Environmental assessment of islets and cays of Tregrosse and Lihou Reefs Coral Sea Marine Park July 2021

An Island Health assessment was undertaken by Parks Australia Division and Queensland Parks and Wildlife Service in July 2021 on 25 islets and cays in the Diamond Islets and Lihou Reef in the Coral Sea Marine Park (CSMP): West Diamond Islet, Central Diamond Islet, East Diamond Islet and South Diamond Islet (all in the Tregrosse Reefs), and South West (Nellie) Cay, Georgina Cay, Edna Cay, Helen Cay, Fanny Cay, Dianna Cay, Carol Cay, Phoenix Cay, Hermit Crab Islet, Betty Cay, Frankie Cay, Observatory Cay, Middle Cay, Turtle Islet, Margaret Cay, Little Margaret Cay, Lorna Cay, Kathy Cay, Juliette Cay and two small unnamed cays.
Birds
The CSMP is a critically important location for Australian seabirds. It represents major populations on the eastern seaboard for great frigatebird Fregata minor, lesser frigatebird Fregata ariel, red-footed booby Sula, red-tailed tropicbird Phaethon rubricauda, sooty tern Onychoprion fuscatus, wedge-tailed shearwater Ardenna pacifica, New Caledonian fairy tern Sternula nereis exsul and at least one colony of Herald petrel Pterodroma heraldica.
The islets and cays offer pest and weed free breeding sites with minimal human disturbance. Minimal human disturbance is particularly important for small tern species.
Access to the islets and cays for research is limited due to logistics, resources and often weather conditions. Where possible further exploration to all sites and subsequent targeted exploration of a handful of more important sites is recommended to understand the overall ecological values and their use by birds.
Drone imagery was very useful and provided a more comprehensive picture of overall numbers than ground counts alone. Imagery was designed to capture vegetation values, so was occasionally less suitable for bird surveys. Further focused drone use specific to bird surveys is encouraged for future trips.
Vegetation
• The vegetation of nine vegetated cays (four Diamond Islets and five Lihou Reef cays) was thoroughly surveyed.
• Vegetation was generally in good condition at the time of the surveys.
• Data was recorded at approximately 200 sites across the nine vegetated cays for the purposes of:
o describing all the vegetation communities present
o obtaining a terrestrial plant species inventory for each cay
o interpreting spatially rectified aerial imagery to map the extent of each of the vegetation communities
Recorded data includes GPS coordinates and site photographs for each site:
• High resolution drone imagery captured during the voyage was used to refine the vegetation mapping and produce accurate current vegetation maps for each of the vegetated cays visited.
• Plant species richness on the cays was low with a total of 16 plant species native to Coral Sea cays recorded during the voyage.
• Species richness was lower on the Lihou Reef cays (total of 8 species recorded) than the Diamond Islets (total of 16 species recorded).
• No weeds were observed growing on any of the cays visited.
• Despite the abundant numbers of Cocos nucifera (coconut) drift fruits observed on the cays (including the unvegetated cays), no plants of this species were observed successfully growing on any of the cays (Only two fruit showed evidence of recent germination).
• The total number of native cay plant species on the Diamond Islets varied between nine (South Diamond Islet) and fifteen (East Diamond Islet).
• The total number of native cay plant species on the vegetated Lihou Reef cays varied between five (Georgina Cay) and seven (all other vegetated Lihou Reef cays).
• Three species previously recorded from Turtle Islet were not found there during the current survey despite thorough searching.
• Triplicate specimens of 80 plants (all species from each cay) were collected and pressed for incorporation into the Qld Herbarium in Brisbane, the Tropical Herbarium in Cairns and the National Herbarium in Canberra together with the data collected at their collection sites to provide verified records of their current locations and habitat. There are currently few herbarium records for most cays visited, no records at all for Central Diamond Islet and Lorna Cay and only two specimen records for West Diamond Islet. Existing Herbarium records from the other cays are not recent except for the 2016 Bush Blitz records for East Diamond Islet (Westaway, 2016).
• Vegetation of the Lihou Reef cays consisted of only herblands, grasslands and occasional low ephemeral shrublands with no trees or large woody shrubs. These vegetation communities currently provide preferred habitat for ground nesting seabirds - huge numbers of nesting sooty terns (Onychoprion fuscatus) and large numbers of common noddies (Anous stolidus) and brown boobies (Sula leucogaster).
• On the Diamond Islets, in addition to grasslands and herblands, vegetation communities containing Argusia argentea (octopus bush) shrubs provided preferred habitat for red-footed boobies (Sula sula), frigatebirds (Fregata spp.), black noddies (Anous minutus) and red-tailed tropicbird (Phaethon rubricauda).
