Memoria de la Fundación La Salle de Ciencias Naturales 2009, 171: 81-98

Mollusk assemblages in seagrasses and macroalgal rocky shores in : implementing the NaGISA Protocol

Patricia Miloslavich and Elizabeth Huck

Abstract. The biodiversity of mollusks associated to Thalassia testudinum beds and rocky shores was determined using the NaGISA protocol at two sites of the Venezuelan , one in the upwelling region (Laguna de Bocaripo and Isla Caribe) and the other in a non-upwelling typical tropical area (Morrocoy). Mean density of mollusks at the seagrass bed was 227ind/m2 at Las Luisas and 193ind/m2 at Guayacán, while at rocky shores it was 83ind/m2 at Cayo Sal and 371ind/m2 at Isla Caribe. Five bivalve species were found at Las Luisas (e. g. Parvilucina multilineata, Lucina nazula) and 3 gastropods (e. g. Cerithium atratum, Tricolia tesselata). At Guayacán, 5 bivalve species (e. g. Brachidontes modiolus) and 6 gastropods (e. g. Prunum prunum) were found. At Cayo Sal, only 1 bivalve species (Barbatia cancellaria) and 8 gastropods (e. g. Cerithium literatum) were found, while at Isla Caribe, 11 species of gastropods were found (e. g. Pyrgophorus parvulus). No common species were observed between the upwelling and non-upwelling zones with the exception of the bivalve Corbula caribaea (seagrasses). Within each area, no common species were observed between rocky shores and seagrasses with the exception of the gastropod Cerithium atratum that was found at both in Morrocoy. Key words. Thalassia testudinum. Bivalvia. Gastropoda. NaGISA protocol. Caribbean.

Comunidades de moluscos asociadas a praderas de fanerogamas marinas y litorales rocosos con macroalgas en Venezuela: implementacion del Protocolo NaGISA

Resumen. Se determinó la biodiversidad de moluscos asociada a la fanerógama Thalassia testudinum y a litorales rocosos, a través del protocolo NaGISA en dos sitios de la costa Venezolana, uno en una zona de surgencia (laguna de Bocaripo e Isla Caribe) y otro en una zona típica tropical (Morrocoy). La densidad promedio de moluscos en las praderas fue de 227ind/m2 en Las Luisas y 193ind/m2 en Guayacán mientras que en litorales rocosos fue de 83ind/m2 en cayo Sal y 371ind/m2 en Isla Caribe. En Las Luisas se encontraron cinco especies de bivalvos (p. ej. Parvilucina multilineata, Lucina nazula) y tres de gasterópodos (p. ej. Cerithium atratum, Tricolia tesselata). En Guayacán se hallaron cinco especies de bivalvos (p. ej. Brachidontes modiolus) y seis de gasterópodos (p. ej. Prunum prunum). En cayo Sal se ubicó una especie de bivalvo (Barbatia cancellaria) y ocho de gasterópodos (p. ej. Cerithium literatum), mientras que en Isla Caribe se encontraron once especies de gasterópodos (p. ej. Pyrgophorus parvulus). No se hallaron especies comunes entre las zonas de surgencia y de no surgencia a excepción del bivalvo Corbula caribaea (fanerógamas). Para una misma localidad, tampoco se pudo observar especies comunes entre litorales rocosos y praderas de fanerógamas a excepción del gasterópodo Cerithium atratum que se encontró en ambas (Morrocoy). Palabras clave. Thalassia testudinum. Bivalvia. Gastropoda. Protocolo NaGISA. Caribe. 82 Biodiversity of mollusks using the NaGISA Protocol

