Dataset: 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

This dataset contains measurements of shell thickness, shell length, shell mass, and tissue mass for the intertidal snail Littorina obtusata 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.

This dataset is part of a broader study conducted in the Gulf of Maine to investigate phenotypic plasticity of prey species in response to predator invasion and warming oceans:

1. Green crab surveys plus historical crab density data (dataset 990378) 
2. Green crab density from field studies at rocky intertidal sites from April 2019 to December 2021 (dataset 911365) 
3. Latitudinal (clinal) variation in Littorina obtusata shell thickness and tissue mass measured 20 years apart (this dataset)
4. Field experiment outplanting Littorina obtusata with predators (green crabs) to examine local and regional geographic variation in inducible defenses conducted from April to August 2021 (dataset 911221)
5. Morphological data from reciprocal transplant experiment in the field (dataset 990830)