Robert W Elner

Environment Canada | EC · PWRC

Dense congregations of shorebirds forage on tidal flats during long-distance migration, and their abundance is presumed to mirror the underlying ecological conditions. We quantified the nutritional content of intertidal biofilm (a thin layer of microalgae, bacteria, and other microorganisms embedded in a mucilaginous matrix that sits on the surface...

Dense congregations of shorebirds forage on tidal flats during long-distance migration, and their abundance is presumed to mirror the underlying ecological conditions. We quantified the nutritional content of intertidal biofilm (a thin layer of microalgae, bacteria, and other micro-organisms embedded in a mucilaginous matrix) to assess whether biof...

The critical importance of mono- and polyunsaturated fatty acids (FAs) in a variety of biological functions, including animal nutrition and as an environmental stress monitor, is well recognized. However, while methods exist for monitoring of fatty acids, few are specific either to the profile of a microphytobenthos matrix or practical in applicati...

The use of stable isotopes of carbon ( δ ¹³ C) and nitrogen ( δ ¹⁵ N) from feces and breath offers potential as non-destructive tools to assess diets and nutrition. How stable isotope values derived from breath and feces compare with those from commonly used tissues, such as blood fractions and liver, remains uncertain, including understanding the...

Shorebirds use key migratory stopover habitats in spring and fall where body proteins are replenished and lipids stored as fuel for the remaining journey. The Fraser River estuary, British Columbia, Canada, is a critical spring stopover site for hundreds of thousands of migrating western sandpiper, Calidris mauri, and dunlin, Calidris alpina. Inter...

Soft‐bottomed intertidal flats are essential foraging areas for shorebirds but are severely impacted by threats such as coastal development and climate change. Notwithstanding the urgency for humanintervention (conservation, restoration and creation) of tidal flats, few ecologically based technical guidelines exist for the artificial (clearly inten...

Biofilm communities on intertidal mudflats are recognized as major producers of nutrients, especially fatty acids. The rising threats posed by both climatic and anthropogenic stressors increase the necessity of understanding and conserving these communities. Shorebirds provide a proxy for studying the complex ecology of biofilm communities because...

A new field of shorebird feeding ecology has been opened, stemming directly from natural history observations of previously overlooked morphological and behavioral features. We describe how the pieces of this puzzle were assembled to reveal a fascinating story of small shorebird migration, trophic level shift, and direct feeding upon mudflat superf...

Intertidal biofilm is a thin layer of microbes and meiofauna enmeshed in an extracellular polymeric matrix within and on top of mudflat sediment. This medium provides a dynamic resource for a variety of consumers in estuarine habitats, and is rich in essential fatty acids that birds require for long-distance migration. We measured seasonal changes...

Shorebirds are major, but thus far under-acknowledged, players in mudflat food webs and associated physio-chemical processes. Mud is a critical habitat type for shorebirds, offering a multi-dimensional matrix of feeding opportunities through space and time. Shorebirds have evolved a spectrum of foraging modes with associated morphologies, and senso...

Roberts Bank tidal flat, which is located at the mouth of the Fraser River, has been wellknown as one of the world's largest tidal flats for migratory birds. In the previous studies, biofilm, which exists in a lower salinity region, is found to be significant source of nutrients. However, it has not been revealed how infiltration flow influences sa...

There eixt huge tidal flats in Roberts Bank, Vancouver, which is one of the world's largest tidal flats for migratory birds. Since Roberts Bank tidal flat is located at the mouth of the large river, Fraser River, it is expected that ecological and hydrological enviromnents are affected by snow melt flood. Although biofilm is revealed to be one of t...

Ecology Letters (2012) 15: 347–356 Food webs are comprised of a network of trophic interactions and are essential to elucidating ecosystem processes and functions. However, the presence of unknown, but critical networks hampers understanding of complex and dynamic food webs in nature. Here, we empirically demonstrate a missing link, both critical a...

A pair of rock crabs, Cancer irroratus, in mating embrace an hour after being placed in a laboratory tank, was observed intermittently until ecdysis of the female and copulation of the pair, and then until escape of the female 27 d after ecdysis. When separated from the mating embrace, the hard-shelled female sought out the male. Approach of female...

Various predation techniques used by rock crabs, Cancer irroratus, and American lobsters, Homarus americanus, to open sea scallop, Placopecten magellanicus, prey are reported. Adult rock crabs and lobsters successfully fed on sea scallops up to 72 and 76 mm in height, respectively. Juvenile lobsters were capable of preying on scallops whose height...

The principal tool for evaluating biomass and, hence, exploitation rate for Atlantic snow crab, Chionoecetes opilio, has been the Leslie method which is based on commercial catch rate and cumulative catch through the fishing season. The method assumes a dosed, homogeneous stock. However, a snow crab stock is often not closed because recruitment can...

Commercial landings of American lobster (Homarus americanus) have increased dramatically in many areas along the east coast of Canada since the late 1970's. Average annual sea surface temperatures (SST) were analysed to test if lobster landings were related to changes in the marine environment. Time series models were fitted to lobster landings and...

