LIFE IN THE MARINE ENVIRONMENT SOME BASICS OF BIOLOGY

Estuaries: Where Rivers Meet the Sea

1What is an EstuaryAn Estuary is where freshwater from rivers merges with the ocean and is bordered by extensive wetlands (mudflats or saltmarshes)

2Characteristics of EstuariesSalinity varies spatially and over the course of a day as the tides move in and outNutrients from the rivers enrich estuarine waters making them one of the most biologically productive environments on earthSalt marsh grasses, algae, and phytoplankton are the major producersMany organisms are found in the muddy bottomEstuaries rank among the environments most affected by humans

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Functions and Values of EstuariesProvide open space and recreationProvide natural flood controlPurify the waterProduce oxygenAre outdoor laboratories for scientists and educatorsProvide sediment traps and erosion controlServe as nurseries for marine fishesProvide homes for endangered speciesProvide habitat for migrating, wintering and breeding birdsServe as repositories for native plants and animalsTypes of Estuaries Four basic groups based on their originsDrowned River Valley or Coastal Plain Fig. 12.1 formed as a result of the sea invading lowlands and river mouths. This is the most common type of estuary.

6Types of EstuariesBar-built estuary Fig. 12.1 formed when a barrier island or sand bar separates a section of the coast where freshwater enters. (Pictured below is an aerial view of Cape Hatteras, North Carolina.)

7Types of EstuariesTectonic Estuary formed as a result from sinking land due to movements of the earths crust. San Francisco Bay formed in this way.

8Types of EstuariesFjords Fig. 12.2 formed in a deep valley created by a retreating glacier. (Kenai Fjord National Park, Alaska)

9Physical Characteristics of Estuaries unique because of mixing of salt and freshwaterSalinity fluctuates as the tides move seawater in and out of an estuary.Organisms are subjected to these changes every day and therefore have adapted to these conditions.Other factors that influence salinity include; the shape of the estuary, the bottom, wind and evaporation, and freshwater runoff10Salt Wedge a layer of denser, saltier seawater that flows along the bottomPhysical Characteristic - Salinity

Salt Wedge11Sand and other coarse material settle out first near the river mouthFiner particles settle out into main body of water, therefore most estuaries are soft mud (silt & clay) which is very dense and rich in organic materialDecomposition by bacteria depletes oxygen in the substrate and produces hydrogen sulfide (rotten egg smell)Tidal flow keeps water in estuaries oxygen rich

Physical Characteristic - Substrate12Close up of Estuary Sand

13Physical CharacteristicsTemperature fluctuates widely because of tides, organisms that are exposed at low tides also face seasonal temperature changesTurbidity estuaries usually have large amounts of suspended sediments which can reduce water clarity

14Maintaining the proper salt and water balance is essential for all organisms.Organisms that live in estuaries must cope with rapid changes in salinity.Most estuarine organisms are marine species that have evolved to tolerate low salinities.Coping with Salinity15Euryhaline species can tolerate a wide range of salinities.

16Stenohaline species can only tolerate a narrow range of salinities (yellow fin tuna)

17Osmoconformers (molluscs and worms) osmotic balance is maintained by changing with the salinity of the water

18Osmoregulators keep internal salt balances constant despite salinity levels of the water in which they live

19Osmoconformer vs Osmoregulator

Osmoconformer vs Osmoregulator

Coping with SalinityMarine fish have a lower salt concentration than seawater, therefore tend to loose water; adaptations to maintain homeostasis include (Fig. 4.14)Drinks seawaterExcretes excess salt through gillsExcretes small volumes of concentrated salty urine

22Coping with SalinityAdaptations of other marine organismsSea turtles/sea gulls/sea lions have glands near the eyes that excrete salty tears (Fig. 4-15)Mangroves/spartina grass excrete excess salt through leaves

Salt crystals on spartina grass23Coping with Salinity Pickleweed accumulates large amounts of water to dilute the salts they take up.

Most animals burrow or live in permanent tubes beneath the sedimentInhabitants tend to be stationary or slow movingSalinity fluctuations are less drastic than in the water columnOrganisms overcome the depletion of oxygen by:Pumping oxygen rich water into their burrowsSome have blood that contains hemoglobin, an oxygen carrying moleculeAdapting to the Mud25Adapting to the Mud

26Different types of communities are associated with various estuariesOpen Water community includes those organisms that come and go with the tide (plankton, fishes, jellies). Other types of communities are permanent parts of the ecosystem, these include:MudflatsSalt MarshesMangrove ForestsSea-grassesOyster Reefs

Estuarine Communities

27Organisms in this type of community include phytoplankton, zooplankton, and marine fish that are flushed in and out by the tides.Many types of marine fish and shrimp use estuaries as nurseries for their young.Some fish migrate through estuaries.Anadromous marine fish that live their lives in the sea but return to freshwater to breed (salmon)Catadromous freshwater fish that migrate to the sea to breed (freshwater eels)Open Water Community28

Open Water CommunityZooplankton29Open Water CommunityPhytoplankton

30Open Water CommunityAnadromous

31Open Water CommunityCatadromous

32Low tides expose organisms to desiccation, fluctuating temperatures and salinity, and predation.Primary produces consist of diatoms, bacteria, and some algaeConsumers are typically burrowing deposit and suspension feeders that feed on detritusMudflat Communities33

Mudflat Communities34Mudflat Communities

35Mudflat Communities

36Mudflat Communities

37Mudflat Communities

38Mudflat Communities

39Mudflat Communities

40Mudflat Communities

41Salt Marsh CommunitiesSalt marshes are grassy areas that extend along the shores of estuaries and sheltered coasts in temperate and subpolar regions.Salt marshes are subject to the same fluctuations in salinity, temperature, and tidal changes that affect mudflats.Pronounced zonation of vegetation in salt marsh communities is a result of fluctuations in salinity, height relative to the tide, and rate of evaporationCordgrass (Spartinia alterniflora) is the most common plant found where the marsh meets the mudflat. Helps to stabilize the bottom.42Salt Marsh CommunitiesZonation depends on several factors: two important ones are salinity and nutrient availability. Salinity changes depending on these conditions:a. frequency of tidal inundation b. rainfall c. tidal creeks and drainaged. soil texture e. vegetation f. depth of water tableg. freshwater inflowNutrient availability varies considerably, especially the supply of usable nitrogen and phosphorous. Often there is not enough oxygen present in marsh soils to combine into useful nitrates and phosphates.

43Salt Marsh Communities

44Salt Marsh Communities

45Salt Marsh Communities

46Mangrove Forest CommunitiesMangrove forests are formed by mangroves, tropical and subtropical trees and shrubs adapted to inundation by seawater.Grow on protected coasts where muddy sediments accumulate.The red mangrove is found along the coast of Florida. Can be identified by its prop roots.47Mangrove Forest Communities

48Mangrove Forest Communities

49Mangrove Forest Communities

50Mangrove Forest Communities

Coral growing on amangrove root.51Mangrove Forest Communities

Snapper living among the mangrove roots.52Mangrove Forest CommunitiesCattle egret and nest in mangrove.

53Sea Grass CommunitiesRoots help to stabilize the sediment and provide shelter to organisms

Florida lobster(yummy)54Oyster Reef Communities

55Oyster Reef CommunitiesFriends of Hunting Island help resort oyster reefs.

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