increase rapidly. The summer increase began 

 when salinity began to decrease, i.e., from 

 runoff of sun-inner rains entering the Bay. Thus, 

 the spring bloom appeared to be temperature- 

 related, probably through the release of nu- 

 trients by bacteria at a critical temperature, 

 whereas the summer increase was probably 

 salinity- related. As would be expected, water 

 transparency decreased at the same time that 

 phytoplankton production increased. 



Ultraviolet absorption was measured during 

 the past year as it has been since February 

 1963. Two peaks occurred, one in early April 

 and the other in September. The early April 

 peak preceded the spring bloom of phytoplank- 

 ton by a few days; the September peak was 

 coincident with a minimum of salinity and a 

 nnaximum of phytoplankton productivity. The 

 fact that the spring increase occurred at a 

 time of increasing salinity shows that river 

 runoff and laltraviolet absorption are not nec- 

 essarily related. 



The ultraviolet absorption test was initiated 

 in 1963 because of its possible utility in pre- 

 dicting red-tide outbreaks. The test is simple 

 and rapid. The reasoning was that ultraviolet 

 absorption might be an indicator of the presence 

 of nutrients which are essential to a bloom of 

 G. breve. Ultraviolet absorption is related to 

 the organic content of water; therefore, un- 

 usually high or low absorption might indicate 

 unusually high or low concentrations of the 

 nutrients associated with organic substances. 

 Field data substantiated this reasoning. In the 

 spring of 1963, ultraviolet absorption increased 

 markedly just before a red-tide outbreak and 

 decreased markedly just after the bloom. There 

 were no red-tide outbreaks from then until 

 September 1967, when a relatively mild one 

 occurred. Again, ultraviolet absorption in- 

 creased markedly just before and during the 

 outbreak. However, unusually high values of 

 ultraviolet absorption are not necessarily ac- 

 companied by a red-tide bloom. An increase 

 in absorption in September 1965 was not ac- 

 companied by unusually high counts of G. breve . 

 Increases of ultraviolet absorption are usually 

 accompanied by decreases of salinity, but the 

 relation is only approximate as shown by the 

 graph of maximum, minimum, and average 

 values of both properties from February 1963 

 to June 1968 (fig. 19). 



How does the phytoplankton primary pro- 

 ductivity of Tampa Bay compare with that of 

 other inshore areas? The average gross annual 

 rate in fiscal year 1968 was 401 g.C/m.^ 

 (grams of carbon per square meter), whereas 

 the annual rates published for other waters are 

 99.6 in shallow North Carolina estuaries, 39 to 

 1 75 in certain Danish bays, and 380 g.C/m.2 in 

 Long Island Sound. Thus, Tampa Bay's phy- 

 toplankton primary production is one of the 

 highest that has been measured. 



The productivity of Tampa Bay can be viewed 

 also in relation to terrestrial plant production. 



SALINITY 

 [Rangt J UtanJ 



W- 



i 



i ^^*l i iltm t ^i i' it ii m t ^ ii i|i»lifttllitfH* i f i 



F A J A 



1963 



ULTRAVIOLET 

 (Rongt a Mtonl 



ODPAJAODFAJAODPAJAOOPAJAODFAJ 



1964 1969 1966 1967 1968 



Figure 19. — The range and mean of monthly salinity and 

 ultraviolet absorption from February 1963 through 

 June 1968. Red tide was coincident with two of three 

 periods of high ultraviolet absorption. 



The orange crop is by far the most valuable of 

 Florida' s agricultural products. Orange groves 

 abound in the Tampa Bay area. The Statewide 

 average production of oranges over a recent 

 representative 5-year period was 3,937 kg./ 

 ha. /year (kilograms per hectare per year) (dry 

 weight) whereas the average production of 

 phytoplankton in Tampa Bay was 10,017 kg./ 

 ha. /year in fiscal year 1968. Benthic algae and 

 grasses boost the total annual production of 

 plant material in Tampa Bay to two or three 

 times the annual phytoplankton production, so 

 that the total is in the range of 20,000 to 30,000 

 kg. /ha. per year. For comparison, the world 

 average annual production of wheat is about 

 3,400 kg. /ha., and the highest production of 

 wheat and corn in northern Europe is about 

 16,000 kg. /ha. per year, including straw and 

 roots. 



Thus, the annual production of plant material 

 in Tampa Bay is high con-ipared with the 

 annual production of terrestrial crops, just as 

 it is high in relation to production of phyto- 

 plankton in other inshore marine areas. The 

 waste of organic material in Tampa Bay and 

 other fertile estuaries is prodigious in terms 

 of potential direct benefits to man. It is tempt- 

 ing to speculate that herbivore yield ashighas 

 10 to 20 percent of primary production of 

 plants is theoretically possible, as has been 

 attained in the conversion of corn to hogs, 

 although a yield of 3 percent is apparently the 

 highest yet achieved in marine farm ponds. The 

 usual harvest of seafood is a small fraction of 

 1 percent of primary production. The losses 

 occur at various stages in the complicated food 

 chains between primary production and edible 

 fishery products. Man's grasp of the facts is 

 fragmentary and hence his control of the 

 processes involved is insignificant. One of the 

 major scientific and engineering challenges of 

 our time is to attain better control of the proc- 

 esses involved in estuarine seafood production. 



24 



