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Mangroves

Habitat and Adaptations

The oceanic habitats support a great diversity of life and ecosystems (Ocean Literacy Principle #5)

Mangrove refers to the species of tree that make up a Mangrove Forest. Mangroves are trees or shrubs that grow in coastal “swamps” that generally have bidaily flooding with high tide. These trees live in some of the harshest environments on earth. Dealing with salt, intense sun exposure and roots inundated with saltwater, Mangrove trees (and shrubs) have some of the most unique adaptations to their roots and shoots.  

Mangrove forests are the swamps of the tropics, found along the coast of tropical and subtropical countries they are a coastal habitat that exist in tidal zones of saltwater that receive little if any fresh water contributionsNearly 75 percent of tropical coastlines, defined as 25 degrees north and 25 degrees south of the equator, have some kind of mangrove tree or shrub. With very little freshwater influence via rivers or streams to water the elaborate root systems, they have leaf and root adaptations to accommodate and rid the plant of excess salt while holding on to the freshwater necessary for survival.   

The roots of mangroves are uniquely shaped to continually give a supply of oxygen to the plant outside of the water, even during high tide. This above and below water root system provides a great place for fish species, acting as a nursery ground for thousands of fish speciesWhile providing a home for juveniles of larger fish and a permanent home for some smaller fish, these roots also provide an incredible amount of protection from erosion for the substrate during tropical storms. 

We do have a subtropic region in North America that contains mangroves. The mangrove species that are found in North America are found along the Gulf Coast (Gulf of Mexico) in Florida, Alabama, Louisiana, Texas, Cuba and Puerto Rico. There are four species that vary in appearance and adaptations. The White, Black, Red and Buttonwood mangroves are all found in and around the gulf and all four can be found in Florida.  

Learning Objectives:

  • Demonstrate a general understanding of the  mangrove ecosystem components (aquatic, terrestrial, avian & physical)
  • Evaluate and explain flora and fauna adaptations that lead to the success of species 
 

Analyzing Adaptations Flora and Fauna in Mangrove Habitats: Species Found in Mangroves

Mangroves are critical habitat for year-round resident species, migratory species as well as provide nursery grounds to various species.  All three add to the biodiversity of mangroves. When mangroves are destroyed so is the habitat necessary for the year round and migratory species as well as those species that need this habitat for security during the juvenile phase.  

Year-round Residents

The Red Mangrove Sea Crab lives in the canopy of the mangrove tree. The color ranges from red to orange and it feeds mainly on the flowers and fruits of plants in the mangrove forest.  Mangrove crabs add to the biodiversity but may actually be one of the most significant players in trapping the energy in the forest. They consume and bury leaf litter, burrow into the ground at high tide, climb trees to escape predators while their feces and larvae provide a food source for juvenile fish.  

Migratory Species

Species that use mangroves for a stopping place on a longer journey or a resting place for the winter months rely on the mud flats, the roots and the canopy for feeding and breeding. The warbler depends on mature mangrove forests for overwintering.  The warmer climate, higher prey abundance and thick canopy provides the perfect place for many species as they leave the snowy cold north for the winter.  

Nursery Grounds

Mangroves play an important role in the reproductive process of many sport and commercially fished species. Gray Snapper and Red Drum are among the species found in the mangrove forests in south Florida. The shallow water and intertwined root system provide protection from above avian predators and within the water from larger fish predators. The juveniles seek shelter here until they are large enough to avoid predators in the open ocean. As mangroves decrease and disappear, so does the population size of the highly prized fish.  

Flora Adaptations: Root Structures

Root systems in plants are some of the most important features and are not always as simple as they may seem.  Roots can be solely responsible for the uptake and supply of nutrients, fresh water, oxygen and provide support and structure for the plant. Here we will take a look at some of the root adaptations of Mangroves, understand why they have this adaptation and provide information on just how complex these adaptations can be and how they overcome the harsh environment in which they live.

