On the Diversity of Microfossils in the Bazhenov Horizon of Western Siberia (Late Jurassic–Early Cretaceous)

Paleontological remains from the Bazhenovo Horizon of Western Siberia (Tithonian–Berriasian) are represented by macro- and microfossils. The Horizon had a marine genesis and the basis of ecosystem of this paleobasin composed of pelagic organisms-producers (phytoplankton: prasinophytes, coccolithophorids, dinoflagellates, as well as brown algae) and consumers (zooplankton: radiolarians, invertebrate larvae, crustaceans; and nekton: pelagic bony fish, ammonites, belemnites, paleosquids-teutids and marine dinosaurs; and, in addition, benthic bivalves, foraminifera, and ostracods). Among microfossils, radiolarians are the leading importance, phytoplankton (dinoflagellates, coccolithophorids) and microbenthos (foraminifera, sponge spicules) are less common. Radiolarians, dinoflagellates, coccolithophorids, and foraminifera are used for biostratigraphic subdividing of sections and their correlation, and, in addition, together with sponge spicules, for reconstruction the paleoenvironments. In literature, a several paper indicated the presence of other siliceous microfossils in paleobiota of the Bazhenovo paleosea – diatoms, silicoflagellates, and acantharians. The article summarized data on radiolaria, coccolithophorids, dinophyta and critically reviewed reports of other microobjects. It is shown that the information about diatoms, silicoflagellates and acantharians from Bazhenovo Horizon and Bazhenovo Formation is probably unreliable.

Response of Fish and Invertebrate Larvae to Backreef Sounds at Varying Distances: Implications for Habitat Restoration

Underwater sound is used by many marine larvae to orient to coastal habitats including backreef, sponge-dominated hardbottom habitat in the Florida Keys (FL, United States)—a particularly “noisy” coastal habitat. However, the distance over which acoustic cues are attractive to settlement-stage larvae is generally unknown. We examined this phenomenon in a region of the Florida Keys where mass sponge die-offs have diminished both underwater soundscapes and larval settlement. The absence of pronounced hardbottom-associated sound over such a large area allowed us to experimentally test in situ the response of fish and invertebrate larvae to broadcasted sounds at different distances from their source. We first measured the signal-to-noise ratio of healthy hardbottom habitat soundscapes broadcast from an underwater speaker at seven distances to determine the maximum range of the signal. Based on those results, larval collectors were then deployed at 10, 100, 500, and 1,000 m from speakers broadcasting sounds recorded at either degraded or healthy hardbottom sites for five consecutive nights during each of three new and full moon periods in summer/fall 2019. Larval settlement onto those collectors was affected by lunar phase and soundscape type, but varied among species. In most cases, the effect was small and not likely to be ecologically significant. The absence of a strong larval settlement response to a sound cue lies in contrast to results from other studies. We suspect that the small (<500 m) radius of the broadcasted soundscapes may have limited the magnitude of the larval response to locally available larvae whose abundance may have been low because the experiment was conducted within a large, relatively quiet seascape. If true, it is possible that planktonic larvae may require a series of acoustic “sign-posts,” perhaps in combination with other cues (e.g., chemical), to successfully orient to distant nursery habitats. Although habitat restoration efforts may be able to restore healthy soundscapes, the typically small size and number of restoration sites may limit the range of the acoustic cue and thus larval attraction to restored habitats.

CRISPR/Cas9 mutagenesis reveals a role for ABCB1 in gut immune responses to Vibrio diazotrophicus in sea urchin larvae

ABSTRACT The ABC transporter ABCB1 plays an important role in the disposition of xenobiotics. Embryos of most species express high levels of this transporter in early development as a protective mechanism, but its native substrates are not known. Here, we used larvae of the sea urchin Strongylocentrotus purpuratus to characterize the early life expression and role of Sp-ABCB1a, a homolog of ABCB1. The results indicate that while Sp-ABCB1a is initially expressed ubiquitously, it becomes enriched in the developing gut. Using optimized CRISPR/Cas9 gene editing methods to achieve high editing efficiency in the F0 generation, we generated ABCB1a crispant embryos with significantly reduced transporter efflux activity. When infected with the opportunistic pathogen Vibrio diazotrophicus, Sp-ABCB1a crispant larvae demonstrated significantly stronger gut inflammation, immunocyte migration and cytokine Sp-IL-17 induction, as compared with infected control larvae. The results suggest an ancestral function of ABCB1 in host–microbial interactions, with implications for the survival of invertebrate larvae in the marine microbial environment.

