Marine heatwave (MHW) events are periods of anomalously high temperatures relative to long-term average sea surface temperatures. In the last decade, MHWs have increased in frequency globally, causing devastating impacts on critical coastal marine ecosystems, such as kelp forests on the California coast (e.g., the 2014-2016 “Blob”). Due to their seasonal timing, MHWs pose a major threat to reproduction and early stage life history events for many benthic marine invertebrates. This study investigated the effects of MHWs on the Kellet’s whelk (Kelletia kelletii), an emerging kelp forest fishery species in the Santa Barbara region in the southern California Current System. In this study, we sought to determine if trochophores (2-week-old larvae) of adult whelks exposed to a MHW simulation would show greater larval thermotolerance. Adult whelks collected from Carpinteria Reef, California, were held under ambient conditions in the laboratory and were allowed to mate and lay egg capsules (March - July 2022). Trochophores were exposed to a “ramp-up-ramp-down” MHW simulation: 15°C ramped up to 23°C and back down to 15°C over the course of 14 days. After a MHW simulation, larvae were challenged in 1-hour thermotolerance trials via an aluminum heat block and then scored for abnormal morphology following the acute thermal stress. We observed that at 25.6°C, 72% of the trochophores were normal. However, at 29°C or higher, the majority of trochophores (78-100%) displayed abnormal morphology, and exhibited slower mobility compared to unaffected larvae. These results indicated that K. kelletii trochophore larvae were moderately affected by high MHW temperatures. Future studies on the effects of MHW temperatures on larval development will provide further insight into the extent of larval thermotolerance under extreme MHW events and inform the next steps for sustainable fisheries management of this species.

Primary Presenter: Kyaralind Vasquez Liriano, Wellesley College (kyaralind2@gmail.com)

Authors:

Xochitl Clare, University of California, Santa Barbara  (xclare@ucsb.edu)

Gretchen Hofmann, University of California, Santa Barbara  (hofmann@ucsb.edu)

Kyaralind Vasquez Liriano, Wellesley College  (kyaralind2@gmail.com)