DataSheet2_Living coralligenous as geo-historical structure built by coralline algae.PDF

The most important reef of the Mediterranean is the Coralligène (Coralligenous = C), including several types of calcareous algal-invertebrate build-ups growing in normal open marine conditions. We analyzed and compared two C samples from the Ligurian Sea developed in different environmental settings: 1) off Portofino on a rocky cliff, at a depth of about 40 m and 2) in front of Bogliasco, on a sub-horizontal substrate at a depth of 10 m. The maximum AMS radiocarbon dating provided an older age for Bogliasco (about 5 ka BP) than for Portofino (about 3.6 ka BP), and the mean accumulation rate of the Portofino build-up (about 80 µm y−1) was found to be higher than the one in Bogliasco (about 65 µm y−1). The different sides of each build-up showed a remarkable heterogeneity in the dominant cover by living organisms, and the comparison between the two build-ups highlighted an evident diversity in their taxonomic composition and structure, although crustose coralline algae (CCA) are the dominant framework builder and major autogenic ecosystem engineers at both localities, in the present as in the past millennia. Other major components of the structure are bryozoans and serpulids, and an important role is played by sediment filling. In Bogliasco, extreme climate events and major peaks of fine matrix and terrigenous grains are observed, lithologically related to the drainage basin of the Poggio creek and associated with charophyte occurrence and reduced CCA abundance. The occurrence of the rare Sporolithon ptychoides was observed both in Portofino at about 750 BCE and in Bogliasco. These Sporolithon phases are likely related to warm and humid spells punctuating the Holocene climate fluctuations in the Ligurian Sea. Because coralline algae are confirmed to be the most important habitat engineer of the Mediterranean reefs, they deserve more attention in the framework of any monitoring initiative aimed at C management and conservation.</p

SEM pictures of microorganisms associated with the <i>Ectopleura crocea</i> epidermis.

<p>A) Surface of a tentacle densely covered with the two morphotypes of microorganisms living on the epidermis: one is horseshoe-shaped (green; named <i>Type I</i>) and the other is fusiform, worm-like (red; named <i>Type II</i>). B) Portion of a broken tentacle, bacteria were present on the surface (s) but not inside (is). C–D) Enlargements of tentacle portions which were densely covered by the two microorganisms. E) Particular of the horseshoe-shaped <i>Type I</i>, showing the peculiar arrangement in the tentacle grooves. F) Particular of a cluster of the worm-like <i>Type II</i>. Scale bars: A, C, E, F 5 μm; B 2 μm; D 10 μm.</p

Main characteristics of <i>Ectopleura crocea</i>.

<p>A) Underwater photograph of the hydroid. B) Scheme of the colony. 1. Feeding and reproductive polyps; 2. Stems (hydrocauli); 3. Tangled stolons anchoring the colony to the substrate (hydrorhizae).</p

Most abundant bacterial genera associated with <i>E. crocea</i> in April 2009 (A) and March 2010 (B), as revealed by tag-encoded amplicon pyrosequencing of the 16S rDNA gene.

<p>Reported are the 20 most abundant genera.</p

TEM pictures of <i>Type II</i> bacteria associated with <i>Ectopleura crocea.</i>

<p>A) Numerous bacteria in transversal sections (arrows) observed on the hydroid ectoderm (ec). B) Bacteria (longitudinal and tranversal sections) present in a groove of the hydroid ectoderm. C) Bacteria lying on the hydroid periderm (p) are often found in correspondence to the microvilles (mv) of the ectodermal cells. D) Close-up view showing the glycocalyx (gl) surrounded the microorganisms. e–f. Longitudinal section of a bacterium. Scale bars: a, c, e 1 μm; b 2 μm; d, f 0.5 μm.</p

Portions of <i>E. crocea</i> examined to find prokaryotes.

<p>A) Scheme illustrating the main features of the polyp stage. GC gastric column, AT aboral tentacles, OT oral tentacles, G gonophores, B basal portion of hydranth, N neck zone, H hydrocaulus (portion covered with perisarc). B–E. Close-up view at scanning electron microscope. B). Aboral tentacle colonized by bacteria. C. Broken female gonophore containing immature actinulae round in shape (a). Bacteria were rarely found on actinulae at this stage. D. Mature female gonophore with actinula's tentacles protruding through the opening (white arrow). Bacteria were often observed on these tiny tentacles. E. Released and free-living actinula with developed aboral (at) and oral (ot) tentacles. Scale bars: B 20 μm; C 500 μm D, E 200 μm.</p

List of the genera identified on the basis of spicular remains recorded in the layers belonging to the considered spans of time.

<p>Genera in bold were also recorded in the recent surveys.</p

Trend of sponge diversity evaluated as number of genera present in each period (grey bars) compared with the trend of sponge abundance evaluated as average amount of spicules per sediment g present in the same periods.

<p>Trend of sponge diversity evaluated as number of genera present in each period (grey bars) compared with the trend of sponge abundance evaluated as average amount of spicules per sediment g present in the same periods.</p

The dynamics of a Mediterranean coralligenous sponge assemblage at decennial and millennial temporal scales - Fig 5

<p><i>Alveospongia</i> sp. A, B two different examples of sinuous acanthomicrostrongyles typical of the genus; C, detail of the microspiny surface of acanthomicrostrongyles; D, magnification of the acanthomicrostrongyle tip.</p

Hypothetical evolutionary scenario of the coralligenous accretions of Bogliasco.

<p>A) In a first phase the algal growth resulted in pillar-like bioherm. B) Periods of heavy floods could have increased the bottom sediments, partially or totally burying the pillars and killing the algal coverage. C) During the burying or after the removal of the sediments, a part of the structure could be prone to erosive processes, giving rise to mushroom-like structures. D) In following phases, the coralline algae could grow again in sciaphilous microhabitats, determining the irregular temporal layering of the structure (the number from 1 to 4 indicated different sheets of deposition from the oldest to the youngest). In this situation, in a core sample (dotted rectangle), younger sheets can be overlapped by older ones.</p