"It's all connected"—an established commandment of environmentalism. This concept also holds true for marine and coastal habitats, connected to each other through the water cycle where rain and snowmelt flow overland and/or underground to rivers, streams, and directly into the sea. Tides, waves, and currents further transport materials through the water and along the shore.

The result is an interconnected web of habitats where nutrients, sediment, and even pollution are transferred from place to place, changing the habitats along the way. For example, the great plant productivity in salt marshes generates large quantities of nutrients, which are flushed away by the tide and then nourish nearby estuaries, bays, and even open ocean ecosystems. This nutrient exchange enhances the growth of rooted and free-floating plants, forming the basis of the food web in these areas. When sediments (including sand, mud, and silt) are carried to rivers and streams that wash them to the sea, larger particles settle out closer to shore, while smaller, lighter particles are carried further, settling to the bottom in quiet waters. Sediments and contaminants are also connected, with pollutants often adhering to fine-grained sediments. Similar pathways carry pesticides, oil, and other pollutants from stormwater discharges, urban runoff, and other sources throughout marine and coastal habitats.

The animals and plants of coastal and marine environments are also free to move from one habitat to the next. As discussed in Moving on Up (and Down): Habitats of the Lobster Lifecycle, many species spend different stages of their lifecycle in various habitats and require a range of habitats to survive. This concept is particularly important when it comes to nursery rounds—the coastal and marine habitats with ready hiding and feeding places for larvae and young. Whether it's the densely packed sheaths of eelgrass or salt marsh, swaying fronds of a kelp bed, or dark spaces among cobble, nursery areas provide biological and/or geological structure that protect progeny from predators. With many species, as the young grow, they spread out and populate new habitats that meet their changing needs.