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21st Annual Intertidal Crab Census

Purchase students, alumni, and Bridges to the Baccalaureate summer research program students helped recorded crab density and distribution at Edith Read Sanctuary.

On Thursday, June 14, a diverse group assisted with the 21st Annual Intertidal Crab Census at Edith Read Sanctuary (Rye, NY). The census recorded the density and the intertidal distribution of crabs as part of a long-running study of the population dynamics of invasive (Hemigrapsus sanguineus, Asian shore crab) and resident species. 

Data collection has occurred during the first spring low tides of June each year since 1998.  Long term marine ecological studies, like this one, are rare; only 15% of marine benthic ecological investigations last more than two years. 

The group assisting with the census included current students from the Environmental Studies and Biology programs at Purchase College and the Bridges to the Baccalaureate summer research program.  Three of the assistants are alumni of the environmental studies program: 

  • Anna Palmer ’15 (ENV; second from left) completed a policy-focused senior project (socioeconomic model predicting freshwater macro-invertebrates) with Prof. Ryan Taylor. She went on to complete a master’s program in environmental studies at Ohio University.  She works as a consultant with the Desert Research Institute. 
  • Emily Selover ’15 (ENV, SOC; third from left) examined in a joint ENV-SOC senior project the relationship between attachment to a special natural place and environmental values and behaviors of college students. The principles she uncovered inform her work as an environmental educator and administrator at The Nature Place (Chestnut Ridge, NY). 
  • Sean Sandell ’18 (ENV; fifth from left) studied the nutrition of the Asian shore crab with Prof. George Kraemer. Sean has remained closer to home, working now at Marshlands Conservancy as ranger/curator’s assistant ( 

Pattern in a variable system like the intertidal zone is more readily seen with more data, in the case of the population dynamics of the Asian shore crab with a larger temporal window. Interestingly, examination of data suggests the Asian shore crab has been in slow decline over the past 10 years. This includes decreases in both numbers and size.  At the same time, the other species of crab that once inhabited the intertidal zone at Read Sanctuary have not returned.