The Pachyseris genus appears to be closely related to Euphylliidae, but family placement remains uncertain (Terraneo et al. 2014, WoRMS online database accessed July 2022).

This species is widespread and common. Global level, species-specific population data are limited; however, coral reefs have declined globally and are expected to continue rapidly declining due to increasing severe bleaching conditions under temperature stress caused by climate change as well as a variety of other threats. Our species-specific vulnerability traits analysis indicates this species is moderately susceptible to major threats related to coral reef degradation (e.g., disease and bleaching). We applied two analytical approaches involving two different global coral datasets and the species’ distribution map as proxies to infer population decline. Based on global coral cover monitoring data, this species experienced a suspected decline of less than 25% over the past three generations, or since 1989. Based on the projected onset of annual severe bleaching (ASB) conditions via both SSP2-4.5 and SSP5-8.5 scenarios of global climate model data, in combination with the species’ depth range, distribution and bleaching vulnerability, this species is suspected to decline by less than 25% over the next three generations, or by 2050. It is listed as Least Concern.

This species is found in the Red Sea, the Gulf of Aden, the Socotra Archipelago, the southwest and central Indian Ocean, the central Indo-Pacific, tropical Australia, Southeast Asia, southern Japan, the South China Sea, the oceanic west Pacific, the central Pacific, Palau and the Marianas (Randall 1995, Veron et al. 2016). It appears to be absent from the eastern Pacific (Glynn et al. 2017). It has also been confirmed from eastern Thailand, northern Vietnam, southern China, Taiwan (Huang et al. 2015) and the Lakshadweep Islands (DeVantier and Turak 2017).

The depth range is 4-80 m (Englebert et al. 2017).

This species is common (Veron et al. 2016, DeVantier and Turak 2017). It is common in the Andaman archipelago (Mondal et al. 2019). It is also a key characteristic species of deeper (20-30 m) coral communities on the inner and mid shelf of the Great Barrier Reef between Townsville and Cairns (Roberts et al. 2015). It was found at over 75% of the sites in a survey of the reefs of the Semporna peninsula, Malaysia (Waheed and Hoeksema 2013).

Species-specific, global level population information is limited. However, coral reefs are experiencing severe global level declines due to increasing water temperatures caused by climate change (Hoegh-Guldberg et al. 2017, Hughes et al. 2018, Donovan et al. 2021). For the purposes of this Red List assessment, we used species-specific vulnerability traits and two analytical approaches based on two global coral datasets to infer past (GCRMN 2021) and future (UNEP 2020) population trends.     

Approach 1: Future population trend
The projected onset of annual severe bleaching (ASB) was applied as a proxy to estimate global level population decline. ASB represents the date at which a coral reef will likely experience severe bleaching conditions annually, and beyond which the species will experience a greater than 80% decline as it is not expected to recover (van Hooidonk et al. 2014). ASB is defined as at least eight Degree Heating Weeks (DHW) occurring over a three-month period within a year, and where a DHW occurs when the sea surface temperature is at least 1°C above the maximum monthly mean (van Hooidonk et al. 2014; 2015). We defined the onset of ASB as corresponding to 80% or more decline, however, this is conservative as other studies have found that coral populations may experience near complete mortality and are unlikely to recover with just two incidences of ASB per decade (Obura et al. 2022).

To calculate ASB for each species we applied spatial data made publicly available via a United Nations Environment Programme report (UNEP 2020) that used the 2019 IPCC CMIP6 global climate models to estimate the projected onset of ASB for the years 2015-2100 on a 27 km x 27 km grid according to the 2018 WCMC-UNEP global coral reef distribution map, which has a resolution to 30 m depth. These data are available via two scenarios of Shared Socioeconomic Pathways (SSP), with SSP5-8.5 representing current global emissions and SSP2-4.5 representing a future reduction in emissions (UNEP 2020). We applied SSP5-8.5 since it follows the precautionary approach recommended by the IUCN Red List methodology and SSP2-4.5 since it represents a more moderate climate change scenario that better tracks current policy projections (Roelfsema et al. 2020, Obura et al. 2022). To acknowledge varying levels of coral adaptation to thermal stress, both of these spatial data layers are available for all quarter degree intervals between 0° and 2°C (UNEP 2020); however, coral adaptation in general is little understood and varies by species and locality (Bay et al. 2017, Matz et al. 2020, Logan et al. 2021). To account for adaptation, we calculated two estimates of ASB onset for both the SSP5-8.5 and the SSP2-4.5, where the first estimate assumes the species has no level of adaptation (0°C) and the second assumes a capacity for 1°C of adaptation. We clipped each of these four UNEP (2020) spatial data layers to the species’ distribution and calculated the average year of ASB onset across all overlapping grid cells. 

