in Bouchet P., Le guyader H. & pascal O. (Eds), The Natural History of Santo. MNHN, Paris; IRD, Marseille; PNI, Paris. 572 p. (Patrimoines naturels; 70). Algal and Seagrass Communities from Santo Island in Relation to Habitat Diversity Claude E. Payri

The coral reef communities of five species from Santo, i.e. Cymodocea rotundata, have been little studied and nothing Halodule uninervis, H. pinifolia, Halophila ovalis and has been previously published on Thalassia hemprechii. the benthic algal flora from Island. Some marine algae The present algal flora and seagrass investigation of from Vanuatu have been found in Santo was conducted during August 2006 as part of the British Museum collections (BM) the "Santo 2006 expedition". This work is a com- and are mainly Sargassum species and panion study to that of the Solomons and Fiji and is Turbinaria ornata. In their report on intended to provide data for ongoing biogeographic Vanuatu’s marine resources, Done and work within the West and Central Pacific.

Benthic Navin (1990) mentioned Halimeda opuntia as occurring in most of the Extensive surveys have been carried out in most sites investigated and noted the high encrustation of the habitats recognized in the southern part of of coralline algae in exposed sites. More work has Santo Island and in the Luganville area, including been done on seagrass communities; earlier authors islands, shorelines, reef flats, channels and deep reported a total of nine species from Vanuatu including outer reef slopes.

Sampling sites and Methods The 42 sites investigated are shown in figure 409 species list for the southern part of Santo. and are distributed from Palikolo in the north- Specimens were sampled to make a taxonomical ernmost part of the study area, down to Urepala collection for the area. islet located in the southern part including the Segond Channel, the Malo passage and Abokisa All the collected specimens were pressed and dried Island on the east coast of . Sites were for herbaria; fragments of specimens were preserved selected to include the largest possible range of in a solution of buffered formalin in seawater (5 %) environments. for further anatomical studies. Tissues from vari- ous taxa were also preserved for further phylog- Most of the sites were surveyed by SCUBA divers eny and molecular analysis and all the herbarium from the surface down to 60 m deep. The shallow specimens were air dried (without formalin) which areas, including fringing reef flats, reef channels allows for extra DNA analysis if necessary. The and rocky shorelines, were sampled by snorkelling collection is currently housed in the phycological and walking on the reef. The sampling effort was herbarium at IRD Nouméa (IRD-NOU) and will standardized and inventory duration at each site be transferred to the Muséum national d’Histoire was fixed to 80 minutes. A species inventory was naturelle in Paris (PC). Part of the collection will compiled in order to create a more comprehensive be deposited at USP in Suva, Fiji.

Marine macrophytes in Santo: general insights Macrophyte communities on coral reefs are In addition, Vanuatu’s reefs have a complex tec- generally distributed in assemblages that more tonic history, having experienced several emer- or less reflect reef zonation. The distribution gence and subsidence events. These have resulted of the marine flora on a coral reef is influenced in some features that are typical of many reefs by various factors including sunlight, salinity, with rocky shorelines, and recent tectonic dis- water turbulence and currents, the nature of placements and uplifts may have affected some the substratum, depth, exposure to air, geo- of their benthic assemblages. However, we did morphology, topography, herbivore pressure not observed a recent influence of tectonic dis- and biological competition with other benthic placement on benthic communities in the study organisms. areas and the most significant disturbances we

337 ... Marine Ecosystems ......

Santo 2006, marine algae habitats ( sampling sites � wrecks 32 ( Reef geomorphology Mainland Shelf patch-reef complex Ocean-exposed fringing reef

main land subtidal reef flat deep terrace

Inner-seas patch-reef complex Inner-seas exposed fringing reef fore reef

enclosed lagoon or basin forereef reef flat forereef pinnacle shallow terrace

reef flat reef flat Shelf slope

subtidal reef flat shallow terrace shelf slope

Cartographie : C. Chauvin IRD 2008. 15 ( Source : Payri Santo 2006, Andréfouët Millenium Coral Reef Mapping Project.

(37 Paikolo

38 ( ( 2 (1

ESPIRITU SANTO Luganville ( ( 41 ( 39 40 ( � ( �4 Segond Channel ( Coolidge Million Dollar Point 13 30 ( ( 34

31 ( (14

8 ((9 (29 12 ( 6 ( Tutuba 28 Aore ( 35 ( 5 ( 36 3 ( 11 ( ( 26 ( 7 (( 42 10 21 Abokisa ( Brigstocke 23 ( ( ( 25 20 ( ( ( 33 ( 18 ( ( 19 16 ( 24 17 Bruat Channel Urelapa 22 27( ( ( (44 45 ( 46

� 43 ( 0 2,5 5km Malo

Datum : WGS 1984 Projection : UTM Zone 58 S Figure 409: Map of sampling sites in the Luganville area, southern part of Santo Island.

observed were the result of recent cyclone activity are generally distributed parallel to the shorelines and bleaching events over the past few years. and reef margins.

However, environmental factors are not homoge- This synthesis comprises an overview of the rep- neous across the reefs, and gradually change from resentative biotopes investigated and describes the the shoreline to outer reef slopes through lagoons different macrophyte (algae and seagrasses) commu- and reef flats. The rather patchy zonation patterns nities associated with the different identified habitats.

...338 ...... The Natural History of Santo

Representative biotopes The main features of the Santo coral reef complex The 42 sites surveyed have been classified into 12 major are the absence of a barrier reef and associated habitat groups which include geomorphology, topog- habitats. Most of the structures comprise narrow raphy and major benthic communities. Schematic fringing reefs, outer reefs, patch reefs in shallow diagrams (profiles) are given in figures 411-422, the water, sheltered and open embayments, deep chan- list of the symbols used in the profiles are given figure nels and shallow passes, exposed outer reef slopes 410. Descriptions of the profiles are as follows. and reef walls or drop-offs. ……Segond Channel (Fig. 411) Most of the sites have reef habitats compressed into This long channel runs between Santo and Aore Island. narrow coastal margins and exposed to ocean influ- Around the Luganville area and down to the south ences. On unsheltered coasts the coral reefs are there are few reef formations and coral communities wave-beaten structures that are heavily encrusted and these are mainly developed on sandy slopes and by coralline algae as well as by coral species that rubble. Narrow reef flats are present, mostly at both are well-adapted to strong turbulence. entrances to the Channel and along the Aore Island coast. Coral communities are mostly Acroporidae and The great ocean depths, large fetches and the refrac- occasional massive Porites. There is also evidence of tion of swells around the small islands adjacent damaged coral in the high proportion of coral rubble. to Santo mean that the open coasts on all sides Large beds of the green macrophyte Halimeda opuntia are subject to strong wave forces, and this limits intermixed with sponges colonise the hard substratum. the types of reefs that can establish. Less robust In the northern area, the middle part of the channel forms of corals and other benthic communities are is deep (70 m depth) and muddy, marked with ghost however able to develop in more sheltered embay- shrimp (Calianasseae) hummocks and small benthic ments. The islands around the Segond Channel communities including some Nephtheidea, Dophleina provide significant shelter from the open ocean, and Asthenosoma urchins. The benthic communities and the channel accumulates siltation originating of the channel environment are dominated by sponges from the terrestrial erosion of the adjacent island and octocorallians (soft corals and sea fans). On the of Santo; the channel supports a range of habi- shallow muddy flats adjacent to the shore of Santo tats with conditions ranging from intermediate to island seagrasses such as Halodule and Cymodocea abundant shelter, and muddy substrata. form sparse patches.

Living massive coral Sponges

Living branched coral Dead corals Living tabular coral Coral rubble Living foliaceous coral Ghost shrimp hummock Tubastrea

Gorgonian Mangrove

Sarcophyton

Lobophyton

Seagrass Coconut tree

Halimeda

Caulerpa Trees

Rhodophyta Native houses

Figure 410: List of symbols used for figures 411-422.

