Calcifying invertebrates succeed in a naturally CO<sub>2</sub> enriched coastal habitat but are threatened by high levels of future acidification

Abstract

CO₂ emissions are leading to an acidification of the oceans. Predicting marine community vulnerability towards acidification is difficult, as adaptation processes cannot be accounted for in most experimental studies. Naturally CO₂ enriched sites thus can serve as valuable proxies for future changes in community structure. Here we describe a natural analogue site in the Western Baltic Sea. Seawater <i>p</i>CO₂ in Kiel Fjord is elevated for large parts of the year due to upwelling of CO₂ rich waters. Peak <i>p</i>CO₂ values of >230 Pa (>2300 μatm) and pH values of <7.5 are encountered during summer and autumn, average <i>p</i>CO₂ values are ~70 Pa (~700 μatm). In contrast to previously described naturally CO₂ enriched sites that have suggested a progressive displacement of calcifying auto- and heterotrophic species, the macrobenthic community in Kiel Fjord is dominated by calcifying invertebrates. We show that blue mussels from Kiel Fjord can maintain control rates of somatic and shell growth at a <i>p</i>CO₂ of 142 Pa (1400 μatm, pH=7.7). Juvenile mussel recruitment peaks during the summer months, when high water <i>p</i>CO₂ values of ~100 Pa (~1000 μatm) prevail. Our findings indicate that calcifying keystone species may be able to cope with surface ocean pH values projected for the end of this century. However, owing to non-linear synergistic effects of future acidification and upwelling of corrosive water, peak seawater <i>p</i>CO₂ in Kiel Fjord and many other productive estuarine habitats could increase to values >400 Pa (>4000 μatm). These changes will most likely affect calcification and recruitment, and increase external shell dissolution

Being young in a changing world: how temperature and salinity changes interactively modify the performance of larval stages of the barnacle Amphibalanus improvisus

“…However, we know that in the Western Baltic, nauplii, to some extent, hatch and survive at this and even lower temperatures as shown by Javidpour et al (2010), who found barnacle nauplii in gut samples of Mnemiopsis leidyi in Kiel Fjord during most of winter. Surprisingly, though nauplii are obviously present in the water column at this time of the year, successful settlement is at an almost undetectable level between November and April (Wahl and Schütt, unpublished data;Thomsen et al 2010). Various reasons for settlement failure of barnacle larvae during winter have been documented as, e.g., food constraint (Barnes and Barnes 1958;Thiyagarajan et al 2002a), low temperature (Anil et al 1995), predation, starvation and misrouting (Crisp 1984), starvation in early naupliar stages (Lang and Marcy 1982), and Wnally the quality of released nauplii (Anil et al 1995).…”

“…If the barnacle population we investigated was optimally adapted to the local conditions, we would have expected best performance (e.g., survival) among those individuals that experienced conditions prevailing during peak settlement in July and August (Thomsen et al 2010), i.e., at about 20°C and 15 psu. However, larval duration was shortest at 28°C (regardless of salinity), metamorphosis success and overall survival (from start to end of Experiment I) was best at 5 psu (regardless of temperature).…”

“…When cyprids appeared in the cultures after 7-8 days, the cultures were sieved (200 m) and cyprids were removed and subsequently used for settlement bioassays. As in Kiel Fjord, settlement peak usually occurs in July and August (mean temperatures of about 20°C and the mean salinities of 15 psu); These cyprids were reared under conditions as prevail in Kiel Fjord during peak settlement time (habitat condition) (Thomsen et al 2010) and thus, presumably, without temperature and salinity stress.…”

“…In coastal lagoons and in shallow waters, the temperature can even be several degrees higher as shown in 1 m depth at the Schlei Fjord (Kiel Bight, Western Baltic) with a maximum temperature of 27°C (K. Maczassek unpublished data). During A. improvisus peak recruitment from July to August (Thomsen et al 2010), SST in Kiel Fjord typically is around 20°C and surface salinity is about 15 psu (own unpublished logger data). These conditions, if not optimal, can at least be considered benign.…”

Long-term exposure to elevated pCO2 more than warming modifies early-life shell growth in a temperate gastropod

“…ocean warming, "OW") and in carbonate chemistry and pH driven by increasing CO 2 emissions (i.e. ocean acidification, "OA") (IPCC 2014) are known to impact the integrity and morphology of the shell of adult marine organisms (Nienhuis et al, 2010;Thomsen et al, 2010;Melatunan et al, 2013). Some defence mechanisms such as decreased shell growth rates to preserve energy (Findlay et al, 2010) and increased calcification in a range of calcifying species across taxa have been observed in acidified conditions (Ries et al, 2009).…”