J. D. SIGWART & L. MCLEAN CONTRIBUTION OF CAULERPA SPP. TO MOLLUSC DIVERSITY VISAYA - APRIL. 2017 Contribution of Caulerpa spp. to Marine Mollusc Species Richness in the Megadiverse Philippines Julia D. Sigwart & Lorraine McLean j.sigwart@qub.ac.uk lmclean05@qub.ac.uk Queen ’ s University Belfast, Marine Laboratory, 12-13 The Strand, Portaferry, N. Ireland Urn: Isid: zoobank.org: pub: 9FC6EF7B-BB01-4F25-8938-241D87AF7EB9 KEYWORDS: Caulerpa, Chlorophycae , molluscan biodiversity, species richness, Philippines. ABSTRACT We report observations from a very short survey of micromolluscs collected on the seaweed Caulerpa from several sites near Cebu, in the Philippines. We recovered 159 morphospecies of bivalves and gastropods on Caulerpa spp. from point sampling of seaweed from across four markedly different habitats: active aquaculture, disused aquaculture sites, mangrove, and coral rubble. The contribution of Caulerpa spp. to local molluscan biodiversity varied at a larger scale among habitats, ranging from a maximum of 108 morphospecies per site in coral rubble adjacent to reef areas, to only 5 species of molluscs found on commercially grown Caulerpa. But there was also substantial fine scale variation, as two adjacent sites in coral rubble had 41 or 76 morphospecies. The limited nature of the sampling yet high species richness highlights known patterns of extremely high marine biodiversity in Southeast Asia and the Philippines in particular. The level of variability reflects the dynamic nature of these habitats and high local-scale variability. The seaweed Caulerpa has commercial importance and is cultured locally in pond aquaculture, but in the wild Caulerpa provides important habitat for molluscan biodiversity. INTRODUCTION The highest levels of marine biodiversity occur in the coastal regions of Southeast Asia (Gray 1996). The coast provides a wide variety of habitats for benthic marine animals, including reefs but also many other ecosystems that contribute to the high faunal diversity. In the Philippines, and the rest of the region, high vicariance leads to very high biodiversity with high variability even at small spatial scales. It is therefore not surprising that many tropical molluscan species remain undescribed, but a lack of comprehensive sampling may produce systemic biases that underestimate diversity and species richness (e.g. Bouchet et al., 2002). Species richness is a key metric often used to promote conservation of a particular region or smaller area, though the resulting value is highly dependent on the methods used to sample and estimate diversity (Albano et al., 2011). In particular, smaller species that are more technically difficult to recover and to identify, will frequently be overlooked. These species continue to be discovered and described though lack of attention to these taxa is a major concern for conservation (Bouchet, 1997). W ithin the tropics, most conservation efforts focus on coral reefs, but other organisms also provide complex bio - genic substrata that support molluscs. Seaweeds in both tropical and temperate latitudes support high diversity of small and often cryptic taxa (Fenwick, 1976; Boaden, 1996). As in larger scale ‘ ecosystem engineers ’ such as reef building mytilid mussel or corals, the impacts of habitat provision are compounding. This was summarised by Boaden (1996) with the observation: Fucus serratus provides a habitable site For much epifauna if conditions are right. Epifaunal colonies in their turn as well Provide habitats in which meiofauna can dwell. The green seaweed genus Caulerpa (Chlorophyceae ) has a tropical and subtropical worldwide distribution including more than 200 valid species and varieties (Guiry, 2016). Some of these provide food and shelter for species and are the obligate food plant of some www .conchology .be 71