Submerged Aquatic Vegetation
Embed Size (px)
Transcript of Submerged Aquatic Vegetation
Submerged Aquatic VegetationWHAT IS IT AND WHY IS IT IMPORTANT?Image provided by Ronald C. Phillips
What Is Submerged Aquatic Vegetation (SAV)?SAV consists of plants that spend their life cycle completely submergedIncludes algae, but usually refers to complex plants such as seagrassesSAV does not include marsh grassesImage provided by NOAA Department of CommerceImage provided by Ronald C. PhillipsSeagrassesMarsh grasses
What Are Seagrasses?Type of SAVExhibit seasonal growthContribute to a rich, productive ecosystemProvide oxygen, food and habitat for many animals
Paige Gill - Florida Keys NMS
Where Do Seagrasses Grow?They require habitats where sunlight can reach the bottomThey typically prefer shallow clear waterThey grow close to the shore in many coastal regionsThey occur from the Tropics to the Arctic
They release oxygen into the waterThey provide habitat and shelterThey are a food resourceThey help stabilize the shorelineThey help maintain water qualityWhy Should We Care about Seagrasses?
Seagrasses Release Oxygen into the WaterSeagrasses use sunlight to produce oxygenMany economically important fish and shellfish require oxygen
Image provided by Fred Short
Seagrasses Provide Habitat and ShelterLeaves provide habitat for tiny plantsThese tiny plants are the food resource of many economically important finfish, shellfish, and crustaceans. Leaves provide hiding spots for juvenile finfish and other animalsRoots and stems prevent efficient foraging by predators who dig for prey
Image provided by SFWMDImage provided by Heather Dine
Seagrasses Are a Food ResourceSeagrasses are a primary food source for manatees and sea turtlesMany migratory waterfowl such as the Canada Goose and Black Brant consume seagrass
Image provided by Ronald C. Phillips
Seagrasses Help Stabilize the ShorelineRoots trap sedimentsSeagrasses buffer the shore from storm effectsThey help prevent erosion
Seagrasses Help Maintain Water QualityRoots trap sediments and promote water clarity They reduce sediment stirring caused by currents Stems and roots hold dead materials in place for decomposition
Images provided by Ronald C. Phillips
Why Are Seagrasses Threatened?Seagrasses grow close to the shore and coastal areas are naturally dynamicSeagrases grow in areas that typically have increased development and recreational pressuresThere are laws that protect seagrasses, but it is hard to protect what you cant see
Natural Threats to SeagrassesOvergrazing can decimate seagrass bedsStorms can uproot or bury seagrassesDrought can change water levels, which can expose seagrassesChanges in rainfall can alter salinity, which can stress or kill seagrasses Outbreaks of diseases can cause diebacks
Human Threats to SeagrassesFertilizer and other chemical runoff reduce water qualityReckless boating can contribute to prop scars Docks shade seagrass bedsDredging destroys habitat Sediment runoff buries seagrasses and clouds waterCertain shellfish harvesting methods destroy seagrass beds
Can SAV Be Harmful?Some SAV can cause problems These plants can grow quickly and crowd out seagrassesThey often thrive in polluted watersTheir quick growth may lead to large population sizes They may contribute to fish and shellfish die-offsPlants clog waterways and choke boat engines
Why Should We Protect Seagrasses?Seagrasses supports a healthy coastal environmentThey are important in maintaining recreational and commercial fisheriesThey are legally protectedSeagrasses help reduce erosion
How Do We Know Where Seagrasses Live?Field monitoringUnderwater surveysUnderwater photographs and videographyRemote sensing technologyAerial imageryUnderwater sensors
How Can You Help?Always use pump-out stations to dispose of boat waste Avoid vegetated shallows when planning dredging or pier construction Participate in water quality monitoring programsPractice responsible boating and navigation
Help environmental organizations plant seagrassesUse environmentally friendly landscaping techniques
Submerged aquatic vegetation, commonly referred to as SAV, is an important and highly productive natural resource. This presentation will outline answers to the following questions: What are SAV and seagrasses? Why are they important? What are the natural and human threats to SAV and seagrasses? What steps can be taken to protect them?SAV is a general term used to describe plants that, under normal conditions, live completely below the water surface in freshwater or marine environments. In general, these plants cannot survive if they are exposed to the air for prolonged periods.
The term SAV may be used in different ways. In general, SAV includes algae because they photosynthesize (convert sunlight and nutrients into sugars and oxygen) and reproduce underwater. However, algae are not complex plants and may not be considered SAV by all researchers and managers. It is important to define what SAV means in terms of your coastline.
