Effects of dams on downstream molluscan predator–prey interactions in the Colorado river estuary

Jansen A. Smith, John C. Handley, Gregory P. Dietl

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


River systems worldwide have been modified for human use and the downstream ecological consequences are often poorly understood. In the Colorado River estuary, where upstream water diversions have limited freshwater input during the last century, mollusc remains from the last several hundred years suggest widespread ecological change. The once abundant clam Mulinia modesta has undergone population declines of approximately 94% and populations of predators relying on this species as a food source have probably declined, switched to alternative prey species or both. We distinguish between the first two hypotheses using a null model of predation preference to test whether M. modesta was preyed upon selectively by the naticid snail, Neverita reclusiana, along the estuary’s past salinity gradient. To evaluate the third hypothesis, we estimate available prey biomass today and in the past, assuming prey were a limiting resource. Data on the frequency of drill holes—identifiable traces of naticid predation on prey shells—showed several species, including M. modesta, were preferred prey. Neverita reclusiana was probably able to switch prey. Available prey biomass also declined, suggesting the N. reclusiana population probably also declined. These results indicate a substantial change to the structure of the benthic food web. Given the global scale of water management, such changes have probably also occurred in many of the world’s estuaries.

Original languageEnglish (US)
Article number20180724
JournalProceedings of the Royal Society B: Biological Sciences
Issue number1879
StatePublished - May 30 2018
Externally publishedYes

Bibliographical note

Funding Information:
This work was supported by funding to G.P.D. (National Science Foundation EAR 1420978) and J.A.S. (Cornell University's Atkinson Center for a Sustainable Future; Geological Society of America; Paleontological Society; Sigma Xi).

Publisher Copyright:
© 2018 The Author(s) Published by the Royal Society. All rights reserved.


  • Manly’s α
  • Mulinia
  • Naticidae
  • Predator preference
  • Salinity gradient
  • Shell-drilling predation


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