Thomas R. Tosteson

Population dynamics and toxicity of natural populations of benthic dinoflagellates in southwestern Puerto Rico

Abstract Population dynamics of two benthic dinoflagellates, which have been implicated in ciguatera fish poisoning, were studied over a 3-yr period in southwestern Puerto Rico. Ostreopsis lenticularis Fukuyo and Gambierdiscus toxicus Adachi et Fukuyo populations were not strongly correlated with temperature or rainfall, however, both dinoflagellates did display seasonal fluctuations. Crude methanolic extracts of wild cell O. lenticularis varied in toxicity from nontoxic to 182 MU · cell −1 (× 10 6 ). Toxic materials found in the aqueous methanolic extracts were not soluble in ethyl acetate, a more nonpolar solvent. Peak toxicities in wild O. lenticularis cells recurred in October 1985 and October 1986. While additional data are needed, present results suggest a seasonality in Ostreopsis toxicity as well.

Seasonal frequency of ciguatoxic barracuda in southwest Puerto Rico

Ciguatoxicity of barracuda (Sphyraena barracuda) head, viscera and flesh tissues has been determined in 219 specimens caught along the southwest coast of Puerto Rico from March 1985 through May 1987. Twenty-nine percent of these specimens were toxic. Monthly frequencies of ciguatoxic barracuda showed an apparent seasonal variability, with peak values (60-70% toxic fish) in the late winter-early spring (January-May) and fall (August-November). Minimal frequencies (0-10% toxic fish) were observed during June-July and December. The most frequently toxic tissues in poisonous animals were the viscera and head. Viscera tissue was the only toxic tissue found in 31% of the poisonous fish assayed, and this tissue was poisonous in all toxic fish. In no case was a poisonous specimen found to have toxic flesh alone. Marked temporal variation in frequency of ciguatoxicity suggests that ciguatera toxins, at least in their active form, are not accumulated in barracuda tissues for extended periods of time. Variability in barracuda ciguatoxicity may reflect fluctuations in the toxicity of smaller reef fish prey, seasonal fluctuations in toxic benthic dinoflagellates and/or changes in the ability of the barracuda to detoxify ingested poisons or their precursors.

The Control of Sea Urchin Metamorphosis: Ionic Effects

Because the cascade of events which comprise sea urchin metamorphosis occur rapidly, regulatory mechanisms able to respond in minutes must function. Employing sea water solutions of altered ionic composition in the presence or absence of metamorphically active microbial films, we tested the ability of particular ions to inhibit or enhance metamorphosis in competent larvae of the sea urchin, Lytechinus variegatus. At 40 mM excess potassium maximally induces normal metamorphosis in the absence of a microbial film. In the presence of metamorphically active microbial films, 40 mM excess magnesium inhibits the process. Increasing concentrations of calcium up to an excess of 40 mM stimulates larvae to undergo metamorphosis but in smaller proportions than similar concentrations of potassium. Divalent cation‐free sea water solutions are toxic to larvae. These studies support the hypothesis that ion fluxes are involved in the regulation of metamorphosis and reveal a complexity of response that parallels the histological complexity of competent echinoid larvae.

The fatty acid composition of a Vibrio alginolyticus associated with the alga Cladophora coelothrix. Identification of the novel 9-methyl-10-hexadecenoic acid

The fatty acid composition of a new strain of Vibrio alginolyticus, found in the alga Cladophora coelothrix, was studied. Among 38 different fatty acids, a new fatty acid, 9-methyl-10-hexadecenoic acid and the unusual 11-methyl-12-octadecenoic acid, were identified. Linear alkylbenzene fatty acids, such as 10-phenyldecanoic acid, 12-phenyldodecanoic acid and 14-phenyltetradecanoic acid, were also found in V. alginolyticus. The alga contained 43% saturated fatty acids, and 28% C16–C20 polyunsaturated fatty acids of the n−3 and n−6 families.

Fatty acid composition of bacteria associated with the toxic dinoflagellate Ostreopsis lenticularis and with caribbean Palythoa species

The fatty acid composition of a Pseudomonas sp. (Alteromonas) and its host, the dinoflagellate Ostreopsis lenticularis, vectors in ciguatera fish poisoning, has been studied. The major fatty acids in O. lenticularis were 16∶0, 20∶5n-3, and 22∶6n-3, but 18∶2n-6, 18∶3n-3, and 18∶n-3 were also identified. In contrast to other dinoflagellates, 18∶5n-3 was not detected in O. lenticularis. Even-chain fatty acids such as 9–16∶1, 11–18∶1, and 13–20∶1 predominated in the Pseudomonas sp. from O. lenticularis, but 16–20% of (E)-11-methyl-12-octadecenoic acid was also identified. The chirality of the latter was confirmed by total synthesis (28% overall yield) starting from oxacyclotridecan-2-one. The fatty acid compositions of two other Pseudomonas species, from the palytoxin-producing zoanthids Palythoa mamillosa and P. caribdea, were also studied and were similar to that of the Pseudomonas sp. from O. lenticularis. The possibility of using some of these fatty acids as chemotaxonomic lipids in identifying marine animals that consume toxic dinoflagellates or zoanthids is discussed.

