Habitat Classification Scheme

Deep fore-reef slope

Images: left is scene taken from WordView2 image mosaic captured in 2015 and 2016, top right is Six Senses IMG_5263, bottom right is Six Senses IMG_5272

Community composition: A diverse benthic community with the dominant scleractinian community differing by location. Shallower areas may be dominated by branching acroporids and (sub)massive poritids with encrusting and plating corals also present. Small mounds of hosting diverse mixed coral assemblages may be present. At greater depths, colonies take on plating morphologies and may form a series of shingle-like structures. Large monospecific stands of foliaceous and plating/encrusting Pachyseris, Leptoseris, Pavona, Montipora, Merulina, Echinopora occur on more gradual slopes while encrusting and laminar morphologies become more common when the slope becomes close to vertical. Prominent macroalgae include Halimeda and Tydemania.

Hydrography: Deep fore reef slope lies below the fair-weather wave base but is episodically exposed to high energy during severe storm events and tsunamis. Alongshore currents may be present. Differences in storms, surge, wind and wave exposure influence the benthic community

Morphology: The transition from shallow to deep fore-reef slope is marked by an increase in slope angle

Water depth: 15 m to 30 m

Shallow fore-reef slope

Images: left is scene taken from WordView2 image mosaic captured in 2015 and 2016. Top right is Isdhoo IMG_4019, middle right is Gasgandhu finolhu IMG_4773 and bottom right Munyafushi

IMG_6201

Community composition: Benthic community structure varies due to the local disturbance regime and resilience. Biota generally similar to that of the deep fore-reef slope.

Hydrography: Water motion is driven by wind and oceanic waves and along-shore currents. Wave influence on the habitat abates as depth increases

Morphology: Gently sloping with some elevated mounds and incipient spur-and-groove morphology

Water depth: 8 m to 15 m

Spur-and-groove zone

Images: left is scene taken from WordView2 image mosaic captured in 2015 and 2016. Top right is Gasgandhu finolhu IMG_4628, middle right is Gasgandhu finolhu IMG_4654 and bottom right is

Gaadhoo IMG_4944

Community composition: Spur tops may host a complex community of short, stout branched acroporids and pocilloporids, small encrusting and submassive faviids, and, on the deeper ends, Montipora, Astreopora, Porites and other scleractinian species take on a plating morphology. Live coral cover in these cases may rarely be very high (60% to 80%). In other cases, the spur top is a scoured hardground with isolated scleractinians and abundant calcareous coralline algae (CCA). Coral density on spur walls ranges from sparse to a dense assemblage of plating and encrusting colonies. Similarly, grooves may be uncolonized coral rock, host CCA accumulations, or support dense coral assemblages.

Hydrography: Long-period ocean swell sculpts this shallow reef zone causing platform-normal alternations of structures consisting of parallel linear spur (ridges) of active coral growth separated by grooves (depressions)

Morphology: Spur and groove reefs are a common feature of windward margins of carbonate platforms, likely due to the continued effects of erosion caused by swell and trade wind waves. Depending on prevailing hydrodynamics, grooves might accumulate sediment and coral debris, else, more commonly, consist of a scoured abrasion surface

Water depth: 1 m to 8 m

Reef crest

Images: left is scene taken from WordView2 image mosaic captured in 2015 and 2016. Top right is Isdhoo site 9 & 10, photo-33, middle right is Gasgandhu finolhu photo 9 and bottom right is Sand bank

photo 10

Community composition: Crustose coralline algae account for the majority of biotic cover. Coral growth is limited due to wave action and episodic aerial exposure and is limited to species tolerant of the chronic disturbances.

Hydrography: A high energy environment exposed to large (often > 1 m) swell on a regular basis. The reef crest may be aerially exposed during low tides. The continuity of the algal ridge is broken at irregular intervals by shore-perpendicular grooves cut by waves and currents. These channels provide paths of tidal water exchange between the open ocean and the lagoon or back reef.

Morphology: The reef crest's ocean-face is the highest point on the reef and is characterized by margin-normal gullies that facilitate the exchange of water between the open ocean and the platform interior. The reef crest is considerably broader and better developed on the windward than the leeward margin of the platform.

Water depth: 0 m (swash zone)

Windward reef flat

Images: left is scene taken from WordView2 image mosaic captured in 2015 and 2016. Top right is Isdhoo, sites 5,6 & 7, photo 6, middle right is Isdhoo, sites 5,6 & 7, photo 7 and bottom right is

Bodumaabulhali 8

Community composition: Biotic cover is low in this zone because the substrate is mobile and largely unconsolidated. Turf algae dominate, and isolated coral colonies are present, but at low density and of a small size. Calcareous red algae and turf algae are prominent, and rhodoliths may accumulate. Coral colonies are typically encrusting, submassive and free living (e.g. Psammocora, faviids and fungiids) and hardier than those found in other zones. In areas of the reef flat that have not accumulated rubble, a planation hardground can develop which is colonized by turf algae and isolated coral colonies (<1% live cover). Scleractinians found in this habitat include Pocillopora and submassive Platygyra, Favites, Montastrea, Porites and Favia

