Phytoplankton size fractions in Tolo Harbour, Hong Kong and their relative contributions to productivity
"PHYTOPLANKTON SIZE FRACTIONS IN TOLO HARBOUR,
HONG KONG AND THEIR RELATIVE CONTRIBUTIONS TO PRODUCTIVITY"
CHAN SHUE SHUM (ft ~ 4-
M.Phil. (HONG KONG)
for the DEGREE OF DOCTOR OF PHILOSOPHY
at the UNIVERSITY OF HONG KONG
in September, 1987.
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Studies on a natural phytoplankton population in Tolo Harbour
based on four categories of size fractions and their relative
contributions to productivity revealed not only the persistant
dominance and superior productivity of the smallest size fraction
but also that phytoplankton primary productivity was inversely
proportional to size. The nannoplankton ?0 ~m) size fractions
were the most important component accounting for 57% of the annual
biomass (in terms of chlorophyll a concentration) at an inner
station T3; and 47% at an outer station T5.
In terms of carbon
uptake, the contribution of the nannoplankton to annual
productivity was also important at both inner and outer stations
(50.57% and 43.87% respectively). Conversely, the netplankton
contributed relatively lower percentages to biomass and
productivity, contributing 4.1% and 19.4% at stations T3 and T5 in
terms of chlorophyll a concentration and 5.41% and 20% at stations
T3 and T5 in terms of carbon uptake. The higher cell surface area
to volume ratio of the nannoplankton is thought to be one of the
major reasons for this.
All forms of nutrient content were high at both stations and
-N (like p) is no longer a growth-limiting factor in Tolo Harbour.
The high concentrations of Nand P should have supported a much
higher level of phytoplankton biomass; but it appeared that the
high Nand P concentrations suppressed further growth.
Productivity in the surface layer was generally higher than
in. the middle and bottom layers of water.
The high productivity, especially at the inner station T3,
resulted in algal blooms. High nutrient concentrations of both N
and P, favourable ambient temperature and light, long retention
time as a result of restricted tidal exchange, absence of
upwelling, but presence of mixing enhanced by both movement of
incoming and outgoing vessels and by river runoffs, especially
during and after torrential rain, promoted 32 red tide incidents
in Tolo Harbour during the study period. The causes of most of
the algal blooms are extremely diverse and include hydrographic,
chemical and biotic effects on cell growth. The control of
destructive blooms (which have caused annual losses of millions of
dollars via fish-kill In cage-fish farming in Tolo Harbour) will
depend upon achieving an understanding of both their basic biology
and their ecology.
Red tide incidents could well be a warning signal of
deterioration in the aquatic ecosystem and indicate that concerted
action against further deterioration is necessary.
In Tolo Harbour, the outbreaks of red tides appeared to be
initiated shortly before the commencement of thermal
Assimilation numbers of all four phytoplankton size fractions
were found to show a better relationship with temperature --
though they were not significantly correlated at the 95% level
than with light and salinity. The variations in assimilation
numbers in each size fraction were related to environmental
fluctuations. The lower assimilation number value given by the
smallest size fraction ?0 ~m ) was probably due to large numbers
of dead cells and detritus present in that size fraction which can
be reflected by the high phaeophytin value given by that size
Minute eukaryotic cells ? ~m) are now receiving more attention in terms of their significant contribution to
productivity. However, further investigation of the physiology and ecology of this ultraplankton would promote a better understanding of energy transformations and recycling in the
School:The University of Hong Kong
School Location:China - Hong Kong SAR
Source Type:Master's Thesis
Keywords:marine phytoplankton china hong kong productivity tolo harbour
Date of Publication:01/01/1988