Preliminary investigation of effects of seawater pH on early development of Limulus polyphemus

Abstract

Estuarine organisms are exposed to periodic strong fluctuations in seawater pH driven by natural O2/CO2 biogeochemical cycles. The average pH of ocean surface waters has decreased by about 0.1 units from 8.2 to 8.1, since the beginning of the industrial revolution. This phenomenon, dubbed ocean acidification, may be exacerbated into the future by increasing atmospheric CO2 from fossil fuel combustion and associated land use changes. The direct biological effect of ocean acidification is not well understood and may vary among organisms. In a preliminary investigation to detect the sensitivity of Limulus polyphemus to pH changes, sets of 100 fertilized eggs were exposed to five isolated systems with pH values ranging from 6.0 to 8.0 for 4 weeks. This preliminary investigation chronicled the effects of pH on larval and/or juvenile carapace length and the development to the post-larval juvenile stage over time. Trends in carapace length (without telson) for larva and juveniles (with telson), measured by scanning electron microscopy (SEM), were positively correlated to pH within the experimental range. The long-term consequences of ocean acidification on early stage horseshoe crab development are unknown, and this work prompts further investigation.