Based on this spatial analysis, the onset of ASB across this species’ range is projected to occur on average by the year 2035 for SSP5-8.5 and by 2038 for SSP2-4.5 assuming no level of adaptation and by the year 2062 for SSP5-8.5 and by 2070 for SSP2-4.5 assuming 1°C of adaptation. For species where the onset of ASB occurs within 3-generation lengths, the 3-generation reduction is calculated as 80% multiplied by two proportions: (i) the proportion of the species' depth range that is in 0-30 m range, and (ii) for widespread species, the proportion of cells within the species' range that are expected to experience ASB under SSP2-4.5 before 2050 (three generation lengths). We inferred that the uncertainty associated with the estimate of population decline based on 1°C of adaptation is lower given this species is not primarily restricted to depths shallower than 30 m and is moderately susceptible to bleaching. For widespread species, the final estimate of decline was further adjusted by excluding the proportion of cells within its range that were expected to experience ASB under SSP2-4.5 after 2050 (three generation lengths), in order to account for the potential resilience of species to the asynchronous variability of bleaching events that occur across the Indo-Pacific. The relative vulnerability to bleaching (i.e., highly susceptible, moderately susceptible, or more resilient) is primarily based on scientific species expert knowledge. The application of the species’ depth range as a vulnerability factor is based on the assumption that a coral species with shallow depth preferences is more frequently exposed to extreme temperatures and might decline at a faster rate in some places than species that also occur in deeper, cooler waters (Riegl and Piller 2003), although this is not always the case (e.g., Smith et al. 2016, Frade et al. 2018). Ocean acidification, which is measured by aragonite saturation, is also considered a major threat to corals due to the impacts of climate change, however, the impacts are expected to be more severe in cooler and/or deeper waters (Couce et al. 2013, van Hooidonk et al. 2014, Hoegh-Guldberg et al. 2017). Although the exact threshold of aragonite saturation that is expected to cause significant decline is not well-known, in the Pacific, changes in aragonite saturation are expected to be most severe in high-latitude reefs (van Hooidonk et al. 2014). Therefore, this species is suspected to experience a projected global level decline of less than 25% by the year 2050, regardless of the SSP2-4.5 or SSP5-8.5 scenario. 

Approach 2: Past population trend
Coral reef monitoring data were also applied as a proxy to estimate global level population decline. The Global Coral Reef Monitoring Network (GCRMN) compiled data related to the status and trends of coral reefs in 10 regions from 1978-2019 via the scientific monitoring observations of more than 300 network members located throughout the world. We applied the publicly available data on estimations of the percent of live hard coral cover loss at the 20%, 50% and 80% confidence intervals in the 37 subregions of the Indo-Pacific (GCRMN 2021) to estimate species population decline over the past three generations (1989-2019). The proportion of the species’ range that overlapped with each of the subregions was estimated using the Red List distribution map. The sum of the proportion of the subregional species distribution multiplied by the percent of coral cover loss in each subregion was then used to calculate the 20%, 50% and 80% estimates of coral loss across this species’ range.

