POST-TSUNAMI CONDITION OF A CORAL REEF IN LAEM PAKARANG (ANDAMAN SEA, THAILAND) INTRODUCTION The Phang Nga Province on the Andaman Sea coast of Thailand lies approximately 460 km east of the point where the 26th December 2004 tsunami waves originated (Fig. 1a). The Laem Pakarang Cape was severly affected by the tsunami. The cape outline was dramatically modified by the waves (Fig. 1b, c), and massive coral boulders were displaced ashore (Fig. 2). The project “Impact of catastrophic events on benthic soft-bottom fauna of the infralittoral and intertidal zones: the case of the coastal area of Khao Lak, Andaman Sea, Thailand” is funded by the italian MURST and focuses on the effects of tsunami event on the soft bottom communities. RESULTS CONCLUSIONS According to our observations the benthic zonation of the seafloor off the Laem Pakarang Cape can be schematically summarized in five zones (Figs. 3 to 7). The first zone (Zone A, 2.5 to 5.5 m depth) corresponds to a shallow fore reef which had already died before 2004. Land and off-shore tin mining starting in the 70s generated increased sediment loading which strongly affected shallow water reefs (Phongsuwan et al., 2006). Most likely the reef in zone A died as the result of such increased siltation generated by the nearby tin mining activities. In this zone small coral colonies survive among muddy algal turf on dead coral blocks (Fig. 4). Zone B (5.5 to 8.5 m depth) is affected by the highest siltation encountered along the transects and in this soft, sandy mud area no living or dead coral were observed (Fig. 5). Hard biogenic substrates and living corals, along with macroalgae and other invertebrates (sponges, hydrozoans, bryozoans, etc.) characterize Zone C (8.5 to 10 m depth). Here we encountered the first recently uprooted coral colonies (Fig. 6) which become the characteristic feature of Zone D (10 to 12 m depth). The latter, corresponding to the submarine topographic relief off the Laem Pakarang Cape, corresponds to a previously unreported coral community. The highest coral diversity and the largest living and dead coral colonies were observed in Zone D (Table 2; Fig. 7). Finally Zone E (12 m depth) could be defined as an impoverished facies of Zone D both for coral diversity and hard substrate discontinuity (Fig. 8). We gathered several evidences of the consequences of severe mechanical disturbance due to the recent tsunami event similar to those found elsewhere along the north Andaman Sea of Thailand (Turak et al., 2005). Figure 1 a) Map of the Khao Lak coastal area, and inset showing its position on the Andaman sea coast of Thailand (arrow). Aerial pictures of the Laem Pakarang Cape before (b) and after (c) the 26th December 2004 tsunami. Transect Length Start End T1 350 m 8°43’,984 N 98°13’,040 E 8°43’,963 N 98°12’,848 E T2 325 m 8°44’,097 N 98°12’,960 E 8°44’,131 N 98°12’,788 E T3 200 m 8°43’,463 N 98°12’,695 E 8°43’,500 N 98°12’,581 E c) b) T3 Ý N Table 1 Code, length, starting and ending point for each transect shown in Fig. 3. Figure 8 In Zone E broken and displaced faviids colonies were found among small to medium sized blocks of dead coral covered in thick turf and mud at 12 m depth. Frondose algae were abundant (a) together with crustose coralline algae, often forming rhodoliths. This zone is similar to Zone D, but the living coral fauna was impoverished and the size of biogenic blocks is smaller, ranging from approximately 15 cm to 1 m in diameter. a) a view of the typical appearance of Zone E; b) a large piece of coral rubble covered in crustose coralline algae, bryozoans, sponges and small coral colonies (P = Psammocora profundacella); c) a broken, displaced and partially dead colony of Favites flexuosa among biogenic rubble densly covered in turf and mud. Table 2 List of the Scleractinia genera found dead (D) or living (L) in the different zones. BENZONI F. 1 , BASSO D. 2 , GIACCONE T. 3 , PESSANI D. 4 , CAPPELLETTI F.S. 2 , LEONARDI R. 3 , GALLI P. 1 , CHOOWONG M. 5 , DI GERONIMO S. 3 , ROBBA E 2 1 Dipartimento di