Marine Biology: Salt Marshes, Mangroves and Seagrass

What causes tides?

Waves caused by the gravitational pull of the moon and sun

When do spring tides occur?

During full or new moon, when the sun, earth and moon are in line

What causes maximal vertical range during spring tides?

The gravitational force of the sun amplifies that of the moon

When do neap tides occur?

When the sun, earth and moon form a right angle-quarter moon

What causes minimal vertical range in neap tides?

The gravitational effects cancel each other out

How many spring and neap tides occur each lunar month (29.5 days)?

2 of each

Why are salt marshes considered carbon sinks?

Because they are extremely efficient at carbon sequestration and carbon storage

What are the 2 reasons that salt marshes can store large quantities of carbon?

-Lots of new plant growth each year

-Anaerobic soils, carbon containing substances decompose very slowly (100 to thousands of years)

What happens when marshes are damaged or destroyed in relation to carbon?

They lose their capacity to sequester and store carbon, and end up releasing this carbon which adds greenhouse gasses to atmosphere

Carbon sequestration

Pulling carbon out of the atmosphere, it is not carbon storage

Carbon storage

Carbon that is not being released into the atmosphere (marshes)

Does more photosynthesis = more sequestration?

yes

What is Spartina alterniflora?

Smooth cordgrass

Where is Spartina alterniflora (smooth cordgrass) found?

Found lowest in the intertidal zone; longest periods of immersion are in salt water where they are more tolerant to salinity that other species

Why is the soil surrounding Spartina anoxic?

Because of regular water inundation (water that occurs above normally dry ground; flooding)

What are the leaf structures of smooth cordgrass?

Smooth, blade-like leaves that taper to a point with tiny white flowers blooming in the summer

What is the root structure of smooth cordgrass?

Strong interconnected root system with aerenchyma tissue (open space devoted to air and oxygen transport in stem). Allows connection between aerobic leaves and stems surrounded by anoxic sediment to use nutrients

Is smooth cordgrass considered a halophyte?

Yes because it has a high tolerance of salinity

What is smooth cordgrass’ adaptation to salinity?

They have salt glands that secrete excess salt through the leaf face

How does Spartina alterniflora have a mutualistic relationship with ribbed mussels (geukensia demissa)

-Mussels move nitrogen from the water column into the sediment which stimulates growth in cordgrass

-Spartina provides a refuge from predators an heat stress to mussels

How does Spartina alterniflora have a mutualistic relationship with Fiddler crabs (Uca pugnax)?

-Burrows aerate Spartina roots, thought to help mycorrhizal fungi

-Spartina binds soil, creates habitat for Fiddler crabs to burrow and feed

Do smooth cordgrass’ salt secretions deter grazing by birds and mammals?

Yes

What is an adaptation of Spartina that deters grazing?

The cellulose composition and mechanically tough leaves, but the leaves decompose and help bacteria/fungi

What organism “farm fungi” on smooth cordgrass leaf blades?

The marsh periwinkle snail (littoraria irrorata)

What is the sexual reproduction of Spartina alterniflora?

They develop flowers and set seeds

What is the mechanism for asexual reproduction in Spartina alterniflora?

Vegetative fragmentation or rhizomes (extend laterally and shoots grow upwards)

How does the rhizome system form baffle against water movement and encourages sedimentation?

Because the morphology creates a series of projections which forms a meadow

How does a single plant colonize a marsh?

Colonizes an open area of sediment by rafting or setting seed

How does marsh grass blades slow current speeds?

Because grass blades develop a density sufficient, and there is an acceleration of the deposition of fine-grained sediment

How does the salt marsh spread and evolve into a meadow?

There is a development of rising sediment surface causing the salt marsh to spread and evolve into a meadow of sediment held together by dense grass stands

How do we get peat?

From the rising sediment surface of salt marshes, when they get too high in organic matter

Where do vegetational zones in salt marshes develop from?

Develops from the interaction of competition and physiological ability to survive salt and drowning

What are the characteristics of most East coat/Gulf coast marshes?

Low to high intertidal, tall form (S. alterniflora) Short form (S. alterniflora, S patens, Juncus geradi and terrestrial shrubs)

Is Spartina perennial?

Yes severing its stem in the fall to make way for new growth in the spring

What is a floating wrack?

They are floating rafts of decaying Spartina stems. Concentrated by currents and then float up to rest on top of grass in the high marsh

What is a bare zone?

When the wrack smothers the grass that is there

How does evaporation impact the bare zone?

It creates a saline environment that can inhibit seed germination

What are the threats to salt marsh ecosystems?

