Philippine Journal of Science 139 (2): 149-159, December 2010 ISSN 0031 - 7683

Survey and Spatial Distribution of Shoreline Malacofauna in Grande Island, Subic Bay

Gizelle A. Batomalaque*, Bryan Geoffrey P. Arce, Ma. Brenda M. Hernandez, and Ian Kendrich C. Fontanilla

Institute of Biology, Quirino St., University of the Philippines, Diliman, Quezon City 1101

Grande Island, Subic Bay is an excellent site for studying spatial distributions on a local scale because of its topographic heterogeneity. This study aimed to provide a systematic survey and spatial distribution of shoreline malacofauna of the island using a total of 956 continuous 2 x 2 m plots. Substrate types were classified as sand, sand-pebble, rock-sand, rock-pebble, pebble- rock-coral rubble, boulder, and wood. One hundred mollusk were identified from 44,465 individuals with 54 additional individuals still unresolved. Mollusks were found to be distributed according to the substrate type (composition and particle size) and are independent of the total area sampled. Substrates that are loose or unstable tend to have only few species while those that are compact have more species. Only bivalves were found in the sand substrate. Planaxids, nerites, trochids, and siphonarids were the dominant groups in substrates with rocks, pebbles, and coral rubble. Nudibranchs only occurred in rocky substrates. Nacellids and littorinids predominate particularly in boulders. Littorinids were also numerous in woody substrates. Juvenile trochids and planaxids were most abundant in regions with calm water while species and adult trochids were particular in areas exposed to strong currents. The morphological adaptations of different species enabled them to occur in specific habitat types.

Key Words: mollusk, shoreline survey, spatial distribution, substrate type

INTRODUCTION testaceos de las Islas Filipinas, Jolo y Marianas (1904- 1905), relying heavily on the records of Cumming, Survey of molluscan species has been a relevant tool included 3,121 species (Springsteen and Leobrera 1986). for storing and organizing taxonomic data, which could More recent publications of mollusk listings include those provide insights on the molluscan distribution of a of Springsteen and Leobrera (1986) and Poppe (2008a; particular area for potential economic, scientific and even 2008b). At present, no systematic studies have been medical applications. The global estimate of described executed on the biodiversity of marine mollusks around molluscan species is 70,000 (IUCN 2004), and around Luzon as confirmed by the scarcity of published literature. 22,000 species are believed to be present in the Philippines There is, however, one study in Mindoro Island conducted (PBCPP 2002). Mollusks are the second most diverse by Berdach (1981) that focused on the inventory of marine invertebrates in the Philippines, with an estimated species gastropods in the Man and Biosphere (MAB) Reserve endemism of 2-4% (PBCPP 2002). Much of the published area in Puerto Galera where Berdach (1981) found a total information regarding Philippine molluscan species is of 343 species from 45 families. Nevertheless, Berdach based on collections made by Hugh Cumming between (1981) failed to mention the sampling effort in terms of 1836 and 1840. Hidalgo’s Catalogo de los Molluskos the total area surveyed. Furthermore, he also included *Corresponding author: [email protected] dead specimens (i.e. shells only) in his inventory because he assumed these specimens inhabited the area. Studies

149 Philippine Journal of Science Batomalaque et al.: Survey and Spatial Vol. 139 No. 2, December 2010 Distribution of Shore Mollusks

