Early life-history ecology of Arctic benthic invertebrates

Abstract

In this dissertation I explore the abiotic and biotic factors impacting early life-history bottlenecks in the Arctic Ocean and Woods Hole, MA. Many marine invertebrates have a biphasic life-history, with larvae that disperse in the water column then settle to the seafloor. Extreme population bottlenecks occur at larval and juvenile stages, which fundamentally alter adult communities. Yet, marine early life-history ecology is severely understudied, leaving us ill-prepared to predict impacts of a changing environment. The Arctic is warming rapidly, making it a natural laboratory for studying change. In addition, the polar oceans are a severe, cold habitat with extreme seasonality in light and food availability. Thus, directly studying the organisms in this region rather than extrapolating based on patterns at lower latitudes is imperative. My primary objective was to elucidate the early life-history bottlenecks shaping seafloor assemblages in the rapidly warming Arctic. Chapter 2 investigates the natural history of larvae during the poorly understood polar night. This multi-month period of complete darkness with no primary production seems ill suited to support larval development, however, my survey of plankton communities in a fjord in Svalbard in January 2023 revealed fifty larval taxa. My samples included many recently spawned embryos, suggesting active reproduction by multiple species, feeding, and active metamorphosis and settlement. Chapter 3 investigates the drivers of dispersal and connectivity of larvae in the Fram Strait. I documented the distribution of marine invertebrate larvae in the summer, demonstrating a significant difference in larval community composition between Atlantic and Arctic water masses, as well as a relationship to phytoplankton community composition. Larvae of many coastal species were observed offshore, suggesting high connectivity and/or high wastage. I also modeled the dispersal of these taxa to understand their origins, finding non-native taxa prevalent in the region suggesting potential for invasion. Finally, I explored how post-settlement processes shape community structure. I utilized a recently developed autonomous camera tool, CATAIN (CAmera To Analyze INvertebrates), which allows observation of settlement and post-settlement mortality in remote environments for the first time. In Chapter 4, I developed and deployed CATAIN over a one-year period in Woods Hole, MA. I captured sub-daily settlement data and found a novel relationship between time of day and settlement frequency for multiple taxa. I also found that post-settlement mortality patterns varied among commonly occurring species, challenging entrenched ideas about this critical stage. In Chapter 5, I deployed CATAIN in Svalbard twice for a total of 20 months. There, I discovered high rates of mortality for the barnacle Semibalanus balanoides, and their ecology differed from the same species in temperate regions. I tied both settlement and mortality to background biotic conditions and punctuated abiotic events in situ. Overall, this work broadens knowledge of Arctic meroplankton, and the unique season of the polar night, and highlights the important processes occurring during early life stages that have lasting implications for seafloor communities.