Biology subjects

Scrosati, R. A.

Publications and source records attributed to Scrosati, R. A..

5 recordsLinked to original sources

bioRxiv2017

Recruitment and abundance of intertidal barnacles and mussels along the Atlantic Canadian coast: pelagic influences and relationships with predator abundance

Benthic species from rocky intertidal systems are irregularly distributed along marine coastlines. Nearshore pelagic conditions often help to explain such variation, but most such studies have been done on eastern ocean boundary coasts. Through a large-scale mensurative study, we investigated possible benthic-pelagic coupling along the Atlantic coast of Nova Scotia, a western ocean boundary coast. We studied the high intertidal zone of nine wave-exposed bedrock locations spanning 415 km of coastline from north to south. At each location in the spring, we measured the recruitment of barnacles and mussels, the two main filter-feeding invertebrates. Recruitment varied irregularly along the coast. Satellite data on coastal phytoplankton and particulate organic carbon (food for intertidal filter-feeders and their pelagic larvae) and in-situ data on seawater temperature explained, to varying degrees, the geographic structure of recruitment. In turn, the summer abundance of both filter-feeders was positively related to their spring recruitment. Ultimately, predator (dogwhelk) abundance was positively related to the recruitment and/or abundance of barnacles and mussels (the main prey of dogwhelks). These results are consistent with bottom-up forcing influencing intertidal community structure on this coast. Sea ice may also influence this predator-prey interaction. Drift ice leaving the Gulf of St. Lawrence in late winter disturbed the northern locations surveyed on the Atlantic coast, making barnacles (owing to their high spring recruitment) the only food source for dogwhelks at such places. Investigating the oceanographic drivers of pelagic food supply and seawater temperature should help to further understand how this large metacommunity is organized.

ecology↗

bioRxiv2017

Nonconsumptive predator effects on prey demography: Dogwhelk cues decrease benthic mussel recruitment

Predators have often been shown to have nonconsumptive effects (NCEs) on prey behaviour, but the demographic consequences for prey remain poorly known. This is important to understand because demography influences the impact of a species in its community. We used an intertidal predator-prey system to investigate predator NCEs on prey recruitment, a key demographic process for population persistence. Pelagic mussel larvae are known to avoid waterborne cues from dogwhelks, which prey on intertidal mussels. Through a field experiment done in Atlantic Canada, we manipulated the presence of dogwhelks in intertidal habitats during the mussel recruitment season. We measured mussel recruitment in collectors that could be reached by waterborne dogwhelk cues but not by dogwhelks themselves. We found that the nearby presence of dogwhelks significantly decreased mussel recruit density. A previous study done in the same habitats under the same experimental conditions showed that dogwhelk cues also limit the recruitment of barnacles, another prey item for dogwhelks. However, such NCEs were four times stronger than those observed for mussel recruitment. This difference relates well to the higher ability of mussels to escape predation, as mussels can relocate while barnacles cannot. Therefore, basic features of natural history may be useful to predict predator NCEs on prey recruitment.

ecology↗

bioRxiv2017

Predator-induced shell plasticity in mussels hinders predation by drilling snails

Sessile invertebrate prey that detect waterborne predator cues often respond by strengthening their structural defenses. Experimental evidence of the functional significance of such modifications using field-raised organisms is lacking. This study addresses that gap using intertidal mussels and predatory dogwhelks from Atlantic Canada. During the spring and summer of 2016, we ran a field experiment that manipulated dogwhelk presence to test their nonconsumptive effects on mussel traits. Dogwhelk cues elicited thickening at the lip, centre, and base of mussel shells, although simultaneously limiting shell growth in length. As shell mass was unaffected by dogwhelk presence, a trade-off between shell thickening and elongation was revealed. Thickening was strongest at the thinnest parts of the shell. Using the field-raised organisms, a lab experiment found that dogwhelks took, on average, 55 % longer to drill and consume mussels previously exposed to dogwhelk cues than mussels grown without such a cue exposure. Dogwhelks drilled at the thinnest parts of the shell but, nonetheless, the consumed cue-exposed mussels had thicker shells at the borehole than the consumed mussels not exposed to cues, which likely explains the observed difference in handling time. As handling time normally decreases predation success, this study indicates that the plastic structural modifications in mussels triggered by dogwhelk cues in the field hinder predation by these drilling predators.

