Metamorphosis of the invasive ascidian Ciona savignyi: environmental variables and chemical exposure

A broad-taxa approach as an important concept in ecotoxicological studies and pollution monitoring

Aquatic invertebrates play a pivotal role in (eco)toxicological assessments because they offer ethical, cost-effective and repeatable testing options. Additionally, their significance in the food chain and their ability to represent diverse aquatic ecosystems make them valuable subjects for (eco)toxicological studies. To ensure consistency and comparability across studies, international (eco)toxicology guidelines have been used to establish standardised methods and protocols for data collection, analysis and interpretation. However, the current standardised protocols primarily focus on a limited number of aquatic invertebrate species, mainly from Arthropoda, Mollusca and Annelida. These protocols are suitable for basic toxicity screening, effectively assessing the immediate and severe effects of toxic substances on organisms. For more comprehensive and ecologically relevant assessments, particularly those addressing long-term effects and ecosystem-wide impacts, we recommended the use of a broader diversity of species, since the present choice of taxa exacerbates the limited scope of basic ecotoxicological studies. This review provides a comprehensive overview of (eco)toxicological studies, focusing on major aquatic invertebrate taxa and how they are used to assess the impact of chemicals in diverse aquatic environments. The present work supports the use of a broad-taxa approach in basic environmental assessments, as it better represents the natural populations inhabiting various ecosystems. Advances in omics and other biochemical and computational techniques make the broad-taxa approach more feasible, enabling mechanistic studies on non-model organisms. By combining these approaches with in vitro techniques together with the broad-taxa approach, researchers can gain insights into less-explored impacts of pollution, such as changes in population diversity, the development of tolerance and transgenerational inheritance of pollution responses, the impact on organism phenotypic plasticity, biological invasion outcomes, social behaviour changes, metabolome changes, regeneration phenomena, disease susceptibility and tissue pathologies. This review also emphasises the need for harmonised data-reporting standards and minimum annotation checklists to ensure that research results are findable, accessible, interoperable and reusable (FAIR), maximising the use and reusability of data. The ultimate goal is to encourage integrated and holistic problem-focused collaboration between diverse scientific disciplines, international standardisation organisations and decision-making bodies, with a focus on transdisciplinary knowledge co-production for the One-Health approach.

Thyroid-like hormone signaling in invertebrates and its potential role in initial screening of thyroid hormone system disrupting chemicals

This review examines the presence and evolution of thyroid-like systems in selected aquatic invertebrates to determine the potential use of these organisms in screens for vertebrate thyroid hormone axis disrupting chemicals (THADCs). Such a screen might support the phasing out of some vertebrate testing. Although arthropods including crustaceans do not contain a functional thyroid signaling system, elements of such a system exist in the aquatic phyla mollusks, echinoderms, tunicates, and cephalochordates. These phyla can synthesize thyroid hormone, which has been demonstrated in some groups to induce the nuclear thyroid hormone receptor (THR). Thyroid hormone may act in these phyla through interaction with a membrane integrin receptor. Thyroid hormone regulates inter alia metamorphosis but, unlike in vertebrates, this does not occur via receptor activation by the ligands triiodothyronine (T3) and thyroxine (T4). Instead, the unliganded nuclear receptor itself controls metamorphosis in mollusks, echinoderms, and tunicates, whereas the T3 derivative tri-iodothyroacetic acid (TRIAC) acts as a THR ligand in cephalochordates. In view of this, it may be possible to develop an invertebrate-based screen that is sensitive to vertebrate THADCs that interfere with thyroid hormone synthesis or metabolism along with interaction with membrane receptors. The review makes some recommendations for the need to develop an appropriate test method. Integr Environ Assess Manag 2023;19:63-82. © 2022 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Does plastic type matter? Insights into non-indigenous marine larvae recruitment under controlled conditions

