The Effect of Temperature on Leaf and Rhizome Growth Rates in the Seagrass Halophila Ovalis (R. Brown) Hooker f

Abstract

Seagrass are marine flowering plants that complete their life cycle submerged in water. They are ecologically and economically important as habitat and food source for the majority of marine biological species. Growth and reproduction in seagrass is affected by environmental parameters such as temperature, salinity, tidal current and nutrients. Following the current global warming trend, ocean temperatures in Tanzania are predicted to increase by 2-4oC from current levels of 27-28oC. Changes in climate are thus likely to affect the reproduction and survival of seagrass in this region. Investigating factors affecting seagrass growth can assist to predict impacts of climate variability and change such as increase in temperature in the marine environment. In the present study Halophila
ovalis (R. Brown) Hooker was studied as an indicator of the influence of temperature on growth. Samples were collected from Kunduchi beach, Dar es Salaam and grown in the laboratory under variable temperatures of 22-23, 25-26, 27-28, 30-31 and 33-34ºC, for 30 days. The length of new and mature leaves was measured at two days intervals; leaf number, leaf weight, rhizome length and rhizome weight were determined at the end of the experiments. Results suggest 25-26ºC to be the optimum temperature for growth of Halophila ovalis. Lowest growth rates were observed at temperatures of 22-23 and 30-31ºC, while samples grown at 33-34ºC survived only for four days. From these results the anticipated temperature increase of 2-4.5 ºC will lead to change in seagrass distribution, abundance and possibly disappearance of higher temperature intolerant species.