河口生态学Lecture_7bEstuarineCommunities

1、 2006 Thomson-Brooks ColeLife in an Estuary Many are species are generalists, and can feed on a variety of foods depending on what is available Species that tolerate temperature and salinity changes can exploit estuaries and grow large populations So, estuaries contain abundant individuals from rela

2、tively few species 2006 Thomson-Brooks ColeLife in an Estuary Maintaining osmotic balanceosmoconformersanimals with tissues and cells that tolerate dilution e.g. tunicates, jellyfishes, sea anemones 2006 Thomson-Brooks Cole 2006 Thomson-Brooks ColeLife in an Estuary Maintaining osmotic balanceosmore

3、gulatorsanimals that maintain an optimal salt concentration in their tissues, regardless of the salt content of the environment concentrate or excrete salts, or shield themselves from their environment 2006 Thomson-Brooks Cole 2006 Thomson-Brooks ColeLife in an Estuary Remaining stationary in a chan

4、ging environmentnatural selection favors benthic organisms because of the difficulty in staying still to feed in constantly-moving waternon-benthic animals (e.g. crustaceans, fishes) maintain position by actively swimming or by moving back and forth with the movement of the tides 2006 Thomson-Brooks

5、 ColeLife in an Estuary Estuaries as nurserieshigh level of nutrients + few predators makes a great habitat for juvenilesjuveniles live in the estuary until they grow large enough to be successful in the open seae.g. striped bass, shad, bluefish, blue crabs, white shrimp 2006 Thomson-Brooks ColeEstu

6、arine Communities Many hardy organisms are euryhalinespecies that can tolerate a broad range of salinity Oyster reefsreefs form from numerous oysters growing on the shells of dead oystersprovide a habitat for many organisms, which may depend on oysters for food, protection, and a surface for attachm

7、entoyster drill snails prey on oysters 2006 Thomson-Brooks Cole 2006 Thomson-Brooks ColeEstuarine Communities Mud flatscontain rich deposits of organic material + small inorganic sediment grainsbacteria and other microbes thrive in the mud, producing sulfur-containing gasesmud provides mechanical su

8、pport for organismscohesiveness permits construction of a permanent burrow 2006 Thomson-Brooks ColeEstuarine Communities Mud flats (continued)mud flat food webs main energy base = organic matter consisting of decaying remains and material deposited during high tides bacterial decomposition channels

9、organic matter to other organisms, and recycles nitrogen and phosphate back to the sea floor deposit feeders prey on bacteria larger organisms eat secondary consumers of bacteria, and so forth 2006 Thomson-Brooks Cole 2006 Thomson-Brooks ColeEstuarine Communities Mud flats (continued)animals of the

10、mud flats most are burrowers living just below surface closely-packed silt prevents good water circulation, so many animals have a “snorkel” soft-shelled clams use a siphon to filter feed and obtain oxygenated water, then metabolize anaerobically during low tide lugworms are common mud flat resident

11、s innkeeper worms house many other organisms in their burrows, as do ghost shrimp 2006 Thomson-Brooks Cole 2006 Thomson-Brooks ColeEstuarine Communities Seagrass meadowsseagrass productivity depends on the ability of seagrasses to extract nutrients from the sediments depends on activity of symbiotic

12、, nitrogen-fixing bacteria also depends on productivity of algae that grow on and among seagrasses nutrients from drawn from sediments are released into the water by seagrasses, for use by algae 2006 Thomson-Brooks ColeEstuarine Communities Seagrass meadows (continued)seagrass food webs seagrasses a

13、re tough, and seldom consumed directly by herbivores seagrasses are a food source to many animals as detritus, when their dead leaves are eaten by bacteria, crabs, sea stars, worms, etc. organisms from other communities feed in seagrass meadows during high tide, exporting nutrients to other communit

14、ies 2006 Thomson-Brooks Cole 2006 Thomson-Brooks ColeEstuarine Communities Seagrass meadows (continued)seagrass meadows as habitat epiphytes and epifauna attach to seagrasses filter feeders live in the sand among blades rhizoids and root complexes provide more permanent attachment sites, and protect

15、 inhabitants from predators larvae and juveniles of many species live here, protected from predators by changing salinity, plentiful hiding places, and shallow water 2006 Thomson-Brooks Cole 2006 Thomson-Brooks ColeEstuarine Communities Salt marsh communitiesdistribution of salt marsh plants low mar

16、shregion covered by tidal water much of the day and typically flushed twice each day by the tides high marshregion covered briefly by saltwater each day and only flushed by the spring tides cordgrass dominates the low marsh short, fine grasses dominate the high marsh 2006 Thomson-Brooks ColeEstuarin

17、e Communities Salt marsh communities (continued)salt marsh productivity tides bring in replenishing supplies of nutrients most primary production supports detrital food chains bacteria eat decaying plant material deposit feeders eat bacteria some salt marshes export large amounts of detritus to near

18、by communities; in others, resident organisms consume most of the detritus 2006 Thomson-Brooks Cole 2006 Thomson-Brooks ColeEstuarine Communities Salt marsh communities (continued)animals of the salt marsh permanent residents include periwinkles, tidal marsh snails, ribbed mussels, purple marsh crab