Climate change effects; sea level rise. Land use change through coastal development and filling for agricultural fields. Invasive species (Phragmities australis) spreads rhizomes and shades out spartina

How are mangroves adapted to the anoxic sediments?

By air projecting and shallow roots; they have root projections into the air so underground parts of the plant root system can get oxygen

What are mangrove prop roots?

Structures that extend midway from trunk and arch downward for support

What are mangrove knee roots/pneumatophores?

Roots that direct upwards into the air

What are mangrove finer roots?

Used for gathering nutrients

How does mangroves ensure aerobic metabolism of the plants?

Oxygen is gathered and directed into the highly chambered, upward directing roots, which transport oxygen to below ground tissues

Are mangroves salt tolerant?

Yes because of various adaptations and the valdose layer

What is the valdose layer?

It is the sediment layer which mangrove roots penetrate into that have a high salt content. Lower salinity than full-strength seawaters because of rainfall

What are the 2 varying adaptations to salt?

-One group of species has salt glands, which secrete salt from the leaves

-Roots are capable of reducing salt uptake by filtration system. Stores Na in vacuoles to maintain osmotic gradient

What is mangrove vertical zonation impacted by?

Tolerance to salt water intrusion, seedling dispersal and invertebrate predation on seedlings

The red mangrove (Rhizophora mangle) in South FL

Dominates the seaward part of the mangrove forests and is the first species to colonized unvegetated shorelines. Prop roots which extend into the water and tolerates full strength seawater and tidal inundation

The black mangrove (Avicennia mangle) in South FL

Lives shoreward of red mangroves and tolerates only occasional sea water inundation, usually at highest tides

How do red mangrove seeds germinate?

Germinate while still attached to the parent plant

How do mangroves support biodiverse communities?

-prop roots of mangrove extend into open sea water and support diverse invertebrate and seaweeds

-Flat tree oyster attaches to roots and live on trunks (barnacles and snails)

-Frequent leaf falls enhance supply of organic matter

Where are sea grass beds found?

Soft sediments, from the low water mark to 3-5 meters, temperate to tropical zone

Do seagrass beds have well defined boundaries?

Yes

How do seagrasses benefit the environment?

Through modification of the physical environment, creation of habitat, foundation of coastal food webs and blue carbon

How do seagrass beds modify the physical environment?

-produce oxygen

-absorb excess P, N and act as a nutrient pump to release nutrients from sediment into nutrient poor areas

-Blades slow water flow and roots/rhizomes trap/stabilize sediment to improve water quality and erosion

How do seagrass beds create habitat?

-Dense leaves are shelter for invertebrates

-Epiphytes live directly on seagrass blades

-Habitat for smaller organisms attracts larger organisms

How do seagrass beds create the foundation of coastal food webs?

-Herbivores/grazers directly eat leaves (manatees, dugongs, green sea turtles)

-Epiphytes fix N and make it available for large organisms while small inverts graze on epiphytes

-Decomposing seagrass leaves support decomposing organisms

How do seagrass beds help blue carbon?

-Sequester and store large amounts of carbon from atmosphere

-Carbon stored underground and dead/decaying plant

-Responsible for 11% of all organic carbon buried in ocean

Where is there a higher density of seagrass?

High density at lower latitudes

What is the general anatomy of seagrass?

Roots, rhizome, shoot, flower and blade

What factors influence seagrass growth and development?

Light availability for photosynthesis, water motion and nutrient acquisition

How does light availability influence seagrass growth and development?

The epiphytes (bryozoa and microalgae) grow ion leaves and may strongly reduce light capture and photosynthesis

How does water motion influence seagrass growth and development?

Seagrass meadows develop more extensively under modest current conditions: moderate currents allow for refreshing of nutrients while fast currents cause erosion

How does nutrient acquisition influence seagrass growth and development?

Seagrass obtain a portion of their nitrogen from N-fixing bacteria in their rhizome but most is taken from surrounding water

How are seagrass beds important to coastal food beds?

Primary production, diversity because seagrasses form dense meadows for organisms (Argopecten irradians have planktonic larvae that recruit to seagrass)

Why is seagrass bed density ecologically important?

-Dense meadows = reduction in water currents which increases diversity of burrowing inverts and settlement of swimming larvae

-Blade density deters carnivores from entering bed because they have a hard time which protects invertebrates

-Larger suspension feeding inverts benefit because suspended food is abundant in beds and predation is reduces so bivalves grow larger

Is a dense rhizome system important in stabilizing sediment within beds?

Yes because stable sediment beds are in very shallow water adjacent to shoreline to protect human shoreline development against erosion. Also more seagrass = less turbid water which = more light for photosynthesis