Accumulation of lipofuscin-like pigments (LLPs) has been shown to be an appropriate index of both age and stress in some aquatic invertebrates. In the present study, LLP was quantified by measuring its autofluorescence intensity (ex 450 nm/em 512 nm) in nutritive phagocytes (NPs) of sea urchins Strongylocentrotus intermedius inhabiting polluted and relatively clean areas of Japan Sea. To avoid variations in LLP content related to sea urchin reproductive condition, only developing gonads with acini occupied mostly by NPs were used for LLP quantification as well as semiquantitative histopathological analysis. LLP concentrations ranged from 0.0 to 4.57 ± 0.53% area fraction in female gonads and from 0.0 to 4.61 ± 0.35% in male gonads. The presence of specimens with extremely high LLP concentrations (>1.5%) in all examined samples, including specimens from the reference station, as well as the absence of strong correlations between LLP concentrations and several parameters related to pollution (heavy-metal concentrations in sea urchin gonads and concentrations of heavy metals, DDT, hexachlorocyclohexane, and total petroleum hydrocarbons in sediments), allow us to conclude that LLP content in sea urchin NPs can not be used as a biomarker in marine pollution monitoring.
Behavioral experiments were conducted on two bivalve species-the Japanese scallop Mizuhopecten yessoensis and the Swift scallop Chlamys swifti -to elucidate the role of their abdominal sense organ (ASO) in directional sensitivity to water-borne vibrations. The thresholds were determined at 140 Hz. Both species displayed the highest sensitivity to vibrations, the source of which was placed above the animal (opposite to the left valve), rostro-dorsally to its vertical axis. Removal of the ASO led to loss of directional sensitivity and a considerable increase in the sound reaction threshold. Both species were sensitive to modulated ultrasonic vibrations in the range of 30-1000 Hz. This is proposed to be caused by modulated ultrasound effects, provoking weak oscillations of the shell valves at a modulation frequency.
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