Boring sponges are an important component of bioeroder assemblages in tropical coral reefs. They are considered as a potential threat for coral reef health, and the increase of dead corals is expected to promote their abundance. The relationship between the availability of dead coral substrata and the development of boring sponge assemblages was evaluated during El Niño 2015–16 at five reefs from Zihuatanejo, Guerrero, Mexico. Environment and substrate quality were assessed. Overall, environment conditions remained normal in relation to previous studies in the area. Only water temperature showed unusually high records at all sites and coincided with bleaching and mortality of corals, possibly caused by the effects of the El Niño event. Abundance of boring sponges in dead corals and coral rubble was lower than during previous studies. Although sponge abundance was not directly related to cover of both dead corals and coral rubble, cover of dead corals showed a high correlation with the variation in the structure of sponge assemblages across sites. Cliona vermifera dominated sponge assemblages at all sites, and its abundance was high under conditions of high cover of live corals and low cover of bleached corals. Since overall sponge abundance responded in a similar way, these results suggest that boring sponge assemblages dominated by C. vermifera are enhanced by conditions favourable for corals. Our results imply that El Niño events in the Mexican Pacific are not likely to cause immediate population outbreaks of boring sponges.

The corallivorous gastropod Coralliophila meyendorffi (family Coralliophilidae) is a well-known predator of the coral Cladocora caespitosa, particularly in the eastern Adriatic Sea, where population outbreaks can drastically reduce coral cover. Coralliophila meyendorffi ranges in size from 5 to 40 mm in shell total length, and smaller specimens are often found living with the coral C. caespitosa. Specimens of C. meyendorffi feed exclusively on live coral tissue, stripping it from the calcium carbonate skeleton. Recent outbreaks of the gastropod C. meyendorffi have caused considerable damage on a C. caespitosa bank in Veliko Jezero (the Mljet National Park, eastern Adriatic Sea). The bank occurs at depths between 6 and 18 m, covering a 65  m2 area. During summer of 2010, a substantial outbreak affected about 5%t of the coral colonies. The gastropods were highly aggregated in sheltered areas of the coral bank (up to 41 specimens/dm2) with smaller clusters (from 8 to 12 specimens/dm2) on coral colonies that were influenced by strong bottom currents (up to 1.23 ms−1).

In 1998, in coincidence with high sea surface temperatures, Maldivian reef corals were severely affected by mass mortality following bleaching. Tabular Acropora corals, formerly abundant in shallow water, were nearly exterminated. Recovery started soon, and in 2004 Maldivian reefs appeared rich in tabular Acropora colonies again, especially at some sites. This study aimed at determining the degree of spatial variability of tabular Acropora abundance and size among reef typologies (ocean versus lagoon reefs) and depth zones (4–6, 10–12 and 16–18 m) 6 years after the mass mortality event. A total of 192 tabular Acropora colonies (Ø > 16 cm) were counted and measured in six sites. Their abundance differed between reef typologies and according to depth zones, with the highest values in deep lagoon reefs. Colony mean size differed only among depth zones, the largest colonies (up to 105 cm) being found in shallow reefs. Assuming a radial extension rate of 10 cm · yr−1, colonies larger than 65 cm can be interpreted as the survivors of the mass mortality of 1998; conversely, they may represent the result of enhanced growth rates in uncrowded situations as those characterizing the coral reefs of the Maldives in 2004.