Introduction

Biodiversity has been a subject of interest for many decades by scientists and conservationists. More recently, other groups such as managers, government agencies and industries have also been involved in establishing its ecological and economical value, as well as the consequences of its loss. Despite the significant amount of research carried out in the oceans, marine biodiversity remains greatly underestimated (Lambshead 1993, Williamson 1997). Up to date, an important number of recent papers have attempted to identify the importance of biodiversity for ecosystem functioning (Loreau et al. 2001, Pachepsky et al. 2001, Cardinale et al. 2002, Pfisterer and Schmidt 2002, Gessner et al. 2004), as well as established its relevance in measuring biological and ecological parameters such as competition, predation, recruitment, and productivity (Petraitis et al. 1989, Bourget et al. 1994, Elis et al. 1996, Worm et al. 1999, Mittelbach et al. 2001, Yamamura et al. 2001, Paine 2002). Coastal marine ecosystems have a very high biodiversity (Ray 1996). Within these, the macroalgal habitats and seagrass communities rank among the highest, due to the fact that they constitute three-dimensional structures, providing substrate, food and habitat complexity, that increases species richness (van Oppen et al. 1996, Phillips 1997, Walker and Kendrick 1998, Duarte 2000, Wysor et al. 2000, 2001, Duffy et al. 2001, Engelhardt and Ritchie 2001, Bulleri et al. 2002, Sommerfield et al. 2002). On the other hand, these coastal areas are also severely impacted by human activities such as fi s h e r ies ove rex p l o i tation, alte ration of the physical env i r onment, pollution, introduction or invasion of alien species, and recreational activities, all of which have inevitably impoverished marine biodiversity (Beatley 1991, Norse 1993, Gray 1997a, Walker and Kendrick 1998, Cury 1999, Bax et al. 2001, Tilman and Lehman 2001, Piazzi et al. 2001, Barnes 2002). In this sense, the study of biodiversity is crucial for the sustainable use of coastal resources, both for conservation and management (Gray 1997, Price 2001), especially in Marine Protected Areas (Ray 1985, Olsen 1999, Ward et al. 1999). Biodiversity has been measured at many different levels and scales and by different methods (France and Rigg 1998). This, has made comparisons difficult, so a unified approach to study biodiversity at a global scale is much needed (Rabb and Sullivan 1995, Valero et al. 1998, Mikkelsen and Cracraft 2001). As a response to this need, the Census of Marine Life (CoML) program and its associated projects provide the necessary framework to study biodiversity at a global scale. Na G I SA or National Geogra p hy in Shore Areas Na G I SA web page : www.nagisa.coml.org (http://www.nagisa.coml.org/Protocol.htm) is an official Census of Marine Life (CoML) field project since 2000. It is a collaborative effort focused on the shore area, which is the most diverse marine zone and the most heavily affected by humans. NaGISA accomplishes its objectives by using a simple, standard and economic protocol in hard substrate macroalgal communities and in soft bottom seagrass beds at less than 20 m depth. Venezuela was incorporated to the NaGISA Mem. Fund. La Salle de Cienc. Nat. 171 83

project in 2005 when the South American region was organized to estabablish sampling sites every 20 degrees of latitude in a north-south gradient along the Caribbean Sea, the Atlantic and the Pacific oceans. In January 2006, the First NaGISA Southamerica and Caribbean Protocol Workshop was carried out in a seagrass bed and macroalgal rocky shore at the venezuelan site of Morrocoy National Park. The community structure associated to seagrass beds has been studied by an increasing number of researchers in a wide spatial scale (Heck 1977, Kenneth and Westone 1977, Stoner 1980a, b and c, Doering and Bone 1983, Lewis and Stoner 1983, Bell and Westoby 1986, Lewis 1987, Bitter 1988, Edgar 1990, Isea 1994, Holmquist 1997, Alvarado 2000, Atienza 2000, Eckrich and Holmquist 2000, Huck 2001). The same can be said about macroalgal hard bottom communities, in which an important background of marine ecological theories are based in experimental research carried out in these ecosystems on competition, herbivory, predation, disturbance, food web complexity, and community organization (Connell 1961, Paine 1966, Dayton 1971, Lubchenco 1978, Underwood et al. 1983, Underwood and Denley 1984, Robles and Desharnais 2002, Underwood 2000, Witman and Dayton 2001). Within both of these ecosystems, mollusk assemblages are a good example to be used as models in community dyanamics since they inhabit a variety of ecological niches (Isea 1994, Levinton 1995, Nybakken 1997, Huck 2001), are easily collectable, preserved and identified, and several local (Bitter 1988, Jiménez 1994, Klein and Cruz 1997, Lodeiros et al. 1999, Huck 2001 for Venezuela), regional (Warmke and Abbott 1961, De Jong and Coomans 1988, Díaz and Puyana 1994, for the Caribbean), and global (Abbott 1974, Abbott and Dance 1982) studies of their abundance and distribution in different communities are available. In order to establish a long-term monitoring program in Venezuela by using the NaGISA protocol as well as to compare the biodiversity at two environmentally different conditions (upwelling and not upwelling), we have carried out seagrass and rocky shore sampling at four sites along the coast of Venezuela. In this paper we provide the inventory of mollusks for each of these sites and discuss our findings in comparison to other biodiversity initiatives in the country.

