The energetic cost of an introduced marine parasite on its new native shrimp host

The eastern Pacific burrowing mud shrimp Upogebia pugettensis was an abundant species that dominated the biogeochemistry of intertidal estuary mudflats; however, their populations have declined dramatically since the late 1990s following the introduction of the bopyrid isopod parasite Orthione griffenis.  Weight losses of Upogebia infested by Orthione are dramatic and only reproductive sized shrimp are infested.  Correlations between individual Orthione and host weights are poor nevertheless.  We tested whether underweight hosts result from arrested growth and weight losses at particular sizes or growth in size without weight gain, an interaction that has not previously been examined. A past complication has been that the reproductive sized hosts could not survive outside of their burrows and also could not be removed and replaced to their intact burrows for experimental manipulations.  We solved this problem by culturing pre-reproductive Upogebia to reproductive sizes in sediment filled tubes that could be repeatedly opened for observations without harming the shrimp or their burrows.  A broad size range of Upogebia were experimentally infested with diverse size ranges of Orthione and cultured in seawater tanks or in the estuary mudflats along with uninfested control shrimp.  Growth of shrimp and parasites were monitored for up to three weeks.  Preliminary results suggest that underweight hosts can result from growth in size without weight gain in addition to the normal expected weight loss among hosts of particular sizes.