To inform the choice of the best (i.e., lowest level of uncertainty) out of the three percentile declines, we considered 11 species-specific traits related to vulnerability to coral cover loss. Given this species’ depth range is 4-80 m and is predominately found at depths greater than 10 m, generalized abundance is considered common, overall population is not restricted or highly fragmented, does not occur off-reef, is highly susceptible to disease, has a moderate recovery potential from bleaching or disease, has a low susceptibility to crown-of-thorns starfish, is moderately susceptible to bleaching, has an unknown susceptibility to the impacts of ocean acidification (Kornder et al. 2018), did not have >10,000 pieces exported annually in the aquarium trade between 2010-2019, it is overall suspected to be moderately susceptible to threats related to reef degradation. Therefore, past decline was inferred from the 50% percentile of estimated coral cover loss, resulting in a suspected global level decline of less than 25% since 1989, or over the past three generations.

This species is found most commonly on lower reef slopes (Phongsuwan et al. 2013) on tropical and high-latitude coral reefs (Roberts et al. 2015, Schleyer and Porter 2018). It may form large mono-specific stands (Phongsuwan et al. 2013). Pachyseris is normally found in deeper water (Sheppard 1980). This species was considered to be geographically and environmentally ubiquitous by Bongaerts et al. (2021). 

The age at first maturity of most reef-building corals is typically three to eight years (Wallace 1999). Based on this, we infer that the average age of mature individuals of this species is greater than eight years. Based on average sizes and growth rates, we also infer that the average length of one generation is 10 years. Longevity is not known, but is likely to be greater than 10 years. Therefore, any population decline rates estimated for the purposes of this Red List assessment are measured over a time period of 30 years.

This species suffered very high mortality (>50%) at 3 m due to bleaching in 1998 in southern Japan (van Woesik et al. 2004). A clear depth gradient in bleaching levels and related mortality of this species has been found in both Japan and on the Great Barrier Reef (van Woesik et al. 2004, Frade et al. 2018). However, even at a depth of 40 m on the Great Barrier Reef, 40% of the colonies exhibited minor bleaching during the 2016 mass bleaching event (Frade et al. 2018). In the Maldives, this species has been predicted to have a high total susceptibility to mass bleaching and a low relative extinction risk (Muir et al. 2017). It had a low susceptibility to bleaching in Okinawa (Tavakoli-Kolour et al. 2023) and a high susceptibility in Singapore (Isa Tanzil et al. 2016).

Pachyseris species are susceptible to bleaching. Thirty-one percent of Pachyseris colonies were bleached on average on shallow reefs (<7 m) in Singapore, with as many as 75% of the colonies at one site in particular bleached (Chou et al. 2016). At a highly disturbed reef (<5 m) south of mainland Singapore in 2010, 80% of Pachyseris colonies were bleached, more so than any other genera, even when compared to Acropora and Montipora (Guest et al. 2016). In the western Indian Ocean, Pachyseris had a relatively low bleaching response during 2004/2005 (McClanahan et al. 2007). 

At least four types of disease have been recorded in this species (Harvel et al. 2007, Tribollet et al. 2011, Jompa et al. 2020, Subhan et al. 2020). Black-band disease appears to be one of the more common diseases affecting this species. The prevalence of black-band disease in this species on reefs in the East China Sea was 6% (Weil et al. 2012). Black-band disease has also been found in this species from the Spermonde Archipelago (Jompa et al. 2020). Brown-band disease was found at all three sites surveyed at Mansuar Island, Indonesia and affected this species (Subhan et al. 2020). White syndrome has also been observed in this species in New Caledonia (Tribollet et al. 2011).

In general, the major threat to corals is global climate change, in particular, temperature extremes leading to bleaching and increased susceptibility to disease, increased severity of ENSO events and storms, and ocean acidification. Global warming is significantly altering coral reef ecosystems through an increasing frequency and magnitude of coral bleaching events (Graham et al. 2007, Graham et al. 2015, Hughes et al. 2017, Dietzel et al. 2020). Marine heatwaves have resulted in widespread coral bleaching and mortality (Hughes et al. 2017).

