Ecological and environmental context shape the differential effects of a facilitator in its native and invaded ranges

Impacts of artificial light at night on the early life history of two ecosystem engineers

Sessile marine invertebrates play a vital role as ecosystem engineers and in benthic-pelagic coupling. Most benthic fauna develop through larval stages and the importance of natural light cycles for larval biology and ecology is long-established. Natural light-dark cycles regulate two of the largest ocean-scale processes that are fundamental to larvae's life cycle: the timing of broadcast spawning for successful fertilization and diel vertical migration for foraging and predator avoidance. Given the reliance on light and the ecological role of larvae, surprisingly little is known about the impacts of artificial light at night (ALAN) on the early life history of habitat-forming species. We quantified ALAN impacts on larval performance (survival, growth, development) of two cosmopolitan ecosystem engineers in temperate marine ecosystems, the mussel Mytilus edulis and the barnacle Austrominius modestus. Higher ALAN irradiance reduced survival in both species (57% and 13%, respectively). ALAN effects on development and growth were small overall, and different between species, time-points and parentage. Our results show that ALAN adversely affects larval survival and reiterates the importance of paternal influence on offspring performance. ALAN impacts on the early life stages of ecosystem engineering species have implications not only for population viability but also the ecological communities that these species support. This article is part of the theme issue 'Light pollution in complex ecological systems'.

Not just range limits: Warming rate and thermal sensitivity shape climate change vulnerability in a species range center

Climate change manifests unevenly across space and time and produces complex patterns of stress for ecological systems. Species can also show substantial among-population variability in response to environmental change across their geographic range due to evolutionary processes. Explanatory factors or their proxies, such as temperature and latitude, help parse these sources of environmental and intraspecific variability; however, overemphasizing latitudinal trends can obscure the role of local environmental conditions in shaping population vulnerability to climate change. Focusing on the geographic center of a species range to disentangle latitude, we test the hypothesis that populations from warmer regions of a species range are more vulnerable to ocean warming. We conducted a mesocosm experiment and field reciprocal transplant with four populations of a marine snail, Nucella lamellosa, from two regions in British Columbia, Canada, that differ in thermal characteristics: the Central Coast, a cool region, and the Strait of Georgia, one of the warmest regions of this species' range and one that is warming faster than the Central Coast. Populations from the Strait of Georgia experienced growth reductions at contemporary summertime seawater temperatures in the laboratory and showed stark reductions in survival and growth under future seawater conditions and when outplanted at their native transplant sites. This indicates a high vulnerability to ocean warming, especially given the faster rate of ocean warming in this region. In contrast, populations from the cooler Central Coast demonstrated high performance at contemporary seawater temperatures and high growth and survival in projected future seawater temperatures and at their native outplant sites. Given their position within the geographic center of N. lamellosa's range, extirpation events in the vulnerable Strait of Georgia populations could compromise connectivity within the metapopulation and lead to gaps across this species' range. Overall, our study supports predictions that populations from warm regions of species ranges are more vulnerable to environmental warming, suggests that the Strait of Georgia and other inland or coastal seas could be focal points for climate change effects and ecological transformation, and emphasizes the importance of analyzing climate change vulnerability in the context of regional environmental data and throughout a species' range.

Extreme heatwave drives topography-dependent patterns of mortality in a bed-forming intertidal barnacle, with implications for associated community structure

Heatwave frequency and intensity will increase as climate change progresses. Intertidal sessile invertebrates, which often form thermally benign microhabitats for associated species, are vulnerable to thermal stress because they have minimal ability to behaviourally thermoregulate. Understanding what factors influence the mortality of biogenic species and how heatwaves might impact their ability to provide habitat is critical. Here, we characterize the community associated with the thatched barnacle, Semibalanus cariosus (Pallass, 1788), in British Columbia (BC), Canada. Then, we investigate what site-level and plot-level environmental factors explained variations in barnacle mortality resulting from an unprecedented regional heatwave in BC, Canada. Furthermore, we used a manipulative shading experiment deployed prior to the heatwave to examine the effect of thermal stress on barnacle survival and recruitment and the barnacle-associated community. We identified 50 taxa inhabiting S. cariosus beds, with variations in community composition between sites. Site-scale variables and algal canopy cover did not predict S. cariosus mortality, but patch-scale variation in substratum orientation did, with more direct solar irradiance corresponding with higher barnacle mortality. The shading experiment demonstrated that S. cariosus survival, barnacle recruitment, and invertebrate community diversity were higher under shades where substratum temperatures were lower. Associated community composition also differed between shaded and non-shaded plots, suggesting S. cariosus was not able to fully buffer acute thermal stress for its associated community. While habitat provisioning by intertidal foundation species is an important source of biodiversity, these species alone may not be enough to prevent substantial community shifts following extreme heatwaves. As heatwaves become more frequent and severe, they may further reduce diversity via the loss of biogenic habitat, and spatial variation in these impacts may be substantial.

Ecological and environmental context shape the differential effects of a facilitator in its native and invaded ranges

Invasive species often exhibit disproportionately strong negative effects in their introduced range compared to their native range, and much research has been devoted to understanding the role of shared evolutionary history, or lack thereof, in driving these differences. Less studied is whether introduced species, particularly those that are important as facilitators in their native range, have persistent positive effects in their invaded range despite a lack of a shared evolutionary history with the invaded community. Here, we manipulated the density of a habitat-forming facilitator, the high intertidal acorn barnacle Balanus glandula, factorially with herbivore density in its native range (Bluestone Point, British Columbia, Canada) and invaded range (Punta Ameghino, Chubut Province, Argentina) to determine how this facilitator differentially affects associated species at these two locations. Given that high intertidal species at Punta Ameghino (PA) are evolutionarily naïve to barnacles, we predicted that the positive effects of B. glandula at PA would be absent or weak compared to those at Bluestone Point (BP). However, we found that B. glandula had an equally positive effect on herbivore biomass at PA compared to BP, possibly because the moisture-retaining properties of barnacle bed habitats are particularly important in seasonally dry Patagonia. Barnacle presence indirectly decreased ephemeral algal cover at BP by increasing grazer pressure, but barnacles instead facilitated ephemeral algae at PA. In contrast, B. glandula increased perennial algal cover at BP, but generally decreased perennial algal cover at PA, likely due to differences in dominant algal morphology. Though our experiment was limited to one location on each continent, our results suggest that shared evolutionary history may not be a prerequisite for strong facilitation to occur, but rather that the nature and strength of novel species interactions are determined by the traits of associated species and the environment in which they occur.