Caribbean Compass Yachting Magazine - June 2020

june 2020 CARIBBEAN COMPAss pAGE 30
This month we continue our foray
into the world of sponges, starting
with the tube sponges, of which you
will recognize the yellow tube sponge
(Aplysina fistularis) immediately. They
are prolific on the shallow reefs all
over the Caribbean and their bright
yellow tubes have greatly contributed
to the beauty of one of my favorite
snorkeling spots in the Eastern
Caribbean, Devil’s Table at Bequia.
Tube Sponges
Their common name is an accurate
description of the species. A single
sponge is actually made up of several
tubes connected at the base. These
hollow tubes provide a refuge for a
variety of sea creatures, so look for
crabs, shrimps or small reef fish like
gobies nestled inside.
Yellow tube sponges are fibrous in
nature, lacking the unpalatable spicule
structure typical of most sponges.
As a result, they do fall prey to some
species of reef fish, but their main
predator is the hawksbill turtle.
Luckily sponges have incredible regeneration
capabilities and even a small
piece broken off by a predator can
reattach itself to the substrate and
grow into a clone of the adult. Not only
can they regrow, but yellow tube
sponges have the amazing ability to
rearrange their cells to create an
upright tube in situations where the
tube was knocked over. Many sponge
species form symbiotic relationships
with algae; yellow tube sponges in
contrast produce chemicals to deter
the settlement of creatures such as
algae and barnacles on their tubes.
In the past these sponges were harvested
for use as bath sponges; luckily
our use of synthetic sponges has eliminated
the market for their collection. Our historical
use of sea sponges dates back to antiquity,
when the ancient Greeks and Romans utilized
the humble sea sponge for bathing and cleaning.
Roman soldiers even used sponges to cushion
their armour. The ancient Greeks, especially,
placed great value on sponges, and sponge
diving became an important industry during
ancient times. The history of the sponge diving
industry on the small Greek island of Kalymnos
makes for interesting reading. Sponge diving
was even an Olympic event in ancient Greece
and their best athletes used sponges to apply
olive oil and perfumes on their bodies before competing.
GET TO KNOW YOUR CARIBBEAN MARINE LIFE
Those Splendid Sponges
Part 2: Tube, Barrel and Encrusting Sponges
by Darelle Snyman
Above: While snorkeling, you
are likely to encounter the
brown bowl sponge.
Right: The giant barrel sponge
is an important member of the
reef community. Its size allows
it to filter large amounts of
water daily.
Bottom right: Bright yellow tube
sponges contribute to the beauty
of snorkeling spots in the
Eastern Caribbean.
The branching tube sponge (Aiolochroia crassa) is another commonly found
tube sponge. This can be the poster child for how variable a single sponge species
can be in terms of color and growth form. I have encountered this species in the
most beautiful hues of pink, green, purple and blue. These colorful sponges generally
grow in dense clusters and have short, thick-walled tubes with a granulated
appearance on the outside.
Barrel Sponges
When it comes to coloration, barrel sponges, in contrast to their colorful kin,
seem to have been cruelly left out. They exist in various shades of brown, with
some species having a touch of yellow to brighten them up. They do, however,
include the largest sponge you will encounter on the reef, the giant barrel sponge (Xestospongia muta). These
sponges are often referred to as “the redwoods of the reef” due to their great size and longevity. These massive
red to brown sponges can reach sizes of at least six feet (1.8 metres) across and some are estimated to be 2,000
years old.
The giant barrel sponge is an important member of the reef community. Its size allows it to filter large amounts of
water daily, thereby contributing greatly to the clarity of the water and the cycling of nutrients within the reef ecosystem.
These rugged-looking sponges are feasted upon by parrotfishes, and many sea creatures call them home.
These impressive sponges are more fragile than they look, and decades of growth can be undone in a matter of
seconds by a dragging fishing line or a dropping anchor. The rim is where most of the new growth takes place
and harm can be done by over-enthusiastic divers and snorkelers kicking it or bumping into it unintentionally.
Other prominent barrel sponges you are likely to encounter is the brown bowl sponge (Cribrochalina vasculum)
and the netted barrel sponge (Verongula gigantea).
Encrusting Sponges
Encrusting sponges include some of the most colorful sponge species you are likely to see in your underwater
explorations. They occur in a variety of sizes and growth forms and can be found on virtually every rocky surface
of the reef, where many grow in a carpetlike layer.
Unlike their free-standing cousins they make complicated webs to filter nutrients out of the water. This web-like
growth form is clearly visible in the orange lumpy encrusting sponge (Scopalina ruetzleri), a soft and delicate
sponge easily recognizable by its color and spiky texture.
The red boring sponge (Cliona delitrix) is a more aggressive species and bores into large stony corals by secreting
minute amounts of acid, excavating deeper into the coral body as it grows. On the outside it is visible as a
red to orange crust with a distinct wart-like appearance and large excurrent openings that bear paler edges.
It kills the part of the coral close to its growing edge and on the inside of the coral it creates a maze of holes
filled with spongy material that eventually kills the coral head.
—Continued on next page