THE EFFECTS OF TEMPERATURE AND SALINITY ON LARVAL GROWTH OF THE HORSESHOE CRABLIMULUS POLYPHEMUS

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Abstract
Horseshoe crab, Limulus polyphemus, eggs were reared through the first tailed stage in factorial combinations of temperature and salinity with respective values of 20, 25, 30, or 35°C and 10, 15, 25, or 35‰. Lowest survival occurred in low temperature, low salinity combinations (20°C, l0‰). Wet weight, and thus linear dimension, of the first tailed stage was only slightly different throughout the temperature-salinity range tested. However, ash-free dry weights, indicating yolk utilization, varied significantly with both temperature and salinity. The least yolk utilization occurred at 30°C and increased in higher and especially lower temperatures. Yolk utilization also increased with a decrease in salinity. Temperature interacted with salinity to cause a greater salinity-dependent difference in yolk utilization at lower temperatures. Comparisons of ash-free dry weights (i.e., yolk utilization) with respiration rates indicate that L. polyphemus has little ability to compensate metabolically for the effects of temperature and, secondarily, of salinity. Nevertheless, the larvae are sufficiently provisioned with yolk to survive the prevailing ranges of these variables in the habitat where adults normally deposit eggs. This suggests that other unexamined physical variables, or more likely biological factors such as predation or competition among the feeding larval stages and adults, are important for larval survival of L. polyphemus.