RAPID: Too hot to hold: Effects of unseasonable warming on the Azores nekton community and its keystone taxon

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Across the globe it has become increasingly clear that climate change is influencing animal movement patterns. The daily vertical migration of marine animals such as squid is often termed “the largest migration on Earth.” Understanding the impacts of climate change on diel vertical migration is essential for an understanding of how ocean ecosystems will fare with increasing temperatures. Central Atlantic waters are ca. 2-3 °C above normal; this unusual warming event provides a short and urgent window of opportunity to examine how global warming will affect this huge migration. The movements and energetics of squid and their larger community are being measured using traditional oceanographic methods and innovative, new high-resolution sensor and motion tags. The new data are providing novel insights into how warm temperatures are affecting movements, migrations, changes in biomass, and other energetic consequences of behavioral responses to environmental change. The project leverages an animal group (squid) that links top predators and smaller prey within a complex trophic web. As a group, squids are one of the world’s largest fisheries, they are of global food-resource importance, and they are prey for many commercially important fish species (tuna, swordfish), sea birds and marine mammals. Predicting climate-driven changes on these animals and their daily migratory patterns is critical for sustainable resource management. Educational broader impacts are focused on training opportunities for graduate and undergraduate students with emphasis on recruiting participants from underrepresented groups. The graduate students are gaining international experience in field work and scientific collaborations.Diel vertical migrations are a vital process of ocean energy exchange that are influenced by the physical environment, yet few experimental data address how warming affects these migrations. Central Atlantic waters are ca. 2-3° C above normal, extending stratified summer conditions and stressful warmer waters into a key time of year when organisms “expect” greater mixing and cooler oceans. These fleeting warm-water conditions present a unique opportunity to study how a vertically migrating nekton community and its key component (squid) are adjusting their movements to balance energetic demands and expenditures. Building from a suite of before-and-after data, this project is examining the response of the migratory community and the squid to unusually warm, physiologically stressful, ocean conditions during a critical life-stage. The prediction is that the community and squid are utilizing an energetically costly set of responses, leading to altered movement patterns and decreased densities of migratory organisms in surface waters at night. The timeframe of the project coincides with a period when squid invest in somatic and reproductive growth via substantial foraging and interactions within the larger nekton community. New data are being collected to (i) examine movement ecology and energetics by tagging Loligo forbesii squid near the Azores using novel motion tags and environmental sensors (ITAGs), (ii) quantify the nekton community and prey layer density and movements via scientific echosounders in locations overlapping with tagged animals, (iii) characterize environmental conditions using standard oceanographic casts, surface satellite data, and the eco-sensor data from animal-borne tags, and (iv) assess vertical movement and habitat use changes as seasonality progresses using longer-term, lower resolution, movement tags. The central hypothesis being tested is that the migratory community is responding to thermal stress by changing vertical migration patterns and feeding strategies. These responses have negative consequences on the squid’s energy balance and lead to higher foraging costs and decreased feeding success.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.