San Ignacio Lagoon Ecosystem
By Tom Lewis, Naturalist
Lagoon is more than a breeding ground for gray whales. It is an entire
ecosystem, where a variety of species depend on one another for their
survival. The lagoon's waters, marshlands, and sandy beaches rank among
the most productive on earth, and support an amazing variety of plants
and animals. Large populations of fish, invertebrates, birds, turtles,
and marine mammals make this place their home. The lagoon ecosystem is
composed of several very different habitats: a sandy beach habitat on
the barrier islands near the lagoon entrance, a mudflat, a mangrove marsh
habitat, and of course the marine habitat of the lagoon itself.
The sandy beach habitat is home to hundreds of different species of crabs,
mollusks (animals with shells), and worms. It is also a vital feeding
area for many different species of wading birds that depend on the other
creatures for food.
The intertidal mudflat habitat is home to thousands of animals including
a variety of tubeworms, crabs, snails, and sea slugs. These animals have
become completely adapted to the mudflat. They could not live in a sandy
The mangrove marsh habitat is perhaps the most productive section of the
lagoon ecosystem. The mangrove is a salt- tolerant tree that grows in
intertidal areas of tropical and subtropical oceans. Mangrove marshes
are a critically important resting and feeding grounds for numerous migratory
bird species, and a home to several resident species of birds. The mangrove
marshes, like all ocean marshes, are also the nurseries for many different
species of ocean fishes and the homes to many different species of invertebrates.
Fishes move into the marsh to lay their eggs. When the young hatch, they
use the quiet waters of the marsh to gain strength before they venture
out into the open ocean.
Laguna San Ignacio is one of the few remaining undisturbed marine lagoon
habitats in North America. It supports a large number of vertebrate and
invertebrate species different from the ones that live in the lagoon's
other habitats. The organic productivity (the amount of life and life-giving
nutrients) of the marine habitat is extraordinarily high. Imagine the
tides flushing and recharging the lagoon ecosystem. Each rising tide stirs
up nutrients from the bottom sediment and recharges areas of stagnant
water with oxygen. Ocean fish ride in with the tide to feed. Ebb tides
flush out dissolved material and carry decaying organic matter as well
as living organisms offshore. The marine habitat is home to green sea
turtles, bottlenose dolphins, numerous species of fishes, and humans.
A small population of Mexican fishing families depends on the lagoon for
their livelihood. They fish the lagoon in harmony with nature, and coexist
with all the other creatures that call this lagoon home.
Lagoon is one of the Earth's true natural wonders. It is our job to make
sure that this place lives on for future generations.
- What might
be some human-caused and natural threats to the lagoon ecosystem?
- Why do
you think Tom says it's our job to make sure the lagoon ecosystem lives
on for future generations?
the ecosystem YOU live in. How are you helping to take care of it?
Science Education Standards
- All populations
living together and the physical factors with which they interact compose
change environments in ways that can be either beneficial or detrimental
for themselves and other organisms.