Orange to brown encrusting mats with fuzzy appearance (Fig. 2).

Figure 2.  

Cyanobacteria stet. sp. 1, Laamu, 30 m.

Dark green to brown encrusting mats with fuzzy appearance (Fig. 3).

Figure 3.  

Cyanobacteria stet. sp. 2, North Male’, 30 m.

A green alga that has a twig-like, creeping rhizome and several upright fonds attached to the substratum by rhizoids. Colouration brown and green shades. Size of patches ~ 16 cm. Species of Caulerpa are characterised by their morphological plasticity and display variation both in response to environmental factors and within species (Fig. 4). Same as Caulerpa sp. indet. 1 reported in Fassbender et al. (2021) from the Seychelles.

a

b

Figure 4.

Caulerpa sp. indet. 1

a: North Male’, 30 m;  
b: North Male’, 30 m.  

A green alga with a creeping inconspicuous rhizome and small flattened blades with serrated edges. Blades are sometimes twisted, spiralling or in a forked y-shape. Size of patches were ~ 13 cm. Colouration in lighter shades of green (Fig. 5).

Figure 5.  

Caulerpa serrulata sp. inc., Addu, 30 m.

A macroalgae with disc-like, calcified segments, with variations in segment shape and size. A dense tuft of rhizoids attaches the thallus to the substratum. Often grows in branching clumps. Sizes of Halimeda patches, often including multiple thalli that were impossible to distinguish from one another, were ~ 18 cm (Fig. 6). Same as Halimeda spp. indet. reported in Fassbender et al. (2021) from the Seychelles, although, on this occasion, we did not collect specimens to verify that more than one species (spp.) were present in our surveys.

a

b

Figure 6.

Halimeda sp. indet.

a: Vaavu, 30 m;  
b: Laamu, 30 m.  

A macroalgae with disc-like, calcified segments, with variations in segment shape and size. A dense tuft of rhizoids attaches the thallus to the substratum. Size of H. miconesica pathes, often including multiple thalli that were impossible to distinguish from one another, were ~ 22 cm. Often grows in branching clumps (Fig. 7).

a

b

Figure 7.

Halimeda micronesica

a: North Male’, 10 m;  
b: North Male’, 10 m.  

A macroalgae that has a green thallus and grows in thick clumps ~ 25 cm. Cylindrical main branches with whorls of branches along the length that form several lateral branchlets. Tydemania expeditionis is the only confirmed species in the Maldives (Fig. 8).

a

b

Figure 8.

Tydemania expeditionis

a: Addu, 30 m;  
b: Addu, 30 m.  

Encrusting algae from bright pink to purple. This group contains a variety of species that are difficult to identify from images. It is also known as crustose coralline algae (Fig. 9).

a

b

c

Figure 9.

Corallinales stet.

a: Huvadhu, 10-30 m;  
b: North Male’, 10 m;  
c: Laamu, 10 m.  

Small interlaced, rounded projections, cone-shaped sponges, separated over the substrate. Apical cavity (oscule) present. The surface is smooth, with some undulating. Size ~ 29 cm in longest dimension. Colouration shades of green and greenish-black (Fig. 10).

a

b

Figure 10.

Spheciospongia sp. indet. 4

a: Huvadhu, 30 m;  
b: Huvadhu, 30 m.  

Thickly encrusting to small pear-shaped or fig-shaped sponges. Surface even, but undulating; colouration light to dark grey. Approximately 11 cm in longest dimension (Fig. 11).

a

b

Figure 11.

Spheciospongia sp. indet. 5

a: North Male’, 120 m;  
b: North Male’, 120 m.  

Large cup- to barrel-shaped sponges. Surface smooth, but undulating and somewhat slippery to the touch. Large sunken indentations visible on the outer surface. Oscules randomly scattered on the inner side of the vase. Approximately 46 cm across. Colour in life brown; in preservative beige (Fig. 12).

Figure 12.  

Spheciospongia excentrica, Addu, 30 m.

Oliaceous sponges attached to substratum by stalk. Usually made up of two concentric plates. The sponge is rubbery with ostia evenly scattered on the rim of the sponge. Surface smooth. Approximately 17 cm in longest dimension. Colouration light brown to pale grey with lighter shades of yellow (Fig. 13).

a

b

c

d

Figure 13.

Phyllospongia foliascens

a: Fuvahmulah, 120 m;  
b: Huvadhu, 120 m;  
c: Laamu, 116 m, in situ photo of collected specimen MAL1_550;  
d: Laamu, 116 m, collected specimen MAL1_550.  

Erect, tubular or cylindrical sponges sometimes growing on top of calcitic substrata. Large oscula opening present. Surface is hispid and undulating with conulose structures (Fig. 14). Approximately 21 cm across. Same as Callyspongia sp. indet. reported in Fassbender et al. (2021) from the Seychelles.

a

b

Figure 14.

Callyspongia sp. indet. 1

a: North Male’, 30 m;  
b: Vaavu, 30 m.  

Thickly encrusting sponges, sometimes with irregular branching structures. Surface smooth and velvety with some punctate structures. Colouration is dark reddish-brown (Fig. 15).

Figure 15.  

Petrosiidae gen. indet. sp. 3, Huvadhu, 30 m.

Dichotomously branching sponges sometimes interconnected by repent structures and attaching to the substrate by stalk at multiple points. Approximately 52 cm in longest dimension. Colouration patchy with lighter colours at the tips, ranging from shades of pink and purple and dark red with lighter colour at the tips (Fig. 16).

a

b

c

d

Figure 16.

Petrosia sp. indet. 1

a: North Male’, 60 m;  
b: North Male’, 60 m;  
c: Vaavu, 30 m;  
d: Vaavu, 60 m.  

Thickly encrusting or encrusting cushion sponges. Surface uneven with turret-like or milk bottle-like oscules densely spread throughout the surface. Approximately 13 cm in longest dimension. Colouration brown to dark brown (Fig. 17).

a

b

Figure 17.

Petrosia (Strongylophora) sp. indet. 2

a: Huvadhu, 30 m;  
b: North Male’, 30 m.  

Arborescent, branching sponges. Smooth surface structure with numerous unevenly-sized circular cavities. Approximately 37 cm in the longest dimension. Colouration blue grey and blue shades with tips a lighter shade of grey white. Surface smooth and hispid (Fig. 18).

a

b

Figure 18.

Haliclona sp. indet. 15

a: North Male’, 30 m;  
b: Huvadhu, 30 m.  

Thinly-encrusting sponges growing whip-like with large oscules on the surface. Approximately 22 cm in the longest dimension. Colouration ranging from shades of pink and orange to yellow (Fig. 19).

a

b

Figure 19.

Haliclona sp. indet. 16

a: Laamu, 60 m;  
b: Laamu, 60 m.  

Thickly-encrusting sponges with an undulating and conulose surface. Approximately 13 cm across. Colouration in shades of brown and brownish-light green (Fig. 20).

a

b

Figure 20.

Haliclona sp. indet. 17

a: North Male’, 60 m;  
b: Addu, 10 m.  

Thickly encrusting sponges with a smooth, velvety surface and numerous smaller oscules spread throughout the surface. Oscules scattered evenly over the surface. Approximately 13 cm across. Colouration in shades of blue to lavender or occasionally brownish-grey (Fig. 21).

a

b

Figure 21.

Haliclona sp. indet. 18

a: North Male’, 30 m;  
b: Huvadhu, 30 m.