Biomass of herbivores consisted of chubs Kyphosus spp.
The multivariate analyses showed large variability in the structure of the coral reef ecosystem benthos and reef fishes among sites within islands, yet obvious distinctions between islands were present Fig. Ducie was the island most clearly distinguished by the high abundance of top predators and high cover of coral. Henderson was also well separated in ordination space with other carnivores explaining most of the difference. Oeno was characterized by lower coral cover and more carnivorous fishes than Pitcairn, which was unique because of its dominance by algae.
Pitcairn was the island with the highest concordance among stations. Ducie and Henderson showed the greatest variability among stations i. Fifty-seven species of deep reef fishes from 34 families were identified from drop-cam deployments, suggesting a rich deep-sea biodiversity including rare species such as the false catshark Pseudotriakis microdon Table S5. Reef sharks, typically associated with shallow reefs, were observed as deep as m, and one dogtooth tuna Gymnosarda unicolor was observed at a depth of m.
Reef fishes were abundant, including predators such as the groupers Epinephelus fasciatus and E. Epinephelus tuamotensis was common between 78— m, and it was the most common large demersal predator observed in the drop-cam footage.
We observed the presence of crustose coralline algae CCA at m depth and probably m Ballesteros et al. The drop-cam footage showed abundant CCA and probably the endolithic green alga Ostreobium sp. Our footage also shows a potentially deeper CCA at m at Henderson. The invertebrate fauna in deeper habitats was dominated by crustaceans, mostly Mysids in the water column, and crabs Paguridae, Parapaguridae, Galatheidae on the bottom Table S6.
The habitats between — m showed a lower diversity of organisms, and the presence of fishes that were not observed shallower, such as the spiny dogfish Squalus sp. The presence of a dogtooth tuna Gymnosarda unicolor , at m at Pitcairn was remarkable, and dramatically expands the known depth range of the species . Our results indicate that the Pitcairn Islands contain healthy coral reef communities that lie at the eastern limits of the Indo-Pacific Province.
Ducie was dominated by top predators and high coral cover.
Coral reefs of the United Kingdom Overseas Territories
The high cover of coral, particularly at Ducie and Henderson, is noteworthy because the islands are at the southern limit of coral reef distribution in the Pacific . Oeno had a healthy population of carnivores, but sharks were rare.
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This may suggest some fishing activity at this atoll, which is the closest in the Pitcairn Group to the inhabited islands of French Polynesia. The lower coral cover in shallow waters at Pitcairn are likely influenced by runoff and sedimentation from the island, but a healthy deeper coral reef ecosystem was found further offshore. Sharks were very rarely observed at Pitcairn, as expected from an inhabited island where sharks are still fished.
The structure of the food web across the island group was clearly influenced by the degree of isolation i. The high endemism throughout the group highlights the isolation of these islands, particularly at Ducie, which had the highest proportion of endemics and is also the most remote island in the group. Most of the marine flora in the island group is typically tropical Indo-Pacific in origin with most species also present in French Polynesia  — .
Macroalgal beds dominated by Sargassum spp. Ducie, Oeno, and Henderson had relatively low cover of algae, which denotes a healthy coral reef environment with high herbivore biomass. Pitcairn had more algae and less coral since it is a more nutrient-rich environment especially in iron because of the high island runoff.
This runoff has accelerated in recent history with land modification by the local population including building of roads and land uses and changes in local weather patterns. The coral cover was comparable to several other significant high latitude reefs  — . Consequently, Ducie should be considered a high priority conservation site given its current lack of local human impacts and the potential to be more resilient to climate change . The extreme water clarity surrounding the Pitcairn Islands measured up to 75 m at Ducie allows for coral growth at depths greater than expected for most Pacific reefs .
This deeper available habitat may help build resilience into ecosystems from potential climate change impacts . In addition, Pitcairn is located near the center of the South Pacific Circulation Gyre, and climate change predictions suggest that this region will show less dramatic changes in SST, carbonate, and pH than most other regions around the globe . The positive correlation between coral species richness and geological age of the islands, while not surprising, highlights some intriguing biogeographical patterns.
