| Summary: | This study investigated the natural phytoplankton assemblage of Ambon Bay,
eastern Indonesia, over a two-year period, including the composition of the dominant
microplankton and the influence of environmental factors with emphasis on the role
of mangrove in Ambon Bay. A hoped-for bloom of the toxic Pyrodinium bahamense
var. compressum did not materialize but other potentially harmful species from
Ambon Bay were isolated and investigated in culture to determine their growth rates
under various environmental conditions and their toxin potential. This constitutes the
first study of its type, not only for the Moluccan region, but Indonesia in general.
In this study, 105 phytoplankton species from Ambon Bay were identified,
including several dinoflagellates new to Indonesia, such as Gymnodinium catenatum,
Alexandrium cohorticula and Fragilidium cf. mexicanum. The former two are known
from S.E. Asia but the latter has not been seen since its description from Mexico.
Due to its close resemblance to the toxic genus Alexandrium it was also tested in
culture for toxicity. The common, occasionally abundant, presence of G. catenatum
was unexpected and raises the possibility of human health hazard due to this
species in Ambon Bay. During the 1997-1998 sampling period, a strong indication of
local upwelling occurred in Ambon Bay. The environmental factors that significantly
influenced phytoplankton abundance were ammonium, salinity, and water
temperature.
Four dinoflagellate species isolated from Ambon Bay were able to grow in
culture in both natural and artificial media and, because of its importance as a
shellfish poison producer in S.E. Asia, a culture of Pyrodinium was also studied.
Addition of Mangrove Soil Extract (MSE) to the culture media has significantly
enhanced the growth of Pyrodinium (a Manila Bay isolate) compared to media
without MSE. Moreover, it preferred MSE with molecular weight higher than 3000 for
increasing growth in culture.
This study has provided the first comprehensive, detailed information of
phytoplankton in eastern Indonesia and Ambon Bay in particular. It has characterized
general features of the phytoplankton community, identified dominants and
investigated possible environmental influences, particularly mangrove emphasizing
the potentially harmful species. It has significant implications for human health
related to shellfish consumption in Ambon.
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