Development of newly metamorphosed juvenile sea urchins (Strongylocentrotus franciscanus and S-purpuratus): morphology, the effects of temperature and larval food ration, and a method for determining age

Following metamorphosis, juveniles of marine benthic invertebrates continue to develop traits that allow them to function and survive in their (new) n on-pelagic environment. The sensitivity of juvenile development to environm ental conditions or larval quality, such as nutritional condition, are not well understood. This study presents descriptions of trait development that allow species identification of newly metamorphosed juvenile sea urchins S trongylocentrotus franciscanus and S. purpuratus. Following metamorphosis, these two species were distinguishable for at least 3 weeks by different pa tterns of coronal and aboral pedicellariae. Temperature studies, conducted at three environmentally relevant levels (8, 11, and 14 degrees C) show tha t developmental rates varied, but the order in which structures formed and became functional in the first 2 weeks after metamorphosis were not affecte d by temperature. Juvenile feeding begins 9 days after metamorphosis at 14 degrees C and after other traits have developed. Based on suites of traits, we identified juvenile stages and quantified effects of temperature on rat e of development (stage day(-1)) with nonparametric regression and with a t emperature coefficient, Q(10). Additional laboratory studies on S. purpurat us show that larval food ration strongly affects the rate of juvenile trait development prior to and after the onset of feeding by juveniles. Comparis ons of size of juvenile rudiments and size at metamorphosis between larvae reared in the laboratory at two food levels and wild-caught larvae and juve niles from coastal Oregon (USA) indicate those from the held were well fed and developed at rapid rates. The above information was used to develop a p rocedure for aging field caught juveniles ( less than or equal to 2 weeks a fter metamorphosis), provided their thermal history is known. This procedur e can be adapted for other invertebrates that acquire traits in an orderly fashion and can be used, in-addition to sampling-intensive surveys, to inve stigate recruitment dynamics in benthic populations. (C) 1999 Elsevier Scie nce B.V. All rights reserved.