of molluscan diversity in the Philippines were mainly to the substrate type. Temporal distribution was not studied focused on regional scales according to ocean basins due to limited data-gathering time and less on local scales according to physical gradients (Vallejo 2001). Little is known of the correlation between habitat types and species composition on a smaller scale. MATERIALS AND METHODS Determining spatial distribution patterns among mollusk species is important in studying the ecology of these species. An accurate description of these patterns Species survey also provides an index for studying relationships and All five sides of the island were surveyed. Sampling was interactions between different mollusks (Springsteen and conducted from May 20 to 22 and May 26 to June 1, 2008 Leobrera 1986). These also reflect how abiotic and biotic during low tide, since the area of interest was the subtidal factors collectively affect species zonations (Azouzi et zone (zone always submerged in water even at low tide). al. 2002). Abiotic factors identified are substrate grain Systematic snorkel-surveys were done in continuous 2 x 2 m size, wave action, water content, and temperature and plots along the edge of the shoreline around nearly the whole salinity of interstitial water (water contained in crevices stretch of the island. The plots were bounded by standard and within the particles of the substrate). Among these, PVC pipes that could sink under water. A maximum of 10 De Arruda and Amaral (2003) pointed to morphodynamic minutes per plot was allotted to search for mollusks. Pebbles states (substrate types and wave action) as the primary and rocks were moved and replaced in order to thoroughly determinant of distribution patterns in environments with survey each plot. For sandy substrates, the surface was a variation of physical characteristics. Biotic factors, slightly swept or dug up for burrowing mollusks. on the other hand, include recruitment (addition of Habitat description was limited only to the type of members to the population or community), predation, substrate. This was characterized according to particle and competition. Together with interactions between size using a modified Wentworth Grain Size Classification abiotic components and biotic relationships, species (El-Shaarawi and Piegorsh 2002): sand (<1 cm), pebble characteristics such as size, feeding habits, mobility, and (1-6.4 cm), rock (rubble/cobble) (6.4-25.6 cm), boulder morphology also determine marine molluscan distribution. (>25.6 cm). In the presence of mixed substrate types, a It is acknowledged that species distribution is shaped by plot was assigned to a particular substrate if that substrate the interplay between these factors at different extents comprised more than 50% of the entire plot. The water and never attributable solely to a single factor (De Arruda movement or current intensity was noted for each side and Amaral 2003). of the island. Furthermore, the presence of associated Grande Island just off the coast of Subic Bay, Zambales fauna such as echinoderms, arthropods, and macroalgae (14˚46’25.40” N, 120˚13’53.45” E, total land area were noted. of 40 hectares and perimeter of 2.2 km) provides an Only live mollusks were considered in the study. For excellent site for studying habitat associations because every plot, the number of individuals of each species the substrate types found in the perimeter of the island encountered was recorded. A voucher specimen from are heterogeneous. The five sides of the island include each encountered species was brought to the laboratory different types of substrates: fine sand, coral rubble, for identification. All mollusks were identified down to pebbles, cobbles, and boulders. Water movements at the species level, where possible, using Marsh (1964), different sides also show variation. Hinton (1972), Dance (1976), Springsteen and Leobrera This study aimed to determine the molluscan species (1986), Abbott (1991), and Poppe (2008a) as references. composition of the subtidal region around Grande Island The soft tissues were then removed and the shells cleaned. using continuous 2 x 2 m quadrats. That is, the subtidal Photographs of the shells were then taken. region examined was within 2 m from the waterline at low tide. Other objectives of this study include the Data analysis determination of the relative abundance of species in The relative abundance (RA) of species in each substrate different habitats, the comparison of species composition type was determined. Comparison of species composition of marine mollusks in different substrate types, and the between sites was facilitated using Sorenson’s Similarity correlation of mollusk morphology with the habitat type. Index (S) based on the presence or absence of species in Since no previous published studies on mollusks have a particular substrate type, which is given by the equation been conducted on Grande Island, baseline data from S (index of similarity) = 2C/ A+B, where A is the number this study would certainly prove useful for future studies. of species in the first substrate type; B is the number of Though several factors could affect the spatial distribution species in the second substrate type; and C is the number and assemblage of marine mollusks, this study was limited of species common to both substrate types. A low index

150 Philippine Journal of Science Batomalaque et al.: Survey and Spatial Vol. 139 No. 2, December 2010 Distribution of Shore Mollusks

value means a large difference in species composition 86 species from 24 families from class , and between the two substrate types compared. Lastly, a 14 species from 11 families from class Bivalvia. Another dendrogram was generated from the distances (1-S) using 54 individuals were unidentified, including one juvenile Unweighted Pair-Group Method with Arithmetic Averages chiton and one octopus. A summary of the species sampled (UPGMA) (Sneath and Sokal 1973) in order to illustrate is shown in Table 1. such similarity or difference (Legendre 1998). Relative species abundance Figure 1 shows the top ten (10) most abundant species among gastropods. Figure 2 shows the top six (6) most RESULTS abundant species among bivalves.