339 ... Marine Ecosystems ......

Depth (m) Mixed seagrass : 20 30 10 40 50 0 G Aore Is. D Nouméa). andpinifolia Halodule R

shoreline 1800 : Dseagrassof iffuse bed D F C (Photos J.-L. Menou & J.-M. Boré I L inward channel slope Gomophia watsoni . : L I ypical community of invertebrates and algae on the deep channel edge. Dophleina . : T : F K K channel bottom milleprorella . Segond Channel Distance from shore (m) Fromia : J ypical mixed community on channel slope dominated by Neiphteidae. by dominated slope channel on community mixed ypical : T C H Juncella . S egond Channel. J B bed. Halimeda : G orgonian I Physogyra . : outward channel slope H E G ypical gentle slope with dense with slope gentle ypical : T B Cymodocea serrulata . seagrass bed

mudflats and mangrove Halimeda minima forming thick mats with sponges and other organisms on the channel slope. 0 : D E 0 20 30 10 40 50 Halodule uninervis and

Depth (m) S chematic diagram 411: of the topography and reef communities of the Santo Is. Mangrove trees on the shoreline. the Mangroveon trees

A : A Figure . Halophila ovalis bed of

...340 ...... The Natural History of Santo

Depth (m) RD Nouméa). 20 30 10 40 0 Aore Is.

reef flat 650 Phyllospongia lamelosa with F : Ellisella . E : F J D : G orgonian. B Thelenota anax . (Photos J.-L. Menou & J.-M. Boré I K : inward channel slope Acropora branches. K I Tubipora musica . Tubipora E J : S egond Channel). C : R ubble of Choriaster granulatus . I : channel bottom Segond Channel Distance from shore (m) D Comanthus bennetti . H Halimeda beds on the edge of the slope. ypical B : T outward channel slope Comantheria briareus and Crinoids H : G rocky reef flat 0 0 20 30 10 40 C Acropora community on channel slope. A Depth (m) Halimeda minima . G : Santo Is. S chematic diagram 412: of the topography and reef communities of Channel Pass (southern entrance of the Branching Figure A : Halimeda .

341 ... Marine Ecosystems ......

……Channel Pass (southern entrance the delicate paddle seagrasses Halophila spp. were of Segond Channel) (Fig. 412) observed on the sandy slope down to 50 m deep. The topography and the environment of the Segond Sparse coral blocks and rubble are the main features Channel changes from the north to the south with from the top down to the mid-slope while coarse the increasing current. The coral communities are sand and debris are dominant further down beyond well developed on the slopes with massive corals in 30 m deep. Species diversity is low except for star- the shallow areas while a rich branched coral com- fish and holothurians with various species such munity is associated with green calcareous algae as Nardoa gomophia, Echinaster callosus, Choriater Halimeda opuntia and the coralline algae Amphiroa granulatus, Holothuria (Microthele) fuscogilva and M. on the gentle sandy slope. The bottom of the chan- fuscopunctata and the that display several nel is a hard substratum supporting large coral gelatinous species in the deeper part of the slope. patches with flourishing communities of benthic invertebrates including octocorallians and numer- ……Sheltered embayment (Palikolo Bay) ous crinoids. This area experiences strong tidal (Fig. 416) currents. The reef flat on the Aore side is narrow From shore to open ocean, this bay contains sev- with a steep slope dominated by Halimeda mac- eral biotopes including: roloba anchored in the muddy sand and various red • Prolific seagrass beds in the fringing muddy algae entangled in dead Acropora branches. flats intermixed with a green macroalgal com- plex of Halimeda and ; ……Sheltered fringing reef • Shallow sheltered reefs on sand dominated by (Brigstocke point, SW Luganville) acroporids; (Fig. 413) • Large areas of coral-construction on deeper Most of the reefs fringing the southern corner of (6 m) patch reefs; Santo are characterized by a narrow area of subti- • A steep slope from 15 m down to 60 m deep. dal grooves adjacent to the rocky shoreline, with The patch reefs here support a high diversity dense macroalgal vegetation of red algae Callophycus of species with a very rich coral community spp, Portieria hornemanii and Amphiroa crassa. The including many fungids and octocorallians. slopes are mostly covered with coral debris with some Large mounds of rubble covered by the brown large blocks of dead Porites. The green calcareous alga Lobophora variegata indicate an accumula- alga Halimeda opuntia develops spectacular beds from tion of coral skeleton fragments that have bro- 15-30 m deep, while Halimeda macroloba and the red ken in recent decades. The diversity decreases foliaceous algae belonging to the Peyssonneliaceae down the slope; some holothurians including form aggregations (soft nodules) up to 10 cm in diam- Thelenota anax and Neoferdina cumingii (50 m) eter that are locally abundant on the top of the slope. have been observed along with green algae Cladophora and Halimeda in the deeper zone. ……Malo water passage (between Aore and Malo Islands) (Fig. 414) ……Open embayment, partially The Aore site is fringed by small Rhizophora clumps sheltered (east Aore) (Fig. 417) that grow on the beaches along a narrow and shal- This habitat occupies the north eastern part of Aore low depression where Acroporids and the seagrass Island. The coral community is developed on a gen- Enhalus acoroides are well developed on sand flats tle sandy slope down to 25 m deep and looks like with moderate tidal currents. The shallow reef flat the silty bottom of a lagoon. Porites with abundant on the side of the islet is covered with many massive soft corals, sponges and various branching Acropora Porites; on the side of the reef is deeper form large beds down to 15 m deep. Various coral- and the corals are more massive and have developed line and red fleshy algae were recorded on hard sub- into large patches with abundant encrusting coral- strata. Corals such as Polyphyllia, Herpolitha limax, line algae. The coral cover is high on the reef slope Sandalolitha robusta and Cynarina lacrymalis were along the water passage. Foliose and branched corals also observed in these sheltered areas. The accumu- are abundant on the reef slopes while they decrease lation of fine carbonate sand in the deeper part is a further down to the bottom of the passage where typical characteristic of lagoons and supports large strong currents limit the development of a benthic patches of mixed green algae including Halimeda, community. Large spurs parallel to the sea floor that Udotea, Avrainvillea and Caulerpa. Visibility was support octocorallians are the main feature of the reduced in this environment due to the abundance base of the slope on the Malo side. of fine carbonate particles in the water column. ……Sheltered sandy slope (Malo passage) ……Sheltered fringing reef (West (Fig. 415) Tutuba Island) (Fig. 418) The Malo passage has typical sandy slopes with On the west side of Tutuba Island adjacent to the little reef formation along the shores of Aore and beach there is a narrow and patchy fringing reef front- Malo islands. Fringing reef flats are narrow, shallow ing in some places an enclosed lagoonal gutter (10 m and protected. No seagrass beds were found, only deep) and then a gentle outer slope that nonetheless

...342 ...... The Natural History of Santo Thelenota G :

Depth (m) 20 30 Peyssonneliaceae. Ball-like 10 0 F : 00 D sandy bottom G community. coral Branching E : S W Luganville). reef slope on sandy bottom. sandy on distorta Halimeda F C D : A with large stand of Halimeda Distance from shore (m) Branched coralline algae. coralline Branched C : reef flat E 0 1 Callophycus serratus . Callophycus B : 0 RD Nouméa). B 20 30 10 Depth (m) Santo Is. S chematic diagram 413: of the topography and reef communities of a sheltered fringing reef (Brigstocke point, beds on the gentle sandy slope. sandy gentle the on beds Halimeda A : Figure anax . (Photos J.-L. Menou & J.-M. Boré I

343 ... Marine Ecosystems ......

