92 LUGO 



We have discussed how each Ufe zone has a different background 

 of stress which determines the potential for structural development 

 in that locality. As more stressors are added to the background, the 

 capacity to recover and to achieve maximum developmental poten- 

 tial decreases. In lowland tropical life zones, high temperatures 

 prevail and accelerate physiological processes. For aquatic ecosys- 

 tems this has serious implications for their capacity to absorb 

 additional stress. Johannes and Betzer (1975) elaborated this point 

 with respect to tropical marine ecosystems. Small temperature 

 increases are very damaging to these systems; e.g., 37°C is lethal to 

 Thallasia beds (Schroeder, 1975) and mangrove seedhngs (Banus and 

 Kolehmainen, 1976). These researchers also pointed out that in the 

 tropics a higher ambient temperature and higher ambient salinity 

 mean that a given concentration of pollutant causes a faster and 

 greater decrease in dissolved oxygen concentration than in higher 

 latitudes. At comparable dilution and dispersion rates, however, the 

 pollutant concentration decreases more quickly with time and 

 distance from the source. Thus the margin of error is smaller in 

 tropical waters. The margin of error is equally small in ecosystems 

 that are naturally stressed to a point near their limit of tolerance. 

 Mangroves tolerate a more severe frost stress if they grow in 

 low-salinity environments; they may not survive low temperatures at 

 high soil salinities. In this case the lower salinity subsidizes high 

 energy drains caused by frost (Lugo and Patterson Zucca, 1977). 



MEASUREMENT OF STRESS AND STRESSORS AND 

 RESEARCH NEEDS 



The broad regional impact of man on the biosphere is probably 

 why there is so much interest in studies of ecosystems and stress. 

 Much of the research appears to ignore this broad issue, however, and 

 instead focuses much effort on specific details that provide elegant 

 results but do not really help society to solve the problem of 

 coupling man to natural systems. We must document ecosystem 

 responses to known intensities of stressors and test the ideas 

 presented here. The researcher must take into consideration not only 

 the intensity of the stress and the stressor but also their energy- 

 quality characteristics relative to other energy sources impinging on 

 the ecosystem. The points of attack in the system also require 

 attention, and particular care should be given to the presence of 

 feedback mechanisms and possible push— pull effects at the eco- 

 system level. 