Materials and Methods Description of localities Sampling was carried out at two Thalassia testudinum beds (Las Luisas and Bocaripo ) and two macroalgal rocky shores (Cayo Sal and Isla Caribe) (Table 1). Las Luisas and Cayo Sal are located at Morrocoy National Park (MNP), a tropical environment located in the northwestern coast of Golfo Triste, Venezuela, between 10°52’N and 69°16’W (Figure 1). This 320 Km2 park includes continental, insular, and marine ecosystems divided in a seaward zone and an inshore zone. The first is connected to the open ocean and is characterized by coralline communities, the 84 Biodiversity of mollusks using the NaGISA Protocol

second is characterized by , mainly of Rhizophora mangle, and sea grass beds of Thalassia testudinum (Bitter 1988, Bone et al. 1998).

Table 1. Density of mollusks at the sampling localities (ind/m2). Values indicate mean ± standard deviation between the five replicas (cores or quadrats according to the case). Numbers in parenthesis indicate range.

Locality Gastropods Bivalves Total

Las Luisas (seagrass) 136.4 ± 191.0 90.9 ± 86.2 227.3 ± 208.8 (114-284) (57-114) (57-398) Guayacán (seagrass) 79.6 ± 95.1 193.2 ± 182.4 113.6 ± 106.3 (57-227) (57-227) (57-455) Cayo Sal (rocky shore) 80.0 ± 136.7 3.2 ± 7.2 83.2 ± 134.5 (16-320) (0-16) (16-320) Isla Caribe (rocky shore) 371.2 ± 474.6 0 371.2 ± 474.6 (112-1040) (112-1040)

Since 1974, the park has been subject to intense tourism, which extensively stresses the marine communities, and to natural phenomena causing mass mortalities of marine organisms (Laboy et al. 2001). In 2000, the park was declared a priority research area to evaluate the degree of alteration, disturbance and pollution in its different marine environments. Consequently, the physical, biological and social components of the park have been studied in a coordinated way (Miloslavich et al. 2005). Las Luisas (10°51’23’’N-69°19’30’’W), is a very calm, semi-enclosed bay, bordered by mangroves. It reaches a depth of up to 5 m, the bottoms are characterized by fine sand and mud, and covered mostly by a dense seagrass bed of Thalassia testudinum, with some patches of macroalgae of the genera Halimeda and Dyctiota. Cayo Sal (10°58.234’N-68°22.147’W) is one of the many coralline keys that conform the park, which used to be surrounded by a fringing coral up to 10 m depth. Nowadays, most of the coral species in the shallow sector of this reef have died mainly due to sedimentation, and the hard substrate left by the dead corals has been colonized by macroalgae. Water temperatures at Morrocoy range between 24-30 °C. Bocaripo Lagoon and Isla Caribe are located in the east upwelling region near Chacopata, between 10°34’-10°36’N and 64°01’-64°04’W (Figure 1). Chacopata is located at the northeast of the Araya Peninsula, it is under the influence of the upwelling system of the Cariaco Gulf and has a high biological productivity (Muller- Karger et al. 1989). In this area, one of the largest populations of the bivalve Arca zebra (“Pepitona”) of the Venezuelan coast is found (Prieto et al. 2001), constituting the main economic source for the human settlements of Chacopata and Guayacán. The first sampling site in this area is at Guayacán (10°39’08”N-63°49’44”W), located at the east of the mouth of Bocaripo Lagoon (Guayacan). This site is Mem. Fund. La Salle de Cienc. Nat. 171 85

