The effect of allometric scaling in coral thermal microenvironments

Abstract

A long-standing interest in marine science is in the degree to which environmental conditions of flow and irradiance, combined with optical, thermal and morphological characteristics of individual coral colonies, affects their sensitivity of thermal microenvironments and susceptibility to stress-induced bleaching within and/or among colonies. The physiological processes in Scleractinian corals tend to scale allometrically as a result of physical and geometric constraints on body size and shape. There is a direct relationship between scaling to thermal stress, thus, the relationship between allometric scaling and rates of heating and cooling in coral microenvironments is a subject of great interest. The primary aim of this study was to develop an approximation that predicts coral thermal microenvironments as a function of colony morphology (shape and size), light or irradiance, and flow velocity or regime. To do so, we provided intuitive interpretation of their energy budgets for both massive and branching colonies, and then quantified the heat-size exponent (b*) and allometric constant (m) using logarithmic linear regression. The data demonstrated a positive relationship between thermal rates and changes in irradiance, A/V ratio, and flow, with an interaction where turbulent regime had less influence on overall stress which may serve to ameliorate the effects of temperature rise compared to the laminar regime. These findings indicated that smaller corals have disproportionately higher stress, however they can reach thermal equilibrium quicker. Moreover, excellent agreements between the predicted and simulated microscale temperature values with no significant bias were observed for both the massive and branching colonies, indicating that the numerical approximation should be within the accuracy with which they could be measured. This study may assist in estimating the coral microscale temperature under known conditions of water flow and irradiance, in particular when examining the intra- and inter-colony variability found during periods of bleaching conditions.

Fleshy Red Algae Mats Influence Their Environment in the Mediterranean Sea

“…While many studies focused on the effect of temperature on algae growth (e.g., Butterwick et al, 2004;Baker et al, 2007;Martin and Gattuso, 2009), the effects of algae on the habitat's temperature are so far unstudied. Studies of another important ecosystem engineer, however, report similar effects on temperature: shallow water scleractinians increased water temperatures in their microenvironment, due to solar radiation and water holding capacities by surface heterogeneity (Jimenez et al, 2008;Ong et al, 2017). While solar radiation plays only a minor role in the deep layer of P. crispa mats, we showed that water movement is low in the algae mats, which could indicate a long water residence time and explain a similar effect on the thermal microenvironment of this habitat.…”

What drives phenotypic divergence among coral clonemates of Acropora palmata?

“…Changes in epigenetic marks based on the detection of environmental cues provides an avenue to effect phenotypic plasticity (Shea et al, 2011). Detailed data on systematic variation in temperature, flow and light regimes depending on polyp location within a colony and colony morphology are accumulating (Edmunds & Burgess, 2018;Ong, King, Kaandorp, Mullins, & Caley, 2017;Stocking, Rippe, & Reidenbach, 2016). Remarkably, there was some correspondence between genes previously shown to be differentially expressed, and those that were differentially methylated, indicating that methylation differences may translate into gene expression differences.…”

Transcriptional response of the heat shock gene hsp70 aligns with differences in stress susceptibility of shallow-water corals from the Mediterranean Sea

“…More generally, coral morphology is thought to influence flow regimes and thermal fluxes at the tissue-water interface (Jimcncz et al, 2011;Nakamura and Van Wocsik, 2001 ), tissuc thickness and availability of resources (Loya et al , 2001 ), and to affect diversity and light-absorbing properties of the zooxanthellae symbionts (Enrfquez et al, 2005;Yost et al, 2013). A recent study modeled the relationsh ips between allometric scaling and rates of heating/ cooling in coral microenvironments as a result of physical and geometric constraints on body size and shape, and showed that, under similar water flow and irradiance conditions, smaller corals are subjected to comparatively higher stress Jevels than bigger corals (Ong et al, 2017). Consequently, during the heat treatments the (smaller) solitary morphotype (B. europaea) investigated in this study may have experienced relatively higher heat fluxes at the water-polyp interface compared to the (bigger) colonial C. caespitosa, thus showing higher hsp70 induction.…”