresan, K. and Thangam, T.S. (1990). A note on the effects of salinity and pH on growth of Rhizophora seedlings. The Indian Forester, 116 (3) : 243‐244.
Kathiresan, K., Rajendran, N. and Thangadurai, G. (1996). Growth of mangrove seedlings in intertidal area of Vellar estuary southeast coast of India. Indian Journal of Marine Sciences, 25 : 240‐243.
Kathiresan, K., Moorthy, P. and Ravikumar, S. (1996b). A note on the influence of salinity and pH on rooting of Rhizophora mucronata Lamk. Seedlings. The Indian Forester, 122 (8) : 763‐764.
Koch, M.S. and Snedaker, S.C. (1997). Factors influencing Rhizophora mangle L. seedling development in Everglades carbonate soils. Aquatic Botany, 59(1‐2) : 87‐98.
Lin, G.H. and Sternberg, L.D.S.L. (1993). Effects of salinity fluctuation on photosynthetic gas exchange and plant growth of the red mangrove (Rhizophora mangle L.). Journal of Experimental Botany, 44 (258) : 9‐16.
Medina, E., Lugo, A.E. and Novelo, A. (1995). Mineral content of foliar tissues of mangrove species in Laguna de Sontecomapan (Veracruz, Mexico) and its relation to salinity. Biotropica, 27 (3) : 317‐323.
Naidoo, G. (1990). Effects of nitrate, ammonium and salinity on growth of the mangrove Bruguiera gymnorrhiza (L.) Lam. Aquatic Botany, 38 (2‐3) : 209‐219.
Twilley, R.R. and Chen, R. (1998). A water budget and hydrology model of a basin mangrove forest in Rookery Bay, Florida. Marine and Freshwater Research, 49 : 309–323.