Hydrography: Water motion in this zone is driven by waves, tides, and wind. Breaking waves transport water and sediment over the reef crest into this zone. Tidal pools form during low tide when water is trapped in topographic lows

Morphology: The windward reef flat is the platform-ward extension of the reef crest. It is fully aggraded to sea level and has low-relief. Large boulders of reef rock moved up over the reef crest by severe storms and tsunamis may be present and mix with outcrops of stranded fossil reef deposited during geological

periods of higher sea level. The windward reef flat has sweeping platform-normal striations created by the hydrodynamically-modulated accumulation of coral rubble. The windward reef flat is considerably broader than the leeward

Water Depth: 1 m to 2 m

Leeward reef flat

Images: left is scene taken from WordView2 image mosaic captured in 2015 and 2016. Top right is Bodufinolhu photo 8, middle right is Sand Bank photo 2 and bottom right is Maavah photo 11

Community composition: As for the windward reef flat

Hydrography: Being situated on the leeward side of the platform, this zone is of lower energy than the windward. Tides and wind-driven currents are the dominant drivers of water motion

Morphology: The leeward reef flat displays varying degrees of aggradation to sea level depending on the width of the zone and hydrodynamic factors. Being of lower energy, the platform-normal striations of reef rubble that characterize the windward reef flat are typically absent from the leeward

Water Depth: 1 m to 2 m

Back reef coral framework

Images: left is scene taken from WordView2 image mosaic captured in 2015 and 2016. Top right is Bokaiyfushi photo 10, middle right is Bodufinolhu photo 2 and bottom right is Bokaiyfushi IMG_4446

Community composition: Coral framework with variable benthic community composition. The coral community may be composed of dense acroporid thickets or massive poritids and agariciids forming microatolls whose tops are colonized by submassive, branching, and foliose coral colonies.

Hydrography: The back reef is a low energy environment as wave energy dissipates across the reef crest and back reef. Tides and wind are the dominant drivers of water motion.

Morphology: The back-reef has little sedimentation, although topographic depressions serve as collection points for coarse carbonate sands such as Halimeda plates and coral rubble. This back reef zone displays varying degrees of reef framework aggradation depending on the width of the back reef and prevailing hydrodynamics.

Water depth: 1 m to 5 m

Back reef-sediment dominated

Images: left is scene taken from WordView2 image mosaic captured in 2015 and 2016. Top right is Isdhoo, site 3, photo 5, middle right is Six Senses photo 2 and bottom right is Munyafushi photo 7

Community composition: Biotic cover is low due to high disturbance rates wrought by sediment motion. Sparse turf and macroalgae seasonally stabilizes the accumulated sediments. Dead coral and coral rubble are interspaced by infilled sand pockets.

Hydrography: As for “Back reef – rubble dominated.”

Morphology: Where wave action is more moderate, the back reef tends to be less rugose and composed of compacted carbonate sands deposited periodically by storm waves.

Water depth: 0 m to 5 m

Platform-top sands

Images: left is scene taken from WordView2 image mosaic captured in 2015 and 2016. Top right is Gan photo 1, middle right is Kadhoo, site 12, photo 2 and bottom right is Olhutholhu photo 3

Community composition: Unconsolidated sediment sheets with little biotic cover by virtue of the dynamic nature of this zone.

Hydrography: A low energy environment dominated by tides and wind-driven waves. Oceanic influence is minimal since long-period ocean swell breaks on the reef crest and is dissipated across the reef flat before reaching this zone.

Morphology: Low relief undulating sedimentary bedforms created by the accumulation of carbonate sands derived from the fore-reef and reef flat

Water depth: 1 m to 5 m

Seagrass meadows

Images: left is scene taken from WordView2 image mosaic captured in 2015 and 2016. Top right is Isdhoo, site 3, photo 2, middle right is Maabaidhoo photo 15 and bottom right is Bokaiyfushi photo 9

Community composition: Meadows of seagrasses namely Thalassia hemprichii and Thalassodendron ciliatum interspersed with macroalgae (Halimeda common) on unconsolidated sand

Hydrography: Restricted water motion with little influence from waves due to sheltering by reefs and islands. Water restriction leads to long resident times for water masses, and the suspension of detritus creates moderate turbidity

Morphology: Low relief undulating sedimentary bedforms seasonally stabilized by submerged aquatic vegetation

Water depth: 1 m to 5 m

Macroalgae on sediments

Images: left is scene taken from WordView2 image mosaic captured in 2015 and 2016. Top right is Olhutholhu photo 5, middle right is Sand Bank photo 5 and bottom right is Isdhoo, sites 5,6 & 7, photo

14

Community composition: An expanse of macroalgae in which thalli are interspersed by unconsolidated sediment.

Hydrography: Restricted water motion with little influence from waves due to sheltering by reefs and islands. Moderate turbidity results from the typically restricted hydrodynamic conditions and the suspension of detritus.