Seagrasses, another example of SAV, are complex plants that grow in saltwater environments. These grasses grow, reproduce, and thrive completely underwater. There are many different species of seagrasses, ranging from lush turtle grass and eelgrass meadows with leaves that reach 1 meter in height, to shorter star grasses and paddle grasses that may grow to only a few centimeters tall.
Regardless of how wet a marsh may be, plants that stand above the water surface are not SAV. Under normal conditions, marsh grasses live only partially submerged and do not reproduce or thrive underwater.
Seagrasses are a type of SAV. They are complex plants that produce flowers and pollen underwater. Because they are photosynthetic plants, they are affected by the amount of sunlight they receive. At the end of the growing season, some species of seagrasses flower and produce seeds. The plants then die back completely and the meadow will be regenerated from seeds the following spring. Some species do not die back completely, but overwinter below the sediments as roots. It is important to note that seagrass meadows may change year-to-year and season-to-season. For that reason, it can be difficult to distinguish between natural seagrass dynamics and significant changes brought about by other factors.
Seagrasses are important contributors to many shallow marine ecosystems. Many marine and estuarine species depend on seagrass meadows for oxygen, food, and habitat.Seagrasses are found in extremely diverse environments, but are most common in shallow water where light for photosynthesis is most available. Turbidity is a term used to describe water that is cloudy or opaque. Turbidity may indicate declining water quality because it can be a result of nutrient runoff. Sunlight does not penetrate through extremely turbid waters and, as a result, could significantly reduce seagrasses in coastal areas. Seagrasses or lack of seagrasses may help serve as an indicator of water quality.
(Nevertheless, there are species of seagrasses that can survive on as little as 1percent of the light penetration. These seagrasses can be found at depths of 30 meters, where they may be extremely difficult to detect and monitor.)
In the U.S., seagrasses are found in all coastal states except South Carolina and Georgia, primarily due to the unique coastline in these states. Nearshore waters are relatively turbid in these areas, and there is a wide tidal range that could expose seagrasses beyond their ability to survive.
Seagrasses are not only found in the Tropics, as seen in this picture of seagrasses growing near corals. Seagrasses also occur in the Arctic.
Healthy seagrasses provide a number of services and functions to coastal marine and estuarine ecosystems. Seagrasses provide a source of oxygen to the water column. Extensive meadows provide habitat and shelter for fish and shellfish. Seagrasses are themselves an important food resource, as are the many animals that live in the meadows. Seagrasses help stabilize the shoreline and maintain water quality.Seagrasses thrive in water where sunlight can penetrate the seafloor because as primary producers they convert sunlight into oxygen. Oxygen is released into the water as dissolved oxygen and is then biologically available for marine and estuarine animals that are dependent upon it.
Commercial and recreational fisheries are a valuable economic entity of coastal environments. Many economically important fish, shellfish, and crustaceans are found in seagrass meadows and utilize the oxygen produced. Examples include the flounder and scallop (see above), as well as many juvenile fish and crabs.Seagrass leaves are naturally buoyant and rise upward in the water column creating texture on the seafloor. Plants and animals can attach to these leaves to prevent burial in the sediments and, tiny plants that attach to seagrass leaves, called epiphytes, are an important food resource for many grazing animals and juvenile fish. In addition, some epiphytes help maintain nutrient levels in the water by converting nitrogen (an important component of plant nutrients) into a form that the seagrasses can use.
Seagrass meadows are often referred to as nurseries because they provide attachment for egg masses, larvae, eggs, and some shellfish, as well as create texture on the seafloor as hiding places from predators.
The roots of seagrass meadows intertwine and form dense mats, which may reduce the efficiency of predators digging for clams or other buried animals.
Seagrasses are a primary food resource for many large species, such as manatees and some species of sea turtles. These large mammals are already stressed due to human activities along the coast. The additional loss of a primary food resource could be detrimental to their survival.
Seagrasses are also consumed by waterfowl. Reductions in waterfowl numbers in the past have been associated with seagrass losses. For many coastal areas, waterfowl hunting is an important source of revenues.
The sea urchin, seen above, is also a consumer of seagrass beds.
Many species of seagrasses grow in soft, unconsolidated sediments (e.g., mud or sand). Nearshore environments are subject to tides and wave action that may scour the sea bottom and wash away sediments.
Typically, seagrasses grow in extensive meadows. The roots and rhizomes reach into the soft sediments to form dense mats that trap and stabilize the sediments. During strong wave and wind events, the roots help prevent the sediments from being washed away or resuspended in the water column. In effect, seagrasses may buffer the effects of erosion.
Seagrasses serve to maintain the clarity of the water. They trap and stabilize sediments, which helps to minimize the waters muddy appearance. In addition, seagrasses retain nutrients within the sediments that, in excess, promote algal blooms (tiny floating algae that grow in large numbers and cloud the water).
