Texas Bays and Estuaries:

Upper Laguna Madre Overview

The upper Laguna Madre is a lagoon located south of Corpus Christi along the Texas coast. It is
found between the mainland and two barrier islands running parallel with the coastline. The upper Laguna Madre covers 76 kilometers of coastline and includes Baffin Bay, as well as Baffin’s tertiary bays: Alazan Bay, Laguna Salada Bay, and Cayo de Grullo Bay. The upper Laguna Madre is unique in the amount of undeveloped shoreline it contains. This is due to much of the shoreline being owned by King and Kenedy ranches. Alazan Bay is also the only bay on the Texas coast that has no development along its shores. The upper Laguna Madre is one of only six hypersaline bays found around the world. This is caused by its minimal freshwater input as well as its limited exchange with the Gulf of Mexico. A single thunderstorm can account for a month’s freshwater input for the whole upper Laguna Madre! Padre Island, the biggest of the two barrier islands, is home to the Padre Island National Seashore, one of only ten National Seashores found in the United States. The upper Laguna Madre is home to many economically important species, including fish and birds. The Laguna Madre region is considered one of the best places on earth for recreational birding, as many migratory birds call the area home during the winter. The upper Laguna Madre is also a fishing hotspot, being used by both commercial fisherman as well as recreational fisherman alike.

Upper Laguna Madre Climate and Hydrology


The upper Laguna Madre is classified as a sub-humid, semi-arid, subtropical climate. It
experiences high temperatures, especially during summertime, low moisture rates, high humidity levels, and sporadic frosts. The prevailing winds blow in the southeast direction, during March – October. A change to northeast wind direction occurs during the months of October – February. The strength and direction of the wind can influence the water levels as much as 0.6m – 0.9m. Humidity levels are quite high, ranging from 85% in December to over 90% in July, with yearly averages of 88%. Precipitation in the upper Laguna Madre is variable and inconsistent. The average rainfall in this area is only 27.8 in (70.6 cm). The month of September is when the greatest of rainfall generally occurs with over two-thirds of the yearly total taking place from May – October. The rain in this region comes from thunderstorms, tropical storms, and hurricanes, making the precipitation unpredictable. In the upper Laguna Madre system, the temperatures are quite high with cold weather seldom present in the area. There are long, hot summers and short mild, winters with the occasional freeze that can result in massive fish kills. Summer highs average at 91.9 °F (33.3 °C) while winter lows hang around 46.9 °F (8.3 °C). There is always a threat of hurricanes during June – November which can bring a lot of wind and rainfall to the area. Water levels may rise significantly during this time. These storms can widen and deepen tidal inlets and wash over passes along with increase the speed of erosion and deposition, thus slightly changing the topography of the upper Laguna Madre over time.


The upper Laguna Madre has an average depth of three feet with an average width of four miles.
Due to the shallow nature of the Laguna the surface and bottom, water temperatures vary minimally. The only freshwater input into the Laguna comes from rainfall, and evaporation often exceeds precipitation directly correlating to higher salinity levels. The average ranges from 50-70 ppt (parts per thousand) but prior to dredging the Gulf Intracoastal Waterway, salinities were commonly above 100 ppt. Prior to the creation of the dredging of the Gulf Intracoastal Waterway, high salinity levels caused high levels of fish mortality but the dredging of this channel has practically eliminated this issue. The opening of Gulf passes of the Laguna Madre in the past has proven to be unsuccessful in some cases, like Yarborough Pass, and successful in others, like Packery Channel. In the case of Yarborough Pass, during the four years of dredging
the pass the area re-silted rapidly after each dredging event and the pass was only open for a 10- month time frame. Dredging the Laguna was an important event which reduced high salinity levels and decrease water residence time within the Laguna. The Laguna currently has a water residence time of one year or more while adjacent bays have an average residence time of a month.

