Before and after a disease outbreak: Tracking a keystone species recovery from a mass mortality event

Unravelling the main immune repertoire of Paracentrotus lividus following Vibrio anguillarum bath challenge

Paracentrotus lividus is the most abundant echinoid species in the North East Atlantic Ocean and Mediterranean Sea. Although there is abundant genomic information of the species, there is no deep characterisation of the genes involved in the immune response. Here, a reference transcriptome of male and female coelomocytes was produced. The generated P. lividus transcriptome assembly has 203,511 transcripts, N50 transcript length of 1079 bp, and more than 90% estimated gene completeness in Eukaryota and Metazoa BUSCO databases, respectively. Differential gene expression analyses showed 54 and 55 up-regulated genes in P. lividus female and male coelomocyte tissues, respectively. These results suggest a similar immune gene repertoire between sexes. To examine the immune response, P. lividus was challenged with Vibrio anguillarum, one of the candidate pathogens for bald disease. Immune parameters were evaluated at cell and humoral levels, as well as the expression analysis of immune related genes at an early response stage. No differences were found at cellular and humoral levels with the exception of the increase of nitric oxide in perivisceral fluid of challenged animals. At the gene expression level, a total of 2721 genes were upregulated in challenged animals, 13.6 times higher expression than control group. Our analysis revealed that four major KEGG pathways were enriched in challenged animals: Autophagy (KEGG:04140), Endocytosis (KEGG:04144), Phagosome (KEGG:04145) and Protein processing in endoplasmic reticulum (KEGG:04141). Several toll-like receptors (TLR), scavenger receptors cysteine-rich (SRCR) or nucleotide-binding oligomerisation domain like receptors (NLR) were identified as major family genes for pathogen recognition and immune defence. This study provides a valuable transcriptomic resource and unfolds the molecular basis of immune response to V. anguillarum exposure. Overall, our findings contribute to the conservation effort of the P. lividus populations, as well as its sustainable exploitation in an aquaculture context.

Toxicity of tire particle leachates on early life stages of keystone sea urchin species

Particles from tires are a major fraction of microplastic pollution. They contain a wide range of chemical additives that can leach into the water and be harmful to aquatic organisms. In this study, we investigated the acute toxicity of tire particle leachates in early life stages of three keystone echinoderm species (Paracentrotus lividus, Arbacia lixula, Diadema africanum). Embryos were exposed for 72 h to a range of leachate dilutions, prepared using a concentration of 1 g L-1. Larval growth, abnormal development, and mortality were the measured endpoints. Furthermore, we estimated the activity of glutathione S transferase (GST) and the electron transport system (ETS) in P. lividus. Strong concentration-dependent responses were observed in all species, though with differing sensitivity. The median effect concentrations for abnormal development in P. lividus and A. lixula were 0.16 and 0.35 g L-1, respectively. In D. africanum, mortality overshadowed abnormal development and the median lethal concentration was 0.46 g L-1. Larvae of P. lividus were significantly smaller than the control from 0.125 g L-1, while the other two species were affected from 0.5 g L-1. ETS activity did not change but there was a non-significant trend of increasing GST activity with leachate concentration in P. lividus. Seven organic chemicals and eight metals were detected at elevated concentrations in the leachates. While we regard zinc as a strong candidate to explain some of the observed toxicity, it can be expected that tire particle leachates exhibit a cocktail effect and other leached additives may also contribute to their toxicity. Our results emphasize the importance of multi-species studies as they differ in their susceptibility to tire particle pollution. We found negative effects at concentrations close to projections in the environment, which calls for more research and mitigation actions on these pollutants.

Taxonomical and functional diversity dynamics of conspicuous echinoderms in the northeastern tropical Pacific over a decade

Understanding what determines spatio-temporal changes in echinoderm assemblages from an integrative perspective that considers biodiversity, species evenness, and species' niches could permit superior community-scale characterizations of habitat resilience to disturbance. Such an approach was taken herein by tracking a Central Mexican Pacific echinoderm assemblage between 2012 and 2021, and higher richness, diversity, evenness, and functional entity counts were associated with more heterogeneous benthic assemblages. Echinoderm taxonomic composition was influenced by ENSO events, with higher functional diversity found during La Niña events. Conservation strategies should focus on species with unique functional traits to maintain the balance of coral community functionality.

The ecological consequences of the timing of extreme climate events

Climate change is increasing the intensity, duration, and frequency of extreme climate events (ECEs). These ECEs can have major ecological consequences, e.g., changing nutrient flows, causing extirpation, and altering organismal development. Many ECEs are discrete events that occur at distinctive times during the biological processes they impact. Because of this, ECEs are likely to have differing ecological impacts depending on when they happen, yet we lack on studies that explore how the ecological consequences of ECEs vary with when they occur. Drawing upon evidence from physiological, population, and community ecology, and previous work on ecological disturbances, we suggest that the consequences of ECEs will be sensitive to when they occur. We illustrate the importance of timing by showing how the effects of an ECE could vary depending on when it occurs through the course of (1) organismal ontogeny, (2) population dynamics, and (3) community assembly. An enhanced focus on the timing of extreme weather in climate change research will reveal how and when ECEs are altering ecosystems, possible mechanisms behind these impacts, and what ecosystems or species are most vulnerable to ECEs, helping us to make more informed predictions about the ecological consequences of climate change.

