Allelopathy in aquatic environments may provide a competitive advantage to angiosperms, algae, or cyanobacteria in their interaction with other primary producers. Allelopathy can influence the competition between different photoautotrophs for resources and change the succession of species, for example, in phytoplankton communities. Field evidence and laboratory studies indicate that allelopathy occurs in all aquatic habitats (marine and freshwater), and that all primary producing organisms (cyanobacteria, micro- and macroalgae as well as angiosperms) are capable of producing and releasing allelopathically active compounds. Although allelopathy also includes positive (stimulating) interactions, the majority of studies describe the inhibitory activity of allelopathically active compounds. Different mechanisms operate depending on whether allelopathy takes place in the open water (pelagic zone) or is substrate associated (benthic habitats). Allelopathical interactions are especially common in fully aquatic s...

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Allelopathy of Aquatic Autotrophs

https://www.int-res.com/articles/meps/207/m207p225.pdf

Marine chemical ecology

ENCORE: the effect of nutrient enrichment on coral reefs. Synthesis of results and conclusions.

Fishes that feed from live corals (corallivores) are a conspicuous component of healthy coral reef environments. However, knowledge of the occurrence and ecological signiﬁcance of this feeding mode is fragmentary. Historically, very few ﬁsh were considered capable of feeding from live coral, and those few that did were
considered ecologically insigniﬁcant. More recently, the role of corallivores has been re-evaluated; published records document 128 corallivorous ﬁsh species from 11
different families, with 69 of these belonging to the family Chaetodontidae. Other families, including the Labridae, Tetraodontidae, Balistidae, Monacanthidae, Poma-centridae and Scaridae, all have between seven and ten coral-feeding species. One-third of coral-feeding ﬁshes feed almost exclusively on corals, with more than 80% of their diet based on coral. Corallivorous ﬁsh show distinct prey preferences and consume only a small subset of available corals, usually the genera Acropora, Pocillopora and Porites. This selective predation by corallivores can limit abundance and distribution of preferred corals. Chronic predation by corallivores may also exacerbate effects of coral disturbance (e.g. climate-induced coral bleaching), impeding reef recovery and causing further coral loss. Conversely, the cover of preferred corals can be a primary determinant of corallivore abundance and physiological condition. Owing to this close association, obligate corallivores invariably decline in response to loss of coral cover. Increased knowledge of the number of corallivores and their diets suggest that this feeding mode is more important to coral reef food webs than traditionally thought.

Diversity and functional importance of coral‐feeding fishes on tropical coral reefs

Marine invertebrates are rich sources of bioactive compounds and their biotechnological potential attracts scientific and economic interest worldwide. Although sponges are the foremost providers of marine bioactive compounds, cnidarians are also being studied with promising results. This diverse group of marine invertebrates includes over 11,000 species, 7500 of them belonging to the class Anthozoa. We present an overview of some of the most promising marine bioactive compounds from a therapeutic point of view isolated from cnidarians in the first decade of the 21st century. Anthozoan orders Alcyonacea and Gorgonacea exhibit by far the highest number of species yielding promising compounds. Antitumor activity has been the major area of interest in the screening of cnidarian compounds, the most promising ones being terpenoids (monoterpenoids, diterpenoids, sesquiterpenoids). We also discuss the future of bioprospecting for new marine bioactive compounds produced by cnidarians.

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Cnidarians as a Source of New Marine Bioactive Compounds—An Overview of the Last Decade and Future Steps for Bioprospecting

Antimicrobial activity of the diterpenes flexibilide and sinulariolide derived from Sinularia flexibilis Quoy and Gaimard 1833 (Coelenterata: Alcyonacea, Octocorallia)

