Nutrition of Corals and Their Trophic Plasticity under Future Environmental Conditions

Abstract

Scleractinian corals obtain metabolic energy from their endosymbiotic autotrophic microalgae, and from remineralization of organic matter by bacteria and viruses, along with the heterotrophic food sources. The mutualistic symbiosis is generally stable but can be disrupted when environmental conditions surrounding the corals, such as increasing seawater temperature, become unfavorable to sustain each component of the holobiont. In this connection, the effects of global stressors such as climate change, and local stressors such as pollution, and their combination, are posing serious threats to the metabolic resistance of corals. However, some more resilient coral species have developed specific mechanisms to cope with fluctuating environmental conditions according to the trophic strategy (autotrophy, heterotrophy, or mixotrophy), and by modulating their energy expenditure. In this chapter, the role of nutrition in the coral symbiosis as the energetic budget for metabolic performance will be discussed, with a focus on the role of acquisition of nutrients through feeding, regulation of energy reserves (lipids, proteins, and carbohydrates), and adaptation capability in the natural environment, including the expression of heat-shock proteins (Hsps). Future environmental conditions under a combination of global changes and local impacts will also be discussed, with the aim of identifying the trophic niches of corals and geographical areas as possible refugia.

Two biomarkers of gene expression plasticity in Pocillopora corals from the Carrizales reef, Mexican Tropical Pacific

“…In terms of gene-by-gene expression analysis, plasticity occurs after the environmental change (stress signal) when the expression of a gene significantly increases to reach a peak of expression under the new stress condition (Hédouin & Berteaux-Lecellier, 2014;Rivera et al, 2021), in this case, thermal and nutrients stresses. Higher hsp70 levels in Pocillopora corals are generally related to a protective response toward environmental and cellular stressors (Poli et al, 2017;Zhang et al, 2018;Dellisanti et al, 2022), with the tolerant phenotypes exhibiting higher expression levels than the susceptible ones. This is true when stress-tolerant populations show higher baseline expressions before the stress condition and less (induction) positive change in gene expression after (Poli et al, 2017), which confers protection from frequent stresses through a pre-emptive response (frontloading) and by maintaining cellular integrity under constant pressure (Brener-Raffalli et al, 2022).…”

“…Before the expression of any gene can be applied as a universal biomarker, however, there must be an understanding of its promises and limitations concerning natural environmental sensitivity, species-specificity response, environmental history, and current anthropogenic impacts and how expression patterns relate to the physiological and ecological consequences of stress tolerance and resilience due to those varying factors (Kenkel et al, 2014;Rivera et al, 2021;Drury et al 2022). For instance, the hsp70 gene expression can change drastically with a variety of environmental stress such as extreme temperatures (high or low), high light intensity and salinity changes, nutrient enrichments, and cellular stress caused by coral bleaching and pathogen invasion in corals (Seveso et al, 2016;Zhang et al, 2018;Dellisanti et al, 2022). Furthermore, when nutrient enrichment is coupled with thermal stress, severe damage occurs to the coral holobiont of Pocillopora damicornis (Linnaeus, 1758) (compared with the individual effects) due to the Hsps upregulation-induced apoptosis and bleaching mechanism amplification by high nitric oxide (NO) production (Thummasan et al, 2021).…”