Stoichiometry of growth under variable scenarios of nutrient limitation: Differential homeostasis of body composition among growth phenotypes of the Manila clam

Fast- and slow-growing phenotypes from two separate breeding families of the Manila clam (Ruditapes philippinarum) were alternatively fed two monoalgal diets with high and low N content (C:N ratios of 4.9 and 13.5, respectively). After 35 days of food conditioning, clams were sacrificed, and the soft body was dissected out into five different tissue fractions to determine the corresponding ponderal ratios (tissue wt./body wt.) and a separate analysis of the elemental composition of these tissues. Previously reported C and N balances performed with the same conditioning diets were integrated and compared with tissue composition of the same phenotypes in order to assess the efficacy of mechanisms elicited to compensate for N deficit. Broad differences in dietary N content resulted in only minor changes in whole-body C:N composition which suggests a noticeable degree of homeostatic regulation of nutrient balances. This regulation was found to be stricter in fast-compared to slow-growing phenotypes and differed among the various body tissues. Using the threshold element ratio approach, physiological mechanisms were identified that partly compensate for large stoichiometric mismatches between low-N food and body tissues.

The loss of crude oil droplets by filter feeders and the role of surfactants

Various methods of oil spill remediation exist, e.g., floating booms, controlled burning and the release of chemical surfactants. These surfactants facilitate the breakup of the slick into micron-sized droplets. Here, we studied the impact such a surfactant has on the size distribution of oil droplets in the water column and in the gut of the filter feeder Daphnia magna. We also studied the effect of surfactants on detachment conditions of chemically and mechanically dispersed oil (respectively MDO and CDO) droplets from capture fibers. Our results show that including solubilized dioctyl sulfosuccinate sodium salt in the mixing of the emulsion produces smaller droplets and a narrower size distribution in the water. In the gut, the size of ingested droplets does not change whether the oil is mixed mechanically or chemically. Also, surfactant coated droplets detach at a lower velocity than mechanically dispersed droplet because of their lower oil/water interfacial tension.

Uptake of microplastics by marine worms depends on feeding mode and particle shape but not exposure time

The uptake of microplastics into marine species has been widely documented across trophic levels. Feeding mode is suggested as playing an important role in determining different contamination loads across species, but this theory is poorly supported with empirical evidence. Here we use the two distinct feeding modes of the benthic polychaete, Hediste diversicolor (The Harbour Ragworm) (O.F. Müller, 1776), to test the hypothesis that filter feeding will lead to a greater uptake of microplastic particles than deposit feeding. Worms were exposed to both polyamide microfragments and microfibres in either water (as filter feeders) or sediment (as deposit feeders) for 1 week. No effect of exposure time was found between 1 day and 1 week (p > 0.19) but feeding mode was found to significantly affect the number of microfibres recovered from each worm (p < 0.001). When exposed to microfibers, filter feeding worms took up ≈15,000 % more fibres than deposit feeding worms (p < 0.001), whereas when feeding on microfragments there was no difference between feeding modes. Our data demonstrate that both feeding mode and particle characteristics significantly influence the uptake of microplastics by H. diversicolor. Using imaging flow cytometry, filter feeders were found to take up a broader size range of particles, with significantly more smaller and larger particles than deposit feeders (p < 0.05), commensurate with the range of plastics isolated from the guts of ragworms recovered from the environment. These results demonstrate that biological traits are useful in understanding the uptake of plastics into marine worms and warrant further exploration as a tool for understanding the bioaccessibility of plastics to marine organisms.

The capture of crude oil droplets by filter feeders at high and low Reynolds numbers

Crustacean filter feeders capture oil droplets with the use of their ramified appendages. These appendages behave as paddles or sieves, based on the system's Reynolds number. Here we used high-speed videography, scanning electron microscopy and fluid mechanics to study the capturing mechanisms of crude oil droplets and the filtering appendage's wettability by two species of barnacles (Balanus glandula and Balanus crenatus) and of the freshwater cladoceran Daphnia magna. Our results show that barnacles appendages will behave as paddles and capture droplets in their boundary layers at low Reynolds number. At high Reynolds number, droplets are most likely to be captured via direct interception. There is an intermediate range of Reynolds number where droplets can be captured by both mechanisms at the same time. Daphnia magna captures droplets in the boundary layers of the third and fourth pair of thoracic legs with a metachronal motion of the appendages. All studied surfaces were revealed to be highly lipophobic, demonstrating captured oil droplets with high contact angles. We also discuss implications of such capture mechanisms and wettability on potential ingestion of crude oil by filter feeders. These results further our understanding of the capture of crude oil by filter feeders, shedding light onto the main entry point of oil in the marine food webs.

