Spatial dynamics of the green sea urchin Strongylocentrotus droebachiensis in food‑depleted habitats

Abstract

Supplement 1 Methods 1. Collection and maintenance of urchins Urchins used in Experiment 1 and Experiment 2 were hand collected by divers at depths of 3 to 6 m in the barrens at Bread and Cheese Cove (BCC) in January, June, and July 2012. They were transported in large containers filled with seawater to the Ocean Sciences Centre (OSC) of Memorial University of Newfoundland. Upon arrival at the OSC (<5 hours after collection), urchins were transferred to 330-L holding tanks supplied with ambient flow-through seawater pumped in from a depth of ∼5 m in the adjacent embayment, Logy Bay, and sorted by size. All individuals with a test diameter of 40 to 60 mm that clung or displaced readily in the tanks, indicating that the podia functioned normally, were kept for the experiments. This size class was chosen because individuals of this size are sexually mature (Himmelman 1986, Raymond & Scheibling 1987, Munk 1992) therefore eliminating potential behavioral differences between mature and non-mature individuals, and it was the most frequent size class at times of collection. Each holding tank contained 200 urchins. Urchins used in Experiment 1 were not fed because urchin feeding in eastern Canada at the time the experiment was conducted (January) is typically low (Scheibling & Hatcher 2007, P. Gagnon, unpublished data) and feeding them could have altered metabolic activity and behavior. Urchins used in Experiment 2 were fed every two days with 25 g (wet weight) of freshly collected Alaria esculenta blades cut into pieces of ∼2.5 x 2.5 cm to standardize hunger levels at a time of year (June and July) when feeding in eastern Canada markedly increases (Scheibling et al. 1999, Gagnon et al. 2004, Lauzon-Guay & Scheibling 2007, Frey & Gagnon 2015). Urchin feces and unconsumed kelp were removed from the holding tanks every two days. Water temperature in the holding tanks prior to trials in Experiment 1 and Experiment 2 was measured with a temperature logger with a precision of ±0.5 °C (HOBO Pendant; Onset Computer Corporation). It averaged 4.1 °C (±0.2) and 10.0 °C (±0.9), respectively.

Long-term study of behaviors of two cohabiting sea urchin species, Mesocentrotus nudus and Strongylocentrotus intermedius, under conditions of high food quantity and predation risk in situ

“…It is known that with increasing water velocity (higher than approximately 15 cm s -1 ), sea urchins decrease their displacement and cease feeding both under laboratory (Kawamata, 1998; Frey & Gagnon, 2016; Cohen-Rengifo et al, 2018; Tamaki, Muraoka & Inoue, 2018) and field (Lissner, 1980; Dance, 1987; Siddon & Witman, 2003; Dumont, Himmelman & Russell, 2006; Dumont, Himmelman & Robinson, 2007) conditions. Escape behavior was also observed in laboratory flume experiments: at flow velocity ≤30 cm s −1 , sea urchins moved in a downstream direction whereas at 35–45 cm s −1 , individuals moved in an upstream direction (Morse & Hunt, 2013; Cohen-Rengifo et al, 2018).…”

Mechanisms of stability of rhodolith beds: sedimentological aspects

“…Interestingly, water flow regimes, even during that time of year (September to December) when wave energy typically increases in southeastern Newfoundland (Brodie et al 1993, Blain & Gagnon 2013, Frey & Gagnon 2016, did not differ between depths. In fact, water flow was generally low throughout the survey, with a few peaks between 0.2 and 0.3 m s -1 at 12 m that lasted only a few hours in November.…”

“…However, since Marrack's pioneering demonstration of bioturbation in a Californian rhodolith bed (Marrack 1999 tens of podia to displace, but unlike the common sea star, the green sea urchin also moves large numbers of spines as it displaces, often bracing them into cracks and crevices to gain purchase (Frey & Gagnon 2016). Moreover, adult-sized common sea stars like those in the present study are considerably larger than rhodoliths and their five arms largely conform to the shape of objects on which they displace.…”

Spatially explicit modelling of kelp-grazer interactions: a seascape approach for effective habitat enhancement using artificial reefs

“…Scheibling and Hamm (1991) reported that sea urchins greatly favored clusters of boulders over an adjacent cobble bed, since these microhabitats offered shelter form predation. On more uniform bedrock bottoms, S. droebachiensis also prefers microhabitats that favor anchorage, such as crevices, troughs and boulders, in the attempt to minimize dislodgement (Frey & Gagnon, 2016). Whether to avoid predation or dislodgement, structurally complex microhabitats drove the urchin distribution at our study site on the rocky matrix but also on sandy bottoms by locally enhancing the heterogeneity.…”