Cobbles colonization pattern from a tsunami-affected coastal area (SW Thailand, Andaman Sea)

Abstract

We studied the sclerobiont community associated with organogenic and lithic cobbles from soft bottoms in the Khao Lak coastal area (Andaman Sea) that was damaged by the 2004 tsunami. The 15 cobbles examined originate from grab and hand sampling carried out in the years 2006 and 2007 in the depth range of 4.6-15.2 m. A rich endo-and epibenthos was identiWed, mainly consisting of algae, foraminifers, sponges, cnidarians, polychaetes, bryozoans and bivalves. Associations on each examined cobble show similarities in composition and structure being characterized by a few dominant groups. DiVerences were noted in the degree and pattern of colonization, distinguishing for each cobble an upward and a downward side at the time of sampling. The mean total coverage is 15.09% being higher on the upper sides (17.4%) compared to the lower sides (12.8%). Calcareous algae, bivalves and sponges prevail on upper sides, while bryozoans prevail on lower sides. The sclerobionts distribution allowed to infer the orientation of cobbles on the seaXoor during colonization.Major colonization values, exceeding 30% coverage, were observed on organogenic cobbles located in the proximity of reefs or collected from below 12 m of water depth. Conversely, cobbles from the shallowest stations result poorly colonized, independently of their composition. The water turbidity and wave motion as a possible cause of the observed distributions were discussed. The Khao Lak cobble community seems to be largely unaVected by the tsunami event, as suggested by the estimated biodiversity, abundance and coverage of sclerobionts.

Sediment distribution on the inner continental shelf off Khao Lak (Thailand) after the 2004 Indian Ocean tsunami

“…No influence of the 2004 Indian Ocean tsunami has been found within the sediments of seafloor types B and C. This supports the findings of Sanfilippo et al (2010), who reported a minor influence on corals living on cobbles in these areas. These areas seem to be mostly unaffected by the tsunami event.…”

“…2). Cobbles from this area, which are covered by colonies of organisms indicating a stable environment, were recently reported by Sanfilippo et al (2010). Additionally, the acoustic base is situated just beneath the surface north and south of Pakarang Cape (Fig.…”

“…A dead fringing reef complex near Pakarang Cape (Sanfilippo et al, 2010) forms a platform that extends down to a water depth of approximately 10 m ( Figs. 1 and 2).…”

Living coralligenous as geo-historical structure built by coralline algae

“…The Bogliasco C is presently growing within the infralittoral Posidonia meadow, with its upper, best-lit side dominated by filamentous and fleshy algae, with subordinate Peyssonneliales and CCA. Bryozoans are also important contributors, especially on sides D and F, together with annelids, confirming their preference for the shadowed and protected substrates (Rosso and Sanfilippo, 2009;Sanfilippo et al, 2011), including the lower surface of calcareous laminar algae.…”

Taphonomy of a Panopea Ménard de la Groye, 1807 shell bed from the Pisco Formation (Miocene, Peru)

“…In this bed, although most carbonates has been dissolved, a large number of invertebrate specimens have been preserved as molds that exhibit an exceptional degree of preservation, recording a complex community of invertebrates that grew on the inside of the Panopea shells. Nowadays, in soft substrates, scattered small hard-substrate settings, such as large clasts and exoskeletons of marine organisms, may become hot-spots of biodiversity (Kauffman 1978;Kidwell 1986;Sanfilippo et al 2011). These "benthic islands" provide sessile benthic organisms with a relatively stable habitat in an otherwise unstable "ocean" of unconsolidated sediment (Brett 1988;Taylor & Wilson 2003).…”