Investigating the effects of marine heatwaves on primary productivity in the California Current Ecosystem

Marine heatwaves (MHWs) have become increasingly frequent and prolonged over the past decades. These events pose significant risks to marine ecosystems including lower trophic levels such as primary producers. Despite their importance, limited research has been conducted on how productivity and underlying physiological mechanisms respond to MHWs on short timescales. This study examined the effects of a simulated MHW in the California Current Ecosystem (CCE) during the P2402 CCE-LTER cruise, aiming to assess the resistance and resilience of the natural photoautotrophic communities. Using temperature-controlled deck-board incubators, both oligotrophic offshore and eutrophic onshore communities were subjected to MHW conditions for five consecutive days, followed by a one-day “recovery” period at ambient temperatures. Photophysiology and gross primary productivity (GPP) was assessed via Fast Repetition Rate Fluorometry (FRRf), net primary productivity (NPP) was measured through ¹⁴C incubations and community composition was assessed using flow cytometry. The results indicated that phytoplankton communities exhibited relatively stable base photophysiology but displayed instability in community composition, growth (measured by chlorophyll a), and carbon fixation rates in both onshore and offshore communities. These findings highlight the complex and variable responses of primary producers to MHWs, underscoring the need for further research to better understand their role in ecosystem resilience.

Presentation Preference: Oral

Primary Presenter: MARGARET BAKER, Rice University (mb203@rice.edu)

Authors:

Margaret Baker, Rice University  (mb203@rice.edu)

Julie Dinasquet, UC San Diego  (jdinasquet@ucsd.edu)

Sven Kranz, Rice University  (skranz@rice.edu)