Chapter 2 – State of the Bay, Third Edition

CHAPTER 2 – STATE OF THE BAY, THIRD EDITION

Galveston Bay: An Overview of the System

Written & Revised by L. James Lester

Ecosystems are open systems, that is, things are constantly entering and leaving, even though the general appearance and basic functions may remain constant for long periods of time. —E. P. Odum, Ecology and Our Endangered Life Support Systems, 1989

Introduction

Galveston Bay is a tremendous recreational, economic, and environmental

asset to Texas and the nation.1 To properly manage human activities that affect this ecosystem, it is necessary to understand the system’s composition, the processes that link its components, and how it interacts with its environs.

Figure 2.1. Sunset on Galveston Bay. Image courtesy ©2006 This bay is a complex, iStockphoto.com/Dave Huss. interconnected system of biological, hydrological, and geological resources providing services and recreation to a large number of people. The watershed provides space and resources for a dynamic metropolitan area, the Houston- State of the Bay

Galveston metroplex. It is important to understand this estuarine system for the betterment of the –

2 population that uses it and the conservation of nature that it represents. Five ecological concepts are important for understanding the physical and biological systems that operate in this space: watershed, estuary, ecosystem, food web, and habitat. CHAPTER

Galveston Bay and Its Environs as a Watershed

Galveston Bay and the land around it fit the concept of a watershed. A watershed is the area of land that drains into a water body. In the case of Galveston Bay, the watershed comprises all of the watersheds of the tributaries—the Trinity River, the San Jacinto River and all of the creeks and bayous that feed into the rivers or directly into the bay, plus a small area of adjacent land that drains directly into the bay. All of the changes that humans make to the land surface and the stormwater drainage system alter the dynamics of water flow through the Galveston Bay watershed. So much land is covered by buildings and roads that it is much less likely for a raindrop to soak into the ground now than 100 years ago. It is likely that the water moving to the bay will carry dissolved or suspended pollutants or debris. Small tributaries to the bay now tend to have more highly variable flows because there are fewer acres of wetlands to hold and slowly release stormwater. Many areas have drainage Figure 2.2. In a watershed, the movement of water ditches or channelized bayous that are designed defines the boundaries and hydrological processes to move water quickly to the bay. connecting the atmosphere, surface and subsurface. Image source: (AWAG 2009). In contrast, the major river tributaries have been dammed as water supplies and have more uniform flows than in the past. The San Jacinto River has 2 major reservoirs: Lake Houston resulted from a dam across the East San Jacinto River in 1953; Lake Conroe, on the West San Jacinto River, was completed in 1973. The Trinity River has several reservoirs along its length, but the most important for the dynamics of Galveston Bay is Lake Livingston- the one farthest downstream, completed in 1969. These reservoirs change the dynamics of runoff and inflow in the Galveston Bay watershed. The network of smaller water bodies has also been altered in the Galveston Bay watershed over the last century (see Chapter 3). Travel across the prairie was very difficult in the 19th century. Agriculture was also challenging due to the periodic wetland nature of much of the land. The solution of developers and State of the Bay

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agriculturists was to dig drainage channels, which still exist, and produce much more rapid runoff than the natural landscape. The Harris County Flood Control District estimates that about 800 miles of natural 2 drainage channels existed in the county before human modification (HCFCD 2009). At the present time

there are more than 2,500 miles of channel in Harris County’s drainage system. CHAPTER

Watersheds in the Galveston Bay system take many shapes and sizes, with smaller watersheds nested within larger ones. Residential, industrial and agricultural lands all reside within these watersheds. Land-based activities often diminish the quality of water within the watershed. Fertilizers and pesticides from lawns, herbicides from fields, and oil and grease from roads and parking lots can progress from the land into the water when transported via surface runoff. In recent years, water management strategies have begun to follow a watershed approach to address these nonpoint sources of water pollution.

Characterization of the Watershed Streams and rivers are longitudinal systems surrounded by watersheds. The Trinity River is a large river system with a watershed that extends north to encompass the Dallas–Fort Worth region. The San Jacinto River is much smaller and confined to Southeast Texas. Galveston Bay is also fed by coastal streams and bayous such as Cedar Bayou, Dickinson Bayou, and Chocolate Bayou. Watersheds play a critical role as contributors of pulses of nutrients, organic matter and contaminants to the estuary. Our current understanding indicates that freshwater inflows transport more than 80 percent of the imported

carbon and nitrogen and 95 percent of the phosphorus to Figure 2.3. Map depicting the entire Galveston Bay Watershed extending from the Gulf of Mexico to the Dallas–Fort Worth Galveston Bay, with the metroplex. The Lower Galveston Bay Watershed is in dark orange.

State of the Bay remainder contributed by Image source: Houston Advanced Research Center.

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2 peripheral marshes and air deposition (Armstrong et al. 1982; Borey et al. 1983; Byun et al. 2008). Also among the inputs are pollutants and debris. CHAPTER

The tributaries are not simply conduits for freshwater, nutrients, and sediment. They also contain dynamic ecological systems that process the materials. Without the inflow of freshwater, nutrients, and sediments transported by rivers and streams, the estuary would not exist. It would be a lagoon, a salty extension of the Gulf. The Galveston Bay watershed is defined by the watersheds of the tributaries that flow into the bay, especially the Trinity River, and the land areas from which stormwater flows directly into the bay. This book is focused on the orange-shaded portion of Figure 2.3, referred to as the Lower Galveston Bay watershed, which excludes the areas on the Trinity River above Lake Livingston dam and on the San Jacinto River above Lake Houston dam. The entire Galveston Bay watershed consists of approximately 24,000 square miles of land and water, which dwarfs the 600 square miles covered by the bay (see Figure 2.3). Within this large system, there is variation in the hydrological pattern of the various tributaries. The characteristic flow regimes of the bayous, streams and rivers are quite different. The Trinity and San Jacinto Rivers are gauged for quantity of water carried to the bay. According to the Texas Water Development Board, on average the