Morphological variation of the relictual alveolar structures in the mandibles of baleen whales

Living baleen whales (mysticetes) are bulk filter feeders that use keratinous baleen plates to filter food from prey laden water. Extant mysticetes are born entirely edentulous, though they possess tooth buds early in ontogeny, a trait inherited from toothed ancestors. The mandibles of extant baleen whales have neither teeth nor baleen; teeth are resorbed in utero and baleen grows only on the palate. The mandibles of extant baleen whales also preserve a series of foramina and associated sulci that collectively form an elongated trough, called the alveolar groove. Despite this name, it remains unclear if the alveolar groove of edentulous mysticetes and the dental structures of toothed mammals are homologous. Here, we describe and quantify the anatomical diversity of these structures across extant mysticetes and compare their variable morphologies across living taxonomic groups (i.e., Balaenidae, Neobalaenidae, Eschrichtiidae, and Balaenopteridae). Although we found broad variability across taxonomic groups for the alveolar groove length, occupying approximately 60–80 percent of the mandible’s total curvilinear length (CLL) across all taxa, the relictual alveolar foramen showed distinct patterns, ranging between 15–25% CLL in balaenids, while ranging between 3–12% CLL in balaenopterids. This variability and the morphological patterning along the body of the mandible is consistent with the hypothesis that the foramina underlying the alveolar groove reflect relictual alveoli. These findings also lay the groundwork for future histological studies to examine the contents of these foramina and clarify their potential role in the feeding process.

The interactions of oil droplets with filter feeders: A fluid mechanics approach

Filter feeding animals capture and lose oil droplets using cilia or ramified appendages. Here we demonstrate that copepod and barnacle appendages capture fish, canola and 1-decanol oil droplets up to 11μm without selectivity for size, chemistry, density, viscosity, or interfacial tension. Following capture, the droplets are ingested or lost via detachment. Capture and detachment did not differ between a barnacle appendage and stainless-steel wires of radii R_f=50 and 250μm. Key parameters to detachment include the ratio of oil droplet radius to fiber radius, and the Weber number. Smaller oil droplet size to fiber size ratio r=R_o∕R_f, required a higher We for detachment. These data plot as a curve that predicts whether a droplet will remain captured or detach and re-enter the fluid stream, based on the fluid, the droplet radius to fiber radius ratio, and the oil droplet properties. Significantly, this curve may be used to plan responses to oil spills in marine environments.

Filter feeding in Late Jurassic pterosaurs supported by coprolite contents

Diets of pterosaurs have mainly been inferred from indirect evidence such as comparative anatomy, associations of co-occurring fossils, and functional morphology. Gut contents are rare, and until now there is only a single coprolite (fossil dropping), with unidentified inclusions, known. Here we describe three coprolites collected from a palaeosurface with numerous pterosaur tracks found in early Kimmeridgian (Hypselocyclum Zone) intertidal deposits of the Wierzbica Quarry, Poland. The specimens’ morphology and association to the tracks suggest a pterosaur producer. Synchrotron scans reveal numerous small inclusions, with foraminifera making up the majority of the identifiable ones. Other small remains include shells/carapaces (of bivalves, ostracods, and other crustaceans/arthropods) and bristles (some possibly of polychaete worms). The high density of the small shelly inclusions suggest that they were not accidently ingested, but constituted an important food source for the pterosaur(s), perhaps together with unpreserved soft-bodied animals. The combined evidence from the tracks and coprolites suggest a filter-feeding ctenochasmatid as the most likely tracemaker. If true, this significantly expands the bromalite record for this pterosaur group, which was previously only known from gastroliths. Moreover, this study also provides the first direct evidence of filter feeding in Jurassic pterosaurs and shows that they had a similar diet to the recent Chilean flamingo (Phoenicopterus chilensis).