• The unvegetated cays as well as beaches and vegetation free shorelines and spits of the vegetated cays provided preferred habitat for predominantly black-naped terns (Sterna sumatrana) and masked boobies (Sula dactylatra). Nesting New Caledonian fairy terns (Sternula nereis exsul) were present in this habitat.
• Eleven marked permanent vegetation monitoring sites were established in a range of vegetation communities on six of the vegetated cays (one on West Diamond Islet, three on East Diamond Islet, one on South Diamond Islet, two on Hermit Crab Islet, two on Turtle Islet and two on Lorna Cay). Detailed vegetation surveys (including photo-monitoring) of these sites were completed to:
o monitor changes over time
o provide benchmark reference data for BioCondition assessment for the same vegetation communities throughout the Coral Sea cays
• Vegetation survey data obtained in July 2021 was compared with vegetation survey data recorded on previous surveys where suitable previous data was available.
• Soil samples were collected from the eleven permanent monitoring sites for analysis.
• The soil analysis data obtained was compared with previous soils data from other CSMP and southern Great Barrier Reef cays.
• Drift seeds washed up on the beaches were collected for identification.
• Potential issues pending further discussion with relevant experts:
o Abundance of locust grasshoppers on Turtle Islet
o Dieback of Cordia subcordata (sea trumpet) on West Diamond and parts of East Diamond Islets.
o Scale insects tended by ants on Cordia subcordata on West Diamond Islet
o Prevalence of scale insects on Achyranthes aspera (chaff flower) and Abutilon albescens (lantern bush) – particularly prevalent on Achyranthes aspera on South West Cay and to a lesser extent on Hermit Crab Islet.
Health checks
The Health Checks undertaken during the July 2021 Coral Sea trip were the first Health Checks for these small, remote and weather prone coral cay environments.
The overall condition rating for all the vegetated cays in the Tregrosse and Lihou Reefs was Good. The exception was on West and East Diamond Islets where the overall condition rating was Good but there was Significant Concern for one vegetation community – 13 Cordia subcordata open shrubland to closed shrub. On West Diamond Islet a small patch of this community was heavily infested by scale tended by ants. On East Diamond Islet a number of patches of Cordia communities showed evidence of dieback with numerous dead mature plants.
The unvegetated cays in the Lihou Reefs ranged from small intertidal sand mounds to larger cays. Unvegetated cays are known to be more mobile. The unvegetated cays surveyed appeared to be subject to varying levels of inundation. Drone photography to monitor cay size and movement over time and geomorphological research would provide valuable knowledge into the nature of these cays and their management.
Introduced pests
Rodents
No signs of invasive rats or mice were detected on any of the cays.
Ants and invertebrates
Three species of invasive (non-native) ants were found on only three cays - one species each for Central Diamond Islet, East Diamond Islet and Turtle Islet. Two of these islets had supported current or past infrastructure - Central Diamond Islet has a current navigational aid and a tower has since been removed from Turtle Islet.
No invasive ants were found on the other islets and cays.
The first invasive ant Monomorium pharaonis found on Central Diamond Islet was the most common and abundant ant species recorded on three of the six islands in the 2019 voyage to the Coringa-Herald cays (Hemson et al. 2020). M. pharoanis have polygynous colonies (nests contain more than one productive queen) so colonies can be prolific hence the scale of potential ecological impact and or human nuisance can be widespread. (Chris Burwell 2021, pers. comm.). The second invasive ant species Tetramorium simillimum found on East Diamond Islet is a tramp species that is now pantropically distributed. It even occurs in some temperate areas, albeit in protected locations such as heated greenhouses. Unlike some other exotic myrmicines in Australia, this species does not seem to adversely affect the native ant fauna. Tetramorium simillimum tends to invade natural environments however it is innocuous and does not occur in huge numbers. Based on current knowledge of this particular species, it does not raise any red flags. In contrast to other invertebrates that inhabit coral cays that can appear and then disappear, ants are known to persist (Chris Burwell 2021, pers. comm.).
The third invasive ant found on Turtle Islet is a very small species that is difficult to identify hence the ‘cf’. It is possibly Monomorium cf intrudens or Monomorium insolens both non-native species.
Other invertebrates collected from both vegetated and unvegetated cays with confirmed identification are all native species.
Recommendations
Recommendations in Hemson et al. 2020 are relevant to the islets and cays of the Tregrosse and Lihou Reefs. The following contains extracts from the 2019 recommendations.
Managing visitation to islets and cays of the Tregrosse and Lihou Reefs
Visitation frequency by free and independent travellers is low in number and probably concentrated to a handful of sites with sufficient anchorages.
Low visitation rates by themselves are not sufficient to ensure the values of the CSMP cays are protected. Biosecurity concerns (see Biosecurity below) and threats to seabird breeding events should be managed to ensure ongoing health and maintenance of island values.
