A green seaweed that grows in twig-like, branched plants with a creeping stolon and multiple erect fonds. The stolon is attached to the seabed by several bunches of rhizoids. Species of Caulerpa are known for their plastic morphologies, which may vary greatly within the same species and between different environmental conditions (Fig. 2).

a

b

Figure 2.

Caulerpa sp. indet. 1

a: D'Arros N1, 60 m.  
b: Desroches S1, 10 m, collected specimen (SEY1_1377).  

A green seaweed with creeping stolon and erect fronds with branchlets consisting of a short pedicel ending in a rounded, disc-like to spherical appendage. Stolons are attached to the substratum by bunches of rhizoids. Species of Caulerpa are known for their plastic morphologies, that may vary greatly within the same species and between different environmental conditions (Fig. 3).

Figure 3.  

Caulerpa sp. indet. 2. Astove W1, 30 m.

Seaweed whose thallus can display erect or prostrate forms, usually stiff. Erect forms (as observed here) display dichotomous branching, attached to the substratum by groups of rhizoids. The colour is dark green, sometimes with a brownish tint (Fig. 4).

Figure 4.  

Codium sp. indet. Poivre E1, 60 m.

Conspicuous, cactus-like macroalgae with jointed, disc-like and calcified segments. Individual segments can vary in shape that ranges from round to kidney-, wedge- or even cylindrical-shaped. The thallus anchors to the bottom by a dense tuft of rhizoids which varies in shape depending on the substratum. Dead specimens have been observed to lose their green colour, revealing their white calcium carbonate skeletons. Five species were identified from collections (Halimeda cylindracea, H. aff. gracilis / H. aff. opuntia, H. minima, H. micronesica, Halimeda sp. indet); however, it was not possible to distinguish between them from underwater images alone (Fig. 5).

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b

c

d

Figure 5.

Halimeda spp. indet.

a: Aldabra N1, 10 m.  
b: Aldabra N1, 10 m.  
c: Halimeda sp. indet. Desroches S1, 10 m, collected specimen (SEY1_1376).  
d: Halimeda cylindracea. Desroches S1, 10 m, collected specimen (SEY1_1367).  

A green calcified seaweed composed of a stipe and either a single or several fan-shaped blades. It is anchored to the bottom by uncalcified tufts of rhizoids, which vary in shape depending on the substratum, most commonly sand. Udotea species are common in coral reef ecosystems and occur globally from tropical to subtropical latitudes. Two species were identified from collections (Udotea sp. indet. 1 and sp. indet. 2); however, it was not possible to distinguish between them from underwater images alone (Fig. 6).

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b

Figure 6.

Udotea spp. indet.

a: Udotea sp. indet. 1. D'Arros N1, 30 m.  
b: Udotea sp. indet. 2. D'Arros N1, 3 m, collected specimen (SEY1_1167).  

Thin, leaf-like green algae made of complanate, monostromatic, reticulate blades that occasionally form dense mats (Fig. 7).

a

b

Figure 7.

Microdictyon sp. indet.

a: Poivre E1, 30 m.  
b: Poivre E1, 30 m.  

A green algae that forms somewhat encrusting, hollow or solid, globose or flattened thalli made of vesicular segments (pseudoparenchymatous cushion of polygonal cells). They are attached to the substratum by rhizoids produced by basal vesicles (Fig. 8).

Figure 8.  

Dictyosphaeria sp. indet. Astove W1, 10 m.

Thallus can vary in shape and resemble lettuce leaves. The thallus is composed of two layers of cells attached to the substratum by a holdfast made of rhizoidal proliferations. The overall shape of the algae is very variable depending on the environmental conditions. Colour varies from light to dark green (Fig. 9).

Figure 9.  

Ulva sp. indet. Desroches S1, 60 m.

Brown fan-shaped blade with a firm texture. The creeping, ascendant or erect fonds can range from foliose to rounded and are attached to the substratum by rhizoids. Previously thought to be represented by only one species (Lobophora variegata), genetics (Vieira et al. 2016) have recently revealed a much wider species diversity than conventional methods of identification, based on macromorphological characters alone (Fig. 10).

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b

Figure 10.

Lobophora sp. indet.

a: Astove W1, 60 m.  
b: Alphonse N1, 60 m.  

Creeping red fleshy algae with small, arborescent and feather-like fonds arising from a decumbent rhizome-like base (Fig. 11).

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b

Figure 11.

Amphisbetema indica

a: Desroches S1, 10 m.  
b: Desroches S1, 10 m.  

