Invertebrate Larvae Research Articles

Latitudinal variation in zooplankton over the Emperor Seamounts (34°–44° N, 170°–171° E) during the summer of 2019

The horizontal and vertical distributions of zooplankton over the Emperor Seamounts (Koko, Jingu, Nintoku, and Suiko guyots) were analyzed. The zooplankton was represented by four genera of amphipods, seven genera of pteropods, 39 genera of copepods, and larvae of benthic invertebrates and fish. The abundance and biomass of zooplankton increased towards higher latitudes along the series Koko < Jingu < Nintoku < Suiko guyots. The highest index of diversity was recorded over the Koko and Jingu guyots; the highest species richness occurred over the Jingu and Nintoku guyots. Small-sized copepods, appendicularians, chaetognaths, euphausiids, and fish eggs and larvae concentrated in the epipelagic; large copepods and ostracods were concentrated in the mesopelagic. We identified three types of zooplankton assemblages: a Subtropical assemblage between 34°–35°N characterized by tropical/subtropical forms; a Transition assemblage characterized by subtropical, subarctic, and widespread species between 38°–41°N; and a Subarctic assemblage characterized by subarctic and widespread species between 43°–44°N. The spatial distribution of zooplankton was a function of environmental variables such as surface salinity, temperature at 200 m, and, to a certain extent, by surface Chl-a concentrations.

Chemical signaling in biofilm-mediated biofouling.

Biofouling is the undesirable accumulation of living organisms and their metabolites on submerged surfaces. Biofouling begins with adhesion of biomacromolecules and/or microorganisms and can lead to the subsequent formation of biofilms that are predominantly regulated by chemical signals, such as cyclic dinucleotides and quorum-sensing molecules. Biofilms typically release chemical cues that recruit or repel other invertebrate larvae and algal spores. As such, harnessing the biochemical mechanisms involved is a promising avenue for controlling biofouling. Here, we discuss how chemical signaling affects biofilm formation and dispersion in model species. We also examine how this translates to marine biofouling. Both inductive and inhibitory effects of chemical cues from biofilms on macrofouling are also discussed. Finally, we outline promising mitigation strategies by targeting chemical signaling to foster biofilm dispersion or inhibit biofouling.

Ocean conditions influence the quality of recruiting benthic marine invertebrate larvae—Insights from fatty acids

AbstractMany marine benthic invertebrates have a pelagic life stage, during which larvae need to accumulate enough reserves to complete metamorphosis to a settled benthic juvenile. Currently, very little is known about how ocean conditions affect quality of the larvae. We studied this for three settlement seasons (2017–2019) by collecting returning Dungeness crab (Metacarcinus magister) megalopae at the Oregon coast and analyzing them for fatty acid biomarkers. We found that the larvae are omnivorous and have versatile diets. The daily larval abundance was positively correlated with larval quality. Despite the relatively high day‐to‐day variation, we found pronounced seasonal and inter‐annual differences in the body condition (size and total fatty acid content) and biomarker composition of megalopae. Especially, the early season recruits of 2017 had lower content of lipids and polyunsaturated fatty acids known to be beneficial to crustaceans. This is likely related to lingering effects of the eastern Pacific marine heat wave (2014–2016) on pelagic communities. The larvae were rich in docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) with lower levels in benthic juveniles, indicating an ontogenetic diet shift and likely lower availability of DHA and EPA in the benthic environment. The pulsed megalopa recruitment may provide substantial carbon and lipid inputs to the nearshore ecosystem as a form of pelagic subsidy. Our results reveal that ocean conditions may have an effect on the quality of returning larvae, which likely influence their recruitment performance and early juvenile success, and thus potentially also the population size and commercial catch 4 yr later.