Morphology: Predominantly fine-grained carbonate sediments trapped by the macroalgae thalli. Low relief

Depth range: From -1 m to -15 m

Barren lagoon floor

Images: left is scene taken from WordView2 image mosaic captured in 2015 and 2016. Top right is Bodumaabulhali IMG_5669, middle right is Bilehtheyraha IMG_6849 and bottom right is Gasgandhu

Finolhu IMG_4697

Community composition: Isolated colonies of sediment-tolerant and low-light adapted coral colonies. Fleshy macroalgae may seasonally inhabit the sediment. Reef rubble and dead reef fragments initiate a debris slide into castic holes and troughs.

Hydrography: Restricted water motion with little influence from waves due to sheltering by the reef. Oceanic wave energy dissipates before reaching this zone, and the orbitals of wind generated waves attenuate before reaching the seafloor. Tidal cycles flush the lagoon, however restricted flow leads to long resident times for water masses and high turbidity

Morphology: Generally has low relief. Local highs created by coral colonies

Water depth: 5 m to 15 m

Fully-aggraded lagoonal patch reefs (Giri)

Images: left is scene taken from WordView2 image mosaic captured in 2015 and 2016. Top right is Six Senses IMG_4994, middle right is six Senses IMG_5006 and bottom right is Dhigufalhu IMG_5131

Community composition: Coral community composition is determined by the development stage of each patch. In the early stage, the coral community is dominated by massive species (e.g., Porites sp.) which build to form a pinnacle. Accommodation space becomes limited as the pinnacle aggrades to sea level, leading to the formation of microatolls from the massive colonies. Plating, branching, submassive, and encrusting coral species colonize the tops of the microatolls. Sometimes they can be completely dominated by plating Acropora. Over time, skeletal debris and sediment collect in the center of the microatoll leading to the formation of cays. A relative sea level drop may expose the top of the pinnacle to form a lagoonal island, which, with time, can then be colonized by vegetation. Simultaneously, the coral community may back-step to form a lagoonal island fringing reef

Hydrography: Low energy platform-interior lagoonal setting

Morphology: Isolated columnar patch reefs that reach the sea surface. Usually circular in shape, but may elongate along hydrodynamic gradients and/or adopt shapes directed by pre-existing antecedent

topography. Patch tops flatten as they near sea level. Patch flanks are steep and onlapped at their base by sands accumulating on the lagoon floor

Water depth: 0 m to 5 m

Partially-aggraded lagoonal patch reefs (Thilas)

Images: left is scene taken from WordView2 image mosaic captured in 2015 and 2016. Top right is Hanhushi IMG_5925, middle right is Bodumaabulhali IMG_5613 and bottom right is Bodufinolhu

IMG_6392

Community composition: As for fully-aggraded patch reefs

Hydrography: Low energy platform-interior lagoonal setting

Morphology: Isolated columnar patch reefs with tops that remain several meters below the sea surface. Usually circular in shape, but may elongate along hydrodynamic gradients and/or adopt shapes directed by pre-existing antecedent topography. Patch tops are domal and flanks are less steep than for giri.

Water depth: 5 m to 30 m

Beach

Images: left is scene taken from WordView2 image mosaic captured in 2015 and 2016. Beaches on Kadhoo and Vadlinolhu

Beach sands and occasionally beachrock are seawardly bounded by the swash and bounded on the landward side by a variably developed beach berm and or wetlands. Seasonally, particularly after storms, the beach can be covered by strandlines of desiccated seaweed and other marine detritus

Wetlands

Images: left is scene taken from WordView2 image mosaic captured in 2015 and 2016. Maavah wetlands

Wetlands can be brackish or freshwater habitats which may or may not be linked to lagoons, almost always surrounded by mangroves.

Mangrove forests

Images: left is scene taken from WordView2 image mosaic captured in 2015 and 2016. Mangrove forests on Manndhoo

Community composition: Coastal area dominated by mangroves. Diverse filter-feeding invertebrate communities including sponges, tunicates, bryozoans and certain cnidarians may occur among prop roots

Hydrography: Restricted water motion with little influence from waves due to sheltering by reefs and islands. Tidal cycles flush the area. The water column has high turbidity due to suspension of detritus.

Morphology: Predominantly fine-grained sediments trapped by mangrove prop roots and seagrasses. Sediments are biogenic, resulting from the breakdown of the marine vegetation. Mud flats around the roots are low relief. Root system provides relief, substrate for invertebrate colonization, and habitat for fishes.

Depth range: Dependent on tidal range. From 0 m to -2 m around the root system.

Terrestrial vegetation

Images: left is scene taken from WordView2 image mosaic captured in 2015 and 2016. Terrestrial vegetation on Mundoo and Kalhaidhoo

Expanse of vegetation (e.g., palm trees, Screwpine and grasses) on emergent features or islands.

Unvegetated terrestrial

Images: left is scene taken from WordView2 image mosaic captured in 2015 and 2016. Unvegetated terrestrial found on Mundhoo and Dhanbidhoo

Soil or rock on islands with no discernible vegetative cover. Urbanized areas including towns, communities, buildings, paved roads, houses and more complex infrastructure also fall into this habitat class