Some effects of turbulence on the activity of the sea urchin Centrostephanus coronatus Verrill

We measured the movement and orientation of sea urchins at 2 sites in each of 4 habitats on urchin barrens in the northern Gulf of St. Lawrence, eastern Canada. We tagged the urchins measuring 25 to 70 mm in test diameter using a non-invasive technique involving a knot of fine monofilament thread tied around one spine. Smaller urchins (< 25 mm) were tagged by tightening a loop around the test. Daily displacement increased markedly going from large juveniles (measuring 10-15 mm in diameter) to small adults (15-20 mm) and from small adults to large adults (> 25-70 mm); however, no effect of size was detectable among large adults measuring from 25 to 70 mm. The increased movement with size was associated with a change in foraging, as gut analysis revealed a marked increase in the proportion of brown algae with increasing size. For large adults, the maximum net distance displaced per day varied among sites from 1.0 to 4.9 m d . Distance moved also varied with habitat, and was greater in habitats that were further from kelp beds. Orientation was random and individuals showed frequent reverses in direction from day to day. Hunger state did not affect displacement, as there was no difference in distance moved between starved and fed urchins which were released in the barrens. However, urchins transplanted from kelp beds to the barrens were less active than urchins removed from and returned to the barrens. The shifts in movement with size are probably important in determining the size structure of urchins at different depths. The great distance covered by larger urchins as they move over open surfaces in search of favourable resources probably leads to their increased numbers in shallow habitats where food is abundant. KEY WORDS: Strongylocentrotus droebachiensis · Movement · Foraging activity · Urchin barrens · TaggingResale or republication not permitted without written consent of the publisher

Section: Introductionmentioning

confidence: 99%

Daily movement of the sea urchin Strongylocentrotus droebachiensis in different subtidal habitats in eastern Canada

Dumont¹,

Himmelman²,

Russell³

2006

“…In common with other diadematid sea urchins (Nelson & Vance 1979, Lissner 1980, 1983, divers observe Centrostephanus rodgersii to shelter in crevices during the day and emerge to forage at night (reviewed by Andrew & Byrne 2001). In Tasmania, C. rodgersii within dense macroalgal beds graze discrete patches surrounding their crevices to form local barren patches, termed 'incipient barrens' (Johnson et al 2005).…”

Section: Open Pen Access Ccessmentioning

confidence: 99%

“…Continued barrens formation throughout the rangeextension region in Tasmania poses a major threat to local biodiversity (Ling 2008) and to the lucrative reef-based abalone and rock lobster fisheries dependent on macroalgal production and habitat . Importantly, removal of predatory spiny lobsters from Tasmanian rocky reefs via commercial and recreational fishing has reduced the resilience of kelp beds, increasing the risk of catastrophic shift to widespread barren habitat (Ling et al 2009a).In common with other diadematid sea urchins (Nelson & Vance 1979, Lissner 1980, 1983, divers observe Centrostephanus rodgersii to shelter in crevices during the day and emerge to forage at night (reviewed by Andrew & Byrne 2001). In Tasmania, C. rodgersii within dense macroalgal beds graze discrete patches surrounding their crevices to form local barren patches, termed 'incipient barrens' (Johnson et al 2005).…”

mentioning

confidence: 99%

Forming sea urchin barrens from the inside out: an alternative pattern of overgrazing

