Final answer:
Salt marshes are found at temperate to subarctic latitudes and are characterized by their wetland environment with halophytic vegetation. Estuaries, as points where fresh and saltwater mix, offer variable salinity that influences the adaptations of organisms living there.
Step-by-step explanation:
Salt marshes are coastal wetlands rich in marine life and are found at temperate or subarctic latitudes. These ecosystems are characterized by being low-lying regions that are flooded by tides and support vegetation adapted to saline conditions. Estuaries, where rivers meet the ocean, serve as nurseries for a plethora of marine species, offering a mix of fresh and brackish water with varying levels of salinity influenced by tidal movements. The unique environmental conditions of estuaries mandate that organisms develop specialized physiological and behavioral adaptations to thrive. For instance, halophytic plants possess adaptations to manage salt stress either by removing salt through specialized root filters or by pumping oxygen into their roots. In contrast, animals such as mussels and clams exert considerable energy to cope with the changing salinities, closing their shells and temporarily ceasing feeding in low salinity conditions, then resuming normal function when salinity levels become more favorable.