Dispersal and connectivity modelling simulations for invertebrate larvae passing through the Strait of Gibraltar

Abstract The link between the northeastern Atlantic and Mediterranean Sea created by the Strait of Gibraltar and the adjacent Iberian and Moroccan coasts marks remarkable transition areas between distinct environments that harbour a diverse mixture of species. The area is interesting regarding marine connectivity and the transport of pelagic invertebrate larvae, crucial knowledge to manage over-exploited populations, and minimize the impacts of climate change and anthropogenic activities. Biophysical models were developed, combining oceanic and particle-tracking Lagrangian simulations with in situ zooplankton distribution data. The conditions driving the larval exchange between the sub-basins and the connectivity throughout the region were explored, using crustacean decapod larvae as biological references. The potential exchange between both sub-basins was confirmed, although specific larval traits revealed contrasting scenarios. The simulations showed that slope-dwelling and mesopelagic larvae have advantage when crossing from the Alboran into the Atlantic, in comparison with shelf-dwelling and epipelagic larvae. Transport pathways and retention areas were identified, and passive drifts were shown to increase the dispersal range of the simulations. The spatial origin of the larval release, larval duration, vertical distribution, and the interaction of larvae with the oceanic features are presented as the main factors impacting the effective larval input into the Atlantic or Mediterranean basins.

Zooplankton in the zones of transformation of river runoff in the north-western Black Sea region and the Mediterranean Sea in 2017–2020

Estuary zones play a key role in the regulation of the impact of continental processes on marine ecosystems. The zone “river–sea” is a unique area with specific conditions, geochemical and biological processes. They belong to the so called “ecological hot spots” and that is why their research is especially needed to understand possible changes in the ecosystems. In the present study we described the spatial distribution of zooplankton in the zones of transformation of river runoff in the Ukrainian part of the north-western Black Sea region and the Turkish coast of the Mediterranean Sea in 2017–2020. In the Black Sea, samples were collected from the coast of the Odesa Marine Region, Danube Region and coastal waters between Dnipro-Bug estuary and Yuzhne town. On the Turkish Mediterranean Sea coasts, samples were collected between Antalya city and Patara village (Mugla province). A total of 64 samples of the zooplankton were studied. We did not establish a direct dependence between zooplankton biomass and annual volume of river runoff (correlation between these metrics is from –0.25 to –0.80). 20 taxa of zooplankton in the Odesa Marine Region, 21 taxa in the Danube Region, 11 taxa in the Dnieper Region, 23 taxa in the Turkish coastal zone of the Mediterranean Sea were registered. Species of forage zooplankton were dominant over non-forage ones in all seasons and all investigated aquatoria. The percentage of Noctiluca scintillans (Macartney) Kofoid &amp; Swezy, 1921 and jellyfish did not exceed 5% of the total biomass of zooplankton. In summer in the Black Sea, the majority of zooplankton by number and biomass was formed by organisms of meroplankton, species of Cyclopoida and Harpacticoida, in autumn species of the genus Acartia, Oithona davisae Ferrari F. D. &amp; Orsi, 1984, larvae of Cirripedia and Penilia avirostris Dana, 1849. The number and biomass of adults and Copepodid Stages of Acartia species increased from spring to autumn in all years. In populations of Acartia species Copepodid stages predominated over adults by number and biomass in all seasons. In the Mediterranian Sea, the majority of zooplankton by number and biomass was formed by larvae of benthic invertebrates and Copepoda. The abundance and biomass of zooplankton at a distance of 300 m from the river mouth were greater than directly at the mouth. The hydro-front was expressed near all investigated rivers, the maximum values of zooplankton number and biomass were observed here and they decreased in direction both towards the mouth of the river and towards the open sea.