How do baleen whales stow their filter? A comparative biomechanical analysis of baleen bending

Bowhead and right whale (balaenid) baleen filtering plates, longer in vertical dimension (≥3-4 m) than the closed mouth, presumably bend during gape closure. This has not been observed in live whales, even with scrutiny of video-recorded feeding sequences. To determine what happens to the baleen during gape closure, we conducted an integrative, multifactorial study including materials testing, functional (flow tank and kinematic) testing and histological examination. We measured baleen bending properties along the dorsoventral length of plates and anteroposterior location within a rack of plates via mechanical (axial bending, composite flexure, compression and tension) tests of hydrated and air-dried tissue samples from balaenid and other whale baleen. Balaenid baleen is remarkably strong yet pliable, with ductile fringes, and low stiffness and high elasticity when wet; it likely bends in the closed mouth when not used for filtration. Calculation of flexural modulus from stress/strain experiments shows that the balaenid baleen is slightly more flexible where it emerges from the gums and at its ventral terminus, but kinematic analysis indicates plates bend evenly along their whole length. Fin and humpback whale baleen has similar material properties but less flexibility, with no dorsoventral variation. The internal horn tubes have greater external and hollow luminal diameter but lower density in the lateral relative to medial baleen of bowhead and fin whales, suggesting a greater capacity for lateral bending. Baleen bending has major consequences not only for feeding morphology and energetics but also for conservation given that entanglement in fishing gear is a leading cause of whale mortality.

The evolution of foraging capacity and gigantism in cetaceans

The extant diversity and rich fossil record of cetaceans provides an extraordinary evolutionary context for investigating the relationship between form, function and ecology. The transition from terrestrial to marine ecosystems is associated with a complex suite of morphological and physiological adaptations that were required for a fully aquatic mammalian life history. Two specific functional innovations that characterize the two great clades of cetaceans, echolocation in toothed whales (Odontoceti) and filter feeding in baleen whales (Mysticeti), provide a powerful comparative framework for integrative studies. Both clades exhibit gigantism in multiple species, but we posit that large body size may have evolved for different reasons and in response to different ecosystem conditions. Although these foraging adaptations have been studied using a combination of experimental and tagging studies, the precise functional drivers and consequences of morphological change within and among these lineages remain less understood. Future studies that focus at the interface of physiology, ecology and paleontology will help elucidate how cetaceans became the largest predators in aquatic ecosystems worldwide.

Suspended sediment causes feeding current arrests in situ in the glass sponge Aphrocallistes vastus

Bottom-contact trawling generates large, moving clouds of suspended sediments that can alter the behaviour of organisms adjacent to trawl paths. While increased suspended sediment concentrations (SSCs) are known to cause glass sponges to arrest filtration in lab studies, the response of sponges to sediment in situ is not yet known. Here we describe arrest behaviours in response to increased SSCs recorded from the glass sponge Aphrocallistes vastus at the Fraser Ridge sponge reef in the Strait of Georgia, British Columbia, Canada. We identified 23 arrests of the sponges' feeding current during experimental disturbances that raised SSC to between 10 and 80 mg l^-1. Single arrests lasted 4.25 ± 1.3 min (±SD) and were characterized by a 2 cm s^-1 reduction in feeding current lasting 0.5-3 min (mean 1.91 ± 0.97 min, n = 19). In comparison, coughing arrests varied in length (31 ± 22.89 min) with arrest phases lasting 4-15 min (10.46 ± 5.26 min, n = 4). Coughing arrests showed a distinctive on/off pattern as sponge filtration returned to normal excurrent velocities, distinguishing them from single arrests. The onset of both arrest types was correlated with elevated SSCs (r = -0.83 to -0.92). Natural SSCs at the reef averaged 4.4 mg l^-1 and were correlated with tidal flow (r = 0.86 to 0.89). The combined data provide evidence that suspended sediments can stop glass sponge feeding in situ even at SSCs below those known to be generated by trawling.

