In the heart of San Jose del Cabo, you'll find Estero San
Jose, a tropical estuary and an important part of the Los Cabos environment. This
unique wetland on the edge of the ocean and desert is a great spot for bird
watching, kayaking or simply wandering along the paths and enjoying the natural
beauty of Los Cabos.
Estero San Jose is located where the fresh waters of Rio San
Jose meet the salt waters of the sea and consists of about 125 acres of marshland
that plays an important role in the history and environment of San Jose. As one
of the only reliable water sources in southern Baja, many bird and animal
species depend on the estuary for freshwater. Over 250 species of birds visit
and many types of waterfowl winter here, as do many other shorebird and wading
bird species. Herons, egrets, two species of cormorant, pelicans, gulls,
frigate birds, Turkey vultures, Caracara and Osprey are among the year round
residents, and the estuary provides a good stopover point for other migrating
birds as well.
The plentiful water of the estuary has also attracted
humans. Pericu Indians were well established in the area when Spanish
missionaries founded Mission San Jose in 1730. Centuries before, pirate ships
sailed into the lagoon to lay in wait for the Spanish galleons returning from the
Philippines laden with treasure in pearls and gold.
Rio San Jose starts high on the sides of the San Lazaro
peaks, part of the Sierra de la Laguna mountain chain. These mountains rise
abruptly from the coast near the Tropic of Cancer, as vast granite blocks that
reach elevations of 6000 to 7000 feet. Unlike the lower slopes of tropical dry
forest and Gulf Coast Sonoran Desert, the mountain tops catch the scarce rain
clouds and receive up to 35 inches of precipitation annually. This water percolates
down through the fissures in the granite, which turn into arroyos and canyons,
and eventually becomes the Rio San Jose.
After larger rainfalls, particularly after hurricanes, the
silty brown water from the mountain storms fills the mile long lagoon until
they spill over and breach the sand barrier. High surf and high tides along the
beach at the river mouth periodically cause the salty ocean waters to push up
into the fresh water lagoon created by the river. The salt and fresh waters mix
in some areas, and brackish water' helps make the estuary extremely nutrient
rich. The fresh water of the river is laden with silt, carrying the detritus of
dead plant life from the mountains and areas above. When this meets the salts
suspended in the brackish water, the fine particles immediately settle to the
riverbed floor of the lagoon as nutrient rich sediments fuelling a rich food chain.
The estuary is ringed by tall Tlaco palms, a species that is
endemic to this and a few other wetlands of southern Baja and which over
millions of years has adapted to withstand the occasional flood conditions. At
the upper end of the lagoon, the water is and plants in this area include
Sedges, young Tlaco palms, Willows (Salix taxifolia), Cattails (Typha
domingensis), Ragweed (Ambrosia bryantii), and other species. On the shores of
the lagoon, ''halophytes'', or plants that can tolerate salinity, dominate the
lower end near the beach. Here and across the inter-tidal flats grow Mangle
Dulce (Maytenus phyllanthoides), Sea Grape (Ipomoea pes-caprae), Spike Grass
(Distichlis spicata), Pickleweed (Salicornia subterminalis), and Alkali Heath
In estuaries along the Pacific Ocean from Alaska to the tip
of Baja California, Zostera marina, or Eelgrass is an extremely important link
in the food web. Eelgrass is found growing abundantly in underwater ''meadows''
with extensive networks of roots and rhizomes binding it to the mud bottoms of
channels and lagoons. Eelgrass and other sea grasses are not true grasses but
actually relatives of freshwater pond plants that have adapted to the saline
conditions of an estuary. Eelgrass is both a food source and a habitat to many
other estuarine community species. The organic detritus layered into the fine
silt mud of the estuary bottom is consumed by millions of tiny bacteria and
other organic molecules, whose waste is consumed by the roots of the Eelgrass.
These microorganisms and bacteria, known as phytoplankton are consumed by
zooplankton, filter feeders, and some fish. As Eelgrass grows and its blades
age, they develop colonies of tiny microorganisms attached to them. These
include algae, bryozoans, protozoans, diatoms, hydroids and tiny mussels. Many
other minute creatures including worms, amphipods, snails, and crustaceans feed
on these epiphytes.
The estuary is important for the juvenile or larval stages
of many fish and other sea dwellers where the nutrient rich waters provide food
until adulthood when they leave the protected waters for the open ocean. Some
of the animals found in the estuary, such as fish, crabs, and wading shorebirds
consume the microorganisms that are attached to the Eelgrass blades. Others,
including Sally Lightfoot crabs (Grapsus grapsus), Hermit crabs (Coenobita
compressus), snails, ducks, geese, and sea turtles, eat the new growth at the
blade tips. Many types of waterfowl also feast on the small fruit or seeds.
Most of the waste generated by all this eating ends up in the estuary again as
detritus and so the cycle continues.
The estuary at San Jose del Cabo is an ever changing
environment. Water levels rise and fall with the season and the tide and
salinity levels change. The Rio San Jose no longer flows like it did in the
days of pirate ships. The demands of man and agriculture have since lowered the
water table and today the lagoon waters only break the sand dam of the beach
during the highest of tides and seasonal floodwaters of late summer. Most
years, the estuary and salt marsh serve to brunt the floodwaters, with
relatively little estuary life being washed out to sea. But once in a while,
one of the hurricanes come ashore, bringing torrential downpours, local
flooding, and then enough water floods down the Rio San Jose to wash much of
the plant and small aquatic life out to the ocean. Even much of the mud that
makes up the bottom of the lagoon is flushed down and out, taking with it many
of the mud dwellers that are such a vital part of the estuarine community. The
upper parts of the estuary may be bare mud for weeks after heavy storms, but
the disturbed community will eventually rebuild itself.
The tough weedy plant species that inhabit this area have
adapted to the rapid changes, many have small seeds that are widely dispersed
and germinate rapidly. Within a few months, these fast growing plants will be
re-established along the banks of the freshwater upper lagoon and the estuary
will be fully re-established within a few years.
This is a local sanctuary that is well worth a visit: try to
get there early in the morning for the best opportunities to see the wildlife
and avoid the heat.