Flukes¹,

Johnson²,

Ling³

2012

Overgrazing by sea urchins on temperate reefs can affect a phase shift from macroalgal beds to 'barrens' habitat largely devoid of seaweeds. Existing models of barrens formation are derived largely from observations of strongylocentrotid urchins, which typically show a behavioural shift from cryptic feeding to exposed grazing fronts that move through and 'mow down' macroalgal beds. Foraging by the temperate diadematid urchin Centrostephanus rodgersii triggers a similar transition from intact macroalgal bed to widespread barren grounds but does not appear to involve a behavioural shift. Fine-scale foraging movements were observed using timelapse photography across the urchin's range-extension region and described with respect to a random walk model. Foraging was highly nocturnal, with individuals homing strongly to available crevices. In situ monitoring of tagged individuals suggests strong fidelity to and thus high stability of barren patches, while similar behavioural patterns across habitat types representing a gradient of foraging intensities indicate no behavioural shift associated with overgrazing. Laboratory experiments showed that C. rodgersii lacks a directional chemosensory response to either macroalgae or conspecifics. Combined evidence suggests a model of barrens formation fundamentally different to the well-established 'feeding front' model, with formation of widespread barrens by C. rodgersii occurring from the 'inside out' via growth and coalescence of small barrens patches that form within macroalgal beds as a result of additive localised grazing radiating from crevice shelters. Regulation of urchin density at the spatial scale of individual barrens patches is proposed as a viable option to manage the formation of widespread barrens habitat within the urchin's recent range-extension to eastern Tasmania. 464: 179-194, 2012 coralline algae, drift algae (Johnson et al. 1981) and invertebrate material (Ling 2008). The transition to barrens habitat is particularly problematic because it represents a catastrophic phase shift between alternative stable states with hysteresis (e.g. Ling et al. 2009a), requiring extensive reductions in sea urchin densities for kelp beds to recover (Harrold & Reed 1985, Carpenter 1990. KEY WORDS: Phase shift · Kelp beds · Barrens · Centrostephanus rodgersii · Foraging ecology · Movement · Grazing effect · Range extension Resale or republication not permitted without written consent of the publisher OPEN PEN ACCESS CCESSMar Ecol Prog SerFew studies have employed an experimental approach to elucidate the mechanism of grazing dynamics leading to the creation of barrens habitat. Among these, most have focussed on species of sea urchins in the family Strongylocentrotidae (e.g. Mattison et al. 1977, Dean et al. 1984, Dumont et al. 2007, Lauzon-Guay & Scheibling 2007b, Feehan et al. 2012). This focus in research is due in part to the wide geographical distribution of strongylocentrotids and their close proximity to northern hemisphere researchers, in combination with ...

“…At shallow depths sea urchins are typically cryptic, due to higher water motion and also a more abundant supply of drift algae (Lissner 1980, Rogers-Bennett et al 1995, and have limited grazing effects on algae. Cryptic behaviour also reduces susceptibility to predation, and subsequently in the shallow permanent sites Evechinus chloroticus remains at moderate but variable densities.…”

Section: Long-term Habitat Change In the Leigh Reservementioning

confidence: 99%

Continuing trophic cascade effects after 25 years of no-take marine reserve protection

Shears¹,

Babcock²

2003

310

248

Between 1978 and 1996 benthic communities in the Leigh Marine Reserve shifted from being dominated by sea urchins to being dominated by macroalgae. This was a result of a trophic cascade thought to be an indirect effect of increased predator abundance. We assessed further changes in communities from 1996 to 2000, differences in benthic communities between reserve and adjacent unprotected sites, and the stability of these patterns from 1999 to 2001. Since 1996, densities of sea urchins Evechinus chloroticus have continued to decline in shallow areas of the reserve (< 8 m), and all sites classified as urchin barrens in 1978 are now dominated by large brown algae. Comparisons between reserve and non-reserve sites revealed differences consistent with a trophic cascade at reserve sites. The greatest differences in algal communities between reserve and non-reserve sites occurred at depths where E. chloroticus was most abundant (4 to 6 m). Reserve sites had lower urchin densities and reduced extent of urchin barrens habitat with higher biomass of the 2 dominant algal species (Ecklonia radiata and Carpophyllum maschalocarpum). At reserve sites densities of exposed E. chloroticus (openly grazing the substratum) declined so that urchin barrens were completely absent by 2001. Lower density of the limpet Cellana stellifera and higher densities of the turbinid gastropod Cookia sulcata at reserve sites are thought to be responses to changes in habitat structure, representing additional indirect effects of increased predators. The overall difference in community types between reserve and non-reserve sites remained stable between 1999 and 2001. Localised urchin mortality events due to an unknown agent were recorded at some sites adjacent to the marine reserve. Only at 1 of these sites did exposed urchins decline below the critical density of 1 m -2 , which resulted in the total replacement of urchin barrens with macroalgae-dominated habitats. At other sites urchin barrens have remained stable. Declines in the limpet C. stellifera occurred across all sites between 1999 and 2001 and may be indirectly associated with urchin declines. Long-term changes in benthic communities in the Leigh reserve and the stability of differences between reserve and nonreserve sites over time are consistent with gradual declines in urchin densities due to increased predation on urchins, thus providing further evidence for a trophic cascade in this system. The rapid declines in urchin numbers at some unprotected sites, however, demonstrate how short-term disturbances, such as disease, may result in shifts in community types over much shorter time frames.