An In Vitro Analysis of Egg Mortality in Cancer anthonyi: The Role of Symbionts and Temperature

¹ Department of Biological Sciences, and the Marine Science Institute, University of California, Santa Barbara, California 93106

Several symbionts occur on crab eggs. These symbionts, and the effect of temperature, have been implicated as causal mechanisms of egg mortality in Cancermagister. The contribution of three symbionts (a fungus, Lagenidium callinectes; bacteria, i.e., Leucothrix sp.; and a nemertean worm, Carcinonemertes epialti) to egg mortality on Cancer anthonyi were investigated in vitro using a multifactorial experimental design at four different temperatures. The nemertean worm was found to contribute most to egg mortality on the individual crab and at the crab population level because its prevalence was high (>95%) and it had a relatively constant feeding rate. Lagenidium callinectes caused from 20-75% egg mortality on individual crabs but its prevalence was nil. A Lagenidium-like fungus had a low prevalence (2.6%) and was not associated with egg mortality. While bacteria were omnipresent, they were found to cause negligible crab egg mortality. Few significant interactions were observed between the symbionts. Temperature had a significant effect on worm feeding rates, worm oviposition, and fungal attack rates. At low temperatures (4 and 10°C), symbionts killed fewer eggs than at higher temperatures (15 and 20°C). Extreme temperatures (4 and 20°C) caused variable degrees of egg mortality, yet some eggs survived at these temperatures. Temperature also had a profound effect on egg development. At 20°C, eggs developed almost twice as fast as those at 10°C. Development appeared to stop at 4°C.

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