Ecology of Red Tide 



John H. Finucane 



Study of the ecology of the Florida red-tide organism, Gymnodinium 

 breve, in Tampa Bay and adjacent neritic waters was continued. 



Geographical distribution and seasonal occurrence Following the sampling 



program employed last year, stations were occupied on a monthly basis from 

 upper Tampa Bay to 60 miles offshore. From June 1960-May 1961, over 800 

 water samples were collected to obtain counts of G. breve and associated phy- 

 toplankton. G. breve was found in 31 percent of these samples, compared 

 with over 45 percent last year. The flagellate occurred at all times in the 

 nearshore and offshore waters, the greatest number of samples containing 

 G. breve occurring from August through October I960 and February through 

 March 1961. This was similar to the seasonal pattern established in the fall 

 and winter of 1959 and I960. 



A minor red tide developed in the neritic waters off Tampa Bay dur- 

 ing July and August I960. Blooms of G. breve as dense as 420, 000 per liter 

 were found off Egmont Key, July 27, I960. Fish kills, principally confined to 



that area, were of a very lim- 

 ited nature. During August the 

 greatest numbers of this organ- 

 ism (up to 150, 000 per liter) 

 were present from 5 to 20 miles 

 off Egmont Key. The number of 

 samples containing G. breve in- 

 creased from a low of 3 percent 

 in June to 64 percent in August 

 during this outbreak. No further 

 fish kills were recorded after 

 the first week in August. From 

 September through May, G. 

 breve was found only in very 



.,, .J , r r. ■, low numbers, occurring prin- 



Abundance index averaged from five abun- ^ ^ 



J 1 • r r\ ^ ^ nnn nnn cipally in areas offshore from 



dance rankings ranging from to 1, 000, 000 ^ ' 



,.. the mouth of Tampa Bay. 

 per liter. ^ ' 



RELATIVE ABUNDANCE OF RED TIDE ORGANISM 



JUN JUL 



NOV DEC 



APR MAY 



Vertical distribution and light penetration Homogeneity of G. breve in the 



water column characterized the vertical distribution of this organism in Tampg. 

 Bay and the nearshore waters. During blooms in the deeper neritic waters, 7- 

 30 miles offshore, the greatest numbers oi.Q. breve were found on or near the 

 surface. Very low numbers were present during October I960, at a depth of 

 148 feet, 50 miles offshore. 



61 



