Periodic Reporting for period 1 - PLEASE (Impact of climate change on twilight zone fishes during early-stage development)
Reporting period: 2023-03-01 to 2025-08-31
Organisms living in the deep ocean, within the twilight zone (TLZ), play a key role in pelagic food webs and provide significant ecosystem services, including carbon transport, climate regulation, and serving as a potential fishery resource for nutraceutical, pharmaceutical, and aquaculture applications. The increasing anthropogenic pressure associated with deep-sea mining, fisheries, and climate change poses a growing threat to TLZ organisms; however, little is known about the basic aspects of their biology. PLEASE project focuses on understanding the impact of future climate change stressors in theTLZ organisms focusing on reproductive aspects and early life stages.
The PLEASE project combined extensive fieldwork, laboratory analyses, and modelling approaches to investigate how climate change affects TLZ ecosystems. Field activities included oceanographic cruises to collect TLZ organisms and environmental data. In the laboratory, reproductive and biochemical analyses were conducted to assess maternal investment and larval responses to environmental stressors. Advanced statistical and modelling tools were applied to integrate field and experimental results, including species distribution models under future climate scenarios.
Together, these activities provide a comprehensive understanding of the vulnerability of TLZ communities to climate change, particularly through the effects of ocean warming and acidification on reproduction, larval survival, and species distribution. These findings highlight how alterations in oceanographic conditions can significantly affect the structure and functioning of the TLZ ecosystem, with cascading impacts on global biogeochemical cycles and carbon sequestration.
Together, these activities provide a comprehensive understanding of the vulnerability of TLZ communities to climate change, particularly through the effects of ocean warming and acidification on reproduction, larval survival, and species distribution. These findings highlight how alterations in oceanographic conditions can significantly affect the structure and functioning of the TLZ ecosystem, with cascading impacts on global biogeochemical cycles and carbon sequestration.
The project has contributed to the characterization of reproductive strategies related to maternal investment, revealing for the first time clear patterns such as species producing few, large, lipid-rich embryos versus those generating numerous, smaller, lipid-poor embryos. These strategies are closely linked to habitat conditions and phylogenetic lineage.
Moreover, the project evaluated the impact of marine heatwaves on planktonic ecosystems and the abundance of TLZ fish larvae. Using satellite imagery, time series of temperature and chlorophyll-a were reconstructed for the Canary Islands region to detect heatwave events. Two contrasting years were analyzed: 2005 (normal conditions) and 2010 (strong warming and weak phytoplankton bloom). Plankton samples collected near Gran Canaria revealed significantly lower abundances of TLZ fishes belonging to Myctophidae and Gonostomatidae during 2010. These results indicate that marine heatwaves may negatively affect TLZ fish recruitment through reduced food availability and/or altered reproductive success.
In addition, PLEASE developed a global ensemble species distribution model for the TLZ Cyclothone, the most abundant genus of fishes on Earth, to forecast its future distribution under climate change scenarios. Using simulations from the CNRM-ESM2-1 Earth system model, we analyzed ocean variables (temperature, salinity, oxygen, pH, and productivity) from the surface to 2,000 m under pre-industrial, historical, and future SSP2–4.5 and SSP5–8.5 scenarios. Species occurrence data were compiled from field samples and global biodiversity databases, filtered by sampling depth. The model accurately reproduced current habitat suitability and also predicted future range contractions in epipelagic and twilight zones, particularly in the Mediterranean and tropical North Atlantic. These results suggest potential poleward and deeper shifts of Cyclothone populations, with implications for ecosystem resilience and ocean carbon cycling.
Moreover, the project evaluated the impact of marine heatwaves on planktonic ecosystems and the abundance of TLZ fish larvae. Using satellite imagery, time series of temperature and chlorophyll-a were reconstructed for the Canary Islands region to detect heatwave events. Two contrasting years were analyzed: 2005 (normal conditions) and 2010 (strong warming and weak phytoplankton bloom). Plankton samples collected near Gran Canaria revealed significantly lower abundances of TLZ fishes belonging to Myctophidae and Gonostomatidae during 2010. These results indicate that marine heatwaves may negatively affect TLZ fish recruitment through reduced food availability and/or altered reproductive success.
In addition, PLEASE developed a global ensemble species distribution model for the TLZ Cyclothone, the most abundant genus of fishes on Earth, to forecast its future distribution under climate change scenarios. Using simulations from the CNRM-ESM2-1 Earth system model, we analyzed ocean variables (temperature, salinity, oxygen, pH, and productivity) from the surface to 2,000 m under pre-industrial, historical, and future SSP2–4.5 and SSP5–8.5 scenarios. Species occurrence data were compiled from field samples and global biodiversity databases, filtered by sampling depth. The model accurately reproduced current habitat suitability and also predicted future range contractions in epipelagic and twilight zones, particularly in the Mediterranean and tropical North Atlantic. These results suggest potential poleward and deeper shifts of Cyclothone populations, with implications for ecosystem resilience and ocean carbon cycling.