characterized by patchy Thalassia testudinum beds among muddy bottoms. The lagoon and part of the coastline in this sector are surrounded by mangroves (Prieto et al. 2003). This system is very homogeneous environmentally and physiographically, it has a natural channel that connects it to the sea and the seasonal hydrological conditions are the only source of oceanographic change (Olivero 1984). Prior to our field work (February 2006), heavy rains affected the area for several days and caused the lagoon to overflow with freshwater, influencing the salinity of the seagrass site. The second sampling site in this area was the patchy rocky shore at Isla Caribe (10°41’24’’ N-63°51’7’’W), a small island located between the mainland Morro de Chacopata and Margarita Island at the north of the Araya Peninsula. The habitat is a mixture of sandy patches, Thalassia testudinum beds, coral rocks, and a discontinuous, shallow rocky shore covered with macroalgae. This area is relatively undisturbed by human activities, however, a small population of local fisherman is established in this island. Water temperatures at the Chacopata region may vary between 22-29 °C, however, during the upwelling season, it may decrease to 18 °C.

Figure 1. Map of the Venezuelan coast showing the sampling localities.

Field and laboratory protocol The NaGISA protocol (http://www.nagisa.coml.org/Protocols) was used to collect mollusk samples, and determine seagrass and macroalgal biomass as well as the number of Thalassia testudinum shoots. A total of 5 cores (15 cm in diameter), separated by 20-30 m each were taken at the seagrass beds at a depth of 1 m. At the rocky shoresthe NaGISA protocol establishes that sampling should be done in the high, mid and low intertidal as well as at 1 m depth, however, we were able to collect only at 1 m depth due to the fact that the tidal regime in these areas of Venezuela is very narrow (less than 25 cm), so the intertidal zone is very limited and does not get exposed to air due to wave action. Also, the rocky shores at these localities are very shallow and do not extend beyond 1.5 m in depth. A total of 5 (25 x 25 cm) quadrats were grasped for fauna, separated by 15-20 m each. The sites at Morrocoy National Park were sampled in January 2006 during the “First NaGISA Southamerica and Caribbean Protocol Workshop” and the two sites at Chacopata were sampled as part 86 Biodiversity of mollusks using the NaGISA Protocol

of the field activities carried out in the Marine Biology Course (Universidad Simón Bolívar) in February 2006 with student’s assistance. We must point out that that the USB- Marine Biology course has visited the Bocaripo Lagoon for several years. This particular year, the conditions in the lagoon were different from the rest of the years due to unusual and out of season heavy rainfalls which altered the salinity and increased the amount of suspended matter (therefore decreasing transparency) in the water column at the lagoon.

Results Mollusk fauna A total of 183 gastropod and bivalve individuals were collected; of these, 34 were sampled on the seagrasses (19 at Las Luisas and 17 at Guayacán) and 145 on the rocky shores (17 at Cayo Sal and 116 at Isla Caribe). In the seagrasses, gastropod density varied between 114-284 ind/m2 at Las Luisas and between 57-227 ind/m2 at Guayacán, and bivalve density varied between 57-114 ind/m2 at Las Luisas and between 57- 227ind/m2 at Guayacán (Table 1). A total of 11 individuals of 3 gastropod species were collected at Las Luisas, being Cerithium atratum and Tricolia tesselata the most abundant with a density of about 57 ind/m2. At Guayacán, we collected 7 gastropod individuals of 6 species, of which Prunum prunum was the most common with a density of about 23 ind/m2. In relation to bivalve species, we found 8 individuals of 5 species at Las Luisas, being Parvilucina multilineata the most abundant with a density of about 34 ind/m2. At Guayacán, we found 10 individuals of 5 species, being Brachidontes modiolus the most abundant with a density of about 34 ind/m2 (Table 2). In the rocky shores, gastropod density varied between 16-320 ind/m2 at Cayo Sal and between 112-1040 ind/m2 at Isla Caribe, and bivalve density varied between 0-16 ind/m2 at Cayo Sal. No bivalves were found at Isla Caribe (Table 1). A total of 16 individuals of 8 gastropod species were collected at Cayo Sal, being Cerithium literatum the most abundant with a density of about 16 ind/m2. At Isla Caribe, we collected 116 gastropod individuals of 11 species, of which Pyrgophorus parvulus was the most common (61 individuals) with a density of about ind/m2. In relation to bivalve species, we found only 1 individual of Barbatia cancellaria at a density of about 3 ind/m2 at Cayo Sal (Table 3). Plant biomass The number of T. testudinum shoots at Las Luisas ranged between 1056-6096 and between 16-80 shoots/m2 at Guayacán. Plant total biomass in fresh weight ranged between 193-4306 gr/m2 at Las Luisas and between 465-2431 gr/m2 at Guayacán (Table 4). Total macroalgal fresh biomass at Cayo Sal ranged between 236-4662 gr/m2 (Table 5). Mem. Fund. La Salle de Cienc. Nat. 171 87

Table 2. Inventory, density and abundance of gastropods and bivalves (ind/m2) found at the seagrass localities.

