Elkhorn coral. Credit: NOAA Fisheries

Elkhorn coral. Credit: NOAA Fisheries

About the Species

Elkhorn coral. Credit: NOAA Fisheries

Elkhorn coral. Credit: NOAA Fisheries

Population Status

Elkhorn coral used to be a dominant coral on Caribbean reefs and was so abundant that an entire reef zone is named for it. Beginning in the 1980s, the elkhorn coral population declined 97 percent from white band disease. This disease kills the coral’s tissues.

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Currently, there are locations such as the U.S. Virgin Islands where populations of elkhorn coral appear stable at low abundance, and some such as the Florida Keys where population numbers are decreasing. Successful reproduction is very rare, so it is hard for elkhorn coral populations to increase.

Appearance

Behavior and Diet

Where They Live

Lifespan & Reproduction

Elkhorn coral reaches reproductive maturity at about 2 square feet. Elkhorn coral is a simultaneous hermaphrodite, meaning each colony produces both eggs and sperm but usually does not self-fertilize. Elkhorn coral sexually reproduces once per year after the full moon in late summer by “broadcast spawning” eggs and sperm into the water column. Fertilized eggs develop into larvae that settle on hard surfaces and form new colonies.  Elkhorn coral can also form new colonies when broken pieces, called fragments, re-attach to hard surfaces. Elkhorn coral is one of the fastest growing corals—when healthy, it can grow up to 5 inches in branch length per year.

 

Threats

Scientific Classification

The elkhorn coral is listed asthreatenedunder theEndangered Species Act. 

Additionally, the elkhorn coral is listed under:

• Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) 
• Annex II of the Protocol for Specially Protected Areas and Wildlife (SPAW)

Recovery Action

Under the ESA, NOAA Fisheries is required to develop and implement recovery plans for the conservation and survival of listed species. The ultimate goal of the elkhorn coral recovery plan is to recover the species so it no longer needs the protection of the ESA. We must combat both global and local threats to help protect elkhorn corals.

The major actions recommended in the plan are:

• Improve understanding of population abundance, trends, and structure through monitoring and experimental research.
• Develop and implement appropriate strategies for population enhancement through restocking andactive management (PDF, 39 pages).
• Implement ecosystem-level actions to improve habitat quality and restore keystone species and functional processes such as herbivory to sustain adult colonies and promote successful natural recruitment in the long term.
• Curb ocean warming and acidification impacts to health, reproduction, and growth, and possibly curb disease threats, by reducing atmospheric greenhouse gas concentrations.
• Reduce locally-manageable stress and mortality threats (e.g., predation, anthropogenic physical damage, acute sedimentation, nutrients, contaminants).
• Determine coral health risk factors and their inter-relationships and implement mitigation or control strategies to minimize or prevent impacts to coral health.

Read the recovery plan for elkhorn coral

Species Recovery Contact

• Alison Moulding, Southeast Corals Recovery Coordinator

Implementation

NOAA Fisheries appointed anAcropora Recovery Implementation Team (ARIT) to assist in the implementation of theAcropora recovery plan and to advise NOAA Fisheries on issues related to the status and conservation ofAcropora corals in the southeast US. ARIT members meet at least annually to evaluate progress of recovery actions and identify priorities for the upcoming year.

ARIT Products

Recovery Priorities (2024).This document identifies the high priority recovery actions the Acropora Recovery Implementation Team identified this year.

Project Implementation Table (MS Excel). This table contains an inventory of projects related to implementation of the recovery plan forstaghorn coral (Acropora cervicornis) andelkhorn coral (A. palmata). The worksheet “Recovery Plan Actions” lists the actions from the recovery plan and their action number. The worksheet “Completed” lists all known completed projects that address actions in the recovery plan. Projects in progress are listed either in the "Long-term" worksheet for those that are ongoing or in the "ALL" worksheet for projects that will have an end-date. Please send updates and additions to Alison Moulding (alison.moulding@noaa.gov), NOAA Fisheries Southeast Regional Office.

Cryobanking Strategy (PDF, 13 pages). This document identifies a strategy and recommendations for range-wide collection ofAcropora sperm for cryobanking.

Critical Habitat Designation

Once a species is listed under the ESA, NOAA Fisheries evaluates and identifies whether any areas meet the definition of critical habitat. Those areas may be designated as critical habitat through a rule making process. The designation of an area as critical habitat does not create a closed area, marine protected area, refuge, wilderness reserve, preservation, or other conservation area; nor does the designation affect land ownership. Federal agencies that undertake, fund, or permit activities that may affect these designated critical habitat areas are required to consult with NOAA Fisheries to ensure that their actions do not adversely modify or destroy designated critical habitat.

For elkhorn corals, facilitating increased successful sexual and asexual reproduction is the key objective to the conservation of these species. NOAA Fisheries has designated (73 FR 72210) four critical habitat areas inFlorida, Puerto Rico, and the U.S. Virgin Islands to protect substrate of suitable quality and availability to support successful larval settlement and recruitment, and reattachment and recruitment of fragments.

