[Coral-List] sea urchin plague threatens world's coral reefs

Thu May 30 01:27:06 UTC 2024

Mysterious sea urchin plague is spreading through the world's oceans

https://www.science.org/content/article/mysterious-sea-urchin-plague-spreading-through-world-s-oceans

Mass mortality of diadematoid sea urchins in the Red Sea and Western Indian
Oceans
https://www.cell.com/current-biology/abstract/S0960-9822(24)00531-1

Highlights

   - •
   Mass mortalities of diadematoid sea urchins spread through the Red Sea
   and WIO
   - •
   Species of both *Diadema* and *Echinothrix* are susceptible to
   mortalities
   - •
   Population declines in *D. setosum* and *E. calamaris* in the Gulf of
   Aqaba reach 100%
   - •
   Molecular analyses confirm the presence of a *Philaster*-like
   scutocilliate protozoan
   - Summary
   - Sea urchins are primary herbivores on coral reefs, regulating algal
   biomass and facilitating coral settlement and growth.
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   Recurring mass mortality events (MMEs) of *Diadema* species Gray, 1825
   have been recorded globally,
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   the most notorious and ecologically significant of which occurred in the
   Caribbean in 1983,
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   contributing to the shift from coral to algal-dominated ecosystems.
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   Recently, first evidence of *Diadema setosum* mass mortality was
   reported from the eastern Mediterranean Sea.
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   Here, we report extensive mass mortalities of several diadematoid
   species inhabiting the Red Sea and Western Indian Ocean (WIO)
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   including first evidence of mortalities in the genus *Echinothrix* Peters,
   1853. Mortalities initiated in the Gulf of Aqaba on December 2022 and span
   the Red Sea, the Gulf of Oman, and the Western Indian Ocean (Réunion
   Island), with population declines reaching 100% at some sites. Infected
   individuals are characterized by spine loss and tissue necrosis, resulting
   in exposed skeletons (i.e., tests) and mortality. Molecular diagnostics of
   the 18S rRNA gene confirm the presence of a waterborne scuticociliate
   protozoan most closely related to *Philaster apodigitiformis* in
   infected specimens—identical to the pathogen found in the 2022 Caribbean
   mass mortality of *Diadema antillarum*.
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   Collapse of these key benthic grazers in the Red Sea and Western Indian
   Ocean may lead to algal dominance over corals, threatening the stability of
   coral reefs on a regional scale.
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   We issue a warning regarding the further expansion of mortalities and
   call for immediate monitoring and conservation efforts for these key
   ecological species.

A scutociliate causes mass mortalities of Diadema antillarum in the
Caribbean Sea.
https://www.science.org/doi/10.1126/sciadv.adg3200
Echinoderm mass mortality events shape marine ecosystems by altering the
dynamics among major benthic groups. The sea urchin Diadema antillarum,
virtually extirpated in the Caribbean in the early 1980s by an
unknown cause, recently experienced another mass mortality beginning in
January 2022. We investigated the cause of this mass mortality event
through combined molecular biological and veterinary pathologic approaches
comparing grossly normal and abnormal animals collected from 23 sites,
representing locations that were either affected or unaffected at the time
of sampling. Here, we report that a scuticociliate most similar to
Philaster apodigitiformiswas consistently associated with abnormal urchins
at affected sites but was absent from unaffected sites. Experimentally
challenging naïve urchins with a Philaster culture isolated from an
abnormal,
field-collected specimen resulted in gross signs consistent with those of
the mortality event. The same ciliate was recovered from treated specimens
postmortem, thus fulfilling Koch’s postulates for this microorganism. We
term this condition D. antillarum scuticociliatosis.

Mass mortalities of the invasive alien echinoid Diadema setosum
(Echinoidea: Diadematidae) in the Mediterranean Sea
https://royalsocietypublishing.org/doi/10.1098/rsos.230251

The sea urchin Diadema setosum is an ecological key species across its
range, particularly on coral reefs. In 2006 D. setosum was first observed
in the Mediterranean Sea, and since, it has proliferated to occupy the
entire Levantine Basin. Here we report the mass mortality of the invasive
D. setosum in the Mediterranean Sea.This is the first report of D. setosum
mass mortality. The mortality spans over 1000 km along the Levantine coast
of Greece and Turkey. The current mortality shows similar pathologies to
previously reported Diadema mass mortality events, suggesting pathogenic
infection as the cause of mortalities. Maritime transport, local currents,
and fish predation of infected individuals may distribute pathogens at
varying geographical scales. Due to the proximity of the Levantine Basin to
the Red Sea, the risk of pathogen transport to the native Red Sea *D.
setosum* population is imminent—with potentially catastrophic consequences.

Cheers, Doug

-- 
Douglas Fenner
Lynker Technologies, LLC, Contractor
NOAA Fisheries Service
Pacific Islands Regional Office
Honolulu
and:
Coral Reef Consulting
PO Box 997390
Pago Pago, American Samoa 96799-6298  USA

Fenner, D. 2023. Corals of Hawai’i, 2nd edition.  Mutual Publishing,
Honolulu, and Maui Ocean Center.  440 pp.  (includes 167 page section on
coral biology and coral reef ecology)

https://mauioceancenter.com/shop/

Sheppard, C., Fenner, D., Sheppard, A.  2017.  Corals of Chagos.
http://chagosinformationportal.org/corals

Fenner, D.  2020.  Can we save coral reefs?

https://www.youtube.com/watch?v=6SM8bEm3ocI&t=76s