Life histories

While a huge diversity of species is demanded for the aquarium trade, a large part of the trade tends to be centred on individual species. These species' vulnerability to collection will depend on a number of life history parameters, in particular growth, reproduction and recruitment54.

Stony corals

Overall, there is very little information available on the life history characteristics, growth rate or reproduction mode of most coral genera in trade. Environmental conditions influencing individual corals tend to be responsible for great variations in life history characteristics. The same species of coral sampled in two different locations may display a different mode of reproduction and great variation in growth rate. For example, coral specimens at shallower depth tend to grow faster than specimens found in deeper water135.

Corals show various sexual characteristics, including two different types of sex, gonochoric (separate male and female colonies) and hermaphroditic (single individual is both male and female). In a hermaphroditic coral (e.g. most corals in the genera Acropora and Cynarina), a single individual is capable of producing both eggs and sperm. Examples of gonochoric corals include Catalaphyllia, Euphyllia, Goniopora and Heliofungia. Corals also exhibit two distinct modes of reproduction: brooding and spawning. In brooding corals, eggs are fertilized inside the coral polyp and are released as fully formed planula larvae that are ready to settle onto reef substrate. Spawning corals, on the other hand, release their gametes into the water column, where fertilization and larval development takes place externally. Spawning in hermaphroditic species is usually restricted to one or a few nights each year, and occurs synchronously throughout each population. Gonochoric spawners, on the other hand, tend to have longer breeding periods and less tightly synchronized spawning episodes136. Significant reductions in population densities of corals due to collection of colonies for the aquarium trade could have implications on their reproductive success, and thus long-term reef stability and health.

Sea anemones

Sea anemones

Of all 100 species of sea anemones occurring throughout the world's oceans, only ten are hosts to anemonefish132. Anemonefish, on the other hand, with the exception of Dascyllus trimaculatus, are always associated with anemones and can only be found in parts of the Indian Ocean, Red Sea and Pacific Ocean (pictured are Barrier Reef anenomefish, Amphiprion akindynos). Anemones and their obligate symbiontsxvl are very popular with marine aquarists due to their colourful displays, ease of care and longevity in captivity. In the Florida Keys, collectors with the appropriate licence may harvest 400 giant sea anemones (Condylactis gigantean) per vessel per day. Estimates show that an annual average of approximately 11.8 million anemones were landed between 1997 and 1999, with more than 90 per cent of these collected in the Florida Keys133. Data from collectors' logbooks in the Olango region, Philippines, revealed that fishers in the region landed 510 sea anemones (equivalent to 1.7 per cent of all collected organisms) and 17,160 anemonefish between January and April 2002134.

In an analysis of the marine ornamental fish trade undertaken in the Maldives in 1992, the authors voiced concern over the potential local overexploitation of sea anemones and the possible negative impacts a lack of suitable habitat (i.e. anemones) may have on local clownfish populations90. Indeed, anemonefish strictly depend on anemones, recruiting to them as larvae and utilizing them as adults. Results of the only study to date addressing the population-level impacts of collecting marine ornamentals (in this case sea anemones) show that close to 60 per cent of the catch of collectors in the Philippines consisted of anemone-fish and anemones, and that both these resources exhibited significantly lower densities at exploited sites134. Moreover, the low abundance of sea anemones explained 80 per cent of the reduced density of anemonefish recorded in collection areas134.

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 community137) 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 pressures138.

Asexual reproduction is a common process for a large number of coral species, particularly in branching corals. Fragmentation, an important means of asexual reproduction139, 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 19 9 732. 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 mm140 and

Cauliflower/alabaster coral, Pociiiopora spp.

branching species (with more porous structures) 30-40 mm, with some Acropora species growing up to 100-200 mm per year141. 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 year142, 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 fission, is very common in soft coral reproduction. Most soft corals, both in the wild and in captivity, propagate themselves this way.

Fish

Although coral reef fish exhibit a wide variety of mating strategies, ranging from mass spawning events to established nests and incubating eggs in a special pouch on the abdomen, most fish larvae distribute widely through wave and wind-driven ocean currents'™" 143-145. This makes replenishment of reefs with new fish larvae highly dependent on these currents, and by e'tension the number of fish available for sustainable aquarium collection is highly variable.

Just as mating systems differ widely between species, fish display unusual plasticity in their sexuality. Some species are gonochoristic, with individual fish being permanently male or female. However, for many species sex is not fixed and is determined through social interactions. In anemonefish, for example, the largest individual is a female. New recruits start their life as male. Should the female be removed from the colony, the largest male changes sex and becomes the dominant

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