ESTUARINE RESEARCH PROGRAM 



The estuarine research program has five 

 projects : bay bottom ecology, plankton ecology, 

 production of marine animals, effects of estu- 

 arine alteration, and an inventory of Gulf of 

 Mexico estuaries. 



BENTHIC PROJECT 



John L. Taylor and Carl H. Saloman 



Introduction 



Study of benthic ecology in estuaries of the 

 eastern Gulf began at this Laboratory in 1963. 

 The work is designed to give detailed informa- 

 tion on the distribution and abundance of ben- 

 thic species and provide guidelines to assess 

 the biological importance of estuaries and the 

 impact of coastal development. 



In fiscal year 1968, the fourth in a series of 

 hydrological reports and a sediment report 

 were con-ipleted for Tampa Bay and adjacent 

 waters. Work continued on the identification of 

 bottom animals from the Bay with emphasis on 

 mollusks, echinoderms, and polychaete worms. 

 Biological research was also directed toward 

 four organisms that have actual or potential 

 value as commercial species--the southern 

 quahog, Mercenaria campechiensis : the lug- 

 worm, Arenicola cristata; the squid, Lolligun- 

 cula brevis; and the sea grass, Thalassia 

 testudinum . Finally, several "fact-finding" 

 surveys were made in Tampa and Sarasota 

 Bays to determine the biological resources 

 that exist in areas proposed for dredge-fill 

 development. 



Hydrology 



Hydrological data are essential for ecologi- 

 cal studies in the estuary and provide a his- 

 torical record of changes in the aquatic en- 

 vironment. Waters of Tampa Bay are sampled 

 each month at 30 permanent stations. Measure- 

 ments include water temperature, salinity, pH, 

 total phosphorus, total nitrogen, dissolved oxy- 

 gen, and turbidity. The same measurements 

 (plus Secchi disc readings) are made on water 

 sannples collected daily at the Laboratory dock 

 on Boca Ciega Bay. In addition, chlorophyll 

 determinations are made once each week for 

 samples taken at the dock. 



Hydrological conditions in the Bay in 1965- 

 67 (fig. 1) differed little from those in 1961-64 

 (given in the Laboratory's report for fiscal 

 year 1967). One exceptional feature is the rise 

 in concentration of total nitrogen throughout the 

 Bay since 1965. A cause for this increase (8- 16 

 Mg.at./l. (microgram atom per liter)) is the 

 progressive enrichment of the estuary from 

 domestic and industrial sewage. 



Sediments 



Sediment composition has a great influence 

 on the occurrence and distribution of benthic 

 organisms, and established bottom communi- 

 ties have an effect on the physical and chemi- 

 cal nature of bottom deposits. Sediment 

 samples are therefore collected and analyzed 

 in benthic studies and other Laboratory pro- 

 grams. Textural, chemical, and statistical data 

 for more than 500 samples from Tampa Bay 

 have been recorded since 1963. Throughout 

 most of the Bay, the bottom consists of sedi- 

 ments that are more than 20 percent sand, and 

 patches of shelly sand exist in a few locations. 

 Soft sediments of silt and clay are found in 

 natural and manmade depressions and other 

 areas where tidal currents are weak (fig. 2). 

 Soft sediment is mostly confined to Hills- 

 borough Bay where sewage sludge is a major 

 source of fine-grained material and Boca Ciega 

 Bay where dredging has caused siltation in 

 bayfill canals and elsewhere. Soft sediment in 

 these two areas of the Bay has greatly reduced 

 or eliminated benthic invertebrates normally 

 found in other parts of Tampa Bay. 



Mollusks 



The study of the relation between mollusks 

 and environmental conditions is complete for 

 three areas of Tampa Bay--Boca Ciega Bay 

 near the mouth of the estuary and Old Tampa 

 Bay and Hillsborough Bay at the head of the 

 estuary. This information shows how the 

 natural environment influences the distribu- 

 tion, abundance, and diversity of shellfish and 

 how development and pollution of parts of the 

 bay can reduce or eliminate mollusks there. 



In bottom samples fronn undisturbed areas 

 of Boca Ciega Bay, we recorded 155 species 

 of live mollusks in 67 families (table 1). The 

 average sample had 60.5 mollusks. Environ- 

 mental factors that favor such great divers- 

 ity and abundance include high salinity 

 ( > 30 p.p.t.), sandy sediment (91 percent sand 

 and shell), and bottom vegetation (sea grasses 

 and algae). In contrast, dredge hauls from the 

 bayfill canals of Boca Ciega Bay had only five 

 species of mollusks, and the average number of 

 individuals per collection was less than one. 



Table 1. — Nujnber of species of iToliusKs collected, salinity, and tottom type in tnree 

 areas of Tampa Bay, Fla. 1963-64 



