Net Fire Coral

Millepora dichotoma Forsskål, 1775

syn. Millepora alcicornis f. dichotoma, Millepora cancellata, Millepora clavaria, Millepora reticularis

60 cmCITES IIDangerousVenomousEndangered

1130

Millepora dichotoma, commonly known as the net fire coral, is a hydrozoan species characterized by a colony of polyps with a calcareous skeleton. This colonial hermatypic coral forms colonies that can reach up to 60 cm in width, with clumps of colonies spanning several meters. Initially, they develop as encrusting corals that adhere to hard substrates and later evolve into different growth forms, including lace-like, leaf-like blades, and box-work structures. The specific growth form of Millepora dichotoma is influenced by factors such as depth, location, and water turbidity. Lace-like structures tend to thrive in deeper, less turbulent waters, while box-work forms are better suited for harsher environments.

As with other hermatypic corals, the metabolic processes of fire corals rely on zooxanthellae. These symbiotic organisms provide vibrant colors to Millepora dichotoma, support their structural growth, and aid in nutrient cycling. Being part of the cnidaria phylum, these corals possess nematocysts, which contain venom that can be fatal to many organisms. However, there have been no recorded fatalities in humans. Nonetheless, contact with Millepora dichotoma can cause extremely painful sensations, burn-like wounds, and skin irritation that can persist for up to two weeks.

Millepora dichotoma can be found in various regions, including the Republic of 🇲🇺 Mauritius, the 🌊 Red Sea, and the Indo-West Pacific. These benthic-dwelling corals are typically found at depths ranging from 0.2 to 3 meters.

As carnivorous suspension feeders, Millepora dichotoma's polyps capture plankton and detritus from the surrounding waters and process their intake in their gastrovascular cavity.

Reproduction in Millepora dichotoma takes place between April and May, although the presence of gametes may continue into June. Synchronized release of gametes facilitates external fertilization, with male gametes being broadcast slightly before females release their eggs to increase the chances of successful reproduction. Multiple distinct periods of gamete release occur during the multi-month reproduction period. Fertilized gametes disperse with currents and eventually settle on the seafloor, where they establish new colonies or contribute to existing ones. After the planktonic stage, the polyps settle, adhere to hard substrates, establish symbiotic relationships with zooxanthellae, and develop calcareous skeletons.

Currently, Millepora dichotoma is not at risk of extinction. However, human activities pose threats to their well-being. Damage can occur due to human interaction such as walking, snorkeling, and diving around these corals. Fragmentation of colonies can lead to structural changes, transitioning from more delicate forms, like lace-like structures, to thicker and less fragile forms, such as box-work ones. Areas with human-induced nutrient additions have observed lower numbers of Millepora dichotoma over extended periods. Similar to other coral species supported by symbiotic zooxanthellae, Millepora dichotoma exhibits bleaching events in response to rising ocean temperatures.

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.