Predicting the survival of coral reefs

Abstract

KEY POINTS
(I) A biophysical model framework (BMF) for corals is developed in which four
environmental factors are included: (1) light; (2) hydrodynamics; (3)
temperature; and (4) acidity. (II) The full feedback loop between corals and
their environment forms the core of this model framework, where the
morphological development is new and closes the feedback loop. (III) The
developed BMF predicts the coral response to environmental input via (mainly)
process-based relations within the accuracy of climate projections. (IV)- The
BMF supports both the deep reef refugia hypothesis and the turbid reef refugia
hypothesis. (V) The BMF contributes to the development of protection and
recovery programs and is not site-specific. (VI) The BMF is developed for
long-term predictions - in the order of decades to centuries - but runs on
daily averages and is therefore applicable for assessing the response of corals
on shorter time-scales; such as months to years. SUMMARY The increasing
pressure on Earth’s ecosystems due to climate change becomes more and more
evident. These pressures are especially visible at coral reefs. Therefore, a
good understanding of the biophysical mechanisms controlling these ecosystems
is needed, so that accurate predictions of their survival can be made. Such an
understanding is also needed to develop efficient recovery and protection
programs vital to the maintenance of these ecosystems. Because the research on
marine ecosystems is relatively young and the phenomenon of coral bleaching is
yet to be fully understood, there is no comprehensive framework in which the
complex interactions between corals and their environment are combined. In this
study, a biophysical model is developed in which four environmental factors are
included in a feedback loop with the coral’s biology: (1) light; (2)
hydrodynamics; (3) temperature; and (4) acidity. Literature from multiple
disciplines is combined to find the interdependencies between the corals and
their environment. These relations include coral growth, coral bleaching, storm
damage, and recruitment/recolonization of corals. For the connection with the
hydrodynamics, a coupling is made between the biological model developed here
and Delft3D-FM. The composed biophysical model is a big leap forward in
understanding the world of coral reefs, as it is the first construction of a
model framework including four environmental factors in which the hydrodynamics
are included in the feedback loop. Furthermore, it creates the ability to
assess recovery and protection programs based on the four aforementioned
environmental factors; e.g. the susceptibility of coral bleaching can be
reduced by increasing the attenuation of light through the water column.
Because more environmental factors have a role to play in the coral dynamics,
the framework is constructed such that these can be added relatively easily.