Two-Round Ca 2+ transient in papillae by mechanical stimulation induces metamorphosis in the ascidian Ciona intestinalis type A

Marine invertebrate larvae are known to begin metamorphosis in response to environmentally derived cues. However, little is known about the relationships between the perception of such cues and internal signalling for metamorphosis. To elucidate the mechanism underlying the initiation of metamorphosis in the ascidian, Ciona intestinalis type A ( Ciona robusta ), we artificially induced ascidian metamorphosis and investigated Ca 2+ dynamics from pre- to post-metamorphosis. Ca 2+ transients were observed and consisted of two temporally distinct phases with different durations before tail regression which is the early event of metamorphosis. In the first phase, Phase I, the Ca 2+ transient in the papillae (adhesive organ of the anterior trunk) was coupled with the Ca 2+ transient in dorsally localized cells and endoderm cells just after mechanical stimulation. The Ca 2+ transients in Phase I were also observed when applying only short stimulation. In the second phase, Phase II, the Ca 2+ transient in papillae was observed again and lasted for approximately 5–11 min just after the Ca 2+ transient in Phase I continued for a few minutes. The impaired papillae by Foxg -knockdown failed to induce the second Ca 2+ transient in Phase II and tail regression. In Phase II, a wave-like Ca 2+ propagation was also observed across the entire epidermis. Our results indicate that the papillae sense a mechanical cue and two-round Ca 2+ transients in papillae transmits the internal metamorphic signals to different tissues, which subsequently induces tail regression. Our study will help elucidate the internal mechanism of metamorphosis in marine invertebrate larvae in response to environmental cues.

Departures from isotropy: the kinematics of a larval snail in response to food

The swimming behavior of invertebrate larvae can affect their dispersal, survival, and settlement in the ocean. Modelling this behavior accurately poses unique challenges as behavior is controlled both by physiology and environmental cues. Some larvae use cilia to both swim and create feeding currents, resulting in potential trade-offs between the two functions. Food availability is naturally patchy and often occurs in shallow horizontal layers in the ocean. Also, larval swimming motions generally differ in the horizontal and vertical. In order to investigate behavioral response to food by ciliated larvae, we measure their behavioral anisotropy by quantifying deviations from a model based in isotropic diffusion. We hypothesize that larvae will increase horizontal swimming and decrease vertical swimming after encountering food which could lead to aggregation at food layers. We consider Crepidula fornicata larvae which are specifically of interest as they exhibit unsteady and variable swimming behaviors that are difficult to categorize. We tracked the larvae in still water with and without food, with a portion of the larvae starved beforehand. On average, larvae in the presence of food were observed higher in the water column, with higher swimming speeds and higher horizontal swimming velocities when compared to larvae without food. Starved larvae also exhibited higher vertical velocities in food, suggesting no aggregation behavior. While most treatments showed strong anisotropy in larval behavior, we found that starved larvae without food exhibited approximately isotropic kinematics, indicating that behavioral anisotropy can vary with environmental history and conditions to enhance foraging success or mitigate food-poor environments.

Calcified macroalgae and their bacterial community in relation to larval settlement and metamorphosis of reef-building coral Pocillopora damicornis

ABSTRACT Calcified macroalgae play an important role in the settlement and metamorphosis of invertebrate larvae in coral reef ecosystems. However, little is known about the algal-associated bacterial communities and their effects on larval settlement. In this study, the responses of larvae of the coral Pocillopora damicornis to calcified algae (Porolithon onkodes, Halimeda cylindracea, Halimeda opuntia and Amphiroa fragilissima) were evaluated. The results revealed that Por. onkodes and H. cylindracea significantly enhanced the rates of settlement and metamorphosis, whereas fewer larvae settled on Am. fragilissima and H. opuntia. Amplicon pyrosequencing of the V3–V4 region of 16S rDNA was applied to investigate the relationship between algal bacterial community and larval settlement. Principal coordinates analysis demonstrated that the bacterial community composition of H. opuntia was more similar to that of Am. fragilissima, but clearly distinct from those of H. cylindracea and Por. onkodes. Furthermore, the relative abundances of bacteria were highly diverse among different algae. H. opuntia had higher percentages of Thalassobius, Pelagibius and SM1A02, whereas the abundances of Mycoplasma and Suttonella were significantly higher in H. cylindracea than other algae. Our results showed that larval settlement/metamorphosis was strongly correlated with the bacterial community composition and with the relative abundance of a few operational taxonomic units.

Carryover effects of brooding conditions on larvae in the slipper limpet Crepidula fornicata

Larval dispersal is a critical step in the life-histories of sessile benthic invertebrates. There is a growing body of research showing plasticity in marine invertebrate larvae, but the causes and ranges of intraspecific variation in larvae are not completely understood. In this study, field-based collections of Crepidula fornicata larvae in 2017 motivated a laboratory experiment on carryover effects in 2019. Experimental conditions that approximated environmental conditions experienced by mothers in the field were used to test whether seasonal environmental variations during brooding could lead to differences in larval size and the time to develop to competency. Mothers were kept in 2 different temperature and feeding treatments during brooding, but larvae were cultured in a common garden. Larvae that were brooded at spring temperatures (~13°C) took longer to develop to competency in the common garden and grew larger before becoming competent than larvae brooded at warmer summer temperatures (~21°C). There was no effect of maternal feeding (fed or not fed) on time to develop to competency or larval size. Thus, C. fornicata larvae released earlier in the year are likely to spend longer periods in the water column. They may disperse farther and grow to larger size before settlement. C. fornicata is a model species for larval biology. The results of this study can be used to inform biophysical modelling efforts and refine predictions of connectivity or species range shifts in a changing climate.