optimum near 30° Celsius and a salinity optimum near 30 parts per thousand. 

 Deviations of these environmental parameters from their optima depress the 

 biotic viability of the plant. Minimum values for the measured variables were 

 encountered during periods of seasonally low temperatures or high temperatures 

 coupled with lowered salinity. Thalassia has a slow response to environmental 

 stress due to the stored starch reserves in the extensive rhizome system. 



143. ZIEMAN, J.C, "The Ecological Effects of Physical Damage from Motor Boats 

 on Turtle Grass Beds in Southern Florida," Aquatia Botany, Vol. 2, No. 2, 

 June 1976, pp. 127-139. 



Observation has shown that beds of turtlegrass (Thalassia testudinum) , 

 although highly productive, do not recover rapidly following physical disturb- 

 ance of the rhizome system. In shallow waters the most common form of rhizome 

 disturbance (boat damage) is from motorboat propellers. 



In turtlegrass beds which are otherwise thriving, tracks resulting from 

 propellers have been observed to persist from 2 to 5 years. The proportion of 

 fine sediment components is reduced in the sediments from the boat markings, 

 and the pH and EH are reduced in comparison to the surrounding grass bed. 



This type of damage is most likely to occur in the shallow passes between 

 islands and keys, areas that are also the slowest to recover due to the rapid 

 tidal currents present in the shallow passes. 



144. ZIEMAN, J.C, BRIDGES, K.W., and McROY, C.P., "Seagrass Literature Sur- 

 vey," Technical Report D-78-4, U.S. Army Engineer Waterways Experiment 

 Station, Vicksburg, Miss., Jan. 1978. 



An extensive review of the published and unpublished literature pertain- 

 ing to seagrasses, up to mid-1977, was prepared. Broad scientific subject 

 areas that relate to seagrasses, such as anatomy, ecology, morphology, tax- 

 onomy, and physiology, were considered together with more specific factors 

 such as substrate selectivity, water quality, productivity, colonization, 

 effect of physical energy (waves, tidal currents, sediment transport), propa- 

 gation, and tolerance to disturbance. The bibliography has a keyword index 

 and also includes two appendixes, an author index and a source index, in 

 microfiche form. 



145. ZIMMERMAN, M.C., and LIVINGSTON, R.J., "Effects of Kraft Mill Effluents 

 on Benthic Macrophyte Assemblages in a Shallow Bay System, Apalachee Bay, 

 North Florida, USA," Mavine Biology, Vol. 34, No. 4, Mar. 1976, pp. 297- 

 312. 



This study determined the impact of kraf t-papermill effluents on the off- 

 shore benthic macrophyte distribution in a shallow north Florida bay. A pol- 

 luted river drainage system was compared to an unpolluted one. The affected 

 area was characterized by elevated levels of color and turbidity. In polluted 

 areas, red and brown algae were proportionately more abundant than chloro- 

 phytes and spermatophytes. Except for areas of acute impact, there was no 

 significant difference in species diversity between polluted and unpolluted 

 parts of the bay. The pattern of macrophyte species composition reflected 

 various water quality parameters. It was postulated that the reduction of 

 normal dominants, such as Thalassia testudinim and Halimeda inavassata, 

 allowed colonization by opportunistic species. Nearshore coastal systems in 

 Apalachee Bay thus were affected by gradients in water quality in addition to 

 natural (seasonal) fluctuations in key physical and chemical parameters. 



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