Density (ind/m2) Locality Gastropod species # species Abundance Mean SD Cerithium atratum 56.82 127.05 LL Cerithium eburneum 22.73 50.82 3 11 Tricolia tesselata 56.82 80.35 Crepidula navicula 11.36 25.41 Gibberula avadne 11.36 25.41 G Prunum prunum 22.73 50.82 6 7 Pyramidella crenulata 11.36 25.41 Terebra protexta 11.36 25.41 Volvarina albolineata 11.36 25.41 Locality Bivalve species LL Corbula caribaea 11.36 25.41 Lucina nassula 22.73 31.12 Lucina pectinata 11.36 25.41 5 8 Parvilucina multilineata 34.09 50.82 Tellina mera 11.36 25.41 Arca imbricata 22.73 50.82 Corbula caribaea 22.73 31.12 5 10 G Corbula contracta 22.73 31.12 Crasinela lunulata 11.36 25.41 Brachidontes modiolus 34.09 50.82

Table 3. Inventory, density and abundance of gastropods and bivalves (ind/m2) found at the rocky shore localities.

Density (ind/m2) Locality Gastropod species # species Abundance Mean SD Cerithium atratum 6.40 14.31 Cerithium literatum 16.00 22.63 Columbella mercatoria 3.20 7.16 CS Hemitoma octoradiata 3.20 7.16 8 16 Pilbryspira albocinta 3.20 7.16 Rissoina catesbyana 3.20 3.16 Simnia uniplicata 9.60 21.47 Tricolia tesselata 6.40 14.31 Anachis coseli 3.20 7.16 Anachis obesa 3.20 7.16 Anachis pulchella 6.40 14.31 Bittium varium 3.20 7.16 Mitrella ocelata 25.60 33.18 IC Pisania tincta 3.20 7.16 11 116 Planaxis nucleus 12.80 28.62 Pyrgophorus parvulus 195.20 436.48 Siphonaria pectinata 22.40 50.09 Tegula viridula 19.20 34.69 Tricolia affinis 76.80 154.46 Locality Bivalve species CS Barbatia cancellaria 3.20 7.16 1 1 88 Biodiversity of mollusks using the NaGISA Protocol

