The Science Behind Holomua

Scientific Literature Behind Holomua

Photo: Bert Weeks

The Holomua Marine Initiative was launched in 2016 to address the critical condition of our nearshore coastal ecosystems by effectively managing our marine resources. Decades of scientific research and recorded observations have documented the drastic decline of our reefs and fisheries, and hundreds of studies have examined the best solutions to manage, protect, and conserve our resources. Here we share a few studies that describe the current status of our reefs and fisheries, the benefits of marine management areas, the need for a holistic and collaborative approach to tackle land-based issues, and how combining traditional ecological knowledge with contemporary research can be beneficial and successful. These selected literature are just a few highlights of existing research available, but is in no means an exhaustive list. The Holomua team will continue to add to this list in the future.

Status of Hawai‘i’s coral reefs and coral reef fisheries

Photo: James Watt

Coral reefs in Hawai‘i and its associated fisheries have been in decline for the past decades, largely threatened by climate change and anthropogenic or human impacts such as urbanization, land-based pollutants, sedimentation, fishing pressure, and more.

Asner et al. 2022 Mapped coral mortality and refugia in an archipelago-scale marine heat wave

Aerial, high-resolution reef mapping surveys showed that on average, 6.3% of coral cover was lost in the main Hawaiian islands after the 2019 bleaching event.

  • Coral refugia are coral reef areas that show stronger resilience to climate change and are considered potential safe havens from heat waves
  • This study used high-resolution reef mapping technology to examine changes in live coral cover prior to and after the 2019 heat wave that impacted Hawai‘i
  • Following the 2019 bleaching event, mapping surveys showed that the average live coral cover lost in the main Hawaiian islands was 6.3%
  • Lāna‘i had the highest percent coral cover lost (9.9%) and O‘ahu had the least percent coral cover lost (5.3%)
  • Most of the coral mortality from the 2019 bleaching occurred in shallow depths between 1 to 9 meters (~3 to 29.5 feet)
  • The results from this research showed that areas that had higher coral cover resulted in lower coral mortality, suggesting that high-cover reefs may serve as coral refugia in marine heat waves

Click HERE to download paper

Donovan et al. 2023 Evidence for managing herbivores for reef resilience

This study assessed data collected by state and federal agencies along with NGOs across the main Hawaiian islands over more than a decade to investigate the impacts of reef herbivores, oceanographic factors, land based stressors and fishing pressure on coral reef health. To provide a pre-bleaching perspective on reef condition, this paper focused on data from the decade before the 2014-2015 coral bleaching event, which contributed to the decline of many reefs across Hawai‘i. The authors focus on the relationship between reef condition and herbivores, along with the relationship between herbivore biomass and different human impacts by moku across the state.

  • Research found that abundant and diverse herbivore populations help Hawaiian coral reefs stay resilient and healthy, which echoes findings of many other studies from across the globe.
  • This paper identified that at least 80% of herbivore biomass, compared to pristine levels, is needed to maintain the balance of coral and algae for healthy reefs. Below this threshold, reef condition may be affected.
  • Abundance of herbivores is low enough to contribute to a decline in reef condition in about 30% of nearshore waters in Hawai‘i. Almost all of these areas are more accessible or near population centers.
  • Overfishing has negative impacts on coral reefs, and fishing regulations are one effective tool marine managers can use to help keep these ecosystems abundant and healthy. This paper identified moku where additional regulations could help to increase herbivore biomass and improve reef condition.
  • Land-based impacts such as pollution, sedimentation and agricultural runoff also contribute to coral reef declines and these stressors need to be mitigated alongside the implementation of marine management strategies. This paper identified areas where land-based impacts should be prioritized instead of fishing regulations to best improve herbivore biomass.

Click HERE to download paper

Friedlander et al. 2017 Human-induced gradients of reef fish declines in the Hawaiian Archipelago viewed through the lens of traditional management boundaries

Strong evidence points to human pressure as the main driver of the low numbers of fish in the main Hawaiian islands.

