Oxygen depletion in estuaries and coastal waters is often associated with reduced biodiversity, coastal dead zones, and the loss of important ecosystem services. However, some species can benefit from low oxygen conditions due to the indirect effects these conditions have on trophic relationships. In Narragansett Bay, Rhode Island, U.S.A., northern quahogs (Mercenaria mercenaria) reach their highest densities in the areas of the Bay most prone to oxygen depletion. One line of evidence suggests that suboxic events (hypoxia and anoxia) can aid quahogs by excluding predators. Here, we analyze data from long-term surveys of water quality and quahog abundances to test whether a hypoxia-induced predation refuge is strong enough to explain quahog population dynamics in Narragansett Bay. We found that quahog cohorts were larger when they had been exposed to low oxygen conditions as juveniles, consistent with the predation refuge hypothesis. However, cohort size was also strongly associated with location and year settled, suggesting that a predation refuge is but one of a suite of factors influencing M. mercenaria populations.

Methods can be found in the associated publication.

The R script (MercenariaHypoxia_GalliganEtAl_12.20.21.R) should process the raw data files and reproduce all results and figures.

• You will need to set the working directory yourself.
• You will also need to create a file structure within the working directory as follows:
  • Folder: raw.data
    • Dredge_Data_Cleaned_7312020.rds
    • Dredge_Data_Sizes_Cleaned_11062020.rds
      • Note: these .rds files can be accessed using the load command in R, but may not work with the standard readRDS command
    • Subfolder: nbfsmn
      • All *.csv files (naming convention is bb.yyyy.csv)

Please see the README file associated with this dataset for additional details. If any issues arise, please contact Bryan P. Galligan, S.J. (bgalligan@luc.edu).