Screening for negative effects of candidate ascidian antifoulant compounds on a target aquaculture species, Perna canaliculus Gmelin.

The natural chemical compounds radicicol, polygodial and ubiquinone-10 (Q10) have previously been identified as inhibitors of metamorphosis in ascidian larvae. Accordingly, they have potential as a specific remedy for the costly problem of fouling ascidians in bivalve aquaculture. In this study, these compounds were screened for their effects on the physiological health of an aquaculture species, the green-lipped mussel, Perna canaliculus Gmelin, at or above the 99% effective dose (IC(99)) in ascidians. Three physiological biomarkers of mussel health were screened: growth (increases in shell height and wet weight), condition (condition index) and mitochondrial respirational function (Complex I-mediated respiration, Complex II-mediated respiration, maximum uncoupled respiration, leak respiration, respiratory control ratios and phosphorylation system control ratios). While polygodial and Q10 had no effect on mussel growth or the condition index, radicicol retarded growth and decreased the condition index. Mitochondrial respirational function was unaffected by radicicol and polygodial. Conversely, Q10 enhanced Complex I-mediated respiration, highlighting the fundamental role of this compound in the electron transport system. The present study suggests that polygodial and Q10 do not negatively affect the physiological health of P. canaliculus at the IC(99) in ascidians, while radicicol is toxic. Moreover, Q10 is of benefit in biomedical settings as a cellular antioxidant and therefore may also benefit P. canaliculus. Accordingly, polygodial and Q10 should be progressed to the next stage of testing where possible negative effects on bivalves will be further explored, followed by development of application techniques and testing in a laboratory and aquaculture setting.

Preventing ascidian fouling in aquaculture: screening selected allelochemicals for anti-metamorphic properties in ascidian larvae.

Fouling by ascidians causes major stock losses and disrupts production in marine aquaculture, especially bivalve aquaculture. Currently, no cost effective solution exists despite the testing of many prospective control techniques. This study examined a range of allelochemicals suspected to inhibit metamorphosis in marine larvae. Five allelochemicals were screened in a larval metamorphosis bioassay using Ciona savignyi Herdman to determine their potential as a remedy for ascidian fouling in bivalve aquaculture. Three of the compounds tested inhibited ascidian larval metamorphosis and increased mortality at low concentrations. These were radicicol (99% inhibition of metamorphosis [IC99], 0.8 µg ml⁻¹; 99% lethal concentration [LC99], 2.5 µg ml⁻¹; 99% lethal time [LT99], 7.0 days), polygodial (IC99, 0.003 µg ml⁻¹; LC99, 0.9 µg ml⁻¹; LT99, 6.4 days), and ubiquinone-10 (IC99, 3.2 µg cm⁻²; LC99, 14.5 µg cm⁻²; LT99, 5.6 days; expressed as µg cm⁻² due to insolubility in water and ethanol). While spermidine significantly affected metamorphosis and mortality of C. savignyi, the effect was insufficient to achieve inhibition in 99% of larvae over the 7-day timeframe of the assay. Muscimol did not affect metamorphosis or mortality at the concentrations tested. The present study demonstrates that radicicol, polygodial and ubiquinone-10 have potential for future development in antifoulant formulations targeted towards the inhibition of metamorphosis in ascidian larvae, while spermidine and muscimol appear unsuitable.

Species composition and cyanotoxin production in periphyton mats from three lakes of varying trophic status.

In lakes, benthic micro-algae and cyanobacteria (periphyton) can contribute significantly to total primary productivity and provide important food sources for benthic invertebrates. Despite recognition of their importance, few studies have explored the diversity of the algal and cyanobacterial composition of periphyton mats in temperate lakes. In this study, we sampled periphyton from three New Zealand lakes: Tikitapu (oligotrophic), Okareka (mesotrophic) and Rotoiti (eutrophic). Statistical analysis of morphological data showed a clear delineation in community structure among lakes and highlighted the importance of cyanobacteria. Automated rRNA intergenic spacer analysis (ARISA) and 16S rRNA gene clone libraries were used to investigate cyanobacterial diversity. Despite the close geographic proximity of the lakes, cyanobacterial species differed markedly. The 16S rRNA gene sequence analysis identified eight cyanobacterial OTUs. A comparison with other known cyanobacterial sequences in GenBank showed relatively low similarities (91-97%). Cyanotoxin analysis identified nodularin in all mats from Lake Tikitapu. ndaF gene sequences from these samples had very low (≤ 89%) homology to sequences in other known nodularin producers. To our knowledge, this is the first detection of nodularin in a freshwater environment in the absence of Nodularia. Six cyanobacteria species were isolated from Lake Tikitapu mats. None were found to produce nodularin. Five of the species shared low (< 97%) 16S rRNA gene sequence similarities with other cultured cyanobacteria.