How does warmer sea water change the sensitivity of a Mediterranean thermophilic coral after immune-stimulation?

Abstract

Anthropogenic climate change is warming sea water worldwide, pushing the limits of tolerance for marine organisms and driving a decline in biodiversity. The risk of thermal anomalies has increased particularly in the Mediterranean region over the last 30 yrs, where intense warming has been identified as one of the main stressors in coastal regions. To determine the influence of warmer conditions on the immunity of an endemic Mediterranean coral species, different immune activity parameters were compared in response to elevated temperature (~ 28 °C) and the presence of a pathogen-associated molecular pattern—Escherichia coli lipopolysaccharide (LPS)—as an elicitor of the innate immune response of Astroides calycularis. Immune parameters, which included phenoloxidase-like, glutathione peroxidase, lysozyme-like, alkaline phosphatase, and esterase enzyme activity, were measured over time after LPS balneation (0-, 12-, 48-, and 120 h time point). All five enzymes demonstrated constant values under environmental conditions (~ 23 °C), indicating a constituent activity. LPS at environmental temperature induced significant upregulation immediately after exposure (0 h-time point), demonstrating an immune response to the pathogen elicitor. Under warmer conditions (~ 28 °C), constituent values increased over time, indicating a shift in the immune strategy to maintain homeostasis. However, warmer sea water, within the summer range experienced by this coral species, impaired the immune response to LPS, delaying it over time. These changes in immune strategy indicate that temperature affects coral immunity and, in thermophilic A. calycularis, results in an energy trade-off that could maintain its health-state through suboptimal conditions during multiple perturbations, such as summertime diseases.

Prior heat stress increases pathogen susceptibility in the model cnidarianExaptasia diaphana

“…This result is in agreement with documented increases in disease and disease-related mortality following coral bleaching in the wild. 24,40,44,96 Notably, while previous laboratory experiments have documented impacts of simultaneous heat stress and pathogen exposure 45,47,50,51,97 ours is the first to document the prolonged consequences of heat stress on pathogen susceptibility, more accurately representing observed environmental patterns in nature. Future studies combining our approach with emergent experimental disease techniques 98,99 will allow for more broadscale applications to complex cnidarian and marine disease systems.…”

“…24,44 Despite these observations, nearly all experimental studies have focused on the synergistic effects of simultaneous heat stress and disease, specifically documenting increases in disease susceptibility when these stressors occur at the same time. 45,46 Synchronous associations between heat stress and increased pathogen susceptibility may be linked to heat induced suppression of immunity, [47][48][49][50][51] though other studies have instead demonstrated minimal or positive effects of heat stress on coral immunity. [52][53][54] Furthermore, it is unclear if similar mechanisms underly sequential associations between heat stress and disease outbreaks.…”