Marine Invertebrate Larvae Research Articles

Vision is highly sensitive to oxygen availability in marine invertebrate larvae.

For many animals, evolution has selected for complex visual systems despite the high energetic demands associated with maintaining eyes and their processing structures. Therefore, the metabolic demands of visual systems make them highly sensitive to fluctuations in available oxygen. In the marine environment, oxygen changes over daily, seasonal and inter-annual time scales, and there are large gradients of oxygen with depth. Vision is linked to survival in many marine animals, particularly among the crustaceans, cephalopods and fish, and early life stages of these groups rely on vision for prey capture, predator detection and their distribution in the water column. Using in vivo electroretinogram recordings, we show that there is a decrease in retinal sensitivity to light in marine invertebrates when exposed to reduced oxygen availability. We found a 60-100% reduction in retinal responses in the larvae of cephalopods and crustaceans: the market squid (Doryteuthis opalescens), the two-spot octopus (Octopus bimaculatus), the tuna crab (Pleuroncodes planipes) and the graceful rock crab (Metacarcinus gracilis). A decline in oxygen also decreases the temporal resolution of vision in D. opalescens These results are the first demonstration that vision in marine invertebrates is highly sensitive to oxygen availability and that the thresholds for visual impairment from reduced oxygen are species-specific. Oxygen-impaired retinal function may change the visual behaviors crucial to survival in these marine larvae. These findings may impact our understanding of species' vulnerability to ocean oxygen loss and suggest that researchers conducting electrophysiology experiments should monitor oxygen levels, as even small changes in oxygen may affect the results.

Development of Xenoturbellida.

Xenoturbellida is a group of benthic marine invertebrates with a very simple bilaterian body plan. Together with Acoelomorpha, it constitutesthe clade Xenacoelomorpha, recently interpreted as a sister group to all other extant bilaterians (=Nephrozoa). Therefore, it occupies an important phylogenetic position for studies on origins and evolution of Bilateria. However, due to a number of reasons, developmental and reproductive studies on Xenoturbella have been scarce. In this chapter, I will summarize what is known concerning the reproduction and development of Xenoturbellida, including information from five species that were recently discovered. Gonads are absent in xenoturbellids, and gametes are found in various parts of the body. The gametes are released through ruptures of the body wall, and therefore, the fertilization is presumably external. After holoblastic radial cleavage, embryos hatch as free-swimming hatchlings with uniform ciliation over the surface. Apical tuft forms later in development, and 5days after hatching, the larvae begin to settle on the substrate. Comparison with the other marine invertebrate larvae suggests that the morphologically simple swimming larvae described in Xenoturbella represent an ancestral larval type of all metazoans and bilaterians.

Temporal variation in invertebrate recruitment on an Eastern Pacific coral reef

The recruitment of marine invertebrate larvae to coral reef ecosystems is critical for the continued productivity of these highly biodiverse habitats. Despite such importance, little is known about temporal variation patterns of invertebrate larval recruitment in coral reefs ecosystems, aside from studies focused only on reef corals themselves. Given this knowledge deficiency, recruitment onto dead coral branches was monitored over a one-year period in the Central Mexican Pacific, and recruit assemblage and density both changed over time. In particular, recruitment was higher in the warmer months, possibly due to reproductive processes and/or increases in metabolic rates associated with high temperatures and seasonal/local events such as upwellings that increase the food resources available for the recruits which just before the warm season, when the recruitment is more more prevalent during the warm season. The most common invertebrate recruits were malacostracans, ostracods, gastropods, maxillopods, and polychaetes, and foraminifers were commonly observed, as well. Future works in this region will seek to understand whether recruit density and diversity change in response to elevated temperatures associated with global climate change.

Effects of ocean acidification on the settlement and metamorphosis of marine invertebrate and fish larvae: a review

M.L. is supported by CARIM (Coastal Acidification: Rate, Impacts & Management), funded by the New Zealand Government through the Ministry of Business Innovation and Employment. This is contribution no. 236 of the Sydney Institute of Marine Science.

