Thermal and Hydrodynamic Environments Mediate Individual and Aggregative Feeding of a Functionally Important Omnivore in Reef Communities

Abstract

In eastern Canada, the destruction of kelp beds by dense aggregations (fronts) of the omnivorous green sea urchin, Strongylocentrotus droebachiensis, is a key determinant of the structure and dynamics of shallow reef communities. Recent studies suggest that hydrodynamic forces, but not sea temperature, determine the strength of urchin-kelp interactions, which deviates from the tenets of the metabolic theory of ecology (MTE). We tested the hypothesis that water temperature can predict short-term kelp bed destruction by S. droebachiensis in calm hydrodynamic environments. Specifically, we experimentally determined relationships among water temperature, body size, and individual feeding in the absence of waves, as well as among wave velocity, season, and aggregative feeding. We quantified variation in kelp-bed boundary dynamics, sea temperature, and wave height over three months at one subtidal site in Newfoundland to test the validity of thermal tipping ranges and regression equations derived from laboratory results. Consistent with the MTE, individual feeding during early summer (June-July) obeyed a non-linear, size- and temperature-dependent relationship: feeding in large urchins was consistently highest and positively correlated with temperature <12°C and dropped within and above the 12–15°C tipping range. This relationship was more apparent in large than small urchins. Observed and expected rates of kelp loss based on sea temperature and urchin density and size structure at the front were highly correlated and differed by one order of magnitude. The present study speaks to the importance of considering body size and natural variation in sea temperature in studies of urchin-kelp interactions. It provides the first compelling evidence that sea temperature, and not only hydrodynamic forces, can predict kelp bed destruction by urchin fronts in shallow reef communities. Studying urchin-seaweed-predator interactions within the conceptual foundations of the MTE holds high potential for improving capacity to predict and manage shifts in marine food web structure and productivity.

Effect of temperature on an alga‐grazer trophic transfer: A dual stable isotope (13C, 15N) labeling experiment

“…Strongylocentrotus droebachiensis evidenced a decrease in feeding rates above 15°C, which is close to the maximum summer temperature (16°C, Frey & Gagnon, 2015). Similarly in the lobster Jasus edwardsii, lower feeding and respiratory rates were observed above the upper thermal limit at 24°C (Thomas et al, 2000).…”

“…The lower metabolism at 20°C contrasts with the findings of several studies on diverse marine taxa (e.g., bivalves, gastropods, echinoderms), which showed higher feeding and respiration rates as the temperature increases (Cáceres‐Puig, Abasolo‐Pacheco, Mazón‐Suastegui, Maeda‐Martínez, & Saucedo, ; Carr & Bruno, ; Gooding et al, ; Noisette et al, ). However, a previous experiment on the high‐latitude urchin Strongylocentrotus droebachiensis evidenced a decrease in feeding rates above 15°C, which is close to the maximum summer temperature (16°C, Frey & Gagnon, ). Similarly in the lobster Jasus edwardsii , lower feeding and respiratory rates were observed above the upper thermal limit at 24°C (Thomas et al, ).…”

“…Temperature is one of the most important environmental factors affecting biological processes in marine ectothermic species (Nguyen et al, ; Uthicke, Liddy, Nguyen, & Byrne, ; Zuo, Moses, West, Hou, & Brown, ). Several studies demonstrated the effect of temperature on physiological processes, including feeding rates (Frey & Gagnon, ; Gooding, Harley, & Tang, ; Thomas, Crear, & Hart, ). However, the response to changes in temperature in terms of assimilation rates remains poorly documented, despite the importance of this process in species ecophysiology.…”

Plasticity in the antipredator behavior of the orange-footed sea cucumber under shifting hydrodynamic forces

“…The bedrock seabed at Bread and Cheese Cove is colonized by grazing-resistant, red coralline seaweeds (mainly Lithothamnion glaciale ). The green sea urchin, S. droebachiensis , maintains the biological communities in a “barrens” state ( sensu Lawrence 1975) for most of the year (Blain and Gagnon 2014; Frey and Gagnon 2015). We monitored sea cucumbers naturally distributed along a 110-m-long depth gradient ranging from the turbulent shallow environment at a rocky point on the north shore of the cove to the calmer deeper waters located near the middle of the cove to the south.…”

“…Activity level in sea cucumbers, like in many other ectothermic marine invertebrates, varies with water temperature (Angilletta et al. 2010; Frey and Gagnon 2015; Kühnhold et al. 2017; Tagliarolo et al.…”