Depth (m) 0 20 30 10 Branching K : 50 Malo Is. 18 Massive corals reef flat J : B I E : R eef slope community composed of branching and E Steronephtya . H D : Candle-like coralline algae on the reef edge. I : water passage G A ore and Malo Island). D Branching corals on the reef flat. C : Malo Passage Distance from shore (m) RD Nouméa). fringing reef A J H : G orgonian community on the bottom of the reef slope. C B : S purs at the top of the reef slope. islet . Aglaophenia G : Enhalus acoroides . lagoon F depression/moat F : S eagrass 0 K 0 20 30 10 S chematic diagram 414: of the topography and reef communities of the Malo passage (between Depth (m) Flourishing community on the hard channel bottom. Aore Is. massive corals. A : Figure Acropora and seagrass community in the moat. (Photos J.-L. Menou & J.-M. Boré I

...344 ...... The Natural History of Santo

Depth (m) 20 30 10 40 50 0 0 30 E : S oft coral on sandy bottom. . (Photos marginata . Dichotomaria K : H Melophlus . deep reef slope with rubble J : S ponge B Rhipilia crassa on rubble. K D : G Phyllospongia lamelosa . Phyllospongia J I : reef slope with rubble and coral patches Strombus luhuanus on shallow sandy bottom. I F D C : Distance from shore (m) on deep rubble. deep on hawaiiensis Gibsmithia H : B : S andy slope. Metalia sternalis . Metalia G : Halophila . ovalis sandy shallow reef flat E A C 0 0 Halimeda cylindracea and 20 30 10 40 50 RD Nouméa). Depth (m) Aore Is. S chematic diagram 415: of the topography and reef communities of a sheltered sandy slope (Malo Passage). ypical mixed beds of A : T Figure olothurian on rubble on the upper part of the slope. the of part upper the on rubble F : Hon olothurian J.-L. Menou & J.-M. Boré I

345 ... Marine Ecosystems ...... Depth (m) 0 10 20 30 50 40 60 A cropora 450 expeditionis . M Branching J : Tydemania E : RD Nouméa). reef slope universis . L C Halodule Fungids growing among rubble. B I : G anax . (Photos J.-L. Menou & J.-M. Boré I patch reef serrulata (large) mixed with K Thelenota Palikolo Bay Palikolo M : Cymodocea D : F A macroloba growing among corals on sandy bottom. reef flat Massive coral on the slope. L : I Halimeda Distance from shore (m) H : J Halimeda bed with E

branching Acropora variegata . C : D eep sandy bottom with massive coral patches. Lobophora Distichopora . B : G : R ubble covered by H Massive corals housing luxuriant octocorallian fauna. K : aggregata . mangrove seagrass bed 0 Rumphella 0 60 D 10 20 30 50 40 S chematic diagram 416: of the topography and reef communities of a sheltered embayment (Palikolo Bay). Depth (m) F : S oft coral community on shallow reef flat. Figure A : Invertebrate assemblage on dead corals. Santo Is.

...346 ...... The Natural History of Santo

Depth (m) Padina 0 20 30 10 RD Nouméa). 1 850 Halimeda and : G . Acropora Branching : F D H K . Polyphylla : E algal bed on sandy and rubble bottom Udotea argentea . (Photos J.-L. Menou & J.-M. Boré I A ore). : S andy lagoon floor. : G reen algae D K G . Padina C Titanophora and Distance from shore (m) B : R ed algae Acanthaster Acanthaster plancii feeding on coral. C : J shallow reef Bohadchia graeffei . F J Fungids growing among rubble. : H olothurian : B I E Phakellia cavernosa . I fringing reef : S ponge H 0 A 0 20 30 10 Depth (m) Aore Is. S chematic diagram 417: of the topography and reef communities of an open and partially sheltered embayment (east : S ponges growing among rubble on the upper slope. Figure A on gentle sandy slope.

347 ... Marine Ecosystems ......

Depth (m) Mixed G : 0 10 20 30 40 50 41 0 . Acropora Large branching Large F : H D sandy bottom oft corals. oft E : S on the floor. floor. the on edulis RD Nouméa). C Holothuria D : G reef slope utuba Island W). . Acropora (Photos J.-L. Menou & J.-M. Boré I , abundant on hard corals. hard on abundant Liosina , abular Distance from shore (m) I : T ponge C : S F I reef flat B

internal channel minima on deep reef slope. ttractive coral community. community. coral ttractive B : A Halimeda H : community. community. Halimeda seagrass bed E 0 0 A and Acropora 10 20 30 40 50 S chematic diagram 418: of the topography and reef communities of a sheltered fringing reef ( T

Depth (m) Mixed A : Figure assemblage of soft and hard corals.

...348 ...... The Natural History of Santo

Depth (m) 0 20 10 30 50 40 Heliopora on Coralline algae. N : 450 G : RD Nouméa). F L laciniosa . Predaea Q E F : r ed algae P K M : O ctocorallian community on the reef edge. fergusoni . deep bottom with massive corals utuba Is. N & E). Caulerpa E : obukhoana on coarse sand. (Photos J.-L. Menou & J.-M. Boré I D L : A bundant large sponges. J O Cladophora Culcita . novaeguinea D : Melophlus . Q : G reen alga reef slope C K : S ponge Distance from shore (m) N I Crinoid assemblage. J : reef front Massive corals on slope in deep water. P : B spurs H ypical reef edge community composed of massive and tabular corals. C : t I : O ctocorallian community on spur edges. reef flat M 0 op of reef. 0 10 20 30 50 40 B : t Luxuriant coral community on mid slope. S chematic diagram 419: of the topography and reef communities of a windward fringing reef and exposed outer reef slope ( T Depth (m) O : Halimeda on rubble. A G A : s purs. Figure slope. H .

349 ... Marine Ecosystems ......

Depth (m) 0 10 20 30 40 50 60 1 200 reef slope D RD Nouméa). reef edge F . noveaguinea (Photos J.-L. Menou & J.-M. Boré I Culcita F : C platform E : R ubble. Distance from shore (m) E D : G orgonian. A B . Acropora Large tabular C : fringing reef 0 0 Acanthaster Acanthaster plancii . 60 10 20 30 40 50 B : Depth (m) S420: chematic diagram of the topography and reef communities of an outer reef platform (Malo Is. W coast). A : R eef platform. Figure

...350 ...... The Natural History of Santo Depth (m) 0 10 20 30 40 50 Choriaster : K Massive coral 950 E : K orgonian on the bottom the on G orgonian Q : cropora on slope. O A fuscogilva . ) Branching P R G detritic accumulation deep reef slope with J : Microthele

C Massive tabular and branching corals. D : Holothuria ( reef slope P : . cropora on sandy slope. weldii A J F N

fringing reef D Nouméa). R Predaea Branching O : I : . cropora on shallow sandy bottom. A B rubrolineata Branching C : islet Thelenota H : Distance (m) oft corals on massive coral head. coral massive on corals S oft N : Linckia guild. G : rocky reef flat Halophila ovalis on deep sandy bottom. (Photos J.-L. Menou & J.-M. Boré I Halimeda cylindracea on shallow sandy bottom. B : and Massive coral community on the terrace. the on community coral Massive A E I M M : . A cylindracea abular T cropora community on patch reef. F : hawaiiensis Halimeda reef slope terrace R : Gibsmithia deep reef slope L H Q L : . 0 on sandy bottom. S421: chematic diagram of the topography and reef communities of a patch reef and outer slope adjacent to a limestone island ( A bokisa Island). 0 D 10 20 30 50 40 A ttractive coral community on the reef flat. the outer slope. heads granulatus A : Figure Depth (m) of

351 ... Marine Ecosystems ...... Depth (m) 0 10 20 30 40 50 60 Coralgal Coralline F S : oliaceous N : 32 0 G : U

gentle wall . Turbinaria L T cf. cf. coral QR E

D Nouméa). F R oliacea : F reef slope K M : G orgonian and crinoids on the drop-off. eef slope and wall. and slope eef : R Cryptic E slope. outer the on algae coralline of community R : P anastomosans .

fringing reef

J heliopora .