Modeling the life history of sessile rotifers: larval substratum selection through reproduction

Although the theoretical underpinnings of habitat selection by marine invertebrate larvae have been well studied, this theory has been neglected for freshwater sessile rotifers. To study how substratum selection affects larval fitness, we developed a dynamic model to examine influences of three elements of larval life (survival, substratum acceptance, substratum encounter probability) and substratum-dependent reproductive success in adults. Monte Carlo simulation models were run using an initial cohort of larvae. Our Basic Model assessed fitness as simply settling on a substratum using only the larval elements and revealed statistically greatest fitness when swimming speed decreased with age and when substratum preference was constant or exhibited mid-age competence. The Reproductive Model assessed fitness (mean number of offspring adult−1) as a function of substratum. We compared reproduction on neutral substrata to substrata where quality varied and separately as a function of adult population density: coloniality (synergism) versus competition. The model showed fitness was statistically greatest when larval swimming speed decreased with age and when coloniality increased reproduction. We also explored conditions where populations of planktonic adults could survive. The model is applicable to sessile organisms and may be modified to examine other life history activities including selection of mates, prey, or territory.

Review of Evolutionary Ecology of Marine Invertebrate Larvae

Review of Evolutionary Ecology of Marine Invertebrate Larvae

Future warming and acidification result in multiple ecological impacts to a temperate coralline alga.

Coralline algae are a crucial component of reef systems, stabilising reef substrate, providing habitat and contributing to accretion. Coralline algae and their surface microbial biofilms are also important as settlement cues for marine invertebrates, yet few studies address the impact of future environmental conditions on interactions between coralline algae, reef microbes and settlement by larvae of marine invertebrates. We exposed the temperate coralline algal species Amphiroa gracilis to warming and/or acidification scenarios for 21 days. Algae became bleached but photosystem II function was not measurably impacted. Settlement by larvae of the sea urchin Heliocidaris erythrogramma was reduced and the structure of the prokaryotic community associated with A. gracilis was altered. Coralline algae in ambient conditions were dominated by Alphaproteobacteria from the Rhodobacteraceae including Loktonella; those under warming were dominated by Bacteroidetes and Verrucomicrobia; acidification resulted in less Loktonella and more Planctomycetes and a combination of warming and acidification caused increases in Bacteroidetes, Verrucomicrobia and the Alphaproteobacteria family Hyphomonadaceae. These experiments indicate that predicted future environmental change may reduce the ability of some temperate reef coralline algae and associated reef microbes to facilitate settlement of invertebrate larvae as well as having a direct impact to algae via bleaching.

Evolutionary Ecology of Marine Invertebrate Larvae

Evolutionary Ecology of Marine Invertebrate Larvae

A microbial perspective on the life‐history evolution of marine invertebrate larvae: If, where and when to feed

AbstractThe feeding environment for planktotrophic larvae has a major impact on development and progression towards competency for metamorphosis. High phytoplankton environments that promote growth and development also correlate with a greater abundance of environmental microbes and incidence of pathogenic microbes, making these habitats potentially risky for larvae. Trade‐offs between metabolic processes for growth and immune functionality have been described throughout the animal kingdom and may influence the life‐history evolution of marine invertebrate planktotrophic larvae. Specifically, larvae would be predicted to regulate time spent between these feeding environments to avoid potential incidences of microbial‐mediated mortality and/or dysbiosis. Using transcriptomic and microbiome data, we provide evidence for this trade‐off in larvae of the sea urchin Strongylocentrotus droebachiensis. When cultured in a well‐fed environment, larvae upregulate genes associated with metabolism while decreasing the expression of genes associated with immune function. At the same time, the associated bacterial community shifts towards a state of dysbiosis that is followed by mortality. To test whether the environmental microbiota is a selective force on if, where and when planktotrophic larvae should feed, we conclude by presenting a strategy for determining the specific interactions of larvae and microbes at a scale representative of their pelagic environment.