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Upper Laguna Madre Geology and Habitat


The upper Laguna Madre dates back as far as the end of the Pleistocene era (2.5 million years
ago – 11.7 thousand years ago), first starting to form about eighteen thousand years ago. During its early stages, sea level was 91-137 meters below today’s level, causing the shoreline to be 80 kilometers further into the Gulf of Mexico. Streams running through the area cut deep valleys into the ground, especially near Baffin Bay. As glacial ice kept melting, these valleys began filling with water and large amount of sediment were deposited in the area. Sea level kept rising with glacial melting, and about five thousand years ago the formation of shoals and sand bars started to occur parallel to the coast. These shoals and sand bars became the barrier islands of the Texas coast. The formation of these barrier islands isolated the body of water we call the upper Laguna Madre. Hurricanes, tropical storms, and heavy winds have also shaped the upper Laguna Madre by depositing sediments over the barrier islands. This has created tidal flats on the mainland side of the barrier islands.

The Upper Laguna Madre is a soft sediment lagoon with very little hard substrate. Coquina beach rock is found in the upper Laguna Madre at the mouth of Baffin Bay, traveling southward for 10 kilometers. This stretch of beach rock is the only lithified bedrock exposure found along the South Texas Coast. Coquina beach rock provides a natural hard substrate for epifaunal attachment.

Serpulid reefs are the hollow, hardened tubes left behind by invertebrate worms called Hydroides dianthus. These serpulid worms are no longer actively building tubes because of hypersaline conditions, but the presence of serpulid reefs indicates a less saline environment in the past. The serpulid reef rock, much like the coquina beach rock, provides a naturally hard substrate for epifauna to grow. Higher species richness for invertebrates has been found in these areas, providing more prey for fish species. Serpulid reef covers sixteen square miles in Baffin and Alazan Bay, mostly occurring at the margins of the bays. Small patches can also be found at the mouth of Baffin Bay. Serpulid reefs throughout this system are being hit by boat motors and being broken down, resulting in less hard substrate and habitat for organisms.

and cover 16 square miles of Baffin and Alazan Bay, most commonly found along the shoreline.7  These reefs were formed by serpulid worms that build protective tubes made of calcium carbonate, the same substance found in coral reefs.  Both types of hard substrate found in the ULM provide valuable structure and habitat for a variety of speciesfound within the bay. 

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Open Bay Bottom

Open bay bottom is one of the most abundant and productive habitats found in estuaries, and the upper Laguna Madre is no different. Being an open system, bay bottom interacts with other systems, including seagrass beds, tidal flats, marshes, etc. Drift algae from seagrass beds can find their way into these areas but don’t stay long as they have nothing to attach to. Gracilaria spp. and Laurencia poitei are the most common species found in the upper Laguna Madre. Open bay bottom is made up of soft sediments, home to many infauna (organisms that live in the sediments). These benthic (bottom living) invertebrates, mostly bivalves and polychaetes, are vital to the system, converting energy from detritus and the sediments back into the water column, making it available for phytoplankton. Phytoplankton, microscopic algae living in the water, are the base of the food web and are important to having a productive system. Anywhere from 30 to 100 percent of nutrients used by these phytoplankton have been recycled, making this process essential for life in these areas.

Open bay bottom and seagrass beds have an inverse relationship, meaning that if one of these habitats is decreased, the other increases. If enough light and nutrients are available and environmental factors are right, seagrass can take root in open bay bottom. This was seen after the Intracoastal Waterway was dredged in the late 1940’s, as exchange with the Gulf of Mexico increased. This caused salinities to decrease in the upper Laguna Madre, making it possible for more seagrasses to become established. As more seagrass moved into the area, they started establishing themselves in open bay bottom, decreasing the overall amount of bay bottom. More recently we have seen the opposite, as decreased freshwater input, brown tide, and prop scarring have all caused decreases in seagrass beds. Once these seagrasses die and are gone, these areas will become open bay bottom again. Most of the open bay bottom is found in Baffin Bay, where the water is deeper and less likely to support seagrass beds because of light availability.

The phytoplankton most commonly associated with open bay bottom are diatoms, a phytoplankton that produces a microscopic shell. Previous studies have shown that about 97-99 percent of phytoplankton species found in local open bay bottom are diatoms. Diatoms most

likely increased with the dredging of the Intracoastal Waterway, as they are rarely found in salinities above 60 ppt.