Trinity River contributes approximately 54 percent Figure 2.4. The Galveston Bay estuary has a salinity gradient. Freshwater enters in the upper estuary and mixes with salt water from of annual freshwater inflow the Gulf of Mexico. to Galveston Bay (Powell et al. 1997; Buzan et al. 2009). Much less is known about the hydrology of bayous, the most common type of tributary to Galveston Bay. Bayous operate primarily as extensions of the tidal bay system and may have no natural source of freshwater beyond precipitation. All of the tributary types are monitored for water quality, which is discussed in Chapter 6. State of the Bay The Upper Watershed –

Galveston Bay has 2 large “upper watersheds,” with a combined area of nearly 20,000 square miles 2 upstream of Lake Houston on the San Jacinto River and Lake Livingston on the Trinity River. The Trinity River extends past the Dallas– Fort Worth metropolitan area and has numerous artificial reservoirs on its CHAPTER

tributaries and on the main stem. Land use and land cover classes within the watershed include forest and wetland along the river floodplain, agriculture in many parts of the watershed, and urban areas and rangeland in the far northwestern part of the drainage area. The San Jacinto River is mostly forested upstream of Lake Houston, with some urbanization in its lower drainage area. Lake Conroe is a large reservoir located on the upper portion of the Western Fork of the San Jacinto River.

The Lower Watershed The lower watershed is defined as the area, exceeding 4,000 square miles, draining to the bay downstream of 2 major impoundments: Lake Houston on the San Jacinto River, and Lake Livingston on the Trinity River. The 2 reservoirs attenuate some runoff and pollutant loads from the upper watershed. Therefore, the lower watershed, below the reservoirs, more directly contributes runoff and runoff-born detritus and pollutants to the bay than does the upper watershed. The metropolis of Houston and its associated suburban communities occupy the western side of the bay, while the eastern side remains largely agricultural and undeveloped. Urban and suburban development is very significant to the bay through the contribution of polluted stormwater runoff from parking lots, streets, highways, roofs, and yards (Newell et al. 1992; Basnyat et al. 1999; Wu et al. 2008). Agriculture on the eastern shore contributes nonpoint sources of herbicides and pesticides. Livestock operations can serve as sources of bacteria. Nutrients may come from a variety of sources, including agriculture, suburban development, and atmospheric deposition. As seen in Figure 2.4, Galveston Bay is commonly divided into 5 major sub-bays. The main body of Galveston Bay is broken into Upper and Lower portions. Upper Galveston Bay receives inflow from the San Jacinto River and much of the local drainage from the City of Houston via the Houston Ship Channel— a human modification of the mouth of the San Jacinto River and the lower reach of Buffalo Bayou and Clear Creek. Trinity Bay receives inflow from Trinity River, Cotton Bayou and Double Bayou. Lower Galveston Bay is divided from Upper Galveston Bay at a line from Smith Point on the east to Eagle Point on the west (the former location of Redfish Bar— see Chapter 3), and continues to the pass at Bolivar Roads into the Gulf of Mexico. Lower Galveston Bay receives freshwater from Dickinson and Moses bayous. East Bay lies toward the mainland from Bolivar Peninsula and receives inflow from Oyster Bayou, the Gulf Intracoastal Waterway, and small tributaries and surface runoff from Chambers County. West Bay is situated landward of Galveston Island, and receives runoff from Chocolate Bayou, Mustang Bayou, and other local bayous. West Bay is largely separated from Lower Galveston Bay by the Texas City Dike, extending to San Luis Pass. Christmas Bay, Bastrop Bay, and Drum Bay are 3 relatively undisturbed, somewhat isolated, secondary bays in the far southwestern part of the estuary that receive inflows from several bayous. There are 3 tidal inlets to the bay, but only 2 are of major importance with regard to flow. Bolivar Roads (Figure 2.5), between Galveston Island and Bolivar Peninsula, accounts for the majority of the tidal State of the Bay

– exchange between the bay and the Gulf of Mexico. San Luis Pass, between the western end of Galveston

2 Island and Follets Island, is a natural inlet that supplies a lesser amount of the bay’s tidal exchange. Rollover Pass is an artificial cut through Bolivar Peninsula that creates minor tidal exchange between the Gulf of CHAPTER

Mexico and East Bay. Rollover Pass will likely be closed by the Texas General Land Office, in response to Hurricane Ike– associated damage to Bolivar Peninsula and SH 87. Areas with greater tidal flushing and less urban and industrial development generally exhibit higher water quality. As noted in Chapter 6, the open-bay waters generally exhibit few water quality problems, but the tributaries with point source discharges or nonpoint source runoff from intensively developed land, particularly in the urban-industrial area around the lower San Jacinto River and Buffalo Bayou, have significant water quality problems. Flooding occurs periodically in the Galveston Bay watershed and can happen in any of the tributaries. Flooding is a natural process connecting the aquatic and terrestrial ecosystems. It periodically introduces pulses of nutrient- and sediment-rich water necessary for the existence of floodplain forests and surrounding wetlands. Floods also bring dissolved and suspended organic material and contaminants to the estuary. Some flooding events in the Lower Galveston Bay watershed are driven by tides and storm surge rather than precipitation.

Figure 2.5. Bolivar Roads is the inlet that lies between Galveston Island and the State of the Bay Bolivar Peninsula. It accounts for the majority of the tidal exchange between –

Galveston Bay and the Gulf of Mexico. Image source: (NAIP 2008). 2

CHAPTER

The Importance of Stakeholders: Meeting the Challenge of Securing Freshwater Inflows to Galveston Bay

