Montipora Natural Habitat

Eudesmanoid diterpene

0^ û Sinulariolide corals, and palythine and palythinol from zoanthids, are substances that absorb ultraviolet light. These have recently been synthesized and patented for use in sun-tan lotions, outdoor paints and plastics (Sammarco, 1996). Soft coral secondary metabolites are also being investigated as anti-foulants for wooden fishing boats in Indonesia. Boring organisms greatly reduce the life-span of these boats and this application has shown promising results (Sammarco, 1996). Although the majority of the work has so far been done with tropical and temperate octocorals, there has recently been a publication on a few Antarctic species that indicates that they too may possess bioactive compounds (Slattery and McClinock, 1995).

Pseudopterogorgia elisabetbae, the "purple frilly" gorgonian commonly collected for the aquarium trade, occurs in some regions of the Caribbean in densities up to ten colonies per square meter. In 1986 William Fenical and his colleagues at the University of California, San Diego and Scripps Institution of Oceanography discovered that this gorgonian contains highly potent anti-inflammatory and tissue-healing agents of a novel chemical class. The combined properties have been patented by the University of California, forming the opportunity for the production of new products based on the discovery. As one might expect, concerns have been raised about harvesting these animals from coral reefs and these concerns have provided a major rationale for an extensive conservation and management program. The single major benefit of harvesting this animal is that it regrows. By clipping the animal and leaving the holdfast and some of the stem intact on the reef, it regrows quite effectively. Because of this it can be collected in large regions of the Bahamas and within sixteen to eighteen months the animals regrow to harvestable size in their original sites. The Pseudopterogorgia project is unique in that it provides a renewable and continuing resource for the development of skin care products. In addition the same compounds, pseudopterosins, are being developed as drug molecules for treatment of a variety of specific illnesses. The major substance under development, called methopterosin, is being investigated for treatment of skin diseases such as psoriasis and perhaps ultimately for arthritis and other autoimmune diseases.

Competition for Space

Space is at a premium on coral reefs and therefore competition can be intense. Whether it be space for coral colony expansion, for larval settlement, or just protecting space already occupied, soft corals have developed a number of mechanisms to compete.

Pseudopterogorgia Elisabethae

This photo shows Tim and Heath Higgs, private entrepreneurs from

Marsh Harbor, Bahamas who have established a rigorously controlled collecting program to harvest and manage P. elisabethae. W. Fenical

Resilience Estee Lauder Pseudopterosins

A bottle of Estee Lauder's Resilience line of cosmetic skin care products based upon the unique healing properties and antiinflammatory effects of the pseudopterosins extracted from Pseudopterogorgia elisabethae. W. Fenical

The use of chemicals to inhibit the growth of one species by another is called allelopathy and is quite common in terrestrial plant ecosystems. It is well known that many soft corals also contain numerous toxic compounds such as sarcophines (isolated from Sarcophyton glaucum, a commonly imported leather coral), terpenoids, and diterpenoids. Even the mucus of some species can contain terpenoids e.g. Litopbyton mucus contains litophynol A and B, litophynin E, H and I monoacetate (Miyamoto et al., 1994). Xenia, Heteroxenia and Antbelia also contain various diterpenes that are toxic to fish and cells (Miyamoto et al., 1995; Rudi et al, 1995). Clavularia viridis contains numerous diterpenoids such as clavi-rolides-B, C, D and E. Caribbean gorgonians also possess a significant range of chemicals, and many of them are being investigated for medical applications (see Faulkner, 1992). For example Pseudoplex-aura spp. release crassin acetate and Eunicea spp. produce eunicin and eupalmerin acetate (Ciereszko and Guillarcl, 1989). Briareum asbestinum contains over eighteen different diterpenes, making it one of the most chemically potent octocorals known (Rodriguez, et al., 1994). Rodriguez (1995) reviews the major chemical compounds being investigated in Caribbean gorgonians.

These chemicals have proven to be very efficient in deterring predators, but they are also released into surrounding waters as a mechanism for maintaining living space (Sheppard, 1979; Sammarco et al., 1983). Coll et al. (1982) isolated toxic terpenes from seawater surrounding several soft corals including the common aquarium Finger Leather Coral, Sinularia spp. at concentrations ranging from 1 to 5 ppm (parts per million).

In various transplant experiments using the soft corals Lobo-pbytum pauciflortim, Sinularia p avid a and Xenia sp., Sammarco et al. (1983) documented effects on the hard corals Pavona cactus and Pontes andrewsi when these soft corals were brought close to the colonies or in direct contact with them. They concluded that the effects of soft corals on hard corals, and the susceptibility of the hard corals, was entirely species specific. In some cases, inter-colony distances of 30 cm (12 in.) resulted in stunted growth j and death of the hard coral, while another species of soft coral only caused damage when in direct contact with the hard coral. For example, Pontes andrewsi was the most sensitive hard coral, reacting to two of the three soft corals used, even at distances of 10 cm (4 in.). However, a soft coral that can cause damage by contact does not necessarily cause damage by releasing compounds into the water. For example, Xenia caused extensive damage to both hard corals tested, but only when in contact with them. On the other hand, if a soft coral (e.g. Lobopbytum pauci-florum) could cause damage from a distance, it could also cause damage upon contact.

