Estuarine Dynamics David Nash and Jenny McDaniel
Overview • Definition of estuary • Estuarine influences • Intertidal estuary • Subtidal estuary • Producers • Consumers • Decomposers
What is an estuary? Cowardin et al. 1977: “ ...deepwater tidal habitats and adjacent tidal wetlands which are usually semi-enclosed by land, but have open, partially obstructed, or sporadic access to the open ocean and in which ocean water is at least occasionally diluted by freshwater runoff from the land.”
Estuarine Boundaries The limits of an estuarine system extend: 1) upsteam and landward to the place where ocean-derived salts measure less than 0.5 ppt during the period of average annual low flow
Estuarine Boundaries The limits of an estuarine system extend: 2) - seaward to a line closing the mouth of a river,bay, or sound - seaward to a line enclosing an offshore area of diluted seawater with typical estuarine flora and fauna - seaward limit of wetland emergents, shrubs or trees where these plants grow seaward of the line closing the mouth of a river, bay, or sound
Estuaries: 2 Major subdivisions • Intertidal - those areas where the substrate is periodically exposed and inundated by tides including the associated splash zone • Subtidal- those areas where the substrate is continuously submerged
Estuarine influences • oceanic tides • currents • precipitation • runoff from the land • evaporation • wind • river flow • meteorological pressure centers
Estuarine influences...cont. • salinity • size and shape of estuary • water temperature • turbidity • substrates • erosion • deposition • pollution
Intertidal Estuary • Characteristics: • high environmental stress • low species diversity • often dominated by salt marshes and flats • transitional area b/w uplands and permanently flooded estuaries and bays • includes both terrestrial and marine organisms
Intertidal Estuary: Producers • Species occurrence limited by: • salinity • drainage • temperature • tidal influence
Intertidal Estuary: Producers • nonvascular flora- various micro/macrophytes including diatoms, blue- green algae, red and brown algae, etc. • vascularflora - diversity is low, Spartina alterniflora tends to be the dominant species.
Producers: nonvascular microphyte substrates • mud flats • marsh pannes (unvegetated sand flats) • creek banks • soils of halophytic angiosperms • macroscopic algae • oyster shells • submerged marsh vegetation
Producers: nonvascular macrophyte substrates • mud flats • marsh pannes (unvegetated sand flats) • creek banks • soils of halophytic angiosperms • oyster reefs • shell banks • pilings and sea walls • surface and subsurface waters
Producers: nonvascular macrophyte substrates…cont. • dead and living spartina stems • marsh periwinkle
Producers: Vascular Flora • Influenced by: • water level fluctuations • salinity • substratum type • acidity • fire • nutrient availability • aeration
Producers: Vascular Flora…cont. • Influenced by: • temperature • light • plant competition • salt spray • animal activity • human activity
Subtidal Estuary • Characteristics: • environmental factors fluctuate more frequently and more widely than in either freshwater or seawater systems. • Abundant nutrients supplied by sediments, seawater, freshwater, precipitation, groundwater,microbial decomposition, bacterial and algal nitrogen fixation, and runoff from intertidal salt marsh and land areas.
Subtidal Estuary: Producers • Phytoplankton • Macrophytes
Subtidal Estuary: Phytoplankton • Influenced and limited by: • salinity • temperature • light intensity at surface • light intensity below surface • nutrients • pollutants
Subtidal Estuary: Macrophytes • Macroscopic algae limited by: • substrates (solid, permanent substrate often absent) • scouring action of the tides • turbidity
Subtidal Estuaries • Productivity is limited by three separate, but interdependent, units of primary production • marshes and their resulting detritus • benthic micro and macrophytes • phytoplankton
Consumers • Benthic meiofauna-animals living in the sediments (0.5-.063mm in size) • - most of these animals are nematodes with copepods second in abundance
Consumers • Benthic macroinvertebrates - animals that live in the sediments and are >0.5mm in size • - the number of these organisms is limited due to the stressful environmental conditions (salinity, drainage, temp, etc.) • - inverts play an important role of reworking the benthic sediments (burrowers, etc.)