By Priscilla Weeks Estuaries are by definition systems in which freshwater from land and rivers mixes with salt water from the ocean. Freshwater enters Galveston Bay from a variety of sources; the Trinity and San Jacinto rivers, along with the bayou watersheds that flow directly into the bay, supply virtually all of the freshwater inflow to Galveston Bay. The amount, timing, location, and quality of freshwater entering the bay have long been issues for management, as human uses of freshwater (e.g., drinking water, irrigation, and industrial processes) affect the amount of water entering the bay, particularly during droughts, when freshwater is scarce. Complicating the matter is the extent of the Galveston Bay watershed. Water use by people as far away as Dallas–Fort Worth is directly tied to the amount of water flowing down the Trinity River to Galveston Bay. The Galveston Bay Freshwater Inflows Group offered the first opportunity for a diverse group of bay stakeholders to sit down, face-to-face, in a neutral venue and have in-depth discussions about freshwater inflows using a collaborative learning model. The GBFIG was established in 1996 to reach consensus among stakeholders in the development of a scientific management plan and implementation strategies to supply freshwater inflows to the Galveston Bay system. That mission is consistent with, and supports, the “Freshwater inflow and circulation action” element of The Galveston Bay Plan. The GBFIG made one of the earliest attempts to deal with ensuring freshwater inflows to bays and estuaries, and its pioneering efforts Once the State of Texas had a are important for 3 key reasons. First, it brought together diverse recommended inflow for the Galveston interests in a neutral venue to focus on the science and policy Bay system, we were still left with the pertaining to inflows, and generated a level of trust not present task of figuring out how to implement before. Second, GBFIG worked exclusively on freshwater inflows that recommendation. The science of and, as a result, some of the key scientific and management issues freshwater inflows can be incredibly being discussed today in other bay systems were first discussed by the complex, but no more complex than the GBFIG— including the identification of target inflow frequencies, a multiple, interrelated, sometimes recognition of the importance of timing (e.g., seasonality) and conflicting human interests that need to location (e.g., river basins) of flows, the identification of diverse be accounted for in a public policy that tools to ensure flows, and the use of criteria and scenarios to discuss secures future inflows to Galveston Bay. these tools. Third, the GBFIG’s work stimulated legislative initiatives GBFIG has been a mechanism for by keeping the issue of freshwater inflows before the policy bringing many of those interests into community. The group can take some credit for the current one room on a fairly regular basis to attention being paid to freshwater inflows. consider the science and to create a path State of the Bay

– to the solution.

2 -Glenda Callaway

CHAPTER 7

The impact of the debate about freshwater inflows on the policy landscape (comprising the institutions and scientific activity devoted to inflow management) has grown since the introduction of water planning in the late 1950s (Figure 2.6). When the GBFIG was created in 1996, the primary policy actors concerned with freshwater inflows were state agencies and the legislature. The current landscape is much more populated, with NGOs, agencies, multi-agency working groups, scientific advisory groups, the legislature and the governor’s office all working on the issue through myriad institutional forums and scientific studies, as can be seen in the illustration below. Individual members of the GBFIG have participated in all of these forums.

Figure 2.6. The impact of the debate about freshwater inflows on the policy landscape has grown since the introduction of water planning in the late 1950s. Image courtesy of Priscilla Weeks.

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CHAPTER

The Estuary

An estuary is defined as an “inlet of the sea reaching into a river valley as far as the upper limit of tidal rise, usually being divisible into 3 sectors: (a) a marine or lower estuary, in free connection with the open sea; (b) a middle estuary subject to strong salt and freshwater mixing; and (c) an upper or fluvial estuary, characterized by freshwater but subject to strong tidal action (Fairbridge 1980). This definition emphasizes 2 aspects of an estuarine system: mixing water of distinct salinities and tidal movements of water. We tend to think of the geography of Galveston Bay, shown in Figure 2.4, as delimiting the estuary from the mouth of the Trinity and San Jacinto rivers to the passes into the Gulf at Bolivar Roads and San Luis Pass. However, the tidal movement of water occurs many miles up some tributaries and the mass of low salinity water sometimes extends many miles into the Gulf. Galveston Bay has the properties of an estuary in several senses. In a geologic sense, the bay can be described as a bar-built estuary, the bar being Galveston Island and Bolivar Peninsula. The rise of sea level into the river valley of the Trinity and the formation of the barrier islands is explained in detail in Chapter 5. In a functional sense, the estuarine properties of the bay can be classified by patterns of water circulation and resultant salinity. Galveston Bay can be characterized as a vertically mixed estuary, and the lower, middle and upper zones described in the above definition can be delineated based on historical monitoring. In the geologic sense, the boundaries of Galveston Bay are fixed as the space between the mouths of the

Trinity and San Jacinto Rivers and San Luis Pass and Bolivar Roads (Chapter 5). In the functional sense, the 9 spatial extent of the estuary is determined by the distance from the upper reach of tidal influence to a zone where the salinity of the water mass is nearly oceanic (~ 35 practical salinity units or psu). Under the latter approach, the size of the estuary varies according to the amount of freshwater flowing into the system. As noted above, Galveston Bay is a bar-built estuary formed in a drowned river delta. From space photography, the bayous appear to have been channels of the deltas separated from the Brazos and Trinity Rivers as their courses meandered. Galveston Island is a sandbar about 5,000 years old that impedes the flow of freshwater from the Trinity River and San Jacinto Rivers into the Gulf of Mexico (see Chapter 5). Bolivar Peninsula is a relatively young barrier, having formed over the last 2,500 years (Rodriguez et al. 2004). Sediments from the river watersheds and the immediate surroundings blanket the bay bottom. Weather, including rainfall and wind, strongly affects the composition and circulation of bay waters. During times of drought in the watershed, the salinity of the bay system may range from 20 psu at the

Trinity River delta to 35 psu at Bolivar Roads. When the Trinity River or all tributaries are under flood conditions, the salinity will be 0 psu well into Trinity Bay and less than 15 psu at Bolivar Roads. In times of normal flow, salinity ranges from less than 10 psu in upper Trinity Bay to around 30 psu at Bolivar Roads, but there is typically a tidal wedge of high salinity water, greater than 30 psu, in the bottom of the Houston State of the Bay

– Ship Channel. A salinity wedge also reaches up the Trinity River; its existence is the reason for the U.S. Army Corps of Engineers Wallisville Lake Project on the Trinity River just west of Lake Anahuac. Those plants and animals that can tolerate fluctuating salinities and temperatures are found permanently in

CHAPTER 2 the estuarine environment. However, as the salinities change, the diversity of species also changes. High

flows of freshwater and low salinities lead to increasing abundance of freshwater species from the connected rivers, streams, and bayous. Low freshwater inflows and high salinities lead to increased abundance of marine species entering the bay from the Gulf of Mexico. The diversity resulting from salinity variation is natural for the Galveston Bay system. It is characteristic of the physical and ecological diversity of an estuary. The Ecosystem