HSP90 regulates larval settlement of the bryozoan Bugula neritina through the nitric oxide pathway.

The larvae of many sessile marine invertebrates go through a settlement process, during which planktonic larvae attach to a substrate and metamorphose into sessile juveniles. Larval attachment and metamorphosis (herein defined as 'settlement') are complex processes mediated by many signalling pathways. Nitric oxide (NO) signalling is one of the pathways that inhibits larval settlement in marine invertebrates across different phyla. NO is synthesized by NO synthase (NOS), which is a client of the molecular chaperone heat shock protein 90 (HSP90). In the present study, we provide evidence that NO, a gaseous messenger, regulates larval settlement of Bugula neritina By using pharmacological bioassays and western blotting, we demonstrated that NO inhibits larval settlement of B. neritina and that NO signals occur mainly in the sensory organ of swimming larvae. The settlement rate of B. neritina larvae decreased after heat shock treatment. Inhibition of HSP90 induced larval settlement, and attenuated the inhibition of NO donors during larval settlement. In addition, the expression level of both HSP90 and NOS declined upon settlement. These results demonstrate that HSP90 regulates the larval settlement of B. neritina by interacting with the NO pathway.

Production of three symbiosis-related fatty acids by Symbiodinium types in clades A–F associated with marine invertebrate larvae

Symbiodinium are dinoflagellates engaged in a mutualistic symbiosis with multiple coral reef taxa. They are divided in nine different clades (A–I), which typically associate with different hosts. However, very little information is available on metabolic differences in Symbiodinium types, especially when associated with metazoan larvae. We tested whether three ω3 fatty acids (stearidonic acid, SDA; docosapentaenoic acid, DPA; and docosahexaenoic acid, DHA) that are typically translocated from Symbiodinium to its host are produced by Symbiodinium types within clades A–F associated with Mussismilia hispida (scleractinian coral), Berghia stephanieae (nudibranch), and Tridacna crocea (giant clam) larvae. We acquired and spawned broodstock for each host, cultured their larvae, and offered Symbiodinium types belonging to clades A–F. Samples were taken during a 72-h window after the offer of Symbiodinium, and fatty acids were extracted and analyzed by gas chromatography. The concentrations of SDA and DPA for all host larvae–dinoflagellate associations were low and variable, without trends. However, M. hispida planula larvae associated with Symbiodinium A1 and C1 had a statistically significant higher amount of DHA. The veliger larvae of B. stephanieae digested the Symbiodinium, and the amount of DHA remained constant throughout the experiment. The veliger larvae of T. crocea associated with Symbiodinium A1 and C1 also presented a higher amount of DHA, although not statistically different from the other types. These results show that Symbiodinium A1 and C1, in the case of M. hispida and T. crocea (which usually harbor strains within clades A and C), may contribute a small amount of DHA to the larvae of these organisms and form a stronger mutualism than other strains.

Transcriptomic Basis of Metamorphic Competence in the Salt-Marsh-Dwelling Polychaete Capitella teleta.

Marine invertebrate larvae typically take hours to weeks after being released into the plankton before becoming "competent" to metamorphose. The mechanisms that govern this transition between the precompetent and metamorphically competent states are unknown. We studied gene expression patterns in precompetent and competent larvae of the salt-marsh-dwelling polychaete worm Capitella teleta (Blake, Grassle & Eckelbarger, 2009)-a species in which precompetent larvae are unusually easy to distinguish from competent larvae-to determine differences in gene expression associated with the onset of metamorphic competence. More than 1530 genes were more highly expressed in precompetent larvae, while more than 1060 genes were more highly expressed in competent larvae. Competent larvae downregulated the expression of genes belonging to gene ontologies relating to growth and development and upregulated those associated with ligand-binding transmembrane channels with possible chemo- and mechanosensory functions. Most of these channels were annotated as being from the degenerin/epithelial sodium channel family or the G-protein-coupled receptor family; proteins from these families can have chemosensory functions. Serotonin and GABA (γ-aminobutyric acid) receptors are among the genes that were upregulated in competent larvae; both have been shown to induce larvae of C. teleta and other marine invertebrates to metamorphose and are thought to be components of the signal transduction pathway that leads to metamorphosis. Overall, it appears that once larvae of C. teleta have completed development of the internal structures and physiology required for juvenile life during the precompetent period, they then upregulate the expression of chemosensory proteins and neurotransmitter receptors that will enable them to detect and transduce a settlement cue signal.