Zooplankton is a community of microscopic organisms that float freely with the current and migrating vertically through the water column. This community is made up of many different types of organisms, from larvae of larger fish and invertebrates that will leave the zooplankton community once bigger, to many species that will stay in the zooplankton community their whole lives, never growing bigger than a couple millimeters. Many species associated with open bay bottom have a planktonic life stage, including bivalves, gastropods, and barnacles. Zooplankton communities can be incredibly diverse, but in the upper Laguna Madre the waters are dominated by copepods, particularly a single species (Acartia tonsa).

Seagrass Beds

Within the upper Laguna Madre ecosystem, one of the most common types of vegetation present is seagrass. Seagrasses are marine angiosperms able to reproduce by sexual via pollen and seeds or vegetatively by extending out the below ground rhizomes and roots. There are five species of seagrass in the upper Laguna Madre region: Shoal grass (Halodule beaudettei), Manatee grass (Cymodocea filiformis), Widgeon grass (Ruppia maritima), Clover grass (Halophila engelmannii), and Turtle grass (Thalassia testudinum). Seagrass covers about 243 km2 of this region.

Shoal grass is the most common of the five species of seagrass in the area. The second most abundant species is widgeon grass followed by manatee grass. Shoal grass and widgeon grass are pioneer species that can grow quickly in areas of little productivity. Clover grass also can colonize in areas of bare or algae-covered substrate or as an understory species within shoal grass, manatee grass, widgeon grass, and turtle grass beds. Small isolated patches of clover grass and turtle grass can be located north of the John F. Kennedy causeway where salinity levels are moderated by the Gulf pass at Packery Channel. Changes in abundance of manatee grass have been observed showing an increase in coverage in the Laguna Madre in the past decade. As the substrate becomes more stable, turtle grass begins to appear last, initiating the climax of succession. It is important to note this because the ecological niche of each species determines
the order of succession, also known as the sequence of when and where each species can/will grow. At these climax species begin to increase in abundance, the structure of the seagrass community becomes more complex, involving the increase of leaf surface area. This allows for epiphytic growth on the blades which provides food to organisms grazing organisms that control the growth of the epiphytes.

Seagrass beds provide many benefits to the ecosystem. One important aspect is that seagrass helps to reduce wave action with their above ground leaf structure and erosion with their below ground root and rhizome structure, thus keeping the substrate firm and maintaining water clarity. Seagrasses help to increase bottom surface areas, allowing for larger and more diverse communities of organisms to exist. Additionally, they serve as nurseries and provide shelter for organisms to live. Some animals that utilize these areas include spotted seatrout, red drum, black drum, blue crabs, shrimp, waterfowl, and sea turtles. Furthermore, seagrass beds are a major contributor to nutrient recycling in the upper Laguna Madre and provide essential organic material in the form of detritus. Seagrasses are among the most productive submerged habitat in existence.


There are various types of algae that exist in the upper Laguna Madre ecosystem. Microalgae (phytoplankton) act as primary producers, providing nutrients for other organisms to survive. Attached algae are uncommon in the upper Laguna Madre but some can be found on soft bay bottoms and/or attached to other solid substrates such as rocks, shells, and even some organisms such as crabs. Most algae in this area are of the Phylum Chlorophtya (green algae) and Rhodophyta (red algae) with a few in the Phylum Phaeophyta (brown algae). A common species of green algae, known as Acetabularia sp., is found in small patches throughout the Laguna Madre. The common name of this alga is mermaid’s wine cup due its unique cup-like shape. Red algae, specifically drift algae, are found drifting in the seagrass meadows of the upper Laguna Madre. Other common genera found in the area are Gracilaria, Laurencia, and Sargassum.

Tidal Flats

Tidal flats are mostly sand/mud habitats that exist in the upper Laguna Madre. These areas received their name from the fact that wind and storm tides are responsible for their existence and highly variable nature. Tidal flats are dominated by filamentous blue/green algae known as Cyanobacteria in the Phylum Cyanophyta. They form thick mats and comprise over 70% of the living community on these flats. Their high rate of primary productivity is actually near that of the seagrass beds, which is quite interesting due to their unique formation and lack of vegetation.

A large number of invertebrates utilize the tidal flats when flooded. Shorebirds consume these invertebrates when the area is uncovered as well as crabs, and fish when the flats are flooded. The flats are an important area for foraging and are home to many wintering and endangered bird species including the piping and snowy plover.

