|Scientific Name:||Acropora divaricata (Dana, 1846)|
|Red List Category & Criteria:||Near Threatened ver 3.1|
|Assessor(s):||Richards, Z., Delbeek, J.C., Lovell, E., Bass, D., Aeby, G. & Reboton, C.|
|Reviewer(s):||Livingstone, S., Polidoro, B. & Smith, J. (Global Marine Species Assessment)|
The most important known threat for this species is extensive reduction of coral reef habitat due to a combination of threats. Specific population trends are unknown but population reduction can be inferred from estimated habitat loss (Wilkinson 2004). It is widespread and common throughout its range and therefore is likely to be more resilient to habitat loss and reef degradation because of an assumed large effective population size that is highly connected and/or stable with enhanced genetic variability. Therefore, the estimated habitat loss of 21% from reefs already destroyed within its range is the best inference of population reduction since it may survive in coral reefs already at the critical stage of degradation (Wilkinson 2004). This inference of population reduction over three generation lengths (30 years) does not meet the threshold of a threat category. However, this species is susceptible to bleaching and disease and is collected for the aquarium trade, therefore it is listed as Near Threatened. Because of predicted threats from climate change and ocean acidification it will be important to reassess this species in 10 years or sooner, particularly if the species is also observed to disappear from reefs currently at the critical stage of reef degradation.
|Range Description:||This species is widespread, found in the Red Sea and the Gulf of Aden, the south-west and northern Indian Ocean, the central Indo-Pacific, Australia, Southeast Asia, Japan and the East China Sea, and the oceanic west Pacific.|
Found in Palau (Randall 1995) and South Africa (Wallace 1999).
Native:Australia; Bahrain; British Indian Ocean Territory; Cambodia; Comoros; Djibouti; Egypt; Eritrea; Fiji; India; Indonesia; Iran, Islamic Republic of; Iraq; Israel; Japan; Jordan; Kenya; Kiribati; Kuwait; Madagascar; Malaysia; Maldives; Marshall Islands; Mauritius; Mayotte; Micronesia, Federated States of ; Mozambique; Myanmar; Nauru; New Caledonia; Oman; Palau; Papua New Guinea; Philippines; Qatar; Réunion; Saudi Arabia; Seychelles; Singapore; Solomon Islands; Somalia; South Africa; Sri Lanka; Sudan; Taiwan, Province of China; Tanzania, United Republic of; Thailand; Tuvalu; United Arab Emirates; Vanuatu; Viet Nam; Yemen
|FAO Marine Fishing Areas:|
Atlantic – southeast; Indian Ocean – western; Indian Ocean – eastern; Pacific – northwest; Pacific – southwest; Pacific – western central
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||This species is common, and may be a dominant species. It was found at 6 of 6 regions in Indonesia (Wallace et al. 2001). Found at five sites of 87 sites surveyed in the Marshall Islands (Richards pers. comm.).|
There is no species specific population information available for this species. However, there is evidence that overall coral reef habitat has declined, and this is used as a proxy for population decline for this species. This species is more resilient to some of the threats faced by corals and therefore population decline is estimated using the percentage of destroyed reefs only (Wilkinson 2004). We assume that most, if not all, mature individuals will be removed from a destroyed reef and that on average, the number of individuals on reefs are equal across its range and proportional to the percentage of destroyed reefs. Reef losses throughout the species' range have been estimated over three generations, two in the past and one projected into the future.
The age of first maturity of most reef building corals is typically three to eight years (Wallace 1999) and therefore we assume that average age of mature individuals is greater than eight years. Furthermore, based on average sizes and growth rates, we assume that average generation length is 10 years, unless otherwise stated. Total longevity is not known, but likely to be more than ten years. Therefore any population decline rates for the Red List assessment are measured over at least 30 years. See supplementary material for further details on population decline and generation length estimates.
