Biological Effects: Microalgae and Bacteria 



The conversion of inorganic to organic carbon by the phytoplankton 

 in the sea represents 60-80% of the total photosynthesis on earth. The 

 phytoplankters are the food for the zooplankters which in turn are the 

 food of higher organisms and so up through the food web of the marine 

 ecosystems. Thus, any substance which inhibits the growth of primary 

 producers is also limiting the food supply of higher trophic levels with 

 potentially disasterous consequences on the entire marine ecosystem. 

 It is therefore extremely important to determine the effects of various 

 chemical contaminants on phytoplankton in order to be able to make 

 informed predictions and. through governmental restriction of the 

 inputs of certain toxic agents to the ocean, avert serious damage. 



Low Molecular-Weight Hydrocarbons 



A group at Texas A&M University is studying the effects of Cr, to 

 Cio aliphatic and aromatic hydrocarbons on the rate of photosynthesis 

 of mixed ocean cultures of phytoplankters at sea and of cultures of the 

 diatom Skeletonema costatum in the laboratory. Carbon fixation rates, 

 using the radiocarbon technique of Stieman-Nielsen, are determined 

 as a function of added pollutant concentrations. A summary of the 

 data is given in Table 1 . 



One of the most striking aspects of the data in Table 1 is that the 

 aliphatic hydrocarbons depress the photosynthetic rate considerably 

 more than do the aromatic hydrocarbons for a given concentration. 

 This is in contrast to the classical LD.^n data which indicate that aro- 

 matic hydrocarbons are the most toxic components of petroleum. 

 These data indicate an increased toxicity related to increased substi- 

 tution on the benzene ring. It was observed that certain concentrations 

 of benzene produced an increase in the uptake of carbon. This appa- 

 rent stimulation has been observed for long term experiments and no 

 ecological significance is attached to it. 

 Spatial and Temporal Distribution of LMWHC in the Gulf of Mexico 



Dissolved low-molecular-weight hydrocarbon concentrations in sur- 

 face water have been determined for several thousand miles of cruise 

 tracks of the Texas A&M University ships. R/V Alaminos and R/V 

 Gyre, in the Gulf of Mexico on each of the five short cruises made in 

 behalf of this Program in the past two years. The data generally in- 



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