P D eyssonnelia . Asteronemia Q : L : Diploastrea : D Celerina . K : op reef. the of C : T islet annuligera .

U : G orgonian on the drop-off (wall). (Photos J.-L. Menou & J.-M. Boré I Distance (m) Montastrea J : A marks. ripple with bottom sandy on cropora P : Acropora on the reef flat.

C I fringing reef community on the sandy terrace. sandy the on community cropora

rubble. on minima O

A Massive branching A T : cropora rubble on the reef crest. I : Halimeda . Branching O : B : speciosa reef slope F N H S P achysiris H : steep wall or drop off assemblage on the reef slope. 0 and octocorallian on the wall 2. wall the on octocorallian and 0 10 20 30 50 60 40 ypical AB G M depth. m 30 at slope outer corals on the wall. Figure S422: chematic diagram of the topography and reef communities of reef wall ( U relapa Island). A : T (coral-algal) Depth (m) algae

...352 ...... The Natural History of Santo goes down to 50 m in depth. The reef flat area is not seen elsewhere during the survey. This reef is very shallow and supports a diffuse seagrass bed com- totally subtidal with broad, irregular and meander- posed mainly of Cymodocea serrulata, intermingling ing spurs and grooves. The site has a high proportion with algae and small coral colonies. The front of the of rubble and corals that have been dead for several stretches of reef and edges of the lagoon are overgrown years. The coral communities were dominated by by a dense covering of erect soft corals such as Sinularia plate and branching forms. At the time of the survey and Sarcophyton, while the narrow silty lagoon con- coral recovery was observed with several living colo- tains isolated massive Porites. The steep internal slope nies of the same size (20-30 cm in diameter). The and the outer reef flat are covered by thick swathes of inshore reef and outer slopes were not studied. rubble without coral communities. This entire zone is exposed at low tide. The outer reef slope is similar Numerous Culcita novaeguineae were observed, to other sheltered slopes with large areas of broken along with one specimen of Acanthaster planci. Acropora branches and plates on white coral sand down to 8 m deep; further down there is an accumulation of ……Patch reef and outer slope adjacent coral branches and other carbonate debris with few to limestone island (Abokisa Island) coral colonies and occasional fleshy algae. (Fig. 421) The small limestone islet located between the In the area outside the lagoonal depression the larger Tutuba Island and Aore is surrounded by an sandy bottom supports a mosaic of patch reefs intermittent fringing reef developed on coral sand dominated by robust massive corals that are highly to about 6 m in depth with an attractive coral com- dissected with spectacular communities of green munity. Structurally they are dominated by stands and red algae. Several Holothuria edulis have been of Acropora in plate (A. danai) and branched forms, observed on the shallow sandy bottom. both living and dead. The dead skeletons provide the substrata for a complex and beautiful coral ……Windward fringing reef and community in shallow sandy water and include exposed outer reef slope (north coralline algae. The adjacent slope is dominated and east Tutuba Island) (Fig. 419) by massive Porites down to 15 m deep with numer- On the windward side, fringing reefs are deeply dis- ous Halimeda and encrusted rubble as well as sected with massive spurs and narrow grooves from rare echinoderms such as Holothuria (Microthele) 3 to 12 m deep that are littered with coarse sand and fuscogilva and Linckia guildingi. Further down the coral rubble. Heavy crusts and candle-like coralline slope drops off to 40 m deep in the north and more algae are well developed in this exposed area along than 60 m on the southwestern side with a steeper with numerous small species in the overhangs and declination. The coral community is replaced by reef interstices. Corals are sparse on the reef top rubble and a few small colonies (< 1 m high). In and mostly consist of massive Pocillopora, Acropora deep water, species diversity is low with some and Millepora. The outer slope is steep from 15 to red gelatinous algae (Predaea and Gibsmithia), the 30 m in depth, with scattered low spurs and large green algae Caulerpa and Cladophora ohkuboana patches of coarse sand with abundant Halimeda and the echinoderms Choriaster granulatus and segments. Beautiful sea fans and other octocoral- Thelenota rubrolineata. lian fauna are present on the top of the reef with numerous crinoids making this a very attractive ……Reef wall (Urelapa Island) (Fig. 422) area. From 30-60 m deep the slope is less steep and Fringing reefs on limestone islands adjacent to comprises rubble and scattered coral heads. The deep water such as Urelapa and Tuvana islets deeper part of this seaward slope is typical of many located off the southern part of Santo have verti- deep slopes, especially with respect to the associ- cal underwater cliffs. These reef walls are distinct ated red gelatinous algae (Predaea, Dudresnaya and features that represent one of the more spectacular Gibsmithia), green algae Caulerpa fergusonii and biotopes for species diversity. Stretches of fringing Cladophora ohkuboana and C. dotyana. reef are found adjacent to limestone and coral sand beaches, which change gradually to a reef slope The reef slopes facing the open sea are less steep dominated by a mixture of massive corals such as from 30 m down to at least 50 m deep. Coral cover Diploastrea, Goniastrea and Montastrea magnistel- is reduced; Halimeda minima coverage is high and lata and branching Acroporidae down to the cliff contributes to sand accumulation from their cal- precipice. The coral walls start beyond 20 to 25 m cified segments. Seriatopora cf histrix, and black deep down at least 60 m deep and are present coral Cirrhipathes anguineus have been observed at around the islets where the coast is neither shel- 45 m deep. tered nor exposed. Coralline algae in association with numerous fleshy red algae (large patches of ……Outer reef platform Halichrysis irregularis and Asteromenia anastomo- (west coast of Malo Island) (Fig. 420) sans) are dominant components with octocoral- Reef formation on the northwest coast of Malo lians. Corals are encrusting or foliaceous such as Island provides an example of a platform that was Pachyseris speciosa.

353 ... Marine Ecosystems ......

representative macrophytes communities ……Algal vegetation belonging to the Dumontiaceae are being studied to The species list of the benthic marine algae and sea- describe new taxa or establish them as belonging to grasses collected from Santo is shown in tables 37 existing species. The study of the coralline algae will & 38. The classification follows The catalogue of the probably reveal new taxa as well. benthic marine algae of the by Silva and coauthors (1996). The 271 listed species of algae con- The algal flora is typically tropical and most of the spe- sist of 163 Rhodophyta (red algae), 83 cies belong to the Indo-Pacific biogeographic province. (green algae) and 25 Pheaophyceae (brown algae). A Comparison with flora from adjacent archipelagos is selection of species is illustrated in figures 423-428. limited due to the difference in sampling effort in the About 150 specimens of coralline algae are under various regions. However, 55 % and 53 % of the species study and are not included in this work; only the of Santo are present in Solomons and Fiji respectively. most common encrusting coralline algae are consid- ered here. The species belong to 12 orders and 45 The Rhodymeniaceae Asteronemia pseudocoalescens families (Figs 429 & 430). Most of the specimens described from Lord Howe Island was observed for have been identified to species level and these repre- the first time outside of its type locality, suggest- sent 90 % of the collection; the 10 % remaining uni- ing that its geographic distribution is broader than dentified species comprise taxa that could be new to originally thought; this discovery enhances the science. Among the identified species, three of them known biogeographic affinities of the Santo marine are newly described from Solomon Islands, Fiji and flora with the tropical west Pacific. New Caledonia; while at least five taxa including four species of , Rhizophyllis, Rhodymenia, Algal assemblages are characterized within the Hypoglossum and Dudresnaya and one new genus biotopes as shown in the following sections.

