The global trade in marine ornamental species

From ocean to aquarium
Stony corals are known to reproduce both sexually
and asexually. A variety of environmental factors are
known to regulate reproduction in corals. These include
sea temperature, day length, lunar phases, tidal cycles,
daily light/dark cycles, water quality, salinity and food
availability. Variations of these factors in aquaria have
allowed public aquaria and a few dedicated hobbyists to
witness sexual reproduction of corals in a closed system.
Sexual reproduction requires the fertilization of eggs by
sperm and results in small planula larvae, which disperse
into the plankton and may eventually settle on their reef
of origin or on distant reefs. Rates of recruitment (the
process whereby newly formed individuals become part
of the reef community 137 ) differ greatly between coral
species, with species of Acropora and Pocillopora characterized
by high recruitment rates, and individual reefs
vary markedly in the number of coral recruits they
receive. Hence, replacement rates of harvested corals for
these two species tend to be relatively high. In contrast
other species, particularly in areas experiencing lower
recruitment rates, may have a lower capacity to recover
from collection pressures 138 .
Asexual reproduction is a common process for a
large number of coral species, particularly in branching
corals. Fragmentation, an important means of asexual
reproduction 139 , is the most common method used by
aquarium hobbyists for propagating corals. It is a
straightforward process that involves carefully breaking off
branches or pieces from the parent colony and placing
them elsewhere in the tank. Fragmentation can be applied
to most species of stony coral. The Waikiki aquarium, for
example, distributed 780 fragments in 1997 32 . Fragments of
various species are frequently traded between individual
hobbyists, thus providing an alternative supply source
(although a minor one), at least for some species, to corals
harvested from the wild.
To date little more information is available at a
species-specific level than the general descriptive
reproduction biology described above. Acquiring more
information and detailed species- and country-specific
data on these basic aspects of coral biology, and how
collection for the aquarium trade may impact populations,
is important and necessary when attempting to derive
management strategies based on sustainable yields for
the aquarium trade.
Coral growth rate is another important factor to
take into consideration when developing a sustainable
coral harvest management plan. Although different
environmental conditions such as light, temperature and
depth can have a tremendous impact on variation in growth
rates, massive corals (with dense skeletons) are said to
exhibit average annual growth rates of 10-12 mm 140 and
Cauliflower/alabaster coral, Pocillopora spp.
branching species (with more porous structures) 30-40
mm, with some Acropora species growing up to 100-200
mm per year 141 . Hence, fast-growing corals will tend to
suffer less from collection pressure whereas slow-growing
species will take longer to recover.
However, overall, it is important to put the
potential impacts of harvesting coral species for the
ornamental trade in perspective. Results from a study
looking at the amount of corals gathered from reef areas
for the production of lime show that in West Lombok 60
families produce an annual total of 900 tonnes of lime per
year 142 , necessitating the collection of approximately
1,600 tonnes of coral. Considering that in the mid-1990s
Indonesian exports never exceeded an annual total of
2,000 tonnes, it is clear that practices such as coral
mining for the production of lime rock have a much more
significant impact on the alteration of coral populations
and community structure than the collection of corals for
the ornamental trade.
Soft corals and sea fans
Similarly to stony corals, soft corals reproduce sexually
(spawning and brooding) and asexually. Most soft coral
and sea fan species are gonochoric; however some
species such as Xenia are hermaphroditic. Many
gonochoric species, such as the genus Clavularia, the
family Xeniidae and many gorgonians, are brooders.
Alcyoniid soft corals (e.g. Cespitularia, Sinularia,
Sarcophyton, Lobophytum) are spawners, where mass
spawning is synchronized by lunar phase and/or water
temperature. Asexual propagation, for example through
38