Snorkel Roots

Peg like single roots that extend from the underwater root to above the water level, sometimes called pneumatophores provide a way for the mangrove to breathe. Also referred to as breathing roots, the pneumatophore would be similar to a snorkel that a human would use, providing oxygen to an oxygen breathing species when underwater.  Usually seen in the White Mangrove, these really neat adaptations can range in numbers from just a few to a few hundred! They extend up to the surface from the underground horizontal root that extends out from the tree.   These snorkel roots are generally seen in the shorter trees or shrubs that would not need as much support as the taller trees

Buttressing Trunks

Buttressed trunks are large wide trunks that extend out on all sides of the tree trunk, almost like a pedestal.  These wide thick trunks provide stability in the otherwise shallowly rooted tree.  Mangroves live in an area of sandy or mud bottom, this bottom or substrate is not deep (thick) so there is very little for the tree to use as a holdfast.  The buttressed or fat bottom tree provides a more substantial area for stability. This wide thick part of the trunk also serves as a long-distance conduit for water and nutrients. Buttressing is generally seen in the taller mangrove trees, not shrubs, it is one level of defense from the strong summer storms seen in the region. Buttressing in mangrove trees has been used architecturally to stabilize buildings and structures for hundreds of years.

Prop Roots

Growing from the branches of the tree and extending down to the water and sand/mud, these prop roots are instrumental in providing structure to the tree.  Just as you would use your arm to prop yourself up while sitting or leaning, these roots prop the tree up and provide support higher on the center of gravity of the tree which is especially necessary during tropical storms and hurricane.  The Red Mangrove, native to Florida, typically has many prop roots that tangle together and make it difficult to distinguish one tree from another. These roots mostly provide support but do also absorb water and nutrients when necessary. Banyon trees are also very popular for their prop roots.

Key Vocabulary

Adaptations 
Anoxic
Black mangrove
Buttressing
Concentration
Evaporation
Holdfast
Hydrophyte                        Inundate  
Juvenile
Lenticels
Migratory
Nursery grounds 
Organic Material                Pneumatophores
Red mangrove
Sediment 
Subtropic   
Tropic  
White Mangrove                          

Environmental Importance

The ocean ecosystems made the Earth inhabitable (Ocean Literacy Principle #4)

Mangrove forests play a vital role in the protection and economy of coastal communities. The unique properties and structure of the root systems provide support for the soil and sand of the coastal communities lending a hand in protection from erosion, storms and waves while at the same time providing homes and refuge for many species of fish and crustaceans. The richness and biodiversity of these ecosystems is an excellent source of food and income, making life sustainable for these (sometimes) remote islands. The interconnectedness of the root systems is excellent in their ability to sequester and remove carbon from the immediate environment (water, soil and plants) while contributing to the detrital food cycle-yes, decomposed organic matter is food for someone! 

The amount of cover provided by the roots and leaves of the mangrove plant is estimated to protect 75% of game fish and 90% of commercial species of fish at some point in their life.  Many of the species that rely on the mangrove cover are either  endangered or threatened.  The Red Mangrove prop root has been quantitatively documented and is said to be more important environmentally to some juvenile fish species than seagrass bedsKnowing the role of that mangroves play in the food cycle and food chain of so many species has led to more pointed governmental regulation of these coastal communities.  Coastal land use and development laws must now take into consideration the mangrove itself, along with the species known in the area and their International Union for Conservation of Nature (IUCN) status 

Learning Objectives:

  • Identify 3 ways that mangroves are environmentally important 
  • Discuss mangrove plant species, the chemicals they reduce and their adaptations 
  • Explain the significance of reducing storm surge 
  • Comprehend the significance of the mangrove forest as a nursery  

Analyzing the significance of mangrove forest functions in the global environment 

The role of a mangrove extends beyond that of coastal buffering and nursery grounds. These nutrient loving plants have the capacity to use or store a variety of nutrients throughout their lives. One of the most notable being the uptake of carbon dioxide gas and storing it as carbon in the wood and soils. Because of their location, transition zone from inland to marine waters, they also play a role in the nitrogen and phosphorus cycles as they take up nitrates, ammonium and phosphates that was downstream from fertilizers. 

Vital role in detrital food cycle

Mangroves are a vital part of both the complex terrestrial and aquatic food cyclesespecially the detrital food cycle.  Detritus, organic matter produced by the decomposition of organisms, plays an integral role in the soil of the ecosystem by breaking down matter,  storing chemicals and organics or converting carbon, nitrogen and other nutrients to usable forms. Since mangrove trees exist over an aquatic environment, the leaves that drop can be colonized with marine fungi and bacteria within a few hours. The colonization on the leaves leads to continual breakdown of the organic material  (the carbon structure in the leaf) that is difficult to digest. The fungi and bacteria convert the carbon compounds along with nitrogen to create a rich material called detritus, which is food for small worms, shrimp and snails that live in the sand of the intertidal zone. These are not the only species that feed on this nitrogen rich material, mollusks, barnacles, clams and oysters have been observed feeding on the material. The food cycle continues as the mussels,  clams and other bivalves are eaten by larger fish and crabs and which are then subsequently preyed upon by birds and larger, game fish that ultimately are consumed by humans. 