Species richness Habitat characterization A total of 956 2 x 2 m plots (total distance of 1,912 m and Seven different habitats were characterized according to total area of 3,824 m2) were surveyed. From these, 44,465 substrate composition. Different substrate types occurred individual mollusks were sampled and attributed to 100 at different sides of the island. The area covered by each molluscan species (90 identified up to the species level substrate type also varied (Table 2). and a further 10 identified only up to the genus level), with

Table 1. Frequency and relative abundance of molluskan species surveyed in Grande Island, Subic Bay, Philippines. GASTROPODA Frequency Relative Abundance Family Buccinidae Engina medicaria 433 0.97 Pollia undosa 16 0.04 Family Bursidae Bursa lamarckii 2 0.00 Family Cerithiidae Cerithium bifasciatum 5 0.01 Cerithium planum 274 0.62 Clypeomorus monoliferus 48 0.11 Clypeomorus tuberculatus 43 0.10 Cerithium sp. 438 0.99 Family Collumbellidae Euplica scripta 105 0.24 Pyrene epamella 16 0.04 Family coronatus 27 0.06 Conus ebraeus 7 0.02 Conus flavidus 2 0.00 Family Coralliophilidae Coralliophila neritoidae 17 0.04 Family Costellariidae Vexillum luculentum 130 0.29 Vexillum pisolinum 4 0.01 Zierliana anthracina 7 0.02 Zierliana ziervogelii 3 0.01 Family Cypraeidae Cypraea annulus 53 0.12 Cypraea arabica 2 0.00 Cypraea caputdraconis 3 0.01 Cypraea caputserpentis 4 0.01 Cypraea errones 12 0.03 Cypraea moneta 2 0.00 Family Fasciolariidae Latirolagena smaragdula 2 0.00 Fasciolaria sp. 3 0.01 Family Haliotidae Haliotis glabra 69 0.16 Family Littorinidae Littorina coccinea 2 0.00 Littorina scabra 605 1.36 Littorina undulata 69 0.16 Table 1 continued next page . . . . .

151 Philippine Journal of Science Batomalaque et al.: Survey and Spatial Vol. 139 No. 2, December 2010 Distribution of Shore Mollusks

GASTROPODA Frequency Relative Abundance Nodilittorina leucosticte 474 1.07 Littorina sp. 1 and 2a 1829 4.11 juvenile Littorina sp. 18 0.04 Family Lotiidae saccharina 193 0.43 Patelloida striata 188 0.42 Family Mitridae Mitra scutulata 10 0.02 Family Muricidae Chicoreus brunneus 6 0.01 Cronia funiculus 47 0.11 Cronia margariticola 1 0.00 Drupella fusconigra 2 0.00 Morula anaxeres 768 1.73 Morula granulata 7 0.02 Morula musiva 41 0.09 Purpura persica 3 0.01 Thais savignyi 783 1.76 Thais tuberosa 2 0.00 Drupa sp. 13 0.03 Family Cellana grata 458 1.03 Cellana testudinaria 1,251 2.81 Family albescens 2 0.00 Nassarius distortus 8 0.02 Nassarius venustus 15 0.03 Family Naticidae Notocochlis gualteriana 1 0.00 Family albicilla 1,724 3.88 Nerita antiquata 5 0.01 Nerita chamaeleon 1,028 2.31 Nerita exuvia 569 1.28 Nerita lineata 11 0.02 Nerita polita 6 0.01 Nerita signata 42 0.09 Nerita undata 32 0.07 Nerita sp. 396 0.89 Family sulcatus 19,998 44.97 Family Siphonariidae Siphonaria javanica 565 1.27 Siphonaria laciniosa 168 0.38 Siphonaria sirius 2 0.00 Family Strombidae Canarium labiatum 1 0.00 Lambis lambis 1 0.00 Strombus labiatus 7 0.02 Strombus mutabilis 14 0.03 Strombus sp. 4 0.01 Family Monodonta labio and canaliferab 489 1.10 Stomatia phymotis 1 0.00 Tectus fenestratus 38 0.09 niloticus 3 0.01 Trochus sacellum 151 0.34 Trochus stellatus 79 0.18 juvenile Trochus sp. 8,697 19.56 Family Turbinellidae Vasum turbinellum 2 0.00

Table 1 continued next page . . . . .