Benthic macroinvertebrates • marsh periwinkle ribbed mussel oyster reef
Benthic macroinvertebrates fiddler crab • polychaete worm
Insects • Insects are significant pathways of energy flow within the marsh ecosystem • Insect fauna is varied and abundant in almost all salt marsh habitats • Diptera (flies, mosquitoes, and midges), Coleoptera (beetles), and Hemiptera (true bugs) comprise about 75% of the species in marshes
Insects Diptera Coleoptera Hemiptera
Insects • Most non-aquatic species tend to avoid areas subject to tidal inundation • Carnivrous insects- most common are spiders, beetles, and mosquitoes • Low plant diversity limits food sources for herbivorous insects examples: grasshoppers, ants • Insects are also important prey items for predators such as birds (marsh wren)
Fishes • Most resident species move in and out with the tide or remain in standing pools of water - example: mummichog, sheepshead minnow • Other species use the marsh for different life stages • - example: mullets, spotted seatrout, spot
Fishes Spot Striped mullet Spotted sea trout
Amphibians and Reptiles • Few species are represented in the saltmarshes of the southeast US • Amphibian examples: Eastern narrowmouth toad Southern leopard frogs
Reptiles Eastern glass lizard Banded water snake Diamondback terrapin
Birds • Salt marsh vegetation serves as a base for reproduction, feeding, and roosting activites • - examples: • long-billed marsh wren- defends its feeding and breeding territory individually • white ibis- colonial nesters remove large amounts of marsh grasses to build nests • red-winged blackbirds- roost in marsh
Birds long-billed marsh wren White ibis • Red-winged blackbird
Birds • Presence of birds helps to cycle nutrients • - dispersal of seeds • - fecal material fertilizes marsh plants and has been shown to enhance growth
Birds • Wood stork- federally endangered species that relies on fish found in marshes for primary food source
Birds • Great egret- year round resident in estuarine marsh habitat. Feeds on small fish, shrimp, and crabs.
Birds • Clapper rail- permanent resident that feeds, nest, and roosts in the Spartina marsh.
Birds • Willet- shorebird that is seen seasonally in the estuarine marsh system. Feeds on crustaceans, molluscs, and annelids.
Birds • Marsh hawk- raptor that preys on clapper rails and small mammals.
Mammals • Herbivores: • Marsh rabbit-feeds on cordgrass, but populations are limited due to predation by marsh hawks • White-tailed deer-tends to graze in the higher marsh regions
Mammals • Omnivore • Marsh rice rat- remains persistently in the marsh. Feeds on cordgrass, crabs, and insects.
Mammals • Carnivores • Racoons- feeds heavily on crustaceans, molluscs, and bird eggs and young
Mammals • Carnivores • River otter- depends on fishes and crabs. Has few predators, yet populations remain low.
Decomposers: bacteria and fungi • 3 primary roles: • decomposition of dead organic matter • conversion of indigestible plant material (cellulose) to a form that is readily used by detritivores and deposit feeders • conversion of dissolved organic and inorganic materials into consumable particulate matter
Subtidal estuarine consumers Zooplankton - animals that live in the water column and are at the mercy of the currents - able to tolerate salinity fluctuations up to 12ppt during a single tidal cycle - zoo. biomass is greatest in estuaries - serve important role in estuarine food web - food for many larval and juvenile fish
Zooplankton...cont. Human impacts: Effluent discharges- indirect effects Channel dredging- decrease primary production which in turn lowers zoo. populations Pesticides and heavy metals- not only effect zoo.populations, but also impact larval fish and invertebrates by causing developmental delays, abnormalities, and death
Benthic meiofauna • Benthic meiofauna-animals living in the sediments (0.5-.063mm in size) • - most of these animals are copepods, including both interstitial and burrowing species • - these animals are highly sensitive to both temperature and oxygen fluctuations