To restore corals to damaged reefs, it will be necessary to produce coral larvae in an aquaculture setting, raise them to metamorphic competence, induce larvae to metamorphosis on suitable substrates, and outplant the young recruits onto the reef. To accomplish this objective, we must develop reliable technologies to predict and control gametogenesis, spawning and larval production, induction of larval settlement and metamorphosis, and successful out-planting. There is a critical need to especially address the first and last of these; we already have the beginning of the technological base for controlling metamorphosis. For restoration purposes, we will be relying on the viability of adult corals brought in from the field as brood stock. In the wake of recent bleaching events, it is clear that the reproductive capacity of corals is negatively affected not only by loss of reproductive mass (Fisk and Done 1985; McField 1999) but also by interference with reproductive physiological functions (Glynn 1996; Morse 1996; Rinkevich 1996; Szmant and Glassman 1990). In addition, reproductive capacity is commonly affected by a number of stresses that include hurricanes, typhoons and storms, elevated water temperatures and increased UV irradiance, elevated nutrient and sediment loads, and disease. There is, therefore, a need for the development of new technologies to predict, assess, and analyze reproductive capacity and factors (intervening environmental factors as well as "stressors") affecting this process. Additionally, we need to update our ability to predict fecundity. To accomplish this, we need to develop simple uniform assays based on the physiological processes involved. Our current methods are unreliable at best.
In spite of recent observations of reduced fecundity, the available number of gametes for potential harvest is enormous compared with our ability to harness this resource. Presently, our needs for laboratory-level gamete capture are adequate (Morse and others 1996), but much more efficient technologies must be developed for aquaculture purposes. Identification of the physiological indicators of timing of release of gametes (and assays for their detection) is critical to efficient capture of gametes that are released on only one night of the year. Methods developed for successful fertilization of gametes and rearing of larvae in the laboratory (Morse and others 1996) must be experimentally modified for aquaculture. In this context, we need to identify environmental factors that limit complete gamete development—a bottleneck in fertilization success. There has been recent success in isolating sperm-attractant molecules from a single montiporid species; three highly unsaturated fatty acids in a particular ratio were identified (Coll and others 1994). Results suggest that particular ratios of related fatty acids might act as sperm attractants in a species-specific manner.
The finding that corals share a common chemosensory mechanism (Morse and others 1996) has made it possible to develop chemoinductive substrates, or "flypapers," with proven efficacy in field tests for successful recruitment of larvae on the reef (Morse and Morse 1996; Morse and others 1994). The purified inducer contains both hydrophobic and ionic moieties, and both properties have guided the development and experimentation of different coupling technologies. The most recent of these uses technologies borrowed from the semiconductor industry. A mono-layer of the purified inducer is coupled by a linker to a silanized surface, resulting in a highly potent inductive substrate that is active for long periods in seawater. There is still room for further development of this product; we are working on the flexibility of the substrate material. This flypaper technology is ideal for controlled settlement and metamorphosis of larvae for aquaculture. It is anticipated that these substrates will also provide a means of easily out-planting newly settled recruits onto the reef, which we have repeatedly demonstrated in a research situation (Morse 1998; Raimondi and Morse forthcoming). Additionally, they are potentially useful for resolution of other factors involved in recruitment. Examples include monitoring the availability of larvae for recruitment from the plankton; assessing variation in recruitment under different environmental conditions, one indicator of reef health; and offsetting the collection of corals from reefs for the aquarium, jewelry, and ornamental trades and providing an alternative source of coral for medical purposes such as bone replacement.
The main criteria that will be used to access the outcome of restoration technology will be establishment of a reproductive population of new adult corals. For a given species, this population will comprise a critical number of survivors when corals reach reproductive age. Additionally, maximum long-term growth rates will be a factor—the larger the colony, the greater its potential capacity. Controlled field studies with newly metamorphosed agariciids have allowed us, for example, to determine those criteria for species in this complex. One of the lessons from these studies has been how critical it is to determine in pilot studies what type of habitat confers the greatest growth and survivorship for a particular species (Raimondi and Morse forthcoming). As soon as corals become reproductive, relative measures of their reproductive capacity will be the other criteria. When the reef becomes reasonably well established, we would expect to see an influx of fish, particularly those associated with corals rather than macroalgae.
Particularly in Florida, transplantation of corals from a healthy coral-rich area to one requiring restoration is being considered as an alternate (but not necessarily competing) approach. Attachment of fragments, or even whole corals, to hard substrates with underwater cement is possible. This approach appears to be a possible viable alternative. There are, however, several considerations, particularly when large areas are to be restored. First it means removing large amounts of coral biomass, whether it be composed of multiple fragments or individual adults, because successful fertilization for any one species depends on a critical number of individual colonies in relatively close proximity to one another. This criterion is true for both mass spawning and planulating corals. Judging from the relatively low success of fertilization in the wild on established reefs compared with that obtained by individual crosses in the laboratory, the required number of colonies is high. The other suggestion to save recently dislodged corals, which involves sending teams of volunteers into the field to transport these corals to an aquaculture facility, also has its limitations. Assuming we had determined the culturing conditions, this approach would work only with rather small corals. Larger corals would overwhelm the capability of most systems to effectively remove the nutrient waste produced by any significant number of larger corals. Rather, it would be better to attempt to cement them back on the reef, even with the inevitable loss of some tissue. We recently removed reat-tached fragments of Acropora palmata to a variety of sites to monitor differential survival and growth; there were no survivors after 1 month. So far, there have been no success stories using this approach, but it is worth consideration.
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