152 Philippine Journal of Science Batomalaque et al.: Survey and Spatial Vol. 139 No. 2, December 2010 Distribution of Shore Mollusks

Astraecalcar 5 0.01 Liotia varicosa 6 0.01 Lunella cinerea 506 1.14 argyrostomus 46 0.10 Turbo chrysostomus 17 0.04 BIVALVIA 0.00 Family Cardiidae Corculum cardisa 1 0.00 Family Crassatelidae Crassatellites japonicus 121 0.27 Family Isognomonidae Isognomon ephippium 773 1.71 Family Mytilidae Brachidontes striatulus 65 0.15 Semele jukesi 13 0.03 Family Ostreidae Crassostrea commercialis 322 0.72 Family Pinnidae Atrina pectinata 20 0.04 Family Psammobiidae Asaphis deflorata 2 0.00 Gari amethystus 2 0.00 Family Spondylidae Spondylus squamosus 1 0.00 Family Tellinidae Tellina alternata 1 0.00 Family Tridacnidae Tridacna sp. 1 0.00 Family Veneridae Gafrarium pectinatum 4 0.01 Gafrarium tumidum 44465 0.01 aLittorina sp. 1 and 2 were originally counted as one species on the field, but two conchologically distinct type specimens were identified based on the shells brought to the laboratory. bMonodonta labio and M. canalifera were originally counted as one species on the field but were found to be two distinct species when specimens were identified in the laboratory.

Figure 1. Relative species abundance of gastropods sampled along the shoreline of Grande Island, Subic Bay. Only the top ten (10) species are shown as expressed in percentages.

153 Philippine Journal of Science Batomalaque et al.: Survey and Spatial Vol. 139 No. 2, December 2010 Distribution of Shore Mollusks

Crossostrea commercialis 24%

Isognomon Crossatellites ephippium japonicus 58% 9%

Brachidontes striatulus 5% Atrina pectinata 1% Semele jukesi 1% Others 2% Figure 2. Relative species abundance of bivalves sampled along the shoreline of Grande Island, Subic Bay. Only the top six (6) species are shown as expressed in percentages.

Table 2. Number of species found in each substrate type around Grande Island, Subic Bay, Philippines. Substrate type Number of plots Area covered (m2) Number of species Sand 227 908 2 Sand-pebble 42 168 32 Pebble-rock-coral rubble 87 348 46 Sand-rock 83 332 17 Pebble-rock 192 768 80 Boulder 315 1,260 67 Wood 10 40 10

The northern side of the island consisted mostly of pebble-rock and pebble-rock-coral rubble substrates were sand substrate, with boulders and sand-rock substrates found. The pebble-rock-coral rubble substrate dominated occurring toward the west end. On its east end, the wooden the area between the western and southern sides, and the dock was included in the sampling. Water movement slope was relatively flat. Associated flora encountered was moderately strong and some fishes were found in were macroalgae (mainly Padina sp.). Associated the area. The northwest side was composed entirely fauna were crustaceans (hermit crabs) and echinoderms of boulders that had a thick cover of algae. Numerous (mainly sea stars and sea cucumbers). The water in this barnacles and juvenile sea urchins were found in the area. area was calm. The stretch of the south side consisted of The west side also consisted of boulders but had no algal pebble-rock-coral rubble, pebble-rock, and sand-pebble cover. The water current was observed to be very strong substrates. Several fallen wooden debris were found on in both the northwest and west sides, and this gradually this side. Water current was moderate. Finally, the east decreased towards the southern end. The west side was side of the island consisted of sand-pebble and pebble-rock not completely sampled because of the danger imposed substrates. The side of the wooden dock at the northern by the intense current, slippery boulders, and the great end was also sampled. Only the north and east sides of depth in the area. This consisted of roughly 150 plots the island are frequented by island guests. covering an area of 600 m2. Towards the southern end,

154 Philippine Journal of Science Batomalaque et al.: Survey and Spatial Vol. 139 No. 2, December 2010 Distribution of Shore Mollusks

Figure 3. Composition of bivalves and gastropods across different substrate types in Grande Island, Subic Bay. The substrates composed of sand and wood had the least number of species while those of the pebble-rock, and boulder were the most species-rich. Only bivalves occurred in the sand substrate.

