Net Fire Coral
Net Fire Coral
Net Fire Coral
Fire coral, Feuerkoralle (Millepora dichotoma)
Fire coral (Millepora dichotoma)
Dangerous© Yevgen Sukharenko
Invertebrate · Stinging · Hydrozoans

Net Fire Coral

Millepora dichotoma Forsskål, 1775
syn. Millepora alcicornis f. dichotoma, Millepora cancellata, Millepora clavaria, Millepora reticularis
colonies to 60 cm across0-30 mCITES IIDangerousVenomousEndangered
1139

Mustard-yellow blades with pale tips, standing in flat sheets across a current-swept edge, joined into an open net. It looks like a coral, it builds limestone like a coral, and it is not one. Fire corals are hydrozoans - closer relatives of jellyfish than of the corals they grow among.

The smooth surface is the giveaway that something is wrong. A stony coral shows its polyps; here they sit in pores too small to see, and the ones that sting are not the feeding polyps at all but separate defensive polyps loaded with nematocysts. They fire on contact and the thread goes straight through skin that a stony coral would not mark.

The sting arrives seconds late, burns for hours and often raises welts that come back itching for days. Rinse with seawater or vinegar, never with fresh water, which sets off the capsules still on the skin; lift anything clinging off with a card edge rather than rubbing; hot water at about 45 C (113 F) helps the pain. A large sting, or one on a face, is a matter for a doctor.

It is a jellyfish in its life cycle too. The colony releases tiny free-swimming medusae that spawn in open water, and the larvae settle to start new colonies - which is how fire coral turns up on a wreck that was clean a year ago.

How to recognise it
  • mustard to yellow-brown blades with white growing tips
  • flat vertical plates joined into an open net
  • surface smooth to the eye, with no visible polyps
  • colonies to 60 cm across

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 species is susceptible to bleaching. However, it might be somewhat weedy and recover quickly or take over disturbed habitats. 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.

Threat classification from the IUCN Red List.

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Last Update: August 14, 2026