Coral larval settlement patterns are influenced by a vast array of factors; however, the relative roles of individual factors are rarely tested in isolation, leading to confusion about which are most crucial for settlement. For example, direct effects of light environment are often cited as a major determinate of settlement patterns, yet this has not been demonstrated under environmentally realistic lighting regimes in the absence of confounding factors. Here we apply programmable multispectral lights to create realistic light spectra, while removing correlating (but not obvious) factors that are common in laboratory settlement experiments.Using two common species of Acropora -key framework builders of the Great Barrier Reef -we find little evidence that light intensity or changes in the spectral profile play a substantial role in larval settlement under most environmentally realistic settings but can under more extreme or artificial settings. We alternatively hypothesise and provide evidence that chronic conditions of light and recent sediment exposures that impact benthic substrates (e.g., crustose coralline algae) preceding settlement have a greater impact, with up to 74% .

The presence of associated endofauna can have an impact on the health of corals. During fieldwork on the southern Caribbean island of Curaçao in 2021, the presence of an unknown coral-dwelling worm snail was discovered, which appeared to cause damage to its hosts. A study of photo archives revealed that the species was already present during earlier surveys at Curaçao since 2014 and also in the southern Caribbean island of Bonaire in 2019. It was not found in St. Eustatius, an island in the eastern Caribbean, during an expedition in 2015. The vermetid snail was preliminarily identified as Petaloconchus sp. Its habitat choice resembles that of P. keenae, a West Pacific coral symbiont. The Caribbean species was observed in 21 host coral species, more than reported for any other vermetid. Because Petaloconchus sp. is a habitat generalist, it is possible that it was introduced from an area with another host-coral fauna. The unknown vermetid is considered to be cryptogenic until future studies reveal its actual identity and its native range.

Some coral-associated invertebrates are known for the negative impact they have on the health of their hosts. During biodiversity surveys on the coral reefs of Curaçao and a study of photo archives of Curaçao, Bonaire, and St. Eustatius, the Caribbean split-crown feather duster worm Anamobaea sp. (Sabellidae) was discovered as an associate of 27 stony coral species (Scleractinia spp. and Millepora spp.). The worm was also found in association with an encrusting octocoral (Erythropodium caribaeorum), a colonial tunicate (Trididemnum solidum), various sponge species, and thallose algae (mainly Lobophora sp.), each hypothesized to be secondary hosts. The worms were also common on dead coral. Sabellids of the genera Bispira and Sabellastarte were all found on dead coral. Some of them appeared to have settled next to live corals or on patches of dead coral skeleton surrounded by living coral tissue, forming pseudo-associations. Associated Anamobaea worms can cause distinct injuries in most host coral species and morphological deformities in a few of them. Since Anamobaea worms can form high densities, they have the potential to become a pest species on Caribbean coral reefs when environmental conditions become more favorable for them.