U. S. Department of the Interior

U. S. Geological Survey

Open-File Report 2005-1017

January 2005

Large transparent chambers (called 

Submersible Habitats for Analyzing 

Reef Quality, or SHARQs) are placed 

over patches of seagrass, trapping bay 

water inside. As the seagrass grows, 

photosynthesis occurs, changing the 

oxygen levels. By measuring such 

changes, scientists can determine how 

fast and how well the seagrass is growIntroduction

Seafloor habitats, such as seagrass 

beds, provide essential habitat for 

fish and marine mammals. For many 

years, the study of seagrass vitality 

has been a priority for scientists and 

resource managers working in Tampa 

Bay. Seafloor habitats are extremely 

sensitive to changes in water quality. 

Like a canary in a coal mine, seagrass 

can serve as an ecological indicator 

of estuary health. Between the 1940s 

and the 1970s, seagrass gradually 

died in Tampa Bay. This loss has been 

attributed to a rise in urbanization and 

an increase in nutrient loading into 

the bay. Better treatment of industrial 

wastewater and runoff beginning in 

the 1980s resulted in the continuous 

recovery of seagrass beds. However, 

in the mid-1990s, the recovery began 

to level off in areas where good water 

quality was expected to support 

continued seagrass recovery, demonstrating that nutrient loading may be 

only one factor impacting seagrass 

health. Researchers now are trying 

to determine what might be affecting the recovery of seagrass in these 

areas. Currently, little is understood 

about the effects that other aspects of 

urbanization and natural change, such 

as groundwater and sediment quality, 

might have on seagrass vitality. This 

segment of the Tampa Bay integrated 

science study is intended to identify, 

quantify, and develop models that 

illustrate the impact that urbanization 

may have on seafloor habitat distribution, health, and restoration.

Approach

Mapping

To understand better the way 

seagrass beds have changed in Tampa 

Bay over time, USGS and Southwest 

Florida Water Management District 

(SWFWMD) scientists have partnered 

to develop historical maps of seagrass 

beds. These maps compare the locations of seagrass with increasing development in the area. Researchers are 

examining changes that have affected 

the area over the years, such as the 

installation of bridges, construction of 

industrial plants, modifications of shipping channels, and destruction wrought 

by hurricanes. Understanding how 

both natural and manmade changes in 

the bay have affected seagrass in the 

past will help scientists understand current impediments to seagrass recovery 

and model how future changes in the 

bay will affect seagrass distribution. 

This information will assist resource 

managers in assessing the health of the 

Tampa Bay ecosystem and in planning 

future seagrass restoration.

Seagrass growth

To help determine what affects 

seagrass growth, USGS researchers are 

conducting a variety of experiments. 

For example, incubation chamber 

studies are being used to measure the 

metabolism of seagrass communities. 

Gulf of Mexico Integrated Science - Tampa Bay Study

Examining the Impact of Urbanization on Seafloor Habitats

Seagrass, known as Halodule wrightii, 

located on a sand bar that is exposed at 

low tide.

Seagrass study sites include Feather Sound, 

Cockroach Bay, Port Manatee, Bishop 

Harbor, Clambar Bay, Mariposa Key and the 

Terra Ceia Aquatic Preserve and Buffer.

Circulation Pump Frame Chamber Body

Sand Bags Circulation Hose

The SHARQ, deployed on a seagrass bed.
Kimberly Yates, Task Leader and 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

Contributing Scientists:

Mike Crane, USGS/National Mapping Discipline

Tae Oh Cho, University of Louisiana at Lafayette

Clinton Dawes, University of South Florida

Suzanne Fredericq, University of Louisiana at Lafayette

Jimmy Johnston, USGS/Biological Resources Discipline

John Lisle, USGS/Geologic Discipline

Dave Tomasko, Southwest Florida Waters Management District

George Xian, USGS/National Mapping Discipline

ing. Scientists then are able to compare 

the growth of seagrass in areas that have 

been strongly affected by urbanization 

or specific environmental disturbances 

with seagrass development in areas 

that are less urbanized. Additionally, 

epiphytes, which are organisms that 

grow on seagrass blades, can be used to 

help idenify whether seagrass beds are 

healthy or stressed. Different types of 

epiphytes found on seagrass can provide an indication of the water quality 

in a particular area. Research partners 

from the University of Louisiana at 

Lafayette are working to identify what 

types of epiphytes may be used as ecological indicators for seagrass health 

and water quality.

Sediment suspended in the water 

column affects how well sunlight 

can penetrate the water and reach the 

seagrass. Scientists are developing a 

model that can be used to predict how 

suspended sediments in Tampa Bay 

may affect seagrass health. Predictive 

models can be used as tools to help 

plan and understand the consequences 

of changes in the bay to natural 

habitats.

Seagrass restoration

Experiments are also being conducted to determine the best techniques 

for restoring seagrass by transplantation. This approach involves testing 

various types of sediments and biodegradable pots in which to replant 

seagrass. Field studies by research 

partners from the University of South 

Florida have shown that coarser sediments, such as crushed oyster shell, 

and peat pots improve the chances that 

new seagrass will survive. Scientists 

also are working to determine whether 

sediment type and quality in the bay 

impacts seagrass.

Other bay bottom habitats

Scientists also are examining 

other seafloor communities, such as 

hardbottom areas containing sponges 

and corals, to determine where different seafloor habitats are located, how 

well their organisms are growing, and 

how urbanization may impact these 

habitats.

Links to other project 

research

Studying seagrass helps scientists 

understand the impact of water and 

sediment quality on important seafloor 

habitats in Tampa Bay. Combining 

results from investigations on surface 

water, groundwater, and sediment quality with information on seagrass distribution and vitality assists researchers 

in identifying potential impediments 

to seagrass restoration and recovery. 

USGS seagrass research activities are a 

small component of a very long history 

of work conducted by numerous other 

federal, state, and local agencies in 

the Tampa Bay area. The work by the 

USGS is coordinated with these other 

organizations through the Tampa Bay 

Estuary Program.

Filters for

Water Sampling

Flow-through

System

Incubation

Chamber

Circulation

System

Fluorometer

Filters for

Water Sampling

Flow-through

System

Incubation

Chamber

Circulation

System

Fluorometer

pH

Probe

Conductivity 

Probe

Dissolved Oxygen

Probe

Probe

Manifold

Scientists deploying the SHARQ over 

seagrass beds located in shallow water in 

the Terra Ceia Aquatic Preserve and Buffer.

Flow through analytical system for the SHARQ. The instruments in this picture are used to 

measure water chemistry changes inside the incubation chamber.