Beschreibung: Ocean acidification (OA) effects on larvae are partially attributed for the rapidly declining oyster production in the Pacific Northwest region of the United States. This OA effect is a serious concern in SE Asia, which produces 〉80% of the world’s oysters. Because climate-related stressors rarely act alone, we need to consider OA effects on oysters in combination with warming and reduced salinity. Here, the interactive effects of these three climate-related stressors on the larval growth of the Pacific oyster, Crassostrea gigas, were examined. Larvae were cultured in combinations of temperature (24 and 30 °C), pH (8.1 and 7.4), and salinity (15 psu and 25 psu) for 58 days to the early juvenile stage. Decreased pH (pH 7.4), elevated temperature (30 °C), and reduced salinity (15 psu) significantly delayed pre- and post-settlement growth. Elevated temperature lowered the larval lipid index, a proxy for physiological quality, and negated the negative effects of decreased pH on attachment and metamorphosis only in a salinity of 25 psu. The negative effects of multiple stressors on larval metamorphosis were not due to reduced size or depleted lipid reserves at the time of metamorphosis. Our results supported the hypothesis that the C. gigas larvae are vulnerable to the interactions of OA with reduced salinity and warming in Yellow Sea coastal waters now and in the future.

Beschreibung: Elevated anthropogenic pCO2 can delay growth and impair otolith structure and function in the larvae of some fishes. These effects may concurrently alter the larva’s proteome expression pattern. To test this hypothesis, Atlantic herring larvae were exposed to ambient (370 μatm) and elevated (1800 μatm) pCO2 for one-month. The proteome structure of the larvae was examined using a 2-DE and mass spectrometry. The length of herring larvae was marginally less in the elevated pCO2 treatment compared to the control. The proteome structure was also different between the control and treatment, but only slightly: the expression of a small number of proteins was altered by a factor of less than 2-fold at elevated pCO2. This comparative proteome analysis suggests that the proteome of herring larvae is resilient to elevated pCO2. These observations suggest that herring larvae can cope with levels of CO2 projected for near future without significant proteome-wide changes.

Beschreibung: The majority of marine benthic invertebrates protect themselves from predators by producing calcareous tubes or shells that have remarkable mechanical strength. An elevation of CO2 or a decrease in pH in the environment can reduce intracellular pH at the site of calcification and thus interfere with animal's ability to accrete CaCO3. In nature, decreased pH in combination with stressors associated with climate change may result in the animal producing severely damaged and mechanically weak tubes. This study investigated how the interaction of environmental drivers affects production of calcareous tubes by the serpulid tubeworm, Hydroides elegans. In a factorial manipulative experiment, we analyzed the effects of pH (8.1 and 7.8), salinity (34 and 27), and temperature (23°C and 29°C) on the biomineral composition, ultrastructure and mechanical properties of the tubes. At an elevated temperature of 29°C, the tube calcite/aragonite ratio and Mg/Ca ratio were both increased, the Sr/Ca ratio was decreased, and the amorphous CaCO3 content was reduced. Notably, at elevated temperature with decreased pH and reduced salinity, the constructed tubes had a more compact ultrastructure with enhanced hardness and elasticity compared to decreased pH at ambient temperature. Thus, elevated temperature rescued the decreased pH-induced tube impairments. This indicates that tubeworms are likely to thrive in early subtropical summer climate. In the context of climate change, tubeworms could be resilient to the projected near-future decreased pH or salinity as long as surface seawater temperature rise at least by 4°C.

Beschreibung: Ocean acidification (OA) is anticipated to interact with the more frequently occurring hypoxic conditions in shallow coastal environments. These could exert extreme stress on the barnacle-dominated fouling communities. However, the interactive effect of these two emerging stressors on early-life stages of fouling organisms remains poorly studied. We investigated both the independent and interactive effect of low pH (7.6 vs. ambient 8.2) and low oxygen (LO; 3 mg/l vs. ambient 5 mg/l) from larval development through settlement (attachment and metamorphosis) and juvenile growth of the widespread fouling barnacle, Balanus amphitrite. In particular, we focused on the critical transition between planktonic and benthic phases to examine potential limiting factors (i.e. larval energy storage and the ability to perceive cues) that may restrain barnacle recruitment under the interactive stressors. LO significantly slowed naupliar development, while the interaction with low pH (LO-LP) seemed to alleviate the negative effect. However, 20-50% of the larvae became cyprid within 4 d post-hatching, regardless of treatment. Under the two stressors interaction (LO-LP), the barnacle larvae increased their feeding rate, which may explain why their energy reserves at competency were not different from any other treatment. In the absence of a settlement-inducing cue, a significantly lower percentage of cyprids (15% lower) settled in LO and LO-LP. The presence of an inducing cue, however, elevated attachment up to 50-70% equally across all treatments. Post-metamorphic growth was not altered, although the condition index was different between LO and LO-LP treatments, potentially indicating that less and/or weaker calcified structures were developed when the two stressors were experienced simultaneously. LO was the major driver for the responses observed and its interaction with low pH should be considered in future studies to avoid underestimating the sensitivity of biofouling species to OA and associated climate change stressors.