Species richness in each habitat type A second cluster, wood and sand-rock, were different A total of 86 gastropod species and 14 bivalve species from the first cluster at 0.74. The sand substrate had a 1.0 were identified. Figure 3 shows the number of species m distance from both clusters, implying that its species identified in each substrate type (see also Table 2). assemblage was completely different from those of the other Juvenile littorinids and trochids have been included and six substrates. Semele jukesi (RA=93%) and Tellina alternata counted as unique species, as they were among the most Sowerby (RA=7%) were the only species found on sand, and abundant in the study site. These juvenile littorinids and both were not found in any other substrate type. trochids have not been identified to the species level. Only two species of bivalves and no gastropods were found in the sand. In the other six substrate types, there were more gastropods than bivalves. The sand-rock substrate DISCUSSION had two bivalve species and 15 gastropods. Both boulder and wood had three bivalve species, but the former had Species richness 64 gastropod species while the latter had only seven. Six The large number of species that was sampled in Grande bivalve species and 40 gastropod species were found in Island (90 identified to species level and 10 to genus the pebble-rock-coral rubble substrate. The pebble-rock level) reflected the high species richness estimated for substrate was the most species-rich, with seven bivalve the Philippines (being a center of wildlife megadiversity) and 73 gastropod species. as a whole. The Philippines is located at the center of the Indo-Polynesian province, an area believed to Comparison of species assemblages in different contain the most number of marine species worldwide substrates (Springsteen and Leobrera 1986; Hall 1997). A study by The comparison of mollusk species assemblages across Bouchet et al. (2002) that surveyed the Indo-Pacific for different substrate types is presented in a dendrogram macrofaunal species found that earlier studies have grossly generated using UPGMA based on their distances (1- underestimated the species richness. Their sampling effort S) (Figure 4). Longer nodes indicate larger differences of 400 day-persons at 42 discrete stations on a 295 km2 site between substrate types. Species assemblages in the on the west coast of , south-west Pacific boulder and pebble-rock substrate were most similar, resulted in 2,738 species of marine mollusks. The present with a distance of 0.19. These two, together with the study on Grande Island only utilized a collected effort of sand-pebble and pebble-rock-coral rubble substrate, three (3) persons for ten (10) days to survey a 3.824 km2 comprised a cluster. area along the shoreline. From these figures, it can be

155 Philippine Journal of Science Batomalaque et al.: Survey and Spatial Vol. 139 No. 2, December 2010 Distribution of Shore Mollusks

boulder 0.19 pebble-rock

0.29 sand-pebble

0.31 pebble-rock- coral rubble

0.74 wood 0.24 sand-rock 1.00 sand distance Figure 4. Comparison of mollusk assemblages between different substrate types in Grande Island, Subic Bay. Short distances indicate large similarity while a 1.0 distance indicates no similarity. Two main clusters were formed, with the sand substrate serving as an outgroup (S=0).

inferred that there is a rich assemblage of species found gastropod P. sulcatus dominated this substrate type, with on such a small island. This is taking into account the other species occurring in fewer numbers. This species is fact that the methodology used underestimated the total usually found in large to vast groups under boulders and number of species since it limited the area sampled to the rocks in the tidal zone (Morton 1983). Although the sand- subtidal region of the island’s shoreline. pebble substrate is not as stable as boulders, the former was in fact compact given that the water in the area was calm and shallow. Other notable gastropod species found Mollusk species in different substrates were the juvenile trochids, which characteristically occur Two bivalve species, S. jukesi and T. alternata, were in shallow pools with substrates having small particle- found in the sandy substrate type. Tellin shells are found size (Castell 1995). Trochids fertilize externally and the in exposed sand shores and are able to survive deeper in location of their settlement depends on the current. Due to the sediment because of their long siphons. According to the weak water currents in the reef flat area, it is possible the mollusk listings of Springsteen and Leobrera (1986), that this led to the aggregation of the juvenile trochids. cockles are among the common sand-dwellers found in The trochids in the sand-pebble substrate were identified Philippine shores. However, cockles were not found in this as juveniles based on their size, which was markedly study. Having only surveyed the plots during the day, there smaller than the adult. The bivalve I. ephippium was was a very small chance of finding gastropods. Among also abundant next to the juvenile trochids. This species gastropods, Natica and Oliva are known to crawl just normally occurs in clusters of several individuals attached below the surface, progressing like a plough but always to the crevices with the massive byssus deeply planted into covered by sand. These mollusks move only when looking the substrate (Yonge 1968). The gastropods N. chamaeleon for food during the night and remain buried during the day and Cerithium planum Anton were nearly as numerous (Owen 1982). Furthermore, the small number of species as I. ephippium. Nerites most often live quite high in and individuals of each species found is probably due the intertidal zone and can tolerate air and sun exposure to the constant disturbance brought about by the water for long periods of time. Ceriths, on the other hand, are current and the swimming activities in the area, although known to occur in shallow water, mostly on seagrasses these factors were not quantified. and seaweeds (Abbott and Morris 2001). The sand-pebble substrate mixture often occurs at the The pebble-rock-coral rubble substrate is considered the lower half of the intertidal zone in coastal shores. Only the most complex because of the three components of the

