Sea urchin behavior in a Southern California Kelp Forest: Food, fear, behavioral niches, and scaling up individual behavior

Public domain sea urchin photo by Kevin Lee
TitleSea urchin behavior in a Southern California Kelp Forest: Food, fear, behavioral niches, and scaling up individual behavior
Publication TypeJournal Article
Year of Publication2017
AuthorsP. Parnell E, Fumo JT, Lennert-Cody CE, Schroeter SC, Dayton PK
JournalJournal of Shellfish Research
Date Published2017/08
ISBN Number0730-8000

Red and purple sea urchins (Mesocentrotus francisanus and Strongylocentrotus purpuratus) cohabit the west coast of North America and exhibit behavioral switching between sheltering, when food is abundant, and emergence and overgrazing, when food is scarce. To better understand individual urchin foraging behavior, we conducted a series of time-lapse behavioral studies within and at the edge of a resilient sea urchin barren. Photographs were taken at 15-min intervals for weeklong periods to observe behavior (1) in different microtopographic settings, (2) in response to food additions, and (3) along a spatial gradient from the leading edge of a sea urchin grazing front to ?100 m behind it. Movement was limited for both species when crowded or in complex microtopography. Consistent differences in sheltering behaviors and diel movement patterns were observed between species in the presence and absence of food indicating behavioral niche differentiation. Red sea urchins responded to food falls at distances of at least 3m and exhibit an ability to return to shelters at similar distances. Both species exhibit (1) local movement for up to weeklong periods indicating constraints on bulk movement and grazing front formation, (2) decreased movement rates owing to crowding and microtopography analogous to traffic jams, and (3) consistent instraspecific differences in individual movement behaviors (i.e., personality). We propose how small-scale behavioral modes may scale to larger-scale local population movements and affect the dynamics of sea urchin overgrazing.

Short TitleJ. Shellfish Res.

In this study, high-frequency in situ time-lapse photography was conducted over weeklong periods with experimental food additions in different microtopographic settings and at different sites relative to a sea urchin grazing front. Our time-lapse study of red and purple sea urchins was conducted to (1) investigate behavioral differences between these two species (i.e., behavioral niches) and how these might contribute to the onset, distribution, persistence, and resilience of barrens, (2) determine the nature of interactions between them, (3) gauge their relative “food versus fear”motivational hierarchies, and relative response intensities to other potential behavioral cues, (4) investigate behavioral patterns of sea urchins within and behind a feeding front and among different structural habitats, (5) gain insight into the perceptual ranges of sea urchins in the field, and (6) identify characteristic modes of individual behavior that can be used to scale up to characteristic modes of group movement (c.f., herd behavior).

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