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 BoundariesThe 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.

• vascular flora - 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 EstuaryCharacteristics:

• 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

Coleoptera

DipteraHemiptera

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

Striped mullet Spot

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

Banded water snake

Eastern glass lizard

Diamondback terrapin

Reptiles: American alligator

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

White ibis

Red-winged blackbird

long-billed marsh wren

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

Zooplankton...cont.

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

Benthic macroinvertebrates

• Species diversity depends on 2 factors:

Substrate

silt, sand, or clay - high diversity

medium to fine grain sand- low diversity

clay and either silt or fine grain sand- low diversity

Benthic macroinvertebrates

• Species diversity depends on 2 factors:

Salinity

< 5 ppt (oligohaline waters)

5-18 ppt (mesohaline waters)

> 18 ppt

(polyhaline/euhaline waters)

* Species diversity tends to increase with an increase in salinity

Benthic macroinvertebrates amphipods, polychaetes, bivalves

Benthic macroinvertebrates

Sand dollar Green Jacknife Clam

Commercially important macroinvertebrates

White shrimp

Brown shrimp

Blue crab

Fishes

• Species composition is abundant and diverse

Atlantic croaker

Spot

Trophic relationships

Primary Producers

HerbivoresMullet and Menhaden

1° Carnivores

Bay Anchovy

Top CarnShark

Reptiles

• One of the only reptiles truly found in the subtidal estuarine system is the:

Diamondback terrapin

Birds• Birds use the subtidal region for:

resting and feeding

•Species include:

Herring gull- scavenger

Ring-billed gull- scavenger

Laughing gull-scavenger

Brown pelicans- piscivore

Royal terns- piscivore

ect….

Birds

Herring gull

Ring-billed gull

Laughing gull

Birds

Brown pelican

Royal Tern

Mammals

• Only 2 consistent components of the subtidal estuarine system:

River otter

Mammals

• Only 2 consistent components of the subtidal estuarine system:

Atlantic bottlenosed dolphin

References

http://www-staff.lboro.ac.uk/~cvcfs/simulations/estuarinedynamics/frame.htmlhttp://www.tulane.edu/~eeob/Courses/Ecology_Materials/estuary_biome.htmlhttp://inlet.geol.sc.edu/nerrsintro/nerrsintro.htmlhttp://riceinfo.rice.edu/armadillo/Galveston/Chap8/ch8.estuarine.food.htmlhttp://www.geog.ucl.ac.uk/~jfrench/EEI.htmlhttp://www.nwrc.gov/about/web/nutrient.htmlhttp://www.ucc.uconn.edu/~skoog/Michaelb.htmhttp://www.environment.gov.au/portfolio/anca/mpa/c_ray.htmlhttp://www.epa.gov/nep/http://www.estuarylive.org/http://www.epa.gov/ceisweb1/ceishome/atlas/maiaatlas/maia__condition_of_the_mid.htmlhttp://pelotes.jea.com/fidcrab.htmhttp://oak.conncoll.edu/~dmwhi/milfordpaper.htmlhttp://www.tpwd.state.tx.us/expltx/eft/gulf/cspecies/wildlife.htmhttp://www.st-and.ac.uk/~seeb/pheromone/pcWorms.html

References…cont

http://ag.arizona.edu/tree/eukaryotes/animals/arthropoda/hexapoda/hemiptera/hemiptera.htmlhttp://www.mdarchives.state.md.us/msa/mdmanual/01glance/html/symbols/reptile.htmlhttp://www.mbr-pwrc.usgs.gov/id/framlst/i1840id.htmlhttp://www.kwic.com/~pagodavista/harrier.htmhttp://www.cviog.uga.edu/Projects/gainfo/wildlife/marshrabbit.htmhttp://employeeweb.myxa.com/rrb/Audubon/VolV/00541.htmlhttp://donb.furfly.net/malheur/birds/willet.htmlhttp://www.otternet.com/galleries/naotter/http://www.csc.noaa.gov/otter/htmls/ecosys/ecology/estuary.htm#tophttp://www.bio.swt.edu/Lavalli/guides/phylum_arthropoda.htmhttp://endangered.fws.gov/i/B2S.htmlhttp://www.camacdonald.com/birding/DesJardin/LaughingGull.html