[Coral-List] Fast coral extension rates DO NOT equate with a healthy coral in a warming ocean

Scott Wooldridge swooldri23 at gmail.com
Fri Aug 11 01:21:50 UTC 2017


Dear Fellow Coral Researchers, most particularly young scientists who are
keen to design experiments that will advance the science behind coral reef
biology.


I urge you to reconsider the outdated concept that fast skeletal extension
rates in symbiotic corals equates to a healthy and resilient coral. In
fact, in a warming (and high pco2) ocean, I contend that it is the complete
opposite.


Here is a very simple experiment that can be done to test. Raise corals
under optimal 'spring' temperature and irradiance conditions. Add variable
concentrations of dissolved inorganic nutrients to different treatments
such as to alter symbiont densities. You will find that under these optimal
'spring-type' conditions, the corals with the largest symbiont densities
will have the fastest growth (extension) rates. Now apply these same corals
to a warming treatment to replicate anomalous summer heat/beaching event.
You will discover that the corals (with elevated symbiont densities) that
have the highest growth as 'optimal' conditions, will be the first to
bleach and die at the anomalous temperatures.


I have previously described this phenomenon in the following manuscript in
BioEssays:


https://www.researchgate.net/publication/265297066_Assessing_coral_health_and_resilience_in_a_warming_ocean_Why_looks_can_be_deceptive


which builds on a new (improved) understanding of the coral
biomineralisation process;


https://www.researchgate.net/publication/307732715_A_new_conceptual_model_of_coral_biomineralisation_hypoxia_as_the_physiological_driver_of_skeletal_extension


This new conceptualisation also explains that 'high' bleaching risk areas,
will also be the areas with the highest growth rates in non-bleaching
years. See for example, the Great Barrier reef Porites dataset (cf fig.8)
in paper 2.


https://www.researchgate.net/publication/308746785_Excess_seawater_nutrients_enlarged_algal_symbiont_densities_and_bleaching_sensitive_reef_locations_1_Identifying_thresholds_of_concern_for_the_Great_Barrier_Reef_Australia


https://www.researchgate.net/publication/308746844_Excess_seawater_nutrients_enlarged_algal_symbiont_densities_and_bleaching_sensitive_reef_locations_2_A_regional-scale_predictive_model_for_the_Great_Barrier_Reef_Australia


Other researchers have also documented the fact that fast skeletal growth
is indicative of areas where the health/resilience of the coral host is
actually the most compromised. For example, Denis et al. 2013, conclude, “High
growth rates seem to impair regeneration capacity. We show that
environmental conditions conducive to high zooxanthellae densities in
corals are related to fast skeletal growth but also to reduced lesion
regeneration rates “


Denis V, Guillaume MMM, Goutx M, de Palmas S, Debreuil J, Baker AC, et al.
(2013) Fast Growth May Impair Regeneration Capacity in the Branching
Coral *Acropora
muricata*. PLoS ONE 8(8): e72618.
https://doi.org/10.1371/journal.pone.0072618




In conclusion, I contend, perhaps more contentiously, that all of these
findings lead to the obvious conclusion that symbiotic corals are “the
living dead” in the modern “Anthropocene” ocean.


https://www.researchgate.net/publication/317100418_Instability_and_breakdown_of_the_coral-algae_symbiosis_upon_exceedence_of_the_interglacial_pCO2_threshold_260_ppmv_the_%27%27missing%27%27_Earth-System_feedback_mechanism



That is, unless they have plasticity for heterotrophic feeding during
periods of autotrophic stress.


https://www.researchgate.net/publication/269991541_2_3_Formalising_a_mechanistic_linkage_between_heterotrophic_feeding_and_thermal_bleaching_resistance



My hope, is that these ideas will challenge us to move forward with some
new thinking.


Scott


https://www.researchgate.net/profile/Scott_Wooldridge



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