Ladd E. Johnson

Ladd E. Johnson
Laval University | ULAVAL · Department of Biology

Ph.D. Univ. of Washington '89

About

97
Publications
19,979
Reads
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4,297
Citations
Citations since 2017
19 Research Items
1540 Citations
2017201820192020202120222023050100150200250
2017201820192020202120222023050100150200250
2017201820192020202120222023050100150200250
2017201820192020202120222023050100150200250
Additional affiliations
April 1995 - present
Laval University
January 1989 - August 1990
Stanford University
Education
September 1981 - April 1989
September 1977 - June 1980
Oregon State University
Field of study
  • Biology

Publications

Publications (97)
Article
Full-text available
Ice scouring is one of the strongest agents of disturbance in nearshore environments at high latitudes. In depths, less than 20 m, grounding icebergs reshape the soft-sediment seabed by gouging furrows called ice pits. Large amounts of drift algae (up to 5.6 kg/m2) that would otherwise be transported to deeper water accumulate inside these features...
Article
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The establishment of non-indigenous species in the Antarctic, an ecosystem isolated for millions of years, could dramatically alter its unique and endemic biota. In coastal waters, calcified species (e.g., echinoderms, gastropods, bivalves) of benthic communities will be particularly vulnerable to shell-crushing (i.e., durophagous) predators such a...
Article
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Spatially concentrated resources result in patch‐based foraging, wherein the detection and choice of patches as well as the process of locating and exploiting resource patches involve moving through an explicit landscape composed of both resources and barriers to movement. An understanding of behavioral responses to resources and barriers is key to...
Article
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Cycling of organic carbon in the ocean has the potential to mitigate or exacerbate global climate change, but major questions remain about the environmental controls on organic carbon flux in the coastal zone. Here, we used a field experiment distributed across 28° of latitude, and the entire range of 2 dominant kelp species in the northern hemisph...
Article
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The coastal zone of the Canadian Arctic represents 10% of the world’s coastline and is one of the most rapidly changing marine regions on the planet. To predict the consequences of these environmental changes, a better understanding of how environmental gradients shape coastal habitat structure in this area is required. We quantified the abundance...
Article
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The choice of the duration and frequency of sampling to detect relevant patterns in field experiments or for environmental monitoring is always challenging since time and material resources are limited. In practice, duration and frequency of sampling are often chosen based on logistical constraints, experience, or practices described in published w...
Article
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The assessment of natural ecosystem status is a fundamental premise to enable environmental management at local scales to maintain ecosystem functioning, services and resilience. Ecologists have developed many biological and environmental indices to inform and support environmental management and policies. To promote efficient use of resources, exi...
Article
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Climate change is transforming marine ecosystems through the expansion and contraction of species’ ranges. Sea ice loss and warming temperatures are expected to expand habitat availability for macroalgae along long stretches of Arctic coastlines. To better understand the current distribution of kelp forests in the Eastern Canadian Arctic, kelps wer...
Article
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Sea stars often function as keystone predators in food webs of intertidal and subtidal communities, especially in temperate and sub-polar regions. In South America the sea star Cosmasterias lurida is distributed along both the Atlantic and Pacific coasts of Patagonia and is one of the most conspicuous and abundant benthic predators in the shallow s...
Article
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The relationship between larval supply and settlement is an integral part of the demographic processes of benthic marine organisms that determine their distribution at subsequent life stages. In ascidians, a strong positive relationship between larval supply and settlement has been previously documented, but only at small spatial scales (one locati...
Data
This dataset contains data described in the paper entitled 'Larval supply is a limited determinant of settlement at mesoscales across an anthropogenic seascape'. Data include larval abundance and recruitment densities of a non-native colonial ascidian, Botryllus schlosseri (Pallas, 1766), in a marina in Ben Eoin, Nova Scotia, Canada.
Article
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Global biodiversity is both declining and being redistributed in response to multiple drivers characterizing the Anthropocene, including synergies between biological invasions and climate change. The Antarctic marine benthos may constitute the last biogeographic realm where barriers (oceanographic currents, climatic gradients) have not yet been bro...
Article
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The rockweed Ascophyllum nodosum is a dominant component of intertidal communities across the North Atlantic Ocean, providing both habitat and primary productivity to nearshore ecosystems. Commercial exploitation of this species is widespread and typically involves cutting the distal portion of fronds thereby permitting regrowth by lateral branchin...
Article
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Herbivory fundamentally shapes ecosystem functioning by influencing the abundance and distribution of plants. Whereas a great deal of attention has been given to factors that influence rates of primary productivity (e.g., light, temperature and nutrients), considerably less attention has been given to factors governing herbivory rates. In the marin...
