78
|
WINTER 2014
shorelines with their extensive root and rhizome systems.
As mangroves stabilize sediment, islands may
eventually form. A mangrove island becomes a habitat
for a set of plants and animals entirely different from
those that would otherwise inhabit the area. Many
wading birds — such as wood storks, herons, egrets,
ibises, roseate spoonbills, cormorants and pelicans —
nest and roost in mangroves. Mangrove islands are
also home to a wide variety of reptile, amphibian and
mammal species. The Sunderban mangroves off India
and Bangladesh — the largest mangrove forest on Earth
— are home to Bengal tigers, spotted deer, saltwater
crocodiles, fishing cats and various dolphin species.
Healthy coastal habitats are also important in mitigating
global climate change. Mangroves and seagrass beds
absorb large quantities of carbon dioxide — a greenhouse
gas — from the atmosphere and store it. These habitats,
known as carbon sinks, contain large stores of carbon
accumulated over hundreds of thousands of years. When
these environments are damaged or destroyed, not only
is their carbon sequestration capacity lost, but also stored
carbon is released, which contributes to increasing levels
of greenhouse gases in the atmosphere.
See for Yourself
All these benefits sound nice, but why would I want
to skip my reef dive for a snorkel in the seagrass
or mangroves? Seagrass meadows and mangrove
forests are amazing places to see all sorts of marine
life, from tiny nudibranchs to massive manatees.
Substrates provided by seagrasses and mangrove roots
are important for sessile organisms such as sponges,
tunicates, oysters and anemones. Even immobile
organisms can be stunning; sponges growing on
mangrove roots add beautiful colors to the habitat.
These environments are home to organisms you
probably won’t see on the reef. These critters include
invertebrates such as horseshoe crabs, sea stars,
nudibranchs, flatworms, sea slugs and brittle stars; fish
such as tarpons and seahorses; and mammals such as
dolphins and manatees. Some protected species such
as the dugong (Dugong dugon) and the green sea turtle
(Chelonia mydas) feed primarily on seagrass. An adult
green sea turtle eats about 5 pounds of seagrass per day,
while an adult dugong eats about 60 to 90 pounds per day.
Mangroves are natural wind buffers; use this to your
advantage by choosing a snorkel site downwind of a
mangrove forest. Visibility can be close to zero in rough
seas on the windward side of a mangrove island, while
the leeward side is perfectly clear and flat. Seagrass
beds are often adjacent to mangrove islands, so you
can see both habitats in a single excursion. The bottom
can be quite silty and may be stirred up easily when it
is windy, but it usually settles fairly quickly. You can
almost always find a clear, flat site to snorkel, but don’t
expect the visibility and crystal blue water found on
the reef. The tannins in the mangroves often dye the
surrounding waters a reddish or brownish hue.
Take Care
Snorkeling among seagrasses and mangrove roots
is quite different from snorkeling on a coral reef.
But like reefs, mangroves and seagrasses are fragile
environments that should be visited with care.
Don’t stand up when snorkeling in mangroves or
seagrass beds, and be careful where you kick. If you only
have large dive fins, ditch them and snorkel without
fins (you shouldn’t need them; currents are minimal
to nonexistent). Not only is the sediment easily stirred
up, but also fragile and/or hazardous organisms such as
jellyfish and stingrays live on or near the bottom, and
stinging cells tend to settle in the sediment. Repeatedly
standing on seagrass blades can kill the seagrass.
Avoid touching the inhabitants, for your benefit as
well as that of the marine life. Immobile organisms
protect themselves in subtle ways. Sponges, for
example, look harmless but have toxins as well as
physical defenses in the form of spicules.
Be aware that because mangroves and seagrasses
act as filters, they unfortunately tend to collect human
debris. If you decide to collect trash for disposal, look
closely first. A bottle, jar or aluminum can may be home
to a fish or an octopus.
In some topical and subtropical locations, cutting back
mangroves is illegal, even if they are in your own backyard.
When boating, be aware of the depth — not just for the
sake of your prop but for the health of the seagrass as well.
Woven Together
The coral/mangrove/seagrass ecosystem can be
thought of as a whole. Some species, such as the gray
snapper, use all three during their life cycle. Each
habitat is dependent on the others; if one is damaged,
the others will be affected, too. To preserve one of
these habitats, all three must be protected.
If you are the type of diver who sees more than just
the sharks, turtles and rays when you are on a coral
reef, you will really enjoy snorkeling among seagrasses
and mangroves. Even if you don’t enjoy these habitats
first hand, you’ll benefit from them indirectly the next
time you have an amazing dive on the reef. Seagrass,
mangrove and coral-reef habitats are interconnected. If
we want to preserve our coral reefs, we must appreciate
and protect these inshore habitats.
AD
86
|
spring