 

 

 

Carbon Sink

Mangrove forests cover 75% of tropical coastlines yet only make up 1% of the earth surface.  These forests contribute to the reduction of atmospheric carbon dioxide (CO2) by collecting and transferring it to the roots. Once there, CO2 and other nutrients are transformed into organic matter and stored in the water-logged soil. CO2 is an important greenhouse gas that helps trap heat within the earth's atmosphere. All species depend on levels of accessible CO2 for normal biological functions to be within a small range.  The rising amount of CO2 in the atmosphere has become a problem for some ecosystems and species. Mangroves and their associated soils could be responsible for sequestering as much as 22.8 million metric tons of carbon each year and converting 10% of the terrestrial dissolved organic carbon (DOC) that is exported to the ocean each year!  Recent research has suggested that mangroves sequester and store more than once thought. Many Scientist believe that mangroves collectively are the answer to removing the highest amount of atmospheric CO2 in the shortest amount of time.  

Water Purification

Left alone to do their job, mangroves can be excellent water purifiers! Many nutrients enter our coastal buffer zones through runoff from the local area, but also from hundreds of miles away especially after large rain events. This runoff can bring in an excess of nitrates and phosphates, mostly found in fertilizers and lawn care/maintenance chemicals used residentially and commercially. Nitrogen and Phosphorus are the primary growth elements of mangroves (nitrogen is obtained from the uptake of ammonium). Mangroves are some of the highest nutrient absorbing angiosperms and are one of the only trees that are known to opportunistically use elements and nutrients when they become available. A healthy thriving mangrove forest can taking up much of the excessive nutrients converting and using or storing the newly found nutrients ultimately preventing excesive nutrients from entering the ocean. 

Coastal Communities

Reducing storm surge in vulnerable communities has become one of the most important of the ecosystem services that mangroves provide. With an increasing number of high intensity tropical storms and with many more people moving to and building on previously undeveloped coastal land, a considerable amount of attention has been given to climate change and protecting the coastThe intricate root systems and multiple branches aid in attenuating waves from storms. With almost 2 million people living in coastal areas,  mangrove mitigation is necessary to safeguard shorelines and continue to provide the nursery and feeding zones for many fish and crustacean species that rely on mangroves  Mangroves are abundant with life and are an essential food source for the 2 million people living in these areas.  Local communities rely on the many fish that inhabit the ecosystem for food and as well as economic income from the many crustaceans and bivalves harvested through aquaculture.  A highly productive and biodiverse ecosystem, mangroves provide seafood to feed millions of people.   The destruction of mangroves and disruptive effects of climate change could lead to a decline in aquaculture, economic loss from tourism and decrease in additional ecosystem services.  Efforts to restore and protect mangrove forests is vital in the sustainability of fisheriescoastal economies and communities around the world.  

Key Vocabulary

Aquaculture
Atmospheric Carbon Dioxide
Attenuate
Bacteria
Bivalve
Colonized
Crustaceans
Detritus
Dissolved Organic Carbon
Ecosystem Services
Endangered
Food Cycle
Fungi
Greenhouse Gas
International Union for the Conservation of
Nature (IUCN)
Intertidal Zone
Mitigation
Organic Material
Sequestering
Storm Surge
Threatened

 

 

The Changing Climate

The ocean is a major influence on climate (Ocean Literacy Principle #3)

Scientist have known for many years that mangrove forests have played and continue to play a vital role in carbon sequestration, removal, storage or transportation of carbon dioxide. Most of the carbon taken up by mangroves during growth is converted to biomass and stored  in the wood and soils where it can remain indefinitely until disturbed.  After studying the inputs and outputs of mangroves, scientist now know that the carbon-rich mangrove forest can store twice as much carbon as a salt marsh of the same acreage. They have also learned that the most uptake and storage carbon occurs in young mangroves during their rapid growth period. The older, more established mangroves continue to store the carbon that was originally taken up during their younger growing phase but they play a more pivotal role in protecting  coastlines from destructive storms and sea level rise. Jin Eong On, a leading mangrove scientist believes that mangroves have the highest net productivity of any natural ecosystem. Mangroves can store as much as 24 million metric tons of carbon in the soil annually, drastically changing the soil and water chemistry in the area surrounding the forest. The effects of the changing climate and impact of human activities on mangrove forests has led to a loss of over 450,000 acres of mangroves worldwide.  The carbon that was once locked away has been released, many species that rely upon the mangroves for habitat are in danger and the increase in powerful storms continues to threaten the survival of mangroves.  Conservation efforts, planting of mangrove trees and reducing our carbon footprint can and will help preserve these vital ecosystems.