Article
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Increasing rates of invasion have led to shifts in dominance, and even replacement, of nonindigenous species. Shifts in invader dominance from the Zebra Mussel (Dreissena polymorpha) to a functionally similar and closely related species, the Quagga Mussel (Dreissena rostriformis bugensis), have occurred in several European and North American water...
Article
Coralline algae are conspicuous members of many marine assemblages, especially those characterized by intense grazing pressure. We explored whether articulated species, especially Corallina vancouveriensis, depend on grazing invertebrates to both establish and flourish in an exposed rocky intertidal setting, and whether this plant-grazer relationsh...
Article
Aux latitudes moyennes, les grandes algues sont une composante essentielle des ecosystemes cotiers comme source de nourriture et d’habitat pour les communautes benthiques. Les assemblages de macroalgues dans l’ecosysteme marin du Saint-Laurent (EMSL) sont largement domines par les fucales (Fucus, Ascophyllum) dans l’etage mediolittoral et par les l...
Article
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Knowledge of urchin age structure is crucial for understanding their ecosystem impacts and improving their management. In sclerochronology, translucent and opaque growth bands (TGB, OGB) in urchin ossicles are used to estimate age. An essential premise for using this technique is that one TGB and one OGB are formed every year, independent of urchin...
Article
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Knowledge of the potential distribution (i.e. abundance and spatial extent) of an invasive species is important to estimating its potential impacts on recipient communities. Most previous studies have focused on the potential spatial extent of invasive species populations at regional scales, but little is known on how species successfully recruit a...
Poster
Full-text available
Titre de l'affiche : La diffusion des connaissances sur les risques et les stratégies de surveillance pour les espèces aquatiques envahissantes dans les ports canadiens de l'Arctique. Résumé de la présentation : Natural barriers to the establishment of aquatic invasive species (AIS) in Arctic Canada are rapidly being reduced by climate change and...
Article
Aim Ecological maps are increasingly used to support marine management and conservation. However, the biological datasets used to produce these maps are typically limited to taxonomic groups identified to the specific taxonomic levels available. Ecological units should, however, reflect the broader marine ecosystem, independent of the datasets used...
Article
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Secondary spread largely determines the distribution and success of invasive species and depends ultimately on the capacity of the invader to disperse and colonise over multiple scales. Spread of the invasive seaweed Codium fragile ssp. fragile (Codium) can occur through the dispersal of vegetative fragments, which can be buoyant or non-buoyant dep...
Poster
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The use of settlement plates and the collection of plankton samples are common methods to monitor for invasive tunicates species. The determination of an optimal depth range for monitoring can be a time- and cost-effective strategy to increase the probability of species detection (larval supply and recruitment being proxies) given that species pres...
Article
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As many marine invertebrates have a dispersive planktonic phase, the spatial scale of demographic connectivity among local populations remains a key, but elusive, parameter driving population and metapopulation dynamics. Temporal variation in the scale of connectivity remains, however, largely undocumented despite its recognized importance for pred...
Article
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A pronounced, widespread and persistent regime shift among marine eco-systems is observable on temperate rocky reefs as a result of sea urchin overgrazing. Here, we empirically define regime-shift dynamics for this grazing system which transitions between productive macroalgal beds and impoverished urchin barrens. Catastrophic in nature, urchin ove...
Article
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A pronounced, widespread and persistent regime shift among marine ecosystems is observable on temperate rocky reefs as a result of sea urchin overgrazing. Here, we empirically define regime-shift dynamics for this grazing system which transitions between productive macroalgal beds and impoverished urchin barrens. Catastrophic in nature, urchin over...
Article
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As the number of introductions of non-indigenous species (NIS) continues to rise, ecologists are faced with new and unique opportunities to observe interactions between species that do not naturally co-exist. These interactions can have important implications on the invasion process, potentially determining whether NIS become widespread and abundan...
Article
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For bivalves, somatic growth is often inferred from shell measurements alone. However, shell growth may not always reflect changes in soft tissue due to confounding factors such as seasonal or ontogenetic asynchrony between shell and tissue, flexible energy allocation, or population differences. This study compares the relationship between shell gr...
Article
Knowledge of dispersal and establishment during the early stages of invasion is essential for allocating monitoring effort, detecting nascent populations and predicting spread. The scarcity of these data, however, provides little guidance for monitoring programs. Here we present data on the adult distribution and the subsequent pattern of larval re...
Article
Full-text available
Recruitment has often been cited as a key factor regulating population abundance and community structure in benthic marine ecosystems, where the life cycle of many species includes a dispersive planktonic phase. Still, the patterns and causes of temporal heterogeneity in the recruitment process, from daily to annual scales, are poorly understood fo...
