Fitness benefits and costs of shelters to the sea urchin Glyptocidaris crenularis

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.

Long-term effects of temperature on gonad production, colour and flavour of the sea urchin Glyptocidaris crenularis

The increasing market demand for Glyptocidaris crenularis shapes its great potential for aquaculture. Temperature is an important factor affecting gonad production and quality of sea urchins. Therefore, it is essential and valuable to carry out an evaluation of the temperature effects on gonad production and quality in G. crenularis before potential aquaculture. Here, we investigated the long-term effects of temperature on gonad production, colour and flavour in G. crenularis. There was no significant difference of test diameter, height and body weight between the sea urchins in high (16–23°C) and low (12–16°C) temperatures (P > 0.05). Glyptocidaris crenularis showed significantly higher gonad production and index in high temperature and in low temperature (P < 0.05). L*, a*, b* readings were slightly higher in the low temperature groups, although no significant difference was found (P > 0.05). Subjective colour and flavour ratings found that G. crenularis in the low temperature group showed significantly better colour (P = 0.003) and flavour (P < 0.001) than those in the high temperature group. The present study provides valuable and insightful information into the establishing G. crenularis aquaculture.