Establishment of a new subfamily for the parasitic isopod genusPleurocryptella(Isopoda: Bopyridae), including recognition of epicaridium larval yolk sacs and description of a new genus and species of hyperparasite

AbstractExternal yolk sacs in free-living larvae of marine invertebrates are extremely rare, with all reported cases exhibiting yolk that is taken up through connection with the anterior alimentary canal. Herein, we confirm a novel yolk sac connected to the posterior end of the alimentary canal in the first larval stage of species in the bopyrid isopod genus PleurocryptellaBonnier, 1900, all known as ectoparasites in the branchial chambers of squat lobsters. Pleurocryptella poseidon Williams &amp; Boyko sp. nov. infesting the munidopsid Galacantha bellis Henderson, 1885 in the Arabian Sea, is described on the basis of adults and larvae. In common with conspecifics, the new species exhibits a suite of putative “primitive” characters including the presence of oostegites on the sixth and seventh pereomeres of females and maxillipeds and articulated uropods in males. Pleurocryptella poseidon Williams &amp; Boyko sp. nov. differs from other species of Pleurocryptella by characters of body shape, antennae, oostegite 1, pleon, and uropods of females and midventral tubercles, pleomeres, and pleopods of males. The epicaridium larvae have a large posterior, external yolk sac and segmented maxillipeds, a unique set of characters within Epicaridea. In addition to larval and adult characters, molecular data (COI) indicate that the genus is distinct from other members of Bopyridae, so we erect the new subfamily Pleurocryptellinae for it. Pleurocryptella poseidon Williams &amp; Boyko sp. nov. bears a new genus and species of hyperparasitic isopod that is herein described based on its cryptoniscus stage. A review of epicaridium larval morphology and a key to the species of Pleurocryptella are provided.

Evaluation of light traps for sampling lobster larvae in the German Bight, North Sea

Biological monitoring of planktonic animals is greatly dependent on the deployment of traps. A variety of specialized traps have been designed for surface plankton and vertebrates. However, certain groups, such as planktonic larvae of benthic marine invertebrates remain underrepresented in sampling efforts. Catching them has proven to be more challenging because of their size, swimming ability, location, and abundance. In the present study a successful light trap for sampling American lobster larvae in New Brunswick, Canada, is evaluated on the island of Helgoland (German Bight, North Sea). Our results showed the traps were successful in catching larvae in laboratory experiments but were unable to catch European lobster larvae in the field. Traps deployed in the field were successful in capturing other benthic and pelagic zooplankton predominantly consisting of crustaceans from the orders: Cumacea, Amphipoda, Mysida and Isopoda. The low density of lobster larvae, the island's topography, and their unique photactic response possibly limited the success rate of the light traps. Future research is needed to construct a specialized trap to sample Helgoland's lobster larvae and provide information on the current larval fitness and population numbers.

Making Your Own Luck: Weak Vertical Swimming Improves Dispersal Success for Coastal Marine Larvae

Dispersive early life stages are common in nature. Although many dispersing organisms (“propagules”) are passively moved by outside forces, some improve their chances of successful dispersal through weak movements that exploit the structure of the environment to great effect. The larvae of many coastal marine invertebrates, for instance, swim vertically through the water column to exploit depth-varying currents, food abundance, and predation risk. Several swimming behaviors and their effects on dispersal between habitats are characterized in the literature, yet it remains unclear when and why these behaviors are advantageous. We addressed this gap using a mathematical model of larval dispersal that scored how well behaviors allowed larvae to simultaneously locate habitats, avoid predators, and gather energy. We computed optimal larval behaviors through dynamic programming, and compared those optima against passive floating and three well documented behaviors from the literature. Optimal behaviors often (but not always) resembled the documented ones. However, our model predicted that the behaviors from the literature performed robustly well, if not optimally, across many conditions. Our results shed light on why some larval behaviors are widespread geographically and across species, and underscore the importance of carefully considering the weak movements of otherwise passive propagules when studying dispersal.

