Effects of spine damage and microhabitat on resource allocation of the purple sea urchin Strongylocentrotus purpuratus (Stimpson 1857)

Abstract

Though phenotypically plastic responses in echinoids are well studied, the majority of the 35 literature examines the effect of altered diet. Some species, however, such as the purple sea 36 urchin, Strongylocentrotus purpuratus, occur over a large geographic range and thus experience 37 a variety of substrate types and wave forces. To determine whether these factors impact resource 38 allocation in adult intertidal S. purpuratus, a laboratory experiment was conducted using two 39 types of microhabitat based on extremes inhabited by sea urchins in the field (flat substratum vs. 40 concave pit), and two levels of spine damage to simulate wave exposure (monthly clipping vs. 41 control). A suite of measurements were taken to determine the effects of these two treatments 42 including: feeding and movement behavior, test morphometrics, demipyramid (jaw) allometry, 43 spine growth cycles, and mass and stereological counts of gonad sections. When given the 44 3 opportunity, sea urchins remained in their pits for the duration of the experiment, which limited 45 their ability to feed. This behavioral response caused a decrease in weight and volumetric 46 growth, and an increase in jaw growth relative to test growth. Sea urchins in pits also grew more 47 spheroid in shape (increased height:diameter ratio), while those on flat substrates decreased in 48 height:diameter ratio. Further, both males and females in pits showed altered gametogenesis. 49 While spine damage did not affect test growth, sea urchins with clipped spines showed decreased 50 gonad index and altered production of mature oocytes. Altogether, these results are congruent 51 with the life history strategy of long living species like S.purpuratus, in that it spreads 52 reproductive efforts over multiple seasons, while diverting resources toward repairing damage, 53 acquiring suitable refuge, and maximizing attachment area. Therefore, microhabitat and spine 54 damage, by impacting movement, feeding, growth, and reproductive output, likely have 55 important indirect impacts on the intertidal community by way of altered sea urchin grazing rates 56 and susceptibility and value to predators. 57

Re-examination of the effects of food abundance on jaw plasticity in purple sea urchins

“…Documenting changes in jaw length to test diameter ratios in response to food availability is relatively common (Ebert 1980b;Fansler 1983;Edwards and Ebert 1991;Levitan 1991;Brockington et al 2001;Pederson and Johnson 2008;Ebert 2014;Epherra et al 2015;Haag et al 2016), and relative jaw length is considered a useful tool for evaluating resource limitation in urchin populations (Ebert 1980a;Black et al 1984;Levitan 1991;Pederson and Johnson 2008;Ling et al 2019). Indeed, our results conirm this inding and show that juvenile S. purpuratus individuals experience similar changes in relative jaw length.…”

“…The possible efects of early life food stress on jaw plasticity suggest that, in addition to habitat, urchin density, and species diferences (Constable 1993;Fernandez and Boudouresque 1997;Epherra et al 2015;Haag et al 2016), resource limitation, which is closely linked to habitat and density diferences, may be an important factor underlying the presence or absence of cyclical reversibility to seasonal changes in food abundance (Ebert 2014). It may also help to explain why diferences in relative jaw lengths between urchins in barrens and macroalgal beds persist and appear to be reinforced over time (Ling et al 2019).…”

“…Indeed, the presence of longer jaws in urchin species may be associated with the availability of diferent types of food (reviewed in Ling et al 2019). For example, larger jaws have been associated with active benthic grazing for eiciently scraping algae of of substrates in urchin barrens (Byrne et al 2008;Ling and Johnson 2009;Epherra et al 2015;Haag et al 2016). The sea urchin, Arbacia dufresnii, has shorter absolute jaw lengths in habitats where algae is available compared to individuals in habitats where ilamentous and calcareous algae and molluscs are more available (Epherra et al 2015).…”

Bottom-up effects on biomechanical properties of the skeletal plates of the sea urchin Paracentrotus lividus (Lamarck, 1816) in an acidified ocean scenario

“…Food shortage (i.e. the lack of macroalgal biomass for feeding) have been reported to cause modifications in plastic resource allocation(Ebert 1980;Haag et al, 2016), differences in mechanical properties of sea urchin spines(Moureaux and Dubois 2012) and, in an acidified scenario, reduction of the buffer capacity of the coelomic fluid to compensate the decrease of external pH(Collard et al, 2013).In the present study, the combined effect of pH level and macroalgal diet was investigated in terms of sea urchin plates biomechanical properties, showing no direct short-term effect of seawater pH nor diet on single plate strain and stiffness, in agreement with previous laboratory studies(Holtmann et al, 2013;Moulin et al, 2015;Collard et al, 2016).A field study, instead, highlighted a role of the diet in mediating sea urchins biomechanical properties, showing that test plates from P. lividus living in tide pools mainly covered by encrusting calcareous algae exhibit a higher fracture force than test plates of sea urchins living in pools containing erected non-calcifying algae(Collard et al, 2016). Similar role of calcifying macroalgae in strengthen P. lividus juvenile tests has been shown by Asnaghi et al (2013) on specimens exposed to the same experimental conditions of the present study, but it is not easy to disentangle the role of plates, ligaments and calcified locking structures in providing test robustness.…”

The role of fasting on spine regeneration and bacteremia in the purple sea urchin Strongylocentrotus purpuratus

“…Sea urchins are also known to limit foraging when damaged or in the presence of predators [8]. During caloric restrictions, urchins are able to maintain metabolism and growth through release of lipids and carbohydrates via somatic and gonadal tissues when food is not available [9][10][11].…”