Kapverden: Feuerkoralle - Millepora exaesa

Invertebrate · Stinging · Hydrozoans

Encrusting Fire Coral

Millepora exaesa Forsskål, 1775

syn. Millepora alcicornis var. nodosa, Millepora exaesa var. incrustans, Millepora gonagra, Millepora nodosa, Millepora tuberculosa, Millepora tuberosa

colonies to 50 cm across0-25 mCITES IIDangerousVenomousEndangered

An encrusting fire coral that takes the shape of whatever it grows over - dead coral, rock, an old anchor - rather than standing up in plates. The surface is smooth to lumpy, mustard yellow through tan to greenish-brown, sometimes pushed into short stubby lobes a few centimetres high, with a pale margin where the colony is spreading. There are no polyp cups to see: the genus name means "thousand pores", and the openings its feeding and stinging polyps emerge from are barely visible without a lens.

That smoothness is exactly what makes it dangerous. A blade of fire coral is obvious and avoidable; a crust that has taken over a dead coral head reads as bare rock, and divers steady themselves on it. The sting comes through on contact and raises the same burning welt as its upright relatives. It lives on reef crests, upper slopes and lagoons from the shallows to about 25 m (80 ft), catching zooplankton with those stinging cells and drawing the rest of its energy from symbiotic algae in its tissues. Colonies spawn into open water and also spread by fragmentation, a broken piece cementing itself and growing on. Like all Millepora it is a hydroid rather than a true coral, and it builds a limestone skeleton anyway - which is why it carries a CITES Appendix II listing, applied across every reef-builder with a skeleton to control the curio trade rather than because this animal is at risk.

How to recognise it

smooth mustard-colored crust following the shape of whatever it covers
knobby or lumpy surface, sometimes with short stubby lobes
pale edge where the colony is still spreading
no visible polyp cups

Why it's threatened

Residential & commercial development

Housing & urban areas · Commercial & industrial areas · Tourism & recreation areas

Transportation & service corridors

Shipping lanes

Human intrusions & disturbance

Recreational activities

Invasive species, genes & disease

Unspecified species · Problematic native species/diseases

Pollution

Type Unknown/Unrecorded · Soil erosion, sedimentation · Ozone

Climate change & severe weather

Temperature extremes · Storms & flooding

This genus is generally susceptible to bleaching. Although in some localities, species from this genus were shown to be very susceptible to bleaching, in other places, they were quite resistant to bleaching and other stressors (Gleason 1993, van Woesik et al. 2011, Brown and Edmunds 2016, Kayal and Kayal 2017, Dubé et al. 2019).

The most critical threat for this species, like for most coral species, is the extensive degradation and reduction of coral-reef habitat because of a combination of local and global threats (Hughes et al. 2017, Hoegh-Guldberg et al. 2017, Donovan et al. 2021). The increasing threats from climate change are being further compounded by additional local stressors, such as pollution and overfishing (Knowlton and Jackson 2008, Lamb et al. 2018, MacNeil et al. 2019, Donovan et al. 2021).

Generally, the biggest threat to the persistence of corals is climate change (Hoegh-Guldberg et al. 2017, Hughes et al. 2017, Sully et al. 2019), and more specifically - ocean warming and marine heatwaves that are leading to an increase in the frequency and intensity of events of anomalously high water temperatures (Hoegh-Guldberg et al. 2019, Laufkötter et al. 2020). Under anomalously high temperatures, the symbiotic relationship between corals and their photosynthetic symbionts is disrupted, and many corals begin to bleach (Glynn 1996, Hoegh-Guldberg et al. 1999, Warner et al. 1999, Loya et al. 2001). Mass bleaching events resulting from thermal stress have become increasingly common in the last two decades and may lead to widespread coral mortality and changes in overall reef community over large areas (Loya et al. 2001, Graham et al. 2015, Hughes et al. 2018, Safaie et al. 2018, Stuart-Smith et al. 2018, McClanahan et al. 2019, Sully et al. 2019).

Superimposed on thermal stress and bleaching are additional stressors that can either directly threaten corals or exacerbate coral mortality after thermal stress (Kennedy et al. 2013, MacNeil et al. 2019, Abelson et al. 2020, Donovan et al. 2021, Knowlton et al. 2021). For example, increasing number of storms per season, overfishing, high levels of nutrients, and other kinds of pollution are steadily increasing in magnitude and threatening coral reefs (Wiedenmann et al. 2013, Zaneveld et al. 2016, MacNeil et al. 2019, DeCarlo et al. 2020, Donovan et al. 2020). Moreover, in some localities, increased amounts of outbreaks of the corallivorous sea star, crown of thorns, can cause substantial damage to the reef, contributing to the overall decline and reef destruction (Saponari et al. 2015, Pratchett et al. 2017).

The prevalence of coral disease is also rising (Aronson and Precht 2001, Rosenberg and Loya 2004, Ward et al. 2004, Sutherland et al. 2004, Sokolow et al. 2009, Weil et al. 2012, Maynard et al. 2015), especially in the Caribbean (Aronson and Precht 2001, Precht et al. 2016, Walton et al. 2018, Aeby et al. 2019, Alvarez-Filip et al. 2019, Kramer et al. 2019, Muller et al. 2020, Williams et al. 2021). Nonetheless, disease outbreaks have also occurred in the Indo-Pacific (Willis et al. 2004, Aeby et al. 2011; 2016), Indian Ocean (Raj et al. 2016) and Persian Gulf (Howells et al. 2020). The increasing spatial spread and extent of diseases are associated with ocean warming (Muller et al. 2008, Ruiz-Moreno et al. 2012, Randall and van Woesik 2015) and additional anthropogenic stressors (Vega Thurber et al. 2014, Maynard et al. 2015). The escalating impacts of global warming alongside the ongoing increases in local anthropogenic stressors and diseases are causing fundamental changes to coral reefs and place entire reef systems at a high risk of collapse.