Long‐term variability and density dependence in Hudson River Dreissena populations

David T. Fischer,Heather M. Malcom,Stephen K. Hamilton,David L. Strayer,Christopher T. Solomon,Michael L. Pace

doi:10.1111/fwb.13444

Abstract

Abstract We used a 27‐year record of Dreissena populations in the freshwater tidal Hudson River to describe interannual variation in population density, body size, and body condition; estimate long‐term variation in recruitment, survivorship, and shell growth; and assess possible controls on the populations. Dreissena populations in the Hudson have been highly variable, with interannual ranges of c. 100‐fold in abundance and biomass, and 7‐fold in mean body mass. This large interannual variation arises from both long‐term trends and 2–5‐year cycles. Long‐term trends include the 2008 appearance of the quagga mussel (Dreissena rostriformis), which still forms a small part (<10%) of the dreissenid community, and a decline in zebra mussel body size. The decline in body size was caused by a long‐term decline in adult survivorship rather than a decline in rates of shell growth. We could detect no long‐term trends in adult abundance or spread of Dreissena onto soft sediments in the Hudson. We observed persistent, strong cycles in adult abundance and body size. These were driven by the appearance and decay of eight dominant year classes over the 27 years of our study, and were a result of temporal variation in recruitment rather than temporal variation in survivorship. The observed strongly irregular recruitment appears to arise from strong adult–larval interactions, and is consistent with previous simulation model results showing that interactions between adults and larvae can drive persistent cycling. We found evidence that negative density dependence affects recruitment, somatic growth, and body condition of Dreissena in the Hudson. Warm summers may also cause high adult mortality. We put our results into the context of a conceptual model of Dreissena population dynamics, and argue that neither the dynamics nor the controls of populations of these important invaders is known satisfactorily.

Highlights

Mussels of the genus Dreissena are among the world’s most problematic invasive species, causing large ecological and economic effects in many lakes, reservoirs, and rivers throughout large invaded ranges in North America and western Europe (e.g. Connelly, O’Neill, Knuth, & Brown, 2007; Higgins & Vander Zanden, 2010)
The observed strongly irregular recruitment appears to arise from strong adult–larval interactions, and is consistent with previous simulation model results showing that interactions between adults and larvae can drive persistent cycling
We put our results into the context of a conceptual model of Dreissena population dynamics, and argue that neither the dynamics nor the controls of populations of these important invaders is known satisfactorily

Summary

Introduction

Mussels of the genus Dreissena are among the world’s most problematic invasive species, causing large ecological and economic effects in many lakes, reservoirs, and rivers throughout large invaded ranges in North America and western Europe (e.g. Connelly, O’Neill, Knuth, & Brown, 2007; Higgins & Vander Zanden, 2010). We used our long-term data on abundance of mussels of different size classes (Figures S1 and S2) to estimate fecundity, year-class (= cohort) strength, survivorship, and body condition, which are demographic parameters that underlie population dynamics, and correlate long-term variation in these parameters with various hypothesised intrinsic and extrinsic (= environmental) controls (Figure 1).

Results

Conclusion