The chemical ecology of alcyonarian corals, Coelenterata: Octocorallia

. Two field experiments were performed on the Great Barrier Reef, Australia, at Orpheus Island and Lizard Island, respectively, to investigate the effects of allelopathic soft corals on survivorship and community structure of scleractinian coral spat. Ceramic tiles were placed around the allelopathic soft corals Sinularia flexibilis (Quoy & Gaimard 1833) and Sarcophyton glaucum (Quoy & Gaimard 1833), and controls. One control consisted of settlement plates surrounding a scleractinian coral (non-allelopathic planktivore); another control had no adult soft or scleractinian coral present. The experimental soft corals affected the recruitment of various taxonomic groups of coral spat differentially, as evidenced by the diversity of coral spat settling in treatments and controls. At Orpheus Island (O.I., n = 1038 spat) and Lizard Island (L.I., n = 7032 spat), there were significant differences between recruitment success of the two dominant coral taxa, Pocilloporidae (O.I., 61.4 %; L.I., 20.5 %) and Acroporidae (O.I., 33.7 %; L.I., 53 %). Settlement plates exposed to Sinularia flexibilis at either site had the lowest proportion of acroporid recruits. Diversity indices (Shannon-Wiener Indices) varied significantly between treatments at both Orpheus and Lizard Islands. This appears to be due to selective inhibition of acroporid spat by Sinularia flexibilis at both sites. Growth of coral spat was higher on settlement plates in the presence of Sarcophyton at Lizard Island. Settlement of most associated epibiota was generally inhibited under these conditions. Coral spat survivorship was highest in the presence of Sinularia at Orpheus ­Island; at Lizard Island, this was the case with the Sarcophyton treatment. Higher survivorship, and in some cases growth, of coral spat near soft corals was apparently due to reduced competition for space between spat and associated epibiota. This hypothesis is supported by the results of a sister experiment where a coating of Sinularia flexibilis extract on settlement tiles significantly decreased fouling by sessile epibiota. Soft corals have an allelopathic effect on recruitment and early development of scleractinian corals and, consequently, on early coral reef community succession.

Effects of soft corals on scleractinian coral recruitment. II: Allelopathy, spat survivorship and reef community structure

Complementary (secondary) metabolites in an octocoral competing with a scleractinian coral: effects of varying nutrient regimes

A long-term study of the effects of nutrient enrichment on coral reefs (ENCORE Experiment) was carried out at One Tree Island (23°30′S; 152°96′E), Great Barrier Reef, between 1992 and 1996. The experiment involved the addition of water-soluble nutrients to 12 microatolls which contained a range of organisms and were situated within the larger lagoon. Three replicates of each of three nutrient treatments (nitrogen, phosphorus, nitrogen plus phosphorus) and an untreated set of three control atolls were prepared using the 12 selected microatolls. As part of the larger ENCORE experiment, changes in the chemical composition of the alcyonacean soft coral Sarcophyton ehrenbergi Marenzeller (Octocorallia: Alcyonacea), placed in the treatment microatolls, were monitored for a 1 yr period in an attempt to detect any responses attributable to nutrient enrichment. Multivariate analyses were performed to determine whether there were any patterns of response in the different nutrient treatments. At the level of individual metabolites, there were no clear treatment effects. However, the ratio of bioactive or stress metabolites (terpenes) to energy storage metabolites (lipids), referred to as the “physiological-change indicator”, revealed effects of nutrient enrichment. Nitrogen enrichment resulted in a trend towards higher physiological-change indicators than control or phosphorus treatments in the majority of cases, while phosphorus enrichment significantly decreased the ratio relative to controls. In most cases, the physiological-change indicator increased in soft soft corals relocated into contact with the scleractinian Pocillopora damicornis. The potential of soft corals to serve as indicators of a changed nutrient regime is discussed.

Effect of nutrient enrichment on the complementary (secondary) metabolite composition of the soft coral Sarcophyton ehrenbergi (Cnidaria: Octocorallia: Alcyonaceae) of the Great Barrier Reef

John C. Coll

Papers

Antimicrobial activity of the diterpenes flexibilide and sinulariolide derived from Sinularia flexibilis Quoy and Gaimard 1833 (Coelenterata: Alcyonacea, Octocorallia)

The chemical ecology of alcyonarian corals, Coelenterata: Octocorallia

Effects of soft corals on scleractinian coral recruitment. II: Allelopathy, spat survivorship and reef community structure

Complementary (secondary) metabolites in an octocoral competing with a scleractinian coral: effects of varying nutrient regimes

Effect of nutrient enrichment on the complementary (secondary) metabolite composition of the soft coral Sarcophyton ehrenbergi (Cnidaria: Octocorallia: Alcyonaceae) of the Great Barrier Reef