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Seaweeds > Division Rhodophyta
Holey sponge seaweed
Ceratodictyon spongiosum*
Family Lomentariaceae
updated Oct 2016

Where seen? This woolly branching organism is sometimes seen on our Southern shores, growing on coral rubble. It looks like a sponge, complete with holes along the 'stems'.

Features: The entire organism can be about 20-30cm across, with 'stems' about 1-1.5cm wide. The 'stems' solid often dividing frequently to form large spreading mats. Tips usually y-shaped. Each 'stem' is made up of fine, branched filaments that are packed together to form structures that feel woolly, velvety, spongey or felt-like. There are tiny holes along the 'stems'. Light to dark green.

This organism is actually a symbiotic combination of an algae (Ceratodictyon spongiosum) and a sponge (Haliclona cymaeformis Family Chalinidae, indicated as Sigmadocia symbiotica in AlgaeBase). The algae makes up the bulk of the organism while the sponge provides the tough exterior and appears to give the organism its shape and form, contributing to the formation of the tiny holes. The algae gets most of the nitrogen it needs from the sponge.

Sometimes confused with the Smooth sponge green seaweed (Cladophoropsis vaucheriaeformis) which looks very similar, its holes along the 'stems' are not obvious when out of water. This is a green seaweed which also has a symbiotic relationship with another kind of sponge. The two organisms are sometimes difficult to tell apart in the field.

Pulau Semakau, Mar 05

Pulau Hantu, Jun 10

Pulau Senang, Aug 10

Cyrene Reef, Oct 07

Sentosa, Feb 08

*Species are difficult to positively identify without close examination of internal parts.
On this website, they are grouped by external features for convenience of display.

Holey sponge seaweeds on Singapore shores

Photos of Holey sponge seaweeds for free download from wildsingapore flickr

Distribution in Singapore on this wildsingapore flickr map

Pulau Tekukor, May 13
Photo shared by Marcus Ng on flickr.

Terumbu Pempang Laut, Aug 16
Photo shared by Marcus Ng on flickr.

Ceratodictyon recorded for Singapore
Pham, M. N., H. T. W. Tan, S. Mitrovic & H. H. T. Yeo, 2011. A Checklist of the Algae of Singapore.

  Ceratodictyon spongiosum

Links References
  • Pham, M. N., H. T. W. Tan, S. Mitrovic & H. H. T. Yeo, 2011. A Checklist of the Algae of Singapore, 2nd Edition. Lee Kong Chian Natural History Museum, National University of Singapore, Singapore. 99 pp. Uploaded 1 October 2011. [PDF, 1.58 MB].
  • Lim Swee Cheng, Nicole de Voogd and Tan Koh Siang. 2008. A Guide to Sponges of Singapore. Singapore Science Centre. 173pp.
  • A. C. Lee, Lawrence M. Liao and K. S. Tan. Dec 2009 New records of marine algae on artificial structures and intertidal flats in coastal waters of Singapore. Pp. 5-40. in the Raffles Bulletin of Zoology.
  • Huisman, John M. 2000. Marine Plants of Australia University of Western Australia Press. 300pp.
  • Calumpong, H. P. & Menez, E. G., 1997.Field Guide to the Common Mangroves, Seagrasses and Algae of the Philippines. Bookmark, Inc., the Philippines. 197 pp.
  • Trono, Gavino. C. Jr., 1997. Field Guide and Atlas of the Seaweed Resources of the Philippines.. Bookmark, Inc., the Philippines. 306 pp.
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