Commonly known as crustose coralline algae, these encrusting algae grow on rocks, coral fragments, shells, other algae or seagrasses. Hard and rock-like, their surface can be smooth or rough. Colours range from bright pink to purple. This group contains a variety of species that are difficult to identify from images, hence, no attempt was made to identify them at a lower taxonomic level (Fig. 12).

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b

Figure 12.

Corallinales stet.

a: Astove W1, 10 m.  
b: Astove W1, 10 m.  

This seagrass species can form dense meadows and is identified by its linear and falcate leaves arising from a rooted rhizome. Its colour is a rich green. One species (Thalassodendron ciliatum) was identified from collections (Fig. 13).

Figure 13.  

Thalassodendron ciliatum. Poivre E1, 10 m.

Species of seagrass with a creeping bifurcated stem from which arise distichously arranged linear, oblong or rounded delicate leaves. Colour light green (Fig. 14).

Figure 14.  

Halophila sp. indet. D'Arros N1, 30 m.

Oval oral disc that is flat or slightly undulating and densely covered with finger-like tentacles. Tentacles are hardly tapered or blunt, sometimes with a swollen end. Oral disc white; tentacles light brown to green. Typically found growing in comparably exposed positions. They can host anemonefish and are associated with the anemonefish species Amphiprion akallopisos (pictured below), in Seychelles waters. Furthermore, Dascyllus trimaculatus and various shrimp species may live inside the anemone. Similar-looking species include Stichodactyla mertensii, with H. magnifica being much more substantial and its oral disc and tentacles of uniform colouration, with a brightly coloured column (where visible) (Fig. 15).

Figure 15.  

Heteractis magnifica. D'Arros N1, 30 m.

Meandering oral disc; surface covered in small tentacles (~ 1-2 cm), sometimes longer (~ 5 cm). Dark brown colouration with whitish stripes throughout the colony. Hosts several species of anemonefish, associated with Amphiprion clarkii or Amphiprion fuscocaudatus (see Fig. 16) in Seychelles waters.

Figure 16.  

Stichodactyla mertensii. Poivre E1, 30 m.

Round oral disc (~ 4 cm in diameter) with numerous short tentacles (~ 1.5 cm) along the outer edge of the disc. Colour orange to reddish. Further microscopic examination is necessary for positive taxonomic identification (Fig. 17).

Figure 17.  

Actiniaria fam. indet. sp. 1. Aldabra W1, 250 m.

Round oral disc (~ 2.5 cm in diameter) with numerous, thin (~ 2.5 cm long) tentacles along the outer edge of the disc. Colour translucent to white. Further microscopic examination is needed for positive taxonomic identification (Fig. 18).

Figure 18.  

Actiniaria fam. indet. sp. 2. Aldabra W1, 250 m.

Round oral disc (7 cm in diameter) with numerous thin tentacles (~ 6 cm long) along the outer edge of the disc. Oral disc pale to bright orange, tentacles translucent to pale white. Further microscopic examination is needed for positive taxonomic identification (Fig. 19).

Figure 19.  

Actiniaria fam. indet. sp. 3. Aldabra W1, 120 m.

Round oral disc entirely covered by thick, long (with respect to the size of the disc) tentacles. Colour of oral disc unknown; tentacles dark brown to dark red with white tips. Further microscopic examination is needed for positive taxonomic identification (Fig. 20).

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b

Figure 20.

Actiniaria fam. indet. sp. 6.

a: Aldabra W1, 250 m.  
b: Astove W1, 250 m.  

Colonies up to 1.7 m in height, mainly bushy and bramble-like, sparsely to densely-branched with fine, elongate branches. Light to dark brown colour (Fig. 21).

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b

Figure 21.

Antipathes sp. indet.

a: Aldabra N1, 30 m.  
b: Aldabra N1, 60 m.  

Colonies observed were large (> 2 m in height), fan-shaped and uniplanar. With thick, central stalk and several finer branches. Colour dark red to orange (Fig. 22).

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b

Figure 22.

Leiopathes sp. indet.

a: Alphonse N1, 250 m.  
b: Alphonse N1, 250 m.  

Colonies up to 20 cm in height, columnar, monopodial or very sparsely branched. Thick bottlebrush-like appearance. Irregularly pinnulate. Brownish to grey colouration. Darker coloured central axis enclosed by bushy, lighter coloured branches and polyps (Fig. 23).

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b

c

Figure 23.

Cupressopathes sp. indet.

a: Desroches S1, 30 m.  
b: D'Arros N1, 60 m.  
c: Desroches S1, 60 m.  

Colonies up to 1.8 m in height, densely branched, appearing rather bushy. Colouration ranges from brownish to grey and orange, with polyps coloured lighter than the branches (Fig. 24).

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b

c

Figure 24.