The mechanisms of filter feeding on oil droplets: Theoretical considerations

Filter feeding animals capture food particles and oil droplets from the fluid environment using cilia or appendages composed of arrays of fibers. Here we review the theoretical models that have provided a foundation for observations on the efficiency of particle capture. We then provide the mathematical theoretical framework to characterize the efficient filtration of oil droplets. In the aquatic and marine environments oil droplets are released from the decay of organisms or as hydrocarbons. Droplet size and flow velocity, oil-to-water viscosity ratio, oil-water interfacial tension, oil and water density difference, and the surface wettability, or surface texture, of the filter fiber are the key parameters for oil droplet capture. Following capture, capillary force maintains the droplet at its location due to the oil-water interfacial tension. If the oil-coated fiber is subject to any external force such as viscous or gravitational forces, it may deform and separate from the fiber and re-enter the fluid stream. We show oil droplet capture in Daphnia and the barnacle Balanus glandula, and outline some of the ecological unknowns regarding oil capture in the oceans. Awareness of these mechanisms and their interrelationships will provide a foundation for investigations into the efficiency of various modes of filter feeding on oil droplets.

Feeding inhibition in Corbicula fluminea (O.F. Muller, 1774) as an effect criterion to pollutant exposure: Perspectives for ecotoxicity screening and refinement of chemical control

Bivalves are commonly used in biomonitoring programs to track pollutants. Several features, including its filter-feeding abilities, cumulatively argue in favour of the use of the Asian clam (Corbicula fluminea) as a biosentinel and an ecotoxicological model. Filtration in bivalves is very sensitive to external stimuli and its control is dictated by regulation of the opening/closure of the valves, which may be used as an avoidance defence against contaminants. Here, we investigate the filter-feeding behaviour of the Asian clam as an endpoint for assessing exposure to pollutants, driven by two complementary goals: (i) to generate relevant and sensitive toxicological information based on the ability of C. fluminea to clear an algal suspension, using the invasive species as a surrogate for native bivalves; (ii) to gain insight on the potential of exploring this integrative response in the refinement of chemical control methods for this pest. Clearance rates and proportion of algae removed were measured using a simple and reproducible protocol. Despite some variation across individuals and size classes, 50-90% of food particles were generally removed within 60-120 min by clams larger than 20 mm. Removal of algae was sensitive to an array of model contaminants with biocide potential, including fertilizers, pesticides, metals and salts: eight out of nine tested substances were detected at the μg l^-1 or mg l^-1 range and triggered valve closure, decreasing filter-feeding in a concentration-dependent manner. For most toxicants, a good agreement between mortality (96 h - LC₅₀ within the range 0.4-5500 mg l^-1) and feeding (2 h - IC₅₀ within the range 0.005-2317 mg l^-1) was observed, demonstrating that a 120-min assay can be used as a protective surrogate of acute toxicity. However, copper sulphate was very strongly avoided by the clams (IC₅₀ = 5.3 μg l^-1); on the contrary, dichlorvos (an organophosphate insecticide) did not cause feeding depression, either by being undetected by the clams' chemosensors and/or by interfering with the valve closure mechanism. Such an assay has a large potential as a simple screening tool for industry, environmental agencies and managers. The ability of dichlorvos to bypass the Asian clam's avoidance strategy puts it in the spotlight as a potential agent to be used alone or combined with others in eradication programs of this biofouler in closed or semi-closed industrial settings.

The energetic cost of filtration by demosponges and their behavioural response to ambient currents

Sponges (Porifera) are abundant in most marine and freshwater ecosystems, and as suspension feeders they play a crucial role in filtering the water column. Their active pumping enables them to filter up to 900 times their body volume of water per hour, recycling nutrients and coupling a pelagic food supply with benthic communities. Despite the ecological importance of sponge filter feeding, little is known about how sponges control the water flow through their canal system or how much energy it costs to filter the water. Sponges have long been considered textbook examples of animals that use current-induced flow. We provide evidence that suggests that some species of demosponge do not use current-induced flow; rather, they respond behaviourally to increased ambient currents by reducing the volume of water filtered. Using a morphometric model of the canal system, we also show that filter feeding may be more energetically costly than previously thought. Measurements of volumetric flow rates and oxygen removal in five species of demosponge show that pumping rates are variable within and between species, with the more oxygen consumed the greater the volume filtered. Together, these data suggest that sponges have active control over the volume of water they process, which may be an adaptation to reduce the energetic cost of filtration in times of high stress.