The concept of an ecosystem was developed to explain how processes relating to population dynamics tied a biological community to its physical environment (Tansley 1935). Lindeman (1942) outlined the principles of trophic dynamics, or energy transfer, through ecosystems. Later, Odum (1953) provided a unifying model that re-defined the ecosystem as “a natural unit that includes living and non living parts interacting to produce a stable system in which the exchange of materials between the living and nonliving parts follows a circular path.” This means that ecosystems recycle their materials and have a stable composition of species and nutrients. This may be a reasonable approximation for a mountain lake, but not for an estuary. As a matter of fact, ecologists have debated the stable versus dynamic nature of biological communities for many decades. In most environments, ecosystems are difficult to define because they have indistinct edges, come in all sizes, and overlap and interact with one another. It has even been suggested that the

ecosystem concept should no longer be used because it exists only as a conceptual paradigm Figure 2.7. An ecosystem includes living and yields almost no falsifiable predictions organisms, nonliving components, and the interactions between them. Image source: (USFWS (O' Neill 2001). Ecosystems, once disturbed, do 2008). not return to an equilibrium state because they are not closed systems. Rather, they are open to movements of organisms and materials. Ecosystems exist in hierarchical structure. As we will see in Galveston Bay, there are ecosystems within ecosystems. There is a spatial pattern that can be discerned, but it must be described in the language of natural history, not scientific observations (O'Neill et al. 1986; Pickett et al. 1992; Levin 1999). We must also not forget that human socio-economic systems cannot be separated from the concept of the ecosystem. Despite our State of the Bay

understanding of the discrepancies between the biological communities observed in Galveston Bay and the –

ecosystem concept, we will use the term because it provides a way to communicate about the biological 2 organization of the bay. CHAPTER

Although it may be convenient to draw a boundary around the bay and call it an ecosystem, there is no boundary in the water that separates the bay from its tributaries. Organisms move through this borderless aquatic space according to their preferences for living conditions. To properly understand the processes and components of the bay, it is necessary to follow the connections of the bay ecosystem up the tributaries and across the water-land interface. In Chapters 7 and 8 we will describe the habitat and organisms that exist in the bay, the freshwater tributaries, and the forests and prairies in the watershed. Galveston Bay is influenced significantly by the interchange of resources and organisms among the bay system, the river and bayou watersheds, and the Gulf of Mexico ecosystem. The Gulf “ecosystem” is a major contributor of larvae and juveniles of many estuarine-dependent species that enter the estuary and seek food and shelter within the system. Due to its smaller size and variability, the estuary exhibits less biodiversity than the Gulf ecosystem. The composition and distribution of organisms varies greatly in time and space. Species seen on the bay shore of Galveston Island will differ somewhat from species frequenting the shoreline of Trinity Bay. For example, smallmouth buffalo, a predominantly freshwater species, can be found on occasion in Trinity Bay, but would rarely be found in the higher-salinity waters of Lower Galveston Bay and West Bay. Seasonal changes occur as well. Species commonly observed at a site during the summer may be replaced with other species in winter. For example, southern flounder make an annual migration into the bay in the spring and back to the Gulf in late fall. Estuaries such as Galveston Bay contain ecosystems that exhibit high variability because they respond to many perturbations of different temporal and spatial scales. Estuaries change in response to daily cycles, tidal cycles, seasonal cycles, hurricanes, droughts and other episodic influences. Knowledge of the components of the ecosystem, the diverse plants and animals that build and inhabit its habitats, does not automatically lead to an understanding of ecological function— that is, how the bay ecosystem acquires, processes, and stores its materials and energy; releases and assimilates its waste products; and interacts with adjacent waters and the surrounding landscape. The aquatic ecosystems of the watershed provide both “goods” and “services” to society (Odum 1997). Ecosystem goods include food, cooling water and shells. Ecosystem services include storing and cycling essential nutrients, absorbing and detoxifying pollutants, maintaining the hydrologic cycle, and moderating the local climate. In human terms, services also include providing sites for recreation, tourism, research and inspiration. When human activities disrupt the essential functions of an ecosystem, the assimilative capacity of the natural system can be exceeded and the normal flow of goods and services provided by healthy ecosystems can become impaired. Estuaries are among the most naturally fertile waters in the world (Schelske et al. 1962; Day et al. 1989; State of the Bay Odum 1997), their high productivity results from their unique juxtaposition at the edge of the continent. –

2 Nutrients from 4 sources contribute to the productivity of estuaries: (1) freshwater flowing off the land, (2) tidal exchange with the ocean, (3) deposition from the atmosphere, and (4) the recycling of material from the estuarine bottom sediments. The most important limiting nutrient for productivity in estuaries is CHAPTER considered by many to be nitrogen (Howarth et al. 2006), a component found in all proteins. However,

phosphorus, silica, carbon, and other compounds also serve as nutrients to ecosystems in the estuary. The relative contribution of nutrients to estuarine productivity is dynamic- it may vary between estuaries, among various locations within estuaries and even at different times of the year.

Galveston Bay Food Webs

From the simplest microscopic plants to the largest animals, organisms are connected to each other in a set of pathways of consumption known as a food web (Figure 2.8). In a food web, paths of energy flow connect plants to herbivores to predators and all 3 to decomposers. While an ecosystem is a theoretical view of the organization of nature, a food web is grounded in the simple observation of which prey species is eaten by which predator species and can be empirically described for such dynamic environments as estuaries (Livingston 2003).

