| Summary: | We compared the species composition, abundance, and cover of sponges in 2 marine lakes (Kakaban Lake and Haji Buang Lake) and adjacent coastal mangroves on the islands of Kakaban and Maratua in the Berau region of Indonesia. We recorded a total of 115 sponge spe- cies, 33 of which were restricted to Kakaban Lake, 18 to Haji Buang Lake, and 30 to coastal man- groves on Maratua Island. Only 13 species were shared among all habitats. The 2 marine lakes are located 10 km apart, but their assemblages were more similar to each other than to the bay man- grove systems just 200 to 500 m away. Our results show that marine lakes represent a distinct habitat with significantly higher sponge cover and abundance as well as a markedly different spe- cies composition when compared with coastal mangroves. In both lake and coastal mangrove habitats there was a pronounced gradient in composition away from the shore with the primary difference between solid (root or rock) and soft substrate (mud or sand). Each substrate type har- bored different sets of species in both lake and coastal mangrove habitats. There was no signifi- cant difference in sponge species composition, abundance, or cover between semi-permanent transects sampled in 2008 and 2009. We show for the first time that mangroves in the Indo-Pacific harbor a diverse array of sponge species and, further, that marine lakes harbor numerous unique species hitherto unknown to science.
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