The use of a brine shrimp (Artemia salina) bioassay to assess the toxicity of diatom extracts and short chain aldehydes Gary S. Caldwell * , Matthew G. Bentley, Peter J.W. Olive School of Marine Science and Technology, University of Newcastle upon Tyne, Ridley Building, Claremont Road, Newcastle upon Tyne NE1 7RU, UK Received 10 April 2003; accepted 9 June 2003 Abstract Water soluble algal extracts, the aldehydes 2E,4E-decadienal, decanal, undecanal and the fatty acid eicosapentaenoic acid (EPA) were assayed for toxicity to hatching success and larval mortality of the brine shrimp Artemia salina. Both crude cellular extracts of the diatoms Skeletonema costatum and Nitzschia commutata and the diatom-derived short chain aldehyde decadienal were found to inhibit hatching success of A. salina cysts in a dose-dependent manner. Decadienal also significantly affected larval mortality rates in 24 and 72 h exposure incubations. The Artemia hatching success assay was the least sensitive of the three (EC 50 ¼ 3.94 mg ml 21 ). A greater sensitivity was observed for the 72 h compared with the 24 h exposure trials (EC 50 for 24 h ¼ 2.14, 72 h ¼ 0.023 mg ml 21 ). Decanal did not significantly affect survival or hatching success at the concentrations tested. Undecanal and EPA showed a limited toxic effect in naupliar mortality trials. We suggest that 72 h Artemia exposure trials represent an acceptable bioassay for diatom toxicity where alternative bioassays are unavailable. q 2003 Elsevier Ltd. All rights reserved. Keywords: Aldehyde; Algal extracts; Artemia salina; Decadienal; Diatoms 1. Introduction Diatoms are ubiquitous within aquatic ecosystems and have essential functions in both pelagic and benthic ecology including the transfer of photosynthetically fixed carbon to higher trophic levels (Legendre, 1990; Mann, 1993). However, the classical view of the importance of diatoms in marine food webs is currently under review. A diatom- dominated diet has been shown to be detrimental for the reproduction of their principal grazers, the copepods, with egg production, hatching success and naupliar survival negatively affected (Ban et al., 1997; Miralto et al., 1999; Carotenuto et al., 2002). Embryos incubated with diatom extracts or spawned from diatom fed mothers were unable to synchronize nuclear division with intracellular membrane formation, expressed blockage of tubulin organization, microtubule de-polymerization, prevention of chromatin condensation and nuclear fragmentation without cytokinesis (Poulet et al., 1995; Buttino et al., 1999). The anti-mitotic and teratogenic components have since been identified as a family of short chain aldehydes (SCAs). The production of toxic SCAs is dependent upon wound activation and has recently been demonstrated for a number of diatom species (Miralto et al., 1999; Pohnert, 2000, 2002; Pohnert et al., 2002; d’Ippolito et al., 2002). The bioactive aldehydes are synthesized under the control of a phospholipase A 2 / lipoxygenase/hydroperoxide lyase enzyme cascade from C 20 fatty acid precursors, particularly EPA and arachidonic acid. Inhibitory concentrations are reached within minutes of cell disruption. Toxicity is due to a reactive a,b,g,d- unsaturated Michael structural element (Pohnert, 2002) and has been demonstrated against copepod, echinoderm, polychaete and tumor cell lines (Miralto et al., 1999; Caldwell et al., 2002). In addition, decadienal has also been shown to possess allelochemical (Casotti et al., 2001) and antibacterial properties (Bisignano et al., 2001). 0041-0101/03/$ - see front matter q 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0041-0101(03)00147-8 Toxicon 42 (2003) 301–306 www.elsevier.com/locate/toxicon * Corresponding author. Tel.: þ44-191-222-6661; fax: þ 44-191- 222-7891. E-mail address: gary.caldwell@ncl.ac.uk (G.S. Caldwell).