  • Datasets consisting of over 25,000 surveys throughout Hawaiian Archipelago, including the remote Northwestern Hawaiian Islands (NWHI), were examined to compare reef fish communities
  • The biomass of over half of the targeted resource fish species in the main Hawaiian islands (MHI) was less than 50% of NWHI biomass
  • Resource fish species biomass had a negative correlation with human population while no relationships were found for other species not targeted by fishing, highlighting the impacts of fishing pressure in the MHI (more people, less food fish)
  • Total resource fish biomass was on average almost 6x higher in the NWHI than in the MHI
  • In the NWHI, top predators such as sharks and jacks comprised more than 53% of resource fish biomass, while in the MHI the group only accounted for less than 11%
  • Total herbivore biomass was more than 4x greater in the NWHI as compared to the MHI
  • Resource fish biomass was positively correlated with coral cover (more coral, more food fish)

Click HERE to download paper

Rodgers et al. 2015 Over a decade of change in spatial and temporal dynamics of Hawaiian coral reef communities

A long-term study on coral reef communities throughout Hawai‘i show that coral cover has been declining over the past decade in areas that are more impacted by human influences, while areas that are not subjected to human pressure or are less severe show relatively stable levels of coral cover.

  • The Hawai‘i Coral Reef Assessment and Monitoring Program (CRAMP) analyzed changes in coral reef communities from surveys conducted over a 14-year period (1999-2012)
  • Almost half of the stations surveyed showed declines in coral cover throughout the study period
  • The cover of blue rice coral (Montipora flabellata) showed a decline on Maui, O‘ahu, and Kaua‘i, and finger coral (Porites compressa) cover on Moloka‘i and O‘ahu was decreasing
  • Open access areas (areas open to fishing) on Maui showed strong patterns of declining coral cover, which has been linked to nutrient input and low herbivore populations most likely due to fishing pressure
  • Marine protected areas and sites that were deeper and farther away from land-based impacts have remained relatively stable across the years
  • Islands that had the highest numbers for human population or sedimentation levels had the highest decreases in coral cover over time
  • Over half of the reefs in the Pacific region are listed as threatened by the Word Resources Institute

Click HERE to download paper

University of Hawai‘i, Social Science Research Institute 2017 Coral Bleaching Recovery Plan

The severe, consecutive bleaching events that occurred in 2014 and 2015 resulted in up to 50% of coral loss in some areas, prompting the creation of a recovery plan that suggests creating marine management areas as the best solution to support reef recovery.

  • The Coral Bleaching Recovery Plan was written to identify management strategies that would be most effective in supporting coral recovery from the mass bleaching events in Hawai‘i
  • Global mass bleaching events in 2014 and 2015 impacted the Hawaiian Archipelago, hitting the main Hawaiian Islands and the Northwestern Hawaiian Islands as well
  • Kaua‘i, Maui, and O‘ahu were the most impacted in the 2014 bleaching event, with Kāne‘ohe Bay as one of the more severely affected areas due to compounding flooding events
  • The 2015 bleaching event was worse, with surveys in West Hawai‘i showing up to 93% of coral bleached at select sites
  • Coral mortality or death was also extremely high in 2015 compared to the relatively healthy recovery from the 2014 event, with West Hawai‘i reporting almost a 50% loss of coral cover from the 2015 bleaching
  • About 20-40% of coral cover was lost on Maui in the 2015 bleaching event
  • The top ranked management actions to help Hawai‘i’s coral reefs recover from the bleaching events were to establish a network of permanent no-take Marine Protected Areas and a network of Herbivore Fishery Management Areas

Click HERE to download paper

The benefits of marine management areas

Photo: Bert Weeks

The creation of marine management areas is an effective tool that is commonly used to manage and conserve resources. In addition to resulting in increases of fish and coral, marine management areas can also improve human wellbeing and the economy.

Friedlander et al. 2018 Characteristics of effective marine protected areas in Hawai‘i

Marine protected areas result in bigger and more fish, especially in areas that have a higher level of protection or regulations.