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||This species occurs in shallow, tropical reef environments on upper reef slopes, in lagoons and on fringing reefs, and is subtidal (Wallace 1999). Acropora cf. divaricata likely spawns annually in October in French Polynesia (Carroll et al. 2006). This species is found from 5-25 m.|
General genus information: throughout its range, Acropora can be found on any stretch of reef and is often the dominant coral, especially along the reef front. Staghorn and plate forms flourish in sheltered areas, whereas clusters and semi-massive types can withstand more exposed conditions. Species that occur from the reef top to the reef slope become gradually more flattened with depth (Wood 1983).
Members of this genus have a low resistance and low tolerance to bleaching and disease, and are slow to recover.
Acanthaster planci, the crown-of-thorns starfish, has been observed preferentially preying upon corals of the genus Acropora (Colgan 1987). Crown-of-thorns starfish (COTS) (Acanthaster planci) are found throughout the Pacific and Indian Oceans, and the Red Sea. These starfish voracious predators of reef-building corals, with a preference for branching and tabular corals such as Acropora species. Populations of the crown-of-thorns starfish have greatly increased since the 1970s and have been known to wipe out large areas of coral reef habitat. Increased breakouts of COTS has become a major threat to some species, and have contributed to the overall decline and reef destruction in the Indo-Pacific region. The effects of such an outbreak include the reduction of abundance and surface cover of living coral, reduction of species diversity and composition, and overall reduction in habitat area.
Acropora species are in the top three genera collected for the aquarium trade. It is not known what threat this presents. The total number of corals (live and raw) exported for this species in 2005 was 3506.
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.
Coral disease has emerged as a serious threat to coral reefs worldwide and a major cause of reef deterioration (Weil et al. 2006). The numbers of diseases and coral species affected, as well as the distribution of diseases have all increased dramatically within the last decade (Porter et al. 2001, Green and Bruckner 2000, Sutherland et al. 2004, Weil 2004). Coral disease epizootics have resulted in significant losses of coral cover and were implicated in the dramatic decline of acroporids in the Florida Keys (Aronson and Precht 2001, Porter et al. 2001, Patterson et al. 2002). In the Indo-Pacific, disease is also on the rise with disease outbreaks recently reported from the Great Barrier Reef (Willis et al. 2004), Marshall Islands (Jacobson 2006) and the northwestern Hawaiian Islands (Aeby 2006). Increased coral disease levels on the GBR were correlated with increased ocean temperatures (Willis et al. 2007) supporting the prediction that disease levels will be increasing with higher sea surface temperatures. 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), changes in native species dynamics (competitors, predators, pathogens and parasites), invasive species (competitors, predators, pathogens and parasites), dynamite fishing, chemical fishing, pollution from agriculture and industry, domestic pollution, sedimentation, and human recreation and tourism activities.
The severity of these combined threats to the global population of each individual species is not known.
All corals are listed on CITES Appendix II. Parts of the species’ range fall within Marine Protected Areas.
Recommended measures for conserving this species include research in taxonomy, population, abundance and trends, ecology and habitat status, threats and resilience to threats, restoration action; identification, establishment and management of new protected areas; expansion of protected areas; recovery management; and disease, pathogen and parasite management. Artificial propagation and techniques such as cryo-preservation of gametes may become important for conserving coral biodiversity.
Having timely access to national-level trade data for CITES analysis reports would be valuable for monitoring trends this species. The species is targeted by collectors for the aquarium trade and fisheries management is required for the species, e.g., MPAs, quotas, size limits, etc. Consideration of the suitability of species for aquaria should also be included as part of fisheries management, and population surveys should be carried out to monitor the effects of harvesting. Recommended conservation measures include population surveys to monitor the effects of collecting for the aquarium trade, especially in Indonesia.
|Citation:||Richards, Z., Delbeek, J.C., Lovell, E., Bass, D., Aeby, G. & Reboton, C. 2008. Acropora divaricata. The IUCN Red List of Threatened Species 2008: e.T132910A3488908.Downloaded on 18 March 2018.|