Terrestrial/Vascular Plants

Though not numerous in abundance, there are certain species of vascular plants that thrive on the shorelines of the upper Laguna Madre. Few plants can survive in this environment due to the lack of freshwater input to the area. These plants are classified as halophytes because they can withstand these harsh salty conditions. The primary vegetation on these shorelines includes glasswort (Salicornia sp.) and saltwort (Batis maritima). Other frequently found species include sea blight (Suaeda linearis), sea ox-eye daisy (Borrichia frutescens), and camphor daisy (Rayjacksonia phyllocephala).

On the barrier islands of the upper Laguna Madre, there is a variety of vegetation within the different zones of the area. These zones include the foreshore, backshore, landward, dune ridge, secondary dunes, and tidal flats. The black mangrove (Avicennia germinans) is the dominant woody vegetation on the barrier islands. It is the only species of mangrove to live successfully in the hypersaline conditions of this bay system. The foreshore zone is bare due to the high influx of saline water. The backshore zone contains the plant Sesuvium portulacastrum, also known as sea purslane. On the landward zone, Uniols paniculata is regularly found. These plants are known as sea-oats due to the fact that they mirror the common oat plant, Avena sativa. The dune ridges support vegetation that stabilizes the substrate so it will not degrade from erosion. A
widespread species found in this part of the barrier islands is the fiddle leaf morning glory (Ipomoea imperati) which can be easily identified by a bright, white flower with a yellow disk. The secondary dunes region is dominated by the seacoast bluestem (Schizachyrium scoparium). This is a tall, grass-like plant that is found throughout Kenedy County. The tidal flats support a small range of halophytic vegetation. The species found in the area include seashore dropseed (Sporobolus virginicus), camphor daisy (Rayjacksonia phyllocephala), sea lavender (Limonium carolinianum), and shoregrass (Distichlis littoralis).

Overall, the vegetation in all parts of the upper Laguna Madre play a vital role in the health and success of the ecosystem. They provide nutrients and habitat for numerous organisms, increase biodiversity, stabilize the substrate, and are important indicators of the overall condition of the system. Without seagrass, algae, and terrestrial plants, this bay system would not support the vast array of life it does today.

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Upper Laguna Madre Fish and Birds


The upper Laguna Madre is home to many commercially and recreationally important fish
species. Twenty-six of the thirty-one identified fish species found in Gulf of Mexico estuaries have commercial or recreational value. This same trend is true along the Texas coast and its estuaries. The three species that make up most of the commercial and/or recreational fishing in the area are black drum, red drum, and spotted seatrout.

Black drum, Pogonias cromis, are found throughout the upper Laguna Madre, with greatest abundance in Baffin Bay. Black drum are long-lived fish that spend most of their time in unvegetated bay bottoms. These unvegetated areas are where black drum feed by using the barbels on their chin to locate shallow infauna (organisms that live in the sediment) such as bivalves like clams. The young black drum will primarily feed on small softer bodied invertebrates such as crabs and shrimp before their pharyngeal teeth develop. located in these areas. Black drum spawn in nearshore waters but have adapted to reproduce in many different areas. Black drum have been found spawning in most areas of the upper Laguna Madre, including creeks and very shallow waters. Spawning season is from January through mid-April. Black drum are popular as a commercially sold food source as well as for recreational fisherman. Regulations state that black drum caught recreationally need to be between 14-30 inches with no more than 5 caught per person per day. This can include one black drum over 52 inches as part of your daily bag limit.