Table 37: List of Rhodophyta, Chlorophyta and Phaeophyceae species from Santo waters. Class Rhodophyta Wrangelia argus Montagne Order Bonnemaisoniales Wrangelia elegantissima R.E. Norris Family Bonnemaisoniaceae Asparagopsis taxiformis (Delile) Trevisan Dasya anastomosans Family Dasyaceae Weber-van Bosse Order Dasya baillouviana Aglaothamnion boergesenii (S.G. Gmelin) Montagne Family Ceramiaceae (Aponte & D.L. Ballantine) L’Hardy-Halos & Rueness Dasyphila plumarioides Yendo Anotrichum tenue (C. Agardh) Nägeli Heterosiphonia crispella (C. Agardh) M.J. Wynne Antithamnionella elegans (Berthold) J.H. Price & D.M. John Thuretia sp. nov.

Balliella repens Huisman & Kraft Frikkiella searlesii Family M.J. Wynne & C.W. Schneider Centroceras clavulatum (C. Agardh) Montagne Haraldia lenormandii (Derbès & Solier) Feldmann Centroceras minutum Yamada Hypoglossum simulans Ceramium flaccidum M.J. Wynne, Price & Ballantine (H.E. Petersen) Furnari & Seiro Martensia cf. australis Harvey Ceramium marshallense Dawson Martensia elegans Hering Ceramium upolense South & Skelton Martensia flabelliforme Corallophila apiculata Harvey ex J. Agardh (Yamada) R. Norris Martensia fragilis Harvey Griffithsia heteromorpha Kützing Martensia sp. nov. Haloplegma duperreyi Montagne Myriogramme melanesiensis Monosporus indicus Børgesen N'Yeurt, Wynne & Payri Spyridia hypnoides Nitophyllum adhaerens M.J. Wynne (Bory de Saint-Vincent) Papenfuss Vanvoorstia spectabilis Harvey Tiffaniella saccorhiza (Setchell & Gardner) Doty & Menez Family Rhodomelaceae Acanthophora pacifica (Setchell) Kraft

...354 ...... The Natural History of Santo

Acanthophora spicifera Amphiroa sp. nov. (Vahl) Børgesen Amphiroa tribulus Amansia rhodantha (Harvey) J. Agardh (Ellis & Solander) Lamouroux

Bostrychia tenella Amphiroa valonioides Yendo (J.V. Lamouroux) J. Agardh Cheilosporum acutilobum Chondria armata (Kützing) Okamura (Decaisne) Piccone

Chondria dangeardii Dawson Cheilosporum spectabile Harvey ex Grunow Chondria minutula Weber-van Bosse Hydrolithon onkodes Chondria ryukyuensis Yamada (Heydrich) D. Penrose & Woelkerling

Chondria simpliciuscula Hydrolithon orthoblastum Weber-van Bosse Hydrolithon reinboldii Chondria bullata N'Yeurt & Payri (Weber-van Bosse & Foslie) Foslie

Chondria sp. Jania adhaerens Lamouroux

Chondrophycus parvipapillatus Jania rubens (Linnaeus) Lamouroux (C.K. Tseng) Garbary & Harper Lithophyllum pygmaeum Chondrophycus succisus (Heydrich) Heydrich (A.B. Cribb) K.W. Nam Lithothamnion proliferum Foslie Exophyllum wentii Weber-van Bosse Neogoniolithon fosliei Herposiphonia nuda Hollenberg (Heydrich) Setchell & mason

Herposiphonia tenella Order Gelidiales (C. Agardh) Ambronn Gelidiella acerosa Family Gelidiaceae Laurencia brachyclados Pilger (Forsskål) Feldmann & G. Hamel

Laurencia cf. distichophylla J. Agardh Gelidium cf. crinale (Turner) Gaillon

Laurencia decumbens Kützing Gelidium isabelae W.R. Taylor

Laurencia sp. 1 Pterocladiella sp.

Laurencia sp. 2 Order Gigartinales

Neosiphonia apiculata Caulacanthus ustulatus Family Caulacanthaceae (Hollenberg) Masuda & Kogame (Turner) Kützing

Polysiphonia scopulorum Harvey Family Corynocystaceaea Corynocystis prostrata G.T. Kraft

Polysiphonia sertularioides Pinnatiphycus menouana Family Dicranemataceae (Grateloup) J. Agardh N'Yeurt, Payri & Gabrielson

Polysiphonia sp Dudresnaya capricornica Family Dumontiaceae Polysiphonia triton P.C. Silva Robins & Kraft

Spirocladia barodensis Børgesen Dudresnaya hawaiiensis R.K.S. Lee

Tolypiocladia glomerulata Dudresnaya sp. nov. (C. Agardh) F. Schmitz Dumontiaceae gen. nov.

Order Corallinales Gibsmithia dotyi Hoyle

Family Corallinaceae Amphiroa anceps (Lamarck) Decaisne Gibsmithia hawaiiensis Doty

Amphiroa crassa Gibsmithia larkumii Kraft Lamouroux in Quoy & Gaimard Family Hypneaceae Hypnea cervicornis J. Agardh Amphiroa foliacea Lamouroux in Quoy & Gaimard Hypnea nidulans Setchell

Amphiroa fragilissima Hypnea pannosa J. Agardh (Linnaeus) Lamouroux Hypnea saidana Holmes

355 ... Marine Ecosystems ......

Hypnea spinella (C. Agardh) Kützing Dichotomaria australis (Sonder) Huisman, J.T. Harper & G.W. Saunders Hypnea valentiae (Turner) Montagne Dichotomaria marginata Family Nemastomataceae Predaea laciniosa Kraft (Ellis & Solander) Lamarck Predaea weldii Kraft & I.A. Abbott Dichotomaria obtusata (Ellis & Solander) Lamarck Peyssonnelia cf. boergesenii Family Peyssonneliaceae Weber-van Bosse Galaxaura divaricata (Linnaeus) Huisman & Townsend Peyssonnelia inamoena Pilger Galaxaura filamentosa R. Chou Peyssonnelia sp. 1 Galaxaura obtusata Peyssonnelia sp. 2 (Ellis & Solander) Lamouroux

Portieria hornemannii Galaxaura rugosa Family Rhizophyllidacea (Lyngbye) P.C. Silva (Ellis & Solander) Lamouroux

Rhizophyllis sp. nov. Tricleocarpa fragilis (Linnaeus) Huisman & Townsend Family Schizymeniaceae Titanophora weberae Børgesen Order Nemaliales Family Solieriaceae Callophycus densus (Sonder) G.T. Kraft Family Liagoraceae Liagora sp. Callophycus serratus Yamadaella caenomyce (Harvey ex Kützing) P.C. Silva (Decaisne) I.A. Abbott Eucheuma horizontale Order Nemaliales Weber-van Bosse Family Scinaiaceae Scinaia furcata Zablackis Eucheuma sp. Order Plocamiales Meristotheca procumbens Family Plocamiaceae Plocamium sandvicense J. Agardh P. Gabrielson & Kraft Plocamium sp. Wurdemannia miniata Order Rhodymeniales (Sprengel) Feldmann & G. Hamel Family Champiaceae Champia compressa Harvey Order Gracilariales Champia parvula (C. Agardh) Harvey Family Gracilariaceae Gracilaria dotyi Hoyle Champia vieillardii Kützing Gracilaria sp. Order Rhodymeniales Order Halymeniales Family Faucheaceae Gloiocladia iyoensis (Okamura) R. Norris Cryptonemia cf. lomation Family Halymeniaceae Order Rhodymeniales (Bertoloni) Agardh Family Lomentariaceae Lomentaria corallicola Børgesen Cryptonemia cf. umbraticola Dawson Order Rhodymeniales Cryptonemia crenulata (J. Agardh) J. Agardh Asteromenia anastomosans Family Rhodymeniaceae (Weber-van Bosse) G.W. Saunders, Cryptonemia umbraticola Dawson C.E. Lane, C.W. Schneider & Kraft Grateloupia ovata Asteromenia pseudocoalescens Womersley & J.A. Lewis G.W. Saunders, C.E. Lane, Halymenia maculata J. Agardh C.W. Schneider & Kraft Halymenia porphyraeformis Parkinson Botryocladia kuckuckii (Weber-van Bosse) Yamada & Tanaka Halymenia stipitata I.A. Abbott Botryocladia skottsbergii Prionitis angusta (Okamura) Okamura (Børgesen) Levring Order Halymeniales Botryocladia spinulifera Family Sebdeniaceae Sebdenia cerebriformis N'Yeurt & Payri W.R. Taylor & I.A. Abbott

