and sales campaigns should be carried 

 on. 



Given a breeding population of sponges, 

 three major factors affect dispersion: 



1. The direction, rate of flow, and charac- 

 teristics of the ocean currents in the 

 sponge-producing area. 



2. The duration of the larval stage. 



3. The growth rate of sponges to maturity. 



There are two types of ocean currents — 

 tidal and semipermanent — affecting the dis- 

 persion of the free larval stage of the sponge. 



Measurements of the tidal flow and its cal- 

 culated excursion show that in the upper Gulf 

 the total distance traveled by the water during 

 a tidal period is about 2 miles where the depth 

 of the water is 24 feet. Excursion varies ac- 

 cording to the depth of water; in water of 

 roughly three times the above depth, excursion 

 is about one half. 



The normal direction of the tidal flow is 

 approximately at right angles to the coast and 

 has a more or less elliptical excursion. Com- 

 pared to the strong inshore current that flows 

 parallel to the shore, the back and forth move- 

 ment of the tide is relatively ineffective in dis- 

 persing the larvae in any set direction. 



Tidal excursion is important, however, to the 

 fertilization process since it carries released 

 sperm back and forth over the sponge-produc- 

 ing area, greatly increasing the chances of 

 fertilization. Wave action plays a similar role 

 on a much smaller but still important scale. 



Semipermanent currents in the Gulf, how- 

 ever, are most important for the wider disper- 

 sion of the commercial sponges from their 

 present limited distribution. These are the 

 northward inshore current and four offshore 

 eddies, the latter dispersing the sponges sea- 

 ward. The current pattern in figure 1 1 has been 

 modified from the determination of the Gulf 

 currents along the west coast of Florida made 

 by members of the Red Tide Project at the Ma- 

 rine Laboratory of the University of Miami. The 



distribution pattern of the sponges along the 

 coast north of Tampa Bay coincided almost 

 exactly with what one would have expected to 

 find as a result of these current directions. 



The most important single current for sponge 

 distribution at present is the inshore current 

 that lies between the shore and the 50 to 60 foot 

 depths. This current flows more or less 

 parallel to the shore. Current flow was meas- 

 ured by dropping a series of drift cards in the 

 area off Piney Point in the upper Gulf at various 

 distances from shore. In June 1957, drift cards 

 released about 4-1/2 miles offshore in 20 feet 

 of water were picked up south of Alligator 

 Harbor. The rate of flow estimated from these 

 cards was 5 miles per day. Those drift cards 

 dropped 10 miles from land in 35 feet of wa^er 

 were picked up near Panama City; the estimated 

 rate of flow was 8.2 miles per day. Between 

 the time of dropping and the time of recovery 

 the wind was very light, and shore recoveries 

 were made a day or so after the beginning of a 

 strong southerly wind. Depending on the 

 strength and direction of the wind, variations 

 in direction and rate of flow would be expected 

 in water of this depth. The summer current, 

 as measured by the drift cards, is probably 

 fairly consistent since the summer winds are 

 usually light and from the southeast. Majority 

 of the sponge larvae are released between May 

 and August. 



The three eddies between Tampa Bay and the 

 Cedar Keys area are between 20 and 25 miles 

 in their greatest diameter where water depths 

 are 50 to 100 feet (fig. 11). Estimated current 

 velocities in these eddies is 1 mile per day. 



The most northerly eddy, located south of 

 St. Marks, is 50 miles in its greatest diameter; 

 and since the shoreward side of the eddy is 

 part of the inshore current, the velocity of the 

 northern part of the eddy is similar to that of 

 the inshore current. With the shoreward side of 

 the eddy flowing in much the same direction as 

 the prevailing winds in the area there are times 

 when the velocity of the current in the eddy 

 should increase substantially. The seaward 

 movement of the eddy, off Carrabelle, would 

 retain much the same velocity as the shore 

 current, because much of the water moves 

 Gulfward with the eddy. In the deeper water 



29 