Many sites will be self-protected due to difficulties of access by vessel, weather conditions and lack of interest by perceived aesthetic values of a site.
Formulating standard operating procedures and zoning via a series of workshops for each cay are recommended. The workshops should consider:
• Specific island values and their protection needs (vegetation, disturbance levels to seabird species, biosecurity considerations, fire threats)
• Access to a cay or cays representing an example of overall values for the enjoyment of free and independent travellers
• Access safety – prohibiting access to those areas deemed as generally unsafe (currents, reef structure, swells)
• No access (apart from approved research) for the protection of sensitive species e.g. New Caledonian fairy tern
Birds
The CSMP and associated land is critically important for Australian seabirds. It represents significant Australian populations of great frigatebird, lesser frigatebird, red-footed booby, red-tailed tropicbird, sooty tern, black-naped tern, New Caledonian fairy tern, wedge-tailed shearwater and at least one colony of Herald petrel.
The islets and cays offer pest and weed free breeding sites with minimal human disturbance. Minimal human disturbance is particularly important for small tern species.
Recommendations:
• Continue gathering seasonal and temporal baseline bird data for all islets and cays. Comprehensive baseline information may take years to ensure seasonal variations, species diversity and habitat requirements are fully understood. The recent discoveries of breeding New Caledonian fairy tern and Herald petrel may not have been made if standardised early winter and summer surveys were maintained.
• Determine key species, key locations and appropriate seasonal scheduling for ongoing monitoring.
• Minimising disturbance - formulate standard operating procedures relating to visitation/access to all areas (see Managing visitation to islets and cays of the Tregrosse and Lihou Reefs). One likely result of standard operating procedures will be designating no access preservation zones, at least seasonally, for threatened species during breeding events.
• Continue improving monitoring methodologies and techniques. Data collection needs to be robust, repeatable, and cause minimal disturbance to species. Methodologies must consider potential time periods between visits. Once a baseline understanding of bird values is known, several key sites, representative of general sites, may warrant focussed monitoring.
• Document data through formal reports and scientific papers. Share relevant data with bird organisations and interest groups.
• Collate an audio and photographic library of all species and their habitats.
• Investigate and discuss potential research opportunities including identifying foraging areas for species and understanding population interactions between the CSMP and adjoining marine areas.
• Ensure biosecurity requirements are outlined and followed by researchers and guidelines are promoted to other visitors.
Vegetation
Vegetation maps are foundational ‘tools’ for land management and ecological assessment. They can also be a means for monitoring change in the extent and distribution of vegetation communities over time. Detailed vegetation mapping is resource intensive. However, vegetation changes detectable via vegetation mapping usually occur relatively slowly and so re-mapping is unlikely to be required at intervals of less than a minimum of 10 years.
Health Checks are likely to be adequate for monitoring the condition of most vegetation communities on the islands.
Vegetation mapping and monitoring, particularly quantitative monitoring requiring intensive assessment of individual sites, should be undertaken outside of the breeding season for wedge-tailed shearwaters because of the significant risk of collapsing active burrows.
Health Checks
Health checks are a useful method to monitor the condition of key values on the vegetated and unvegetated cays over time.
Health Checks provide a simple and rapid means to regularly evaluate the condition of ecosystems and habitats on the cays. They can be undertaken by non-scientists – assessors do not require experience in scientific methods nor scientific equipment. Training in the method and concepts, and a camera, clipboard and datasheets, are sufficient.
It is recommended that ‘key value’ ecosystems and habitats (e.g. bird nesting/roosting and turtle nesting habitat) be selected for both vegetated and unvegetated cays for long term monitoring. Once the number of key values are determined, then decisions can be made regarding the frequency of monitoring and the season in which to monitor. It is preferable that Health Checks are undertaken in the same season each time. Post wet season in late summer through autumn is preferable for monitoring vegetation communities when it is in good condition and when weeds are likely to present, but summer months are optimal for monitoring levels of turtle nesting activity.
Values assessments - Key values
It is recommended that Values Assessments are undertaken for the islets and cays of the Tregrosse and Lihou Reefs. The Values Assessment (VA) process selects and defines the key values - those values that are most significant to individual protected areas. The values assessment also prioritises values, risks and management responses, and informs decisions around where monitoring is vital for management, useful or a low priority.