Article
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Bivalve aquaculture can influence coastal marine ecosystems by increasing organic material deposition, which, in turn, can have multiple direct and indirect effects on the surrounding benthic community. We assessed the influence of blue mussel Mytilus edulis aquaculture on the epibenthic macrofauna at 4 sites in Prince Edward Island, eastern Canada...
Article
The photosynthetic response of juvenile stages of the brown alga F. distichus subsp. edenatus (Fucales, Heterokontophyta) was examined at different tidal heights at an intertidal site located on the Gaspé Peninsula, Québec, Canada. During the low tide, we used pulse-amplitude modulated (PAM) fluorometry to examine the effective quantum yield (ΦPSII...
Article
Post-establishment spread of invasive species is a major determinant of their impact, but the spatial pattern and temporal rhythm of secondary spread are often poorly known or understood. Here we examine the spread of the European rockweed Fucus serratus over 1,500km of shoreline after its initial discovery in Pictou, Nova Scotia (Canada) in 1868....
Article
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Supplementary information to: Non-natives: 141 scientists object Full list of co-signatories to a Correspondence published in Nature 475, 36 (2011); doi: 10.1038/475036a. Daniel Simberloff University of Tennessee, Knoxville, Tennessee, USA. dsimberloff@utk.edu Jake Alexander Institute of Integrative Biology, Zurich, Switzerland. Fred Allendorf Univ...
Article
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The capacity for long-distance dispersal is an important factor in determining the spread of invasive species. For algae, positive buoyancy generally is correlated with increased dispersal potential, and the light environment has been previously identified as a possible determinant of buoyancy in several species. We examined the effect of light int...
Article
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Biological invasions can vary in the extent of their effects on indigenous communities but predicting impacts for particular systems remains difficult. In coastal marine ecosystems, the green seaweed Codium fragile ssp. fragile is a notorious invader with its reputation based on studies conducted largely on rocky shores. The green seaweed has recen...
Article
Warming of the planet has accelerated in recent years and is predicted to continue over the next century. Environmental consequences include increasing water temperatures, and evidence of ecological responses to current warming in marine coastal ecosystems is found in poleward shifts in the geographic range of species as well as changes in the comp...
Article
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ABSTRACT: The present study examined how species-specific attributes of the invasive alga Codium fragile ssp. fragile (hereafter Codium) and eelgrass Zostera marina influenced faunal assemblages associated with eelgrass ecosystems in îles de la Madeleine, eastern Canada. Direct association of species with Codium (<1 m) was evaluated and compared to...
Article
This paper presents a hydrodynamic study of the St. Lawrence Estuary's estuarine transition zone, a 100 km region where fresh water from the river mixes with salt water from the estuary. The circulation of the estuarine transition zone is driven by strong tides, a large river flow, and well‐defined salinity gradients. For this study, a three‐dimens...
Article
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The zebra mussel, Dreissena polymorpha, is widespread in the St. Lawrence River while the conspecific quagga mussel, Dreissena bugensis, is found only in the Lake Ontario outflow region of the river. This situation provided an opportunity to evaluate in situ environmental and interspecific heterogeneity in shell and tissue growth. Shell dry weight,...
Article
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Early invasions of the North American shore occurred mainly via deposition of ballast rock, which effectively transported pieces of the intertidal zone across the Atlantic. From 1773-1861, >880 European ships entered Pictou Harbor, Nova Scotia, as a result of emigration and trade from Europe. The rockweed Fucus serratus (1868) and the snail Littori...
Article
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The recruitment Of a In multi-species assemblage of fucoid algae, Ascophyllum nodosum (L.) Le Jolis, Fucus vesiculosus L., and F distichus L. ssp. edentatus (Pyl.) Powell, onto artificial substrata over different temporal and spatial scales was examined on a semi-exposed rocky shore in Quebec, Canada. Measurements were taken at daily (1 d), fortnig...
Article
1. Field experiments conducted in Lake Wawasee in 1995 and 1996 measured the response of shell growth of Dreissena polymorpha to environmental gradients. 2. Shell growth decreased with initial shell length in four mussel size classes ranging between 8 and 22 mm, and decreased with depth, with mussels in shallow water (<4 m) having growth rates near...
Article
Chl fluorescence during and immediately after low tide under four meteorological conditions was measured in embryos of three fucoid algae [Ascophyllum nodosum (L.) Le Jol., Fucus vesiculosus L., and Fucus distichus subsp. edentatus Bach. (Pyl.) H. T. Powell] vertically distributed in the intertidal zone in Québec, Canada. Artificial substrata with...
