Bay has remained at about its present level since 

 1952 or before (Odum, 1958)— see table 4. In areas 

 of the estnary less aft'ected by niinino; runoi!'. hiirh 

 concentrations of phosphorus and nitrog-en record- 

 ed since the early 1960's are due to an increase 

 in industrial and domestic sewage. Population in 

 the area around Tampa Bay was less than one- 

 half million in 1950, rose to about three-fourths 

 million by 1960, and is now near 1 million. As 

 population rose, the method of sewage disposal 

 was converted from septic tanks to treatment, plant 

 in the late 1950"s and early 19fiO's. This change 

 introduced treated sewage directly into all areas 

 of the estuary. In Boca Ciega Bay, the mean an- 

 nual concentration of total phosphorus rose from 

 '2.5 /xg.a./l. in 19,54-58 to 4.4 in 1959, and 8 by 19(il. 

 At i)resent, total phosphorus averages 10 ;ug.a./l. 

 and total nitrogen 45.1 ;iig.a../l., and sewage volume 

 is about 17 million gallons per day (secondary 

 treatment) from outfalls located throughout the 

 lagoon. Along with progressive eutrophication of 

 Boca ("iega Bay, counts of coliform l:iacteria have 

 risen so high that shellfisliing has been prohibited 

 near all outfalls and in all waters of the bay north 

 of Pinellas County Bayway (fig. 13)— Pinellas 

 County Healtli Department, personal communica- 

 tion. 



Relative as well as total concentration of nitro- 

 gen and phosphorus influences the occurrence and 

 abundance of marine life (Raymont, 1963) . Within 

 limiting values, studies of marine plankton indi- 

 cate that growth and reproduction of marine 

 phytoplankton are greatest when the ratio of nitro- 

 gen to phosphorus is 10 or higher (Odum, Lackey. 

 Hynes, and Marshal, 1955; Lackey, 1963). In Boca 

 Ciega Bay the observed N/P is about 2. The dis- 

 proportionately high level of phosphonis may 

 limit kinds and numliers of phytoplankton in the 

 lagooia and perhaps explains why plankton blooms 

 are infrequent and planktonic primary production 

 is not extremely high ( Dragovicli, Kelly, and 

 Kelly, 1965; Rounsefell and Dragovich, 1966: 

 Dragovich and Johnson, 1966). 



Attached algae and sea grasses also respond to 

 eutrophy. McNulty (1961) noted an abundance of 

 GracUai-ia hlodgcttii Harvey, other red algae, and 

 the green alga Vltut. la-ctuca Linnaeus in Biscayne 

 Bay, Fla., before pollution abatement. Wilkinson 

 (1964) found a direct relation between eutroplii- 

 cation of a. New Zealand estuary and marked in- 

 crease of two gi'een algae, Ulva sp. and Entero- 



morpha sp. He wrote that foul odor of hydrogen 

 sulphide was emitted from decay of algal mats 

 and that wliite paint was turned black on homes 

 nearliy. Production of hydrogen sulphide by 

 Enieromorpha has also teen studied by Baas 

 Becking and Mackay (1956). 



Species of <Traeilaria have been implicated in 

 reports of offensive odors arising from Hills- 

 borough Bay (Florida State Board of Health, 

 1964). The Federal Water Pollution Control Ad- 

 ministration is now investigating this matter. In 

 Boca Ciega I^ay, Graeilaria is present, as are ZUnja 

 and Enteronwrpha. We observed windrows of 

 Tli'ii lactuea in bayfill access canals after residents 

 reported objectional^le odors in the central part of 

 the l>ay in the spring of 1965. Further nutrifica- 

 tion of Boca Ciega Bay would increase growth of 

 these and perhaps other filamentous algae that 

 become fetid as they decoanpose. 



TURBIDITY 



Data from 1963-64 show that secchi discs were 

 visible to depths greater than 150 cm. only in 

 southern Bcx^a Ciega Bay (PB-6) , well away from 

 bayfill developments (table 1). Here, average light 

 transmission through the water column is 53 per- 

 cent of incident radiation at about 40 cm. beneath 

 the surface (Saloman et al., 1964). In contrast, 

 water in the open bay nearer bayfills is turbid. 

 Within protected watei's of access canals, however, 

 transparency approaches that of the lower bay. 

 For example, average monthly light transmission 

 in one canal was 45 percent at 40 cm. (Saloman et 

 al., 1964). Even so, canal bottoms are far too deep 

 to receive light required for the growth of sea 

 grass. 



Much of the silt and clay raised by dredging 

 will eventually be removed from circulation in the 

 lagoon by ])iological fixation and tidal transport 

 (Dapples, 1942; Ginsburg and Lowenstam, 1958; 

 Van Stratten and Kuenen, 1958; Phillips, 1960a; 

 Lyiitz, 1966) . Until water is clarified l)y these proc- 

 esses, turbidity will continue to limit biological 

 production in central and northern parts of Boca 

 ( 'iega Bay. 



CHLOROPHYLL A AND PRIMARY 

 PRODUCTION 



Neither clilorophyll n nor rate of planktonic 

 primary production difl'ercd consistently in 



232 



U.S. FISH AND WILDLIFE SERVICE 



