The San Ignacio Lagoon Ecosystem
By Tom Lewis, Naturalist

San Ignacio 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.

Sandy Beach Habitat
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.

Intertidal Mudflat Habitat
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 beach habitat.

Mangrove Marsh Habitat
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.

Marine Habitat
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.

San Ignacio 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.

Try This! Journaling Questions

  • 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?
  • Describe the ecosystem YOU live in. How are you helping to take care of it?

National Science Education Standards

  • All populations living together and the physical factors with which they interact compose an ecosystem.
  • Humans change environments in ways that can be either beneficial or detrimental for themselves and other organisms.