Seaweed sex pheromones and their degradation products frequently suppress amphipod feeding but rarely suppress sea urchin feeding

Summary. A diverse group of brown seaweeds produce bouquets of C₁₁ metabolites, some of which act as pheromones that cue gamete release or attract sperm to eggs following release. We demonstrate that these C₁₁ metabolites and their degradation products also frequently and strongly deter feeding by the herbivorous amphipod Ampithoe longimana, but rarely by the herbivorous sea urchin Arbacia punctulata. Across the range of concentrations tested, seven of twelve C₁₁ metabolites or mixtures that we tested deterred feeding by the amphipod, but only two of eleven deterred the sea urchin. For those compounds where we could rigorously contrast the magnitude of deterrence against the amphipod with the magnitude of deterrence against the urchin, the amphipod was deterred significantly more than the urchin by five of six metabolites. Thus, C₁₁ compounds were more frequently and more strongly deterrent to the amphipod than to the sea urchin. These findings for C₁₁ metabolites conflict with previous investigations, where other classes of seaweed chemical defenses have been shown to deter feeding by large mobile herbivores like urchins and fishes but to be relatively ineffective against mesograzers, especially the species of amphipod that we used here. Our results suggest that C₁₁ metabolites are unusual among the known seaweed chemical defenses in that they are especially effective against mesograzers, which often consume seaweed spores, zygotes, and juveniles. The high concentrations of C₁₁ metabolites in brown algal eggs could allow these defenses to be especially important in defending gametes, zygotes, or young sporelings from herbivorous mesograzers. Received 26 February 1998; accepted 9 April 1998.     

Heavy metal accumulation by freshwater hydrobionts in a mining area in the south of the Russian Far East

The contents of heavy metals (HMs) were studied in freshwater hydrobionts from the south of the Russian Far East, including the area of wastewater discharge from a lead smelter (the village of Rudnaya Pristan, Primorye). The results showed that most invertebrates disappeared from the ecosystem as the toxicity of the aquatic environment increased. Mollusks of the genus Lymnaea proved to be most tolerant of HM pollution. As the contents of Pb, Mn, Cd, and Zn in bottom sediments increased, the amounts of these metals in mollusk bodies increased as well but to a much lesser extent, with the intensity of HM accumulation decreasing at their higher concentrations in the environment. The range of HM concentrations accumulated in the bodies of limneids noticeably broadened with an increase in technogenic impact. This is evidence for differences in the efficiency of mechanisms regulating the contents of trace elements in individuals of the same species under conditions of extreme pollution.     

Size-related bioaccumulation and between-year variation of organochlorines in ice-associated amphipods from the Arctic Ocean

Organochlorines are found even in organisms living in remote areas such as the Arctic marginal ice zone. Organochlorine concentrations in ice-associated (sympagic) amphipods are related to their diet. Therefore, the size-dependent diet shift of Gammarus wilkitzkii may influence its organochlorine content. In this preliminary study, the organochlorine concentrations in two size classes (small 29 mm and large >29 mm) of G. wilkitzkii were analysed. The concentrations of more lipophilic compounds [e.g. polychlorinated biphenyls (PCBs)] were lower in the small than the large size class, whereas concentrations of less lipophilic compounds [e.g. hexachlorocyclohexanes (HCHs)] did not differ by size class.

Since contamination transport by the atmosphere, ocean currents and sea ice may vary, the organochlorine burden in sympagic organisms may also vary. There are no data available on temporal variation of organochlorine burden in Arctic sympagic fauna. Therefore, we compared organochlorine concentrations in sympagic amphipods (G. wilkitzkii, Apherusa glacialis and Onisimus spp.) between 1998 and 1999. Organochlorine concentrations in all amphipods were low in both years, with sum organochlorines from 50.7 to 621.9 ng g⁻¹ lipid weight. The concentrations of hexachlorobenzene (HCB), chlordanes, DDTs and PCBs were higher in 1999 than 1998, whereas the HCH concentrations were lower in 1999 than 1998. The organochlorine concentrations differed between the taxa in both years in a similar increasing manner from A. glacialis to both G. wilkitzkii and Onisimus spp.

In studies of bioaccumulation relative to body size and temporal variation, a thorough interpretation requires samples from several size classes and years. Nevertheless, the present data provide new knowledge on contaminants in Arctic invertebrates where data are scarce.     

Baseline activities of four biomarkers in three life-stages of the amphipod,Leptocheirus plumulosus

This study investigated differences in baseline levels of four cellular biomarkers (glutathione (GSH), lipid peroxidation (LPx), acetylcholinesterase (AChE), and cholesterol (CHL)) in the larval, juvenile, and adult stages of the estuarine amphipod, Leptocheirus plumulosus. Glutathione, LPx, and AChE exhibited the same pattern of decreasing levels with increasing developmental stage. Cholesterol showed an inverse relationship of increasing levels with increasing developmental stages. This research provides valuable background information that may be used in future assessments of amphipod biomarker research.     

Interspecific interactions of amphipods <Emphasis Type="Italic">Gammarus lacustris</Emphasis> and <Emphasis Type="Italic">Gmelinoides fasciatus</Emphasis>

Experimental studies of interactions between two amphipod species (Gmelinoides fasciatus and Gammarus lacustris) showed that predation is the basic mechanism accounting for their mutual exclusion in nature. Mortality from predation among similar-sized specimens of both species at an equal abundance ratio was similar (24–25% in G. lacustris and 27–30% in G. fasciatus). The displacement of G. lacustris by G. fasciatus was observed when the latter was dominant. Adult G. fasciatus and G. lacustris successfully preyed on juveniles of their competitors and did not differ significantly in daily food consumption as a percentage of body weight: 6–24% at a fresh body weight of 18–24 mg in both species. The potential for rapid population growth under new conditions contributed to the success of the invasive Baikal species G. fasciatus in displacing G. lacustris from many water bodies of Russia.