Vulnerability of Tritia reticulata (L.) early life stages to ocean acidification and warming

Abstract

Ocean acidification and warming (OA-W) result mainly from the absorption of carbon dioxide and heat by the oceans, altering its physical and chemical properties and affecting carbonate secretion by marine calcifiers such as gastropods. These processes are ongoing, and the projections of their aggravation are not encouraging. This work assesses the concomitant effect of the predicted pH decrease and temperature rise on early life stages of the neogastropod Tritia reticulata (L.), a common scavenger of high ecological importance on coastal ecosystems of the NE Atlantic. Veligers were exposed for 14 days to 12 OA-W experimental scenarios generated by a factorial design of three pH levels (targeting 8.1, 7.8 and 7.5) at four temperatures (16, 18, 20 and 22 °C). Results reveal effects of both pH and temperature (T °C) on larval development, growth, shell integrity and survival, individually or interactively at different exposure times. All endpoints were initially driven by pH, with impaired development and high mortalities being recorded in the first week, constrained by the most acidic scenarios (pH target 7.5). Development was also significantly driven by T °C, and its acceleration with warming was observed for the remaining exposure time. Still, by the end of this 2-weeks trial, larval performance and survival were highly affected by the interaction between pH and T °C: growth under warming was evident but only for T °C ≤ 20 °C and carbonate saturation (pH target ≥ 7.8). In fact, carbonate undersaturation rendered critical larval mortality (100%) at 22 °C, and the occurrence of extremely vulnerable, unshelled specimens in all other tested temperatures. As recruitment cohorts are the foundation for future populations, our results point towards the extreme vulnerability of this species in case tested scenarios become effective that, according to the IPCC, are projected for the northern hemisphere, where this species is ubiquitous, by the end of the century. Increased veliger mortality associated with reduced growth rates, shell dissolution and loss under OA-W projected scenarios will reduce larval performance, jeopardizing T. reticulata subsistence.The netted whelk, Tritia reticulata (Linnaeus, 1758) is a common neogastropod, ubiquitous in the North East Atlantic shore -along the European coastline, from the Canaries to Norway-and throughout the Mediterranean, Baltic and the Black Seas 1 . Its occurrence extends from the low water of spring tides to sublittoral depths down to at least 40 m, along the open coast and the outer parts of estuaries. Adults spawn from mid-winter to summer, laying egg capsules onto hard substrates 2,3 . Inside the capsule, organisms pass through a trochophore larval stage before hatching as veliger, roughly after one month of development 1,3 . The veliger stage corresponds to the free-swimming, planktonic larval period, and is anatomically characterized by the presence of a shell, foot and velum. Depending mainly on the temperature, this stage may last between 1 to 3 months as larvae reach...

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