Complex habitat generated by marine bryozoans: a review of its distribution, structure, diversity, threats and conservation A. C. L WOOD a, *, P. K. PROBERT a , A. A. ROWDEN b and A. M. SMITH a a Department of Marine Science, University of Otago, PO Box 56, Dunedin, New Zealand b National Institute of Water and Atmospheric Research, Private Bag 14901, Kilbirnie, Wellington, New Zealand ABSTRACT 1. Habitat-forming bryozoans are here defined as extant, heavily-calcified species which regularly attain sizes over 50 mm in three-dimensions and which contribute significantly to benthic habitat structure as living colonies. 2. Records of habitat-forming bryozoans were collated and mapped, together with information about the location, environment, habitat-forming species, the nature and size of the habitat formed, any associated fauna, and relevant threats and/or conservation measures. 3. Records collated here indicated that habitat-forming bryozoans occurred from ~59  N to 77  S, but that they did not occur frequently in the tropics, being found most commonly in temperate continental shelf environments, on stable substrata in places where water movement was relatively fast and consistent. 4. Habitat-forming bryozoans are particularly abundant and diverse in New Zealand, where 27 species, a quarter of which are cyclostomes, provide habitat over hundreds of square kilometres of sea floor. Other areas where they are particularly rich and/or abundant include Antarctica (Weddell, Lazarev and Ross Seas), the North Pacific around Japan, the northern Mediterranean and Adriatic, and along the southern edge of the North Sea, through the English Channel and around the United Kingdom. 5. Large bryozoans provide habitat for diverse associated assemblages, particularly for other bryozoans, molluscs, annelids, arthropods, cnidarians, sponges, echinoderms and macroalgae. 6. Protected areas which include habitat-forming bryozoans occur throughout the distribution of this frequently unrecognized habitat type, but despite this they are prone to damage by anthropogenic impacts including pollution and bottom fishing. Copyright # 2012 John Wiley & Sons, Ltd. Received 12 November 2011; Revised 31 January 2012; Accepted 14 February 2012 KEY WORDS: reef; biodiversity; distribution; invertebrates; benthos; dredging; trawling; pollution INTRODUCTION Complex biogenic structures provide habitat for diverse associated fauna. Habitat-forming organisms include seagrasses (Bell and Westoby, 1986; Boström and Mattila, 1999; Bowden et al., 2001), sponges (Klitgaard, 1995), corals (Abele and Patton, 1976; Austin et al., 1980; Buhl-Mortensen and Mortensen, 2005), tube-building polychaetes (Nalesso et al., 1995; Moore et al., 1998) and molluscs (Hall-Spencer and Moore, 2000a; Beck et al., 2011). Certain marine bryozoans are also habitat-forming organisms, which while not well documented, can make important contributions to habitat complexity as they have done over evolutionary time. Bryozoans have generated habitat for macrofauna since the Middle Ordovician, and there is a rich literature describing *Correspondence to: A.C.L. Wood, Department of Marine Science, University of Otago, PO Box 56, Dunedin, New Zealand. E-mail: anna.wood@ otago.ac.nz Copyright # 2012 John Wiley & Sons, Ltd. AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS Aquatic Conserv: Mar. Freshw. Ecosyst. 22: 547–563 (2012) Published online 28 March 2012 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/aqc.2236