Development of a microplate-based novel toxicity bioassay using Chlorophyta and Phaeophyceae macroalgae.

Macroalgae are one of the main producers in marine environments. However, only a few toxicity test methods have been established that use reference strains of macroalgae to evaluate the effects of chemicals on the growth and reproduction of macroalgae to monitor water quality. We selected reference strains of Chlorophyta, Ulva aragoënsis; Phaeophyceae, Ectocarpus siliculosus; and wakame, Undaria pinnatifida, as test species to establish a microplate-based method to investigate the toxicity of potassium dichromate, 3,5-dichlorophenol, and two common herbicides (diuron and simazine). We determined the growth of the three macroalgae in their early life stages and during the sporangia formation stage in E. siliculosus under laboratory conditions. We observed that the growth and sporangia formation in these algae were impaired in a dose-dependent manner. Additionally, we investigated the sensitivity of these macroalgae by comparing the toxicity values of toxicants used in this study with those obtained from a database. Compared to other microalgae and plant species, macroalgae showed a relatively high sensitivity to organic compounds, including herbicides. Growth tests using U. aragoënsis and E. siliculosus produced reliable results at 0-32 and 25-32 practical salinity units (PSU), respectively. The tests established in this study could test the toxicity of chemical substances in macroalgae and are thus expected to contribute to a better understanding of the environmental risks of chemical substances on aquatic biota. The tests could be applied to all effluent toxicity tests used for the management of seawater and brackish water quality.

Molting enhances internal concentrations of fipronil and thereby decreases survival of two estuarine resident marine crustaceans.

In aquatic arthropods, molting is a pivotal physiological process for normal development, but it may also expose them to higher risks from xenobiotics, because the organism may take up additional water during that time. This study aimed to assess the effects of molting on bioconcentration and survival after 96-h exposure to insecticide fipronil with or without oxygenase (CYP450s) inhibitor piperonyl butoxide (PBO) of two estuarine resident marine crustacean species: the sand shrimp Crangon uritai and the kuruma prawn Penaeus japonicus, with 96-h LC50 value of fipronil = 2.0 µg/L and 0.2 µg/L, respectively. Two graded concentrations included group high (H) (equivalent to the 96-h LC50 values) and low (L) (one-tenth of the H group concentration). Molting and survival were individually checked, and internal concentrations of fipronil and its metabolites (fipronil desulfinyl, fipronil sulfide, fipronil sulfone) were measured. The results showed that, only fipronil and fipronil sulfone were detected from organism, and that internal concentrations of these insecticides in molted specimens were higher than those of unmolted ones but comparable with those of dead ones. Accordingly, mortality was more frequent in molted specimens than those that were unmolted. Furthermore, involvement of oxygenase and higher lethal body burden threshold may confer higher tolerance to fipronil in sand shrimp than in the kuruma prawn. This study is the first to demonstrate that the body-residue-based approach is useful for deciphering the causal factors underlying fipronil toxicity, but highlights the need to consider physiological factors in arthropods, which influence and lie beyond body burden, molting and drug metabolism.

Occurrence of neonicotinoids and fipronil in estuaries and their potential risks to aquatic invertebrates.

This study aimed to evaluate and qualify field-based potential risks of seven neonicotinoid and phenylpyrazole (fipronil) insecticides on aquatic invertebrates, including estuary-resident marine crustaceans. One hundred and ninety-three estuarine water samples, with salinity ranging from 0.5 to 32.7, were collected from four estuarine sites in the Seto Inland Sea of Japan, in 2015-2018 and the insecticide levels were measured. Five neonicotinoid and fipronil insecticides were successfully identified, and their occurrence varied temporally. Marine crustaceans were simultaneously harvested every month from one of the estuarine water sampling sites in 2015-2017. Three predominant crustacean species, kuruma prawn (Penaeus japonicus), sand shrimp (Crangon uritai), and mysid (Neomysis awatschensis), were captured and their seasonal presence was species independent. A 96-h laboratory toxicity study with the insecticides using kuruma prawn, sand shrimp, and a surrogate mysid species (Americamysis bahia) indicated that fipronil exerted the highest toxicity to the three crustaceans. Using both toxicity data and insecticide occurrence in estuarine water (salinity ≥10, n = 169), the potential risks on the three marine crustaceans were quantified by calculating the proportion of mixture toxicity effects (Pmix). The Pmix of seven neonicotinoids on the crustaceans was less than 0.8%, which is likely to be too low to indicate adverse effects caused by the insecticides. However, short temporal detection of fipronil (exclusively in June and July) significantly affected the Pmix, which presented the maximal Pmix values of 21%, 3.4%, and 72% for kuruma prawn, sand shrimp, and mysid, respectively, indicating a significant effect on the organisms. As for estuarine water (salinity <10), some water samples contained imidacloprid and fipronil exceeding the freshwater benchmarks for aquatic invertebrates. The present study provides novel insights into the seasonally varying risks of insecticides to estuarine crustaceans and highlights the importance of considering whether ecological risk periods coincide with crustacean presence.

Gazelletta kashiwaensis sp. nov. (Medusettidae, Phaeodaria, Cercozoa), Its Morphology, Phylogeny, Distribution, and Feeding Behavior.

A phaeodarian morphotype, characterized by the feet surrounded with forked pedal spines with anchor-like structures, was collected in the subtropical North Pacific. Considering the morphological and phylogenetic uniqueness, this morphotype is described as Gazelletta kashiwaensis sp. nov. The distribution of this new species is possibly affected by the Kuroshio Current. The feeding behavior of living phaeodarians was first filmed: the present new species floated in the water column stretching "protoplasmic webs" and collected diatoms by repeating the expansion and retraction of "pseudopodium-like tentacles".

The complete mitochondrial genome of the burrowing ghost shrimp, Nihonotrypaea harmandi (Bouvier, 1901), (Crustacea, Decapoda, Axiidea, Callianassidae) - a validation of the genus and species classifications.

The complete mitochondrial genome of the burrowing ghost shrimp Nihonotrypaea harmandi was reconstructed using the Illumina HiSeq platform. The genome was 15,272 bp in length made up of 37 mitochondrial genes (13 CDSs, 22 tRNAs, and 2 rRNAs) in the same order as other Nihonotrypaea species. Phylogenetic analyses suggested that Nihonotrypaea is a valid genus, and that N. harmandi can be phylogenetically marginally separated from N. japonica, though some authors considered the former as a synonym of the latter.