Marine Invertebrate Larvae Associated with Symbiodinium: A Mutualism from the Start?

Symbiodinium are dinoflagellate photosynthetic algae that associate with a diverse array of marine invertebrates, and these relationships are comprehensively documented for adult animal hosts. Conversely, comparatively little is known about the associations during larval development of animal hosts, although four different metazoan phyla (Porifera, Cnidaria, Acoelomorpha, and Mollusca) produce larvae associated with Symbiodinium. These phyla represent considerable diversities in larval forms, manner of symbiont acquisition, and requirements on the presence of symbionts for successful metamorphosis. Importantly, the different requirements are conveyed by specific symbiont types that are selected by the host animal larvae. Nevertheless, it remains to be determined whether these associations during larval stages already represent mutualistic interactions, as evident from the relationship of Symbiodinium with their adult animal hosts. For instance, molecular studies suggest that the host larval transcriptome is nearly unaltered after symbiont acquisition. Even so, a symbiosis-specific gene has been identified in Symbiodinium that is expressed in larval host stages, and similar genes are currently being described for host organisms. However, some reports suggest that the metabolic exchange between host larvae and Symbiodinium may not cover the energetic requirements of the host. Here, we review current studies to summarize what is known about the association between metazoan larvae and Symbiodinium. In particular, our aim was to gather in how far the mutualistic relationship present between adult animals hosts and Symbiodinium is already laid out at the time of symbiont acquisition by host larvae. We conclude that the mutualistic relationship between animal hosts and algal symbionts in many cases is not set up during larval development. Furthermore, symbiont identity may influence whether a mutualism can be established during host larval stages.

Low concentrations of large inedible particles reduce feeding rates of echinoderm larvae

The planktonic larvae of many marine invertebrates must feed to develop to metamorphosis. The rate at which feeding larvae accumulate energy affects the amount of time they must spend in the plankton, which affects larval dispersal and mortality; it may also affect the amount of energy gained before metamorphosis, and thus limit growth or survivorship of early juveniles. Rates of energy acquisition are partly determined by the quantity of edible particles in the plankton. However, the plankton also contains many particles that are too large to be ingested. Prior studies suggest that high concentrations of such large inedible particles reduce larval feeding rates. This study examines whether the feeding rates of larvae of southern California echinoderms are reduced by lower, more frequently encountered concentrations of large inedible particles. Larvae of a holothuroid, two asteroids, and three echinoids were fed 6-µm beads alone or with large inedible beads at 25–500 inedible beads mL−1. Five of the six species showed reduced clearance rates on 6-µm beads when exposed to as few as 25 inedible beads mL−1. In similar experiments on an asteroid and an echinoid using natural large inedible particles (centric diatoms), larval clearance rates were reduced at 25 cells mL−1 and higher. Larval clearance rates were reduced by ~50% in treatments of 100 or 500 large inedible particles mL−1. These results suggest that in nature, rates of food acquisition by larvae may depend not only on the abundance of food particles, but also on the abundance of potentially interfering non-food particles.

