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SAUCHYN, L.K., J.-S. LAUZON-GUAY, R.E. SCHEIBLING, 2011. Sea urchin fecal production and accumulation in a rocky subtidal ecosystem. Aquat. Biol., 13(3): 215-223 .
We used a spatial model of destructive grazing of kelp beds by dense aggregations (fronts) of sea urchins Strongylocentrotus droebachiensis, together with measures of sea urchin absorption efficiency and fecal degradation rate, to predict rates of fecal production and accumulation during the transition from a kelp bed to a barrens state in a rocky subtidal ecosystem of Nova Scotia, Canada. The rate of fecal production as dry mass reached 9.17 g m-12 d-1 at 10 yr after the formation of a grazing front, with associated rates of carbon and nitrogen production of 2.12 g C m-2 d-1 and 0.21 g N m-2 d-1. Fecal production rate exceeded the rates of physical, chemical, and microbial degradation, such that up to 193.6 g of feces, 70.2 g of C, and 4.0 g of N accumulated per linear m of front after 10 yr. The extent of sea urchin grazing fronts along the Atlantic coast of Nova Scotia was estimated at 280 km in 2000, which translates to a total fecal production rate of 6423 kg of feces d-1 and an accumulation of 54200 kg of feces after 10 yr of front formation, based on our model. This temporally variable flux of organic matter likely has a profound effect on adjacent deeper-water macrobenthic communities utilizing the feces as a food source.©2011 Inter-Research
LAUZON-GUAY, J.-S., D.A. LYONS, 2011. Reproducibility in simulation experiments : comment on Munguia et al. (2010). Mar. Ecol. Prog. Ser., 79: 275-287 .
In a recent article, Munguia et al. (2010; Mar Ecol Prog Ser 413:229–240) presented a spatially explicit mathematical model of competition among 4 sessile species of benthic invertebrates. We argue that, based on the description of the model, it is impossible to repeat the analysis without making numerous guesses and assumptions. Furthermore, the results do not correspond to the model as it is described. We highlight elements of the model formulation and description relating to dispersal, colonization, and competition that, if clarified, would help the reader to understand, evaluate, and extend the results of this study.©2011 Inter-Research
SCHEIBLING, R.E., J. -S. LAUZON-GUAY, 2010. Killer storms: North Atlantic hurricanes and disease outbreaks in sea urchins. Limnol. Oceanogr., 55(6): 2331-2338 .
An increase in the incidence of disease in various marine organisms over the past few decades has been linked to ocean climate change, In Nova Scotia, Canada, mass mortalities of sea urchins, due to an amoebic disease, are associated with tropical cyclones of relatively high intensity that pass close to the coast when water temperature is above a threshold for disease propagation. These conditions increase the likelihood of introduction and spread of a nonindigenous water-borne pathogen through turbulent mixing. Our analysis shows that the most deadly storms, in terms of the probability of a sea urchin mass mortality, have become more deadly over the past 30 years. We also found that storms have been tracking closer to the coast and that surface temperature has increased during the hurricane season. These trends are likely to continue with climate warming, resulting in a regional shift to a kelp bed ecosystem and the loss of the urchin fishery.©2010 American Society of Limnology and Oceanography, Inc.
LAUZON-GUAY, J.-S., R.E. SCHEIBLING, 2010. Spatial dynamics, ecological thresholds and phase shifts : modelling grazer aggregation and gap formation in kelp beds. Mar. Ecol. Prog. Ser., 403: 29-41 .
On the Atlantic coast of Nova Scotia, transitions between alternative states of the subtidal ecosystem, kelp beds and sea urchin barrens, occur on a decadal scale. To explore the process of urchin aggregation within kelp beds that leads to the shift to barrens, we developed a coupled map lattice model to simulate the spatial dynamics of kelp and green sea urchin Strongylocentrotus droebachiensis abundance over time. Our simulations show that the following factors can cause sea urchins to form grazing aggregations that create gaps in a kelp bed: (1) random movement by >60 % of sea urchins residing in the bed, (2) moderate to high levels of spatial variability in sea urchin recruitment (30 to 90 [urchins m-2]2), (3) localized aggregation of sea urchins (150 urchins m-2) amid a moderate to high background density of sea urchins within the kelp bed (>10 urchins m-2), with or without a chemotactic response of sea urchins to kelp, and (4) removal of kelp from areas >20 m2 (to simulate physical or biological disturbance, or harvesting). Gaps formed at random locations within the spatial domain and expanded and coalesced to form barrens in which sea urchins were randomly distributed. Sea urchins formed circular fronts around gaps in the kelp bed. The rate of advance of fronts (and increase in gap size) was linearly related to the density of sea urchins at the front. The duration of the transition to the barrens state decreased with increases in (1) the proportion (Pm) of sea urchins moving (from >6 yr for Pm = 0.8 to <2 yr for Pm = 1) and (2) the variance of sea urchin recruitment (from >5 yr for 30 [urchins m-2]2 to <3 yr for 90 [urchins m-2]2). Our findings support observations of gap formation within kelp beds that resulted in widespread destructive grazing on this coast in the late 1960s. Our model provides a predictive tool for the design of monitoring programs and field experiments to explore the underlying mechanisms of an ecosystem phase shift that has major ecological consequences.©2010 Inter-Research
SCHEIBLING, R.E., C. FEEHAN, J.-S. LAUZON-GUAY, 2010. Disease outbreaks associated with recent hurricanes cause mass mortality of sea urchins in Nova Scotia. Mar. Ecol. Prog. Ser., 408: 109-116 .
Field observations and laboratory experiments support the hypothesis that diseaseinduced mass mortality of the sea urchin Strongylocentrotus droebachiensis can be associated with hurricane events that introduce a pathogenic amoeba Paramoeba invadens to coastal waters. The temporal pattern of morbidity and mortality of sea urchins observed in a large embayment on the Atlantic coast of Nova Scotia following Hurricane Juan in September 2003 and Hurricane Bill in August 2009, and in laboratory infection experiments during the 2009 event, closely conformed to that expected based on the known temperature-dependent dynamics of this amoebic disease.©2010 Inter-Research
LAUZON-GUAY, J.-S., R.E. SCHEIBLING, 2009. Food dependent movement of periwinkles (Littorina littorea) associated with feeding fronts. J. Shellfish Res., 28(3): 581-587 .
Consumer aggregations have the potential to drastically change the distribution and availability of resources. One form of aggregation observed in marine benthic invertebrates is the feeding front: a dense band of consumers that travels in a directional manner through a food patch, leaving a cleared area behind it. By artificially creating spatial heterogeneity in the distribution of a filamentous green alga, the formation of a feeding front of periwinkles Littorina littorea was induced on a rocky intertidal shore. The position of the front, the density of snails that comprised it, and the movement of individual snails in and around the front were monitored over a period of 14 days. During that period, the front advanced at an average speed of 2.25 cm d-1 and the density of snails in the front varied between 10 and 24 snails 100 cm-2. Temporal variation in snail density was negatively correlated with wave action. Snails on the trailing edge of the front or on bare rock behind the front exhibited directional movement towards the front, but snails in the front moved shorter distances than those on bare rock. These results support previous findings of resource-dependent movement as a causal mechanism of front formation in marine benthic habitats.©2010 National Shellfisheries Association
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