Impacts of ocean acidification on multiplication and caste organisation of parasitic trematodes in their gastropod host

Ocean acidification is predicted to impact the structure and function of all marine ecosystems in this century. As focus turns towards possible impacts on interactions among marine organisms, its effects on the biology and transmission potential of marine parasites must be evaluated. In the present study, we investigate two marine trematode species (Philophthalmus sp. and Parorchis sp., both in the family Philophthalmidae) infecting two marine gastropods. These trematodes are unusual in that their asexually multiplying stages within snails display a division of labour, with two distinct castes, a large-bodied morph producing infective stages and a smaller morph playing a defensive role against other competing parasites. Using a potentiometric ocean acidification simulation system, we test the impacts of acidified seawater (7.8 and 7.6 pH) on the production of free-living infective stages (cercariae), the size and survival of encysted resting stages (metacercariae), and the within-host division of labour measured as the ratio between numbers of the two morphs. In general, low pH conditions caused an increase in cercarial production and a reduction in metacercarial survival. The ratio of the two castes within snail hosts tended to shift towards more of the smaller defensive morphs under low pH. However, the observed effects of reduced pH were species specific and not always unimodal. These results suggest that ocean acidification can affect the biology of marine parasites and may also impact transmission success and parasite abundance of some trematodes, with possible consequences for marine communities and ecosystems.

CO2-induced fertilization impairment in Strongylocentrotus droebachiensis collected in the Arctic

Fertilization depends on distribution and aggregation patterns of sea urchins which influence gamete contact time and may potentially enhance their vulnerability to ocean acidification. In this study, we conducted fertilization experiments to assess the effects of selected pH scenarios on fertilization success of Strongylocentrotus droebachiensis, from Spitsbergen, Arctic. Acidification was achieved by aerating seawater with different CO2 partial pressures to represent pre-industrial and present conditions (measured ~180-425 µatm) and future acidification scenarios (~550-800, ~1,300, ~2,000 µatm). Fertilization success was defined as the proportion of successful/unsuccessful fertilizations per treatment; eggs were classified according to features of their fertilization envelope (FE), hyaline layer (HL) and achievement of cellular division. The diagnostic findings of specific pathological aberrations were described in detail. We additionally measured intracellular pH changes in unfertilized eggs exposed for 1 h to selected acidification treatments using BCECF/AM. We conclude that (a) acidified conditions increase the proportion of eggs that failed fertilization, (b) acidification may increase the risk of polyspermy due to failures in the FE formation supported by the occasional observation of multiple sperms in the perivitelline space and (c) irregular formation of the embryo may arise due to impaired formation of the HL. The decrease in fertilization success could be also related to the observed changes in intracellular pH at pCO2 ~ 1,000 µatm or higher.

Performance of the Arctic calanoid copepods Calanus glacialis and C. hyperboreus under elevated pCO2 and temperatures

The sensitivity of copepods to ocean acidification (OA) and warming may increase with time, however, studies >10 days and on synergistic effects are rare. We therefore incubated late copepodites and females of two dominant Arctic species, Calanus glacialis and Calanus hyperboreus, at 0 °C at 390 and 3000 µatm pCO2 for several months in fall/winter 2010. Respiration rates, body mass and mortality in both species and life stages did not change with pCO2. To detect synergistic effects, in 2011 C. hyperboreus females were kept at different pCO2 and temperatures (0, 5, 10 °C). Incubation at 10 °C induced sublethal stress, which might have overruled effects of pCO2. At 5 °C and 3000 µatm, body carbon was significantly lowest indicating a synergistic effect. The copepods, thus, can tolerate pCO2 predicted for a future ocean, but in combination with increasing temperatures they could be sensitive to OA.

Impacts of groundwater discharge at Myora Springs (North Stradbroke Island, Australia) on the phenolic metabolism of eelgrass, Zostera muelleri, and grazing by the juvenile rabbitfish, Siganus fuscescens

Myora Springs is one of many groundwater discharge sites on North Stradbroke Island (Queensland, Australia). Here spring waters emerge from wetland forests to join Moreton Bay, mixing with seawater over seagrass meadows dominated by eelgrass, Zostera muelleri. We sought to determine how low pH / high CO2 conditions near the spring affect these plants and their interactions with the black rabbitfish (Siganus fuscescens), a co-occurring grazer. In paired-choice feeding trials S. fuscescens preferentially consumed Z. muelleri shoots collected nearest to Myora Springs. Proximity to the spring did not significantly alter the carbon and nitrogen contents of seagrass tissues but did result in the extraordinary loss of soluble phenolics, including Folin-reactive phenolics, condensed tannins, and phenolic acids by ?87%. Conversely, seagrass lignin contents were, in this and related experiments, unaffected or increased, suggesting a shift in secondary metabolism away from the production of soluble, but not insoluble, (poly)phenolics. We suggest that groundwater discharge sites such as Myora Springs, and other sites characterized by low pH, are likely to be popular feeding grounds for seagrass grazers seeking to reduce their exposure to soluble phenolics.

