Warming and pollutants interact to modulate octocoral immunity and shape disease outcomes

Abstract

Warming environments can alter the outcome of host–parasite relationships with important consequences for biodiversity. Warming often increases disease risk, and interactions with other environmental factors can intensify impacts by modifying the underlying mechanisms, such as host immunity. In coastal ecosystems, metal pollution is a pervasive stressor that influences disease and immunity in many organisms. Despite the crisis facing coral reefs, which stems in part from warming‐associated disease outbreaks, the impacts of metal pollutants on scleractinian and octocoral disease are largely unknown. We investigated how warming oceans and copper pollution affect host immunity and disease risk for two diseases of the abundant Caribbean octocoral, the sea fan Gorgonia ventalina. Field surveys across a sediment copper concentration gradient in Puerto Rico, USA revealed that cellular immunity of sea fans increased by 12.6% at higher sediment copper concentrations, while recovery from multifocal purple spots disease (MFPS) tended to decrease. MFPS severity in the field increased at warmer sites. In a controlled laboratory experiment, sea fans were inoculated with live cultures of a labyrinthulid parasite to test the interactive effects of temperature and copper on immune activation. As in the field, higher copper induced greater immunity, but the factorial design of the experiment revealed that copper and temperature interacted to modulate the immune response to the parasite: immune cell densities increased with elevated temperature at lower copper concentrations, but not with high copper concentrations. Tissue damage was also greater in treatments with higher copper and warmer temperatures. Field and lab evidence confirm that elevated copper hinders sea fan immune defenses against damaging parasites. Temperature and copper influenced host–pathogen interactions in octocorals by modulating immunity, disease severity, and disease recovery. This is the first evidence that metal pollution affects processes influencing disease in octocorals and highlights the importance of immune mechanisms in environmentally mediated disease outbreaks. Although coral conservation efforts must include a focus on global factors, such as rapid warming, reducing copper and other pollutants that compromise coral health on a local scale may help corals fight disease in a warming ocean.

Little evidence for genetic variation associated with susceptibility to sea star wasting syndrome in the keystone species Pisaster ochraceus

“…While the viral candidate sea star-associated densovirus (SSaDV) has been debunked (Jackson et al, 2020), other possible causative or exacerbating agents remain unknown, with hypotheses including pathogen(s) (Lloyd & Pespeni, 2018), inconsistent aetiology stress responses between locations, species and environment (Hewson et al, 2018), microbial dysbiosis (Lloyd & Pespeni, 2018), and microbial-driven depletion of oxygen at the animal-water interface (Aquino et al, 2021). There is also mixed evidence for whether anomalously warm waters linked to global warming initiated the outbreak (Aalto et al, 2020;Eisenlord et al, 2016;Menge et al, 2016Menge et al, , 2016bMiner et al, 2018;Tracy et al, 2020). Regardless, it is clear that the disease is exacerbated in warmer conditions (Bates et al, 2009;Eckert et al, 1999;Eisenlord et al, 2016;Kohl et al, 2016), and that severe population reductions occurred in warmer southern regions (Gravem et al, 2021;Harvell et al, 2019;Miner et al, 2018).…”

The indirect effects of ocean acidification on corals and coral communities

“…Coral disease results from interactions between the host corals and the pathogen causing the disease. Worldwide, the prevalence of coral diseases has increased in recent decades due to a number of factors, such as rising water temperatures (Tracy et al 2020), and decreasing water quality including nutrient enrichment (Vega-Thurber et al 2014), plastic pollution (Lamb et al 2018) and metal pollution (Tracy et al 2020). However, the effect of acidification on coral diseases is largely unknown and remains a significant knowledge gap (Vega Thurber et al 2020).…”

Similarities and Differences Between Two Deadly Caribbean Coral Diseases: White Plague and Stony Coral Tissue Loss Disease

“…Particularly important is to adopt a holistic approach to better decipher the disease dynamics in corals. The idea is to integrate modern paradigms that consider multiple and variable interactions among the three major players in an epizootic event: the host, its associated microbiome, and the environment (Tracy et al, 2020;Vega Thurber et al, 2020). Secondly, permanent monitoring programs not only depend on resources but also in building capacity to increase the number of observers with standardized protocols.…”