Gulf of Mexico Integrated Science - Tampa Bay Study

Characterization of Tidal Wetlands 

cal effects and ecological functions 

of mosquito ditches to plan and 

access restoration of ditched wetlands. 

U.S. Geological Survey (USGS) 

scientists have permanently tagged 

mangrove trees to measure their 

growth and survival rates in a variety of hydrological and ecological 

settings, both natural and altered. 

At ditched sites, sediments were 

side cast during ditch construction, thereby forming raised areas, 

termed berms, along ditches. These 

berms tend to act as dams, thereby 

changing the timing and duration 

of fl ooding of adjacent forests as 

well as the composition of streamside vegetation. For example, 

Introduction

Tidal wetlands in Tampa Bay, 

Florida, consist of mangrove forests and salt marshes. Wetlands 

buffer storm surges, provide fi sh 

and wildlife habitat, and enhance 

water quality through the removal 

of water-borne nutrients and contaminants. Substantial areas of 

both mangroves and salt marshes 

have been lost to agricultural, residential, and industrial development 

in this urban estuary. Wetlands 

researchers are characterizing the 

biological components of tidal 

wetlands and examining the physical factors such as salinity, tidal 

fl ushing, and sediment deposition 

that control the composition of 

tidal wetland habitats. Wetlands 

restoration is a priority of resource 

managers in Tampa Bay. Baseline 

studies such as these are needed for 

successful restoration planning and 

evaluation. 

Approach

Mangrove health

Mangroves are trees that are 

adapted to grow in salt water, 

and are the dominant feature of 

the intertidal landscape in Tampa 

Bay. Mangroves are sensitive to 

sediments contaminated by oil and 

oil by-products. Red mangroves 

affected by such contaminants 

show changes in their physical 

appearance in the form of albinism in their propagules, i.e., 

seedlings that germinate while still 

on the tree. Albinism is an easily 

observed characteristic because 

affected propagules are pink or 

yellow instead of their normal 

green color. Thus, a high percentage of albino propagules can be 

used as an indicator of contaminants in red mangrove-dominated 

wetlands.

Mangrove vegetation and fi shes

Tampa Bay tidal wetlands are 

fl ooded and drained by both natural tidal creeks and by man-made 

mosquito control ditches constructed primarily between 1940 

and 1970. These ditches were built 

to control salt marsh mosquitoes by 

promoting access by small fi shes 

that eat mosquito larvae throughout the tidally inundated forests. 

More advanced means of mosquito 

control, including larvicides that 

solely target mosquito species, are 

now available. Therefore, resource 

managers need data on the biologiMap of Tampa Bay study area showing 

locations of sampling sites (red - fi sh sampling sites, green - landscape history and 

ecology, blue - mangrove genetic survey, 

gold - vegetation study).

Normal propagules of the red mangrove 

are green. Those propagules lacking 

normal pigments are termed albino and 

are pink or yellow in color.

USGS Open-File Report 05-1174

April 2005

U. S. Department of the Interior

U. S. Geological Survey
Carole McIvor, Task Leader

U.S. Geological Survey, Biological Resource Discipline

600 4th Street South, St. Petersburg, FL 33701

Email: carole_mcivor@usgs.gov

Kimberly Yates, Project Chief 

U.S. Geological Survey, Geologic Discipline

600 4th Street South, St. Petersburg, FL 33701

Email: kyates@usgs.gov 

For more information, please contact:

http://gulfsci.usgs.gov

Tom Smith, USGS/Biological Resource Discipline

Ed Proffi tt, USGS/Biological Resource Discipline

Steve Travis, USGS/Biological Resource Discipline

Ellen Raabe, USGS/Geologic Discipline

Randy Runnels, Florida Dept. of Environmental Protection

Karen Hill, Pinellas County Dept. of Environmental Management

Contributing Scientists:

elevated berms favor undesirable 

invasive species like Brazilian 

pepper over native mangroves. 

USGS scientists are also characterizing the species composition 

of fi sh, shrimp, and crabs that 

use natural creeks and man-made 

mosquito ditches. Wetland ditches 

with good tidal fl ushing support a 

wide variety of commercial and 

recreational species, including 

red drum, snook, spotted seatrout, 

sheepshead, mullet, black drum, 

pink shrimp, and blue crab.

Coastal landscape

USGS scientists are incorporating data from modern and historic 

sources to identify changes in 

coastal vegetation communities. 

Cartographic and photographic 

analyses strongly suggest that 

mangroves have been replacing 

salt marsh and low-salinity coastal 

wetlands in a gradual northerly 

and landward direction in Tampa 

Bay since 1874. Factors favoring 

mangroves over salt marsh vegetation include a warming climate, 

freshwater diversions, and altered 

wetland hydrology such as mosquito ditches. Rising sea levels 

mean that mangroves will also 

expand inland and upriver where 

there are no barriers such as berms 

or seawalls. Apparent mangrove 

expansion has implications for 

restoration. Long-term, freshwater 

wetlands and low-elevation coastal 

forests will need relatively greater 

protection as they receive simultaneous pressures from mangrove 

expansion from seaward, and urban 

expansion from inland. USGS scientists are working with resource 

managers from state and county 

agencies to defi ne the hydrological 

and physical conditions that favor 

the dominance of a particular intertidal species over another. They 

are examining conditions under 

which engineering actions such as 

plugging mosquito control ditches 

and excluding tidal waters might 

promote long-term development 

of freshwater wetlands in selected 

locations.

Links to Other Project 

Research

Wetlands scientists use core 

data collected by geologists to 

understand the past history and 

longevity of tidal wetlands in their 

present locations. On a different 

timescale, remote sensing experts 

supply high-resolution mapping 

data that give a current view of 

bay wetlands and their elevations. 

Data from the water quality team 

on sediment contaminants adjacent 

to tidal wetlands supply information on past and ongoing stressors.

27o 54’

82o39’

1874 Historic Topographic Chart

1999 CIR Aerial Photography

27o 54’

82o39’

Salt Marsh

Mangrove and 

Mosquito Ditch

Complex

Mangrove

 fringe Uplands

1874 coastline

0 0.5 1 km 

USGS scientists track changes in Tampa 

Bay tidal wetlands by comparing historic 

shoreline and wetland features at Feather 

Sound.

Researchers sample fi sh and crustaceans 

(shrimp, crabs) in a manmade mosquito 

control ditch in a modifi ed wetland.