Species-specific crab predation on the hydrozoan clinging jellyfish sp. (Cnidaria, Hydrozoa), subsequent crab mortality, and possible ecological consequences.

Here we report a unique trophic interaction between the cryptogenic and sometimes highly toxic hydrozoan clinging jellyfish sp. and the spider crab . We assessed species-specific predation on the medusae by crabs found in eelgrass meadows in Massachusetts, USA. The native spider crab species consumed medusae, often enthusiastically, but the invasive green crab avoided consumption in all trials. One out of two blue crabs () also consumed , but this species was too rare in our study system to evaluate further. crabs could consume up to 30 jellyfish, which was the maximum jellyfish density treatment in our experiments, over a 24-hour period. consumption was associated with mortality. Spider crab mortality increased with consumption, and 100% of spider crabs tested died within 24 h of consuming jellyfish in our maximum jellyfish density containers. As the numbers of medusae used in our experiments likely underestimate the number of medusae that could be encountered by spider crabs over a 24-hour period in the field, we expect that may be having a negative effect on natural populations. Furthermore, given that overlaps in habitat and resource use with , which avoids consumption, populations could be indirectly benefiting from this unusual crab-jellyfish trophic relationship.