Spatial Variation in Red Sea Urchin Reproduction and Morphology: Implications for Harvest Refugia

Abstract

Red sea urchins (Strongylocentrotus franciscanus), residing in shallow habitats in Bodega Bay, California are morphologically distinct and possibly enhance recruitment by spawning larvae and sheltering juveniles. This suggests shallow beds of urchins would be ideal candidates for harvest refugia promoting the production of larvae to replenish deeper harvested habitats. Red urchins from shallow beds (5 m) had significantly heavier gonads (63 ± 30 g, N = 45, mean ± 1 SD) compared with urchins from intermediate (14 m) and deep (23 m) habitats (12 ± 8 g, N = 39, mean ± 1 SD). Gonad indices from spring, summer, and fall of 1991 and 1992 show this pattern persisted. Shallow water urchins co‐occurred at high densities (4.6 individuals/m2), with seasonally abundant drift algae and wave surge. Recruitment of juvenile urchins was examined in nine 1‐m2 quadrats randomly placed in three shallow sites with red urchins and three intermediate depth sites with red urchins in the Bodega Marine Reserve. Juvenile urchin (Strongylocentrotus spp.) recruitment (5‐50 mm) was highest in association with adults in shallow habitats over a 4‐yr period (October 1988‐October 1992). Adult red urchins in shallow habitats resided in rock bowls where they were 12 times more likely to shelter juveniles than more mobile adults in deep water. Principal component analysis identified five morphological characteristics of shallow water urchins: short spines, large gonads, thick tests, small lanterns, and small peristomial openings. External morphological characteristics (e.g., spine length) could be used to ensure the protection of reproductive urchins in shallow harvest refugia offering an alternative urchin management strategy for northern California.

Detrital kelp subsidy supports high reproductive condition of deep-living sea urchins in a sedimentary basin

“…Previous studies have recorded a decrease in gonad size and fecundity with increasing depth and distance from macroalgal beds for Strongylocentrotus droebachiensis (Keats et al 1984, Bertram & Strathmann 1998, Wahle & Peckham 1999, Brady & Scheibling 2006, Kelly et al 2012) and congeneric species (Rogers-Bennett et al 1995, Wahle & Peckham 1999, Konar & Estes 2003. In contrast, we found that sea urchins at 60 m depth in a sedimentary basin can have comparable or in some cases greater reproductive effort (mean GI at spring or autumn peak: 10 (2009) found that S. franciscanus feeding on macroalgal detritus at 24 m depth also a had similar GI compared to sea urchins in barrens at 6 m depth in the San Juan Islands, Washington, USA.…”

“…In less productive habitats below the depth limit of kelp beds, the spatial extent and duration of detrital subsidy can play an important role in supporting sea urchin populations (Rogers-Bennett et al 1995, Basch & Tegner 2007, Britton-Simmons et al 2009). Sea urchins associated with accumulations of kelp detritus have been documented in deep submarine canyons off central California (Harrold et al 1998) and in other rocky subtidal habitats in Alaska (Duggins et al 1989), Washington (Britton-Simmons et al 2009) and Western Australia (Vanderklift & Wernberg 2008).…”

Reproductive output and consistency of source populations in the sea star Pisaster ochraceus

“…However, the quality of reproductive habitat often varies among sites (Crowder et al 2000, McIntyre & Hutchings 2003, Leslie et al 2005, and thus identifying sources of larval production has become one consideration in the placement of marine reserves (Quinn et al 1993, Rogers-Bennett et al 1995, Sala et al 2002. In practice, incorporating this ABSTRACT: Although a common goal of marine reserves is to protect areas of high reproductive output, few studies have tested whether these source populations are spatially and temporally consistent.…”

“…Similarly, the reproductive output of barnacles is often higher in areas of high primary productivity (Bertness et al 1991, Leslie et al 2005. However, only a handful of studies have tested whether the reproductive output of marine consumers at higher trophic levels is sensitive to resource quality, and these studies have focused mostly on herbivores such as limpets and sea urchins (Rogers-Bennett et al 1995, Kido & Murray 2003, Wing et al 2003; but see also McIntyre & Hutchings 2003).…”

“…This result lends support to the idea that reproductive source populations may be spatially and temporally consistent for a given species. Siting marine reserves to protect such populations may help replenish non-protected areas through larval export (Rogers-Bennett et al 1995, Roberts 1997, Crowder et al 2000. However, in our study, the population with greater per capita reproductive output was found at the site with lower quality prey.…”