Red drum, Sciaenops ocellatus, have many common names, including reds, redfish, and bull reds for the larger fish. Red drum are top predators and can live to be over 37 years old. Most natural mortality results from predation of smaller sized fish, red tide bloom events, parasitism, disease, and old age. Some threats are manmade such as overfishing and destruction of nursery habitat which includes shallow open water and seagrass beds. By age three most adults move offshore but come to Gulf passes to spawn from summer to early winter. Juvenile red drum feed on copepods, mysid shrimp, and amphipods, while larger adult drum feed on crustaceans and fish. They are a very popular recreational fish and have a must be between 20-28 inches with no more than 3 caught per person per day. Anglers are allowed two red drum over 28 inches in addition to their daily bag limit, but must have an ‘oversized red drum’ tag.
Spotted Seatrout, Cynoscion nebulosus, are another highly sought-after recreational species. They spend their entire life cycles in estuaries and are completely dependent on the estuarine habitat. Trout have the unique ability to spawn in hypersaline conditions, such as those found in the upper Laguna Madre. However, even with this adaptation, the extreme salinities that can be reached in the upper Laguna Madre can lead to low recruitment in young trout. Spotted Seatrout are considered top level predators, feeding on swimming prey in surface waters as well as mid- depths. Adult spotted seatrout are often associated with seagrass, as their prey can usually found in seagrass beds. Regulations state that spotted seatrout caught recreationally must be between 15-25 inches with no more than 5 caught per person per day. This can include one spotted seatrout over 25 inches as part of the daily bag limit. Anglers, fishing north of the Highway 457 Bridge near Sargent, Texas may keep up to 10 fish per person per day.


With over 253 bird species documented in 2008, it is no surprise that Nueces county gained the title of the ‘birdiest’ county on the Gulf Coast. Corpus Christi held the title for the ‘birdiest’ city in the United States with 241 species documented within the city limits from 2003 to
2008. Many birds use the Central Flyway to migrate south during winter months and stop off at local Texas ponds, bays and estuaries for resting and feeding. In fact, Texas supports more waterfowl than any other state in the Central Flyway. More than two dozen waterfowl species fly to Texas for wintering habitats including white-fronted geese from Alaska, Canada geese from the Arctic, lesser snow geese from the Hudson Bay, mallards, redhead ducks, Northern Pintails, gadwalls, American widgeons, lesser and greater scaups, and canvasbacks from many plains areas. Of the winter migrating species, a few of the most common are sandpipers, banded plovers, blackbellied plovers, dowitchers, and willets. Like the blue-winged teal, some birds only rest shortly on the Texas coast before moving farther south to Central and South America. However, some birds end their migration along the Texas coast, like the redhead duck where the journey ends at a salty bay or lagoon like the Laguna Madre.

Of the 38 documented waterfowl species on the south Texas coast, U.S. Fish and Wildlife Service recorded a staggering 2.4 million redhead ducks from September through March of 1997 and 1998 where populations peaked in December, January and February. The majority of the
North American redhead duck population and 75% of the world population winter in the Laguna Madre. Redhead ducks feed on the below ground root structure of seagrass, primarily shoal grass (Halodule beaudettei), which is abundant in the Laguna Madre. They seek out shallow water seagrass beds for feeding and resting and in close proximity to freshwater ponds for access to drinking water. The availability of healthy shoal grass is critical for the migrating redhead duck population.

The National Audubon Society identifies other birds, such as the black skimmer, brown pelican, least tern, piping and snowy plover, reddish egret, and ruddy turnstone as priority birds migrating through the Central Flyway. These types of birds are considered shorebirds and are common in the upper Laguna Madre ecosystem. In 1991, 55% of the federally protected piping plover population wintered in Texas with nearly half occupying tidal flats in the Laguna Madre. Padre Island National Seashore exists within the upper Laguna Madre ecosystem and 30 shorebird species and 20 gull and tern species have been recorded in this area. The most common birds recorded were sanderlings, laughing gulls and royal terns but piping and snowy plovers as well as ruddy turnstones can often be seen picking through debris washed up on the beach shoreline.
Most of the shorebirds recorded are found in areas of the upper Laguna Madre system during winter or migratory periods. During January and February reddish egrets, a wading bird, are two times more abundant in the upper Laguna Madre than the Lower Laguna Madre.

Many birds rely on Texas bays and estuaries due to the availability of habitat near suitable foraging and breeding grounds. In the upper Laguna Madre, natural and artificial islands provide a necessary haven for many bird species. Pita Island and the small spoil island surrounding Humble Channel in the upper Laguna Madre consists of a natural island with 5.4 hectares of land as well as 10 spoil islands (dredged materials) encompassing 1.8 hectares. South Bird Island also provides five hectares for extensive colonial bird nesting while many spoil islands exist within the Padre Island National Seashore boundary. These natural and artificial islands have become essential for nesting and are also referred to as Rookery Islands. The loss of nesting grounds in inland areas have pushed many species, like the little blue heron, out to these islands to find suitable breeding and nesting grounds. Some of the waterbird rookeries at Bird Island in the upper Laguna Madre include tricolored herons, snowy egrets, reddish egrets and great blue
herons. In the winter it is common to see reddish egrets and snowy plovers nesting on the spoil islands but other birds such as black skimmers can be seen nesting on the islands between March and September. Great blue herons may begin courtship and nesting as early as January to avoid competition.

