as a population of organisms increases , the resources used by those organisms will decrease & an bacterium requires oxygen for survival / to breathe ->  as a population of bacteria increases the amount of oxygen will decrease  as a population of bacteria increases the amount of oxygen will decrease & an algal bloom causes an increase of bacteria in an environment ->  an algal bloom causes the amount of oxygen in an environment to decrease  an animal / bacterium requires oxygen for survival / to breathe & a fish is a kind of animal ->  fish require oxygen to survive  fish require oxygen to survive & a required resource being low in availability has a negative impact on the something that requires that resource ->  oxygen being low in availablilty has a negative impact on fish  oxygen being low in availablilty has a negative impact on fish & danger has a negative impact on a thing ->  oxygen being low in availabliltyis a danger to fish  an algal bloom causes the amount of oxygen in an environment to decrease & oxygen being low in availabliltyis a danger to fish ->  an algal bloom is a danger to fish because it decreases the amount of oxygen in an environment  an algal bloom is a danger to fish because it decreases the amount of oxygen in an environment & oxygen levels are a measure of the amount of oxygen in an environment -> an algal bloom is a danger to fish because it decreases the oxygen levels in an environment