Abstract
Infectious diseases not regulated by host density, such as vector-borne diseases, have the potential to drive population declines and extinctions. Here we test the vector potential of the snail Drupella sp. and butterflyfish Chaetodon plebeius for two coral diseases, black band (BBD) and brown band (BrB) disease. Drupella transmitted BrB to healthy corals in 40% of cases immediately following feeding on infected corals, and even in 12% of cases 12 and 24 hours following feeding. However, Drupella was unable to transmit BBD in either transmission treatment. In a field experiment testing the vector potential of naturally-occurring fish assemblages, equivalent numbers of caged and uncaged coral fragments became infected with either BrB, BBD or skeletal eroding band, indicating that corallivorous fish were unlikely to have caused transmission. In aquaria, C. plebeius did not transmit either BBD or BrB, even following extended feeding on both infected and healthy nubbins. A literature review confirmed only four known coral disease vectors, all invertebrates, corroborating our conclusion that polyp-feeding fishes are unlikely to be vectors of coral diseases. This potentially because polyp-feeding fishes produce shallow lesions, not allowing pathogens to invade coral tissues. In contrast, corallivorous invertebrates that create deeper feeding scars increase pathogens transmission.
Highlights
Infectious diseases not regulated by host density, such as vector-borne diseases, have the potential to drive population declines and extinctions
To synthesise new insights into whether and how vector-borne diseases circumvent density-dependent infection dynamics that prevent species extinctions, we review existing knowledge of coral disease vectors and their potential to amplify coral disease impacts on coral population dynamics
This study demonstrates that Drupella snails transmit the virulent coral disease, brown band disease (BrB), both immediately after feeding and for at least 24 h after feeding on diseased coral nubbins
Summary
Infectious diseases not regulated by host density, such as vector-borne diseases, have the potential to drive population declines and extinctions. Vector-borne pathogens and sexually-transmitted diseases are commonly frequency-dependent, and their prevalence can continue to increase even when host density is low, leading to disease-mediated population declines and extinctions[7,8]. Maynard et al.[13] predicts that “increases in the prevalence and severity of coral diseases will be a major future driver of decline and changes in coral reef community composition”, given projections of how rising sea temperatures are likely to affect pathogen virulence and host susceptibility Such projections are consistent with evidence that changes in host-pathogen interactions following environmental and/or ecosystem modification have been key to the emergence of most infectious diseases[14]. Black band disease (BBD) affects at least 40 coral species on the Great Barrier Reef[17,18], enabling the disease to circumvent more typical density-dependent, host-pathogen dynamics. A good understanding of a vector’s identity, and the timeframes and biological processes involved in the transmission process, are required to establish control procedures in disease management for syndromes with known or unknown pathogens
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