Myriopathes sp. indet.

a: Aldabra N1, 30 m.  
b: Desroches S1, 60 m.  
c: D'Arros N1, 60 m.  

Colonies have two rows of fine and long branches on either side of the central axis and grow up to ~ 15–20 cm in height. Branches are thin and rounded, giving the colony a feather-like appearance. Colonies are pink to purple coloured (Fig. 25).

a

b

Figure 25.

Bathypathes sp. indet.

a: D'Arros N1, 350 m.  
b: D'Arros N1, 350 m.  

Colonies up to 50 cm in height, columnar, monopodial or very sparsely branched. Thin bottlebrush-like appearance. Irregularly pinnulate. Whitish to pink colouration. Darker coloured central axis enclosed by bushy, lighter coloured branches and polyps. Appears similar to Cupressopathes, but the latter has a much more pronounced bottlebrush appearance (Fig. 26).

Figure 26.  

Stylopathes sp. indet. D'Arros N1, 350 m.

Colonies up to 1 m in height, fan-shaped and uniplanar with a high degree of ‘anastomosis’ (branch joins), giving the colonies a net-like appearance. In larger colonies, smaller branches may grow perpendicular to the main plane. Colour bright green to yellow. Occasionally with crinoid commensals (Fig. 27).

a

b

Figure 27.

Muricella sp. indet.

a: Alphonse N1, 60 m.  
b: Alphonse N1, 60 m.  

Colonies thickly encrusted with lobed projections, typically < 50 cm across (= in the longest dimension). Some species are bowl-shaped or stand more erect. Generally following the substrate, colonies look like large plates. Some form small individual bumps (1), others have long valleys and walls (2). Polyps are only present on the upper surface. Colouration brown to grey. The tips of the individual lobes are often coloured lighter than the sides. Similar species include Pectinia, which has deeper valleys towards the centre of the colony. Sinularia looks similar, but has smaller gaps between bumps (Fig. 28).

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b

c

Figure 28.

Lobophytum sp. indet.

a: Poivre E1, 10 m.  
b: Poivre E1, 10 m.  
c: Aldabra N1, 10 m.  

Colonies are digitiform, with a short tapered stalk resembling a carrot, up to 10 cm long. Polyps are only extended at night. Colouration yellow, orange or red, with white polyps (Fig. 29).

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b

Figure 29.

Paraminabea sp. indet.

a: Alphonse N1, 97 m.  
b: Alphonse N1, 97 m.  

Colonies are lobate with conspicuous bare stalks merging into a wide, fleshy, disc-like head (polypary). The polypary is concave at the centre and wavy around the edges, giving it a mushroom appearance (especially in juveniles). Polyps are only found on top of the polypary. Colouration shades of brown, beige, yellow or green. Polyps are generally of the same colour as the colonies, but can be yellow or white in brown individuals. In downward facing videos typical for benthic surveys, the stalk will not always be visible. Maximum recorded size: 20 cm across. Similar species include Lobophytum, lacking the prominent stalk and the folds around the periphery (Fig. 30).

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b

c

d

Figure 30.

Sarcophyton sp. indet.

a: Aldabra N1, 10 m.  
b: Aldabra N1, 10 m.  
c: Aldabra N1, 10 m, collected specimen (SEY1_250)  
d: Aldabra N1, 10 m, collected specimen (SEY1_250)  

Sinularia colonies have the largest morphological variation amongst all soft corals. Colonies form low tabular mounds that can have ridged or digitate surfaces. Growth forms can be low encrusting, branching, tall and lobed,or lead and dish-like. Colonies form finger-like projections. Polyps are fully retractable. In this survey, colonies were typically < 50 cm across and their colouration ranged from grey and pale brown to pinkish and green. Similar species include Cladiella and Lobophytum, with C. and L. colonies typically having wider ridges between lobes (Fig. 31).

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b

c

Figure 31.

Sinularia sp. indet.

a: Aldabra N1, 30 m.  
b: Poivre E1, 10 m.  
c: Aldabra W1, 10 m.  

Colonies were up to 40 cm in height (Fig. 32b) and identified by their irregular and uniplanar branches. Polyps are conspicuous and give the colony a fuzzy appearance. Colouration ranges from red or light brown to pink and yellow, the latter two commonly encountered during this survey. Polyps are normally whitish (Fig. 32).

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b

c

Figure 32.

Solenocaulon sp. indet.

a: Aldabra W1, 60 m.  
b: Aldabra W1, 60 m.  
c: Astove W1, 60 m.  

Colonies are small (< 25 cm in height) and growing as stubby, finger-shaped branches. No central stalk was visible on the captured footage. Surface covered with polyps giving it a fuzzy appearance. Colony colour was orange with orange polyps (Fig. 33).