Biotecnologie e Bioscienze, Università degli Studi di Milano-Bicocca, Piazza della Scienza, 2, Milano – Italy 2 Dipartimento di Scienze Geologiche e Geotecnologie, Università degli Studi di Milano-Bicocca, Piazza della Scienza, 4, Milano – Italy 3 Dipartimento di Scienze Geologiche, Sezione di Paleoecologia e Oceanografia, Università degli Studi di Catania, Corso Italia, 155, Catania – Italy 4 Dipartimento di Biologia Animale e dell’Uomo, Università degli Studi di Torino, Via Accademia Albertina, 13, Torino – Italy 5 Department of Geology Faculty of Science, Chulalongkorn University, Bangkok – Thailand zone coral genus A B C D E Acropora L Montipora L L Astreopora L L Pocillopora Pachyseris D Turbinaria L L L L Pectinia L Echinophyllia L Mycedium L Symphyllia L L Lobophyllia L Galaxea L L Fungia D, L L Hydnophora L L L Oulophyllia L Montastrea L Diploastrea D D D, L L Leptastrea L Cyphastrea L L L Plesiastrea L Goniastrea L L Favia L L L Favites L L L Coscinaraea L Siderastrea L L Psammocora L L L L Porites D, L L L L Goniopora L L L Alveopora L Merulina L P b) a) 20 cm c) 5 cm c) Zone C Figure 2 One of the large Porites boulders washed onto the Laem Pakarang tidal flat by the 26th December 2004 tsunami. Figure 5 Zone B extends from 5.5 to 8.5 m depth and is characterized by a rather uniform, 8 cm thick layer of soft sandy mud covering the sea floor. This muddy layer overlies a stiff muddy sand. Ripples parallel to the shore (N-S) were visible on the muddy substrate. Invertebrate traces such as holes (a) and signs of excavating activity (b) were commonly found on the soft substrate. Living irregular echinoids (c and inset) on the muddy bottom. Corals, biogenic blocks and rubble were not observed in Zone B. a) 10 cm b) c) REFERENCES Phongsuwan N., Yeemin T., Worachananant S., Duangsawasdi M., Chotiyaputta C., Comley J. (2006) Post-tsunami status of coral reefs and other coastal ecosystems on the Andaman Sea coast of Thailand. In : Wilkinson C., Souter D., and Goldberg J. (eds.) Status of coral reefs in tsunami affected countries: 2005. Australian Institute of marine Science: 63 – 77 a) 8°30 Zone B Zone A Zone D Zone E T2 T1 Figure 7 In Zone D hard substrate represented by living and dead coral colonies dominates over the sedimentary cover characterized by biogenic sandy gravel. A thin mud layer locally covers the coarser biogenic sand as shown by the sweeping effect of fleshy macroalgae (a). Coral blocks and dislodged colonies ranging from 30 cm to 2.5 m in diameter were on the seafloor. The largest uprooted living colonies were Diploastrea heliopora (b) and a Porites sp. (c). Displaced colonies piled up locally forming a secondary framework (d). Cases of large massive colonies broken, displaced and settled in growth position were common, though mostly showing partial death possibly due to scouring like the Astreopora sp. in figure e. The largest living colony observed in the area was a massive Porites approximately 2 m high and 5 m long (f). This colony was still in growth position and showed no visible damage nor signs of mud accumulation. 40 cm 20 cm 20 cm 40 cm 20 cm 2 cm g) E E h) i) j) k) l) b) c) d) f) 20 cm D L a) 20 cm e) B Some colonies were partially buried in the sediment, like the Turbinaria in g and h. The exposed part was still living (E) while the buried part (white dashed lines) was recently dead. Note the coarse biogenic sand and coral rubble still visible on the buried part after digging from the sediment (h). The buried part of the colony showed clear signs of recent breakage (white arrows). Slabs of Porites, Diploastrea heliopora, Mycedium elephantotus and Galaxea astreata were loose among the rubble and still living, possibly deriving from the colony margin (i). When digged from the mobile substrate some turf-covered blocks revealed the occurrence of recently dead coral colonies (white arrows) on the buried side (B) (j). Encrusting and small massive colonies were totally or partially buried under the sand (k). Few young colonies of Acropora, Fungia and Turbinaria were spotted