Role of neuropeptide F in regulating filter feeding of Manila clam, Ruditapes philippinarum

Endogenous signals which may be involved in the regulation of filter feeding in bivalves have never been examined. NPY/NPF homologue has been proved to play an important role in the regulation of food intake in vertebrate and several invertebrates. In this study, a NPF homologue was cloned from visceral ganglia of clam Ruditapes philippinarum. The full-length cDNA sequence was 892bp in length and encoded a precursor of 82 amino acid residues. We then examined the effects of fasting and refeeding on the filtration rates (FR), plasma glucose concentration (PGC), 5-HT, DA and the expression level of the rp-NPF and insulin transcript. The mRNA expression level of rp-NPF in visceral ganglion was increased during fasting, and rose to highest level on 72h after starvation and declined immediately after food had been supplied. Hemocoel injection of rp-NPF(5μg/g)significantly increased FR of clams within 2h. Compared to the controls, a significant increase in insulin mRNA levels was observed at 8h after injection. Contents of 5-HT and DA also increased in the 5μg/grp-NPF administrated clams at 8 and 24h after injection. These results suggest that, similar to vertebrates, NPF, insulin, 5-HT and DA may play a role in the regulation of feeding in R. philippinarum.

Anatomy, feeding ecology, and ontogeny of a transitional baleen whale: a new genus and species of Eomysticetidae (Mammalia: Cetacea) from the Oligocene of New Zealand

The Eocene history of cetacean evolution is now represented by the expansive fossil record of archaeocetes elucidating major morphofunctional shifts relating to the land to sea transition, but the change from archaeocetes to modern cetaceans is poorly established. New fossil material of the recently recognized family Eomysticetidae from the upper Oligocene Otekaike Limestone includes a new genus and species, Waharoa ruwhenua, represented by skulls and partial skeletons of an adult, juvenile, and a smaller juvenile. Ontogenetic status is confirmed by osteohistology of ribs. Waharoa ruwhenua is characterized by an elongate and narrow rostrum which retains vestigial alveoli and alveolar grooves. Palatal foramina and sulci are present only on the posterior half of the palate. The nasals are elongate, and the bony nares are positioned far anteriorly. Enormous temporal fossae are present adjacent to an elongate and narrow intertemporal region with a sharp sagittal crest. The earbones are characterized by retaining inner and outer posterior pedicles, lacking fused posterior processes, and retaining a separate accessory ossicle. Phylogenetic analysis supports inclusion of Waharoa ruwhenua within a monophyletic Eomysticetidae as the earliest diverging clade of toothless mysticetes. This eomysticetid clade also included Eomysticetus whitmorei, Micromysticetus rothauseni, Tohoraata raekohao, Tokarahia kauaeroa, Tokarahia lophocephalus, and Yamatocetus canaliculatus. Detailed study of ontogenetic change demonstrates postnatal elaboration of the sagittal and nuchal crests, elongation of the intertemporal region, inflation of the zygomatic processes, and an extreme proportional increase in rostral length. Tympanic bullae are nearly full sized during early postnatal ontogeny indicating precocial development of auditory structures, but do increase slightly in size. Positive allometry of the rostrum suggests an ontogenetic change in feeding ecology, from neonatal suckling to a more specialized adult feeding behaviour. Possible absence of baleen anteriorly, a delicate temporomandibular joint with probable synovial capsule, non-laterally deflected coronoid process, and anteroposteriorly expanded palate suggests skim feeding as likely mode of adult feeding for zooplankton. Isotopic data in concert with preservation of young juveniles suggests the continental shelf of Zealandia was an important calving ground for latitudinally migrating Oligocene baleen whales.

Does the marine biotoxin okadaic acid cause DNA fragmentation in the blue mussel and the pacific oyster?

