Jörn Thomsen

Naturally acidified habitat selects for ocean acidification–tolerant mussels

Mussels are able to adapt to ocean acidification over multiple generations. Ocean acidification severely affects bivalves, especially their larval stages. Consequently, the fate of this ecologically and economically important group depends on the capacity and rate of evolutionary adaptation to altered ocean carbonate chemistry. We document successful settlement of wild mussel larvae (Mytilus edulis) in a periodically CO2-enriched habitat. The larval fitness of the population originating from the CO2-enriched habitat was compared to the response of a population from a nonenriched habitat in a common garden experiment. The high CO2–adapted population showed higher fitness under elevated Pco2 (partial pressure of CO2) than the non-adapted cohort, demonstrating, for the first time, an evolutionary response of a natural mussel population to ocean acidification. To assess the rate of adaptation, we performed a selection experiment over three generations. CO2 tolerance differed substantially between the families within the F1 generation, and survival was drastically decreased in the highest, yet realistic, Pco2 treatment. Selection of CO2-tolerant F1 animals resulted in higher calcification performance of F2 larvae during early shell formation but did not improve overall survival. Our results thus reveal significant short-term selective responses of traits directly affected by ocean acidification and long-term adaptation potential in a key bivalve species. Because immediate response to selection did not directly translate into increased fitness, multigenerational studies need to take into consideration the multivariate nature of selection acting in natural habitats. Combinations of short-term selection with long-term adaptation in populations from CO2-enriched versus nonenriched natural habitats represent promising approaches for estimating adaptive potential of organisms facing global change.

Ammonia excretion in mytilid mussels is facilitated by ciliary beating

ABSTRACT The excretion of nitrogenous waste products in the form of ammonia (NH3) and ammonium (NH4+) is a fundamental process in aquatic organisms. For mytilid bivalves, little is known about the mechanisms and sites of excretion. This study investigated the localization and the mechanisms of ammonia excretion in mytilid mussels. An Rh protein was found to be abundantly expressed in the apical cell membrane of the plicate organ, which was previously described as a solely respiratory organ. The Rh protein was also expressed in the gill, although at significantly lower concentrations, but was not detectable in mussel kidney. Furthermore, NH3/NH4+ was not enriched in the urine, suggesting that kidneys are not involved in active NH3/NH4+ excretion. Exposure to elevated seawater pH of 8.5 transiently reduced NH3/NH4+ excretion rates, but they returned to control values following 24 h acclimation. These mussels had increased abundance of V-type H+-ATPase in the apical membranes of plicate organ cells; however, NH3/NH4+ excretion rates were not affected by the V-type H+-ATPase specific inhibitor concanamycin A (100 nmol l−1). In contrast, inhibition of ciliary beating with dopamine and increased seawater viscosity significantly reduced NH3 excretion rates under control pH (8.0). These results suggest that NH3/NH4+ excretion in mytilid mussels takes place by passive NH3 diffusion across respiratory epithelia via the Rh protein, facilitated by the water current produced for filter feeding, which prevents accumulation of NH3 in the boundary layer. This mechanism would be energy efficient for sessile organisms, as they already generate water currents for filter feeding. Highlighted Article: The plicate organ of mytilid mussels is a main site for ammonia excretion, which is facilitated by Rh channels and ciliary beating.

Mussel larvae modify calcifying fluid carbonate chemistry to promote calcification

Understanding mollusk calcification sensitivity to ocean acidification (OA) requires a better knowledge of calcification mechanisms. Especially in rapidly calcifying larval stages, mechanisms of shell formation are largely unexplored—yet these are the most vulnerable life stages. Here we find rapid generation of crystalline shell material in mussel larvae. We find no evidence for intracellular CaCO3 formation, indicating that mineral formation could be constrained to the calcifying space beneath the shell. Using microelectrodes we show that larvae can increase pH and [CO32−] beneath the growing shell, leading to a ~1.5-fold elevation in calcium carbonate saturation state (Ωarag). Larvae exposed to OA exhibit a drop in pH, [CO32−] and Ωarag at the site of calcification, which correlates with decreased shell growth, and, eventually, shell dissolution. Our findings help explain why bivalve larvae can form shells under moderate acidification scenarios and provide a direct link between ocean carbonate chemistry and larval calcification rate.The sensitivity of mussel larvae to ocean acidification, particularly during the time of shell formation, remains uncertain. Here, the authors show that larvae can elevate calcium carbonate saturation state beneath their shell to enhance calcification, but this ability is compromised by ocean acidification.

Acidification-sensitivity of M. edulis

HCl molecules emitted from volcanoes breakdown to form chlorine free radicals via heterogeneous chemical reactions and photolysis, which act as catalysts to the breakdown of ozone in the stratosphere. Ozone depletion of up to 2-7% was estimated following the Pinatubo 1991 eruption [1]. However, only stratospheric HCl is dangerous to ozone, and the amount of HCl that reaches these levels is often lower than expected [2]. This suggests that HCl is removed from the eruption column at tropospheric levels. Previously suggested mechanisms include inclusion of HCl into supercooled droplets or ice crystals [3]. In order to investigate the removal of HCl from the atmosphere by adsorption onto ash in volcanic plumes, glass with the composition of the Pinatubo 1991 dacite [4] was synthesised and ground to ash-sized particles using a planetary mill. The ash was then placed in a simple volumetric vacuum device, which was purged with HCl gas to a desired pressure. The ash was connected to the system and the adsorption of HCl onto the ash surface recorded by the resulting pressure drop until an equilibrium pressure was reached. Preliminary results from experimental runs beginning with an HCl gas pressure of 31 mbar, 100 mbar, 250 mbar, 504 mbar and 975 mbar indicate that adsorption on the order of 0.5 mgm-2 occurs even at low partial pressures of HCl. [1] Robock (2000) Rev. Geophys. 38, 191-219. [2] Oppenheimer (2003) In Treatise on Geochemistry. [3] Textor et al. (2003) Geol Soc Lon Spec Pub 213, 307-328. [4] Scaillet & Evans (1999) J. Petr. 40, 381-411

The mytilid plicate organ: revisiting a neglected organ

Jörn Thomsen, Brian Morton, Holger Ossenbrügger, Jeffrey A. Crooks, Paul Valentich-Scott and Kristin Haynert J.F. Blumenbach Institute of Zoology and Anthropology, University of Göttingen, Göttingen, Germany; School of Biological Sciences, The University of Hong Kong, Hong Kong SAR, China; Tijuana River National Estuarine Research Reserve, Imperial Beach, CA 91932, USA; Santa Barbara Museum of Natural History, Santa Barbara, CA 93105, USA; and Senckenberg am Meer, Department of Marine Research, 26382 Wilhelmshaven, Germany

Kiel fjord pCO2 datasets between 2012 (July) and 2015 (January) measured using a HydroC® pCO2 sensor

In addition to the standard copper anti fouling cap installed on the stainless steel strainer pump intake, the sensor was equipped with a coarse plastic mesh or a perforated plastic bottle to prevent clogging of the inflow by jellyfish and/or other large floating objects. Macrofoulers (mainly mussel and barnacle settlers) were removed and the sensor – including the sensor head – was repeatedly cleaned. During deployment intervals 1 and 2 this procedure happened occasionally while during interval 3 the cleaning happened weekly during summer season and biweekly during winter season. The sensor membrane was exchanged during routine maintenance at the manufacturer, Kongsberg Maritime Contros GmbH (Kiel, Germany, see calibration dates below), and once additionally in September 2014.