Different bird species exhibit different nesting behaviors. Ground nesters, such as American white and brown pelicans, black skimmers, gulls and terns make nests and lay eggs directly on the ground while shrub nesters, roseate spoonbills, herons, egrets and ibises prefer to make nests on elevated shrubs. Great blue herons tend to use tall vegetation like the sea-ox-eye daisy (Borrichia frutescens) near Baffin Bay but will use common cattail (Typha spp.) or even Mesquite (Prosopis sp.) based on the availability of vegetation on the island. Reddish egrets often use common ragweed (Ambrosia sp.) or sea-ox-eye daisy (Borrichia frutescens) for nesting. While using the islands for habitat and nesting, many birds will wade in shallow water and forage on fish and crustaceans while other birds like ducks and cormorants will forage for benthic and nektonic invertebrates by floating or diving. Gulls, terns, pelicans and osprey are aerial hunters and typically find prey in deeper water.

Artificial and natural islands are also important for other bird species. Resident and migratory waterbirds, shorebirds, songbirds and raptors use these islands for resting and feeding. The American white pelicans average population in the upper Laguna Madre is 262 and colonizing populations on these islands are becoming more popular near areas like Bird Island. Due to these islands being used by many different species of birds during different life stages they can act as indicators of ecosystem health.

Although the islands within the upper Laguna Madre system are a major habitat area for the birds observed on the Texas coast, other areas such as King and Kenedy Ranch are vital to many waterfowl, such as ducks, and other migratory birds. These areas provide necessary breeding grounds and if destroyed would negatively impact many species. Maintaining a healthy ecosystem is vital to all of the birds that call the upper Laguna Madre their home either permanently or temporarily. The consequences of anthropogenic effects can be illustrated by the drastic decline of Brown Pelican populations in Texas in the early 1960s as a result of DDT
(Dichloro-diphenyl-trichloroethane), a pesticide once commonly used in coastal areas for mosquito control and agriculture. DDT caused a reduction in thickness of brown pelican eggshells by 15-20% resulting in increased mortality due to ease of the shell being crushed. In the early 1960s there were less than 100 brown pelicans with only 10 breeding pairs in Texas. After DDT was banned from use in the early 1970s the brown pelican population has seen a steady recovery. In 1995 it was estimated that Texas had over 2,400 breeding pairs of brown pelicans. This is an example of a successful recovery of an endangered species due to regulatory control. Continued monitoring of areas like the upper Laguna Madre is critical for ensuring that birds like the redhead duck and the brown pelican have a place to rest, forage for food, and nest.

Other Notable Marine Life

Many marine animals call the upper Laguna Madre home and utilize the productivity of this
system for foraging or habitat. A marine mammal that can commonly be seen in the Laguna is the Atlantic Bottlenose Dolphin (Tursiops truncatus). Pods of dolphins can typically be seen swimming throughout the Laguna, especially early in the morning. Of the five species of sea turtles known to occur in Texas, the green sea turtle is the most common in the upper Laguna Madre. Many sea turtles utilize the beach shoreline for nesting during certain months of the year. Padre Island National Seashore, one of 10 nationally recognized seashores in the United States, has a Sea Turtle Science and Recovery program which assists with sea turtle nesting and hatching success (http://www.nps.gov/pais/naturescience/stsr.htm). Leatherback (Dermochelys coriacea), Hawksbill (Eretmochelys imbricate), Green (Chelonia mydas), Loggerhead (Caretta caretta), and Kemp’s Ridley (Lepidochelys kempii) are five of the world’s seven threatened or endangered species of sea turtles that utilize Padre Island National Seashore for nesting. This area of Padre Island National Seashore is the only place along the Texas coast where all five species nest. Along with assisting with nesting and hatching success the organization assists with sea turtle stranding’s and public education efforts. The Padre Island National Seashore offers public viewings of sea turtle hatchling releases during the summer months.

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