Acropora florida, (DANA, 1846)

Santodomingo, Nadiezhda, Wallace, Carden C. & Johnson, Kenneth G., 2015, Fossils reveal a high diversity of the staghorn coral genera Acropora and Isopora (Scleractinia: Acroporidae) in the Neogene of Indonesia, Zoological Journal of the Linnean Society 175 (4), pp. 677-763 : 722-724

ACROPORA FLORIDA ( DANA, 1846)

FIGURE 22

Madrepora florida Dana, 1846: 466 , pl. 37 fig. 1

Madrepora gravida Dana, 1846: 470

Madrepora brachyclados Ortmann, 1888: 149 , pl.6 fig. 1

Madrepora compressa Bassett-Smith, 1890: 452

Madrepora polymorpha Brook, 1891:161 , pl. 31B–D

Madrepora affinis Brook, 1893: 60 , pl. 28 fig. F = Madrepora ornata Brook, 1891 (non Defrance): 464

Acropora multiramosa Nemenzo, 1967: 73 , pl.24 figs 1, 2

Diagnosis

Colony hispidose, thick branches; radial corallites with consistent size and even distributed on main branches, although commonly clustered around short branchlets; coenosteum with lateral flattened simple spinules aligned into costae on corallites and reticulate on intercorallite areas ( Wallace & Wolstenholme, 1998; Wallace, 1999).

Material studied

East Kalimantan: NHMUK PI AZ 6905 , TF516 , 16 specimens ; NHMUK PI AZ 8800 , TF516 , 47 specimens . Additional material from East Kalimantan: NHMUK PI AZ 6894 , TF516 , 9 specimens ; NHMUK PI AZ 8801 , TF526 , 1 specimen .

Modern comparative material: Holotype, USNM 282 , Fiji; MTQ G50270, Derawan Island, 6 m depth; MTQ G50801, Ambon, Hila, 3 m depth; MTQ G39792, Pemancingan , Pulau Laut, S. Kalimantan, Indonesia.

Skeletal characteristics

Corallum . Thick main branches with multiple short branches suggesting a simple hispidose growth form; primary branches and branchlets arise mainly from one side of the main axis giving an asymmetric appearance to the main branch; length 34.50–48.26– 72.50 mm, basal branch diameter 21.40–32.15– 47.30 mm, mid branch diameter 9.80–14.78– 20.20 mm, branch tip diameter 7.30–10.59– 15.30 mm; primary branches arising regularly from main axis in angles of 55.35–66.11–81.11°, distance between primary branches 12.80–16.24– 21.30 mm, with tips mostly broken or abraded, slightly tapering, secondary branches short, secondary branch length 3.70–8.38– 12.50 mm, basal branchlet diameter 4.20–8.22– 10.90 mm, middle branchlet diameter 3.80–5.03– 6.90 mm, portions in between branchlets with sparse radial corallites.

Corallites. Axial corallites visible at some branchlet tips, oval calice, 0.84–1.35– 1.81 mm exsert, outer diameter 2.06–2.27– 2.46 mm, inner diameter 1.14– 1.29– 1.46 mm, wall thickness 0.52–0.60– 0.75 mm, primary septa up to two-thirds R, secondary septa up to ½ R, arranged as S1>> S2; radial corallites evenly sized, evenly distributed with tendency to be crowded around branchlets, mostly not touching, tubular with thick lower wall, almost labellate, round calice with spines around calicular margin, profile length 0.12– 0.52– 0.76 mm, angle 32.62–61.09–78.17°, outer diameter 0.66–0.99– 1.23 mm, inner diameter 0.48–0.62– 0.73 mm, wall thickness 0.10–0.22– 0.37 mm, distance between centres 2.13–3.01– 4.19 mm, primary septa up to one-half R, secondary septa up to one-quarter R or present as spines. Corallite arrangement sequence 1–2– [3–4]–6–up to 10.

Coenosteum. Simple flattened spinules evenly distributed, reticulate between radial corallites, aligned into costae on branchlets and radial corallite walls. Coenosteum amount 2.22–3.55– 5.06 mm.

Occurrence

Early Miocene (?) to Recent. The specimen from the locality TF526, Kari Orang, East Kalimantan, represents the earliest occurrence of A. florida of Langhian to Burdigalian age, ∼13 to ∼18 Ma, although its preservation makes it difficult to be certain of its identification. Most of the well-preserved material is from the Tortonian locality TF516, Sangatta, 8.9–9.3 Ma. Previous fossil records include specimen MTQ G55127 from Niue (Pacific Ocean) of Pleistocene age, 119–132 ka age ( Pickett et al., 1985; Wallace, 1999). In modern reefs A. florida is widespread in the entire Indo- Pacific, from the east coast of Africa to the Cook Islands ( Wallace, 1999). This species is very common in Indonesian reefs with records in most of the islands, including localities in East Kalimantan ( Table 4).

Palaeoenvironment

Outcrop TF516 was characterized by orange finegrained sand sediment matrix and abundant large massive corals of the genera Dipsastraea , Diploastrea , Cyphastrea and Favites , and others, with colonies up to 1 m in diameter. This palaeoenvironment has been interpreted as a well-lit reef environment that favoured coral development. Abundant branching corals of the genera Porites , Goniopora , Seriatopora and Stylophora , and a few specimens of Isopora brueggemanni , were also present.

Remarks

The fossil specimens compare well with the modern material of A. florida MTQ G 50270 from Derawan Island and MTQ G39792 from Pulau Laut in East Kalimantan, and MTG G50801 from Ambon, in terms of size of main branches, asymmetric position of the branchlets, size and arrangement of corallites. The specimens recovered in Sangatta outcrops, NHMUK PI AZ 6905, have the thickest branches of the studied fossil record of Acropora in Indonesia so far. They were found in growth position ( Fig. 22A ) and their well-preserved skeletons have original aragonite and allow the observation of micromorphological characters of the coenosteum.

Figures

Figure 22. Acropora florida. NHMUK PI AZ 6905, TF516, Sangatta, East Kalimantan, Late Miocene (8.9–9.3 Ma). A, colony in the field preserved into a fine-sand and silt matrix. B, AZ 6905a–c, three fragments of a colony showing middle part of a primary branch (left) and branch tips with branchlets (centre and right). C, AZ 6905a, transverse section of a branch showing axial corallite. D, AZ 6905d, one fragment from the basal part of the colony showing asymmetric distribution of branchlets mainly on the upper side (left) and almost devoid from underneath (right). E–H, AZ 6905b: E, electron micrograph of a branchlet showing radial corallites around axial; F, detail of a tubular radial corallite; G, detail of costae on radial corallite wall; H, electron micrograph of reticulate coenosteum formed of simple flattened spinules in between radial corallites.