Beschreibung: Ocean acidification (OA) is well-known for impairing marine calcification; however, the end response of several essential species to this perturbation remains unknown. Decreased pH and saturation levels (Omega) of minerals under OA is projected to alter shell crystallography and thus to reduce shell mechanical properties. This study examined this hypothesis using a commercially important estuarine oyster Magallana hongkongensis. Although shell damage occurred on the outmost prismatic layer and the undying myostracum at decreased pH 7.6 and 7.3, the major foliated layer was relatively unharmed. Oysters maintained their shell hardness and stiffness through altered crystal unit orientation under pH 7.6 conditions. However, under the undersaturated conditions (Omega Cal ~ 0.8) at pH 7.3, the realigned crystal units in foliated layer ultimately resulted in less stiff shells which indicated although estuarine oysters are mechanically resistant to unfavorable calcification conditions, extremely low pH condition is still a threat to this essential species.

Beschreibung: Unprecedented rate of increased CO2 level in the ocean and the subsequent changes in carbonate system including decreased pH, known as ocean acidification (OA), is predicted to disrupt not only the calcification process but also several other physiological and developmental processes in a variety of marine organisms, including edible oysters. Nonetheless, not all species are vulnerable to those OA threats, e.g. some species may be able to cope with OA stress using environmentally induced modifications on gene and protein expressions. For example, external environmental stressors including OA can influence the addition and removal of methyl groups through epigenetic modification (e.g. DNA methylation) process to turn gene expression “on or off” as part of a rapid adaptive mechanism to cope with OA. In this study, we tested the above hypothesis through testing the effect of OA, using decreased pH 7.4 as proxy, on DNA methylation pattern of an endemic and a commercially important estuary oyster species, Crassostrea hongkongensis at the time of larval habitat selection and metamorphosis. Larval growth rate did not differ between control pH 8.1 and treatment pH 7.4. The metamorphosis rate of the pediveliger larvae was higher at pH 7.4 than those in control pH 8.1, however over one-third of the larvae raised at pH 7.4 failed to attach on optimal substrate as defined by biofilm presence. During larval development, a total of 130 genes were differentially methylated across the two treatments. The differential methylation in the larval genes may have partially accounted for the higher metamorphosis success rate under decreased pH 7.4 but with poor substratum selection ability. Differentially methylated loci were concentrated in the exon regions and appear to be associated with cytoskeletal and signal transduction, oxidative stress, metabolic processes, and larval metamorphosis, which implies the high potential of C. hongkongensis larvae to acclimate and adapt through non-genetic ways to OA threats within a single generation.

Beschreibung: The majority of common edible oysters are projected to grow more slowly and have smaller impaired shells because of anthropogenic CO2-induced reductions in seawater carbonate ion concentration and pH, a process called ocean acidification (OA). Recent evidence has shown that OA has carryover effects, for example, larvae exposed to OA will also exhibit either positive or negative effects after metamorphosis. This study examined the hidden carryover effects of OA exposure during parental and larval stages on post-metamorphic traits of the commercially important oyster species Crassostrea hongkongensis. Adults of C. hongkongensis were exposed to control pH (pHNBS 8.0) and OA-induced low pH (pHNBS 7.4) conditions. Their larval offspring were then exposed to the same aquarium conditions before being out-planted as post-metamorphic juveniles at a mariculture site for 10 months. Initially, larval offspring were resilient to low pH with or without parental exposure. The larvae exposed to low pH had significantly faster development and higher percentage of settlement success compared to control groups. The out-planted juveniles with parental exposure had improved survival and growth compared to juveniles without parental exposure, regardless of the larval exposure history. This implies that transgenerational effects due to parental exposure not only persists but also have a greater influence than the within-generational effects of larval exposure. Our results shed light on the importance of linking the various life history stages when assessing the OA-induced carryover capacity of C. hongkongensis in the natural environment. Understanding these linked relationships helps us better predict the species rapid adaptation responses in the face of changing coastal conditions due to OA.