Figure 2.8. Composite food web for the Galveston Bay estuary. This diagram shows the dependence of the estuarine food webs on primary productivity and detritus. Modified from (TDWR 1981). Estuarine food webs (Monroe et al. 1992) are organized by energy flow from green plants (such as planktonic algae) to higher consumers (such as bay anchovy, red drum, and humans) and to consumers of State of the Bay

– dead organisms (such as bacteria and blue crab). The same organization can be analyzed by describing the 2 cycling of compounds like carbon and phosphorus, which are essential for life. When following the consumption of biomass from the bay, it is obvious that there are connections that cross the water-land

interface. Gulls, herons, egrets, and terns feed in the bay, but nest and rest on the land and excrete and die CHAPTER

on land. They are sometimes prey to coyotes and raccoons, which are not normally considered part of the estuarine ecosystem or food web. In this way, biomass leaves the bay ecosystem through food-web connections. Food webs in Galveston Bay are essentially of 2 types (Armstrong 1987). One food web is based on production and consumption of living plant tissue in the form of free floating phytoplankton or submerged vegetation. The second web is based on detritus—dead plant and animal tissue—produced both within and outside the bay system. Detritus is received from the watershed in river and bayou inflow and from the fringing marshes. Detritus-based food chains are complex and the flow of nutrients poorly understood (Livingston 2003), but in Galveston Bay, detritus-based food chains likely contain more biomass than food webs based on living plants. McFarlane (1994) modeled 6 food webs associated with different habitat types in the bay. Occasionally some species in the Galveston Bay food web exhibit dramatic increases or decreases in abundance. One example of an increase is algal blooms. Phytoplankton species can become so abundant that their nocturnal metabolism uses most of the available oxygen in the water and larger organisms either leave the area or die. Some species of dinoflagellates (e.g., Karenia brevis) cause the phenomenon known as red tide when they bloom and produce toxins (brevetoxins). Red tide brevetoxins can kill or harm organisms in or near the water. Lethal exposures to fish and shellfish are typical when organisms encounter high concentrations of toxins in the water. Brevetoxins have serious impacts on sessile benthic animals, such as oysters, which have no ability to escape areas undergoing harmful algal blooms. Humans can experience respiratory illness through the inhalation of brevetoxin aerosols in the surf zone or contract neurotoxic- shellfish poisoning (see Chapter 9), which can cause severe gastrointestinal and neurological symptoms when brevetoxin-contaminated shellfish are eaten (Cheng et al. 2005). Human activities can also shift the dynamics of food webs. Commercial shrimp trawls in Galveston Bay not only capture shrimp, but also accidentally capture other estuarine species of invertebrates and finfish not desirable for commercial harvest. The non-target species, also known as bycatch, are separated from the shrimp catch and discarded into bay waters. Similarly, recreational fishermen may catch, handle, and release non-target species. The fish may survive, die from handling stress or injury or may be used as bait for sportfishing. In both commercial and recreational instances, the biomass is extracted from the bay as living organisms, but may be returned dead (as detrital material), thus modifying the flow of energy and materials through the bay food web.

Galveston Bay Habitats

Estuarine habitats include marshes, mud and sand flats, seagrass beds (submerged aquatic vegetation), oyster

State of the Bay reefs, open-bay bottom and open-bay water; all of which occur in the Galveston Bay system. The

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2 abundance of nutrients and the diversity of available habitats within the estuary provide for very high levels of biological productivity. Many of the commercially and recreationally harvested seafood species in the Gulf of Mexico and its bay systems require estuarine environments like Galveston Bay for one or more of

CHAPTER their life stages.

Habitats are a standard way to ecologically subdivide a physical environment, such as a watershed. It is much easier to understand the diversity of the bay and its watershed by describing habitats than by trying to define ecosystems. Habitats are parts of the system that are distinctive by their physical and biological characteristics and are used preferentially by some of the species in the larger ecosystem. A preferred habitat affords an organism space to live in, but of particular importance is the habitat’s ability to provide needed shelter (for nesting or protection from predators), food, and other resources so that an organism can complete its life cycle and produce offspring. The description of most habitats is based on physical characteristics— e.g., mudflat or open-bay water— or dominant organism— e.g., oyster reef or seagrass bed. The most common habitats in the bay are open-bay water, open-bay bottom, oyster reef, marsh, mudflat and seagrass meadow. Galveston Bay habitats are described in more detail in Chapter 7. All of the habitats are defined by their relationship with the sediment and those things that live on it and in it. Each habitat in the bay is connected (directly or indirectly) to the upstream freshwater, riverine-floodplain ecosystems, to the downstream marine waters of the Gulf, and to the terrestrial ecosystems in the watershed. The largest habitat in Galveston Bay is the 3-dimensional, open-bay water itself, to which all other bay habitats are linked. Open-bay water (the water column) is the only habitat without a place for immobile organisms. It is a habitat for nekton and plankton: fishes, squid, floating algae, and jellyfish. The underlying open-bay bottom covers an equal area. The bottom

functions as a matrix upon which Figure 2.9. The open bay is a habitat for nekton and plankton, several different types of habitat can fishes, squid, floating algae and jellyfish. Image courtesy © be found. The open-bay bottom is Jarrett Woodrow. home to worms, snails, and clams that live on and in the bay sediment. Patches of oyster reef rise up from the bay bottom where stable sediment and ample current flow occur. The oyster reef is home to oysters and the worms, clams, crabs and fish that have close relationships with them. On softer sediments in shallow water, patches of submerged aquatic vegetation— the subtidal seagrass meadows— can be found near the periphery of the bay. Seagrass meadows are dominated by species of plants adapted to submerged growth and are home to many species of crustaceans and juvenile finfish. Much of the bay bottom is soft, rippling mud and silt, uncovered by oysters or plants. State of the Bay

