Baseline Assessment of Ecological Quality Index (EQI) of the Marine Coastal Habitats of Tonga Archipelago: Application for Management of Remote Regions in the Pacific
2. Materials and Methods
2.1. The Atlas of the Marine Coastal Habitats of the Kingdom of Tonga
2.2. The Habitat Classification and the Ecological Quality Index (EQI)
- Sparse Coral/Coral Beds (SC): This class groups all colonies or beds of colonies sparse on sand or gravel bottoms around islands or in the lagoons. SC has a great importance as a fish refuge and area with coral recolonization potential after mortality events.
- Reef Banks (RB): These banks are found offshore. In the classification procedure, RB were considered all reefs isolated from barrier reefs or islands from a depth greater than 30 m. They can emerge at the surface with reef crest (RC) and go deeper behind the depth limit of the satellite detection. RB may be considered as submerged, coralline islands or coralline shoals. In some cases, RB may reach hundreds of meters of depth with active exchanges of larvae and nutrients from the bottom to the surface. For this reason, offshore RB may be considered as pristine areas with high biodiversity and high fish abundance that act as true marine biosphere reserves.
- Patch Reef (PR): Normally formed by the fragmentation of the Back Reef (BR). PR is found mainly in lagoons and on large, shallow, submerged coral platforms out of the Fore Reef (FR). PR are visible in satellite images as tens of meters isolated coral knobs and little coral platforms of various forms emerging from lagoons or in large areas in shallow, offshore bottoms. PR is important because it includes isolated, living reef that represent a reservoir both in terms of larvae and individuals of different coral species.
- Fore Reef (FR): It is the outward part of the Back Reef (BR) or of the Fringing Reef (FRI). On its underwater cliff, all coral biodiversity is concentrated along the first 20–40 m of depth. It represents the most important reservoir for coral and fish maintenance and survival. The class includes the shelf-break with various coral formations, and it may be extended at large and behind the depth limit of the satellite detection (20–30 m).
- Reef Crest (RC): It is the edge of the Barrier Reef. It is the part of the Barrier Reef more exposed to open-ocean waves. It is the most important area of the barrier for the defense of the coastline, and it is most sensitive to mortality due to low tides, elevated seawater temperatures and storms. This class is also associated to the emerging part of the Patch Reef (PR) and Reef Banks (RB).
- Back Reef (BR): It is the area of the Barrier Reef between the Reef Crest (RC) and the coast; it is formed by a coral platform and is limited towards the coastline by the lagoon. It may be very large and, in its shallow areas, is characterized by an eroded platform and rubbles with associated subclasses of coralline algae, massive corals and algal turf. The Back Reef class is divided into three subclasses/subzones:
- Subzone 1 (BR 1): Behind the Reef crest, it is the zone where mainly coralline algae and living corals can be found. It may be masked by the wave breaker front of the Reef Crest.
- Subzone 2 (BR 2): Between the Subzone 1 and the Subzone 3, it is formed by an eroded platform with scattered, little living coral colonies and fleshy algae.
- Subzone 3 (BR 3): It is the zone situated between the Subzone 2 and the lagoon; it is formed by a platform with massive corals. Here, fragments of corals of the reef crest damaged by open-ocean waves may survive.
- Fringing Reef (FRI): Named also ‘coastal reef crest’, it is the seaward fringe of the coastal Reef Flat (RF). The abundance of living corals is related to its exposition to storms. FRI is the most important indicator of coastal reef erosion.
- Reef Flat (RF): It includes the reef platform formed by dead coral surrounding the coast of the major islands, and it can reach the coastline as a rocky substrate where boulders formed by the dead coral may be found. Massive corals and fleshy algae and seagrasses may occur in submerged areas where wave action is reduced.
- Seagrasses (SE): It is the class grouping all the marine, submerged plants living in sand patches or bars; seagrasses may be found on barrier and coastal reefs and in front of Mangrove (MA) forests. Seagrasses are important for primary production and coastal defense, as foraging areas for turtles and dugongs and nursery ground for fish, crab and mollusks. The seagrasses class is divided into two subclasses/subzones:
- Subzone 1 or High density (SE H): Dense seagrasses beds near the coast or in lagoons.
- Subzone 2 or Low density (SE L): Seagrasses in sparse patches on sand, variable in time and space.
- Algae (AL): Large patches of algae that may be present on sandy and rocky bottoms of the Barrier Reef and Coastal Reef.
- Mangrove (MA): Terrestrial plant forests growing in coastal saline or brackish water. Mangroves act as the final defense from storms and land erosion and are important as the greatest primary producers; moreover, mangroves are a refuge and feeding area for juvenile fish.