Sebdenia flabellata Zablackis Chamaebotrys boergesenii (Weber-van Bosse) Huisman Order Nemaliales Chrysymenia procumbens Family Galaxauraceae Actinotrichia fragilis (Forsskål) Børgesen Weber-van Bosse

...356 ...... The Natural History of Santo

Coelothrix irregularis Caulerpella ambigua (Okamura) (Harvey) Børgesen Prud'homme van Reine & Lokhorst

Gelidiopsis intricata (C. Agardh) Vickers Order

Gelidiopsis repens Family arabicum Kützing (Kützing) Weber-van Bosse Codium geppiorum O.C. Schmidt

Gelidiopsis scoparia Codium mamillosum Harvey (Montagne & Millardet) De Toni Codium ovale Zanardini

Halichrysis irregularis Order Bryopsidales (Kützing) A.J.K. Millar Family Halimedaceae Halimeda borneensis W.R. Taylor Leptofauchea sp. Halimeda cuneata K. Hering Rhodymenia intricata Halimeda cylindracea Decaisne (Okamura) Okamura Halimeda discoidea Decaisne Rhodymenia pacifica Kylin Halimeda distorta Rhodymenia sp. 1 (Yamada) Hillis-Colinvaux Rhodymenia sp. 2 Halimeda gigas W.R. Taylor Class Chlorophyta Halimeda heteromorpha N'Yeurt

Order Bryopsidales Halimeda lacunalis (W.R. Taylor) Hillis

Bryopsis pennata J.V. Lamouroux Halimeda macroloba Decaisne Family Bryopsidaceae var. secunda (Harvey) Collins & Hervey Halimeda macrophysa Askenasy

Order Bryopsidales Halimeda micronesica Yamada

Family Caulerpa biserrulata Sonder Halimeda minima (W.R. Taylor) Colinvaux Caulerpa brachypus Harvey Halimeda opuntia Caulerpa cupressoides (Linnaeus) Lamouroux (Vahl) C. Agardh Halimeda taenicola W.R. Taylor Caulerpa fastigiata Montagne Order Bryopsidales Caulerpa fergusonii Murray Pseudocodium floridanum Family Pseudocodiaceae Dawes & Mathieson Caulerpa manorensis Nizamuddin Order Bryopsidales Caulerpa microphysa Avrainvillea erecta (Weber-van Bosse) Feldmann Family Udoteaceae (Berkeley) A. Gepp & E. Gepp Caulerpa nummularia Avrainvillea lacerata Harvey ex J. Agardh Harvey ex J. Agardh Caulerpa racemosa (Forsskål) J. Agardh Boodleopsis pusilla var. clavifera Turner (Weber-van Bosse) (Collins) W. Taylor, Joly & Bernatowicz Caulerpa racemosa (Forsskål) J. Agardh Chlorodesmis fastigiata var. lamourouxii (Turner) Weber-van Bosse (C. Agardh) Ducker Caulerpa racemosa (Forsskål) J. Agardh Chlorodesmis hildebrandtii var. peltata (Lamouroux) Eubank A. Gepp & E. Gepp

Caulerpa sedoides C. Agardh Rhipidosiphon javensis Montagne

Caulerpa serrulata (Forsskål) J. Agardh Rhipilia crassa A.J.K. Millar & G.T. Kraft Rhipilia penicilloides N'Yeurt & Keats Caulerpa sertularioides (S. Gmelin) M. Howe Rhipilia sinuosa Gilbert Rhipilia sp. nov. Caulerpa taxifolia (Vahl) C. Agardh Rhipiliopsis carolyniae Kraft Caulerpa verticillata J. Agardh Rhipiliopsis echinocaulos Caulerpa webbiana Montagne (A.B. Cribb) Farghaly

357 ... Marine Ecosystems ......

Rhipiliopsis howensis Kraft Valonia macrophysa Kützing Siphonogramen sp. Valonia ventricosa J. Agardh Tydemania expeditionis Valoniopsis pachynema Weber-van Bosse (G. Martens) Børgesen Udotea argentea Zanardini Order Ulvales Order Family Ulvaceae Ulva intestinalis (Linnaeus) Nees Family Anadyomenaceaea Anadyomene wrightii Harvey ex J. Gray Ulva lactuca Linnaeus Microdictyon umbilicatum (Velley) Zanardini Class Phaeophyceae Order Siphonocladales Order Dictyotales anastomosans Dictyopteris repens Family Boodleaceae Family Dictyotaceae (Harvey) Kraft & M.J. Wynne (Okamura) Børgesen Order Cladophorales Dictyopteris sp. Chaetomorpha antennina Dictyota bartayresiana Lamouroux Family Cladophoraceae (Bory de Saint-Vincent) Kützing Dictyota ceylanica Kützing Cladophora dotyana Gilbert Dictyota cf. canaliculata Cladophora glomerata (L.) Kutzing O. De Clerck & E. Coppejans Cladophora liebetruthii Grunow Dictyota cf. friabilis Setchell

Cladophora ohkuboana Holmes Dictyota cf. pfaffii Schnetter

Cladophora prehendens Kraft & Millar Dictyota divaricata Lamouroux

Cladophora sp. Dictyota friabilis Setchell Order Siphonocladales Dictyota grossedentata De Clerck & Coppejans forbesii Family Siphonocladaceae (Harvey) J. Feldmann Dictyota hamifera Setchell Order Dictyota sp.

Family Dasycladaceae nitida Sonder Distromium sp. Bornetella sphaerica Lobophora papenfussii (Zanardini) Solms-Laubach (W.R. Taylor) Farghaly

Neomeris vanbosseae Howe Lobophora variegata (Lamouroux) Order Siphonocladales Womersley ex Oliveira

Family Boodleaceae composita (Harvey) F. Brand Padina boryana Thyvi herpestica Padina melemele (Montagne) M.A. Howe Abbott & Magruder in Abbott Cladophoropsis vaucheriaeformis Padina sp. (J.E Areschoug) Papenfuss Padina sp. nov. elegans Børgesen Stypopodium flabelliforme Order Siphonocladales Weber-van Bosse cavernosa Order Ectocarpales Family Siphonocladaceae (Forsskål) Børgesen Family Acinetosporaceae Hincksia indica (Sonder) J. Tanaka Dictyosphaeria intermedia Order Fucales Weber-van Bosse Sargassum aquifolium Dictyosphaeria versluysii Family Sargassaceae Weber-van Bosse (Turner) C. Agardh sp. Spatoglossum asperum J. Agardh

Order Siphonocladales Turbinaria ornata (Turner) J. Agardh

Family Valoniaceae Valonia aegagropila C. Agardh Order Sphacelariales

Valonia fastigiata Harvey ex J. Agardh Family Sphacelariaceae Sphacelaria tribuloides Meneghini

...358 ...... The Natural History of Santo

A B

C D

E F

G H

Figure 423: Rhodophyta. A: Amansia rhodantha. B: Amphiroa crassa. C: Amphiroa foliacea. D: Asteronemia anastomosans. E: Botryocladia spinuligera. F: Callophycus serratus. G: Cheilosporum spectabile. H: Corallinales complex. (Photos J.-L. Menou IRD Nouméa).

359 ... Marine Ecosystems ......