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As the bay bottom slopes upward at the edge of the bay, emergent intertidal marsh lines the shore. Marsh is 2 dominated by species of grass (e.g., Spartina alterniflora) that emerge from the sediment at the tidally influenced border of the bay. Some low-sloping shore zones do not support emergent vegetation, and remain as intertidal mudflats. Mudflats have no obvious vegetation, but are home to worms and snails that CHAPTER 14

feed on detritus. Patches of very soft, unconsolidated subtidal bottom are scattered within various shoreline wetlands to create the peripheral marsh embayments. In most places, the marsh and mudflats intergrade into coastal prairie. The types of grasses and broad-leaved plants that make up the prairie change with elevation and distance from the salty water. At points around the periphery of the bay, the shoreline is perforated by the mouths of tributaries. In these places the open-bay water and the open-bay bottom are continuous with the habitat of the tributaries. As these habitats are affected by lower salinity water, the biological community using the habitat changes, as well. When the water is fresh, the habitat along the periphery of the tributary may be riparian forest instead of marsh. Figure 2.10. Riparian floodplain forest in Houston. Image © 2008 iStockphoto.com/Aaron Frankel. Open-Bay Water The open-bay water consists of a large volume of water composed of multiple water masses. The high- salinity water mass from the Gulf of Mexico lies below, but mixes with, the freshwater masses that enter from the tributaries. This habitat’s occupants include all of the active swimmers (nekton) and passive drifters (plankton) found in the water column. The open-bay water is essentially featureless except for an invisible horizontal and vertical salinity gradient, and at times, gradients of temperature and dissolved oxygen. Open-bay water also varies spatially in the load of suspended solids, the concentration of nutrients and contaminants, and the abundance of organisms. The open-bay water habitat of Galveston Bay covers nearly 600 square miles and has an average depth of 7 feet (2.1 meters) (Armstrong 1987). Subsidence has increased the volume of the bay by increasing its depth and the area inundated by open water. The land surface in and around Galveston Bay has sunk by as much as 10 feet in some places since 1906 (HGCSD 2008). The open-bay habitat is associated with a food web based on photosynthetic plankton, including diatoms,

State of the Bay cyanobacteria, dinoflagellates, chrysophytes, and cryptophytes (Sheridan et al. 1989; Buskey et al. 1992;

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2 Ornolfsdottir et al. 2004a, 2004b; Pinckney et al. 2008). The primary consumers that feed upon these phytoplankton are the numerous and diverse zooplankton (small animals that are suspended in and transported by water) and phytoplanktivorous fishes, e.g., menhaden. The secondary consumers are principally fish and

CHAPTER small crustaceans. The predators of the open-bay waters are fish species of varying size, e.g., pinfish and

spotted seatrout; birds, e.g., terns and cormorants; marine mammals, e.g., bottle-nosed dolphins; and humans. Food chains in this habitat are typically short (Akin et al. 2006), extending to 3 or 4 levels (Winemiller 2004; Akin et al. 2008). However, longer food chains involving small or rare species are common and increase ecological complexity (Winemiller 2004). Longer food chains also permit high concentrations of some pollutants at the top trophic levels through biomagnification. Energy leaves the open-bay water habitat through a variety of pathways, making application of an ecosystem model difficult. Death of plankton and nekton results in the sinking of biomass to the bay bottom habitat for processing by decomposers. Suspension feeders on the bottom can capture plankton from the water column in Galveston Bay because the bay is shallow and well-mixed. Successful fishing by birds and humans results in biomass leaving the bay and being consumed by components of the terrestrial habitats and ecosystems.

Open-Bay Bottom The open-bay bottom is the second largest habitat of the bay, consisting of those areas of the bay bottom not covered with oyster reef or seagrass meadow. This habitat is nearly 2-dimensional; its depth is measured in inches. For the most part, the sediment surface seems featureless except for undulations, trawl marks, and evidence of burrowing animals. To a benthic organism, however, the features of this environment can be patchy, caused by the specific distribution of sediments of different particle size and the clumped distribution of life forms themselves. The interface between sediment and water is the location of chemical and physical exchanges essential to species living in and above the sediment. The size of this habitat has increased over the last 100 years by the removal of shell from large areas of the bay bottom, by the open- bay disposal of dredged material, and loss of submerged aquatic vegetation. The food web of the bottom habitat is supported more by detritus than by primary productivity (Akin and Winemiller 2006). The open-bay bottom is connected to the open-bay food web through the capture of phytoplankton circulated from the water column and predation of swimming organisms on occupants of the benthic habitat. Although depths within Galveston Bay are generally shallow enough for light to penetrate to the bottom, turbidity of the water typically precludes significant light penetration and photosynthetic activity on the bottom. Except for some shoreline areas, primary productivity on the bay bottom is limited or nonexistent (Day et al. 1989). Many of the primary consumers in the bay system consume detritus as well as the bacterial and fungal decomposers associated with it. These detritivores include many benthic organisms such as marine worms, bivalves, gastropods, crustaceans, bottom-feeding fishes and macro-invertebrates (Gosselink et al. 1979; Sheridan et al. 1989). Fungi, bacteria, and protozoans play a key role as benthic decomposers. Their actions release nutrients from decomposing plant and animal tissue to the sediment and water column. Preying upon the microfauna (< 0.1 millimeters in diameter) is a diverse meiofauna (0.1 to 2 mm in

length). Nematodes are most numerous, but copepods and juvenile stages of the larger invertebrates are State of the Bay

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also abundant. Larger organisms (macrofauna—2 to 20 mm in length) subdivide the habitat into 2 2 components (LaSalle et al. 1991; Harper 1992; Ray et al. 1993). The epifauna live on the surface of the bottom sediment, while the infauna burrow into the bottom sediment. Some feed by straining suspended particles from the water column (i.e. filter feeders, including most bivalve mollusks). Others feed by CHAPTER

ingesting sediment and extracting nutrients in the digestive tract (i.e., deposit feeders, including many worms). Crabs and shrimp scavenge on the surface and prey on smaller animals. The open-bay bottom habitat is closely coupled with the open-bay water habitat. Numerous fishes such as croaker, spot, mullet and drum forage on benthic organisms. Diving birds (particularly ducks) reach the benthos to consume small mollusks and other organisms. Production of planktonic larvae by benthic invertebrates and predation by birds and pelagic fishes transfer energy from the open-bay bottom ecosystem to other ecosystems.

