Abstract
Understanding the ecological role of shelters is greatly hampered by the scarcity of long-term laboratory experiments on the trade-off between fitness benefits and costs. This lack probably leads to an underestimation of the negative and/or positive effects on behaviors and growth of marine invertebrates in benthic ecosystems. Although our previous study revealed a significant effect on fitness-related traits of Glyptocidaris crenularis after 31 months, the present study extended it and investigated fitness benefits and/or costs of long-term sheltering on sea urchins to over 7 years. The present long-term study suggests that the previously reported reduction in feeding rate probably resulted from a reduction in reflexive feeding motions (Aristotle’s lantern reflex) rather than changes in foraging behavior. Actively seeking sheltering behavior was negatively impacted in individuals with continuous access to shelters. However, covering and righting behaviors did not differ in sheltered sea urchins, indicating that these behaviors are maintained to escape from adverse environments regardless of shelter. Body size of sea urchins in the group with shelters was significantly lower than those without shelters after 7 years. Weights of gonads and gut were not significantly different after 7 years despite previous observations of differences after ~2.5 years. The present study provides valuable information on the trade-off between fitness benefits and costs to sea urchins residing in shelters. However, the present study is only a laboratory investigation for one urchin species (G. crenularis) which does not consider the complexity of natural environments. Field studies should be carried out with G. crenularis and other sea urchin species, before a more universal conclusion can be drawn.
Highlights
Besides evolutionary adaptation, acclimation is important for fitness benefits of marine invertebrates (Sanford & Kelly, 2011; Foo & Byrne, 2016)
Shelters are important for the fitness of many benthic marine invertebrates such as sea urchins, the environments without shelters are ubiquitous in benthic ecosystems
The present long-term study suggests that the previously reported reduction in feeding rate of G. crenularis probably resulted from a reduction in reflexive feeding (Aristotle’s lantern reflex), rather than changes in foraging behavior
Summary
Acclimation is important for fitness benefits of marine invertebrates (Sanford & Kelly, 2011; Foo & Byrne, 2016). The trade-off between fitness benefits and costs probably shapes the evolutionary process of marine invertebrates in different environments (Abarca & Boege, 2011). Fitness benefits and costs of shelters to the sea urchin Glyptocidaris crenularis. Shelters are important for the fitness benefits of marine invertebrates in benthic ecosystems. We hypothesized the foraging behavior of Glyptocidaris crenularis would be affected in the long-term shelter conditions. Understanding the ecological role of shelters is greatly hampered by the scarcity of long-term laboratory experiments on the trade-off between fitness benefits and costs. This lack probably leads to an underestimation of the negative and/or positive effects on behaviors and growth of marine invertebrates in benthic ecosystems
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