156 Philippine Journal of Science Batomalaque et al.: Survey and Spatial Vol. 139 No. 2, December 2010 Distribution of Shore Mollusks

substrate type and the associated algal flora. Heterogenous appears to provide supplementary food to snails such as substrates tend to provide more microenvironments (Calow Littorina sp. and a habitat or refuge from predation. and Petts 1994). Forty-six species were identified in the area, with N. chamaeleon as the most abundant. Nerita Species occurrence is determined by the substrate type. chamaeleon’s relative abundance is less than the sum of all Results of this study show that species occurrence is not dependent on the area covered by a particular substrate the other species, indicating a more dispersed assemblage. 2 Notable mollusks found were three Conus species, the type, such as that observed in the sand substrate (908 m ) which has only two species whereas there are ten species bivalve A. pectinata, and some nudibranchs (sea slugs). 2 Kohn (1968) studied Conus assemblages in Maldives and found in the wood substrate (40 m ). Chagos Islands and found that topographically diverse environments had larger species (in terms of size) but with Spatial distribution lower population densities. Atrina pectinata are sessile According to assemblage differences, two general clusters and generally live partly embedded in heterogenous soft of substrate types were generated, with the sand substrate bottoms, with the narrow anterior tip of the shell fixed as an outlier. This implied that the mollusk assemblage in downward as it filter-feeds (Morton 1983). Three different sand substrate is unique for that habitat type and did not species of nudibranchs were found but have not been occur in the other substrate types. identified to the genus level. Nudibranchs inhabit a wide range of environments from the intertidal to great depths, The first cluster consisted of the wood and sand-rock and from tropical to Antarctic regions. In the intertidal and substrates with a 0.24 difference. Both substrate types subtidal zones, nudibranchs are found in more complex were particularly abundant in limpets (Littorina sp. and substrates such as those associated with macroalgae (King Siphonaria sp.) and small bivalves (B. striatulus and I. and Fraser 2002). ephippium). The high similarity between the assemblages in both substrate types is accounted for by the fact that the The sand-rock substrate was dominated by the gastropod plots having wood substrate were distributed along those Siphonaria javanica (Lamarck) followed by the bivalve C. having sand-rock substrate. commercialis. Rocks provide a large and stable substrate for permanent attachment of C. commercialis and other The second larger cluster consisted of boulder, pebble- bivalves, and for S. javanica and all other limpets (Morton rock, sand-pebble, and pebble-rock-coral rubble 1983). substrates. The boulder and pebble-rock substrates were found to be the most similar (distance = 0.19). This could Two species dominated in the pebble-rock substrate— be partly explained by the presence of a large number of juvenile trochids and P. sulcatus. The region covered by species for both substrate types, which is probably due to this substrate type was shallow and flat, thus experiencing their physical stability, thus increasing the possibility of minimal disturbance from water currents. This substrate overlap between the two. It is noted, however, that the contained the most number of species (80 species). abundant trochids found in the pebble-rock substrates were juveniles, while those in the boulder substrates were Boulders provide wide and stable substrates. The number adults. Castell (1995) studied juvenile Trochus niloticus of individuals per species was relatively even, with the Linnaeus populations and found that as juveniles increased dominating species belonging to nacellids, littorinids, in size, there was a change in microhabitat: from pebbles and trochids. Nacellids and littorinids were found on the (<10 mm) to larger rocks and from shallow pools to exposed surfaces while trochids were at the substrate deeper pools. Several species of nerites were present and floor or bottom substrate. Due to their wide foot muscle, abundant in the four substrates. In a survey in Ceylon by nacellids are able to firmly adhere to the substrate even Atapattu (1972), nerites were among the species occurring with the strong currents. Littorinids, on the other hand, over the whole island. It is also possible that the high have relatively small foot muscle area in contact with the species similarity was by chance because these substrate substrate. It was observed that these gastropods formed types covered a larger area and were adjacent to each other. large aggregations, which appears to be an adaptive behavior to avoid the risk of dislodgement (Coleman et The clustering of substrate types reflects their actual al. 2004). locations in the island. Hence, the factors of water movement, morphology, and dispersal modes have a Only ten species were found in substrates composed role in the spatial distributions observed. The northwest of wood. Of these ten species, Littorina scabra and I. and west sides of the island, which were dominated by ephippium were the most dominant. L. scabra were found boulder substrate, were exposed to intense wave action. on the upper air-exposed regions of the fallen logs while I. Mollusk species found in these regions are particularly ephippium were found on the submerged regions. Storry adapted to exposure to such currents. Limpets, having et al. (2006) found that coarse wood debris (CWD) in the a large area of foot muscle in contact with the substrate, intertidal region of the rocky shores of Vancouver Island

