international conference on ecology and environment

guillermo guzman GGUZMAN at UCRVM2.BITNET
Thu Sep 16 19:38:26 CDT 1993




              Costa Rica - Central America.
                  June 20-24th, 1994
                    (Indian summer)

                                               Bulletin No. 4.


                      *  ISLA DEL CANO.  *

it was once used as a pre-Columbian cementery by cultures with
a clear South American influence. It is still possible to see
some of the perfectly round stone spheres made by the former,
native Indian peoples. The spheres are the subject of a good
many theories with regard to their purpose and continue to
pose one of the major puzzles of the pre-Columbian cultures of
America. The geological composition of the island consists of
a large block of basalts, which data from the Eocene (50-56
million years ago). The rocks are similar to those that form
the substratum of the Osa Peninsula. They have raised fairly
quickly-some 10 metres every 1,000 years- as a result of the
subduction of the Coco Tectonic Plate beneath the Caribbean
Tectonic Plate and along the Middle American Trench. This
causes a bulge in the Earth's crust.

     The island rises 90 metres above sea level to a wide
plateau, which is covered with a very tall evergreen forest.
The predominant species is the enormous cow tree (Brosimun
utile),which can grow up to 50 metres high. It is also known
as the milk tree because it exudes a white latex that can be
drunk like milk and also has other medicinal properties
according to local lore. Other species of giant trees that
grow on the island include locust (hymenaea courbaril), crown
fig (ficus sp.) and Calophyllum longifolium. Some of the
smaller trees are wild cocoa (Amphitecna latifolia), rubber
tree (castilla tunu), and Casearia Aculeata, which is easily
identified by its large and lovely thorns.

     It would seem that the plant life on the island today is
the remains of an orchard planted by the native Indians. The
fact that an almost unmixed grove of cow tree grows in the
middle of the island and that the island itself was used as a
burial ground support this explanation. The cow tree has
large, edible seeds, and it is believed that it was planted on
the island to protect the fruit from raids by parrots,
collared peccaries (Tayassu tajacu) and rodents that abound on
the mainland.

     Wildlife is scarce, perhaps as a result of the
disappearance of the natural forest. Nonetheless, among the
few birds that can be seen are the cattle egret (bubulcus
ibis), common black-hawk (buteogallus anthracinus), which
feeds mainly on the red land crab (Gecarcinus guadratus),
osprey (pandion Baliaetus), brown boody (sula leucogaster),
Northern phalarope (Lobipes lobatus), least tern (Sterna
Antillarum) and brown noddy (anous stolidus). The insects on
the island are limited to only 5 species of beetles, 4 of
butterflies,2 of moths, 7 of bees (the population of the bees
of the Euglossa genus numbers in the thousands), several of
ants and other insects. The only other animals seen on the
island are the grey four-eyed opossum (Philander opossum),
which belongs to the same family as the Southern opossum but
is smaller, paca (Agounti paca), which has been reintroduced,
boa (boa constrictor), which feeds on small and medium-sized
mammls and small birds and reptiles, brown tree frog (Smilisca
phaeota), great frog (leptodactylus pentadactylus),
transparent tree frog (centrolenella fleishmanni), and some
species of rats, bats, small snakes and lizards. There is more
marine life in the tidal pools. Besides a myriad of fish,
there are numerous brittle starfish (ophiocoma sp) and sea
urchins (Echinometra sp.and diadema sp).

     The rocks are covered with limpets (Siphonoria gigas),
keyhole limpets (fissurella spp.) which are especially
abundant,chitons (chiton stokesii),nerites (nerita spp.) and
Sally lightfoot crabs (grapsus frapsus). There is a large
population of the latter and their exoskeletons are frequently
found stuck to the rocks. Two endangered species the live in
the water around the island are lobster (panulirus sp.) and
giant conch (strombus galeatus).

     The island is surrounded by five platforms or low coral
reefs where 15 species of stony coral have been identified.
The most abundant is porites lobata, which grows all over the
reed in large colonies. Other thriving coral species are
Pavona clarus, Pocillopora damicornis,p. elegans, and
Psammocora superficialis. Some of the coral-eaters that live
in these waters are the arothron meliagris and Pseudobalistes
naufragium fish, the janneria pustulata and quoyula
monodontica mollusks, the trizopagurus magnificus and aniculus
sp. hermit crabs, the acanthaster planci starfish and the
diadema mexicanum and eucidaris thouarcii sea urchins.

It rises to 110 metres above sea level at its highest point
and most of the coastline is made up of cliffs that can climb
as high as 70 metres. The white, sandy beaches are small, no
more than 100 metres long, and some almost vanish at high
tide. At low tide visitors can walk along the coast for some
distance, following the beaches and a rocky platform that
surrounds a large part of the island and is riddled with tidal
pools. An old lighthouse stands on the southwestern tip of the
island and commands a view of the forest and a large stretch
of the coast.

      // GUILLERMO GUZMAN L.                                         //
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