Chapter 7 Environmental Variability
pCO2 variability
Wall et al 2020: shifting baselines; physiotypes
paper link here.
Back to back regional bleaching events 2014, 2015. Compared C vs. D symbiont dominated corals from 2 pCO2 variability distinct reefs (see Wall 2018 paper below for start).
Physiological legacy effects / coral multivariate trait space (physiotype)
Melanin - immune cytotoxic response can provide an initial first line of defense and potentially primes antioxidant activity (legacy effect). Melanin synthesis pathway that is active in wound-healing and pathogen invasion while serving as a photoprotectant.
Host and symbiont have enzymatic defenses to mitigate oxidative stress (peroxidase, catalase, superoxidate dismutase). Sources of damage in host = heat-damaged mitochondrial membranes); symbiont source of damage = D1 protein of photosystem II (PSII). Ultimately lead to apoptosis and dysbiosis.
Bleaching was strongly related to symbiont community and their sensitivity to thermal stress, which was influenced by site environmental history. Physiotypes were shaped by immune and antioxidant activity in bleaching and recovery periods not related to symbiont community = host driven. Constitutive immunity from one year to the next.
Shifting baselines concept:
fig1
Wall et al 2018: Env hist / Thermal stress on coral phys / immunity
Paper link here.
Effect of env. history of low vs. high variable pCO2 in Mcap on response to elevated temp to 30.5C (+6C above ambient).
- Heating decreased maximum photochemical efficiency (Fv/Fm) and chlorophyll a pigmentation, but increased melanin.
- Intxn of env. history & temp treatment not observed.
- Greater pCO2 variability had higher constitutive antioxidative and immune activity (catalase, superoxide dismutase, prophenoloxidase) and Fv/Fm but lower melanin and chl-a.
- Greater variability promotes greater antioxidant and immune activity.
- Antioxidant levels were not influenced by thermal treatment, just as a fxn of environmental history.
- History did not interact with thermal stress to determine physiological state. Env history shaped starting point not during stress response.
Higher constitutive melanin exp in coral spp considered thermally tolerant (see Palmer papers).
Rivest et al 2017: natural variability in shaping response
Paper link here.
Temp & pCO2 variability review.
Lagoons and back reefs experience greater daily temp/pCO2 than fore-reef. Habitats dominated by corals rather than algal expression a smaller diel pH variability b/c photosynthesis elevates pH.
History can present itself in four general ways:
1. recent env. conditions can prime future responses to stress.
2. Experience of one life history stage can carry over to affect the performance of a later life history stage.
3. Transgenerational acclimatization - parents can integrate information from their environment and affect performance phenotypes of offspring.
4. Local adaptation of populations.
Site five papers that tested variability:
1. A. hyacinthus in American Samoa; high temp var = less mortality and retained higher photosynthetic efficiency when exposed to heat stress (Oliver and Palumbi 2011)
2. Corals transplanted to high variability site showed greater bleaching resistance in a thermal challenge (Palumbi et al 2014), but corals from HV and stayed at HV had the highest performance.
3. Coral spp in NW Australia from thermally HV were more thermotolerant and less bleaching (Schoepf et al 2015)
4. Coral larvae in Mo’orea with lower temp var but higher mean temp had more tolerance than larvae in Taiwan with higher temp var but lower mean temp (Rivest et al papers)
5. No effect of temp history in thermal stress of +2C (Camp et al 2016).
pH variability:
Cites ~6 experiments that all yielded no significance in response from pH distinct reefs.
> This similarly lines up with Wall et al in that pH history didn’t influence response in thermal stress but there were baseline differences. pH variability might not be critical in immediate stress response but chronic environmental signal may change physiological baselines.
Two ways to estimate difference b/w expt condition and natural regime of env. conditions:
1. diff b/w expt conditions and mean condition reported from collection site
2. diff b/w expt conditions and min or max of env. condition
When calculating response ratios across the two ways to estimate difference in expt condition and natural regime:
fig2-rivest
Caveats to higher variability environments act as a refugee:
1.) Greater pH variability might not select solely for low-pH tolerance in resident organisms b/c high pH during the day may impose independent selective pressures for photosynthetic spp.
- seawater carbonate chemistry affects calcification and photosynthesis.
- Higher pH during the day = lower concentrations of CO2 (opposite effect of OA), which could be a brief period of recovery that allows for faster calcification.
- increases in pH could constrain photosynthesis or increase use of E expensive carbonate concentrating mechanisms CCMs. CCMs allow uptake of dissolved inorganic carbon as bicarbonate during periods of low [CO2] - which happens during high variability.
- use of CCMs becomes more prevalent when [oxygen] co-occur with high pH - during the day in diurnally variable pH. HV pH env may select for organisms that are efficient at using bicarbonate when pH is high, these organisms may be outcompeted by organisms that don’t investe their E heavily in CCMs when OA results in lower pHs.
2.) Organisms living in highly variable environments could be living on the edge of their physiological capacity to cope with multiple varying stressors. Integration of stressors may push organisms over their tolerance levels - diel variation in temp AND pH. Shifting means could push this over.
3.) Limited environmental measurements limit our ability to seperate differential mean conditions from variable conditions. This has not been tested adequately in pH variable conditions.
4.) If local adaptation is the main driver, translocation from HV to LV environments may not be effective since the signal has disappeared and that coral’s history would have come from several generations.
Cornwall et al 2018: Corals/CCA to OA: phys control under pH var
Paper link here.
Goniopora sp. (coral) and Hydrolithon reinboldii (CCA) from two sites of distinct pH variability grown for 100 days under differing variability and means.
- Coral calcification rates were unaffected by the above.
- Calcification rates of CCA were faster in HV and HV high mean conditions.
- Only mean seawater pH influenced pH calcifying fluid (pHcf).
- calcifying taxa may be capable of maintaining rates by actively modifying omega cf (Ocf).
Corals and CCA from greater variability in pH are not more tolerant to OA than those from LV. Species specific mechanisms seem to be more important. Both spp are capable of physiological control.
Maintenance of constant aragonite saturation state of calcifying fluid could occur via 3 possibly complementary mechanisms:
1. maintenance of constant pHcf
2. elevation of DICcf
3. elevation of Ca2+ cf
Thermal variability
High variability reduces the risk of coral bleaching: Safaie et al 2018
Thermal variability did not enhance tolerance: Klepac and Barshis 2020
Seasonal variability/range and influence on microbiome: Shiu et al 2017
Thermal variability did not play a role in symbiont community determination: Baumann et al 2018
Same sites as above: microbiome vs symbiont in those HV and LV sites: Speare et al 2020
Corals from most extreme thermal environments escape mortality: Pineda et al 2013
Preconditioning and recurrent signal
Short term preconditioning to higher temperatures provides tolerance: Bellantuono et al 2012
History matters: influence of origin (general)
Warmer water gorgonians have increased tolerance: Linares et al 2013
Castillo and Helmuth 2005 here
Kevin Wong’s Global change biology paper
Papers to sort through later..
Reefs with higher frequency of thermal anomalies displayed differential susceptability to coral disease (Randall et al 2014).
Differential thermal regimes influence lesion recovery: Kaufman et al 2021
Environmental memory
Squirts and antioxidant capacity and how they define ways of environmental memory.
Decadal ‘memory’ after previous high solar irradiance exposure: Brown et al 2014