157 Philippine Journal of Science Batomalaque et al.: Survey and Spatial Vol. 139 No. 2, December 2010 Distribution of Shore Mollusks

are able to suction themselves to the exposed surfaces of species. The morphological adaptations of different the boulders. Other mollusks present in the area occurred species enabled them to occur in specific habitat types. near the bottom substrate, where the water movement It is recommended that further studies should be done was less intense. Trochids, turbinids, and nerites are more in Luzon, which has been largely neglected in terms of susceptible to dislodgement than limpets due to their malacofaunal surveys. higher shell shape and lower adhesive tenacity (Rilov et al. 2004). The southern side, being a shallow reef flat that was sheltered and exposed to minimal wave action, had mollusk species that were typical of intertidal zones ACKNOWLEDGEMENTS and those that occurred in crevices in the substrate. Most This work was supported by the Ecology and bivalves occurred in this region as well. Academic Unit (ETAU) of the Institute of Biology, The effect of dispersal modes was particularly demonstrated University of the Philippines Diliman and the Grande by the littorinid species identified. Littorinids are known to Island Resort. We also thank Dr. Perry S. Ong for helpful aggregate in varying degrees among shores (Chapman and comments on the manuscript. Underwood 1989) and also show a range of reproductive strategies and dispersal modes (Underwood 1979). Some littorinids are direct developers and hence are not pelagically dispersed. Most develop planktotrophic veliger REFERENCES which disperses widely. The magnitude of their dispersal ABBOT RT, MORRIS PA. 2001. A Field Guide to Shells: is dependent on local current systems (McQuaid 1996). Atlantic and Gulf Coasts and the West Indies. USA: Littorina sp. 1 occurred only in the boulders of the west Houghton Mifflin Harcourt. 512 p. side, while P. sulcatus was most abundant in the south side. Therefore, this distribution was due to water movement. ABBOTT RT. 1991. Seashells of the World. Chicago: Littorina sp. 1 could not possibly occur in other areas Golden Press. 160 p. because the westward direction of the current restricted ATAPATTU DH. 1972. The distribution of mollusks on it to such a location. It should be noted that the westward littoral rocks in Ceylon, with notes on their ecology. direction of the water current occurs mostly throughout Marine Bio 16: 150-164. the year because the island is located at the shelved cove of Subic Bay. Planaxis sulcatus had large aggregations AZOUZI L, BOURGET E, BROCARD D. 2002. Spatial at the south side due to limited dispersal brought about variation in the intertidal bivalve Macoma balthica: by the calm water. biotic variables in relation to density and abiotic factors. Mar Ecol Prog Ser 234:159-170. Human activities also appeared to play a role in species occurrence. The north and east sides, which were most BERDACH JT. 1981. Inventory of marine gastropods frequented by resort guests, had the least number of in the Man and the Biosphere (MAB) Reserve area, species, while the west and south sides had the most Puerto Galera, Oriental Mindoro, Philippines. Philipp number of species. J Biol 10(1):95-108. It is however noted that such factors—wave action and BOUCHET P, LOZOUET P, MAESTRATI P, HEROS human activity—were not quantified. V. 2002. Assessing the magnitude of species richness in tropical marine environments: exceptionally high numbers of mollusks at a New Caledonia site. Biol J Linnean Soc 75 (4): 421 – 436. CONCLUSION CALOW P, PETTS GE. 1994. The Rivers Handbook. Wiley-Blackwell. 536 p. Results from this study demonstrate a rich assemblage of shoreline malacofauna in Grande Island using CASTELL L. 1995. Population studies of juvenile Trochus the continuous 2x2 m quadrat sampling technique. niloticus on a reef flat on the northeastern Queensland This study provides a preliminary look at the spatial coast, Australia. Mar Freshwat Res 48(3)211-217. distributions of shore mollusks around Grande Island. CHAPMAN MG, UNDERWOOD AJ. 1989. Experimental It was found that mollusks were distributed according analyses of the influences of topography of the to the type (composition and particle size) of substrate substratum on movement and density of an intertidal and distribution is independent of the total area. snail, Littorina unifasciata. J Exp Mar Biol Ecol 134: Substrates that are loose or unstable tend to have only 175-196. few species while those that are compact have more

