Environmental Engineering Reference
In-Depth Information
akashiwo ) were reported to graze on bacteria to acquire phosphate, when inorganic
nutrients are limited (Nygaard and Tobiesen 1998 ).
HAB cells become more abundant when nutrients increase, although the resultant
cellular toxicity may be either higher or lower than under non-eutrophic conditions.
Proctor et al. ( 1975 ) demonstrated that the toxin concentration in HAB cells is
inversely associated with the mean growth rate of cells. However, Kodama ( 1990 )
reported no correlation between growth rate and cellular toxicity. Generally, altering the
nutrient ratio affects the growth and cellular toxicity of HAB cells. Alexandrium sp.
grow optimally at N/P ratios of 0.18-0.38 (Lim et al. 2010 ). Whereas, other HAB spe-
cies, such as Prorocentrum micans , P. sigmoides , and P. triestinum , grow optimally at an
N/P ratio of 5-15 (Hodgkiss and Ho 1997 ). In addition, the nutrient ratio also infl u-
ences the cell size of HABs. Increased N/P ratios produce increased cell size of
A. minutum due to the arrest of cells in the G1 phase (i.e., they do not undergo cell divi-
sion), while other non-P compounds continued to be synthesized (Vaulot et al. 1996 ).
The amount of toxin produced by HAB species is affected by the types and con-
centration of nutrients to which they are exposed. The dinofl agellate D. acuminata
produced enhanced toxin levels during N and P deprivation; the enhancement was
sixfold larger during N-deprivation (Johansson et al. 1996 ). In contrast,
Chrysochromulina polylepis produced toxin that was sixfold more toxic under P
enrichment than during N-limited conditions (Johansson and Graneli 1999 ).
Moreover, saxitoxin production in A. tamarense was fi ve to tenfold higher during
P-deprivation, than when deprived of N (Lippemeier et al. 2003 ; Anderson et al.
1990 ). Enrichment in organic nutrients also infl uences cellular toxicity of HABs.
For example, increasing the dissolved organic nutrients concentration (urea level up
to 1 mM) stimulated toxin production in K. brevis by sixfold and caused K. brevis to
switch from autotrophic to heterotrophic nutrition (Shimizu et al. 1993 ). Lim et al.
( 2010 ) observed a similar phenomenon with A. minutum , in which ammonium
induced toxin production under a P-deprivation condition. However, the N/P ratio has
no effect on the toxin composition of A. minutum .
3.2
Environmental Parameters
The nutrient supply does not necessarily correlate with the rate at which nutrients are
assimilated by phytoplankton, because the nutrient uptake capability of organisms
vary (Anderson et al. 2002 ). Diatoms physiologically adapt to better exploit a high
concentration of nitrate (Lomas and Glibert 2000 ). Therefore, diatom growth is
highly correlated with ambient nitrate concentration. How effectively nutrients are
assimilated by phytoplankton and the resultant effects on organism growth depend
heavily on several environmental factors, e.g., salinity, light, temperature, and water
column stability.
There is evidence that environmental parameters play a major role in modulating the
growth and cellular toxicity of HABs. In Sabah, blooms of Pyrodium bahamense var.
compressum appeared to be associated with increased salinity (Anton et al. 2000 ).
Moreover, the growth rate of A. tamarense is relatively low at low salinities
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