Behavior and chela function associated with precopulatory clasping in morphometrically mature (MM) and morphometrically immature (MI) male snow crab, Chionoecetes opilio, were compared. MM males clasp receptive females more readily and for a more protracted period than MI males. Moreover, smaller MM males were more successful in initiating and main...

In the laboratory, early stage juvenile American lobsters, Homarus americanus, showed a preference for spending time and selecting shelters in gravel when given a choice between silt–clay deposited over gravel versus gravel substrates. Lobsters excavated shelters in the gravel by various combinations of pushing, plowing, and carrying stones with th...

For adult snow crabs (Chionoecetes opilio), from the western Gulf of St. Lawrence, eastern and western Cape Breton Island, and eastern Newfoundland, we compared morphometric, meristic, electrophoretic, and fecundity characteristics. Our morphometric, meristic, and fecundity data indicated that snow crabs from the four areas are morphologically and...

Male snow crabs, Chionoecetes opilio (Majidae), use their modified chelae to retain females for weeks before copulation. Consequently, adaptations for such sustained activity were examined in the chela-closer muscle responsible for clasping. Based on an allometric increase in the ratio of chela size to carapace width, male snow crabs were categoriz...

The effect of spionid worm, Polydora websteri, infestation on the strength of shell valves of the sea scallop, Placopecten magellanicus, was investigated in relation to valve weight and degree of bioerosion. Compression tests indicated that the strength of upper valves increased with weight but were weakened in proportion to the degree of P. webste...

Seven hundred and twenty-one brachyuran crabs (Cancer borealis, Cancer irroratus, Carcinus maenas, Chionoecetes opilio, Geryon quinquedens) were collected in waters off eastern Canada during 1980–1982 and the prevalences of metazoan parasites and commensals determined. The survey revealed larval stages of three species of parasite, Microphallus sp....

Coastal landscapes with extensive intertidal mudflats provide non-breeding habitat for Arctic shorebirds. Few attempts have been made to develop and test landscape-level models predicting the intertidal distribution of these birds. We modelled the distribution of a Holarctic species, Dunlin (Calidris alpina), at a hemispherically important non-bree...

The dimorphic chelae from both sexes and a wide size range of American lobsters, Homarus americanus, were studied with respect to allometry, mechanical advantage, closer muscle apodeme area and occlusive surface morphology. The maximum forces produced by the crusher and cutter chelae were estimated by an in vitro and a static in vivo technique. Ano...

La variación en los perfiles de metabolitos del plasma puede brindar información sobre el estado fisiológico y sobre las tasas relativas de cambio de peso en las aves silvestres que son capturadas sólo una vez. Esta técnica puede ser usada para comparar las tasas de cambio de peso entre poblaciones o sitios con relación a la calidad del hábitat. Co...

Resumen.—Examinamos la influencia de factores ecológicos y de comportamiento sobre el éxito reproductivo de Catharus frantzii en ambientes contiguos de bosques primarios y secundarios durante las temporadas reproductivas de 2000 a 2003 en las tierras altas centrales de Chiapas, México. La densidad de aves reproductivas fue más alta en bosques prima...

We used long-term population data for the ruddy-capped nightingale thrush (Catharus frantzii Cabanis), to examine the influence of forest conditions on annual productivity, survival and growth rate (λ) in a montane forest reserve of Chiapas, southern Mexico, from 1995 to 2003. Productivity was higher in primary, mature forest than in secondary, you...

To migrate successfully, birds need to store adequate fat reserves to fuel each leg of the journey. Migrants acquire their fuel reserves at stopover sites; this often entails exposure to predators. Therefore, the safety attributes of sites may be as important as the feeding opportunities. Furthermore, site choice might depend on fuel load, with lea...

Western sandpipers (Calidris mauri (Cabanis, 1857)) exhibit slight female-biased sexual size dimorphism (5%) but disproportionate bill length dimorphism (15.9%). We test two predictions of the niche differentiation hypothesis at two wintering sites in Mexico with uniform western sandpiper densities, and use sex ratio as an index of intersexual comp...

We show that a higher vertebrate can graze surficial intertidal biofilm, previously only considered a food source for rasping invertebrates and a few specialized fish. Using evidence from video recordings, stomach contents, and stable isotopes, we describe for the first time the grazing behavior of Western Sandpipers (Calidris mauri) and estimate t...

Declines in avian populations are a global concern, particularly for species that migrate between Arctic-temperate and tropical locations. Long-term population studies offer opportunities to detect and document ecological effects attributable to long-term climatic cycles such as the El Nino/Southern Oscillation (ENSO). In this study, we report poss...

We report that a latitudinal cline in intertidal food distribution is associated with the nonbreeding distribution of the Western Sandpiper (Calidris mauri). This novel result is the first to demonstrate a clear relationship between patterns of differential nonbreeding distribution and food availability for any shorebird species. Within each age cl...

Variation in plasma metabolite profiles can provide information on physiological state and relative rates of mass change in free-living birds caught only once, and this technique could be used to compare rates of mass change (fattening) among populations or sites in relation to habitat quality. We compared plasma metabolite levels, as an index of r...

