The effects of crude oil and dispersant on the larval sponge holobiont

We all know that oil spills are deadly to animals and plants in marine environments. But do you want to know how important filter feeding organisms of the reefs such as sponges, their larvae and their microbial symbionts respond to petroleum derivatives at the molecular level?  

ABSTRACT: Accidental oil spills from shipping and during extraction can threaten marine biota, particularly coral reef species which are already under pressure from anthropogenic disturbances. Marine sponges are an important structural and functional component of coral reef ecosystems; however, despite their ecological importance, little is known about how sponges and their microbial symbionts respond to petroleum products. Here, we use a systems biology-based approach to assess the effects of water-accommodated fractions (WAF) of crude oil, chemically enhanced water-accommodated fractions of crude oil (CWAF), and dispersant (Corexit EC9500A) on the survival, metamorphosis, gene expression, and microbial symbiosis of the abundant reef sponge Rhopaloeides odorabile in larval laboratory-based assays. Larval survival was unaffected by the 100% WAF treatment (107 μg liter−1 polycyclic aromatic hydrocarbon [PAH]), whereas significant decreases in metamorphosis were observed at 13% WAF (13.9 μg liter−1 PAH). The CWAF and dispersant treatments were more toxic, with decreases in metamorphosis identified at 0.8% (0.58 μg liter−1 PAH) and 1.6% (38 mg liter−1 Corexit EC9500A), respectively. In addition to the negative impact on larval settlement, significant changes in host gene expression and disruptions to the microbiome were evident, with microbial shifts detected at the lowest treatment level (1.6% WAF; 1.7 μg liter−1 PAH), including a significant reduction in the relative abundance of a previously described thaumarchaeal symbiont. The responsiveness of the R. odorabile microbial community to the lowest level of hydrocarbon treatment highlights the utility of the sponge microbiome as a sensitive marker for exposure to crude oils and dispersants.

ABC news. This photo shows oil leaking from the MV Wakashio, a bulk carrier ship that recently ran aground off the southeast coast of Mauritius, Friday, Aug. 7, 2020. Anxious residents of the Indian Ocean island nation of Mauritius are stuffing fabric sacks with sugar cane leaves to create makeshift oil spill barriers as tons of fuel leak from a grounded ship. The government has declared an environmental emergency and France says it is sending help from its nearby Reunion island. (Eric Villars via AP)

IMPORTANCE: Larvae of the sponge R. odorabile survived exposure to high concentrations of petroleum hydrocarbons; however, their ability to settle and metamorphose was adversely affected at environmentally relevant concentrations, and these effects were paralleled by marked changes in sponge gene expression and preceded by disruption of the symbiotic microbiome. Given the ecological importance of sponges, uncontrolled hydrocarbon releases from shipping accidents or production could affect sponge recruitment, which would have concomitant consequences for reef ecosystem function. Read the full paper here

Author Video: An author video summary of this article is available.

From the tropics to the pole and back again: Radiation in the flathead fishes (Platycephalidae) across Australia and the Indo‐West Pacific

In this paper we develop a comparative phylogeographic framework to understand the origins, evolution, taxonomic richness, and distribution of Australian demersal fish endemics in the context of the Indo‐West Pacific .

Nuclear and mitochondrial phylogenies of flathead fishes were inferred from 46 of 85 nominal species, and 14 additional cryptic species‐level lineages, representing 17 of the 18 genera. Molecular clocks and habitat trait reconstructions were used to infer the palaeoclimatic and geological events responsible for shaping the evolution and diversification of the group.

Results

The family Platycephalidae comprises two sister subfamilies; Platycephalinae and Onigociinae, which diverged in the Eocene into predominantly temperate and tropical assemblages respectively. The basal platycephalin taxa are confined to southern Australia with the most derived groups in the tropics, following a high‐ to low‐latitudinal evolutionary trajectory. In contrast, the onigociins are predominantly associated with the tropics, and have diversified across the region since the early Miocene with very few introductions into temperate Australia.

Main conclusions

Platycephalinae and Onigociinae show contrasting evolutionary scenarios. Platycephalins have a temperate to tropical evolutionary trajectory consistent with their arrival into the region via tectonic rafting and subsequent dispersal. This dispersal was likely facilitated by formation of shallow‐water environments along the Sunda Arc margin following collision of the Australian and Eurasian Plates. In contrast, the Onigociinae has likely maintained a tropical presence across the IWP since the Eocene and has experienced higher diversification rates leading to circa three times the species diversity found in the Platycephalinae. Rounds of dispersal and allopatric speciation have subsequently played out across both low and high latitudes with both subfamilies harbouring cryptic species‐level lineages. This work provides an explicit working hypothesis for exploring origins and diversification in other demersal fishes endemic to the Australian continent. Read full paper here!

Assessing global range expansion in a cryptic species complex: insights from the red seaweed genus Asparagopsis (Florideophyceae)

The mitochondrial genetic diversity, distribution and invasive potential of multiple cryptic operational taxonomic units (OTUs) of the red invasive seaweed Asparagopsis were assessed by studying introduced Mediterranean and Hawaiian populations. Invasive behavior of each Asparagopsis OTU was inferred from phylogeographic reconstructions, past historical demographic dynamics, recent range expansion assessments and future distributional predictions obtained from demographic models. Genealogical networks resolved Asparagopsis gametophytes and tetrasporophytes into four A. taxiformis and one A. armata cryptic OTUs. Falkenbergia isolates of A. taxiformis L3 were recovered for the first time in the western Mediterranean Sea and represent a new introduction for this area. Neutrality statistics supported past range expansion for A. taxiformis L1 and L2 in Hawaii. On the other hand, extreme geographic expansion and an increase in effective population size were found only for A. taxiformis L2 in the western Mediterranean Sea. Distribution models predicted shifts of the climatically suitable areas and population expansion for A. armata L1 and A. taxiformis L1 and L2. Our integrated study confirms a high invasive risk for A. taxiformis L1 and L2 in temperate and tropical areas. Despite the differences in predictions among modelling approaches, a number of regions were identified as zones with high invasion risk for A. taxiformis L2. Since range shifts are likely climate‐driven phenomena, future invasive behavior cannot be excluded for the rest of the lineages. Read full paper here...