  • Datasets representing over 1,000 individual surveys were used to evaluate fish communities among different marine protected areas in Hawai‘i and compared based on level of protection/regulations
  • Significant differences were detected in total fish biomass and resource fish biomass among the three levels of MPA protection- Resource or food fish biomass was significantly greater in fully or highly protected areas than areas with intermediate or low protection
  • Human population had a negative effect on fish assemblages where more remote marine protected areas (MPA) with lower human population had higher fish biomass
  • The Pūpūkea Marine Life Conservation District (MLCD) did not show significant increases in resource fish biomass until it was expanded with increased protection
  • Significant increases in resource fish biomass were seen at Hanauma Bay since it was first established as an MLCD in 1967
  • When Pūpūkea MLCD was first established, wrasses and surgeonfish were the most abundant, but after protection was increased, resource species such as jacks and parrotfishes became more prominent
  • The median size of MPAs currently in Hawai‘i is too small and inefficient when looking at the geographic extent of the species they are aiming to protect, however, if smaller MPAs are designed as a component of a larger MPA network, they can be effective and useful

Click HERE to download paper

Kittinger et al. 2014 From reef to table: Social and ecological factors affecting coral reef fisheries, artisanal seafood supply chains, and seafood security

Fisheries Management Areas, such as Kīholo Bay in West Hawai‘i, can play a huge role in providing social, cultural, and economic benefits to communities by providing meals and supporting the perpetuation of cultural practices.

  • The decline of coral reefs also threatens economic, social, and cultural benefits to communities in Hawai‘i
  • This study is set in Kīholo Bay, a Fisheries Management Area (FMA) on the leeward side of Hawai‘i Island, and assessed fishing effort and catch data and the distribution of seafood catch from that area
  • About 91% of the catch within Kīholo Bay was kept and used for subsistence or consumptive purposes, while only the remaining 9% was sold to commercial markets
  • The calculated total annual market-equivalent value for Kīholo’s fishery was estimated to be about $78,000
  • It was estimated that the fish harvested within the FMA provides about 30,000 meals per year
  • The Kīholo fishery also plays an important role in contributing to the health of the community, as it provides enough daily requirements of omega-3 fatty acids for almost 600 people per year
  • It was also documented that about 21% of the catch was given away or used for cultural practices, which indicates the cultural value of the fisheries

Click HERE to download paper

Williams et al. 2016 Responses of herbivorous fishes and benthos to 6 years of protection at the Kahekili Herbivore Fisheries Management Area, Maui

The establishment of an herbivore fisheries management area on Maui shows evidence of success as dramatic increases in herbivores (especially parrotfish and surgeonfish) and crustose coralline algae (a fundamental building block for coral reefs) were detected, while no differences were seen in other fish species that were not protected.

  • The Kahekili Herbivore Fisheries Management Area (FMA) was established in 2009 in response to the dramatic declines in coral cover there and persistent blooms of macroalgae
  • The take of herbivorous fishes (surgeonfishes, parrotfishes, and chubs) and sea urchins are prohibited there, but other types of fishing are allowed
  • Since the establishment, 2014/2015 surveys showed that biomass of parrotfishes increased by 139%
  • Total biomass of surgeonfishes also increased by 28%, especially for kole (Goldring Surgeonfish) which increased by 142%
  • Coral cover slightly declined the first couple of years, but then stabilized and showed signs of an upward trend before the 2015 bleaching event caused coral cover to return to previous levels
  • Macroalgal cover remained low since the establishment of the FMA, and was virtually non-existent in the last surveys years of this study
  • A steady increase was documented for crustose coralline algae (important for coral recruits), which rose from 2.5% to almost 14% from 2008/2009 to 2014/2015

Click HERE to download paper

Tissot et al. 2004 Evaluating the effectiveness of a marine protected area network in West Hawai‘i to increase productivity of an aquarium fishery

The average abundance of aquarium fishes significantly increased after the establishment of a network of Fish Replenishment Areas along the west coast of Hawai‘i Island.

