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

Abstract

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

Evaluation of passive integrated transponder (PIT) tags in studies of sea urchins: caution advised

“…tetracycline and calcein) do not permit individual identification (Hagen 1996, Duggan & Miller 2001, Dumont et al 2006. Laboratory studies have demonstrated the potential of PIT tags in measuring growth and survival, without detectable adverse effects, in 2 species of sea urchin: Strongylocentrotus droebachiensis (Hagen 1996) and Evechinus chloroticus (Woods & James 2005).…”

Sea-urchin feeding fronts

“…whereas others find either no effect (Dumont et al, 2006) or the opposite relation (Klinger and Lawrence, 1985). It has also been shown, by using physical models of large algae, that the movement of foliose algae by the water may restrict urchin movement (Konar and Estes, 2003).…”

“…Both the flow and the chemical signals 32 are likely to be more complex in the urchins' natural environment. In field studies the direction of urchin movement is usually found to be either ran-34 dom or weakly directional (Duggan and Miller, 2001;Dumont et al, 2006;Lauzon-Guay et al, 2006). The question then is how to explain the formation 36 of intense aggregations in an asocial animal, which appears not to be able to move in a directed manner.…”

“…A recurrent observation is that there is an inverse relation between urchin movement and macrophyte density (Mattison et al, 1977;Andrew and Stocker, 40 1986; Dance, 1987;Dumont et al, 2006). A study by Mattison et al (1977) of red sea-urchins (Strongylocentrotus franciscanus) near Santa Cruz found that 42 urchins within a kelp forest moved by 7.5 cm day −1 , whereas outside it the movement rate increased to over 50 cm day −1 (Fig.…”

“…The model we discuss is a mini-74 mal model. The complexities of differential feeding on multi species algal assemblages (Gagnon et al, 2004;Wright et al, 2005), size dependent urchin 76 movement (Dumont et al, 2004(Dumont et al, , 2006, seasonal variations in movement rate (Konar and Estes, 2001;Dumont et al, 2004), relation between behaviour and 78 the supply of drift algae (Dayton et al, 1984), interactions between movement and the substrate (Laur et al, 1986), or between water movement and urchin 80 movement (Kawamata, 1998) are not included. All demographic processes such as urchin growth, recruitment and mortality have also been ignored.…”