Bivalve molluscs, the primary vectors of paralytic shellfish poisoning (PSP) in humans, show marked inter-species variation in their capacity to accumulate PSP toxins (PSTs) which has a neural basis. PSTs cause human fatalities by blocking sodium conductance in nerve fibres. Here we identify a molecular basis for inter-population variation in PSP resistance within a species, consistent with genetic adaptation to PSTs. Softshell clams (Mya arenaria) from areas exposed to 'red tides' are more resistant to PSTs, as demonstrated by whole-nerve assays, and accumulate toxins at greater rates than sensitive clams from unexposed areas. PSTs lead to selective mortality of sensitive clams. Resistance is caused by natural mutation of a single amino acid residue, which causes a 1,000-fold decrease in affinity at the saxitoxin-binding site in the sodium channel pore of resistant, but not sensitive, clams. Thus PSTs might act as potent natural selection agents, leading to greater toxin resistance in clam populations and increased risk of PSP in humans. Furthermore, global expansion of PSP to previously unaffected coastal areas might result in long-term changes to communities and ecosystems.

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suitable for microalgal biofuel production due to unfavorable climate and solar insolation levels. However, these conditions can potentially be mitigated by coupling microalgal cultivation to industrial processes such as wastewater treatment. In this study, we have examined the biomass and lipid productivity characteristics of 14 microalgae isolates (Chlorophyta) from the Canadian province of Saskatchewan. Under both photoautotrophic and mixotrophic cultivation, a distinct linear trend was observed between biomass and lipid productivities in the 14 SK isolates. The most productive strain under cultivation in TAP media was Scenedesmus sp.-AMDD which displayed rates of biomass and fatty acid productivities of 80 and 30.7 mg L −1 day −1 , respectively. The most productive strain in B3NV media was Chlamydomonas debaryana-AMLs1b which displayed rates of biomass and fatty acid productivities of 51.7 and 5.9 mg L −1 day −1 , respectively. In 11 of the isolates tested, secondary municipal wastewater (MCWW) supported rates of biomass productivity between 21 and 33 mg L −1 day −1 with Scenedesmus sp.-AMDD being the most productive. Three strains, Chlamydomonas debaryana-AMB1, Chlorella sorokiniana-RBD8 and Micractinium sp.-RB1b, showed large increases in biomass productivity when cultivated mixotrophically in MCWW supplemented with glycerol. High relative oleic acid content was detected in 10 of the 14 isolates when grown mixotrophically in media supplemented with acetate. There was no detectable effect on the fatty acid profiles in cells cultivated mixotrophically in glycerol-supplemented MCWW. These data indicate that biomass and lipid productivities are boosted by mixotrophic cultivation. Exploiting this response in municipal wastewater is a promising strategy for the production of environmentally sustainable biofuels.

Brown tides of Aureococcus anophagefferens occur in shallow mid-Atlantic bays in the USA and attain peak summer densities of ~1000 to 2800 cells µl -1. Blooms coincide with the period of spawning and planktotrophic larval development of the hard clam Mercenaria mercenaria, a commercially important bivalve in the region. This laboratory study investigates the effects of A. anophagefferens (toxic isolate from Provasoli-Guillard Center for Culture of Marine Phytoplankton [CCMP 1708]) on hard clams throughout their larval development as a function of increasing (1) supplement and (2) contributor to total phytoplankton cell volume in the diet. Brown tide consistently inhibited veliger growth rates in a dose-dependent manner, leading to arrested development in the D-stage; yet mortalities varied greatly among larval batches and were attributed to secondary effects of nutritional stress. Growth of larvae exposed for 2 wk to brown tide at 800 cells µl -1 was 89 to 90% less than controls fed Isochrysis galbana (clone T-iso) in both the presence and absence of alternate food. No recovery was observed when larvae were returned to the control diet. However, larvae showed variable intrapopulation susceptibility to brown tide when exposed to a mixed suspension of A. anophagefferens and I. galbana (400 and 50 cells µl -1 , respectively). Exposure to low levels of brown tide (50 cells µl -1 ) resulted in relatively small but significant growth reduction. Larvae had reduced larval clearance rates (ingestion) when exposed to unialgal brown tide, as confirmed by analysis of gut autofluorescence and negative feeding selectivity for A. anophagefferens in a mixed suspension. Therefore, primarily through their inhibitory effects on growth, brown tides at ≥200 cells µl -1 are expected to cause metamorphic failure of hard clam larval populations. These will lead to extended larval life in the plankton and increased vulnerability to secondary mortality factors. In turn, hard clam larvae are expected to make a negligible contribution to microzooplankton grazing on brown tide. KEY WORDS: Brown tide · Aureococcus anophagefferens · Clam larvae · Mercenaria mercenaria Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 331: [147][148][149][150][151][152][153][154][155][156][157][158][159] 2007 Brown tides have caused considerable economic losses by adversely affecting wild and cultured populations of bivalves, including the hard clam Mercenaria mercenaria, which supports valuable commercial and recreational fisheries and aquaculture in Atlantic North America. Brown tides have caused feeding inhibition of adult suspension-feeding bivalves (e.g. M. mercenaria and Mytilus edulis), mass mortalities of adult mussels M. edulis, growth inhibition and recruitment failure of bay scallops Argopecten irradians (reviewed by Bricelj & Lonsdale 1997) and severe (67%) mortalities of 1 mm hard clams (Greenfield et al. 2002). The inability of the hard clam fishery in Great South Bay to recover from over...

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