  • Due to the pressure of aquarium fishing, a network of nine Fish Replenishment Areas (FRA) were created in 2000 along the west coast of Hawai‘i Island which prohibited aquarium fish collecting
  • Fish surveys were conducted before and after the new FRAs were established, and were also done in areas open to aquarium fish collecting (open sites) and sites that already did not allow aquarium fish collecting prior to the implementation of the new FRAs, such as Marine Life Conservation Districts (reference sites)
  • Before the establishment of the new FRAs, surveys showed significantly less aquarium fishes
    (-26%) as compared to reference areas in seven of the nine species examined
  • The top three aquarium fish species that had significantly lower numbers as compared to reference sites were pāku‘iku‘i (Achilles tang or Acanthurus Achilles), lauhau (Fourspot butterflyfish or Chaetodon quadrimaculatus), and lauwiliwilinukunuku‘oi‘oi (Longnose butterflyfish or Forcipiger species)
  • Two years after the FRAs were created, the average abundance of aquarium fishes significantly increased by 26%
  • Lau‘īpala (Yellow tang or Zebrasoma flavescens) and the Potter’s angelfish (Centropyge potteri) showed statistically significant increases in abundance in the new FRAs compared to reference sites (74% and 80%, respectively)
  • Because no significant overall changes were detected in fish populations in open sites next to FRAs, the results of this study show evidence that the creation of FRAs or similar marine management areas does not always lead to declines outside of marine management areas due to a shift in increased pressure

Click HERE to download paper

Land-based impacts and the need for a holistic and collaborative management approach

Photo: Bert Weeks

While land-based sources of pollution and other impacts such as sedimentation from urbanization contribute greatly to the degradation of our reefs, a holistic approach is needed to combat these threats mauka to makai.

Gove et al. 2023 Coral reefs benefit from reduced land-sea impacts under ocean warming structure

This study assessed 20 years of change to the coral reefs of Hawai’i Island before and after the 2015 coral bleaching event and found that sediment input and urban runoff were the most detrimental to reef health, while higher total fish biomass and particularly uhu (parrotfish) biomass were associated with reef recovery following bleaching.

  • Some coral reefs along Hawai’i Island continued to increase in coral cover after bleaching in 2015, while most reefs experienced declining coral cover.
  • The two strongest factors negatively impacting corals on the Kona coast were sediment input smothering corals, and urban runoff which puts harmful chemicals onto reefs
  • Coral reefs that showed increasing coral cover had 21-114% higher fish biomass (more fish!), showing the important relationship between corals providing habitat for fish and herbivores keeping corals healthy (To learn more about the importance of herbivores, please click the link to our Holomua page on herbivores)
  • The amount of scrapers, herbivores that feed by scraping algae off the surface of reefs (uhu), had the biggest positive impact on corals, particularly after bleaching events
  • Models showed that reducing wastewater inputs while increasing the number of uhu through effective management lead to much higher likelihood of coral recovery following bleaching.
  • Authors recommend prioritizing protections for uhu and increasing regulation of land-based stressors for coral reefs, as integrating land and sea management are critical to protect reefs in the face of climate instability

Click HERE to download paper

Smith et al. 2010 The effects of top-down versus bottom-up control on benthic coral reef community structure

Herbivorous fish play a huge role in supporting coral recruitment and preventing algal overgrowth, and can be used in degraded reefs affected by nutrients to restore coral reef ecosystems.

  • Climate change is the main global threat to coral reefs, but the two main local threats to reefs are fishing pressure and nutrient pollution
  • Study was conducted at Puakō Reef on Hawai‘i Island, a fisheries management area that has relatively healthy and high coral cover, abundant herbivore communities, and relatively low levels of nutrients at the time
  • PVC tiles were attached to the reef to measure community structure and biomass estimates (from organisms that recruited on the tiles), and were exposed to one of four treatments: 1) control, 2) nutrient enrichment, 3) herbivore exclusion (using exclusion cages), or 4) both nutrient enrichment and herbivore exclusion
  • In the treatments where herbivores were removed, fleshy algae was dominant while in the treatment where herbivores were present, crustose coralline algae and corals were dominant
  • Reef building corals only settled/colonized on tiles that were in the treatment that allowed herbivore grazing (even with nutrient enrichment), highlighting the importance of herbivores for coral recruitment
  • When herbivores were allowed to graze again in exclusion treatments, rapid changes in benthic communities away from algal dominance were witnessed even when nutrients were still being added
  • Results show that increasing herbivore fish on reefs that are impacted by nutrients is an effective strategy for restoring coral reef ecosystems and reversing coral-algal phase shifts

Click HERE to download paper

Stender et al. 2014 Thirty years of coral reef change in relation to coastal construction and increased sedimentation at Pelekane Bay, Hawai‘i

Pelekane Bay shows strong signs of recovery after suffering from severe land-based activities because of collaborative management strategies that involved both watershed restoration and the reduction of fishing pressure.

