Half a century of echinoid population decline in the northern Gulf of Aqaba, Red Sea

In the face of global coral decline, coral reefs in the Gulf of Aqaba,
northern Red Sea are considered a coral reef refuge from global warming
and acidification, with echinoid herbivory playing a fundamental role in
maintaining their balance. Like many echinoderms, echinoids are known for
their ‘boom-and-bust’ population fluctuations. However, as population
fluctuations are influenced by multiple, complex, and non-linear processes
that operate at various temporal scales, short-term studies may fail to
capture the true trajectories of population trends. We explored echinoid
population dynamics in the Gulf of Aqaba, spanning 15 years (2007 to
2022), complemented by historical data dating back to the 90’s and 70’s.
We show that while some species oscillated around a steady mean, others
collapsed by up to 98%. Consequently, the once most common herbivores on
these reefs currently account for only a fraction of their population size
from half a century ago. Increased anthropogenic stress attributed to the
accelerated regional urbanization, rather than the direct effect of a
single environmental variable, is suggested as a key facilitating driver
of the observed declines. This study reveals ongoing, alarming declines of
key echinoid species, calling for rapid, species-aware management. We
highlight the necessity to transition from year-long to decades-long
monitoring to facilitate the detection of ongoing, long-term trends.