Beschreibung: Biomineralization is one of the key biochemical processes in calcifying bivalve species such as oysters that is affected by ocean acidification (OA). Larval life stages of oysters are made of aragonite crystals whereas the adults are made of calcite and/or aragonite. Though both calcite and aragonite are crystal polymorphs of calcium carbonate, they have different mechanical properties and hence it is important to study the micro and nano structure of different life stages of oyster shells under OA to understand the mechanisms by which OA affects biomineralization ontogeny. Here, we have studied the larval and juvenile life stages of an economically and ecologically important estuarine oyster species, Crassostrea hongkongensis, under OA with focus over shell fabrication under OA (pHNBS 7.4). We also look at the effect of parental exposure to OA on larvae and juvenile microstructure. The micro and nanostructure characterization reveals directional fabrication of oyster shells, with more organized structure as biomineralization progresses. Under OA, both the larval and juvenile stages show directional dissolution, i.e. the earlier formed shell layers undergo dissolution at first, owing to longer exposure time. Despite dissolution, the micro and nanostructure of the shell remains unaffected under OA, irrespective of parental exposure history.

Beschreibung: Rising anthropogenic carbon dioxide (CO2) dissolving into coastal waters is decreasing the pH and carbonate ion concentration, thereby lowering the saturation state of calcium carbonate (CaCO3) minerals through a process named ocean acidification (OA). The unprecedented threats posed by such low pH on calcifying larvae of several edible oyster species have not yet been fully explored. Effects of low pH (7.9, 7.6, 7.4) on the early growth phase of Portuguese oyster (Crassostrea angulata) veliger larvae was examined at ambient salinity (34 ppt) and the low-salinity (27 ppt) treatment. Additionally, the combined effect of pH (8.1, 7.6), salinity (24 and 34 ppt) and temperature (24 °C and 30 °C) was examined using factorial experimental design. Surprisingly, the early growth phase from hatching to 5-day-old veliger stage showed high tolerance to pH 7.9 and pH 7.6 at both 34 ppt and 27 ppt. Larval shell area was significantly smaller at pH 7.4 only in low-salinity. In the 3-factor experiment, shell area was affected by salinity and the interaction between salinity and temperature but not by other combinations. Larvae produced the largest shell at the elevated temperature in low-salinity, regardless of pH. Thus the growth of the Portuguese oyster larvae appears to be robust to near-future pH level (〉 7.6) when combined with projected elevated temperature and low-salinity in the coastal aquaculture zones of South China Sea.

Beschreibung: As a consequence of anthropogenic CO2-driven ocean acidification (OA), coastal waters are becoming increasingly challenging for calcifiers due to reductions in saturation states of calcium carbonate (CaCO3) minerals. The response of calcification rate is one of the most frequently investigated symptoms of OA. However, OA may also result in poor quality calcareous products through impaired calcification processes despite there being no observed change in calcification rate. The mineralogy and ultrastructure of the calcareous products under OA conditions may be altered, resulting in changes to the mechanical properties of calcified structures. Here, the warm water biofouling tubeworm, Hydroides elegans, was reared from larva to early juvenile stage at the aragonite saturation state (Omega A) for the current pCO2 level (ambient) and those predicted for the years 2050, 2100 and 2300. Composition, ultrastructure and mechanical strength of the calcareous tubes produced by those early juvenile tubeworms were examined using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and nanoindentation. Juvenile tubes were composed primarily of the highly soluble CaCO3 mineral form, aragonite. Tubes produced in seawater with aragonite saturation states near or below one had significantly higher proportions of the crystalline precursor, amorphous calcium carbonate (ACC) and the calcite/aragonite ratio dramatically increased. These alterations in tube mineralogy resulted in a holistic deterioration of the tube hardness and elasticity. Thus, in conditions where Omega A is near or below one, the aragonite-producing juvenile tubeworms may no longer be able to maintain the integrity of their calcification products, and may result in reduced survivorship due to the weakened tube protection.