The older islands have experienced greater reef development and coral proliferation than the younger islands due to the longer colonization time. This pattern has been documented with many taxonomic groups throughout the Pacific  and is an important component of island biogeographic theory . Holocene reef growth over the past 11, years would have been relatively similar among the four islands. Pitcairn likely did not benefit from prior species introductions during the Pleistocene when it was still tectonically active  and when Henderson was experiencing high coral reef growth .
The older islands were geographically closer to French Polynesia, which has higher coral species richness  and therefore it is reasonable to assume that coral species richness would decrease with increasing remoteness. The exception to this hypothesis is Pitcairn, which is closer to the Gambier Islands than Ducie and Henderson, yet had the lowest coral species richness.
While it is possible that the uniqueness of Pitcairn i. This northern underwater ridge, with a more extensive shallow water habitat  than the isolated southerly ridgeline with Pitcairn, might have enhanced colonizing fauna and flora by acting as stepping stones from the Gambier island group . Even though this colonization pattern is counter to the direction of the prevailing winds and currents coming from the east in the central South Pacific  , the species distribution patterns suggests that species moved from west to east and from older islands to younger islands, inferring that the current patterns must have been reversed on occasion.
Total reef fish biomass for all islands combined was relatively low ca. The relatively low biomass at the Pitcairn Islands may be due to the extremely low productivity of the waters of the Pitcairn EEZ, compared to the waters in much of the Pacific Ocean  , . The low productivity results in low plankton abundance, which results in extremely clear waters . Nevertheless, the fish biomass found at the Pitcairn Islands is larger than most fished sites in the Indo-Pacific and the Caribbean  ,  — .
Coral reefs of the Chagos archipelago, Indian Ocean - WRAP: Warwick Research Archive Portal
Total fish biomass in the tropical Pacific is determined by the background productivity of the oceanic waters  —  and possibly the level of species diversity. However, the health of the fish assemblages is determined by the degree of fishing: lower fishing pressure results in a larger proportion of the fish biomass that is accounted for by predators since fishers typically target the largest individuals in a population  — . We identified 57 species of fishes in only 21 drop-cam deployments. Taking into account that the average size of the area filmed by the drop-cam is only 3 m 2 , the diversity of fish found on the deep habitats of the Pitcairn Islands is notable.
By comparison, similar drop-cam deployments around Easter and Salas y Gomez islands, km further to the east along the Nazca Ridge, yielded only 26 fish species . Seamounts worldwide are being trawled, depleted, and abandoned, and their recovery seems unlikely within our lifetime, or not at all, because many target species are long-lived, mature late, and have a small reproductive output  — .
The Pitcairn Islands seamounts appear to be relatively intact, and therefore have high global conservation value.
We found eight probable new species of reef fishes on our deep camera surveys, mostly between — m, which suggests that more extensive surveys will probably yield many more species new to science. Determining how many of these new species are endemic to the Pitcairn Islands or are regional endemics will require additional sampling and collections. In addition, the extreme water clarity allows marine plants at the Pitcairn Islands to live deeper than in any other reported location on earth.
The previous depth record for benthic algae was CCA observed at m in the Bahamas . In summary, our findings clearly show the unique biodiversity in the deep habitats of the Pitcairn Islands EEZ and the need to explore these deeper habitats elsewhere. Because of the nearly pristine and unique nature of most marine ecosystems of the Pitcairn Islands, its EEZ has a unique global value that is irreplaceable.
These places allow us to envision what the ocean was like before heavy human impacts, to understand what we have lost in other places because of human impacts, and most importantly, to set proper conservation and management goals for our oceans  — .
niaroudistepe.tk Pitcairn islands and the surrounding EEZ are currently being considered for protection in what would be the largest marine reserve in the world, containing approximately , km 2. In September , the Pitcairn community unanimously agreed to support the creation of a marine reserve, and in January a joint proposal was submitted to the UK Government for consideration. If protection of this area proceeds, scientific research and monitoring will be established.
This study, as the first to quantitatively assess the community structure of the organisms inhabiting the coral reefs on the Pitcairn islands, will provide a valuable baseline by which future changes in ecosystem components can be measured. List of algal species observed during expedition to Pitcairn Island group.
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List of coral species observed during expedition to Pitcairn Island group. Sea urchin density mean no.