Effects of fine sediments on settlement and survival of the sea urchin Evechinus chloroticus in northeastern New Zealand

Abstract

Populations of the sea urchin Evechinus chloroticus were monitored at wave-exposed low-sediment reefs and wave-sheltered high-sediment reefs in the Hauraki Gulf, northeastern New Zealand. Urchin populations on both wave-exposed and sheltered reefs were dominated by adults. Wave-exposed reefs supported higher densities (2.7 to 9.6 ind. m ). Juvenile urchins (< 30 mm test diameter [TD]) were 25 times more abundant on wave-exposed reefs. Urchin settlement of 0.2 to 0.6 ind. 100 cm -2 was recorded at wave-exposed reefs but was undetectable at wave-sheltered reefs. Laboratory experiments were conducted to assess whether the volumes of sediment loads observed on sheltered reefs could affect the survivorship of early life stages of urchins in the absence of other environmental factors. Results indicated that fine sediments at one-third and two-thirds of concentrations found on wave-sheltered reefs inhibited the settlement of larvae and reduced the survival of urchin recruits (2 to 5 mm TD) and juveniles (10 to 30 mm TD). Survival rates of juveniles were higher than for more recent recruits, suggesting size-dependent mortality. A lack of significant differences between high and low treatments in all experiments suggests that urchin settlement and survival can be affected negatively at low levels of sediment that are common in natural environments.

Context‐dependent Effects of Fishing: Variation in Trophic Cascades Across Environmental Gradients

“…Furthermore, in systems where multiple anthropogenic stressors are acting on kelp forests and their inhabitants, the importance of top-down effects, and our ability to detect them, may be diminished. This may be the case when fishing occurs at multiple trophic levels such that reef predators, urchins and kelp are harvested (Dayton et al 1998), or where land-based activities influence the persistence of key components of the trophic cascade (e.g., Walker 2007). Nevertheless, as highlighted by gaps in our understanding of northeastern New Zealand's kelp forest ecosystem, we contend that the way forward is to measure important processes (e.g., productivity, recruitment, grazing, and predation rates) and how these vary with environmental context at multiple spatial scales.…”

“…Environmental stress associated with wave action, sedimentation, and low salinity have been shown to restrict the abundance of sea urchins and/or their grazing efficiency (Witman and Grange 1998, Siddon and Witman 2003, Walker 2007. Furthermore, these environmental factors can vary at many spatial scales, e.g., among regions, sites within regions, and across depths within sites.…”

The effect of suspended sediment on fertilization success in the urchin Evechinus chloroticus: Analysis of experimental data using hierarchical Bayesian methods

“…The early life history of marine organisms is an important determinant of adult population structure (Menge and Sutherland, 1987;Menge, 1991Menge, , 2000Caley et al, 1996). Consequently, environmental stressors such as sedimentation may ultimately impact community structure and function (Airoldi, 2003;Thrush et al, 2004) by altering the outcomes of key early life-history events for these important macroalgal grazers e.g., by reducing larval recruitment, settlement, and survival (Phillips and Shima, 2006;Walker, 2007), and potentially also via reduced fertilization success. E. chloroticus has already been identified as a species vulnerable to the effects of sediment in its early development.…”

Leigh Marine Laboratory contributions to marine conservation

“…Trophic cascades and other higher order indirect effects of marine reserves were not observed in the inner Hauraki Gulf (Salomon 2008;Shears et al 2008a), where high turbidity and sedimentation inhibit the recruitment and survival of urchins Evechinus chloroticus (Andrew & Choat 1985;Walker 2007). Without urchins, the critical middle link between predators and primary producers, there is no cascading effect to lower trophic levels because predatorÁprey interactions occur among a much more diffuse web of herbivores and omnivores, few of which, if any, are direct grazers on kelps or other large brown algae (Pinkerton et al 2008;Lozano-Montes et al 2011).…”