  • Historical baseline data from 1976 and 1996 were compared with re-surveys conducted in 2012 to assess changes to the coral reef community at Pelekane Bay located on the south Kohala coast on Hawai‘i Island
  • Pelekane Bay has historically been subjected to extensive large-scale modifications that include dredging, construction of breakwaters, and explosive blasting by the U.S. Army to create a small boat harbor which resulted in extreme sedimentation and coral mortality
  • Fish abundance and diversity have improved greatly since the declines observed between 1976 and 1996 surveys, most likely due to increased fishing restrictions in combination with watershed restoration efforts
  • Coral cover increased in 2012, which was attributed to the increase in fish, especially herbivores
  • Factors that may have contributed to reduced fishing pressure and/or increased fish abundance include the re-location of a road to restore shoreline conditions, new rules that prohibited camping at the south end of the bay, increased enforcement from park rangers, increased restriction through some access points, and spillover effects from the establishment of the West Hawai‘i Fisheries Management Area and Fisheries Replenishment Areas
  • It is concluded that when applied simultaneously, watershed restoration projects, reduced fishing pressure, and establishment of marine management areas allow for recovery of coral reef communities

Click HERE to download paper

Wolanski et al. 2009 Quantifying the impact of watershed urbanization on a coral reef: Maunalua Bay, Hawai‘i

Maunalua Bay is severely degraded due to extreme development and nutrient pollution, and the best solution to restore the ecosystem will require multiple land-based efforts and replenishing their low herbivorous fish populations.

  • Human activities that include increased population, urbanization, stream channelization, construction of seawalls, breaching of a peninsula, and dredging have resulted in the collapse of Maunalua Bay’s nearshore ecosystems on O‘ahu
  • In 2008, all coral patches over the reef flat were dead and virtually non-existent over the reef crest, with coral cover generally less than 5% over the reef slope
  • While there are no historical data on herbivore populations in the Bay, herbivore fish density in 2008 was only 5-10% of nearshore reefs elsewhere, which was suggested that it may be due to fishing pressure
  • Application of a coral reef ecosystem model suggests that coral larval supply cannot be replenished because of the consistent high turbidity and lack of suitable substrate due to algal overgrowth from nutrient input
  • The ecosystem model also indicates that the small number of herbivores, which are too low to make an impact on grazing algae, is inhibiting the recovery of reef populations at Maunalua Bay
  • Overall the study claims that restoring Maunalua Bay will require an integrated ecosystem approach that involves proper land use management, recovering groundwater storage and restoring natural stream flow, physical efforts to remove sediment in the bay, restoring coastal wetlands, and replenishing herbivorous fish populations

Click HERE to download paper

Utilizing indigenous/traditional ecological knowledge and practices with contemporary research to guide marine management

Photo: Brandon Kelley

The degradation of our coastal areas have also been linked to the loss of traditional conservation practices, which is why the Holomua Marine Initiative recognizes how important traditional ecological knowledge is and aims to weave together indigenous knowledge and practices with contemporary research to guide marine management strategies.

Friedlander et al. 2013 Customary marine resource knowledge and use in contemporary Hawai‘i

Research shows that areas co-managed with communities that incorporate traditional and customary practices can be successful, resulting in increases of fish while also improving compliance.