Interactive roles of temperature and food availability in predicting habitat suitability for marine invertebrates

Natural variability in habitat characteristics, including their interactions, can affect marine invertebrate development. Controlled laboratory experiments seek to assess responses to such variability. For marine invertebrates, responses to temperature are typically assessed but a continuous gradient of all temperatures that a species may encounter is not frequently used. For planktonic larvae of marine invertebrates, biotic factors such as food availability receive less attention due to difficulty in simulating planktonic biotic interactions in a controlled laboratory setting. Here, a laboratory experiment was used to quantify larval development (growth, pelagic larval duration and survival) of the Atlantic surfclam, Spisula solidissima, in response to a continuous range of temperatures and food (phytoplankton) concentrations, allowing quantification of thermal and food availability niches. A second experiment was conducted to quantify the thermal and food availability niches for recruit (post-settlement) surfclams. These experiments were uniquely designed to inform future climate change-based forecasting and habitat suitability modeling. Larval growth and survival increased with increased food availability, while pelagic larval duration decreased with increased food availability. Larval survival decreased with increased temperature, growth peaked near 22 °C and pelagic larval duration was lowest near 22 °C. For recruits, survival and growth increased with both temperature and food availability, but growth decreased at temperatures >22 °C. Broadly, results suggest potential food limitation for continental shelf bivalve larvae and demonstrate that natural variation in food availability may affect thermal tolerances. Results also suggest that throughout the range of the surfclam, high food and moderate temperature areas such as New York Bight and Georges Bank are ideal for larvae and early recruits, whereas low food and high temperature areas, including continental shelf waters in the southern Middle Atlantic Bight, are suboptimal for early life stages of surfclams. This framework may be used for habitat suitability modeling, from an energetic perspective, for other marine invertebrate taxa.

Metabolic Regulation of Copper Toxicity during Marine Mussel Embryogenesis.

The development of new tools for assessing the health of cultured shellfish larvae is crucial for aquaculture industries to develop and refine hatchery methodologies. We established a large-volume ecotoxicology/health stressor trial, exposing mussel (Perna canaliculus) embryos to copper in the presence of ethylenediaminetetraacetic acid (EDTA). GC/MS-based metabolomics was applied to identify potential biomarkers for monitoring embryonic/larval health and to characterise mechanisms of metal toxicity. Cellular viability, developmental abnormalities, larval behaviour, mortality, and a targeted analysis of proteins involved in the regulation of reactive oxygen species were simultaneously evaluated to provide a complementary framework for interpretative purposes and authenticate the metabolomics data. Trace metal analysis and speciation modelling verified EDTA as an effective copper chelator. Toxicity thresholds for P. canaliculus were low, with 10% developmental abnormalities in D-stage larvae being recorded upon exposure to 1.10 μg·L-1 bioavailable copper for 66 h. Sublethal levels of bioavailable copper (0.04 and 1.10 μg·L-1) caused coordinated fluctuations in metabolite profiles, which were dependent on development stage, treatment level, and exposure duration. Larvae appeared to successfully employ various mechanisms involving the biosynthesis of antioxidants and a restructuring of energy-related metabolism to alleviate the toxic effects of copper on cells and developing tissues. These results suggest that regulation of trace metal-induced toxicity is tightly linked with metabolism during the early ontogenic development of marine mussels. Lethal-level bioavailable copper (50.3 μg·L-1) caused severe metabolic dysregulation after 3 h of exposure, which worsened with time, substantially delayed embryonic development, induced critical oxidative damage, initiated the apoptotic pathway, and resulted in cell/organism death shortly after 18 h of exposure. Metabolite profiling is a useful approach to (1) assess the health status of marine invertebrate embryos and larvae, (2) detect early warning biomarkers for trace metal contamination, and (3) identify novel regulatory mechanisms of copper-induced toxicity.

Having cake and eating too: The benefits of an intermediate larval form in a brittle star Amphiodia sp. opaque (Ophiuroidea).

