Habitats of Galveston Island State Park
Galveston Island State Park's ~ 2000 acres span the width of the island from the Gulf of Mexico to the waters of Galveston Bay. Barrier Islands are common along the Gulf and Atlantic coasts but the vast majority of them have been heavily developed. The building of homes, hotels, businesses, roads, and seawalls has greatly diminished native barrier island habitat. Galveston Island State Park (and similar parks like Island Beach State Park in New Jersey) serve an increasingly vital role in preserving and protecting barrier island habitats. If you spend some time exploring Galveston Island State Park you can begin to imagine what all of Galveston Island once looked like. You will then notice, as you travel outside of the park, how much of the island has been transformed and how little native habitats remains.
Beach / Dune
The open sandy beach is a habitat that many people are familiar with. The beach extends from the Gulf shoreline to the beginning of the fore dune, which is the part of the dune that faces the Gulf. No plants grow on the beach primarily from the frequent inundation of this area by salty seawater. Plant material, primarily Sargassum seaweed, does wash up onto the beach during certain seasons. This and other debris attracts the attention of foraging birds. Other bird species such as snowy plovers, sanderlings, and willets regularly forage at the water's edge. They search for small invertebrates that live in the wet sand. While the birds are looking for their next meal as the scavenge along the beach, humans enjoy beachcombing for pleasure - where we hope to discover treasures that the Gulf waters have washed up on the beach.
Dunes are one the most important physical structures on a barrier island. They form at the back edge of the beach, just beyond the place where the Gulf waters regularly reach. The dune is an accumulation of drifting and blowing sand and is partially held in place by vegetation. All the plants growing in this area face harsh conditions: low nutrient sandy soil, a scarcity of fresh water, and salt laden breezes that deposit salt on exposed plant tissues. The plants that do grow in this area, such as panicum, morning glory, and sea purslane, have characteristics that help them to tolerate the rough conditions. The roots of a number of common dune plant species grow deep and spread themselves wide in order to collect the sparse nutrients and water. This network of plant roots in turn helps to stabilize the dune and allows it to grow larger.
Beach dunes on barrier islands mitigate the effects of unusually high tides and storm surges. They absorb energy delivered by stormy weather and unusually high water. They can prevent salt water from reaching areas behind the dune and even when they are overtopped the dunes lessen the physical impact a rough storm can have on a barrier island. The dunes also function as a sand reservoir that will replenish some of the sand that is stripped away from the beach during a storm. This will decrease the size of the dunes but they will begin the slow but steady process of rebuilding once a disturbance has passed and the beach has attained a new equilibrium state. Just as dunes serves as a buffer for a barrier island, the barrier island itself helps to protect the mainland coast from bearing the the brunt of the destructive energy delivered by violent storms that sweep in from the Gulf.
Grassland / Prairie
There are a number of open grassland areas, mixed shrub/grass sites, and woody plant dominated habitats in Galveston Island State Park today. Many of these areas were once native seacoast bluestem - gulfdune paspalum habitat that were heavily grazed by cattle before the park was established. These grasslands have changed since cattle have been excluded but they have not entirely reverted back to their previous natural state. One of the most important changes that occurred once cattle grazing ended was the abundant growth of woody plant species. Non-native Chinese tallow (Sapium sebiferum) and native Baccharis (Baccharis halimifolia) came to dominate in many places. This type of coastal scrub habitat was not found on Galveston Island in the past. Similarly, most of the woodland vegetation that you see today did not occur on Galveston Island before. There is evidence that some scattered live oaks (Quercus virginiana) were once present but it does not appear that any woodlands existed. Some of the woody plant species present today are also introduced plant species. These arrived on the island sometime after Europeans explorers began exploring North America.
Galveston Island State Park management plans call for actively working towards reducing native and exotic woody vegetation. One of the aims of this management is to restore native prairie habitat, which is one of the most threatened habitats of Gulf coast barrier islands. Burning and mowing are being used to reduce woody vegetation even further in what are already relatively open grasslands. Scrub habitat and woodland vegetation, with the exception of live oaks, are being eliminated and reduced. Exotic non-native plants are also targeted for removal. Live oaks mottes (the Texas equivalent of a small grove of trees) will be allowed to grow and increase in area. This is being done to accommodate the needs of migrating birds that use this habitat for resting grounds.
