Phytoplankton Distribution 



Toxins produced by the dinoflagellate Gymnodinium breve were implicated as a 

 proximate cause of the mass mortality of bottlenose dolphins along the U.S. east coast 

 during 1987-88 (Geraci, 1989). For this reason, 123 phytoplankton samples from the Texas- 

 Louisiana offshore area were examined for the presence of the G. breve. Eighty percent of 

 these samples contained G. breve cells. Seventy samples from the upper half of the water 

 column were examined in detail, and quantitative counts confirmed that 94% contained some 

 G. breve cells while 65% contained >50 cells 1'^ (see Section IV, Figure 1). These 

 concentrations are far below those considered a "bloom" (>5 x 10^ cells 1'^). Comparative 

 samples fi-om other areas in the Gulf of Mexico suggest that G. breve concentrations in the 

 primary study area during the March 1990 sampling period were within normal background 

 levels but consistently higher than quantitative counts of samples from similar areas in the 

 northern Gulf of Mexico of from the primary study area later in the summer. 



Discolored water patches noted during aerial observations of the primary study area 

 were blooms (approx. 1 x 10^ cells 1'^) of the dinoflagellate Noctihica spp. This genus is not 

 known to normally be toxic. However, it should be noted that a toxic dinoflagellate species, 

 Gonyaulax monalata, was found in elevated concentration near the Mississippi delta in late 

 summer 1990. 



Brevetoxin Analysis 



Brevetoxin is a neurotoxin produced by a toxic dinoflagellate, G. breve. Poisoning by 

 this toxin was believed to have caused the 1987-88 mass mortality of bottlenose dolphins 

 along the U.S. east coast. Because of the previous implication of brevetoxin as a cause of 

 mass mortalities of bottlenose dolphins, a total of 50 bottlenose dolphin liver samples were 

 analyzed for individual brevetoxins (40 samples from 1990 Gulf of Mexico samples, and 10 

 control samples). Toxicity was determined by several methods: 1) fish bioassay - Gambusia 

 affinis, fish death at a fixed interval indicates toxin present but does not necessarily indicate 

 brevetoxin; 2) HPLC separation of toxin fractions - HPLC separation provides a means to 

 confirm or deny the presence of brevetoxins in comparison to valid Pb Tx-standards; 3) 

 Radioimmunoassay provides a means to positively identify brevetoxin-like materials and is 

 sensitive to authentic Pb Tx-3. 



Following the first thin-layer chromatography (TLC) plate, 33 of the 50 samples were 

 found non-toxic in the fish bioassay and were not tested further. Of the remaining 17 

 samples that tested positive in at least one fraction of the first TLC plate, nine had multiple 

 toxic fractions. Of the 17 samples, 12 tested negative by fish bioassay following the second 

 TLC plate. Of the five fi-actions found toxic after the second TLC separation, three were 

 judged to be in such limited quantity to preclude further TLC separation. The other two 

 retained toxicity after the third TLC separation. 



