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. 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 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 ( mm 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 crabpolychaete 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 Diptera 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 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 ( mm 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 dollarGreen 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 Herbivores Mullet and Menhaden 1° Carnivores Bay Anchovy Top Carn Shark

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

References…cont