Lower thermal limits to larval development do not predict poleward range limits of the introduced tropical barnacle Megabalanus coccopoma

As the earth's climate has warmed, many tropical species have expanded their ranges poleward and encountered high-latitude seasonal temperature regimes, in which further permanent expansion is limited by physiological vulnerability to cold temperatures. The barnacle Megabalanus coccopoma is native to shorelines from Baja California to Peru and has been introduced to many locations worldwide, including the southeastern USA. The ability of larvae to develop successfully at local temperatures can be an important factor limiting the spread of invasive species. To determine if cold temperatures limited larval success near the northern range limit of M. coccopoma along the Atlantic southeastern USA coast, we measured lower temperature limits to larval development, examined the effects of temperature on larval growth and energy accumulation, and calculated a larval energy budget to estimate the extent of potential larval dispersal in this region. Larvae were able to develop through metamorphosis at 16°C, which is much colder than sea surface temperatures during the spawning season in their invasive range, making it unlikely northern range limits are set by a lower temperature limit to larval development. Energy budgets suggest that for larvae produced at the northern end of the invasive range, long distance dispersal to sites far poleward of the current range limit is possible. Similar to the findings of the handful of other studies on cold tolerances of tropical marine invertebrate larvae, larvae should be successful far poleward of current adult distributions.

Sugars as supplemental cryoprotectants for marine organisms

AbstractCryopreservation has been extensively used in various mega‐industries and has recently been applied in genetic banking for conservation purposes. Compared with conventional cell preservation methods, cryopreservation can maintain the viability of cryopreserved cells for an indefinite time at a relatively lower cost and lesser manpower, with lower probabilities of contamination and genetic changes. This study presents the crucial role of sugar, a cryoprotectant supplement in cryopreservation. Sugar molecules typically interact with the lipid bilayer during the freezing phase to maintain plasma membrane integrity when cells undergo dehydration. When combined with other permeable cryoprotectants such as glucose with methanol and trehalose with dimethyl sulphoxide, sugar prolongs and enhances cellular post‐thaw viability. Moreover, terrestrial and marine organisms have benefited from the inclusion of sugar in the cryopreservation protocol. For wide range of cells such as the sperm, oocytes, embryos and larvae of marine vertebrates and invertebrates, as well as marine algae, cryopreservation with sugar produced positive results compared with cryopreservation without sugar. Not all sugar is beneficial, and the type and concentration of sugar should be applied according to the species. Moreover, the freezing method may also affect the function of sugar. Nevertheless, understanding the role of sugar in cryobiology and conducting a preliminary trial of sugar for cryopreserving cells would benefit future research on cryopreservation.

Silver Nanoparticles Impact Biofilm Communities and Mussel Settlement.

Silver nanoparticles (AgNPs) demonstrating good antimicrobial activity are widely used in many fields. However, the impact of AgNPs on the community structures of marine biofilms that drive biogeochemical cycling processes and the recruitment of marine invertebrate larvae remains unknown. Here, we employed MiSeq sequencing technology to evaluate the bacterial communities of 28-day-old marine biofilms formed on glass, polydimethylsiloxane (PDMS), and PDMS filled with AgNPs and subsequently tested the influence of these marine biofilms on plantigrade settlement by the mussel Mytilus coruscus. AgNP-filled PDMS significantly reduced the dry weight and bacterial density of biofilms compared with the glass and PDMS controls. AgNP incorporation impacted bacterial communities by reducing the relative abundance of Flavobacteriaceae (phylum: Bacteroidetes) and increasing the relative abundance of Vibrionaceae (phylum: Proteobacteria) in 28-day-old biofilms compared to PDMS. The settlement rate of M. coruscus on 28-day-old biofilms developed on AgNPs was lower by >30% compared to settlement on control biofilms. Thus, the incorporation of AgNPs influences biofilm bacterial communities in the marine environment and subsequently inhibits mussel settlement.

