A. Martinez-arroyo et al., On the influence of hot-water discharges on phytoplankton communities froma coastal zone of the Gulf of Mexico, WATER A S P, 119(1-4), 2000, pp. 209-230
The influence of thermal discharges on the phytoplankton community from a c
oastal zone of the Gulf of Mexico was evaluated through their structure and
photosynthetic behaviour focusing on responses to changes in light and tem
perature. Biological and physicochemical parameters were measured over a pe
riod of two years in an area with permanent hot water discharges from a the
rmoelectric plant. The temperature in the sampling area ranged from 23.5 to
36 degrees C with differences between the coldest and the hottest station
from 5.3 to 9.2 degrees C. Photosynthetically active radiation (PAR) were r
educed in the discharge area water column, due to turbulence. One hundred a
nd one different taxa were identified with a strong predominance of Diatoms
. The chlorophyll a concentration ranged from 0.3 to 6.1 mu g L-1, with hig
hest values of the phaeophytin:chlorophyll ratio found at the hottest stati
on. The community structure did not show significative differences among sa
mpling stations with respect to temperature variations. However, in the alg
al assemblages influenced by thermal discharges, it was possible to observe
alterations in the photosynthesis behaviour. Phytoplankton response to sho
rt term photosynthesis experiments was segregated according to composition
and origin of microalgal assemblages. Samples with larger heterogeneous com
position had more consistent oxygen production responses. Algal communities
exposed to hot effluent showed different degrees of photosynthesis rate re
duction, higher light requirements (> 500 mu E m(2) s(-1)) and lower temper
ature (25 degrees C) to achieve Pmax than algae sampled in sites without su
ch exposure.