Date of Award

1987

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

Salinity effects on the developmental rates, larval tolerances and various metabolic processes of five species of echinoderms were investigated. Development of Lytechinus variegatus (Lamarck), Strongylocentrotus droebachiensis (O. F. Muller, 1776), Strongylocentrotus purpuratus (Stimpson, 1857), Strongylocentrotus pallidus (G. O. Sars, 1871), and Pisaster ochraceus (Brandt, 1835) larvae were observed. Developmental rates and larval survival to metamorphosis of S. droebachiensis and S. pallidus varied directly with salinity and were well within the observed salinity tolerance and distributional limits for the adults. For each species, embryos and larvae at lower salinities (20, 22.5, and $25\sp{o}\!/\!\sb{oo})$ tended to develop more slowly than those at higher salinities. P. ochraceus and S. droebachiensis survived all salinity treatments throughout the experimental period. F$\sb1$ hybrid larvae exhibited salinity tolerances and developmental rates intermediate between values reported for the more stenohaline larvae of S. pallidus and those for the more euryhaline larvae of S. droebachiensis. S. purpuratus larvae were stenohaline and tolerated salinities as low as $27.5\sp{o}\!/\!\sb{oo}{\rm S.}$. Gonadal ninhydrin positive substances were significantly lower at $17.5\sp{o}\!/\!\sb{oo}{\rm S}$ and coelomic cavity lactic acid values were significantly higher at $20\sp{o}\!/\!\sb{oo}{\rm S}$ for S. droebachiensis and S. pallidus, although, histological examination revealed no observable differences in gonadal structure between adults acclimated to high and low salinity. Temperature and salinity effects on the development, metabolic rates, and larval tolerance of Lytechinus variegatus (Lamarck) were also examined. Developmental rates and survival to metamorphosis of larval L. variegatus varied directly with salinity. Respiration rates of L. variegatus plutei varied directly with salinity and temperature; whereas, excretion rates varied directly with temperature and indirectly with salinity. O:N ratios suggest increased reliance on protein catabolism thus indicative of physiological stress at $27.5\sp{o}\!/\!\sb{oo}{\rm S.}$ The back transfer of juvenile L. variegatus to low salinities correlates well with 28 day LC$\sb{50}$ data of adults indicating $18\sp{o}\!/\!\sb{oo}$ to be the low salinity tolerance limit of adult urchins. Data obtained from this study indicate that the larval tolerances of echinoderms may limit adult distributions along salinity gradients.

Pages

101

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