  • Marked declines of marine resources have been linked to fishing pressure, land-based pollution, the destruction of habitats, climate change, the loss of traditional conservation practices, and impacts from increasing human population that include technological innovations and new fishing methods/gear
  • New approaches to marine management in the Hawaiian Islands and other Pacific islands, such as incorporating traditional ecological knowledge and customary practices into contemporary strategies, are gaining interest because of the many current failures in conventional marine management
  • In Hawai‘i, natural resources were traditionally managed at local (ahupua‘a) and district (moku) levels, and harvesting rules were based mainly on specific times and places that allowed fishing as opposed to regulating the amount of fish you are allowed to catch
  • Native Hawaiians were able to keep a healthy fisheries status for hundreds of years before Western contact by allowing fish populations to replenish and understanding the spawning cycles- they knew how much to take without greatly reducing the supply
  • Some examples of marine management from other Pacific islands that are recognizing customary practices include Fiji, who have a network of over 200 locally managed areas that include traditional resource practices, and Palau, who is looking back and modeling off their traditional Bul system in which the Council of Chiefs designate areas of the reef as off-limits during spawning and feeding periods or if a species is in immediate threat
  • Some areas in Hawai‘i that are already being managed informally by communities have shown that it can maintain the same or even greater fish biomass levels than in no-take marine protected areas
  • Many studies have shown that co-management is extremely successful at accomplishing both social and ecological goals, and can also help increase compliance

Click HERE to download paper

Rodgers et al. 2021 2016-2020 Five-year efficacy study of the management regulations within the Community Based Subsistence Fishing Area of Hā‘ena, Kaua‘i

The  Hā‘ena Community-Based Subsistence Fishing Area on Kaua‘i shows strong supporting evidence that collaboratively managed areas that include customary practices can be successful, as increased fish populations were detected inside the reserve boundaries but not outside.

  • The main purpose of Community-Based Subsistence Fishing Areas (CBSFA), a type of marine management area, is to recognize and protect customary and traditional Native Hawaiian fishing practices of the area that are used for subsistence, cultural, and religious purposes to conserve marine resources
  • Over 600 surveys of fish and benthic habitat assessments were conducted at the Hā‘ena CBSFA, a collaboratively managed area by the Hā‘ena community and the State Division of Aquatic Resources, to evaluate the effectiveness of the CBSFA since its establishment in 2015
  • Total fish abundance or density was higher inside the CBSFA as compared to outside the CBSFA boundaries across almost all years of the study period
  • Fish biomass was higher inside the CBSFA as compared to outside the boundaries across almost all years of the study duration
  • Food or resource fish biomass was higher inside the CBSFA boundaries as compared to outside the CBSFA across almost all years of the study period
  • Biomass and density of native fishes (indigenous and endemic species) inside the CBSFA showed a significant increase since the establishment prior to the storm event in 2018
  • Significant increases in the number of fish since the establishment of the CBSFA was detected, while no differences were found outside the CBSFA boundaries

Click HERE to download paper

Tait et al. 2024. Holomua Marine Initiative: community-generated socio-cultural principles and indicators for marine conservation and management in Hawaiʻi

Socio-cultural principles and indicators were developed through a series of community workshops as a tool to assist marine managers in Hawaiʻi achieve conservation goals while tracking the impacts of management decisions on local communities’ relationships with their environment.

  • Researchers at the University of Hawaiʻi collaborated with the Division of Aquatic Resources and community members to develop a method that measures the impacts of resource management decisions on the reciprocal relationship stakeholders in Hawaiʻi have with their nearshore environment.
  • Socio-cultural principles are “the fundamental values or goals communities wish to perpetuate through management,” and indicators are the measurable factors used to evaluate how marine management decisions affect these goals through time.
  • Principles and indicators were developed in a series of community workshops held with Hawaiian cultural practitioners, fishers, community stewards, conservationists and resource managers from Kaua‘i, Hawaiʻi island, O‘ahu, Maui, Lāna‘i and Moloka‘i.
  • 9 principles emerged from these workshops, with 61 indicators that can be used to measure them. The principles are nested into four categories: 1) Place-Based Knowledge and Education, 2) Physical, Mental and Spiritual Well Being, 3) Community Relationships, Engagement and Commitment, and 4) Efficacy and Equitable Governance.
  • Note: The proposed indicators from this study have been further refined and are currently being tested by the Division of Aquatic Resources to monitor marine management areas throughout Hawaiʻi with the aim of improving management outcomes while fostering co-management and shared decision making with community members. More information and a full list of principles can be found on the Holomua website at

Click HERE to download paper