96. Higher sensitivity to ocean warming and acidification in boreal than temperate great scallop, Pecten maximus

Gisela Lannig (1)*, Burgel Schalkhausser (1), Hans-O. Pörtner (1,2), Christian Bock (1)

1 Alfred Wegener Institute Helmholtz Centre for Polar & Marine Research, Bremerhaven, 27570, Germany
2 University of Bremen, Bremen, 28359, Germany

Background
Under the framework of the concept of oxygen and capacity limited thermal tolerance (OCLLT) we investigated the impact of OA – in particular at the borders of the thermal tolerance window – on the metabolic response of scallops which are exceptional among bivalves due to their swimming capacity.

Methods
P. maximus from two populations (boreal from Norway, temperate from France) were incubated under ocean warming and acidification (OWA) conditions (0.04 vs. 0.11 kPa CO2; boreal: 4 vs. 10°C; temperate: 10 vs. 20°C). We determined haemolymph parameters (via blood gas analyzer), routine and maximal metabolic rates (RMR/MMR by intermitted flow respirometry) and metabolic profiles in mantle using 1H-HRMAS NMR spectroscopy.

Findings
After OA exposure both populations showed a drop in pHe, which was stronger in boreal than temperate scallops in the warmth. Irrespective of OA and population, RMR increased and PeO2 values decreased with warming. However, under OWA MMR and swimming performance decreased in boreal scallops only. Similarly, multivariate statistics of metabolic profiles revealed a population dependent OA response. While adenylate levels increased in both populations, reduced levels of some amino acids and osmolytes were observed in the boreal population only.

Conclusions
Capacity for acid-base regulation seemed less in boreal than temperate scallops under OWA. Warming brought both populations into their upper pejus range (low PeO2) indicating insufficient oxygen supply mechanisms to keep up with the warming-induced rise in RMR. In contrast to temperate P. maximus, additional OA exposure decreased swimming performance further in boreal scallops in the warmth, paralleled by decreased amino acid and osmolyte levels in mantle tissue.

In line with the OCLTT concept the present findings revealed impaired performance of scallops in a warming ocean suggesting negative implications for their swimming capacity. At thermal extremes constraints may be exacerbated by OA as seen in the boreal population.