Bertarelli-Annual-Report-2024-LR - Flipbook - Page 38
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Science
Impacts
This year saw 23 scientific papers and
one book published by scientists in the
marine science programme, bringing the total
number of published papers since 2018 to
175. Of the 23 papers published in 2023, eight
were published in journals with an Excellent
Impact Factor (>10) and a further 13 in journals
with a Good Impact Factor (>3).
Given their extensive distribution and high biodiversity,
understanding their susceptibility to the warming ocean
is imperative.
Mesophotic Coral Bleaching
Associated With Changes in
Thermocline Depth
Diaz, C., Foster, N.L., Attrill, M.J., Bolton, A., Ganderton,
P., Howell, K.L., Robinson, E., Hosegood, P. (2023)
‘Mesophotic coral bleaching associated with changes in
thermocline depth’ - Nature Communications https://doi.
org/10.1038/s41467-023-42279-2
In this multidisciplinary study of an atoll in the Chagos
Archipelago, central Indian Ocean, coral bleaching was
recorded at a depth of 90 metres, despite the absence
of shallow-water bleaching. This is the deepest known
evidence of coral bleaching.
As global temperatures continue to rise, shallow
coral reef bleaching has become more intense and
widespread. Mesophotic coral ecosystems reside in
deeper (30–150 metre), cooler water and were thought to
offer a refuge to shallow-water reefs. Studies now show
that mesophotic coral ecosystems instead have limited
connectivity with shallow corals but host diverse and
endemic communities.
Marine science programme authors in bold.
The study used a combination of in situ monitoring,
remotely operated underwater vehicles equipped with
cameras, and satellite-generated oceanographic data
to observe the status of the corals and understand the
oceanographic and environmental processes that were
driving the bleaching event. Images from the underwater
cameras were transmitted live onto the research vessel,
giving the research team their first glimpse of the corals
that had been bleached. While coral bleaching was
virtually absent on shallow-water (15-20 metres) and
upper-mesophotic reefs (30 – 40 metres), mid- and
lower-mesophotic depths (60–70 and 80–90 metres,
respectively) experienced significant coral bleaching.
The bleaching was associated with a strong positive phase
of the Indian Ocean Dipole – a climate phenomenon that
affects the Indian Ocean – that resulted in a sustained
deepening of the equatorial Indian Ocean thermocline. While
temperatures at the ocean surface barely changed during
this period, temperatures beneath the surface climbed
from 22°C to 29°C, further influenced by local internal
waves within atolls. These temperature changes harmed up
to 80% of the reefs in certain parts of the seabed, at depths
previously thought to be resilient to ocean warming.
These results demonstrate that corals at mesophotic
depths are susceptible to thermal stress and bleaching in
the same manner as that experienced by shallow-water
reefs. These deeper reefs are harder to access and less
studied and are not covered by the current early warning
bleaching indicators for shallow reefs. Therefore, it is likely
that many mesophotic bleaching events go unnoticed
due to the lack of appropriate monitoring techniques.
This highlights the need for oceanographic knowledge to
predict bleaching susceptibility and increased monitoring
of these important yet understudied ecosystems.