ecology↗

bioRxiv2017

Limitation Of Dogwhelk Consumption Of Mussels By Crab Cues Depends On Dogwhelk Density And Cue Type

Predator nonconsumptive effects (NCEs) on prey activity are common in nature. Upon sensing predator cues, a common prey response is to reduce feeding to avoid being detected by predators. Using an aquatic system, this study investigated how prey density and predator cue type affect predator NCEs on prey feeding. Prey density was investigated because, as it increases, the individual risk of being preyed upon decreases, which may reduce NCEs if prey can detect conspecifics. Predator cue type was investigated because waterborne cues would trigger weaker NCEs than waterborne and tactile cues combined, as predation risk may be perceived by prey to be stronger in the second case. Specifically, a factorial experiment tested the hypotheses that (i) increasing dogwhelk (prey) density reduces the limitation that crab (predator) chemical cues can have on dogwhelk consumption of mussels and that (ii) chemical and tactile crab cues combined limit dogwhelk feeding more strongly than chemical crab cues alone. The results broadly supported these hypotheses. On the one hand, crab chemical cues limited the per-capita consumption of mussels by dogwhelks at a low dogwhelk density, but such NCEs disappeared at intermediate and high dogwhelk densities. On the other hand, the combination of chemical and tactile cues from crabs caused stronger NCEs, as dogwhelk consumption of mussels was negatively affected at all three dogwhelk densities. The structurally complex mussel beds may provide not only food for dogwhelks but a refuge from crab predation that allows dogwhelk density to limit crab NCEs when mediated by waterborne cues. Overall, this study suggests that prey evaluate conspecific density when assessing predation risk and that the type of cues prey are exposed to can affect their interpretation of risk.

animal behavior and cognition↗

bioRxiv2016

Community-level facilitation by macroalgal foundation species peaks at an intermediate level of environmental stress

This paper examines how community-level facilitation by macroalgal foundation species changes with environmental stress. In rocky intertidal habitats, abiotic stress (mainly due to desiccation and thermal extremes during low tides) increases sharply with elevation because of tide dynamics. A previous study done on the Atlantic coast of Nova Scotia (Canada) showed that, at low elevations, where conditions are benign because low tides are brief, fucoid algal canopies (Ascophyllum nodosum and Fucus spp.) do not affect the structure of benthic communities. However, at middle and high elevations, where low tides last longer, fucoid canopies limit abiotic extremes near the substrate and, in that way, increase the richness of benthic communities. Richness was measured as the number of benthic algal (except fucoids) and invertebrate species found in replicate quadrats. Using the published data from that study, the present study compares the intensity of facilitation and its importance (relative to all other sources of variation in richness) between middle and high elevations, which represent intermediate and high stress, respectively. Facilitation intensity was calculated as the percent increase in benthic richness between quadrats with low canopy cover and quadrats with high canopy cover, while the importance of facilitation was calculated as the percentage of observed variation in richness that was explained by canopy cover. Data for a total of 688 quadrats surveyed along 350 km of coastline were used. The analyses revealed that both the intensity and importance of facilitation were greater at middle elevations than at high elevations. As canopies were previously found not to affect benthic communities at low elevations, this study indicates that the facilitation-stress relationship viewed at the community level is unimodal for this marine system. Such a trend was already found for some terrestrial systems involving canopy-forming plants as foundation species. Thus, this unimodal pattern may be ubiquitous in nature and, as further studies refine it, might help to predict community-level facilitation depending on environmental stress.

ecology↗