importance for fishery development on Guam. Exceptions
to the general low pelagic ecosystem are the diversity of fish
communities in the deep mesopelagic and bathypelagic fish communities
which are, as yet, only poorly explored in the waters around Guam,
but which typically contain many unusual, and sometimes grotesque,
species of fish. The coral reef ecosystem encompasses a
variety of distinct habitats and zones (Figure
1). Its upper boundary consists of rocky shoreline surge pools,
sandy beaches, or brackish water river mouths; its lower boundary
is the base of the deep reef where low light levels or low temperatures
inhibit the growth of corals and their associated fauna and flora.
Below lies an intermediate zone that extends down through
progressively cooler and darker waters until the perpetually cold
and dark deep benthic region is reached.
The coral reef ecosystem,
in its broad sense, can be roughly divided into two regions: the
coral reef proper where reef-building (hermatypic) corals and
algae are able to live and flourish, and the deep reef, where
only a few of the most hardy corals and algae penetrate and where
the fauna is dominated by gorgonians (sea fans), antipatharians
(black corals and sea whips), and nonreef-building (ahermatypic)
corals. In Guam’s waters, reef-building corals flourish
to a depth of roughly 100 m. The habitats and zones of this
region are relatively well known. Its upper reaches are
safely accessible to scuba divers and contain a great diversity
of tropical fish species. Most of the fishes in this book
are found in this shallow reef region. At depths below 30
m, near the of safe scuba diving, these shallow species are replaced
by deeper-dwelling relatives, such as the brightly colored members
of the genus Pseudanthias (p.
37). With increasing depth, the fish fauna becomes increasingly
inaccessible and less well known. At depths below 100 m,
the fish species best known are the snappers, groupers, and jacks
which are caught by Guam’s bottomfish fishermen.
Each of the three marine
ecosystems is characterized by its own food chain or food web,
the patterns of energy exchange among the various constituent
organisms. At the base of the coral reef food chain are
the marine plants, including seaweeds, seagrasses, phytoplankton
(microscopic floating plants), and zooxanthellae (microscopic
plant cells) which live in association with corals and some other
reef animals. These plants carry out photosynthesis to produce
the food which ultimately nourishes all the animals which dwell
on the reef. The plants themselves are fed upon directly
by herbivorous fishes and invertebrates, including zooplankton
(microscopic floating animals) which feed on phytoplankton. Each
of these herbivorous animal groups then provides a potential food
source for other fish species, and there are fishes which specialize
in eating zooplankton, crustaceans (crabs and shrimps), mollusks
(snails, clams, and oysters), corals, echinoderms (sea urchins
and starfish), and other fishes. Some plant and animal material
is not eaten directly, but falls to the reef surface as detritus
which is fed upon by yet other species of fish. Part of
this detritus undergoes decomposition and decay through the activities
of bacteria on the reef. One of the results of this decomposition
is the release of various nutrients which act as fertilizer for
the marine plants promoting their growth and completing the natural
process of recycling. It is largely because of this