The Citizen Science Paradox

Citizen science (CS) is now very popular in ecology. The number of scientific publications referencing CS has increased steadily over the past 15 years, with more than 1150 publications today. However, the multiplicity of research involved suggests that this number is highly underestimated. Based on this paradox, a literature review on CS shows that while its formalization in 2009 facilitated its referencing, about 70% of the publications are not referenced using CS as keyword. To understand this under-representation, an analysis of 149 publications related to the famous Christmas Bird Count program shows that this underestimation is not mainly related to the diversity of keywords used to describe CS, but rather to the fact that CS is mainly considered as a method (four publications out of five). The results also show that taking into account the whole text of a publication would represent a substantial improvement for the analysis of scientific databases, whatever the field of research.

Effects of eliminating interactions in multi-layer culture on survival, food utilization and growth of small sea urchins Strongylocentrotus intermedius at high temperatures

Poor growth and disease transmission of small sea urchins Strongylocentrotus intermedius in summer greatly hamper the production efficiency of the longline culture. Reducing the adverse effects of high stocking density while maintaining high biomass is essential to address these problems. Here, we conducted a laboratory experiment to simulate the multi-layer culture for sea urchins at ambient high temperatures (from 22.2 to 24.5 °C) in summer for ~ 7 weeks. Survival, body size, lantern growth, gut weight, food consumption, Aristotle's lantern reflex, 5-hydroxytryptamine concentration, pepsin activity and gut morphology were subsequently evaluated. The present study found that multi-layer culture led to significantly larger body size than those without multi-layer culture (the control group). This was probably because of the greater feeding capacity (indicated by lantern growth and Aristotle's lantern reflex) and food digestion (indicated by morphology and pepsin activity of gut) in the multi-layer cultured sea urchins. These results indicate that multi-layer is an effective approach to improving the growth efficiency of sea urchins at high temperatures. We assessed whether eliminating interaction further improve these commercially important traits of sea urchins in multi-layer culture. This study found that eliminating interactions displayed greater body size and Aristotle's lantern reflex than those not separated in the multi-layer culture. This approach also significantly reduced the morbidity compared with the control group. These novel findings indicate that eliminating interactions in multi-layer culture greatly contributes to the growth and disease prevention of sea urchins at high temperatures. The present study establishes a new technique for the longline culture of sea urchins in summer and provides valuable information into the longline culture management of other commercially important species (e.g. scallops, abalones and oysters).

Invertebrate health in marine protected areas (MPAs)

Marine protected areas (MPAs) consist of various categories of safeguarded areas in the marine environment, from semi-protected areas to total no take zones. The reported effects of MPAs are overwhelmingly positive, with numerous reports of fish size (biomass), abundance (recovery) and diversity increases, however, literature is lacking on the role and consequences of MPAs on parasite and disease dynamics, and in particular, invertebrate health. The implementation of MPAs has been known to alter trophic cascades and community dynamics, and with invertebrates commonly at the base of these systems, it is vital that their status is investigated. Overcrowding in areas closed to fishing is known to have parasitological consequences in some scenarios, and land/water use change has been known to alter host and vector communities, possibly elevating disease risk. Equally, reserves can be used as tools for alleviating impacts of marine disease. This review aims to consolidate extant literature and provide a comprehensive viewpoint on how invertebrates (and their health status) can be affected by MPAs, which are increasingly being implemented based on the relative urgency now being placed on protecting global biodiversity. In highlighting the paucity of knowledge surrounding MPAs and disease, especially that of the unenigmatic invertebrate groups, this review, published in the Special Issue on 'Invertebrates as One Health Sentinels', provides an opportunity for wide dissemination and provocation of further research in this area.

Uncommon southwest swells trigger sea urchin disease outbreaks in Eastern Atlantic archipelagos

Recurrent sea urchin mass mortality has recently affected eastern Atlantic populations of the barren-forming sea urchin Diadema africanum. This new episode of die-off affords the opportunity to determine common meteorological and oceanographic conditions that may promote disease outbreaks. The population dynamics of this sea urchin species are well known-urchin barrens have persisted for many decades along most of the coastlines off the archipelagos of Madeira, Selvages, and the Canary Islands, where they limit macroalgae biomass growth. However, this new and explosive mortality event decimated the sea urchin population by 93% on Tenerife and La Palma Islands. Two severe episodes of southwestern rough sea that led to winter storms, in February 2010 (Xynthia) and February 2018 (Emma), preceded both mass mortality events. The autumn and winter months of those years were anomalous and characterized by swells with an average wave height above 2 m that hit the south and southwest sides of the islands. The amoeba Paramoeba brachiphila was the only pathogen isolated this time from the moribund and dead sea urchins, suggesting that the amoeba was the primary cause of the mortality. This new sea urchin die-off event supports the "killer-storm" hypothesis that has been already described for western Atlantic coasts. These anomalous southwest storms during winters generate pronounced underwater sediment movement and large-scale vertical mixing, detected in local tide gauge, which may promote paramoebiasis. This study presents valuable insights about climate-mediated changes in disease frequency and its impacts on the future of coastal marine ecosystems in the Atlantic.