Editing Estuary (section)

==Implications for marine life==
Estuaries are incredibly dynamic systems, where temperature, salinity, turbidity, depth and flow all change daily in response to the tides. This dynamism makes estuaries highly productive habitats, but also make it difficult for many species to survive year-round. As a result, estuaries large and small experience strong seasonal variation in their fish communities.<ref>{{cite thesis|last=Osborn|first=Katherine|title=Seasonal fish and invertebrate communities in three northern California estuaries|date=December 2017|degree=M.S.|publisher=Humboldt State University|url=https://digitalcommons.humboldt.edu/etd/101/}}</ref> In winter, the fish community is dominated by hardy marine residents, and in summer a variety of marine and anadromous fishes move into and out of estuaries, capitalizing on their high productivity.<ref>{{Cite journal|last=Allen|first=Larry G.|date=1982|title=Seasonal abundance, composition and productivity of the littoral fish assemblage in Upper Newport Bay, California|url=https://spo.nmfs.noaa.gov/sites/default/files/pdf-content/1982/804/allen.pdf|journal=Fishery Bulletin|volume=80|issue=4|pages=769–790}}</ref> Estuaries provide a critical habitat to a variety of species that rely on estuaries for life-cycle completion. Pacific Herring (''Clupea pallasii'') are known to lay their eggs in estuaries and bays, surfperch give birth in estuaries, juvenile flatfish and rockfish migrate to estuaries to rear, and [[Fish migration|anadromous]] [[Salmonidae|salmonids]] and [[lamprey]]s use estuaries as migration corridors.<ref>{{cite journal |doi=10.3354/meps247281 |jstor=24866466 |title=Evidence of connectivity between juvenile and adult habitats for mobile marine fauna: An important component of nurseries |journal=Marine Ecology Progress Series |volume=247 |pages=281–295 |year=2003 |last1=Gillanders |first1=BM |last2=Able |first2=KW |last3=Brown |first3=JA |last4=Eggleston |first4=DB |last5=Sheridan |first5=PF |bibcode=2003MEPS..247..281G |doi-access=free |hdl=2440/1877 |hdl-access=free }}</ref> Also, [[Bird migration|migratory]] bird populations, such as the [[black-tailed godwit]],<ref>{{cite journal |doi=10.1038/35086568 |pmid=11473317 |title=The buffer effect and large-scale population regulation in migratory birds |journal=Nature |volume=412 |issue=6845 |pages=436–438 |year=2001 |last1=Gill |first1=Jennifer A. |last2=Norris |first2=Ken |last3=Potts |first3=Peter M. |last4=Gunnarsson |first4=Tómas Grétar |last5=Atkinson |first5=Philip W. |last6=Sutherland |first6=William J. |bibcode=2001Natur.412..436G |s2cid=4308197 }}</ref> rely on estuaries.

Two of the main challenges of estuarine life are the variability in [[salinity]] and [[sedimentation]]. Many species of [[fish]] and [[invertebrate]]s have various methods to control or conform to the shifts in salt concentrations and are termed [[osmoconformer]]s and [[osmoregulator]]s. Many animals also [[burrowing|burrow]] to avoid [[predation]] and to live in a more stable sedimental environment. However, large numbers of bacteria are found within the sediment which has a very high oxygen demand. This reduces the levels of oxygen within the sediment often resulting in partially [[Anoxic waters|anoxic]] conditions, which can be further exacerbated by limited water flow.

[[Phytoplankton]] are key primary producers in estuaries. They move with the water bodies and can be flushed in and out with the [[tide]]s. Their productivity is largely dependent upon the [[turbidity]] of the water. The main phytoplankton present are [[diatoms]] and [[dinoflagellates]] which are abundant in the sediment.

A primary source of food for many organisms on estuaries, including [[bacteria]], is [[detritus]] from the settlement of the sedimentation.