Diterpenoids have been shown to have a very specific mode of action on stony coral polyps. Aceret et al. (1995a) studied the effects of diterpenes isolated from Sinularia flexibilis and Lobopbytum bed ley i on Acropora formosa and Pontes cylindrica fragments. Sinularia flexibilis is known to release flexibilide, dihydroflexibilide and sinulariolide. Lobopbytum spp. release various chemicals such as denticulatolide, lobolide, crassolide and an eudesmanoid diterpene (Aceret ct al., 1995a). Flexibilide, dihy-

droflexibilide and the eudesmanoid diterpene all caused inhibition of polyp activity in A. formosa and P: cylindrica {Acropora was the most sensitive), while sinulariolide did not. Within a few hours of exposure to levels greater than 5 ppm, zooxanthellae were expelled, followed by expulsion of nematocysts. The loss oi zooxanthellae and nematocysts left the stony coral polyps unequipped to acquire nutrition, and death followed shortly thereafter (Aceret et al., 1995a). The lack of toxicity of sinulariolide was not surprising as its main function is as an anti-foulant against algae. Flexibilide exhibited the highest level of toxicity and is a known inhibitor of stony coral growth, while cli hydro flexibilide is a major olfactory feeding deterrent.

Soft corals can also compete for space by inhibiting the settlement oi stony coral planulae. Atrigeno and Alino (1996) showed that Xenia puertogalerae inhibited the settlement of stony coral planulae near it except for Acropora (and to a much lesser extent Montipora and Fungia), which often settled right between the Xenia colonies, By being tolerant of Xenia chemicals, this Acropora species has an advantage over other stony corals in colonizing new areas for settlement and growth. Studies of planula settlement showed that in areas down current from S. flexibilis and Sarcopbyton glaucum the number of settled stony coral spat was significantly lower than in other areas (Maida et al., 1995). This could have been due to avoidance of the area by planulae upon detection of soft coral chemicals in the water, or of allelo-chemicals adsorbed onto the substratum, or once the planulae settle out they are killed by allelochemicals in the water or on the substratum; the mechanism inhibiting successful stony coral recruitment is still unknown (Maida et al., 1995). When investigating the effects of diterpenes isolated from Sinularia flexibilis on the eggs, sperm and embryos of Montipora digitata and Acropora tenuis, Aceret et al (1995b) found that only eggs that were fertilized in the presence of these chemicals lost there cellular integrity and burst just a few hours after exposure. So it appears that the diterpenes can act upon the developing eggs themselves but only within the first twenty four hours.

Although laboratory studies have demonstrated the toxicity of many of these compounds to stony corals, one rarely finds evidence of local mortality or tissue necrosis on the reef itself (Coll and Sammarco, 1986). When interactions first occur between corals, tissue damage occurs very rapidly, but over the course of a few days or weeks the colonies can either grow, or in the case of soft corals, move away from each other. So one often sees colonies that have shapes indicative of avoidance behaviour (Coll and Sammarco, 1986). The fact that many soft corals such as Nephthea spp. can move over the substratum further helps to decrease the probability of contact with potential competitors.

Anti-Fouling

Soft corals such as Sarcophyton, Lobophytum and gorgonians, periodically shed a waxy film, sometimes with their epidermis in an attempt to rid it of epiphytic growths and release excess carbon (see volume one and Coll et al, 1987). Soft corals can also employ their secondary metabolite chemicals as anti-foulants to retard the persistent growth of algae. Coll et al. (1987) showed that some diterpenes isolated from Lobophytum pauciflorum,, could inhibit the growth of the red alga Ceramium flaccidum. Interestingly, the basal portions of most soft corals contain higher concentrations of sclerites and lower concentrations of diterpenes while the tips are the opposite.

Feeding Deterrence

Soft corals are rich in nutritional substances (fats, proteins, and carbohydrates) and should serve as valuable food sources to predators, but the incidence of predation is rather low (Williams, 1993). Obviously they must have developed some mechanisms to

Lobophytum

This Lobophytum sp. is shedding a waxy film to help clean its surface of growths of algae. J. Sprung discourage predation. There are four methods by which soft corals can deter predation: the use of toxic chemicals, the use of chemicals to reduce palatability, the production of calcium carbonate spicules, and the ability to retract polyps.