The Friends of Galveston State Park have been instrumental in organizing the many dedicated volunteers that have been needed to carry out much of the habitat restoration work that has been accomplished so far. This is still much more work that remains to be done. Any donations of time or money that you can provide to this organization will be helpful in insuring Galveston Island State Park maintains its dual purpose of providing an enjoyable place for people to visit and playing an important role in preserving increasingly rare barrier island habitats.
Freshwater can be found in ponds and swales, which are low marshy areas that can contain standing water during certain times of the year. Both of these habitats are important in serving as a source of freshwater for animals. Most small mammals, some invertebrates, and even some birds that live on Galveston Island would either be greatly reduced in abundance, be only occasional visitors to the island, or be prohibited from living on the island if freshwater was not present. Cattails, reeds, and some exotic plant species can grow in dense single species stands around the edges of these areas.
A combination of gently rising and falling tides and small elevational differences in the land help create an interesting collection of habitats where the bay meets the land. Broad expanses of land that are regularly flooded by high tides form extensive marshes. These are primarily monocultures of cordgrass (Spartina alterniflora). When high tides inundate the low lying marsh land the bases of the plants become completely submerged. Juvenile fish and aquatic invertebrates can hide and forage among the basal stalks of submerged cordgrass during this time. Small crabs, worms, snails, mussels, larval fish, and other marsh animals often inhabit microhabitats (for example just above the water on the cordgrass blades) that are constantly shifting as the tides rise and fall. When the waters recede from the marsh during low tide, detritus and other nutrients are swept out into the bayous and sloughs, where it is then brought out into the open waters of the bay. These nutrient inputs play a vital role in enriching the base of a productive Galveston Bay food chain. At the edge of the marsh the ground elevation is just low enough to prevent cordgrass from growing. These areas may become exposed mudflats during portions of the day when the tide is at its lowest point.
Sloughs and bayous are finger like extensions of the bay that form a matrix of open waters within the marshland. These water bodies serve as conduits for organisms that move between the flooded marshes, the edges of the marsh lands, and the open bay. During periods of very low water (primarily during the winter) the slough and bayou bottoms become exposed as expansive open mudflats. Many organisms that normally live in larger bodies of water can become trapped in shallow, isolated pools. The normally common marsh and shoreline birds are attracted become even more abundant as they feast upon the profusion of trapped prey.
In the past large beds of seagrass were found in Galveston Bay. Like the flooded cordgrass marsh, underwater seagrass offers hiding cover for many small organisms and can serve as rich foraging grounds. They are also a source of food for grazing herbivores, add oxygen to the water when they are actively photosynthesizing during the day, and help stabilize bottom sediments. Their grass blades intercept and knock down suspended particles and, with the abundance of filter feeding organisms they support, can improve water clarity. Some marine organisms are also highly dependant on seagrass \. Bay scallops, for example, ideally live out their earliest larval stages attached to blades of seagrass. Galveston Bay's seagrass has been greatly reduced due to a number of human caused disturbances. Efforts have been underway to restore this habitat, in part because it is deemed crucial to maintaining some commercial seafood stocks. The planting of new seagrass beds has been successful but it does require the replanting of many small plugs of living seagrass into the bottom of the bay. Unfortunately this is a labor intensive process that cannot easily be accomplished on a large scale.
Galveston Bay, like many bay systems between mainland coasts and barrier islands, forms a large estuarine ecosystem that has traditionally served as a productive nursery grounds for many aquatic species. The marshlands, bayous, sloughs, mudflats, open waters, and seagrass beds are collectively important as vital pieces of an interconnected larger ecosystem. Numerous commercial seafood species, that can be present in great abundance, live out their lives in the bay. There are also many more Gulf marine species that spend their earliest juvenile stages in the bay until they grow large enough to be able to survive in the Gulf waters.
For many decades every component of the estuarine bay ecosystem was steadily degraded by habitat loss and disturbance. With a relatively new understanding that we have concerning the importance of all of these habitats, how they are interconnected, and how they can be both harmed and supported by changes we create, has come an appreciation of how we can better manage all of these resources to support a healthier Bay. Galveston Island State Park has served as a testing ground for a number of innovative conservation measures in Galveston Bay, including the planting of sea grass beds and the installation of artificial marsh terracing.
You can find out more about Galveston Bay restoration and preservation efforts by visiting the website of the Galveston Bay Estuary Program