Dentomuricea aff. meteor and Viminella flagellum are two important bioengineering cold-water octocorals (CWCs) in the Azores that often form mixed coral gardens at 200 to 500 m depth. D. meteor distribution is limited to seamounts close to the North Mid-Atlantic Ridge, while V. flagellum has a wider distribution, spanning the Mediterranean, Macaronesia, and the eastern North Atlantic. As the oceans are warming, it becomes essential to assess the effects of increasing seawater temperature on CWCs, particularly on the poorly studied early life stages that are critical for dispersal and population connectivity.
BioProtect PhD student Anais Sire de Vilar from the University of the Azores, performed aquaria experiments that investigated how ocean warming affects the early life stages of D. meteor and V. flagellum, focusing on spawning time, embryonic development, larval swimming, settlement, polyp formation, and survival.
For this purpose, parental colonies and early life stages were exposed to three temperature regimes: 14°C and 16°C, representing the species’ minimum and maximum natural temperature range, respectively, and 19°C, simulating the IPCC RCP8.5 scenario (+3°C above the maximum natural temperature) (Figure 1).
of the octocoral Dentomuricea aff. meteor to three temperature regimes:
14°C, 16°C, and 19°C. Image © A.Sire de Vilar
Developmental progress was tracked over 2–3 months, while larval swimming speeds and trajectories were evaluated using time-lapse photography on larvae aged of one and two weeks old (Figure 2a and 2b).
Image © A.Sire de Vilar
Image © A.Sire de Vilar
Horizontal and vertical swimming speeds, as well as larval trajectories (upward or downward), were evaluated using time-lapse photography on larvae aged of one, two, and three weeks old (Figure 3).
Although data analysis is still ongoing, preliminary results suggest that higher temperature increases mortality and accelerates development, leading to earlier metamorphosis with potential malformations. This is likely due to the acceleration of metabolic processes, especially in D. meteor, which may be more sensitive to increased seawater temperature due to the observed fragility of the parent colonies. The analysis of lipid reserves in parental colonies will help understand how global warming can alter energy management under thermal stress.
Larval swimming speed increased at higher temperatures but gradually decrease over time as larvae approached metamorphosis, with V. flagellum larvae swimming faster and longer, possibly related to the species’ broader geographic distribution.
The findings of this study contribute to a better understanding of how ocean warming may affect CWCs across life history stages. Generated data on embryo/larvae development and larval swimming speed can be combinated with oceanographic, species distribution models, to improve predictions of larval dispersal in the Azores under future climate change, and human uses scenarios. Forecasting population connectivity in future oceans is crucial to develop effective marine spatial planning strategies, identify climate refugia and improve the design and placement of marine protected areas.
