Now showing items 1-2 of 2

    • Conference paper

      Effects of CO2-induced ocean environmental changes on marine life: implications for aquaculture. 

      A Ishimatsu & H Kurihara - In BO Acosta, RM Coloso, EGT de Jesus-Ayson & JD Toledo (Eds.), Sustainable aquaculture development for food security in Southeast Asia towards 2020. Proceedings of the Regional Technical Consultation on Sustainable Aquaculture Development in Southeast Asia Towards 2020, 2011 - Aquaculture Department, Southeast Asian Fisheries Development Center
      The world's oceans are becoming warmer and acidic. The atmospheric carbon dioxide concentration has increased from 280 ppm at pre-industrial revolution to above 380 ppm today. The 4th IPCC report predicts that it will range from 540 to nearly 1,000 ppm by the end of the century. The increased CO2 not only warms surface seawater, but also acidifies it (usually termed as ocean acidification) by diffusing across the ocean surface and forming carbonic acid. Our knowledge is still scarce as to how these ocean environmental changes will affect marine life. The early studies on the impact of ocean acidification focused on corals aiming to clarify effects of high-CO2 seawater on their calcification processes. However, more recent studies have revealed that in fact ocean acidification, either alone or coupled with warming, could have detrimental impacts on a variety of biological processes in different taxa. We have shown that early development of marine bivalves (oysters and mussels) could be severely disrupted under elevated CO2 conditions (ca. 2,000 ppm). When a marine shrimp was exposed to seawater equilibrated with air containing 1,000 ppm CO2 for 30 weeks, survival was only 55% as compared with 90% in the control. Gonad maturation of a sea urchin was delayed by one month under the same CO2 conditions at ambient temperature, but when accompanied with increased temperature of 2 degree C above ambient, gonad maturation was not only delayed but also significantly suppressed; the number of eggs in the ovary was reduced to only 20% of the control. It has been shown that tropical animals already live near their thermal tolerant maxima, and therefore even small increases of environmental temperature could reduce their environmental fitness. These recent findings bear significant implication in aquaculture and fisheries production, in particular, in tropical countries. This paper will summarize recent data on these topics and discuss possible adaptation measures.
    • Article

      Growth and survival of hatchery-bred giant clams (Tridacna gigas) in an ocean nursery in Sagay Marine Reserve, Philippines 

      MJHL Lebata-Ramos, K Okuzawa, RJ Maliao, JBR Abrogueña, MDN Dimzon, EFC Doyola-Solis & TU Dacles - Aquaculture International, 2010 - European Aquaculture Society
      To restore the diminishing population of the giant clam Tridacna gigas in Sagay Marine Reserve (SMR), Negros Occidental, central Philippines, two size classes [8- and 10-cm shell length (SL)] of hatchery-bred T. gigas were reared in an adjacent ocean nursery for restocking to Carbin Reef later upon reaching grow-out size of ≥20 cm SL. Growth rates did not significantly differ for both sizes and were on average 0.67 cm month−1. However, survival after 382 days of rearing T. gigas was significantly higher in the 10-cm SL clams than the 8-cm SL clams (96 and 83%, respectively). For future restocking projects, the use of 8-cm SL clams is recommended because the lower survival of this size class is compensated by its cheaper price. While rearing the clams to attain grow-out size, the population of wild clams (Family Tridacnidae) in Carbin Reef was assessed using ten 50 × 2-m belt transects. Four species of tridacnid clams have been recorded: Hippopus hippopus, Tridacna crocea, T. maxima>, and T. squamosa. T. crocea comprised 12.5–93.9% of all the clams observed in all ten transects. There was a significant difference in clam density between species (ANOVA, F = 6.94, P < 0.001), with T. crocea having the highest density. Living T. gigas were absent, but presence of dead shells was indicative of its presence in the reef in the past. It can be expected that the release of hatchery-bred T. gigas juveniles in Carbin Reef could provide future breeders that will repopulate this reef and the adjacent reef communities.