Elevated pCO2 from late summer coastal upwellings in the western Baltic Sea enhances vegetative growth in the brown algae Fucus serratus: a laboratory assessment

The brown algae Fucus serratus is one of the major meadow forming algae of the Western Baltic Sea nearshore ecosystem. At the end of summer, those meadows are exposed to local upwelling suddenly increasing the pCO2 and DIC up to 2500 µatm and 2250 µmol/kg resp., for period of days to weeks. This study investigates the growth response of summer's vegetative Fucus serratus to elevated pCO2 (1350 and 4080 µatm) during a 40 days laboratory incubation. After 10 days, increases of growth rates of 20 % and 47 % of the control were observed in the 1350 and 4080 µatm pCO2 treatments respectively. Beyond 20 days, the growth rates collapsed in all treatments due to nutrients shortage, as demonstrated by high C:N ratios (95:1) and low N tissue content (0.04 % of dry weight). The collapse occurs faster at higher pCO2. On day 30, growth rates were reduced by 40 % and 100 % relative to the control at 1350 and 4080 µatm respectively. These results are consistent with a fertilizing effect of elevated pCO2 on Fucus serratus presumably linked to the transition from active HCO3- to passive CO2(aq) uptake. This positive effect is limited by nutrients resources, low seawater dissolved inorganic N and P and shortage of the nutrients reserves accumulated over the previous autumn and winter.

Limited effects of increased CO2 and temperature on metal and radionuclide bioaccumulation in a sessile invertebrate, the oyster Crassostrea gigas

This study investigated the combined effects of reduced pH and increased temperature on the capacities of the Pacific cupped oyster Crassostrea gigas to bioconcentrate radionuclide and metals. Oysters were exposed to dissolved radiotracers (110mAg, 241Am, 109Cd,57Co,54Mn, and 65Zn) at three pH (7.5, 7.8, 8.1) and two temperatures (21 and 24°C) under controlled laboratory conditions. Although calcifying organisms are recognized as particularly vulnerable to ocean acidification, the oyster did not accumulate differently the studied metals when exposed under the different pH conditions. However, temperature alone or in combination with pH somewhat altered the bioaccumulation of the studied elements. At pH 7.5, Cd was accumulated with an uptake rate constant twofold higher at 24°C than 21°C. Bioaccumulation of Mn was significantly affected by an interactive effect between seawater pH and temperature, with a decreased uptake rate at pH 7.5 when temperature increased (27 ± 1 vs. 17 ± 1 /day at 21 and 24°C, respectively). Retention of Co and Mn tended also to decrease at the same pH with decreasing temperature. Neither pH nor temperature affected strongly the elements distribution between shell and soft tissues. Significant effects of pH were found on the bioaccessibility of Mn, Zn, and 241Am during experimental in vitro simulation of human digestion.

Geographical variation in shell morphology of juvenile snails (Concholepas concholepas) along the physical-chemical gradient of the Chilean coast

Changes in phenotypic traits, such as mollusc shells, are indicative of variations in selective pressure along environmental gradients. Recently, increased sea surface temperature (SST) and ocean acidification (OA) due to increased levels of carbon dioxide in the seawater have been described as selective agents that may affect the biological processes underlying shell formation in calcifying marine organisms. The benthic snail Concholepas concholepas (Muricidae) is widely distributed along the Chilean coast, and so is naturally exposed to a strong physical-chemical latitudinal gradient. In this study, based on elliptical Fourier analysis, we assess changes in shell morphology (outlines analysis) in juvenile C. concholepas collected at northern (23°S), central (33°S) and southern (39°S) locations off the Chilean coast. Shell morphology of individuals collected in northern and central regions correspond to extreme morphotypes, which is in agreement with both the observed regional differences in the shell apex outlines, the high reclassification success of individuals (discriminant function analysis) collected in these regions, and the scaling relationship in shell weight variability among regions. However, these extreme morphotypes showed similar patterns of mineralization of calcium carbonate forms (calcite and aragonite). Geographical variability in shell shape of C. concholepas described by discriminant functions was partially explained by environmental variables (pCO2, SST). This suggests the influence of corrosive waters, such as upwelling and freshwaters penetrating into the coastal ocean, upon spatial variation in shell morphology. Changes in the proportion of calcium carbonate forms precipitated by C. concholepas across their shells and its susceptibility to corrosive coastal waters are discussed.