Foraging behaviour in birds co-varies with bill morphology. Shorebirds exhibit pronounced inter- and intra-specific variation in bill length and shape as well as in foraging behaviour. Pecking, or feeding on epifaunal intertidal invertebrates, is associated with a straight bill, while probing, feeding on infaunal prey, is facilitated by bill curvat...

Sandpipers of the genus Calidris tend to have similar body shapes and use narrow, tubular bills to feed on invertebrates in aquatic habitats over an extensive migratory range. Highly plastic foraging behaviours have been displayed but the associations between diet and feeding mechanics are less well understood. Here, scanning electron microscopy wa...

Migrating Western Sandpipers, Calidris mauri (Cabanis, 1857), observed feeding at an intertidal stopover site on the Fraser River delta, British Columbia, shifted their foraging mode from surface-pecking to probing over a 3-week period in April and May. We tested possible mechanisms to account for the field observations. Using control and shorebird...

We examined the responses of two tropical sea urchins, Lytechinus variegatus and Tripneustes ventricosus, to cues from predators, simulated predation events and food. Cues released from damaged conspecifics, heterospecifics and heteroclassics (holothurian) were used to simulate predation events in field experiments. Responses to the presence of sea...

Western sandpiper (Calidris mauri) predation was examined by concurrent experiments and direct observations of foraging behaviour on high intertidal mudflats of the Fraser River estuary, British Columbia. Western sandpipers foraged by either “pecking” on the surface (64% of observational time) or probing into sediment (29%). The first experiment (p...

We investigated the influence of soft-shell clam (Mya arenaria) burial depth on red rock crab (Cancer productus) foraging behaviour. In laboratory tanks, crabs searched for and excavated clams buried at depths of 5, 10, and 15 cm. Handling time of prey was partitioned into excavation time, breaking time, and eating time. Prey excavation formed 23%...

We evaluate the potential impact of the European green crab Carcinus maenas (Linneaus) (Decapoda: Portunidae) on possible prey species in British Columbia, Canada, and Washington State, USA. This crab was first observed on the west coast of North America in San Francisco Bay, CA, in 1989. In early 1997, adult green crab were found in Coos Bay, Oreg...

We review the three major reproductive pathways displayed by snow crab, Chionoecetes opilio. Females can copulate in either a soft- or hard-shelled condition and also fertilize eggs with sperm stored in their spermathecae. Spermatophore partitioning and preservation mechanisms in the spermatheca plus postulated spermatophore removal abilities in ma...

A management strategy that involves issuing a varying number of temporary fishing licenses is proposed for new and expanding limited-entry fisheries. This strategy affords managers a means of stabilizing earnings per license and limiting increases in the cost of fishing during years of fluctuating stock abundance, Catch predictions are not required...

Histological, histochemical, ultrastructural, and microbiological techniques were used to elucidate the structure and function of the female reproductive system in the snow crab Chionoecetes opilio (O. Fabricius). The anatomy of the ovary and oviduct conform to that of other brachyuran species. The spermatheca comprises a dorsal (glandular) and a v...

The existing literature concerning reproduction of snow crab ( Chionoecetes opilio ) is critically reviewed and discussed in the context of recent conceptual paradigms and ongoing research. The functional anatomy of the male and female reproductive systems is presented and interpreted in terms of the various mating pathways available to this specie...

ABSTRACT To further elucidate the reproductive processes of the snow crab Chionoecetes opilio (O. Fabricius) the first and second gonopods of adult specimens were examined using scanning electron microscopy and histology. Surface features and setal types are described for both gonopods. The gonopods are highly modified compared to other brachyuran...

During 1981 and 1982, 933 Atlantic cod Gadus rrwrhoo and 119 thorny skate Raja radiata were collected off the northwestern coast of Cape Breton Island, Nova Scotia. Danish seines, jigs, gillnets, and trawls were used for sampling. Stomach contents were analyzed to investigate predator-prey relation­ ships between cod and snow crab Chionoecetes opil...

Defensive aggregation by Strongylocentrotus droebachiensis has been invoked as the fulcrum for the transformation of macroalgal beds into coralline barrens in the northwest Atlantic. We critically examined some of the mechanisms contributing to aggregation behavior by experimentally manipulating sea urchins, purported predators and food during autu...

Un crabe Cancer borealis mâle a été observé, tenant une femelle tournée à l'envers dans un embrassement de pré-copulation. Après 5 jours, la femelle s'est retournée et pendant une période additionnelle de 8 à 9 jours, jusqu'à la mue, elle était soit transportée contre le dessous du mâle ou simplement reposait sous ce dernier. L'approche de la mue a...

Foraging rate was highly variable among shore crabs of the same size category and for individual crabs from day to day. Possible physiological reasons for this variability are discussed. Shore crab foraging rate, both in terms of mussels eaten per day and energy intake per day, was estimated to be higher at 17°C than at 10°C. The shape of diet curv...

Mechanical aspects of predation by the shore crab, Carcinus maenas, on the edible mussel, Mytilus edulis, were examined. The shore crabs from the population studied utilized five distinct, largely size-related, mussel-opening techniques. Crushing the mussel umbone appeared the most successful opening method for medium-sized prey. Small mussels were...