Abstract
The effect of thermal stress (heat shock) on survival was evaluated for advanced larval stages and the possible effect on delay of metamorphosis in competent larvae was also evaluated in the purple sea urchin Strongylocentrotus purpuratus under laboratory conditions. Eight-arm precompetent and competent larvae were kept at 15, 19, 23, 28, and 31 ºC during 24 h to estimate their thermal tolerance and measure their survival in each treatment. Delay of metamorphosis was evaluated in competent larvae exposed to heat shock treatments of 15, 20, 24, 28, and 32 ºC for 30 min. After this, larvae were induced to metamorphose in the presence of biofilms and KCl. Our results indicated that the thermal tolerance limit for precompetent and competent larvae was 27 ºC; temperatures equal or above this value are lethal for both stages of development, where we observed 100% mortality in a period of 24 h for the treatment at 27 ºC and of 2 h at 31 ºC. Competent larvae subjected to a heat shock treatment of 28 ºC for 30 min delayed the onset of metamorphosis (<40%) and showed high percentage of larvae with incomplete metamorphosis (55%). These results indicate the sensitivity of late larval stages to temperatures above 27 ºC for short periods of time, and that this sensitivity may compromise the onset of metamorphosis. This could have some effect on the settlement and recruitment patterns of the purple sea urchin, particularly in intertidal sites exposed to high temperatures during the summer.
Highlights
The purple sea urchin Strongylocentrotus purpuratus (Stimpson 1857) is distributed in warm waters of the Pacific Ocean, from Alaska to Cedros Island off Baja California, Mexico, and experiences a wide range of temperatures, from 4 to 20 oC (Osovitz and Hofmann 2005)
Our findings show that eight-armed precompetent larvae and competent larvae of the purple sea urchin S. purpuratus possess high thermal tolerance for a short period of time (24 h)
The results reported indicate that larvae of the purple sea urchin S. purpuratus in advanced stages of development have a high thermal tolerance; larval exposure to temperatures of about 28 oC for short periods of time (30 min) can affect the onset of metamorphosis
Summary
The purple sea urchin Strongylocentrotus purpuratus (Stimpson 1857) is distributed in warm waters of the Pacific Ocean, from Alaska to Cedros Island off Baja California, Mexico, and experiences a wide range of temperatures, from 4 to 20 oC (Osovitz and Hofmann 2005). It inhabits the shallow subtidal zone, where mean annual sea surface temperature is between 16 and 20 oC off Baja California (McClatchie et al 2008). También habita en la zona del intermareal rocoso en donde puede llegar a experimentar temperaturas por encima de 8 oC del promedio anual (Palleiro-Nayar et al 2008)
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