Describe conditions necessary for natural selection

Reproduction: the act or process of producing offspring.

Heredity: the mechanism of transmission of specific characters or traits from parent to offspring.

Variation in fitness of organisms . Definitions of fitness:

Variation in individual characters among members of the population.

Hope This Helps!

Shoreline environments are highly variable, both in space and time. Organisms occupying the shoreline have adapted to a certain degree of natural variation in habitat and environmental conditions. For example, the breaching of normally closed estuaries to the sea during rough/high seas and high rainfall allows juvenile fish to enter the ocean and for adult fish to enter the estuary to spawn. 
Protective structures to prevent sand loss or counteract high tides may act to disrupt this natural variation in habitat and environment. On the other hand, it must be acknowledged that due to climate change, shoreline environments are experiencing more frequent extreme conditions, such as storms and higher sea levels. Protective structures could act to provide slightly more stable environmental conditions under which certain organisms can survive.