Learning Objectives:

  • Develop an understanding of the interdependence humans have with mangrove including how our actions directly or indirectly change mangrove forests 
  • Identify and understand sources of climate change, describing and explaining the causes and discuss the adverse effects as well as long-term solutions 

Anthropogenic Actions and Climate Change

Mangrove forests are the wetlands of the tropics. Many tropical and coastal communities depend on these areas for food, wood, and clean water. Achin Steiner, United Nations Under-Secretary General told the Times of London, “We already know that marine ecosystems are multitrillion-dollar assets linked to sectors such as tourism, coastal defense, fisheries and water purification services. Now they are emerging as natural allies against climate change."

Carbon dioxide in our atmosphere acts like a blanket for earth, trapping just enough heat within the atmosphere to keep us warm.  As carbon dioxide is released in abundance in the atmosphere, it traps and holds more and more heat, increasing the temperature of the atmosphere and the ocean. The exchange of carbon dioxide between the ocean surface waters and the atmosphere historically has been an equal exchange.  With increasing surface water temperatures, there is a decrease in the rate of carbon dioxide uptake of (warmer water releases CO2). At the poles where the water is cold, the ocean can absorb more carbon dioxide which in turn upsets the balance of the atmospheric versus ocean surface carbon dioxide. The rise in atmospheric and oceanic temperatures has led to a decrease in the polar ice, ice caps and glaciers all which contribute to sea level rise. Over the past century, sea levels have been rising at an average rate of about one eighth of an inch per year. Although this does not seem like a large increase, in a coastal mangrove area that is delineated by the daily tides, this can force big changes in the flora found in the area.   

Sea Level Rise

Sea level rise is changing coastlines all over the world. Coastal habitats are unique in that they face changing water levels daily and throughout the month and year.  The plants and animals that live in the coastal ecosystems have special adaptations to allow for the daily inundation of saltwater. The zonation (arrangement) of the plants starting at the oceans edge and moving inland varies with the plants ability to handle excess amounts of salt.  With the changing climate, we have seen a shift inland of many mangroves, disrupting inland plant and animal species.   In some areas human development blocks the migration of mangrove forests inland.   As sea levels continue to rise, some mangroves may experience higher high tides and erosion of the mud surrounding their roots that could result in the inundation and loss of the mangroves. 

Decrease in Biodiveristy

The biodiversity of the mangrove forests reaches far beyond what can be seen in the immediate area. These areas of high biodiversity contain many trophic levels that include numerous fish, crustaceans, birds, worms, snails, sharks, marine mammals and humans all which depend on the mangrove ecosystems for life. When humans disrupt one area of the food web it has a cascading effect and bringing it back into balance can take many years. In the past few decades, we have seen many species disappear from some of the most productive mangrove forests. When mangroves are removed, the calm water nurseries used as protection for smaller juvenile fish diminish or disappear. As these fish nurseries disappear, there is a drastic decline in subsequent years in the number of large fish and avian species that depend on the small fish for substance.  The destruction of mangrove forests is also associated with an increase in wave action. The upsurge in wave energy results in an inland movement of small crustaceans and bivalve species, or an exit all together, which adds to the decline in species biodiversity in the area. Restoring the biodiversity and food web that took hundreds or thousands of years to achieve is not something that can be easily or quickly achieved.

Water and Soil Chemistry

Left alone to do their job, mangroves can be excellent water purifiers! Many nutrients enter our coastal buffer zones through  runoff from the local area, but also from hundreds of miles away especially after large rain events. This runoff can bring in an excess of  nitrates and phosphates, mostly found in fertilizers and lawn care/maintenance chemicals used residentially and commercially. Nitrogen and Phosphorus are the primary growth elements of mangroves (nitrogen is obtained from the uptake of ammonium). Mangroves are some of the highest nutrient absorbing  angiosperms and are one of the only trees that are known to opportunistically use elements and nutrients when they become available. A healthy thriving mangrove forest can benefit from such runoff, absorbing, converting and using or storing much of the nitrates and phosphates ultimately preventing the excess nutreints from entering the ocean waters.

