Current understanding of how calcifying organisms respond to externally forced oceanic and coastal acidification (OCA) is largely based on short-term, controlled laboratory or mesocosm experiments. Studies on organismal responses to acidification (reduced carbonate saturation and pH) in the wild, where animals simultaneously interact with a range of biotic and abiotic circumstances, are limited in scope and interpretation. The present study aimed to better understand the value of gastropod shell attributes and their interrelations in informing about responses to coastal acidification. We investigated shell chemical erosion, shell roundness, and growth rate of Planaxis sulcatus snails, which are locally exposed to acidified or non-acidified rocky intertidal water. We trialed a new approach to quantifying shell erosion based on the spiral suture length (EI, erosion index), and found that shell erosion mirrored field acidification conditions. Acidification caused shells to become rounder (width/length) compared to those of snails from a non-acidified shore. Field growth rate, determined from apertural margin extension of marked and later recaptured snails, was strongly negatively related to both shell erosion and shell roundness. Because the different shell attributes inform about different associations – shell erosion represents an extrinsic passive marker of acidification, and shell roundness and growth rate are intrinsic performance responders – their interrelations imply causation, infer predictive power and improve interpretation confidence. This study contributes to the methodology and interpretation of findings of trait-based field investigations to understand organismal responses to coastal acidification.
Marshcall D. J. & Rashid A., 2023. Organismal responses to coastal acidification informed by interrelating erosion, roundness and growth of gastropod shells. Zoological Studies 62: 41. Article.
