Anthropogenic impacts on an oyster metapopulation: Pathogen introduction, climate change and responses to natural selection

Abstract

Humans rely on marine ecosystems for a variety of services but often impact these ecosystems directly or indirectly limiting their capacity to provide such services. One growing impact is the emergence of marine disease. We present results from a unique case study examining how oysters, a dominant organism in many coastal bays and estuaries that is often harvested for food, have responded to pathogens influenced by human activities, namely the introduction of novel pathogens. Climate change has enabled a northward spread and establishment of Dermo disease in oysters along the eastern seaboard of North America and human activities inadvertently introduced MSX disease along this same coast. Oysters in Delaware Bay have responded differently to each pathogen, and uniquely to MSX disease by developing a highly resistant baywide population not documented in any other bay. Offspring were produced using parents collected from low or high disease (MSX and Dermo) regions of Delaware Bay and exposed in a common garden experiment along with a naïve population from Maine. Results indicated widespread resistance to MSX disease, but not to Dermo disease, across Delaware Bay. One striking result was the demonstration of resilience in the population through its capacity to spread, presumably through larval transport, resistance to MSX disease into portions of the population that have experienced little to no MSX disease pressure themselves. Related studies indicated that larval transport mechanisms allowed widespread dispersal such that the entire metapopulation could acquire a high level of resistance over time if disease resistance is sufficiently heritable. The findings have implications for restoration, management and recovery of diseased populations. Namely, that if left to their own devices, natural selection may find a solution that enables populations to recover from introduced pathogens.

Effects of Infectious Diseases on Population Dynamics of Marine Organisms in Chesapeake Bay

“…Although low salinitymay mitigate the negative effects of Dermo disease, it does not eradicate the pathogen (Paynter and Burreson 1991), indicating that future periods of high salinity may lead to further epizootics. Over the decades, there is evidence that natural populations of oysters become more tolerant of MSX and Dermo, presumably through natural selection (Bushek and Ford 2016). Two parasites closely related to P. marinus (P. andrewsi and P. chesapeaki) and disseminated neoplasia (also referred to as sarcoma) cause infections and are associated with high mortality rates in soft clams (Mya arenaria and Macoma balthica) and razor clam (Tagelus plebeius) populations in Chesapeake Bay (Dungan et al 2002;Reece et al 2008).…”

“…Shifting environmental conditions may affect interactions between hosts and pathogens, which can tilt the balance toward or away from high disease states (Burge et al 2014;Barbieri et al 2018). Our understanding of how climate change will affect marine infectious diseases in the Chesapeake Bay is restricted to hosts for which there are long-term infectious disease datasets (Harvell et al 2002), in particular oysters and striped bass (Hofmann et al 2001;Bushek and Ford 2016;Groner et al 2018b). Predicting responses to climate change is further complicated by the synergistic effects of populations responding to multiple climate variables and subsequent changes in the marine community (Harvell et al 2002;Ward and Lafferty 2004).…”

Effective Surface Area and the Potential for Recovery from Mass Mortality in Eastern Oyster Populations, with a Vignette on the Critical Period For Reef Recovery

“…Notwithstanding the likely negative impact of climate change (Oviatt 2004, Garland & Kimbro 2015, Bushek & Ford. 2016, Powell 2017, Moore et al 2020) and the continuing challenge of fishery management (Powell et al 2009, Wilberg et al 2013, Powell et al 2018, Solinger et al 2022), both of which have increased the challenge posed by oyster restoration, an important, yet undervalued, constraint is the limited understanding of the balance between live and dead shell on the reef and the equivalently limited understanding of the details of the recruitment process and the larval behavioral attributes taken advantage of by methods used for recruitment enhancement (Mann et al 2009, Harding et al 2012, Hemeon et al 2020, Ashton-Alcox et al 2021, Soniat et al 2021, Solinger et al 2022).…”