Two bivalve species of global economic importance: the blue mussel, Mytilus edulis and the pacific oyster, Crassostrea gigas were exposed in vivo, to the diarrhoetic shellfish toxin okadaic acid (OA), and impacts on DNA fragmentation were measured. Shellfish were exposed using two different regimes, the first was a single (24 h) exposure of 2.5 nM OA (∼0.1 μg/shellfish) and algal feed at the beginning of the trial (T0), after which shellfish were only fed algae. The second was daily exposure of shellfish to two different concentrations of OA mixed with the algal feed over 7 days; 1.2 nM OA (∼0.05 μg OA/shellfish/day) and 50 nM OA (∼2 μg OA/shellfish/day). Haemolymph and hepatopancreas cells were extracted following 1, 3 and 7 days exposure. Cell viability was measured using the trypan blue exclusion assay and remained above 85% for both cell types. DNA fragmentation was examined using the single-cell gel electrophoresis (comet) assay. A significant increase in DNA fragmentation was observed in the two cell types from both species relative to the controls. This increase was greater in the pacific oyster at the higher toxin concentration. However, there was no difference in the proportion of damage measured between the two cell types, and a classic dose response was not observed, increasing toxin concentration did not correspond to increased DNA fragmentation.

Microbiological accumulation by the Mediterranean invasive alien species Branchiomma bairdi (Annelida, Sabellidae): potential tool for bioremediation

We examined the bacterial accumulation and digestion in the alien polychaete Branchiomma bairdi. Microbiological analyses were performed on worm homogenates from "unstarved" and "starved" individuals and on seawater from the same sampling site (Ionian Sea, Italy). Densities of culturable heterotrophic bacteria (22 °C), total culturable bacteria (37 °C) and vibrios were measured on Marine Agar 2216, Plate Count Agar and TCBS Agar, respectively. Microbial pollution indicators were determined by the most probable number method. B. bairdi was able to accumulate all the six considered microbiological groups which, however, differ in their resistance to digestion. B. bairdi results more efficient than the other two co-occurring sabellids in removing bacteria suggesting that it may counteract the effects of microbial pollution playing a potential role for in situ bioremediation. Thus a potential risk, such as the invasion of an alien species, could be transformed into a benefit with high potential commercial gain and economic feasibility.

Particle retention in suspension-feeding fish after removal of filtration structures

The suspension-feeding cichlids Oreochromis aureus (blue tilapia) and Oreochromis esculentus (ngege tilapia) are able to selectively retain small food particles. The gill rakers and microbranchiospines of these species have been assumed to function as filters. However, surgical removal of these oral structures, which also removed associated mucus, did not significantly affect the total number of 11-200 μm particles ingested by the fish. This result supports the hypothesis that the branchial arch surfaces themselves play an important role in crossflow filtration. Both species selectively retained microspheres greater than 50 μm with gill rakers and microbranchiospines intact as well as removed, demonstrating that neither these structures nor mucus are necessary for size selectivity to occur during biological crossflow filtration. After removal of the gill rakers and microbranchiospines, O. esculentus retained significantly more microspheres 51-70 μm in diameter and fewer 91-130 μm microspheres compared to retention with intact structures, but the particle size selectivity of O. aureus was not affected significantly. These results support conclusions from previous computational fluid dynamics simulations indicating that particle size can have marked effects on particle trajectory and retention inside the fish oropharyngeal cavity during crossflow filtration. The substantial inter-individual variability in particle retention by suspension-feeding fish is an unexplored area of research with the potential to increase our understanding of the factors influencing particle retention during biological filtration.

Assessment of toxicity of dissolved and microencapsulated biocides for control of the Golden Mussel Limnoperna fortunei

Biological invasions currently pose major threats to ecosystems worldwide. Invasive bivalves such as the Golden Mussel Limnoperna fortunei can act as 'environmental engineers', altering biogeochemistry, reducing biodiversity, and literally changing the landscape of aquatic environments. The risk that this mussel will invade the Amazon basin is a great concern for environmental authorities, especially because no efficient control methods presently exist. In this study, we tested new microencapsulated chemicals, along with the traditional dissolved chlorine and KCl, as alternatives to control L. fortunei infestation in industrial and water supply plants along rivers. Because these bivalves can close their valves when they sense toxic substances in the water, microencapsulation has improved the effectiveness of the chemicals in controlling L. fortunei, reducing variation in the application and increasing toxicity compared to dissolved chemicals. Microencapsulation should be seriously considered as an alternative to replace hazardous chlorine.