Hypoxic events are becoming frequent in some estuaries and coastal waters due to over-enrichment of anthropogenic nutrients, organic matter, and/or due to restricted water circulation. The coastal lagoons and estuaries of Sri Lanka are facing high population pressure and lacking sufficient infrastructure. Coastal lagoons may receive high anthropogenic inputs of natural or untreated nitrogen and phosphorus wastes, and consequently result in hypoxic conditions while sluggish circulation occurred. In this study, we examined the spatiotemporal variability of eutrophication and hypoxia in the Negombo Lagoon, one of the most productive and sensitive coastal ecosystems in Sri Lanka. Based on seasonal measurements of dissolved oxygen, nutrients, chlorophyll-a (Chl-a), particulate and dissolved organic carbon (POC and DOC), we concluded that eutrophication and hypoxia occurred in both the dry and wet seasons. The main contributing factors were high seawater temperature and poor water circulation in the dry season and high nutrient loading combined with elevated POC and DOC inputs in the wet season.

Recent research has revealed that shrimp sensory quality may be affected by ocean acidification but we do not exactly know why. Here we conducted controlled pH exposure experiments on adult tiger shrimp, which were kept in 1000-L tanks continuously supplied with coastal seawater. We compared survival rate, carapace properties and flesh sensory properties and amino acid composition of shrimp exposed to pH 7.5 and pH 8.0 treatments for 28 days. Shrimp reared at pH 7.5 had a lower amino acid content (17.6% w/w) than those reared at pH 8.0 (19.5% w/w). Interestingly, the amino acids responsible for the umami taste, i.e. glutamate and aspartic acid, were present at significantly lower levels in the pH 7.5 than the pH 8.0 shrimp, and the pH 7.5 shrimp were also rated as less desirable in a blind quality test by 40 volunteer assessors. These results indicate that tiger shrimp may become less palatable in the future due to a lower production of some amino acids. Finally, tiger shrimp also had a lower survival rate over 28 days at pH 7.5 than at pH 8.0 (73% vs. 81%) suggesting that ocean acidification may affect both the quality and quantity of future shrimp resources.

A method to measure the salt secretion by mangroves which are open to the sea spray was developed and used to measure the salt secretion by mangrove species of Rekawa lagoon, an ecosystem with the highest diversity of true mangroves in southern Sri Lanka. Out of the twelve species of mangroves, only four species i.e. Acanthus ilicifolius, Aegiceras corniculatum, Avicennia marina, and Avicennia officinalis proved to be able to secrete salts. Under the salinity regime (26.2 ± 4.41 ppt) existed during the experimental period, the salt secretion by leaves of these four species were 47.2 ± 18.3, 35.1 ± 16.0, 149.3 ± 45.9, and 81.6 ± 30.5 mg salt cm −2 day −1 respectively. This result corroborates the published records and, hence validates the technique used in this study to measure the salt secretion. These four species exhibited increases in salt secretion with increases in soil salinity, consistent with previous reports. Results of this study also shows that the capacity to secrete salts at any given salinity was different between four species, following an order of Av. marina > Av. officinalis > Ac. ilicifolius, and Ae. corniculatum. The salt secretion by these species immediately after reducing the soil salinity was increased significantly implying an opportunistic removal of salt, which was accumulated in the plant body under high saline condition. Capacity for salt secretion by the four species as well as the magnitude of the increase of salt secretion as a response to increasing soil salinity, vary in parallel to the variations in salt tolerance given in published reports for the same species.