I J

K L

M N

O P

Figure 424: Rhodophyta. I: Dasyphila plumarioides. J: Dichotomaria marginata. K: Dichotomaria obtusata. L: Galaxaura divaricata. M: Gibsmithia hawaiiensis. N: Halymenia porphyraeformis. O: Halymenia stipitata. P: Lithothamnion proliferum. (Photos J.-L. Menou IRD Nouméa).

...360 ...... The Natural History of Santo

Q R

S T

U V

W X

Figure 425: Rhodophyta. Q: Martensia flabellata. R: Martensia sp. nov. S: Neogoniolithon fosliei. T: Peyssonnelia inamoena. U: Plocamium sandvicense. V: Portieria hornemanii. W: Predaea laciniosa. X: Titanophora weberae. (Photos J.-L. Menou IRD Nouméa).

361 ... Marine Ecosystems ......

A B

C D

E F

G H

Figure 426: Chlorophyta. A: Caulerpa bisserulata. B: Caulerpa fergusoni. C: Codium mamillosum. D: Halimeda cuneata. E: Halimeda discoidea. F: Halimeda lacunalis. G: Halimeda macroloba. H: Halimeda minima. (Photos J.-L. Menou IRD Nouméa).

...362 ...... The Natural History of Santo

I J

K L

M N

O P

Figure 427: Chlorophyta. I: Halimeda taenicola. J: Avrainvillea erecta. K: Rhipilia sp. L: Tydemania expeditionis. M: Cladophora ohkuboana. N: Bornetella nitida. O: Cladophorospsis herpestica. P: Valonia ventricosa. (Photos J.-L. Menou IRD Nouméa).

363 ... Marine Ecosystems ......

A B

C D

E F

G H

Figure 428: Phaeophyceae. A: Dictyota barteyresiana. B: Dictyota ceylanica. C: Dictyota friabilis. D: Distromium sp. E: Padina boryana. F: Padina melemele. G: Padina sp. H: Stypopodium. (Photos J.-L. Menou IRD Nouméa).

...364 ...... The Natural History of Santo

Rhodomelaceae Rhodymeniaceae Corallinaceae Ceramiaceae Delesseriaceae Galaxauraceae Halymeniaceae Dumontiaceae Solieriaceae Hypneaceae Dasyaceae Peyssonneliaceae Gelidiaceae Champiaceae Liagoraceae Sebdeniaceae Gracilariaceae Rhizophyllidacea Nemastomataceae Lomentariaceae Faucheaceae Plocamiaceae Scinaiaceae Schizymeniaceae Dicranemataceae

Families Corynocystaceaea Caulacanthaceae Bonnemaisoniaceae

Dictyotaceae Sargassaceae Acinetosporaceae

Caulerpaceae Udoteaceae Halimedaceae Cladophoraceae Valoniaceae Siphonocladaceae Boodleaceae Dasycladaceae Dasycladales Codiaceae Ulvaceae Anadyomenaceaea Pseudocodiaceae 0510 15 20 25 30 number Figure 429: Species richness of the families of Rhodophyta (red), Phaeophyceae (brown) and Chlorophyta (green).

……Algal assemblages the very bright green pompom-like morphology of Chlorodesmis hildenbrandtii and Rhipilia penicilloides. ••• Algal vegetation on outer reefs and slopes Further down the reef slope, from 8-20 m deep, the down to 20 m motion of the water is reduced and the reefs sup- The algal community on the outer reef and slope port a higher coral cover and articulated calcareous down to 20 m in depth comprises a large number of algae such as Amphiroa crassa, A. tribulus and A. encrusting coralline algae mixed with several dozen foliacea, and the green Halimeda cuneata, H. gigas, H. species growing among corals. Near the top of the minima and H. taenicola dominate some reef slopes. reef, many species — mainly red algae — grow within Fleshy algae are less abundant and mostly comprise the interstices of corals, and include Chondrophycus Gibsmitha hawaiiensis, Amansia rhodanta and Valonia parvipapillatus, Avrainvillea lacerata, Martensia flabelliformis, Halymenia porphyraeformis, Meristotheca procum- bens, Champia vieillardii, Caulerpa nummularia, C. biserrulata and Halimeda micronesica. In the break- water area coralline algae Hydrolithon onkodes and Neogoniolithon fosliei develop thick candle-like crusts, with Hydrolithon orthoblatum or branched clumps of Lithophyllum pygmaeum. The vegetation can vary according to the topography and the presence of gutters and grooves is often associ- ated with large clumps of Callophycus serratus, Cheilosporum spectabile, Bryopsidales Dictyotales Ceramiales Asparagopsis taxiformis, Dasyphila plumarioides, Tricleocarpa fragilis, Cladophorales Ectocarpales Corallinales Caulerpa spp. and Halimeda spp. and Siphonocladales Fucales Gelidiales small species such as Chondria armata, Botryocladia spp., Chamaebotrys Ulvales Bonnemaisoniales Gigartinales boergesenii and Portieria hornemanii. Figure 430: Repartition of the algal community in Orders The pinkish colours of coralline algae contrast with Rhodophyta (red), Phaephyceae (brown), Chlorophyta (green).

365 ... Marine Ecosystems ...... fastigiata. Rubble is often found at the bottom of the This sheltered and silty environment supports slope rupture, at ~ 15 m deep and Caulerpa serru- luxuriant vegetation including: Udotea argentea, lata, C. sedoides, Microdictyon umbilicatum, Avrainvillea erecta, Halimeda borneensis, H. distorta, van-bossea, Halimeda distorta, Valonia aegagropila, Caulerpa verticilata, C. cupressoides, C. racemosa, C. Myriogramme melanesiensis, Stypopodium flabelli- sedoides, C. serrulata, C. taxifolia as well as some forme and Padina spp. grow among the coral debris. red algae such as Martensia, Titanophora webera Various thin and small fronds of dark green Rhipilia and the brown alga Stypopodium flabelliforme with spp. and Rhipiliopsis spp., Anadyomene wrightii its fan-like shape and iridescent blue on the thallus form small associations in the shady areas with surface. Corynocystis protrata and Cryptonemia crenulata. ••• Algal vegetation on shallow reef flats ••• Algal vegetation on deep outer slopes The shallow fringing reef flat along the shoreline to In the outer slope from 40 m to at least 60 m deep, the north of Luganville supports many algae from the coral debris and coarse sand dominate the substra- beach to the reef front. The flats are exposed at low tum. At the first glance fleshy algae are relatively tide and corals are therefore reduced in abundance, few in species number and the vegetation is not except at the outer part of the reef flat where large luxuriant. Most of the gelatinous red algae such as stands of staghorn Acropora grow in the gutters per- Dudresnaya capricornica, Predaea weldii, P. laciniosa, pendicular to the reef front. Adjacent to the beach, the Gibsmithia hawaiiensis, G. larkumii, and the green reef is covered with a green underwater "turf" mainly algae Caulerpa fergusonii, C. sedoides, C. micro- composed of Cladophora glomerata, Boodlea composita physa, Codium mamillosum, Rhipilia sp. nov. grow and Boergesenia forbesii that is partially buried in the in this environment on and among the coral debris, sand. Several Caulerpa, C. fastigiata, C. racemosa, C. while the delicate green Cladophora ohkuboana, C. serrulata along with light green Chlorodesmis fastig- dotyana are found on sand. Brown algae are very iata, Halimeda opuntia and the red pompom-like algae few and Dictyota bartayresiana and Padina groupe Galaxaura filamentosa and G. rugosa grow on the inner melemele can be observed in this deep habitat. part of the reef. Among the coral branches there are numerous green algae Dictyosphaeria cavernosa and ••• Algal vegetation on coral walls H. micronesica. The edible red seaweed Meristotheca Coral walls usually start deeper than 30 m on the procumbens was abundant within the coral branches edge of limestone islands located in deep open water. and in the interstices on the reef margin. The vegeta- This environment is often dark due to a heavily vari- tion on the front part is dominated by nongeniculated egated surface with numerous interstices, overhangs coralline algae including crusts of Hydrolithon onkodes and small caves. Coral walls are of great beauty with and the candle-like thallus of H. orthoblastum. Various spectacular encrustations by coralline algae and articulated coralline algae such as Amphiroa spp. form Peyssonnelia spp. giving an attractive mosaic of forms clumps on the reef top. Surprisingly, no stands of and colours. The dominant Lithothamnion prolifer is Sargassum were observed except occasional young easily recognisable by its pink crust and numer- stages of Sargassum aquifolium. ous short knobs. Numerous Rhodymeniales includ- ing several species of Leptofauchea and Rhodymenia ••• Algal vegetation in shallow live in the caves and interstices with Cryptonemia sandy coral communities crenulata, C. umbraticola, Corynocystis prostrata and The algal vegetation associated with the coral com- Callophycus serratus, while the iridescent Halichrysis munity in shallow sandy environments is mainly rep- irregularis and the star-like Asteromenia anastomo- resented by patches of the fan-like brown alga Padina sans grow luxuriantly on the walls with the large boryana mixed with another brown alga Turbinaria foliose Peyssonnelia inamoena and P. capensis. The ornata and various species of green algae such as golden-yellow Padina melemele and the green ball- Caulerpa cupressoides, C. racemosa, C. racemosa var like Codium mamillosum are present in discrete lamourouxii, C. fergusonii, Boodlea composita and clumps among coral debris with very occasional Udotea argentea and the red algae Galaxaura rugosa, Sebdenia flabellata and S. cerebriformis. Hypnea spp. and Tolypiocladia glomerata. Microdictyon umbilicatum, Halimeda discoidea and Myriogramme All these species can be found in other deep areas melanesiensis grow among the branches of staghorn but in less abundance. The shady environment and Acropora. Moreover, the delicate red algae Martensia open ocean influences enhance this algal community fragilis, Neomartensia flabelliforme, Haloplegma dup- that is generally sheltered in the reef interstices. pereyi, along with Laurencia spp., Exophyllym wentii and several Rhodymeniales form small associations of a rich algal flora in the interstices of submassive ••• Algal vegetation on the sandy bottom corals Porites rus and Montipora. of deep lagoons Various green algae grow together and develop ••• Algal vegetation in channel environments meadows between coral colonies located on the coral In general, the algal vegetation of the channels is not sandy bottom at 25-30 m deep in the embayments. very rich due to the silty and muddy environment that