Most marine invertebrate larvae either obligately feed or depend on maternally provided reserves during planktonic development. A small number of species have the capacity to do both, in a mode of development known as facultative planktotrophy. We describe facultative feeding in a larva from the Oregon coast, and identify it as being an undescribed species in the genus Amphiodia, which we refer to as Amphiodia sp. opaque. We quantified the effects of food on larval and juvenile quality by culturing larvae, collected as embryos, with and without microalgal food at 15°C. The resulting juveniles were monitored under conditions of starvation. A cohort of juveniles of larvae caught as plankton was subjected to the same starvation treatment for comparison with our laboratory-reared larvae. We observed benefits to offspring that received food: larvae provided with microalgae developed more quickly and metamorphosed at higher rates. Furthermore, juveniles resulting from fed larvae were larger and were able to avoid starvation for longer after metamorphosis. Our results varied across two experimental years, suggesting that provisions provided by parents vary between populations and years. Juveniles from planktonic larvae exhibited sizes not statistically different from larvae cultured in the absence of food, but died from starvation more quickly.

The occurrence and zoonotic potential of Cryptosporidium species in freshwater biota

BackgroundProtozoan pathogens from the genus Cryptosporidium cause the diarrhoeal disease cryptosporidiosis in humans and animals globally. Freshwater biota could act as potential reservoirs or zoonotic sources of Cryptosporidium infections for livestock and people, but Cryptosporidium occurrence in aquatic biota is largely unexplored. The aim of this study was to investigate the occurrence of Cryptosporidium in a range of freshwater organisms in upland rivers across England and Wales.MethodsFish were sampled by electrofishing, invertebrate larvae by kick sampling and the otter Lutra lutra and mink Mustela vison through faecal samples collected opportunistically as part of a nation-wide study. PCR targeting the small subunit ribosomal RNA gene was used to detect Cryptosporidium species.ResultsCryptosporidium occurred in just 0.8% of all the samples and in none of 73 samples from nine invertebrate genera. Cryptosporidium was detected in two of 2/74 fish samples (2.7%), both salmonids, and in 2/92 otter faecal samples (2.17%), but there were no positive samples in mink (0/24) or the bullhead Cottus gobio (0/16).ConclusionsLow detection rate of human-infective Cryptosporidium species in aquatic fauna indicates they may present a low risk of contamination of some upland freshwaters.Graphical

Global Changes Alter the Successions of Early Colonizers of Benthic Surfaces

The successions of benthic communities over time are strongly influenced by the first colonizers, because surface associations are facilitated by modifications to the adhesive properties promoted by primary colonizers, such as bacteria, protozoans, diatoms, algal propagules, spores, and invertebrate larvae. Bacteria are often the first colonizers on marine submerged surfaces, both organic (e.g., algae, seagrasses and invertebrates) and inorganic. However, they are promptly followed by diatoms and other microorganisms. Consequently, diatoms may represent key elements in the determination of the colonization patterns, although the development of epiphytic communities is a dynamic process influenced by several factors, including nutrient availability, the ability to synthesize and secrete extracellular material, the competition among species and the influence of grazers on individual colonizers. The process may be drastically impacted by global warming and ocean acidification due to the increasing atmospheric levels of CO2. The impact of such global stressors on benthic ecosystems, especially on the primary microphytobenthic assemblages, is still poorly investigated, and may have deleterious consequences for the benthic successions. In this review, we analyze the adhesion patterns of marine microorganisms according to their surface features and the effects of global changes on critical pioneer colonizers, such as the benthic diatoms. The results are remarkable, as they highlight emergent concerns in ecosystem conservation and the prediction of benthic communities.

Multisensory integration by polymodal sensory neurons dictates larval settlement in a brainless cnidarian larva.