158 Philippine Journal of Science Batomalaque et al.: Survey and Spatial Vol. 139 No. 2, December 2010 Distribution of Shore Mollusks

COLEMAN RA, UNDERWOOD AJ, CHAPMAN MG. [PBCPP] Philippine Biodiversity Conservation Priority- 2004. Absence of costs of foraging excursions in relation setting Program. 2002. Philippine Biodiversity to limpet aggregation. J Appl Ecol 73(3):577-584. Conservation Priorities: A Second Iteration of the National Biodiversity Strategy and Action Plan: Final DANCE PS. 1976. The World’s Shells. New York: Report (Ong PS, Afuang LE, Rosell-Ambal RG Ed.). McGraw Hill Book Company. 192 p. Quezon City: Protected Areas and Wildlife Bureau- DE ARRUDA E, AMARAL C. 2003. Spatial distribution Department of Environment and Natural Resources, of mollusks in the intertidal zone of sheltered beaches Conservation International-Philippines, Biodiversity in southeastern Brazil. Rev Bras Zool 20(2): 291-300. Conservation Program-University of the Philippines Center for Integrative and Developmental Studies. EL-SHAARAWI AH, PIEGORSH WW. 2002. 114 p. Encyclopedia of Environmetrics. Australia: John Wiley and Sons. 2502 p. POPPE GT. 2008a. Philippine Marine Mollusks, Volume 1: Gastropoda. Germany: Conchbooks. 758 pp. HALL R. 1997. Cenozoic plate tectonic reconstructions of SE Asia. J Geol Soc 120: 11-23. POPPE GT. 2008b. Philippine Marine Mollusks, Volume 2. Germany: Conchbooks. 849 p. HINTON A. 1972. Shells of New Guinea and the Central Indo-Pacific. UK: Rigby Limited. 94 p. RILOV G, BENAYAHU Y, GASITH A. 2004. Life on the edge: do biomechanical and behavioral adaptations to [IUCN] International Union for the Conservation of wave-exposure correlate with habitat partitioning in Nature. 2004. 2004 IUCN Red List of Threatened predatory whelks? Mar Ecol Prog Ser 282: 193-204. Species. Accessed on August 2008. www.redlist.org SNEATH PHA, SOKAL RR. 1973. Numerical Taxonomy: KING D, FRASER V. 2002. More Reef Fishes and the Principles and Practice of Numerical Classification. Nudibranchs: East and South Coast of Southern Africa. San Francisco: W.H. Freeman and Co. 573 p. South Africa: Struik. 136 p. SPRINGSTEEN FJ, LEOBRERA FM. 1986. Shells of the KOHN AJ. 1968. Microhabitats, abundance and food of Philippines. Manila: Carfel Seashell Museum. 377 p. Conus on atoll reefs in the Maldive and Chagos Islands. Ecology 49(6):1046-1062. STORRY KA, WELDRICK CK, MEWS M, ZIMMER M, JELINSKI DE. 2006. Intertidal coarse woody LEGENDRE P. 1998. Numerical Ecology, 2nd ed. debris: a spatial subsidy as shelter or feeding habitat for Netherlands: Elsevier Science and Technology. 853 p. gastropods? Estuar Coast Shelf Sci 66(1-2):197-203. MARSH JA. 1964. Cone Shells of the World. Brisbane: UNDERWOOD AJ. 1979. The ecology of intertidal Jacaranda Press. 185 p. gastropods. Adv Mar Biol 16: 111-210. MCQUAID CD. 1996. Biology of the gastropod family VALLEJO BM. 2001. The biogeography of Philippine Littorinidae: I. Evolutionary aspects. Oceanogr Mar marine mollusks. Loyola Schools Review 1:58-77 Biol Annu Rev 34: 233-262. YONGE CM. 1968. Form and habitat in species of MORTON B. 1983. The Sea Shore Ecology of Hong Malleus (including the "hammer oysters") with Kong. Hong Kong: Hong Kong University Press. comparative observations on Isognomon isognomon. 350 p. Biol Bull 135:378-405. OWEN J. 1982. Feeding Strategy. USA: University of Chicago Press 160 p.

159