19、s, fiddler crabs, amphipods, grass shrimp burrowing animals play an important role in bringing nutrient-rich mud from deeper down to the surface, while oxygenating deeper sediments tidal visitors that come to the salt marsh to feed include predatory birds, herbivorous animals from land, fishes and b

20、lue crabs 2006 Thomson-Brooks Cole 2006 Thomson-Brooks ColeEstuarine Communities Salt marsh communities (continued)succession in salt marshes salt marshes can be the first stage in a succession process that produces more land roots of marsh plants trap sediments until the area becomes built up with

21、sand/silt that combine with organic material to make mud mud islands appear and merge, and high tide covers less and less of them tall cordgrass is replaced by short cordgrass, which is replaced by rushes and then land plants 2006 Thomson-Brooks ColeEstuarine Communities - MangalsSalt marshes are in

22、tertidal flats covered by grassy vegetation. Marshes are most commonly found in protected areas with a moderate tidal range, such as the landward side of barrier islands. Marshes flood daily at high tide and then drain through a series of channels with the ebb tide. They are one of the most producti

23、ve environments. Marshes can be divided into two parts: Low salt marshes and High salt marshes. Distribution and density of organisms in salt marshes strongly reflects availability of food, need for protection, and frequency of flooding.12-3Salt MarshesSalt Marsh SuccessionA salt marsh is born by th

24、e arrival of a seed or the rafting of a plant of the cord grass Spartina alterniflora. The grass spreads asexually by means of a subterranean rhizome system. The grass becomes dense and forms a baffle, which encourages the deposition of fine particulate sediment, including organic matter (salt marsh

25、 peat). This, in effect, causes a rise of the sediment surface and makes the habitat more terrestrial. As this happens, other somewhat less salt-tolerant grasses are able to invade. Eventually, this series of invasions and takeovers leads to a vertical zonation of grasses and a spread of the entire

26、marsh system.SAS = Spartina alterniflora - short formSP = Spartina patens, the next higher grass speciesBorder of Spartina patens - Spartina alterniflora zoneIn the foreground we see the Spartina patens zone, which is higher (though that is hard to tell from the photo) than the S. alterniflora zone

27、(taller grass in the background). S. patens is less salt tolerant than S. alterniflora.Marsh System Cross-Sectional ViewThis is a schematic cross section of a marsh with creeks. Note the tall form of Spartina patens, which tends to live adjacent to creek edges, which are bathed in nutrient-rich wate

28、r. The short form lives in higher sites away from creek edges. The ribbed mussel Geukenzia demissa often lives among Spartina spp. and its production of nitrogen-rich feces and pseudofeces enhances grass growth.Ribbed Mussel Geukenzia demissaThe high intertidal marsh mussel Geukensia demissa is ubiq

29、ui-tous in Spartina salt marshes. The late Charles Lent showed that this mussel was capable of breathing air, and often got more of its oxygen from air than from water.The diagram at left shows that Geukensia demissa is more elongate than the mussel Mytilus edulis, and lives semi- infaunally in the

30、sediment, with byssal threads attached to sedimentary grains or rhizomes of Spartina. Marsh mussels can be quite densely packed. Mark Bertness and colleagues demonstrated that this mussel enhances the growth of Spartina. The mechanism may relate to biodeposition of nitrogen-rich feces and pseudofece

31、s. The byssal threads of this mussel also help bind the sediment and may retard erosion. Another common salt marsh resident, the fiddler crab Uca pugnax, also aids in Spartina growth by burrowing and aerating the sediment. Note the barnacles attached to mussel shells, which is possible owing to the

32、mussels semi-infaunal habit. The aerenchymal tissue allows Spartina to exchange gases, even when surrounded by an anoxic soil. The tissue in this photograph is visible as a series of circular passageways around the periphery. Plants cannot use nutrients efficiently without oxygen, so this tissue all

33、ows a connection between the aerobic leaves to the stems, that are surrounded usually by anoxic water. Salt Marsh in Fall In the fall, Spartina leaves senesce and eventually calve off at the base. This material then is deposited on the sediment surface. By the time the particulate organic material i

34、s deposited on the surface, nearly all nitrogen has been removed by microbes, so it is very carbon rich and nitrogen poor. The carbon is mainly in the form of cellulose, which is largely indigestible by invertebrates. The senesced leaves accumulate on the sediment surface as shown at left. This mate

35、rial will smother any grass beneath, but a high spring tide or a storm may remove it all quite rapidly and transport it out of the marsh system to the shelf. Several species of Salicornia can be found in eastern American Spartina salt marshes in the highest part of the intertidal zone. They are all

36、very salt tolerant. This plant is only about 5 cm high. 2006 Thomson-Brooks ColeEstuarine Communities Mangrove communitiesdistribution of mangrove plants red mangroves are usually pioneering species, and grow close to the water where the amount of tidal flooding is greatest black mangroves occupy ar

37、eas that experience only shallow flooding during high tide white mangroves and buttonwoods (not true mangroves) live closest to land, but can tolerate flooding during high tide and saline soil 2006 Thomson-Brooks ColeEstuarine Communities Mangrove communities (continued)mangrove root systems shallow, widely spread root systems anchor the plants and provide oxygen for parts buried in the mud red mangroves have prop roots, and black mangroves hav