Multisensory integration (MSI) combines information from more than one sensory modality to elicit behaviours distinct from unisensory behaviours. MSI is best understood in animals with complex brains and specialized centres for parsing different modes of sensory information, but dispersive larvae of sessile marine invertebrates utilize multimodal environmental sensory stimuli to base irreversible settlement decisions on, and most lack complex brains. Here, we examined the sensory determinants of settlement in actinula larvae of the hydrozoan Ectopleura crocea (Cnidaria), which possess a diffuse nerve net. A factorial settlement study revealed that photo-, chemo- and mechanosensory cues each influenced the settlement response in a complex and hierarchical manner that was dependent on specific combinations of cues, an indication of MSI. Additionally, sensory gene expression over development peaked with developmental competence to settle, which in actinulae, requires cnidocyte discharge. Transcriptome analyses also highlighted several deep homological links between cnidarian and bilaterian mechano-, chemo-, and photosensory pathways. Fluorescent in situ hybridization studies of candidate transcripts suggested cellular partitioning of sensory function among the few cell types that comprise the actinula nervous system, where ubiquitous polymodal sensory neurons expressing putative chemo- and photosensitivity interface with mechanoreceptive cnidocytes. We propose a simple multisensory processing circuit, involving polymodal chemo/photosensory neurons and mechanoreceptive cnidocytes, that is sufficient to explain MSI in actinulae settlement. Our study demonstrates that MSI is not exclusive to complex brains, but likely predated and contextualized their evolution.

Plankton depletion by mussel grazing negatively impacts the fitness of lobster larvae

Bivalve aquaculture has rapidly expanded in shallow coastal habitats, leading to substantial changes in the natural environment. While the grazing pressure of mussels (Mytilus edulis) on phytoplankton and zooplankton has been well documented, cascading effects of plankton depletion on the development and survival of resident fish and invertebrate larvae remains largely unexplored. This study experimentally assessed the impact of control (no mussel grazing), low (20 mussels·m−3) and high (80 mussels·m−3) mussel densities on a model community composed of various phytoplankton and zooplankton and how changes in plankton characteristics influence the development and survival of lobster (Homarus americanus) larvae. Mussels fed primarily on nanophytoplankton, while the picophytoplankton experienced significantly less grazing. Zooplankton was readily ingested by mussels, showing a sharp decline under low mussel density, whereas it was eliminated from the plankton under high density of mussels. A 65% decrease of polyunsaturated fatty acids (∑ PUFA) was observed in the plankton under mussel filtration compared to control. Lobster larvae reared under control plankton conditions exhibited the fastest development, highest survival rate, carapace length, total lipid and ∑ PUFA contents, and TAG/ST (triacylglycerols/sterols) ratio, indicating the best nutritional condition. Larvae reared under low mussel density showed longer developmental time, lower survival rate and carapace length than that for controls. In addition, these larvae showed a significant reduction in total lipid, ∑ PUFA, and TAG/ST, which collectively suggests poor nutritional status due to limited dietary intake. Under high mussel density, larvae did not molt to stage II and died within 14 days, suggesting that the depleted plankton community was unable to sustain physiological requirements for survival and development of the larvae. Overall, mussel grazing altered the meroplankton community structure and its biochemical composition, ultimately impacting the development, survival, and quality of lobster larvae. These findings provide novel information on complex trophic interactions between bivalves and a meroplankton species and adds a new perspective to fuel discussions on energy and nutrient pathways, particularly long-chain PUFA, in ecosystem carrying capacity studies for shellfish aquaculture in shallow coastal habitats.

Impact of anthropogenic sounds (pile driving, drilling and vessels) on the development of model species involved in marine biofouling

