The Structurally similar diterpenoid alcohols pachydictyol-A and dictyol-E are produced by the brown seaweed Dictyota dichotoma. This seaweed and several related species that also produce these compounds are known to be relatively low preference foods for tropical fishes and urchins. We evaluated the effect of various concentrations of these compounds on feeding by the three common types of herbivores that co-occur with Dictyota in coastal North Carolina. Fish (Diplodus holbrooki), sea urchins (Arbacia punctulata), and a mixed species group of gammarid amphipods were offered pieces of the palatable seaweed Gracilaria tikvahiae coated with either (1) dictyol-E or pachydictyol-A dissolved in diethyl ether or (2) diethyl ether alone. Dictyol-E significantly reduced consumption by fish and urchins at concentrations of 0.5 and 1.0% of algal dry mass, but had no effect on amphipod grazing. Pachydictyol-A significantly reduced fish grazing at the relatively high concentrations of 1.0 and 1.3% of plant dry mass; at 0.5% it tended to decrease grazing, but the effect was not significant (P = .07). Pachydictyol-A had no effect on urchin grazing and significantly increased amphipod grazing. When Pachydictyol-A was fed to fish as 1.0% of food dry mass, their growth rate was reduced by a significant 48%. In feeding preference experiments with several seaweeds, Dictyota ranks low for fish and urchins but high for amphipods. This is consistent with the hypothesis that the secondary metabolites produced by Dictyota play a major role in determining its susceptibility to herbivores. The ability of amphipods to circumvent the chemical defenses (Dictyota, and the fact that the two species of algae most readily consumed by amphipods (Codium and Dictyota) were the two species least readily consumed by fish, suggest that predation and herbivory by fishes may be major factors selecting for amphipods that can live on, and eat, seaweeds that are unpalatable to fishes. Amphipods that fed on Dictyota did not appear to sequester the Dictyota metabolites; when exposed to fish predation, Dictyota-fed amphipods were eaten as readily as amphipods that had fed on an alga with no defensive chemistry. Tubicolous amphipods and other small marine herbivores that may spend significant portions of their lives on only a few plants my be under very different evolutionary constraints than the larger, more mobile herbivores that commonly moved between many plants. Several characteristics of these smaller, less mobile, and much less studied, marine herbivores suggest that they may be ecologically similar to terrestrial insects and may play a large, but presently unappreciated, role in structuring marine plant communities.

Starke und selektive Cytotoxizität gegenüber einer Reihe von Krebszelllinien kennzeichnen Salinosporamid A (1), das aus dem Rohextrakt eines einzigartigen marinen Aktinomyceten der Gattung Salinospora isoliert wurde.

Celite and rinsed with 1.0 mL of dichloromethane, 1.0 mL of ethyl acetate, 12 mL of dichloromethane with 2% acetic acid, and 10 mL of ethyl acetate with 1% acetic acid. The filtrate was concentrated in vacuo to give a brown solid. The residue was chromatographed over 0.6 g of silica gel (eluted with ethyl acetate-hexane, 1:5 progressing to 1:1, and then with ethyl acetate-hexane-acetic acid, 66:31:2) to give 2.9 mg (32%) of pleurotin (1) as a pale yellow solid:

No abstract

Embryos of the shrimp Palaemon macrodactylus are remarkably resistant to infection by the fungus Lagenidium callinectes, a recognized pathogen of many crustaceans. An Alteromonas sp. bacterial strain consistently isolated from the surface of the embryos, produces 2,3-indolinedione (isatin), a compound that inhibits the pathogenic fungus. If exposed to the fungus, bacteria-free embryos quickly die, whereas similar embryos reinoculated with the bacteria or treated only with 2,3-indolinedione live well. The commensal Alteromonas sp. bacteria protect shrimp embryos from fungal infection by producing and liberating the antifungal metabolite 2,3-indolinedione.

No abstract

Five secondary metabolites from tropical marine algae and one related compound from an herbivorous sea-hare (Aplysidae) were coated, at approximately natural concentrations, onto the palatable seagrass Thalassia testudinum and placed on coral reefs where they could be eaten by the diverse group of herbivorous fishes that occur there. Laboratory feeding assays with the herbivorous sea urchin Diadema antillarum were also conducted. When compared to appropriate controls, the following terpenoid compounds significantly reduced the amount of Thalassia eaten by both Diadema and reef fishes: stypotriol, from the brown seaweed Stypopodium zonale; pachydictyol-A, which is produced by several genera of tropical (Dictyota and Dilophus) and warm-temperate (Pachydictyon and Glossophora) brown seaweeds; elatol, from the tropical red alga Laurencia obtusa; and isolaurinterol, which is produced by several tropical and warm-temperate species of Laurencia. Under very mild acid conditions, isolaurinterol is converted to a structurally similar compound, aplysin, found in high concentrations in sea-hares that feed on isolaurinterol-containing Laurencia species. Aplysin did not deter feeding by either type of herbivore. Cymopol, a terpenoid bromohydroquinone from the green alga Cymopolia barbata, significantly reduced feeding by reef fishes but significantly stimulated feeding by Diadema. Pharmacological and crude bioactivity tests suggest that several of these compounds function as generalized toxins. However, these generalized laboratory assays are not necessarily good predictors of how compounds will affect feeding by herbivores. For example, pachydictyol-A and stypotroil were equally effective at deterring fishes and Diadema, even though pachydictyol-A shows almost no bioactivity in laboratory assays while stypotriol and its oxidation product, stypoldione, are very bioactive. Herbivory on coral reefs is more intense than in any other habitat studied and the diversity of herbivore types is high. It appears that this intense grazing has provided strong selection for seaweeds that synthesize unique secondary metabolites that significantly reduce the consumption of plants exposed to attack by a diverse group of reef herbivores.

Forty marine algae of the order Caulerpales were chemically investigated. Virtually all produce toxic secondary metabolites of a unique and unprecedented class. These metabolites are generally Linear terpenoids, but unusual structural features such as aldehydes and bis-enol acetate functional groups make these compounds uruque. The conlpounds are t o n c or deterrent toward microorganisms, sea urchin larvae, and herbivous fishes, and when incorporated into diets at naturally occurring concentrations cause mortality in juvenile conch. Concentrations of bioactive metabolites were found to show httle variation in different plant parts such as blades, shpes and holdfasts. Young growlng tips and reproductive structures contained higher concentrahons than mature plant tissues on a dry weight and ash-free dry weight basis. Chemical variation, both qualitahve and quantitative, was observed in different populations of the same species. In the cases examined, algae growing in areas known to have the highest herbivory produced the greatest concentrations and varieties of secondary metabolites. Based upon these observations and pnor feeding preference data, we conclude that chemical defense IS a major factor In the sumval of marine algae within this order.