  

Carbon Sequestration

Similar to the effect of changes in air quality that may impede our ability to breathe or make us sick, changes in  the air or “gas” that exist in the soil and water of mangrove forest may also inhibit their ability to function. Mangroves take up carbon dioxide gas just as any plant does, but they do it more efficiently and at a much faster pace. After mangroves remove CO2, it is stored in the wood and soil where it can stay for hundreds of years. Between 2000 and 2015 roughly 122 million tons of carbon was released to the atmosphere due to the loss of mangrove forests. In the past 40 years, as much as 40% of the world's mangroves have been deforested. When we cut and remove mangrove, we not only take away a valuable source of carbon sequestration but also release the stored carbon back into the atmosphere and the ocean 

 

Key Vocabulary 

Ammonium
Angiosperm  
Biodiversity
Carbon Dioxide
Delineated
Food Web
Inundation
Migration
Nitrate
Nutrient
Phosphate
Run off
Sea Level Rise
Sequestration
Trophic level
Wave Action
Zonation

Shipping and Navigation

The ocean and humans are inextricably interconnected (Ocean Literacy Principle #6) 

Ocean literacy principal six embarks upon one of the most important relationships between humans and our physical world.  Humans have always taken to the sea for food but around 60,000 years ago, we started to see humans sailing the seas in vessels. This allowed for exploration far beyond the local shores, opening up more food and land possibilities as well as creating an interconnectedness between cultures. The important relationships we had early on have grown into international and global commerce and trade. 

Learning Objectives:

  • Understand the relationship between shipping and mangroves specifically the navigation challenges.  
  • Apply prior knowledge of biodiversity and discuss what this means in an ecosystem when invasive species arrive 

Balancing Commerce and Conservation

90% of all goods is transported by ships. As both conservation and commerce continue to advance and grow, the challenge of balancing both is increasing as well. Here we will look at the challenges of navigating through mangroves and what this means for the biodiversity in the ecosystem.

Channels and Navigation through Mangroves

There is a subtropic region in North America that contains mangrove forests. The mangrove species in North America are found along the Gulf Coast (Gulf of Mexico) in Florida, Alabama, Louisiana, Texas, Cuba and Puerto Rico. There are four species that vary in appearance and adaptations. The White, Black, Red and Buttonwood mangroves are all found in and around the Gulf of Mexico and all four can be found in Florida. Some of the busiest  shipping lanes in North America are also the location of the mangrove forest that exist in North America.   Navigating through many mangrove forests requires channels to accommodate for the depth of the vessel. We know that mangroves have intricate root systems that exist above and below the ground. These roots may be inundated with water for hours at a time during high tide and cannot be seen by vessels.  Dredging channels through mangrove forest is common practice but once done it will have to be repeated every few years as water flowing brings in sediment and the root systems are specifically designed to capture and hold sediment essentially filling in the channel. 

Legal Protection of Mangroves

Mangroves lie at the intersection of inland terrestrial law and aquatic marine law making it often a controversial and confusing decision as to who governs the land. The majority of mangroves are governed mainly by three prominent entities: forestry, fisheries and marine.  These jurisdictional divisions control the law and legislation surrounding mangroves. Most countries define mangroves as either a coastal forest  that is handled by the forestry commission or as a coastal waterway and handled by marine commissions. There are rare cases, even in the United States, that provided vague definitions and are govern based on the tide.  For example, if the tide is in (high tide) it is controlled by marine law; if the tide is out (low tide), it is controlled by forestry. This creates a lot of confusion for the coastal people and the maritime industry alike.  The delineation of mangrove law also extends to the species living in the area. Mangrove forests are protected areas but some species that frequent the area or live there permanently are protected due their status as being threatened or endangered. The enforcement of law under the Endangered Species Act becomes blurred as well.  In general, it is left up to each country on how to protect and enforce laws in and around mangrove forests. Without universal laws, this can create a lot of confusion for navigating through mangroves that lie cross international borders.  

Key Vocabulary 

Channels
Dredging
Forestry Commission
Jurisdictional
Marine Commission
Navigating
Shipping Lane
Subtropic

Activities

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Multimedia 

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Next Generation Science Standards

MS-ESS-3 Earth and Human Activity. Application of scientific principles for monitoring and minimizing human activity on the environment  

 LS1A-Structure and function of animals as it applies to their habitat  

LS1B- Growth and development of organisms  

LS2A- Interdependent relationships in organisms  

LS2C- Ecosystem Dynamics, Functioning and Resilience  

LS4A- Evidence of common ancestry and diversity  

LS4C- Adaptation  

HS-LS2-2 Ecosystems: Interactions and Dynamics 

HS-LS4-6 Biological Evolution: Unity and Diversity 

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