Marine plastic debris (MPD) are a global threat to marine ecosystems. Among countless ecosystem impacts, MPD can serve as a vector for marine 'hitchhikers' by facilitating transport and subsequent spread of unwanted pests and pathogens. The transport and spread of these non-indigenous species (NIS) can have substantial impacts on native biodiversity, ecosystem services/functions and hence, important economic consequences. Over the past decade, increasing research interest has been directed towards the characterization of biological communities colonizing plastic debris, the so called Plastisphere. Despite remarkable advances in this field, little is known regarding the recruitment patterns of NIS larvae and propagules on MPD, and the factors influencing these patterns. To address this knowledge gap, we used custom-made bioassay chambers and ran four consecutive bioassays to compare the settlement patterns of four distinct model biofouling organisms' larvae, including the three notorious invaders Crassostrea gigas, Ciona savignyi and Mytilus galloprovincialis, along with one sessile macro-invertebrate Spirobranchus cariniferus, on three different types of polymers, namely Low-Linear Density Polyethylene (LLDPE), Polylactic Acid (PLA), Nylon-6, and a glass control. Control bioassay chambers were included to investigate the microbial community composition colonizing the different substrates using 16S rRNA metabarcoding. We observed species-specific settlement patterns, with larvae aggregating on different locations on the substrates. Furthermore, our results revealed that C. savignyi and S. cariniferus generally favoured Nylon and PLA, whereas no specific preferences were observed for C. gigas and M. galloprovincialis. We did not detect significant differences in bacterial community composition between the tested substrates. Taken together, our results highlight the complexity of interactions between NIS larvae and plastic polymers. We conclude that several factors and their potential interactions influenced the results of this investigation, including: (i) species-specific larval biological traits and ecology; (ii) physical and chemical composition of the substrates; and (iii) biological cues emitted by bacterial biofilm and the level of chemosensitivity of the different NIS larvae. To mitigate the biosecurity risks associated with drifting plastic debris, additional research effort is critical to effectively decipher the mechanisms involved in the recruitment of NIS on MPD.

Effect of regio- and stereoisomerism on antifouling 2,5-diketopiperazines

Marine biofouling is a problem that plagues all maritime industries at vast economic and environmental cost. Previous and current methods to prevent biofouling have employed the use of heavy metals and other toxic or highly persistent chemicals, and these methods are now coming under immense regulatory pressure. Recent studies have illustrated the potential of nature-inspired tetrasubstituted 2,5-diketopiperazines (2,5-DKPs) as eco-friendly marine biocides for biofouling control. These highly active symmetrically substituted 2,5-DKPs can be generated by combining structural motifs from cationic innate defence peptides and natural marine antifoulants. A balance between a threshold hydrophobic contribution and sufficient cationic charge has been established as key for bioactivity, and our current study further increases understanding of the antifouling mechanism by investigating the effect of both regio- and stereochemistry. Novel synthetic routes for the generation of unsymmetrical 2,5-DKPs were developed and a library of nine compounds was prepared. The compounds were screened against a series of four model macrofouling organisms (Ciona savignyi, Mytilus galloprovincialis, Spirobranchus cariniferus, and Undaria pinnatifida). Several of the evaluated compounds displayed inhibitory activity at sub-micromolar concentrations. The structural contributions to antifouling bioactivity were studied using NMR spectroscopy and molecular modelling, revealing a strong dependence on a stable amphiphilic solution structure regardless of substitution pattern.

Discovery of Ircinianin Lactones B and C-Two New Cyclic Sesterterpenes from the Marine Sponge Ircinia wistarii

Two new ircinianin-type sesterterpenoids, ircinianin lactone B and ircinianin lactone C (7 and 8), together with five known entities from the ircinianin compound family (1, 3–6) were isolated from the marine sponge Ircinia wistarii. Ircinianin lactones B and C (7 and 8) represent new ircinianin terpenoids with a modified oxidation pattern. Despite their labile nature, the structures could be established using a combination of spectroscopic data, including HRESIMS and 1D/2D NMR techniques, as well as computational chemistry and quantum-mechanical calculations. In a broad screening approach for biological activity, the class-defining compound ircinianin (1) showed moderate antiprotozoal activity against Plasmodium falciparum (IC₅₀ 25.4 μM) and Leishmania donovani (IC₅₀ 16.6 μM).