Learn more about elkhorn coral critical habitat

Working to Enhance Populations

Severely reduced successful reproductive recruitment into the population is one of the major things impeding recovery of elkhorn corals. There are many factors that are contributing to this problem. NOAA Fisheries, with many partners, is taking several steps to help, including:

• Establishing a network of coral nurseries throughout the species' range to grow and asexually produce fragments and outplant them to the reef.
• Developing aplan to guide elkhorn coral population enhancement (PDF, 39 pages) which coral restoration partners, including non-governmental organizations, academia, zoos, aquaria, and federal, state, and local agencies, are requested to follow.
• Researching and implementing sexual reproduction techniques such as cryopreservation (preserving through a cooling process) of sperm and collection and fertilization of eggs and sperm for short-term rearing in the lab and outplanting to the reef.

Responding to Physical Impacts

Ship grounding and other physical impacts can break the branching elkhorn corals. If the broken fragments are stabilized quickly after being broken, the corals can survive and continue to grow. NOAA Fisheries supports aprogram to respond to these events in Puerto Rico and the U.S. Virgin Islands where tens of thousands of corals have been rescued.

Conserving Coral Reefs

NOAA Fisheries is part of theNOAA Coral Reef Conservation Program which brings together expertise from across NOAA for a multidisciplinary approach to understanding and conserving coral reef ecosystems. The Program focuses on implementing projects to address the impacts from the top three recognized global threats to coral reefs: climate change (including ocean acidification), land-based sources of pollution, and unsustainable fishing practices.

Issuing Protective Regulations

NOAA Fisheries issued aprotective regulationcalled a "4(d) rule" to prohibit import, export, commercial activities, and take including killing, harming, and collecting elkhorn coral.

Learn more about the 4(d) rule for elkhorn coral

NOAA Fisheries conducts various research activities on the biology, behavior, ecology, and threats to elkhorn coral. The results of this research are used to inform management decisions and enhance recovery efforts for this threatened species.

Status Assessments

Determining the size of the elkhorn coral population—and whether it is increasing or decreasing from year to year—helps resource managers assess the success of the conservation measures enacted. Our scientists and partners collect population information on elkhorn coral using astandard protocol. The population assessments also document the rate of population growth (recruitment) and decline (mortality), as well as the number of clones in a given population. In the Florida Keys, for example, the elkhorn population contains many colonies that are clones, meaning that there are fewer genetic individuals in the population than we would guess from the number of colonies. Also, we have not observed any new genetic individuals (sexual offspring) in the population in over 12 years, though there are new clonal colonies derived from naturally occurring fragments.

Also, NOAA’snational coral reef monitoring program tallies colony size and density for all coral species in reef habitats throughout U.S. jurisdictions. This broad scale monitoring program can give useful information about status and trends for coral species that are abundant enough to be detected in this survey.

Elkhorn Bleaching Assessment

In 2023, an unprecedented marine heatwave caused a global bleaching event, including the Florida Reef Tract. This event was unlike any other in recorded history for the region. It had a significant effect on the elkhorn coral population. NOAA Fisheries scientists compiled data from numerous partners to assess the status of the population after the event, and published the results in the report: The Status ofAcropora palmata founders in South Florida after the 2023 marine heatwave(PDF, 5 pages), which is accompanied by an interactive map (.kml file).

Two major back-to-back bleaching events severely affected elkhorn coral in the Florida Keys in 2014 and 2015. NOAA Fisheries scientists observed bleached elkhorn corals at various sites in the Upper Florida Keys during a period of unusually warm water temperatures (warmer than 87.8°F) in mid-to-late August 2014. During summer 2015, we observed bleaching among the upper Florida Keys elkhorn population for a second consecutive year. Bleaching response varied between sites, but was consistent with the response observed at these sites during the 2014 bleaching event.

Overall, we estimate that 50 percent of the monitored elkhorn coral population died due to the 2014 and 2015 bleaching events. In 2005, the Upper Florida Keys population suffered similar losses due to the 2005 hurricane season. Recovery was only minimal over the decade prior to the recent bleaching events. While other coral species on the Florida Keys reefs have experienced moderate bleaching events in the past decade, this is the first bleaching event to affect elkhorn since the 1998 El Niño-associated bleaching event.

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Restoration of Threatened Corals

NOAA Fisheries and partners have ramped up population enhancement of elkhorn corals. This developing field is supported by NOAA Fisheries’ research program to reduce uncertainties and enhance success in coral outplanting restoration activities. Some of our key questions are:

• How do genetically unique individuals of elkhorn coral outplants survive and grow differently in different habitats or sites?
• What factors worsen or mitigate the effects of predators on restored corals?
• What factors can help outplanted coral fragments form important thicket structures?
• Does disease affect restored versus wild corals differently? Are some nursery coral individuals resistant to disease?

NOAA Fisheries conducts controlled experiments at offshore coral nurseries and restored reefs to help answer these questions and improve the design of future coral restoration activities.

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NOAA Fisheries coordinates spawning observations and larval culture with a network of researchers working throughout the Caribbean, including academic researchers and professional aquarists from public zoos and aquaria. Broadcast-spawning corals, like elkhorn, release eggs and sperm into the water column for fertilization only over a few nights per year. NOAA Fisheries collects sperm and eggs, fertilizes them and cultures and observes the larvae in the lab to better understand factors that may enhance the likelihood of larvae successfully settling and surviving to adulthood.

We also conduct experiments to understand the impacts of current and future ocean warming and ocean acidification on these vulnerable early life stages of corals. An ongoing goal is also to develop reliable methods to culture the baby corals to adulthood in order to enhance coral recovery on the reef by adding new genetic individuals.

Learn more about the latest coral spawning observations from the Florida Keys

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