Cross-generational response of a tropical sea urchin to global change and a selection event in a 43-month mesocosm study.

Long-term experimental investigations of transgenerational plasticity (TGP) and transgenerational acclimatization to global change are sparse in marine invertebrates. Here, we test the effect of ocean warming and acidification over a 25-month period of Echinometra sp. A sea urchins whose parents were acclimatized at ambient or one of two near-future (projected mid and end of the 21st century) climate scenarios for 18 months. Several parameters linked to performance exhibited strong effects of future ocean conditions at 9 months of age. The Ambient-Ambient group (A-A, both F0 and F1 at ambient conditions) was significantly larger (21%) and faster in righting response (31%) compared to other groups. A second set of contrasts revealed near-future scenarios caused significant negative parental carryover effects. Respiration at 9 months was depressed by 59% when parents were from near-future climate conditions, and righting response was slowed by 28%. At 10 months, a selective pathogenic mortality event led to significantly higher survival rates of A-A urchins. Differences in size and respiration measured prior to the mortality were absent after the event, while a negative parental effect on righting (29% reduction) remained. The capacity to spawn at the end of the experiment was higher in individuals with ambient parents (50%) compared to other groups (21%) suggesting persistent parental effects. Obtaining different results at different points in time illustrates the importance of longer term and multigeneration studies to investigate effects of climate change. Given some animals in all groups survived the pathogenic event and that effects on physiology (but not behavior) among groups were eliminated after the mortality, we suggest that similar events could constitute selective sweeps, allowing genetic adaptation. However, given the observed negative parental effects and reduced potential for population replenishment, it remains to be determined if selection would be sufficiently rapid to rescue this species from climate change effects.

Reduced seawater pH alters marine biofilms with impacts for marine polychaete larval settlement.

Ocean acidification (OA) can negatively affect early-life stages of marine organisms, with the key processes of larval settlement and metamorphosis potentially vulnerable to reduced seawater pH. Settlement success depends strongly on suitable substrates and environmental cues, with marine biofilms as key settlement inducers for a range of marine invertebrate larvae. This study experimentally investigated (1) how seawater pH determines growth and community composition of marine biofilms, and (2) whether marine biofilms developed under different pH conditions can alter settlement success in the New Zealand serpulid polychaete Galeolaria hystrix. Biofilms were developed under six pH(T) treatments (spanning from 7.0 to 8.1 [ambient]) in a flow-through system for up to 14 months. Biofilms of different ages (7, 10 and 14 months) were used to assay successful settlement of competent G. hystrix larvae reared under ambient conditions. Biofilm microbiomes were characterized through amplicon sequencing of the small subunit ribosomal rRNA gene (16S and 18S). Biofilm community composition was stable over time within each pH treatment and biofilm age did not affect larval settlement selectivity. Seawater pH treatment strongly influenced biofilm community composition, as well as subsequent settlement success when biofilms were presented to competent Galeolaria larvae. Exposure to biofilms incubated under OA-treatments caused a decrease in larval settlement of up to 40% compared to the ambient treatments. We observed a decrease in settlement on biofilms relative to ambient pH for slides incubated at pH 7.9 and 7.7. This trend was reversed at pH 7.4, resulting in high settlement, comparable to ambient biofilms. Settlement decreased on biofilms from pH 7.2, and no settlement was observed on biofilms from pH 7.0. For the first time, we show that long-term incubation of marine biofilms under a wide range of reduced seawater pH treatments can alter marine biofilms in such a way that settlement success in marine invertebrates can be compromised.

Ocean acidification has little effect on developmental thermal windows of echinoderms from Antarctica to the tropics.

As the ocean warms, thermal tolerance of developmental stages may be a key driver of changes in the geographical distributions and abundance of marine invertebrates. Additional stressors such as ocean acidification may influence developmental thermal windows and are therefore important considerations for predicting distributions of species under climate change scenarios. The effects of reduced seawater pH on the thermal windows of fertilization, embryology and larval morphology were examined using five echinoderm species: two polar (Sterechinus neumayeri and Odontaster validus), two temperate (Fellaster zelandiae and Patiriella regularis) and one tropical (Arachnoides placenta). Responses were examined across 12-13 temperatures ranging from -1.1 °C to 5.7 °C (S. neumayeri), -0.5 °C to 10.7 °C (O. validus), 5.8 °C to 27 °C (F. zelandiae), 6.0 °C to 27.1 °C (P. regularis) and 13.9 °C to 34.8 °C (A. placenta) under present-day and near-future (2100+) ocean acidification conditions (-0.3 pH units) and for three important early developmental stages 1) fertilization, 2) embryo (prehatching) and 3) larval development. Thermal windows for fertilization were broad and were not influenced by a pH decrease. Embryological development was less thermotolerant. For O. validus, P. regularis and A. placenta, low pH reduced normal development, albeit with no effect on thermal windows. Larval development in all five species was affected by both temperature and pH; however, thermal tolerance was not reduced by pH. Results of this study suggest that in terms of fertilization and development, temperature will remain as the most important factor influencing species' latitudinal distributions as the ocean continues to warm and decrease in pH, and that there is little evidence of a synergistic effect of temperature and ocean acidification on the thermal control of species ranges.