National Committee on Marine Sciences (NCMS)
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- Growth and metabolic responses of the giant clam-zooxanthellae symbiosis in a reef-fertilisation experimentBelda-Baillie, C. A.; Leggat, W.; Yellowlees, D. (Inter-Research Science Center, 1998)To evaluate the impact of elevated nutrients on reef organisms symbiotic with zooxanthellae, giant clams Tridacna maxima were exposed daily to increased ammonia and phosphate (N, P, N+P) in their natural reef environment for 3 to 6 mo. The results strongly corroborate the major responses of the symbiotic association to nutrient enrichment previously observed (with T. gigas) under controlled outdoor conditions. Exposure of the clams to elevated N (10 µM) increased zooxanthellae density, reduced zooxanthellae size, down-regulated N uptake by zooxanthellae freshly isolated from their hosts, and reduced glutamate in the clam haemolymph, with increased pools of some free amino acids (methionine, tyrosine) in the zooxanthellae. These results confirm that the zooxanthellae in giant clams are N limited in situ and have free access to inorganic N from the sea water. There is also corroborating evidence that the zooxanthellae are P limited in situ as well, possibly due to host interference. While the N:P ratios of the animal host reflected ambient N and P concentrations in the sea water, those of the zooxanthellae did not. Regardless of P exposure (2 µM P) of the clams, zooxanthellae N:P ratios were consistently high(>30:1) and phosphate concentrations in the clam haemolymph bathing the zooxanthellae tube system consistently low (<0.1 µM). These field findings, consistent with previous laboratory observations, confirm the limiting roles of both N and P in the giant clam-zooxanthellae symbiosis. That significant changes occurred earlier and at lower nutrient loading compared to some reef organisms investigated within the same experimental framework further demonstrates organism-level responses of a potential bio-indicator of the early onset of eutrophication in reef waters.
- Fishkill hits cages in Taal LakeCinco, Maricar (Philippine Daily Inquirer, Inc., 2018-11-06)The local government of Agoncillo town in Batangas province will distribute tilapia fingerlings to local cage operators affected by the recent fishkill in Taal Lake. The incidence of “fish mortality,” a term preferred by local officials in referring to a smaller area where fish turn belly up, occurred at Barangay Subic Ilaya, said Agoncillo Mayor Daniel Reyes. He said 105 cages, out of 1,555 operating in the town, were affected, with about P5 million worth of mature and juvenile tilapia killed in a phenomenon called “sulfur upwelling.”