After a heavy rain, water is transported to the marine environment, carrying with it debris and dead organic material. The leaves and roots help trap the excess material while bacteria and other microbes to break it down.Seagrasses are essential to the maintenance of a healthy coastal ecosystem. Coastal areas are naturally dynamic due to currents and tides, storm events, rainfall, and feeding activity of animals.
In addition, coastal areas are changing drastically due to increased development pressure. Recreational and commercial boating increases the risk of contaminant spills and physical damage to seagrass beds, while coastal development results in many invisible threats such as runoff of fertilizers, sediments, and herbicides. There are laws that protect seagrasses, but it is hard to protect what you cant see.It is natural for some species to consume seagrasses; however, overgrazing may be a result of population booms, such as the sea urchin in Florida Bay. Overabundance of these predators can destroy many acres of seagrass in short periods of time.
The increased wave activity that results from hurricanes and storms threatens meadows by either exposing or burying the plants with shoals of sand, silt, or mud.
Seagrasses also are impacted by reduced salinity due to freshwater runoff or by increased salinity due to drought. These changes may be the result of a change in the frequency of rainstorms or the formation of new rivers and inlets.
In addition, natural disease outbreak can impact seagrass species. Plants may be already stressed due to increased turbidity and as a result are more susceptible to disease. For example, the wasting disease of the 1930s is thought to be due to a fungus that is present in many healthy seagrass meadows.Seagrass meadows are sensitive ecosystems that can easily be damaged or destroyed. Some species of seagrasses are very slow growing and, as such, take years to recover from extensive damage, if at all.
Sediment runoff from floods or cleared lands flows into estuaries and can cover or shade out SAV. In addition, fertilizer and animal waste runoff are rich in nutrients that promote the growth of large algal blooms in the water. Algal blooms cloud the water, which may stress or kill seagrasses and result in a net loss of oxygen in the water.
Reckless or inexperienced boating can cause scars in the seagrass beds, as can some methods of shellfish harvesting.
New docks can shade out SAV directly by blocking the sunlight.
Dredging and bottom sediment movement destroy SAV by increasing turbidity, directly removing and burying seagrasses, and changing the hydrodynamic regime that increases energy or alters salinity.Not all SAVs are beneficial. Harmful SAVs are usually freshwater species that can bloom in the same way as algae. In a stable environment, freshwater SAVs contribute nutrients to the aquatic environment, provide shelter and food for aquatic creatures, and help slow erosion. However, when excess nutrients exist in a system, these plants can multiply uncontrollably and beyond the ability of the environment to sustain them. This problem can also happen when exotic SAVs are introduced into a system where there are no natural controls on their populations.Beneficial seagrasses should be protected for many reasons. Because of its habitat value and effects on the seafloor, seagrasses contribute to a healthy coastal ecosystem.
The protection of seagrasses supports both recreational and commercial fishermen. A strong recreational fishery can be the basis of a healthy tourist economy in certain coastal areas.
Seagrasses are protected by federal laws that govern wetlands, such as the Clean Water Act Section 404, and the Rivers and Harbors Act, Section 10. A host of state laws also pertain specifically to wetlands, seagrasses, and other SAVs.
Coastal erosion of beaches and tidal estuaries is a major problem facing many communities. Because the leaves of seagrasses baffle waves and wakes, it helps to stabilize these shoreline areas thereby ensuring property values and helping to maintain a healthy ecosystem.Because seagrasses have so many positive values for the coastal environment, natural resource agencies usually are involved in conserving seagrass habitat. In many cases, conservation efforts include the mapping and monitoring of SAV.
Because it is usually located in shallow water with sufficent light penetration, SAV can be detected in remotely sensed imagery. A common remote sensing technology that has proven useful for mapping seagrass is aerial photography. This produces data at high resolution and can assist normal permitting processes.
Despite the utility of aerial imagery, environmental conditions such as tidal stage, sea state, clouds, haze, and water clarity strongly affect what can be detected from aerial platforms.
In areas where remote sensing is not feasible or is unsuccessful, underwater videography can fill in the gaps or be used to interpolate a map. This technology has the advantage of producing a permanent observational record that can be reviewed later for further analysis or for change analysis. Video systems range in complexity from simple handheld cameras to large fixed-mount systems that require dedicated vessels for deployment.This slide illustrates the many ways that concerned citizens can help protect and conserve seagrasses. All of these practices will benefit SAV and indirectly benefit us as residents of the coastal environment.
By practicing these recommendations, we help to ensure stable shorelines and waterways, healthy commercial fish stocks, a vibrant tourist economy, enhanced waterfront property values, and a diverse natural environment.