Article
Because zebra mussels spread rapidly throughout the eastern United States in the late 1980s and early 1990s, their spread to the western United States has been expected. Overland dispersal into inland lakes and reservoirs, however, has occurred at a much slower rate than earlier spread via connected, navigable waterways. We forecasted the potential...
Article
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The feeding ecology of 2 sympatric mysid species within the food web of the St. Lawrence Middle Estuary was studied to determine their trophic position and potential mechanisms of coexistence. These abundant predators were clearly distinguished by differences in foraging behaviour. In feeding experiments involving multi-prey assemblages, predation...
Article
We used a three-dimensional physical-biological model consisting of a Eulerian circulation model and a Lagrangian particle-tracking model, which included vertical sinking and swimming, to explore zooplankton retention in the estuarine transition zone of the St. Lawrence Estuary (SLETZ). To test the accuracy of the model, the results were temporally...
Article
We describe an easy and inexpensive way to determine whether intertidal microhabitats remain wet during tidal emersion. This new technique uses agarose beads (120 üm diameter when fully hydrated) that shrink in a graded fashion as they dry. The agarose beads allow variability in surface wetness to be gauged over distances of less than 1 mm. Describ...
Article
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Extrinsic factors such as the physical environment can control the activities of animals, but their effect on behaviour can vary substantially among individuals within a given population depending on more intrinsic factors such as differences in the need to search for food or mates. We examined the activity of the brooding intertidal gastropod Litt...
Article
The role of anti-herbivore organismal defenses in algae–herbivore interaction is frequently investigated without taking into account the potential role of environmental factors in mediating the interaction. Here we reexamine the interaction between the highly acidic, brown alga Desmarestia viridis and the green sea urchin, Strongylocentrotus droeba...
Article
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The zebra mussel, Dreissena polymorpha, has spread through eastern North American aquatic ecosystems during the past 15years. Whereas spread among navigable waterways was rapid, the invasion of isolated watersheds has progressed more slowly and less predictably. We examined the patterns of overland spread over multiple spatial and temporal extents...
Article
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Intertidal invertebrates are model organisms for examining the environmental control of life-history traits because of the sharp gradients in biological and physical factors found in their habitat, including wave action, temperature, food availability, and predation. However, the effect of a particular factor on ecological and evolutionary processe...
Article
The brown alga Agarum clathratum (Dumortier) is the only large, perennial, fleshy macrophyte commonly found on urchin-dominated barrens in the northwestern North Atlantic. We examined the spatial and temporal stability of A. clathratum stands and their impact on algal recruitment in the Mingan Islands, northern Gulf of St. Lawrence. The stands were...
Article
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Large numbers of the filter-feeding larval stage of zebra mussels (Dreissena polymorpha) (veligers) have been advected into the estuarine transition zone (ETZ) of the St. Lawrence River. In 1994, they became the dominant member of the tidal freshwater zooplankton assemblage of the ETZ (and subsequently the true estuarine assemblage) during summer m...
Article
Embryos of the fucoid alga Pelvetia fastigiata (J. Ag.) DeToni were outplanted into the intertidal zone to assess survival during the physical stress brought about by emersion during a single low tide. Survival varied among microhabitats. Under the adult Pelvetia canopy, survival of 6-h-, 24-h-, 48-h-, and 1-wk-old embryos was nearly 100%. Almost a...
Article
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We examined, over 2years, factors affecting the temporal stability of the lower limit of kelp beds (Alaria esculenta) at five subtidal sites in the Mingan Islands, northern Gulf of St. Lawrence. The position of the lower limit of the beds varied markedly among sites and over time and was largely controlled by the green sea urchin, Strongylocentrotu...
Article
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We examined the invertebrate assemblages associated with macroalgal canopies in the Mingan Islands (northern Gulf of St. Lawrence, eastern Canada) in the summer and fall of 2001. Invertebrates were sampled in patches or beds of 4 species of macroalgae (Alaria esculenta, Agarum cribrosum, Desmarestia viridis and Ptilota serrata) as well as in adjace...
Article
Although activity patterns are an important component of the ecology of animals as they search for food, mates and appropriate habitats, substantial variation can be observed even within a single population. The source of this variation is the combination of intrinsic and extrinsic factors acting at an individual level. We documented the activity p...
Article
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The invasion of the freshwaters of Belarus by the zebra mussel, Dreissena polymorpha (Pallas), began at least 200 years ago by the opening of shipping canals linking the Black Sea and Baltic Sea drainage basins. However, zebra mussels have invaded only 93 (16.8%) of 553 studied lakes; at least 20 of these lakes were invaded within in the past 30 ye...