Selective depolarization of the muscle membrane in frog nerve-muscle preparations by a chromatographically purified extract of the dinoflagellate Ostreopsis lenticularis

The actions of a chromatographically identified extract of the marine dinoflagellate Ostreopsis lenticularis, named ostreotoxin‐3 (OTX‐3), were studied on frog isolated neuromuscular preparations. OTX‐3 (1–10μg ml−1) applied to cutaneous pectoris nerve‐muscle preparations depolarized skeletal muscle fibres and caused spontaneous contractions. The depolarization was neither reversed by prolonged washing nor by (+)‐tubocurarine. OTX‐3 decreased the amplitude of miniature end plate potentials (m.e.p.ps) but did not affect their frequency. Extracellular recording of compound action potentials revealed that OTX‐3 affected neither excitability nor conduction along intramuscular nerve branches. End‐plate potentials (e.p.ps) elicited by nerve stimulation were reduced in amplitude by OTX‐3 and even showed reversed polarity in junctions deeply depolarized by the toxin. Membrane depolarization induced by OTX‐3 was decreased about 70% in muscles pretreated for 30min with 10μm tetrodotoxin. In contrast, muscles pretreated with 5μm μ‐conotoxin GIIIA were completely insensitive to OTX‐3‐induced depolarization. OTX‐3 did not affect e.p.p. amplitude and the quantal content of e.p.ps in junctions in which muscle depolarization was abolished by μ‐conotoxin GIIIA. OTX‐3 is a novel type of sodium‐channel activating toxin that discriminates between nerve and skeletal muscle membranes.

Culturable and nonculturable bacterial symbionts in the toxic benthic dinoflagellate Ostreopsis lenticularis.

The toxic benthic dinoflagellate Ostreopsis lenticularis hosts a variety of symbiont bacterial flora. Laboratory cultured Ostreopsis clones require the presence of symbiotic Pseudomonas/Alteromonas bacterial strains for growth and toxicity development. Three culturable bacterial strains associated with Ostreopsis were identified as Pseudomonas/Alteromonas strain 1, Pseudomonas/Alteromonas strain 2 and Acinetobacter. Denaturing gradient gel electrophoresis (DGGE) analyses of extracted Ostreopsis associated bacterial DNAs indicated that there were three culturable and four non-culturable associated bacterial strains. The results presented here are the first report of the presence of unculturable bacterial symbionts in a toxic benthic dinoflagellate. Ostreopsis lost toxicity when exposed to elevated temperatures in the field and laboratory culture and subsequently recovered toxicity at reduced temperatures. Ostreopsis associated culturable Pseudomonas/Alteromonas bacterial strains were significantly reduced in dinoflagellate cultures exposed to elevated temperatures. The decreased toxicity of O. lenticularis exposed to elevated temperatures and their subsequent recovery of toxicity in periods of reduced thermal stress may have resulted from the effects of elevated temperature on the spectrum of culturable and unculturable bacterial species interacting with their Ostreopsis host.

The effect of lodide and various lodocompounds on initiation of strobilation in Aurelia

Abstract The effect of iodide and various iodocompounds on initiation of strobilation in Aurelia polyps was studied. Iodide was found to be active in initiating strobilation at concentrations between 10 −4 and 10 −7 M . The order of effectiveness of iodide, bromide and iodocompounds, tested at 10 −6 M concentrations, was (highest first): DIT, MIT, I − , T 3 , T 4 , Br − . The last had no effect. Results of experiments using different polyp concentrations indicated that strobilating polyps release a factor into the media that induces strobilation in other polyps. All agents shown to be active in initiating strobilation were tested in the presence of thiourea. At a concentration of 10 −4 M , thiourea completely inhibited the effect of all of the agents except DIT, which was only partially inhibited. New buds were found to be capable of strobilating only when tested in the presence of older polyps. None of the agents tested induced strobilation in new buds tested in the absence of older polyps. The data indicate that none of the iodocompounds tested is itself responsible for initiating strobilation and that each must be altered to be effective. Because its effect persisted in the presence of thiourea, DIT may be similar in the putative actual compound.

Study of organic-calcium interactions: gypsum precipitation in tropical surface waters

Abstract This paper demonstrates the involvement of dissolved organic compounds in the precipitation of gypsum from near-surface seawater. The general solubility and oxidation behavior of these compounds is discussed. Qualitatively different results have been obtained between samples collected from remote areas and those collected from areas of intensive human use.