Oyster Reef Clusters of oyster shell, live oysters and other commensal organisms form a distinct oyster-reef habitat. Oyster reefs tend to form where a hard bottom and sufficient current exist to transport planktonic food to the filter-feeding oysters and to carry away sediment and waste. The reefs in Galveston Bay form in the open bay, along the periphery of marshes, and near passes and cuts, and can be either subtidal or intertidal (Powell 1993). Reefs are typically elongated in form and run perpendicular to the direction of the current. They are particularly abundant along the side slopes of navigation channels where tidal exchange currents are dependable. The reef itself is 3-dimensional because oyster larvae settle on the top of old shells to permit growth into the water column above the established oysters. The shells cemented together create an irregular surface that establishes myriad microhabitats for smaller species. The oyster-reef community is very diverse. While Eastern oysters (Crassostrea virginica) are dominant, other bivalve mollusks, gastropods, barnacles, crabs, amphipods, isopods, and polychaete worms are normally abundant. Although shallow reefs often have some primary production from algae growing on the shells, they are dependent on the importation of food resources from open-bay water and peripheral marshes. Plankton is filtered from water moving over the reef by oysters and other suspension feeders. Predators in this habitat include fish capable of crushing mollusks (e.g., black drum); blue crabs and stone crabs, which prey on small oysters with thin shells; and oyster drills, snails that prey on oysters by drilling a hole in their shell. At low tide, avian predators can obtain prey from an oyster reef and transfer it to terrestrial systems. Also, a large amount of oyster biomass is transferred from Galveston Bay to human-dominated ecosystems every year by the oyster fishery. Oysters have a valuable ecological role as filter-feeders in the estuary. The volume of water filtered per hour is approximately 1,500 times the volume of their body (Powell et al. 1992). A large, healthy oyster population is able to filter large volumes of bay water, and may therefore influence conditions such as water clarity and phytoplankton abundance. At the same time, oysters’ propensity to bioaccumulate some pollutants (Wade et al. 1991; Sericano et al. 1994; Sericano et al. 1996) combined with their lack of State of the Bay

– mobility make them important indicator organisms for determining the health of the estuary.

2 CHAPTER

Seagrass Meadow In some areas of the bay where water is shallow and usually clear, certain plants can establish dense meadows on the bay bottom. This submerged aquatic vegetation (SAV) and associated animals make up the seagrass meadow community in soft sediments along the shorelines. In the low-salinity northern parts of the estuary, wigeongrass (Ruppia maritima) is the dominant species of SAV creating seagrass habitat. Shoalgrass (Halodule wrightii) is the dominant species forming seagrass meadows in the higher salinity waters of West and Christmas Bays. Shoalgrass beds often contain clovergrass (Halophila engelmannii) and turtlegrass (Thalassia testudinum). The sunlight requirements of these plants limits their distribution to low turbidity, shallow waters (Whaley et al. 2002). Sea grasses are also sensitive to high-nutrient conditions because they can be overgrown by epiphytic algae. The fauna associated with patches of SAV is quite diverse (i.e. 20 fish and 15 crustacean species) (Zieman et al. 1989; Czapla 1991). Many juvenile and small organisms are residents in the seagrass. Juveniles of shrimp, crab, and finfish Figure 2.11. Seagrass meadows were once extensive in Upper Galveston Bay and West Bay. species use this habitat as a nursery and migrate Image courtesy Texas Parks and Wildlife to other habitats when they mature (Beck et al. Department.

2003). Many predators, such as spotted seatrout and blue crab, are transients in the habitat. Some herbivores, such as ducks, are transient because they migrate to the Galveston Bay system for overwintering. Seagrass meadows were once extensive in Upper Galveston Bay and West Bay. Over the last 50 years this habitat has almost disappeared from West Bay (Chapter 7). The rapid decline in acreage of sea grass from the 1950s to 1990s is cause for concern because seagrass meadows are important nurseries and may be a habitat indicator of water quality. Some areas of Galveston Bay have seen a resurgence of sea grass. Since State of the Bay

1998, beds of shoalgrass and clovergrass have developed in West Bay. In 2005, there were 437 acres in –

Drum Bay and Christmas Bay with some additional acreage around Galveston Island State Park in West Bay. 2

CHAPTER

Marsh Emergent wetlands (better known as marshes) provide valuable ecological and economic benefits including habitat for economically important estuarine species, flood attenuation and improved water quality (TPWD 1997). Smooth cordgrass (Spartina alterniflora) is the dominant species of shoreline vegetation found in the fringing marshes of Galveston Bay (Minello et al. 1997). This and other species of wetland plants found in the bay’s estuarine marshes are ecologically adapted to a special set of environmental parameters associated with a tidal coastline. Emergent marshes produce an enormous biomass, a fraction of which supports terrestrial herbivores. The remainder flows to a large detritivorous estuarine food chain (Wiegert et al. 1990). One of the most significant ecological roles of tidal wetlands is their function as habitat for key estuarine species, particularly for those requiring food and cover as juveniles. Fringing marshes have pools, channels, and embayments of water that are hydrologically connected to the open bay, but make up the most significant component of marsh habitat (Minello et al. 2002). The entire marsh is inundated at high tides. The closely ranked stems of the emergent plants create an environment at their base that supports epiphytic algae and shelters phytoplankton and epibenthic algal assemblages (Zimmerman 1992). These, in turn, support additional grazer and planktivore food webs, which include important fishes and crustaceans. Wading birds are common at the marsh-water interface where they prey on invertebrates or fish.

State of the Bay

– Figure 2.12. Marshes have valuable ecological and economic benefits, including 2 habitat for economically important estuarine species, flood attenuation, and improved water quality. Image courtesy © Jarrett Woodrow. CHAPTER

Intertidal Mudflat Mudflats develop on shorelines of very low wave energy where small particles of mud or silt are deposited and the area is alternately inundated by high tides or exposed by low tides. The intertidal mudflat habitat is an exceptionally open ecosystem both physically and biologically (Peterson et al. 1979). It lacks the emergent grasses and other plants of the peripheral marshes, or the submerged grasses of the seagrass meadows. The intertidal mudflat habitat is vegetated by microalgae, macroalgae, and phytoplankton. The only animals Figure 2.13. On intertidal mudflats, members of the higher trophic levels appear as transients with the tides. Image restricted to this habitat are the courtesy © Jarrett Woodrow. infauna, such as worms and bivalves. Bacteria and fungi play important ecological roles, converting organic matter into inorganic nutrients and serving as a trophic intermediate between relatively indigestible plants and consumers of detritus (Peterson and Peterson 1979). This process of microbial growth on detritus may determine the abundance of deposit-feeding species, such as snails. The majority of the organisms in mudflat ecosystems are invertebrate deposit feeders, i.e. mollusks and polychaetes. On mudflats, members of the higher trophic levels appear as transients with the tides. At high tide, fishes move onto the flats to feed on the benthic consumers, followed by piscivorous predators, both birds and fishes. At low tide, gleaning and probing shorebirds feed on and in the exposed surface while waders seek prey stranded in tidal pools.

