Responses of the sea urchin Strongylocentrotusdroebachiensis (O.F. Müller) to water-borne stimuli from potential predators and potential food algae

The interrelation between the sea urchin Evechinus chloroticus and the spiny lobster Jasus edwardsii was investigated in the shallow subtidal zone of rocky reefs in northern New Zealand. Both species were found in large numbers in the Shallow Broken Rock hab~tat. During the day spiny lobsters and sea urchins were spatially segregated on a small scale. Movement patterns of spiny lobsters indicate that sea urchins are accessible to nocturnally foraging lobsters. Laboratory experiments demonstrated that large lobsters ate all sizes of sea urchins. All sizes of lobster ate small sea urchins (< 50 mm TD) in preference to larger sea urchins. The provision of herbivorous gastropods (also eaten by lobsters) and shelter for sea urchins did not mean that more larger sea urchins were eaten. The removal of large brown algae or sea urchins and gastropods from areas of reef did not cause significant reductions in the daytime density of J. edwardsii. We argue that differing micro-habitat requirements of the 2 species mean that large abundances of E. chloroticus are unlikely to depress 3. edwardsii densities.The neccessary experiments to test this hypothesis are discussed.

Section: Discussionsupporting

confidence: 84%

“…Laboratory experiments have repeatedly demonstrated that lobsters are capable of eating sea urchins (e.g. Elner 1980, Tegner & Levin 1983, Mann et al 1984. Demonstrations of capability, while necessary, are not sufficient evidence from which to claim that these predators control sea urchin populations in nature.…”

Section: Introductionmentioning

confidence: 99%

Interrelations between sea urchins and spiny lobsters in northeastern New Zealand

Andrew¹,

MacDiarmid²

1991

“…This suggests that urchins move randomly while foraging (Lauzon-Guay et al 2006) until they encounter a rich food patch and stop to graze, rather than direct their movement toward the kelp bed. Although previous work has shown that urchins can detect food and move toward it (Larson et al 1980, Mann et al 1984, whether they can discriminate patches with different amount of food and direct their movement toward the highest quality food patch is unclear.…”

Section: Front Advancementioning

confidence: 99%

Behaviour of sea urchin Strongylocentrotus droebachiensis grazing fronts: food-mediated aggregation and density-dependent facilitation

Lauzon-Guay¹,

Scheibling²

2007

The occurrence of destructive grazing fronts is a common phenomenon in sea urchins, but mechanisms governing front formation and dynamics remain poorly understood. We experimentally examined the effect of kelp biomass on the aggregative behavior and movement of a front of green sea urchins Strongylocentrotus droebachiensis at a wave-exposed site on the Atlantic coast of Nova Scotia. We varied kelp (Laminaria digitata and L. longicruris ) abundance in 2 × 2 m plots adjacent to the front in 3 treatments: 50% plant removal, and 100% frond removal and unmanipulated control. In each treatment, we monitored the position of the front and urchin density at the leading edge over 24 d. The mean advance of the front in 24 d (2.27 m) did not differ between treatments, but urchin density was greatest in the control (74.9 urchins 0.25 m -2 ) and lower in whole plant (54.3) and frond (39.4) removal treatments. When urchin density was used as a covariate, front advance was inversely related to kelp biomass and greater in frond and plant removal treatments than in the control. Together, urchin density and kelp biomass explained 75% of variation in front advance. These findings provide the first direct evidence that urchins redistribute themselves along a front to concentrate in patches of greatest food availability. Temporal variation in urchin density at the front was inversely correlated with wave height, and individual grazing rates increased with urchin density, which may explain seasonal variation in front dynamics observed in previous studies.

“…However, less is known about the behaviour of urchins in the barrens zone, even though processes in the barrens will likely contribute to the intensity of urchin grazing at the kelp-barrens boundary. Sea urchins display a wide range of behaviours including chemodetection of food sources (Mann et al 1984, see Sloan & Campbell 1982 for review), aggregation (Garnick 1978, Hagen & Mann 1994, Rodriguez & Farina 2001, agonistic behaviour (Grünbaum et al 1978, Tusuchiya & Nishihira 1985, Shulman 1990, predator avoidance (Jensen 1966, Bernstein et al 1981, Scheibling & Hamm 1991, Hagen & Mann 1992, Hagen et al 2002, homing (Carpenter 1984, Tuya et al 2004, and diel (Nelson & Vance 1979, Tertschnig 1989, Jones & Andrew 1990, Rogers et al 1998, Freeman 2003 and seasonal activity rhythms (Agatsuma et al 2000, Konar 2001. Predation can limit the foraging activity of urchins, for example urchins that feed only at night to avoid visual predators (mainly fish) and return to refuges during the day (Carpenter 1984, Jones & Andrew 1990).…”

Section: Introductionmentioning

confidence: 99%

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

Dumont¹,

Himmelman²,

Russell³

2006

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