Parasites of the past: Tracking change in marine parasite abundance over time

Abstract

In recent years, disease ecologists have perceived a dramatic increase in infectious-disease-related mass mortality events among marine organisms. But does this increase reflect an actual rise in rates of infectious disease, or is it merely the artefact of improved detection and monitoring capacity? To help answer this question, I took two approaches: (1) I used meta-analysis to assess change in the abundance of two economically and ecologically important parasites over the past several decades and (2) I performed a manipulative experiment to test whether it might be possible to use liquid-preserved fish held in natural history collections to resurrect reliable information on parasites of the past. In Chapter 1, I harnessed the statistical power of the many published empirical studies that have measured the abundance of Anisakis spp. and Pseudoterranova spp. nematodes to reconstruct fifty years of change in the abundance of these economically and ecologically important parasites, finding a 208-fold increase in Anisakis spp. and no change in Pseudoterranova spp. With this method, we can reconstruct change in disease for the past half-century, but we are constrained by the limited availability of electronic records for studies published prior to ~1970. To get back further in time, in Chapter 2, I performed an experiment to assess whether preservation biases parasite detectability in liquid-preserved fish held in natural history collections, finding only a minimal influence of museum preservation protocols on the ability to detect parasites. Because preservation has little influence on parasite detectability, parasitological dissection of such natural history specimens could provide a reliable estimate of the parasites that were present in a host at the time of its death. Thus, my work extends our ability to assess change in parasite abundance over time, arming disease ecologists with the tools needed to assess whether rates of infectious disease are indeed on the rise.