Isamu Sakaguchi

Antifouling Substances Against Larvae of the Barnacle Balanus amphitrite from the Marine Sponge, Acanthella cavernosa

A total of 118 Japanese marine invertebrates were extracted with methanol, and their chloroform-soluble materials tested for antifouling activity as well as toxicity against barnacle ( Balanus amphitrite ) larvae. Among 86 species that showed more than 80% larval settlement inhibition, 13 species, including 8 sponges were weakly toxic to the barnacle larvae. The sponge Acanthella cavernosa , which showed most promising activity, was extracted with ethanol and fractionated by solvent partitioning, silica gel column chromatography, gel filtration, and ODS HPLC to give two active compounds which on the basis of spectral data and chemical transformation were identified as a new compound, 10-formamido-4-cadinene and a known compound, T-cadinol, They inhibited larval settlement at concentrations of 0.5 w g ml m 1 .

Antifouling Activity of Simple Synthetic Isocyanides Against Larvae of the Barnacle Balanus amphitrite

Twelve simple linear isocyanides were synthesized and examined for antifouling activity and toxicity against cyprid larvae of the barnacle, Balanus amphitrite. Larval settlement was inhibited, with EC50 values of 0.046 – 1.90 μg ml−1, and they were much less toxic (LD50 values ranging over 21.28 μg ml−1) than CuSO4 (EC50 0.30 μg ml−1 and LD50 2.95 μg ml−1). The data indicate that simple linear isocyanides are promising non-toxic antifouling agents.

Synthesis and Anti-barnacle Activities of Novel Isocyanocyclohexane Compounds Containing an Ester or an Ether Functional Group

Ten novel isocyanocyclohexane compounds that possess an oxygenic functional group at the 4-position were synthesized and evaluated for their antifouling activity against the larvae of the barnacle Balanus amphitrite with the aim of exploring the structure – activity relationships further. The anti-barnacle effect of the synthesized compounds was in the EC50 range of 0.0096 – 17.0 μg ml−1. Some ester derivatives exhibited extremely high antifouling activities, and none of the synthesized isocyanocyclohexane compounds showed significant toxicity. The results suggest that the ester function is one of the important groups in the expression of potent antifouling activity in isocyano compounds.

Synthesis and anti-barnacle activities of novel 3-isocyanotheonellin analogues

An antifouling active natural compound, 3-isocyanotheonellin, and its analogues were synthesized and evaluated for antifouling activity against the larvae of the barnacle Balanus amphirite in order to explore structure-activity relationships. The anti-barnacle effect of the 3-isocyanotheonellin analogues was in the EC 50 range 0.18-7.20 w g ml m 1 . Some synthesized analogues exhibited potent antifouling activity as high as 3-isocyanothoenllin, and none of the synthesized isocyano compounds showed significant toxicity. The results of the present study suggest that an isocyano group and a hydrophobic site at a suitable position are important for potent antifouling activity without toxicity.

Synthesis and antifouling activity of 3-isocyanotheonellin and its analogues

A new synthesis of 3-isocyanotheonellin, a marine sesquiterpene with potent antifouling activity against the larvae of the barnacle Balanus amphirite, and its analogues is described. The highlight of the synthetic strategy is the one-step construction of a tertiary isocyanide from an alcohol using trimethylsilyl cyanide and a silver salt. The antifouling activities of 3-isocyanotheonellin and its analogues are also reported.

Changes in the drift and the settlement of the freshwater mussel Limnoperna fortunei along a headrace channel

The nuisance species Limnoperna fortunei is a freshwater mussel whose infestations have harmed water intake facilities, such as water supply systems. We investigated the changes in the drift and the settlement of L. fortunei along a headrace channel. The densities of the drift and the settlement both decreased dramatically with the downstream distance from the L. fortunei source (a reservoir). In comparison with larval densities in the reservoir, drift densities decreased by 10 to 25% at 0.5 km downstream from the reservoir, and were less than 2% at sites more than 4.8 km downstream. Although larval densities at midnight (0:00-2:00) were approximately 1.5 times higher than those at noon (12:00-14:00) in a shallow layer (3 m depth) of the reservoir, we found no diurnal variation of drift densities in the headrace channel. Settlement densities at the site nearest the intake gate were much higher than those of the other sites further downstream in the headrace channel. The L. fortunei adult population in the channel could reduce drift individuals by attracting the larva. The attraction probably induces the massive aggregation at the location of the channel immediately below the drift source, resulting in biofouling.

Reproduction and larval developmental stages of the freshwater mussel Limnoperna fortunei at three sites in a temperate reservoir

Abstract Longitudinal changes in larval densities and developmental stage compositions of the freshwater mussel Limnoperna fortunei were investigated to understand the patterns of reproduction and development at three sites in Lake Ohshio, a small reservoir in the temperate region of central Japan. Onset and termination of L. fortunei larval presence were coincident at the three sites in the reservoir. This may have been caused by environmental homogenization owing to artificial aeration for water quality improvement of the reservoir. The observations in this study support temperature as the trigger for onset of reproduction as suggested by previous studies. Occurrence of high turbidity that reduced food availability for mussels was probably the trigger for termination of reproduction in Lake Ohshio. During the period when L. fortunei larvae were present, the D-form larva of the earliest developmental stage was always observed and at much higher density than later developmental stages. The results indicate that spawning of L. fortunei continued in the reservoir throughout the period that larvae were observed and that predation and other factors reduced the proportion of later developmental stage larvae.

Population Dynamics and Growth of Limnoperna fortunei

During its first year of life, Limnoperna fortunei grows from ~ 10 to > 30 mm in shell length, primarily depending on water temperature. Two-year-old individuals attain 20–30 mm, and 30 mm is usually the largest size, although specimens up to > 50 mm in size have been reported. The life span is 2–3 years. Water temperature, including the season of each cohort, is the most important factor that determines the growth rate, but other constraints can play important roles too, including calcium concentrations, pollution, food availability and intraspecific competition.