This is the final report for the red tide monitoring project conducted at The University of
Texas at Austin Marine Science Institute (UTMSI) and covers the period from 1 Nov. 1998 to 10
April 2000. The study was designed to examine the seasonal dynamics of the toxic red tide
dinoflagellate Karenia brevis (Davis) G. Hansen and Moestrup at 5 locations off the Texas coast.
The work was conducted in collaboration with the Texas Parks and Wildlife Department
(TPWD) utilizing bimonthly finfish surveys (Coastal Fisheries Division) to collect samples. The
samples were shipped to UTMSI for chl a, nutrient, and cell count analyses.
Significant interannual variability occurred in the temperature and salinity fields.
Temperature was lowest in Jan.-Feb. of each year and increased. In general, the 5 stations
showed little concordance with each other. There was no annual pattern in nutrient distributions.
Individual stations appeared to reflect local inputs, rather than coast wide events. The only
exception was a generalized silicate increase noted in Feb-April 2001 at all stations except
Brazos Santiago near Brownsville.
Karenia brevis was observed sporadically along the coast during the winter and most
observations were limited to the summer/fall months. The sporadic occurrences and numerous
"no cells" observations do not support the hypothesis that a year round resident red tide
population exists in the Texas coastal zone. It appears that are transported into the area by large
scale oceanographic features. The mechanism for this remains unknown.
A minor red tide occurred along South Padre Island in Oct./Nov 1999. The bloom
advected south into Mexico, and no further fish kills were noted in 1999. However, K. brevis
occurred sporadically along the coast during this time. These events suggest that K. brevis may
be seeded into the area from further offshore regularly at very low levels. Until fish-killing
populations develop, it likely remains undetected. One major red tide event occurred during
2000 that affected the entire Texas coast. A small red tide occurred along South Padre Island in
July, 2000 but disappeared after moving north to Padre Island National Seashore. Fish-killing
concentrations of K. brevis were first detected in mid August off Sabine Pass in the north and
moved south along the coast over the following months. However, low level occurrences of K.
brevis were found at intermediate stations well before the main red tide advected into the region,
and were nearly coincident with the initial observations off Sabine Pass. It is impossible from
this data to determine if the July bloom in south Texas was related to the events off Sabine, but
there is a possibility that offshore continental shelf currents may well be transporting cells north
from Mexico into northern Texas waters.
Another toxic species closely related to K. brevis has been seen at reasonably high
abundance. This species, Karenia mikimotoi, is toxic to fish and has been reported to co-occur
with K. brevis in blooms. Maximum abundance of this species was 6000 cells L-1, and appeared
to exhibit a distinct increase and decline in population levels at 3 different stations.Marine Scienc