...366 ...... The Natural History of Santo limits algal diversity. There is no typical association of in marine and estuarine biotopes that are gener- algae from this environment except the brown alga ally sheltered from wave action and offer a suitable Spatoglossum asperum which has only been recorded substratum for rooting in mud, sand or coarse rub- in the Segond Channel and Malo passage. The algal ble. In many places they can also develop into large flora has characteristics that are typical of sheltered meadows or beds in deeper lagoon zones down to areas; Halimeda spp. and Caulerpa spp. can locally 40 m deep, on barrier reefs or surrounding lagoon cover the substratum and most of the investigated islands. They are remarkable habitats in tropical sites showed coral damage. The algal vegetation asso- shallow waters and they often form a key func- ciated with dead coral communities is described in tioning system on sandy bottoms along shorelines the next section. between mangroves and coral reefs.

••• Algal vegetation on dead coral communities Most coastal areas around Santo do not have these Santo coral reefs have experienced heavy damage typical seagrass habitats and only the fringing from successive cyclones, bleaching events and sandy flats adjacent to estuarine and river catch- crown-of-thorns starfish Acanthaster( ) outbreaks in ments, sheltered embayments and inner reef sandy the past decades. Thus on the outer reefs and slopes flats provide the necessary conditions for seagrass along the channel, the dead corals are colonized by development. However, deep sandy slopes, sandy small prostate algae such as the brown Dictyota fria- channel slopes and bottoms also support the pad- bilis, Lobophora variegata and large green calcareous dle-like Halophila seagrasses. Halimeda distorta and H. minima. In more exposed locations, dead and collapsing branches are over- Eight species of seagrass were reported from our grown by coralline algae, turfs of filamentous red survey (Table 38), four of these are new records algae and cyanobacteria assemblages. Depending for Santo: Cymodocea serrulata, Enhalus acoroides, on the local environmental and reef condition, this Halophila capricorni and H. decipiens, and the pioneer stage of colonization will evolve into a sec- two species of Halophila had not been previously ondary succession of algal-dominated communities recorded for the Vanuatu archipelago. or revert to coral recolonization. Seagrass diversity and abundance were relatively ••• Remarks on the absence of Sargassum beds low in the investigated areas. Plants never form large Sargassum species are common features of the algal meadows; they mostly developed in scattered patches vegetation of tropical islands in the Pacific. However, except in Palikolo bay where they form dense mats around Santo this genus is restricted to limited germ- (> 75 % coverage) in 70 m wide zones that repre- lings and the reduced thalli of Sargassum aquifolium on sent the most extensive bed surveyed. The seagrass reef flats, while personal observations in at the communities generally comprised few species; most same period have shown the presence of large beds of of the sites had just one to three species growing Sargassum including several common tropical species together. The inner sandy areas such as Palikolo such as S. polycystum. The lack of suitable habitats such bay, the Aore shoreline in the Malo passage and the as sheltered shallow lagoons could explain the absence estuarine zone adjacent to Luganville showed the of the species in these biotopes around Santo. highest species diversity with four species growing together. However, most of the time one species ……Seagrass communities was dominant in the bed, i.e. Halodule uninervis Seagrasses are flowering plants belonging to the in Luganville, Cymodocea rotundata in Palikolo. In Cymodoceaceae and the Hydrocharitaceae families some localities seagrasses form mixed communities which are placed in the Alismatales order (nomen- with marine algae such as Halimeda macroloba, H. clature based on molecular analysis). In tropical cylindracea, H. borneensis, Caulerpa serrulata, Padina regions they are mostly permanently submerged boryana and Acanthophora spicifera.

Table 38: List of seagrass species from Santo waters. Class Order Family Genus Species Authority Anthophyta Alismatales Cymodoceacea Cymodocea rotundata (Hemprich & Ehrenberg) Aschers & Schweinf Cymodocea serrulata (R. Brown) Aschers & Magnus Halodule uninervis (Forsskål) Ascherson in Boissier Hydrocharitacea Enhalus acoroides (Linnaeus) Royle Halophila capricorni Larkum Halophila decipiens Ostenfed Halophila ovalis (R. Brown) J.D. Hooker Thalassia hemprichii (Ehrenberg) Ascherson

367 ... Marine Ecosystems ......

Except for the species of Halophila, all the other changes, which may have prevented the establish- taxa were confined to very shallow waters although ment of seagrasses or removed beds which would they are known to grow in deeper habitats both have limited the development or the absence elsewhere. of this key functioning habitat. This situation could turn critical with the predicted increase of threats It is clear that the coastal physiography of Santo as a result of human activities and climate change. does not provide ideal habitats for seagrass mead- Seagrass habitats must be considered as associated ows, but it is not clear why seagrasses are so ecosystems to coral reefs just like mangroves. All restricted in shallow waters and are not well devel- these habitats are important and integral compo- oped in other areas that appear to be suitable. Part nents of the natural environment of Santo and they of the explanation could be due to climatic condi- must be considered as priorities in conservation tions. The high occurrence of cyclones and rough efforts. This study provides information that could seas can provoke sediment movements and salinity aid coastal zone planning and development.

A B

C D

E

Figure 431: Seagrass species. A: Cymodocea serrulata. B: Halodule uninervis. C: Enhalus acoroides. D: Thalassia hemprechii. E: Halophila capricorni. (Photos J.-L. Menou IRD Nouméa).

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