Seasonal changes in phytoplankton composition in an extensive fish culture area in Bolinao, Pangasinan, northern Philippines

The proliferation of fish cages and pens in Bolinao, Pangasinan, northern Philippines seemed to have reached its limit in 2002 when a massive fish kill coinciding with a bloom of Prorocentrum minimum occurred. Since then, various measures have been taken by the local government to decrease the number of fish cages to allow recovery of the waters of Bolinao. Samples collected in April, June and November 2004 representing summer, southwest and northeast monsoons, respectively, from five stations were analyzed for phytoplankton composition. Diatoms generally dominated the phytoplankton and peaked during summer which can be attributed to a very high concentration of Thalassiosira sp. constituting 92% of the phytoplankton in that season. The dinoflagellates constituted a small portion of the phytoplankton composition in all seasons. The flagellates represented a small fraction of the phytoplankton and followed the trend of the dinoflagellates. Cyanobacteria thrived during the wet seasons, almost co-existing with the diatoms. The results seem to suggest that the management of the fish cages or the aquaculture ponds might have resulted to changes in the present (2004) phytoplankton composition compared to previous years (1995-2002)

Domoic acid in a bivalve Spondylus cruentus in Nha Trang Bay, Khanh Hoa Province, Vietnam

Recently we have found that domoic acid (DA), a toxin responsible for amnesic shellfish poisoning, is always detected in bivalve species belonging to a genus Spondylus randomly collected from various parts of the tropical areas including Vietnam. In Vietnam, 10 species of Spondylus are known to grow. Among these species, S. cruentus is a commercially valuable species. Domoic acid in S. cruentus collected in Nha Trang Bay is analyzed by ELISA and LC/MS/MS. Remarkable individual difference was observed in DA level among 28 specimens of S. cruentus collected from the same area at the same time. The DA level in S. cruentus apparently showed a seasonal variation. However, the variation of DA content seems to be due to a large individual difference among the specimens. When the specimens were reared in plankton-free conditions, DA level in S. cruentus did not decreaseds for 45 days, showing that S. cruentus maintains DA for a long period

Seasonal variation of paralytic and amnesic shellfish toxicities in bivalves and microalgae in Haiphong area, Vietnam

Monitoring survey was conducted to know the distribution and seasonal variation of PSP and ASP toxicities in bivalves and the abundance of toxic microalgae in Haiphong area, Vietnam. Sampling was carried out at the stations in Cat Ba and Do Son every two weeks from February 2002 to March 2004. Low levels of PSP and DA were detected in shellfish samples from both stations, showing seasonal and yearly variation. Toxicity of plankton samples also showed fluctuation, though the clear correlation could not be observed with the shellfish toxicities. HPLC or LC-MSMS analysis provided clear evidence of shellfish contamination with these toxins and indicated the existence of causative microalgae for these toxicities in this area. Several species of Alexandrium such as A. minutum, A. tamiyavanichii, A. ostenfeldii, A. tamarense were found, though the abundance of them was very low. On the other hand, massive bloom of Pseudo-nitzschia occurred in January at both stations. However, these blooms did not always cause the increase of DA level both in plankton and shellfish samples

Seasonal variation of paralytic and amnesic shellfish toxicities in bivalves and microalgae in Haiphong area, Vietnam

Monitoring survey was conducted to know the distribution and seasonal variation of PSP and ASP toxicities in bivalves and the abundance of toxic microalgae in Haiphong area, Vietnam. Sampling was carried out at the stations in Cat Ba and Do Son every two weeks from February 2002 to March 2004. Low levels of PSP and DA were detected in shellfish samples from both stations, showing seasonal and yearly variation. Toxicity of plankton samples also showed fluctuation, though the clear correlation could not be observed with the shellfish toxicities. HPLC or LC-MSMS analysis provided clear evidence of shellfish contamination with these toxins and indicated the existence of causative microalgae for these toxicities in this area. Several species of Alexandrium such as A. minutum, A. tamiyavanichii, A. ostenfeldii, A. tamarense were found, though the abundance of them was very low. On the other hand, massive bloom of Pseudo-nitzschia occurred in January at both stations. However, these blooms did not always cause the increase of DA level both in plankton and shellfish samples

Distribution of dinoflagellate cysts in the surface sediment of the coastal areas in Chonburi Province, Thailand

Distribution of dinoflagellate cysts were investigated in rainy and dry seasons in the surface sediment of the coastal areas in Ang-sila, Bang-pra, Si-racha and Laem-chabang, Chonburi Province, Thailand. Sampling cruises were conducted in February and September 2005 that were during the dry and rainy seasons, respectively. Thirty types of cysts were found of which 28 cysts belonged to the orders Gonyaulacales, Gymnodiniales and Peridiniales and two were of unknown cyst types. The dominant species were Pheopolykrikos hartmannii and Pyrophacus steinii and the most common species were P. hartmannii, Gonyaulax spinifera (Spiniferites mirabilis), Lingulodinium polyedrum, P. steinii, Protoperidinium pentagonum and P. leonis. Dinoflagellate cysts were widely found in most stations of the study area. The total numbers of dinoflagellate cysts in dry season were higher than those in rainy season. The abundance of dinoflagellate cysts in both seasons was higher at the stations deeper than 10 meter around Ang-sila and Bang-pra areas than at the stations near Laem-chabang areas. These findings suggest that cyst abundance and distribution might be affected by seasonal changes of environment and fishery activity.Proceedings of the Horiba International Conference "New Direction of Ocean Research in the Western Pacific" : Past, Present and Future of UNESCO/IOC/WESTPAC Activity for 50 years and the JSPS Project "Coastal Marine Science"Section I: Research Articles/Harmful microalga

Is the archeopyle of Tuberculodinium vancampoae (Rossignol) (Gonyaulacales, Dinophyceae) on the hypocyst?

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Vertical distribution of Pyrodinium bahamense var. compressum (Dinophyceae) cysts in Ambon Bay and Hurun Bay, Indonesia

Pyrodinium bahamense var. compressum (Pbc) is one of the causative species of Paralytic Shellfish Poisoning (PSP). Incidents of PSP and red tides caused by Pbc are increasing, as well as the geographic distribution of Pbc expanding in Southeast Asia, where it has recently occurred in several areas that previously have not experienced blooms, such as Ambon Bay and Lampung Bay in Indonesia. Five factors including anthropogenic activities, natural activities, visual realization with red tide discoloration, development of techniques like RNA sequence and ELISA toxin kits, and the establishment of a regular monitoring system have been suggested to have led to the increase in reports of dinoflagellate blooms. Occurrence of dinoflagellate cysts in sediments has been used as evidence to which species of vegetative cells occurred in the water column. In this study, the vertical distribution of dinoflagellate cysts in sediments was investigated to confirm the first occurrence of Pbc cysts and to examine the floral changes of dinoflagellate cysts in Ambon Bay and Hurun Bay, Indonesia. In Ambon Bay, Pbc cysts first occurred in ca. 1850 and the cysts were continuously observed since ca. 1870. In Hurun Bay, Pbc cysts were found at 50-52 cm depth, and also at 42-44 cm depth. Cysts of Pbc first occurred at least in 1883, using depositional age calculated from the historical eruption of Mt. Krakatau. Cysts of Pbc have continuously occurred since ca. 1910, and the cyst densities rapidly increased in ca. 1960. Based on these findings, we consider that anthropogenic activities such as ballast water and transportation of shellfish seeds probably did not cause the introduction of Pbc in both bays