Estero Bay
The Estero Bay estuarine system encompasses more than 15 square miles and
with its supporting watershed includes an additional 300 square mile area.
Estero Bay extends more than ten miles north to south and includes San Carlos
Bay, Hurricane Bay, Hell Peckney Bay, Ostego Bay, Rocky Bay, and Big Hickory
Bay. The northern end of the bay is almost three miles wide and gradually
narrows to the south creating a triangular shape. The bay is bound to the
west by a chain of barrier islands. From north to south these islands included
Estero Island, the Lovers Key Complex (Lovers Key, Black Island and Long Key),
Big Hickory Island, Little Hickory Island, and Bonita Beach. These islands
are separated from the mainland and each other by a series of passes which
also connect the estuary to the Gulf of Mexico. From north to south these
include Matanzas Pass, Big Carlos Pass, New Pass, Big Hickory Pass and Little
Hickory Pass. The northern and eastern margins of the bay are contained by
the mainland, and to the south the bay interconnects with several smaller
bays through a series of tidal channels eventually reaching the Cocohatchee
River at Wiggins Pass.
Freshwater enters the Estero Bay estuarine system primarily through rivers
and creeks. From north to south these include Hendry Creek, Mullock Creek,
the Estero River, Spring Creek, and the Imperial River. Other important sources
of fresh water included Cow Creek, Halfway Creek, Six-Mile Cypress Strand,
Ten Mile Canal, and ground water sources.
Throughout the bay are numerous mangrove islands and tidally exposed oyster
bars and shoals. Estero Bay has an average water-depth between one and three
feet. While naturally occurring and artificially dredged channels are deeper,
they too are shallow and typically less than seven feet in depth. The shallow
water-depth enables sunlight to reach much of the bay floor. Sun light combined
with nutrients provided by fresh water run-off support large expanses of sea
grass meadows. Sea grass meadows and mangroves play an important roll in the
health of the estuary.
What is an Estuary?
An estuary is a partially enclosed coastal water body where freshwater runoff
from the land mixes with the salty ocean. Entire watersheds contribute freshwater
to the estuary through gradual ground water seepage, streams, and rivers,
and thus events and activities far inland can influence an estuary. The estuary
is one of many environments participating in the larger hydrological cycle.
Freshwater run-off is rich in nutrients from eroded top soil and other plant
and animal sources. These nutrients coupled with other food sources and protective
habitats offered by sea grasses and mangroves create an ideal environment
for many species of wildlife. Estuaries are vital nurseries for salt water
fishes and over 90 percent of all oceanic creatures spend part of their life
cycle in estuarine waters. The estuaries are an equally important habitat
for birds that fish the shallow waters and take roost along the mangrove shoreline.
Sub-tropical estuaries are the most biologically productive environments in
the world.
Water salinity within an estuary varies widely due to the mixing of fresh
and salt water. Generally, the water is saltier near the ocean side, brackish
in the middle, and fresher near river outflows. This variation, coupled with
water depth gives rise to diverse micro-environments within the estuary, which
in turn influence the distribution of wildlife and, in particular, the distribution
of relatively immobile shellfish.
Change is constant in estuary ecosystems. Cycles of day and night, high and
low tides, and annual rainy and dry seasons all influence the size and distribution
of micro-environments within the estuary. In addition, tropical storms and
hurricanes can dramatically reshape micro-environments within an estuary.
For example, the opening and closing of barrier island passes can influence
greatly local salinity characteristics.
Mangroves and Sea Grasses
The foundation of the estuarine food chain and the over all health of the
system is highly dependent on mangrove forests and sea grass meadows. Sea
grasses are flowering aquatic plants that blanket the estuary floor in shallow
waters. Five species of sea grass are found in southwest Florida estuaries
including turtle grass, manatee grass, shoal grass, widgeon grass and the
less common star grass. Sea grasses help keep bay-waters clean and clear by
trapping suspended solids such as soil particles. They are also an important
food source in the estuary. Large animals such as manatee and sea turtles
feed directly on the grasses. This is why some of the grasses are named after
them. The sea grasses also provide host sites for algae, larvae (eggs), and
small crustaceans that in turn are food for the many small fish that find
refuge in the thick sea grass beds.
Mangrove Forests, like sea grass beds, are important to estuarine health.
Mangroves are a group of plants associated by the environment they inhabit
not by their genetic relationship. Three different genus of mangrove are found
in southwest Florida and they occur in a succession that is determined by
elevation. Red mangroves, distinguished by their entangled red roots and creamy
smooth bark, enjoy having their feet wet and are found along the shoreline
and in areas frequently inundated by high tides. Black mangroves are found
behind the red mangroves where the ground is slightly elevated. They like
very moist environments and can withstand frequent short term tidal surges.
They are distinguished visually from the red mangrove by their dark scaly
bark, single straight trunks, and are also surrounded by many small vertically
protruding roots known as pneumatophores. Pneumatophores work like snorkels
enabling the Black mangrove to breathe when the ground around them is inundated.
White mangroves prefer to stay dry and occur in common with buttonwood at
the very back of the coastal wetland strand. White mangroves are distinguished
from the red and the black by their oval shaped, light green leaves. Button
wood is easily recognized by its tiny, button-head green flowers that bloom
from late spring to early fall. In addition, the buttonwood leaves diverge
alternately from the branch, while mangrove leaves occur opposite each other.
All three species of mangrove have evolved ways of removing or excreting salt
from the estuary water. This is accomplished either through specialized glands
in the roots (excluding) or on the leaves (excreting). Red mangroves are predominantly
salt excluders while black and white mangroves are salt excreters, thus their
leaves are a source of salt, and black mangrove honey is a local treat.
The mangrove forest is a gigantic rookery where birds rest, nest, breed, and
hunt. The forest also serves as a protective buffer against flooding and erosion
caused by tropical storms and hurricanes. Red mangroves help stabilize the
coast line by trapping water born sediments in their roots. Filter feeders
such as oysters and barnacles attach to the roots and constantly clean the
water. Fallen leaves from the mangroves are an important estuarine food source
as their breakdown promotes algae and bacterial growth that forms the base
of the food chain.