Nutrient Pollution and Predation Differentially Affect Innate Immune Pathways in the Coral Porites porites

Abstract

Reef-building corals face a multitude of threats not only from global climate change but also local stressors such as nutrient pollution. Nutrient enrichment can amplify the negative effects of predation on corals by facilitating dysbiosis in the coral microbiome that leads to coral mortality. These patterns suggest that nutrient pollution might suppress the capacity of the coral immune system to respond to microbial infections that follow mechanical injury from predation. Here, we measured the impact of nutrient enrichment and predation on tyrosinase-type and laccase-type phenoloxidase (PO) activities, which are key components of immune defense pathway involved in melanin synthesis and wound healing in corals. Corals were exposed in situ to either ambient or enriched nutrient levels in combination with either no damage, mechanical damage, or predation damage from parrotfishes. The activity of PO enzymes in response to both tyrosinase-type substrates significantly decreased under nutrient enrichment, suggesting that corals became immune-compromised. Predation damage also increased laccase activity, implicating it in tissue repair and potentially defense from pathogens. Our findings highlight the need to mitigate nutrient pollution on coral reefs, as higher nutrient levels suppress important coral immune pathways and likely contribute to patterns of increased coral disease and subsequent mortality on reefs plagued by nutrient enrichment.

Spatial and Temporal Patterns of Stony Coral Tissue Loss Disease Outbreaks in The Bahamas

“…Even in Grand Bahama, which is only 100 km from Florida, the reefs to the west that were closest to Florida had lower infection or mortality rates than those closer to the port of Freeport. An alternative hypothesis that may explain this pattern is that SCTLD may not have originated close to the port on either island, but corals there may have been more vulnerable to the disease due to pollution, nutrients, or other environmental conditions (e.g., Dougan et al, 2020). We believe that this is a less likely scenario, however, as previous studies have documented declines in reef condition associated with pollution in both the east and west of New Providence (Sealey, 2004;Dahlgren et al, 2020) and the area of eastern Grand Bahama where Hurricane Dorian significantly impacted reefs (Dahlgren et al, 2020), but all of these areas showed lower effects of SCTLD than more centrally located reefs close to the ports in this study.…”

Education and Research: A Symbiosis to Better Understand a Novel Coral Disease

“…A number of environmental factors have been investigated concerning the emergence of the disease, which include increased sea surface temperatures (SSTs), increased turbidity from a concurrent dredging project (Miller et al, 2016;Gintert et al, 2019;Precht, 2021), and eutrophication (Dougan et al, 2020). Eutrophication from nutrient run off in the South Florida region, may have led to a reduction in immune function making corals susceptible to infection (Dougan et al, 2020). Although the exact biological causative agent is still unknown, it seems probable that a bacterial component exists.…”

Functional Characterization of Hexacorallia Phagocytic Cells

“…Through an intricate cellular recognition system, non-self can be recognized and initiate downstream signaling pathways that ultimately lead to effector responses such as phagocytosis, coagulation, and antimicrobial defense (1). Among the Cnidaria, significant progress has been made within Class: Hexacorallia (i.e., scleractinian corals and sea anemones) on our understanding of innate immune system responses to environmental stress (2)(3)(4)(5)(6)(7)(8). Coral reefs are currently one of the most endangered ecosystems on the planet due to anthropogenic climate change and local human impacts (9)(10)(11)(12)(13)(14).…”