Many of the chemicals mentioned previously are also powerful toxins to fish. Wylie and Paul (1989) showed that compounds isolated from three species of Sinularia acted as feeding deterrents for naturally occurring reef fish. Gerhart (1984) and Harvell et al. (1988) showed the same for Caribbean gorgonian secondary metabolites. Studies of several soft coral genera on the Great Barrier Reef showed that 50% of the thirty eight extracts isolated were toxic to fish (guppies) at the lowest concentration, increasing to 88% at the highest concentration. However, feeding deterrence (presumably based on taste) was found to be as common in non-toxic corals as in toxic corals. When extracts were made of non-toxic corals, high levels of feeding deference were found in almost 90% of the high concentration samples (LaBarre et al., 1986). This implies that other defenses are of equal if not greater importance. Toxicity has also been found to be highly variable within genera, with some species being much more toxic than others. Given these findings there does not appear to be any relationship between feeding deterrents and toxicity; some palatable corals are highly toxic while some unpalatable corals are not.

Octocorals are characterized by the presence of calcium carbonate spicules (sclerites) within their tissues. These vary in size and shape between genera and species, and within a colony. Several studies have demonstrated the ef fectiveness of these structures as feeding < deterrents against fish and gastropods (Harvell et ah, 1988; Van Alstyne and Paul, 1992; Van Alstyne el al., 1992). Since the number and size of sclerites vary within a colony, different parts of a colony are more susceptible to pre elation. For example, in Sinularia; the sclerites are generally larger and much more numerous in the base than in the tips of the tentacles, which are more prone to being eaten by fish (Van Alstyne et al., 1992). Sclerite shape may also play a role in acting as a feeding deterrent, especially when comparing different species and genera. Although sclerites play a role in reducing predation in soft corals, they have other functions in supporting the coral tissues. Their presence or absence in certain areas may be more a reflection of their structural function than their role as a feeding deterrent. For example, the tips of Sinularia lack a great deal of sclerites but have high concentrations of predator deterrent chemicals (Van Alstyne et al. ,1992).

It seems that some of these methods can act together whereas others are negatively correlated. Soft corals that are heavily spiculated tend to be non-toxic, while those with fewer or smaller spicules tend to be more toxic. Also in many species the polyps are protected by bundles of spicules arranged around them (e.g. Nephtbea spp. and

Dendronepbtbya spp.) while in other genera the polyps can be fully retracted and protected within the tissue of the coral (e.g. Sarcopbyton spp. and Pachyclavularia spp.). In genera where the polyps cannot be retracted and sclerites are reduced (e.g. Antbelia spp. and Xenia spp. ) chemicals may be more abundant.

Of course the presence of toxic chemicals and physical defenses does not provide an absolute protection against prédation. There are organisms that have evolved to counter these defense mechanisms. The ovulid snail, Ovula ovum (commonly called the Egg Cowry even though it is not a cowry) feeds on soft corals of the genus Sarcopbyton. This snail can transform the highly toxic chemical found in Sarcopbyton species into less toxic forms (Coll et al., 1983 • Other predators are immune to the toxic chemicals and store them in their bodies for use in their own defense. For example, the aeolid nudibranch, Pbyllodesmium longicirra, (see photo in vol. one and chapter 11 in vol. two) stores the toxins of S. trocbeliopborum in its ce rata (Sammarco, 1986). When attacked by a fish, it releases the cerata so that the fish gets a very distasteful and likely toxic mouthful! The butterfly fish, Cbaetodon unimaculatus (Tear Drop butterfly), appears to be immune to the chemicals and spicules in soft corals and feeds readily on them, allowing it to utilize a resource most other carnivorous fish cannot (Wylie and Paul, 1989).

Reproductive Role

Egg-specific terpenes and diterpenes have been found in the eggs of Lobopbytum and Sinularia inviting speculation as to their role (Sammarco and Coll, 1988). One obvious conclusion woulci be that these compounds confer protection to the eggs by rendering them toxic, however, there is as yet no evidence to support this conclusion. In fact we have observed a butterflyfish (Cbaetodon ulietensis) eagerly eating eggs released by a Heteroxenia colony. The same fish would not eat the polyps after first tasting two or three when the colony was first introduced into the tank, indicating that feeding deterrent chemicals were most likely present in the colony. Either the eggs contain no such deterrent chemicals, they do not play a protective role in the eggs, or they contain different chemicaI s.

Recent research has showrn that the hermaphroditic stony coral Montipora digitata has a mixture of chemicals (acetylenic alcohols) that act as sperm attractants (Coll et al., 1994) This would confer a definite advantage during mass spawning to ensure that

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The COMPLETE guide to Aquariums

The COMPLETE guide to Aquariums

The word aquarium originates from the ancient Latin language, aqua meaning water and the suffix rium meaning place or building. Aquariums are beautiful and look good anywhere! Home aquariums are becoming more and more popular, it is a hobby that many people are flocking too and fish shops are on the rise. Fish are generally easy to keep although do they need quite a bit of attention. Puppies and kittens were the typical pet but now fish are becoming more and more frequent in house holds. In recent years fish shops have noticed a great increase in the rise of people wanting to purchase aquariums and fish, the boom has been great for local shops as the fish industry hasnt been such a great industry before now.

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