Towards eco-friendly marine antifouling biocides - Nature inspired tetrasubstituted 2,5-diketopiperazines

Marine biofouling plagues all maritime industries at vast economic and environmental cost. Previous and most current methods to control biofouling have employed highly persistent toxins and heavy metals, including tin, copper, and zinc. These toxic methods are resulting in unacceptable environmental harm and are coming under immense regulatory pressure. Eco-friendly alternatives are urgently required to effectively mitigate the negative consequence of biofouling without causing collateral harm. Amphiphilic micropeptides have recently been shown to exhibit excellent broad-spectrum antifouling activity, with a non-toxic mode of action and innate biodegradability. The present work focused on incorporating the pharmacophore derived from amphiphilic micropeptides into a 2,5-diketopiperazine (DKP) scaffold. This privileged structure is present in a vast number of natural products, including marine natural product antifoulants, and provides advantages of synthetic accessibility and adaptability. A novel route to symmetrical tetrasubstituted DKPs was developed and a library of amphiphilic 2,5-DKPs were subsequently synthesised. These biodegradable compounds were demonstrated to be potent marine antifoulants displaying broad-spectrum activity in the low micromolar range against a range of common marine fouling organisms. The outcome of planned coating and field trials will dictate the future development of the lead compounds.

Instant Ocean Versus Natural Seawater: Impacts on Aspects of Reproduction and Development in Three Marine Invertebrates

Marine invertebrate larvae have often been reared in artificial rather than natural seawater, either for convenience or to avoid potentially confounding effects of unknown contaminants. This study sought to determine the impact of artificial seawater on various aspects of development for three marine invertebrate species. We examined the impact of Instant Ocean on growth, survival, and fecundity of the deposit-feeding polychaete Capitella teleta at 2 salinities: 24 and 34 ppt; the impact on survival, growth rate, and time to metamorphic competence for the slipper limpet Crepidula fornicata; and the impact on larval growth for the sea star Asterias forbesi. Juveniles of C. teleta survived better in natural seawater than in Instant Ocean at both salinities but at the higher salinity grew more quickly in Instant Ocean; fecundity was not significantly affected by the type of seawater used at either salinity. Using Instant Ocean in place of natural seawater had no pronounced impact on the survival of C. fornicata larvae or on how long it took them to become competent to metamorphose; however, larvae grew somewhat more quickly in Instant Ocean than in natural seawater for the first 4 days of development, but by day 7 they were about 4.5% larger if they had been reared in seawater. The type of seawater used affected the growth of A. forbesi larvae, with larvae growing significantly more slowly in Instant Ocean than in natural seawater, no matter how growth was measured. In conclusion, our results suggest that although Instant Ocean may be a reasonable substitute for natural seawater for work with some species, using it may affect experimental outcomes in some aspects of work with other species.

Antifouling activity of portimine, select semisynthetic analogues, and other microalga-derived spirocyclic imines

A range of natural products from marine invertebrates, bacteria and fungi have been assessed as leads for nature-inspired antifouling (AF) biocides, but little attention has been paid to microalgal-derived compounds. This study assessed the AF activity of the spirocyclic imine portimine (1), which is produced by the benthic mat-forming dinoflagellate Vulcanodinium rugosum. Portimine displayed potent AF activity in a panel of four macrofouling bioassays (EC₅₀ 0.06-62.5 ng ml^-1), and this activity was distinct from that of the related compounds gymnodimine-A (2), 13-desmethyl spirolide C (3), and pinnatoxin-F (4). The proposed mechanism of action for portimine is induction of apoptosis, based on the observation that portimine inhibited macrofouling organisms at developmental stages known to involve apoptotic processes. Semisynthetic modification of select portions of the portimine molecule was subsequently undertaken. Observed changes in bioactivity of the resulting semisynthetic analogues of portimine were consistent with portimine's unprecedented 5-membered imine ring structure playing a central role in its AF activity.