Levitan DR et al. (2023), Sea urchin mass mortalities 40 y apart further ...

ECB-ART-51574

Proc Natl Acad Sci U S A 2023 Mar 07;12010:e2218901120. doi: 10.1073/pnas.2218901120.

Show Gene links Show Anatomy links

Sea urchin mass mortalities 40 y apart further threaten Caribbean coral reefs.

Levitan DR , Best RM , Edmunds PJ .

???displayArticle.abstract???
In 1983 to 1984, a mass mortality event caused a Caribbean-wide, >95% population reduction of the echinoid grazer, Diadema antillarum. This led to blooms of algae contributing to the devastation of scleractinian coral populations. Since then, D. antillarum exhibited only limited and patchy population recovery in shallow water, and in 2022 was struck by a second mass mortality reported over many reef localities in the Caribbean. Half-a-century time-series analyses of populations of this sea urchin from St. John, US Virgin Islands, reveal that the 2022 event has reduced population densities by 98.00% compared to 2021, and by 99.96% compared to 1983. In 2021, coral cover throughout the Caribbean was approaching the lowest values recorded in modern times. However, prior to 2022, locations with small aggregations of D. antillarum produced grazing halos in which weedy corals were able to successfully recruit and become the dominant coral taxa. The 2022 mortality has eliminated these algal-free halos on St. John and perhaps many other regions, thereby increasing the risk that these reefs will further transition into coral-free communities.

???displayArticle.pubmedLink??? 36848553
???displayArticle.pmcLink??? PMC10013861
???displayArticle.link??? Proc Natl Acad Sci U S A
???displayArticle.grants??? [+]

???attribute.lit??? ???displayArticles.show???

	Fig. 1. D. antillarum population densities at shallow sites (mean and standard error). Data from 4 m and 7 m from current study, data from 1.5 m from Randall et al. (17) in Greater and Little Lameshur Bays, St. John, US Virgin Islands. St. Croix (1) is a shallow patch reef. Note log scale. N = 5 sites at 2 to 6 m (4 m) and 6 sites at 5 to 9 m (7 m).
	Fig. 2. Diadema population density (mean, standard error) prior to the 2022 mortality event decreased with depth (mean, range). Mortality in 2022 leveled D. antillarum densities at all depths to near zero. N = 5, 6, 13, and 3 for each depth each year.
	Fig. 3. Size–frequency distribution of D. antillarum test diameter pre- and post- the first (A) and second (B) mass mortality events. The 1984 and 2022 surveys were 7- and 5-mo postmortality, respectively. Most individuals following the 2022 event were likely recruited following the mortality event (asterisks). Proportions are plotted to visualize shifts in size distribution and do not reflect density differences among years.
	Fig. 4. Distribution of D. antillarum among 100 m2 quadrats (N = 50 each year) 7 (1984) and 5 (2022) mo following the two mass mortality events. Almost all individuals in the summer of 2022 were isolated on the reef.
	Fig. 5. The average number (and standard error) of corals per 0.25 m (N = 28) quadrats within and outside of D. antillarum algae-free halos. (A) individual species; P. astreoides, P. porites, S. radians, Agaricia spp., F. fragum, S. siderea (broadcaster), and M. alcornis (Hydrozoan). (B) Corals grouped by reproductive mode (brooders, broadcaster or the medusa spawning hydrozoan Millepora). Letters indicate significant differences from Tukey’s pairwise tests; A > B&C, P < 0.001; B > C, P < 0.015.

References [+] :

Alvarez-Filip, Coral identity underpins architectural complexity on Caribbean reefs. 2011, Pubmed