Latitudinal variation in the shell thickness and tissue mass of Littorina obtusata snails across 20 years as measured in samples collected from the Gulf of Maine from 1995-1997 and 2017-2018

<p>This dataset contains measurements of shell thickness, shell length, shell mass, and tissue mass for the intertidal snail <em>Littorina obtusata</em> collected from rocky shore sites throughout the Gulf of Maine. Samples were collected during two time periods (1995–1997 and 2017–2018) to assess spatial and temporal variation in morphological traits across a latitudinal gradient.</p> <p>This dataset is part of a broader study conducted in the Gulf of Maine to investigate&nbsp;phenotypic plasticity of prey species in response to predator invasion and warming oceans:</p> <ol> <li>Green crab surveys plus historical crab density data (dataset 990378)&nbsp;</li> <li>Green crab density from field studies at rocky intertidal sites from April 2019 to December 2021&nbsp;(dataset 911365)&nbsp;</li> <li>Latitudinal (clinal) variation in&nbsp;<em>Littorina obtusata</em>&nbsp;shell thickness and tissue mass measured 20 years apart&nbsp;<strong>(this dataset)</strong></li> <li>Field experiment outplanting&nbsp;<em>Littorina obtusata&nbsp;</em>with predators (green crabs) to examine local and regional geographic variation in inducible defenses&nbsp;conducted from April to August 2021 (dataset&nbsp;911221)</li> <li>Morphological data from reciprocal transplant experiment in the field&nbsp;(dataset 990830)</li> </ol>