For the vegetated cays the detailed assessment work undertaken during the July 2021 voyage will inform the values assessments together with past research undertaken on similar cay environments in the CSMP. However there appears to be limited studies of the unvegetated cays of the CSMP (including the 11 unvegetated cays in the Tregrosse and Lihou Reefs). Excluding the intertidal cays (Phoenix, Frankie, Little Margaret and Unnamed Cays) the unvegetated cays visited during July 2021 ranged in size from approx. 400 m² to 8.1 ha above high water and supported important bird nesting/roosting and turtle nesting habitat. Six of the eleven cays were > 2.3 ha in area. It is documented that the two largest unvegetated cays in the Great Barrier Reef region are 4.1 ha (Sandbank No. 7) and 2.7 ha (Waterwitch Cay). All remaining unvegetated cays in the region are <1.6 ha (Hopley et al. 2007). Given the number, size and habitat values of the unvegetated cays in the Tregrosse and Lihou Reefs a study into their geomorphology would provide a better understanding of cay dynamics and stability particularly with the impacts of climate change. This knowledge will inform the value of these cays and guide future management.
Island Watch
The Island Watch tool was developed by QPWS&P as an early warning system for pest incursions (biosecurity surveillance) and the detection of other threats or changes to natural values, so that early management intervention can be undertaken. An Island Watch survey should be completed for each island visited during a trip.
Introduced pests
Pest invertebrates
Autumn is the preferred season to survey insects and detect weeds on the CSMP cays. Insects with the potential to impact on the key vegetation communities on the cays in the CSMP would be most abundant following the growth flushes induced by the summer wet season.
Invasive ants
Consideration should be given to assessing the feasibility and likely benefits of eradicating exotic ant species, all of which have known, albeit varied impacts on native Australian wildlife and may cause significant impact to native ecosystems on remote cays such as those in the CSMP.
Evaluate whether invertebrates have contributed to the decline of Cordia subcordata on West Diamond and East Diamond Islets. A better understanding of the impact of invertebrates on the health of this species is important for developing an effective biological control program should it be required in the future.
Drone mapping
Drones provide an efficient means to monitor cay movement, changes in island profile and area, and gross changes in vegetation structure and composition, and available habitat. The imagery is also highly valuable for bird counts and for informing ground truthing for vegetation mapping.
Consideration should be given to procuring a differential GPS and set of ground control point markers to improve spatial precision of resulting maps. Spatial precision commensurate with the very high resolution of the maps would enable detailed assessments of beach volumes, vegetation shifts and other changes.
Biosecurity
It is recommended that all camping (e.g. recreational, commercial, educational, scientific), be prohibited in the CSMP to minimise the biosecurity risk. The equipment campers typically use provides significant opportunities for invasive species to ‘stow away’ and be introduced to the native ecosystems of the CSMP. Camping is unnecessary given that all vessels will need to have overnight accommodation in order to legally transport visitors to the CSMP from Australian mainland ports.
It is further recommended that day visitors, for recreational and commercial purposes, be restricted to the beaches and not be permitted to take equipment (e.g. tables, chairs) ashore. Shade structures, water containers, first aid gear and other equipment that could be considered necessary from a health and safety perspective should not be taken above the highest tidemark. Ideally all such equipment should be brand new at the start of trips from the mainland or otherwise very thoroughly cleaned. All equipment must be inspected and sprayed (e.g. crawling insect surface spray) before going ashore and between each island. Multilayered containers and structures made from materials such as corflute should not be taken aboard vessels nor ashore.
No fresh food, including cooked or uncooked meats, breads, fruit and vegetables should be taken ashore. The timing and average length of stay on an island should be such that only drinking water and pre-packaged snacks (e.g. muesli bars, dried fruits, sweets etc.) are needed.
Visitors undertaking research and/or monitoring on the CSMP islands should adhere to similar protocols, as recreational and commercial visitors regarding food and equipment, but will need additional protocols, particularly when working above the high tide mark. For example, when moving between islands they must ensure that their field equipment and boots are thoroughly cleaned in VirkonS® or similar. Wearing clean clothes washed in detergent and water at >40°C for each new cay, and washing and inspecting hats and backpacks including Camelbaks will also reduce the chances of transporting pests between cays.
Signs and building materials including site and transect markers and other installations must be new and sourced from authorised/guaranteed clean suppliers. Immediately prior to installation, such material must be thoroughly cleaned and inspected before deployment and again before being redeployed or repurposed.
It is recommended that a study be commissioned to identify the most significant biosecurity risks to cay values, along with their likely sources, vectors and pathways of introduction.

This dataset record is provided by Parks Australia to highlight research conducted within or relevant to Australian Marine Parks. The original publication and associated intellectual property remain with the source organisation.
This publication was previously made available via the Australian Marine Parks Science Atlas and is provided here to maintain access following the decommissioning of that platform









Tags: Australian marine parks, Coral Reef Health, Invasive Species, MARINE BIRDS, coral sea, environmental assessments, tropical vegetation
Organization: Parks Australia