Faure (1989) noted that crown of thorns starfish generally avoided Pachyseris and did not predate on it in French Polynesia. Pachyseris did also not rank within the top-10 genera being preyed upon at Malapascua, Philippines, but it was nevertheless predated on (Kensington 2019). The corallivorous gastropods, Drupella spp. are also known to prey on Pachyseris in the Maldives and inhibit the recovery of reefs after mass bleaching has occurred (Bruckner et al. 2017).
Coral disease has emerged as a serious threat to coral reefs worldwide with increases in numbers of diseases, coral species affected, and geographic extent (Ward et al. 2004, Sutherland et al. 2004, Sokolow et al. 2009). Outbreaks of coral diseases have damaged coral reefs worldwide with the most widespread, virulent, and longest running coral disease outbreak currently occurring on the Florida Reef Tract and throughout the Caribbean. The disease, stony coral tissue loss disease, has been ongoing since 2014 (Precht et al. 2016) and has devastated affected reefs along Florida (Walton et al. 2018, Williams et al. 2021) and throughout the Caribbean (Alvarez-Filip et al. 2019, Kramer et al. 2019). Numerous 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). Escalating anthropogenic stressors combined with the threats associated with global climate change of increases in coral disease, frequency and duration of coral bleaching and ocean acidification place coral reefs in the Indo-Pacific at high risk of collapse.

Localized threats to corals include fisheries, human development (industry, settlement, tourism, and transportation) (Nguyen et al. 2013), changes in native species dynamics (competitors, predators, pathogens and parasites), invasive species (competitors, predators, pathogens and parasites) (Hume et al. 2014), dynamite fishing (Wells 2009), chemical fishing (Madeira et al. 2020), pollution from agriculture and industry (Bruno et al. 2003), domestic pollution, sedimentation (Babcock and Davies 1991, Cunning et al. 2019), and human recreation and tourism activities. The severity of these combined threats to the global population of each individual species is not known. However, all of the threats listed above are known to occur within the distribution range of this species and negatively affect it differentially.

This species was first recorded in the CITES Trade Database in 1991 when 450 live harvested specimens were exported from Indonesia (CITES 2020). Exports remained relatively low until 2010 when 1,247 wild harvested specimens were exported globally. Global exports of wild harvested material subsequently peaked in 2012 with 1,602 specimens. Since 2010, the median annual global number of wild harvested specimens was 400. However, almost half (43%) of the specimens traded are simply called Pachyseris spp. and therefore it is possible that specimens of Pachyseris speciosa may comprise some of these. The first records of Pachyseris spp. trade collectively on the CITES database was in 1991 when 1,592 wild harvested specimens were exported. Since then, trade in Pachyseris species has increased, peaking in 2015 when 8,554 wild harvested specimens were exported globally. Since 2010, the median global number of annually wild harvested specimens of Pachyseris was 5,927.

All stony corals are listed on CITES Appendix II. All stony corals (Scleractinia) fall under Annex B of the European Union Wildlife Trade Regulations (EU 2019), and have done so since 1997. Furthermore, several countries (India, Israel, Somalia, Djibouti, Solomon Islands and the Philippines) at various stages have banned either the trade or export of CITES II listed species, which includes all stony corals, since 1999. Parts of the species’ range overlaps with Marine Protected Areas.

Export quotas for Pachyseris spp. were first set in Fiji at 173 pieces in 2003 before they were progressively increased to 900 pieces in 2010, where the quota has remained as of 2020 (UNEP-WCMC 2020). Export quotas for Pachyseris spp. were first set at 2,200 per annum in Malaysia in 2015. In Sabah, Malaysia a quota of 700 pieces of Pachyseris was implemented in 2019 before quotas of 1,120 and 1,080 pieces from Sarawak and the Malaysian Peninsula respectively were set in 2020 (UNEP-WCMC 2020).

The Convention on Biological Diversity adopted an updated Strategic Plan for Biodiversity 2011–2020, which now includes Aichi Biodiversity Target 11, calling for 10% of coastal and marine areas to be conserved by 2020. And in 2016, the IUCN World Conservation Congress agreed upon a target of >30% global marine protection by 2030.

It is crucial that global warming is constrained well below 2°C (the goals of the Paris Agreement) (Hoegh-Guldberg et al. 2018).