Terrestrial Habitats In the lower watershed, two important habitats are tightly linked to the ecological functions of Galveston Bay. Along the tributaries are riparian or floodplain forests. These forest habitats are nourished by episodic flooding events and provide nutrients in the form of dissolved or suspended organic matter in stormwater runoff. Predators of aquatic organisms, such as herons and egrets, use the forest as habitat, especially nesting habitat. In some areas, the boundary forest is a wetland, such as a cypress swamp, with the associated ecological services a wetland provides. State of the Bay

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2 CHAPTER

Upland from the salt marsh habitat, and between the riparian forests, is the coastal prairie habitat. In the Lower Galveston Bay watershed, this habitat is often a mosaic of wetland and upland ecosystems. The prairie is a habitat defined principally by the vegetative dominance of grasses. It also contains a wide variety of broad- leaved plants, but the appearance is of a sea of

grass. Historically, this Figure 2.14. Native coastal prairie at the Houston Coastal Center near habitat supported large La Marque. Image by Carolyn Fannon, courtesy Houston Coastal Center, University of Houston. populations of grazers (e.g., buffalo and deer) which were replaced by cattle. Today this ecosystem is endangered and has been largely converted to agriculture or development. More detail on this and all of the habitats described above will be provided in Chapter 7.

Summary

The Galveston Bay system can be represented in a variety of ways. Galveston Bay is the geographic end point of a large watershed that stretches from the source of the Trinity River to the Gulf of Mexico. It is an estuary that joins 2 rivers and multiple coastal tributaries to the Gulf and mixes the waters and organisms found in the freshwater and saltwater systems. A wide variety of ecosystems interact both in and around the bay, as indicated by the connections of identifiable food webs. The Galveston Bay system is composed of a complex set of habitats that function with interlinking processes to transfer energy, materials and organisms. Energy is constantly transferred among open-bay water, open-bay bottom, seagrass meadow, oyster reef, marsh and mudflat. The integrity of these distinct but interacting habitats is vital to the continued natural function and ecosystem services of the estuary. The importance of these concepts and interactions can be easily illustrated. An oyster reef is an easily

State of the Bay observed habitat. There is a boundary where oysters stop. The location of that boundary is set by many

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2 factors, but the salinity regime is one factor that is a characteristic of an estuary. Oysters feed on phytoplankton and bacteria that are produced in the connected tributaries or from nutrients entering from the watershed. Oysters are the major primary consumer of the bay and support higher trophic levels of CHAPTER

predators in a food web. It is possible to analyze the transfer of materials in an oyster-reef habitat as an ecosystem. All of the concepts explained in this chapter relate to the nature and functions of Galveston Bay. This complex system is subject to many forces that cause changes. Some drivers are direct, such as the flow of water or the migration of larvae into the bay. Other drivers are indirect, such as the economic forces that determine the level of shipping or manufacturing in and around the bay. It is incumbent on those interested in sustainably managing Galveston Bay to learn how the system operates as a watershed, an estuary, a variety of ecosystems, multiple food webs and various habitats. The forces that are likely to change Galveston Bay in the future will be covered in Chapter 10. If we wish to conserve the value of this system, we will need to understand how it works.

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TDWR. 1981. Trinity San Jacinto estuary: a study of the influence of freshwater inflows. In Texas Department of Water Resources Report LP-1 13. Austin, Texas: Texas Department of Water Resources. TPWD. 1997. Texas Wetlands Conservation Plan. Austin, Texas: Texas Parks and Wildlife Department. USFWS. Managing invasive plants: volunteers and invasive plants. of the United States Fish and Wildlife Service 2008 [cited 1 March 2009. Available from http://www.fws.gov/invasives/volunteersTrainingModule/invasives/plants.html. Wade, T. L., J. M. Brooks, J. L. Sericano, T. J. McDonald, B. Garcia-Romero, R. R. Fay, and D. L. Wilkinson. 1991. Trace organic contamination in Galveston Bay: results from the NOAA National Status and Trends Mussel Watch Program. In Proceedings of the Galveston Bay Characterization workshop; 1991 Feb 21-23, edited by F. S. Shipley and R. W. Kiesling. Webster, Texas: Galveston Bay National Estuary Program Publication GBNEP-6. Whaley, S. D., and T. J. Minello. 2002. "The distribution of benthic infauna of a Texas salt marsh in relation to the marsh edge." Wetlands no. 22 (4):753-766. Wiegert, R.G., and B.J. Freeman. 1990. Tidal salt marshes of the southeast Atlantic coast: a community profile. In U. S. Fish and Wildlife Service Biol. Report Winemiller, K.O. 2004. Floodplain river food webs: generalizations and implications for fisheries management. In Proceedings of the second international symposium on the management of large rivers for fisheries (Volume II), edited by R.L. Welcomme and T. Petr. Phnom Penh, Cambodia: Mekong River Commission. Wu, C. J., L. L. S. Lin, R. Bajpai, and D. D. Gang. 2008. "Nonpoint Source Pollution." Water Environment Research no. 80 (10):1827-1843. Zieman, J.C., and R.T. Zieman. 1989. The ecology of the seagrass meadows of the west coast of Florida: a community profile. In U.S. Fish and Wildlife Service Biol. Report. Zimmerman, R. 1992. "Marsh benthos " In Status and trends of selected living resources in the Galveston Bay System, GBNEP-19, edited by A. Green, M. Osborn, P. Chai, J. Lin, C. Loeffler, A. Morgan, P. Rubec, S. Spanyers, A. Walton, R. D. Slack, D. Gawlik, D. Harpole, J. Thomas, E. Buskey, K. Schmidt, R. Zimmerman, D. Harper, D. Hinkley and T. Sager, 376-412. Webster, Texas: Galveston Bay National Estuary Program.

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