on dead coral blocks (l) despite the overwhelming dominance of muddy algal turf. Grab sampling for quantitative analysis of living and dead macrobenthic fauna was complemented by underwater observations along profiles perpendicular to the coast. A bathymetric profile crossing a submarine topographic relief off the Laem Pakarang Cape revealed the occurrence of previously unreported coral communities at 10 - 12 m depth. Hereafter we present the preliminary results of a benthic assemblages characterization from the shallow fore-reef to the coral communities found off-shore along E-W transects (Fig 1c) and a schematic zonation on major changes in sediment and coral assemblages composition and structure. Figure 3 Schematic representation of the three surveyed transects (see Table 1 for positions). Six zones (from A to F) were identified corresponding to different benthic assemblages and sedimentary conditions. The zones are described in Fig.s from 3 to 6. Large uprooted and displaced coral blocks and colonies (Fig. 7 b-e) often piled onto each other (Fig. 7d) and massive toppled and/or partially buried corals still alive in patches are what remains of the coral communities off the Laem Pakarang cape. Most of the encrusting and all of the branching corals commonly found on Indo-Pacific reefs (Agariciidae, branching Acroporidae and Pocilloporidae) were not recorded either dead or living above the seafloor surface, with the exception of some young Acropora. However these corals were abundant as rubble onshore and locally deeper in the sediment. Sixteen months after the tsunami hit the coral community in Zone D all the hard substrate available was covered in algal turf and mud, and young coral colonies were very rare. Moreover patches of living coral on many of the coral colonies which had survived the tsunami event and that would have been expected to regenerate were often overgrown by sponges (Fig. 9). A rapid recovery of the coral community in Zone D seems highly unlikely under present conditions mainly because of the turbidity and mud deposition and re-suspension. Joint results of monitoring and ongoing comparative studies of living and dead soft bottom macrobenthic communities will hopefully clarify the factors which lead to the observed conditions, and allow us to follow the future recovery and evolution of the reefs of the Laem Pakarang cape. Turak E., Veron J.E.N., Sanpanich K. (2005) Post-tsunami coral reef surveys of Thailand’s north Andaman Coast: coral reef status after 26 December 2004 tsunami. In Allen G.R., and Stone G.S. (eds.) Rapid Assessment survey of tsunami- affected reefs of Thailand. New Engladn Aquarium Technical Report 02-05: 16 – 30 98°00 5 cm b) 3 cm a) Figure 4 Zone A extends from 2.5 to 5.5 m depth. Dead coral blocks (15 cm to 1 m in diameter) covered in muddy algal turf were scattered on the sea bottom among very coarse to coarse biogenic sand. Small colonies of Coscinaraea columna (a), Favia pallida (b), Turbinaria sp., and Cyphastrea sp. were living on the larger biogenic blocks. Encrusting sponges and macroalgae (e.g. Halimeda, Padina) were also frequent on the hard substrate. a) b) Figure 9 Sponges were often observed overgrowing the living coral tissue on displaced (a) and attached (b) coral colonies, or their fragments. 30 cm 10 cm Figure 6 The rippled soft bottom in Zone C (from 8.5 to 10 m) is made of coarse to very coarse biogenic sand covered by a thin veneer of mud (a). Coral blocks ranging from 30 cm to 1.5 m in diameter were scattered on the seafloor. Frondose fleshy algae and encrusting peyssonneliaceans were growing on them. Some partially buried blocks revealed to be recently dead coral colonies when digged from the mobile substrate (b). The exposed portion (below the dashed line) of the colony was covered in algal turf and sponges (arrow). Small faviids, siderastreids and poritids were growing onto the hard substrate (Table 2). A living Turbinaria colony in growth position was showing signs of recent breakage (arrows) (c). b) c) 20 cm 20 cm 20 cm a)