The uncontrolled colonization of benthic organisms on submerged surfaces, also called biofouling, causes severe damage in the shipping and aquaculture industries. Biofouling starts with a benthic biofilm composed of a complex assemblage of microbes, bacteria and benthic diatoms, called microfouling, on which macrofouling invertebrate species settle and grow. Invertebrate larvae may use natural soundscapes to orientate inshore and choose their optimal habitat. Recent studies have demonstrated that ship sounds enhance the larval settlement and growth of several invertebrate species, such as mussels, associated with biofouling. Among invertebrates, effects of sound generated by offshore human activities are still poorly studied. This study aims to assess the effect of pile driving, drilling and vessel sounds on model species associated with micro and macrofouling. First, the biofilm development of Navicula pelliculosa and Amphora coffeaeformis was assessed, then, the larval development of the blue mussel (Mytilus edulis) was evaluated from the D-veliger to the postlarval stage. Mussel larvae and microalgae were exposed 12 h each day in tanks (Larvosonic) adapted to sound experiments under controlled conditions. All anthropogenic sounds induced a thinner N. pelliculosa biofilm coupled with a lower microalgae concentration. The drilling sound had a stronger effect on the biofilm thickness. The drilling sound significantly reduced the pediveliger settlement and the postlarvae clearance rate by 70.4% and tended to diminish settler sizes compared to control sound. Contrary to our expectation, pile driving tended to enhance larval recruitment by 22% (P=0.077) and the boat sound did not stimulate larval settlements or recruitment. Drilling sound generated a stressful acoustic environment for pediveliger settlements and postlarvae seem to maintain their shell valves closed to preserve energy. We identify potential causes and mechanisms involved in these impacts of anthropophony on larval ecology and microfouling dynamics.

Biofouling and Antifouling: Interactions between Microbes and Larvae of Invertebrates

The biofouling process refers to the undesirable accumulation of micro- and macro-organisms on manufactured surfaces [...].

Stage-Specific Transcriptomes of the Mussel Mytilus coruscus Reveals the Developmental Program for the Planktonic to Benthic Transition.

Many marine invertebrate larvae undergo complex morphological and physiological changes during the planktonic-benthic transition (a.k.a. metamorphosis). In this study, transcriptome analysis of different developmental stages was used to uncover the molecular mechanisms underpinning larval settlement and metamorphosis of the mussel, Mytilus coruscus. Analysis of highly upregulated differentially expressed genes (DEGs) at the pediveliger stage revealed enrichment of immune-related genes. The results may indicate that larvae co-opt molecules of the immune system to sense and respond to external chemical cues and neuroendocrine signaling pathways forecast and trigger the response. The upregulation of adhesive protein genes linked to byssal thread secretion indicates the anchoring capacity required for larval settlement arises prior to metamorphosis. The results of gene expression support a role for the immune and neuroendocrine systems in mussel metamorphosis and provide the basis for future studies to disentangle gene networks and the biology of this important lifecycle transformation.

The rangeomorph Pectinifrons abyssalis: Hydrodynamic function at the dawn of animal life

Rangeomorphs are among the oldest putative eumetazoans known from the fossil record. Establishing how they fed is thus key to understanding the structure and function of the earliest animal ecosystems. Here, we use computational fluid dynamics to test hypothesized feeding modes for the fence-like rangeomorph Pectinifrons abyssalis, comparing this to the morphologically similar extant carnivorous sponge Chondrocladia lyra. Our results reveal complex patterns of flow around P.abyssalis unlike those previously reconstructed for any other Ediacaran taxon. Comparisons with C. lyra reveal substantial differences between the two organisms, suggesting they converged on a similar fence-like morphology for different functions. We argue that the flow patterns recovered for P.abyssalis do not support either a suspension feeding or osmotrophic feeding habit. Instead, our results indicate that rangeomorph fronds may represent organs adapted for gas exchange. If correct, this interpretation could require a dramatic reinterpretation of the oldest macroscopic animals.

Features of the formation of microecotones in aquatic ecosystems

The formation of ecotones in aquatic ecosystems on artificial mechanical barriers placed on fouling glasses has been studied. A positive statistically significant relationship was established between the size of an organism and the width of the ecotone formed by this organism in the series from bacteria to bryozoans and polyps. In relation to microorganisms, a more intensive formation of biofilms and mats was revealed in the marginal areas of biotopes. Larger fouling, such as algae, also more quickly develop the marginal areas of a discrete landscape and serve as a secondary biotope already for phytophilic invertebrates, which are characterized in these artificial biotopes by several times and sometimes by an order of magnitude greater abundance and biomass compared to adjacent standard conditions. The marginal ecotone aggregations also revealed increased polyp size and elevated concentrations of catalase in some molluscs and invertebrate larvae.