card
179

estuaries

OLogy Series
place
card
179

estuaries

OLogy Series
place

Estuaries are places where a river meets the sea. This ever-changing ecosystem is bursting with life. Saltwater from the sea, brought in by the tides, mixes with freshwater from the river. This constant blending gathers and distributes nutrients. Estuaries are among the most abundant regions on Earth, teeming with vast blooms of plankton and algae, huge schools of fish, and countless numbers of invertebrates.

Estuaries Under Attack!
Even if it is done with the best intentions, the introduction of a new species into an estuary can be dangerous for the species already living there. In the 1940s, populations of Eastern oysters were disappearing in the Chesapeake Bay estuary. Scientists tried to help by adding Pacific oysters to the ecosystem. But the new oysters carried a parasite that killed up to 95 percent of the native oysters. Sometimes species are added to an ecosystem by accident. In 2000, a "killer alga" appeared off the coast of Carlsbad, California, threatening to overrun native plants and destroy the food web. Typically a tropical species, the alga may have been introduced to California by people dumping the water out of their home aquariums.

The lined sea horse lives in Northeastern estuaries. One unusual fact about sea horses is:

they are closely related to horses

they survive by eating grass on the estuary floor

males give birth to baby sea horses

Are you right?

Correct!

Female sea horses lay their eggs in a pouch in the male's belly. He carries the fertilized eggs and eventually gives birth to a group of tiny babies.

Fish cannot survive in estuaries because the salinity level changes when freshwater mixes with saltwater.

Fact
or
Fiction
?

Fiction

In fact, some species thrive in these changing conditions. Estuaries around the world provide some of the biggest harvests of fish, mollusks, and crustaceans.

Description: a place where incoming seawater mixes with outgoing freshwater from rivers
Locations: around the world
Number in the United States: 102 estuaries along the coastlines of the U.S.
Threats: overfishing, introduction of alien species, pollution
Significance: provide nearly half of the world's commercial fish harvest

Image credits: courtesy of NOAA, Mary Hollinger.