A true test of colour effects on marine invertebrate larval settlement

Past tests of settlement by marine invertebrate larvae on different colours were not designed to distinguish between responses to substrate colour and substrate brightness. Using colour vision testing methods, the design of this study provided a true test for responses to colour by including both coloured and grayscale settlement plates. The dominant fouling taxa at the test sites (the solitary ascidian, Ciona intestinalis; the colonial ascidians Botryllus schlosseri or Botrylloides violaceous; and a bryozoan Bugula sp.) showed no significant differences in settlement between blue, red or green plates. In contrast, the ascidians responded to substrate brightness with significantly lower settlement on lighter plates, while the bryozoans showed no significant preference relative to substrate brightness. The methods used here are a model for future tests of responses to colour during settlement. In addition, the contrasting responses to brightness are at odds with previous laboratory experiments that showed larvae of both ascidians and bryozoans are negatively phototactic at settlement. These results suggest that other cues must supersede any phototactic responses in the bryozoans, or alternatively that the range of light intensities near darker and lighter substrata were not part of the tests in the earlier reports.

Predicting phenotypic variation in growth and metabolism of marine invertebrate larvae

Understanding the mechanisms that establish variation in growth and metabolism is fundamental in evolutionary and physiological ecology. Although a genetic basis is frequently invoked to explain variation in performance, it remains challenging to study such processes in marine animals due to the lack of genetically-enabled “model” organisms. The Pacific oyster Crassostrea gigas is a species for which pedigreed genetic lines have been established. In this study, a series of larval families was produced by crossbreeding pedigreed lines to yield large-volume larval cultures to provide sufficient biomass for biochemical and physiological analyses. Major phenotypic contrasts in larval growth rate were evident. A primary goal of this study was to investigate the physiological bases for this variation in growth and to identify biomarkers that are predictive of growth potential. To that end, measurements were undertaken to define the relationship between rates of growth, respiration, and ion transport by the sodium-potassium pump (in vivo Na+,K+-ATPase activity). The relationship of respiration and ion transport during larval growth showed that, on average, 17% of total energy demand was allocated to support ion transport. Further analyses of total Na+,K+-ATPase activity (in vitro enzyme assay) revealed that 41% of the total metabolic rate could be accounted for by this single process if all of the enzyme was physiologically active. Significant biological variation was evident, however, when size-specific comparisons were made across different larval families. These differences were up to (i) 2.2-fold in ion transport rates; (ii) 2.8-fold in the allocation of energy to support the metabolic demand of ion transport; (iii) 3.5-fold in total enzyme activity; (iv) 3.9-fold in the physiologically active fraction of total enzyme; and (v) 3.1-fold in gene expression. These differences among families highlight the need to distinguish genetic from environmental causes of biological variation. Notably, for inferences of physiological changes based upon molecular biological analyses, the measured rates of ion transport were not predicted from concurrent measurements of gene expression or enzyme activity. Size-corrected rates of ion transport were predictive of variation in growth rates among different larval families, supporting the application of physiological rates of ion transport as a predictor of growth differences. Evolutionary variation in physiological performance has important implications for understanding the ecology of larval forms. Developing physiological indices will be of value in predicting growth and metabolism and corresponding survival of larval forms of different genotypes in response to environmental change.

Biofilm history and oxygen availability interact to affect habitat selection in a marine invertebrate

In marine systems, oxygen availability varies at small temporal and spatial scales, such that current oxygen levels may not reflect conditions of the past. Different studies have shown that marine invertebrate larvae can select settlement sites based on local oxygen levels and oxygenation history of the biofilm, but no study has examined the interaction of both. The influence of normoxic and hypoxic water and oxygenation history of biofilms on pre-settlement behavior and settlement of the bryozoan Bugula neritina was tested. Larvae used cues in a hierarchical way: the oxygen levels in the water prime larvae to respond, the response to different biofilms is contingent on oxygen levels in the water. When oxygen levels varied throughout biofilm formation, larvae responded differently depending on the history of the biofilm. It appears that B. neritina larvae integrate cues about current and historical oxygen levels to select the appropriate microhabitat and maximize their fitness.