- Mud (MU): The Mud zones (MU) in front of mangrove forests are important transition areas creating a link among littoral and offshore areas.
3.1. The Atlas of the Marine Coastal Habitats of the Kingdom of Tonga
3.2. The Habitat Classification and the Ecological Quality Index (EQI)
Data Availability Statement
Conflicts of Interest
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|Level 1: Landscape||Level 2: Vegetation Cover Type|
|Level||Classification||Sentinel-2 Image (13 Bands)|
|Level 1||Water||Chessboard Seg: 1 |
MNDWI > 0
FDI < 0
Brightness < 1250
|Vegetation||WFI > 0.7|
|Level 2||Mangroves||Multiresolution Seg: 64|
~600 < Band 11 (SWIR1) < ~1000
|Biological Habitat Classes||Abbreviation||Sub Zones||Geomorphological Setting||Biological Value (1 = Low, 2 = Medium, 3 = High)||Ecological Quality Index|
|Nursery Ground||Connectivity||Species Reservoir||Fish Attraction||Biodiversity||Primary Production|
|SPARSE CORAL||CS||Sparse colonies on sand and gravel bottoms||1||2||2||2||2||0||2|
|REEF BANK||RB||Offshore sparse banks and shoals in the open ocean||3||3||3||3||3||0||3|
|PATCH REEF||PR||Coral Pinnacles and broken reef, may reach the surface with a reef crest (RC)||2||3||3||3||3||0||3|
|FORE REEF||FR||Coral cliffs and continuous, dense coral beds and bank shelves outward fringing reef and barrier reef. It includes spur and grooves||2||3||3||3||3||0||3|
|REEF CREST||RC||Outward edge of barrier reef, coral and coralline algae exposed to wave action, and to air at low tide||2||3||3||3||3||3||3|
|BACK REEF||BR||1||Coral and coralline algae. Just behind reef crest||2||3||3||3||3||3||3|
|2||Scattered corals and flesh algae on coral platform behind the BR zone 1||1||1||1||1||1||1||1|
|1||Scattered coral on coral platform with moderate slope with sand and gravel. Between the BR zone 2 and internal lagoon and sand bar.||1||1||2||1||1||0||2|
|FRINGING REEF||FRI||Coral on the edge of RF. Exposed to air at low tide and to wave action.||2||2||2||3||3||1||2|
|REEF FLAT||RF||Coral platform among the FRI and the coast rare, sparse coral, sand patches, and algae||1||1||1||1||1||1||1|
|SEAGRASSES||SE||1 = High Density||dense plant cover on sand patches on barrier reef in lagoons and on RF||3||3||3||3||3||3||3|
|2 = Low density||plant patches variable in space and time on sand bars in lagoons and on RF||2||2||1||2||2||2||2|
|ALGAE||AL||large patches of algae may be present on sandy and rocky bottoms of the Barrier Reef and Coastal Reef||1||1||1||2||1||3||2|
|MANGROVE||MA||Terrestrial plant forest implanted along coastline where rivers are present||3||3||3||3||3||3||3|
|MUD||MU||Mud fringe in front of mangrove water limit||2||1||1||1||0||0||1|
|SAND||S||Sand bottoms, sand bars||0||0||0||0||0||0||0|
|NO REEF||NR||Rocky, basaltic reefs of volcanic island, boulder beaches||0||0||0||0||0||0||0|
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Peirano, A.; Barsanti, M.; Delbono, I.; Candigliota, E.; Cocito, S.; Hokafonu, T.; Immordino, F.; Moretti, L.; Matoto, A.L. Baseline Assessment of Ecological Quality Index (EQI) of the Marine Coastal Habitats of Tonga Archipelago: Application for Management of Remote Regions in the Pacific. Remote Sens. 2023, 15, 909. https://doi.org/10.3390/rs15040909
Peirano A, Barsanti M, Delbono I, Candigliota E, Cocito S, Hokafonu T, Immordino F, Moretti L, Matoto AL. Baseline Assessment of Ecological Quality Index (EQI) of the Marine Coastal Habitats of Tonga Archipelago: Application for Management of Remote Regions in the Pacific. Remote Sensing. 2023; 15(4):909. https://doi.org/10.3390/rs15040909Chicago/Turabian Style
Peirano, Andrea, Mattia Barsanti, Ivana Delbono, Elena Candigliota, Silvia Cocito, Ta’hirih Hokafonu, Francesco Immordino, Lorenzo Moretti, and Atelaite Lupe Matoto. 2023. "Baseline Assessment of Ecological Quality Index (EQI) of the Marine Coastal Habitats of Tonga Archipelago: Application for Management of Remote Regions in the Pacific" Remote Sensing 15, no. 4: 909. https://doi.org/10.3390/rs15040909