Problem:
Summarize: The type and abundance of plankton inhabiting estuaries vary tremendously with the currents, salinity, and temperature. The murky water restricts the penetration of light and can limit primary production by phytoplankton, even when the density of plankton is typically very high. Most of the phytoplankton and zooplankton in small estuaries are marine species flushed in and out by the tides. Larger estuaries can also have their own, strictly estuarine, species. One reason many of the world's great cities developed around estuaries is the rich supply of fish and shellfish in or near estuaries. Many species of commercially important fishes and shrimps use estuaries as nurseries for their young, taking advantage of the abundant food and relative safety from predators. About 90% of the marine commercial catch in the northern Gulf of Mexico, for example, is of species that depend on estuaries at some point in their lives. A relatively rich variety of fishes live in most estuaries. Many are the juveniles of marine species that breed at sea but use estuaries as nurseries. Examples are the menhaden, anchovies, mullets, croakers, and many species of flatfishes. Some fishes move through estuaries during their migrations. Such fishes are either anadromous-like salmon, smelts, and shad-or catadromous-like freshwater eels. Relatively few fishes spend their entire lives in estuaries. Killifishes are one example. Shrimps and crabs are often common in estuaries, and many commercially valuable species of invertebrates as well as vertebrates use estuaries as nurseries. Need Assignment Help?