3.3. SPECIFIC CONSIDERATIONS 
Inadvertent modification occurs in many forms. The most widely 
spread and most pervasive ones are various kinds of pollution. Pol- 
lutants include garbage, sewage, agricultural and industrial wastes, 
pesticide and herbicide residues, and waste heat. Future pollutants 
may include radioactive waste from nuclear reactors and salt wastes 
from desalinization plants. 
The marine environment is particularly susceptible to pollution be- 
cause most avenues of disposal terminate in the oceans. In the past, 
pollution of the oceans has been of little concern because the oceans 
have always been considered so large. However, most pollution occurs 
at the margins where human activities are centered and the concen- 
trated wastes remain for varying times in this region before dispersal 
into the vast open ocean. Moreover, the potential for pollution is in- 
creasing as more of man’s activity is concerned with the oceans. It 
was once thought that rivers could not be polluted seriously, but the 
truth is now obvious. It is also becoming evident that large bodies 
of water such as the Great Lakes can be drastically altered and reduced 
in value as natural assets. We have paid a great price to learn these 
lessons and should not make similar mistakes as we inhabit and exploit 
the oceans. 
Fishing and other means of harvesting plant and animal popula- 
tions have produced dramatic changes in distribution and abundance 
of marine organisms. Classical cases in this category are found 
among the marine mammals: especially baleen whales in the Antarctic ; 
blue California gray whales; sea otters; fur seals, and southern and 
northern elephant seals. Habitat destruction by improper fishing 
techniques have affected our biological resources. An example of the 
latter is oysterbed destruction. 
Introduction of organisms into areas has sometimes been extremely 
successful and valuable. Atlantic oyster culture in Nantucket and 
Martha’s Vinyard sounds off Cape Cod and importing Japanese seed 
oysters to the Pacific Northwest are examples. In other cases intro- 
ductions have been disastrous. Predatory Japanese snails introduced 
into the Black Sea in 1949 virtually eliminated mussel populations and 
apparently caused a sharp decline in flounder fisheries. Introductions 
have been planned or inadvertent. A great number of inadvertent 
introductions into the Atlantic and Pacific Oceans may result from 
opening the proposed sea-level canal across Central America. De- 
liberate modification of the coastline, such as channel dredging for 
marinas, shoreline modification for beach stabilization and filling in 
marsh areas for developmental purposes, Pose serious problems. 
These modifications are occurring in estuaries which are important 
natural resources for recreation and food production. These areas 
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