Discussion Seagrass beds The composition of gastropod species at both seagrass localities, one in the central west and the other in an upwelling focus in the east coast, was completely different with no species in common, however, the species Cerithium atratum was found at both the seagrass bed and the rocky shore at Morrocoy National Park. Regarding bivalves, only one species was found to be common for both localities (Corbula caribaea). This difference in species assemblages could be due to the fact that the zones have different spatial and temporal variations in species composition (Huck 2001, Prieto et al. 2006), or to the low number of samples collected at both sites. Our results would indicate that these sites have a low abundance and biodive rsity of mollusks, howeve r, th i s contradicts the available literature that reports a high biodiversity of this group at Morrocoy (Miloslavich et al. 2005), at Bocaripo (Prieto et al. 2006) and at the nearby area of Mochima (Jiménez-Prieto 1994, Jiménez-Prieto et al. 2000, Prieto et al. 2003). In this sense, a previous study of the mollusk community at Las Luisas carried out during 2000 with a comparable methodology (Miloslavich et al. 2005), reported a total of 28 species at this area (Alvania auberiana, Antillophos candei, Assiminea succinea, Bittium varium, Bulla striatta, Caecum cornucopiae, C. pulchellum, Careliopsis bermudensis, C. octona, Cerithiopsis emersoni, C. greeni, Cerithium eburneum, C. atratum, Crepidula navicula, Cyclostremiscus pentagonus, Eulima compsa, Finella a d a n s i, Modulus modulus, O d o stonia canaliculata, P y r g o c y th a r a cox i, R i s s o i n a catesbyana, Solariorbis cupidinensis, Tricolia tesselata, Turbo castanea, T. arnoldoi, T. ornatta, T. pyrrha, and Zebina browniana), a number significantly higher than in our present study. Also, total gastropod abundance and density in the previous study at Las Luisas has been reported to range between 8012 and 31296 ind/m2 (Miloslavich et al. 2005). At Guayacán, Prieto et al. (2006), also found a much higher number of species to those found in our study. For this area, they reported 18 gastropod species (Bulla striata, Crepidula convexa, C. glauca, C. plana, Engoniophos unicinctus, Facsiolaria t u l i p a, Haminoea antillaru m, M e l o n g ena melonge n a, M i t rella lunata, M u r ex chrysostoma, M. recubirrostris, Nassarius albus, N. vibex, Oliva reticulata, Olivella sp., Persicula interruptolineata, P. rosvelti and Prunum prunum), of which only Crepidula navicula and Prunum prunum were collected in our study, and 13 bivalve species (B ra ch i d o n tes ex u st u s, Chione cancellata, C ra s s o st re a rh i z o p h o ra e, M . americanus, M. squamosus, Musculus lateralis, Ostrea equestris, Perna perna, Perna viridis, Pinctada imbricata, Pitar albidus, Tellina sp. and Trachicardium muricatum), none of them collected in our study. The total area in which Prieto et al. (2006) collected these 33 mollusk species was 16 m2. The total abundance was 354 individuals, which represents about 22 ind/m2, a number which is much lower to our result of almost 200 ind/m2, having sampled a total area of less than 1 m2 (0.088 m2). This discrepancy is probably due to the fact that sampling 5 cores of 0.0176 m2 each in a seagrass is not enough to give an accurate idea of the mollusk assemblage because Mem. Fund. La Salle de Cienc. Nat. 171 89

in the first place, it is underestimating the biodiversity, and in the second place, it is overestimating the abundance and density, especially if the species are distributed in patches. On the other hand, we found a high variability in mollusk density between samples. This could be the result of the patch distribution of mollusks in the seagrasss bed (Huck 2001), and it also confirms that 5 cores are not enough to characterize the species composition in such a dynamic environment.

Table 4. Number of shoots (shoots/m2) and fresh biomass (gr/m2) of Thalassia testudinum at the seagrass localities.

# shoots/ m2 Fresh weight (gr/m2) Locality Mean SD Mean SD LL 3228.80 2172.45 2669.07 1758.01 G 48.00 32.00 1436.00 983.11

Table 5. Macroalgal biomass (gr/m2) at Cayo Sal rocky shore.

Fresh weight (gr/m2) Locality Mean SD

CS 3193.37 2239.58

In relation to other studies carried out in Venezuela and the Caribbean, we found that the number of species we found at both Morrocoy and Guayacán seagras beds is lower than those reported in the literature. In the northeast coast of Venezuela, Vera (1978) found a total of 56 mollusk species, Graterol (1986) found a total of 75 species at two localities of the Cariaco Gulf, of which 36 were bivalves and 35 were gastropods. Bitter (1988) reported 9 species of mollusks for Morrocoy National Park and Rebolledo et al. (1993) found 30 species of gastropods and 8 species of bivalves also for Morrocoy. Almeida (1974) reported a total of 24 mollusk species at seagrass beds also of Thalassia testudinum between Patanemo and Punta Tucacas in the central west coast of Venezuela. Within other Thalassia testudinum beds in the Caribbean, Jackson (1972) reported 72 species at Jamaica, and Bello (1989) reported 29 species of gastropods at the Virgin islands. Howard (1987) reported day-night variations in the abundance of the motile epifauna associated to seagrass beds of Halodule wrightii and Syringodium filiforme in Florida, however, species composition did not show diel variations. As a general rule, the diversity and density of species are correlated with habitat diversity. In the case of a seagrass bed, habitat diversity would increase with an increase in seagrass biomass or an increase in the number of shoots (Heck and Welstone 1977, Heck and Orth 1980). Despite the fact that using plant biomass to predict the abundance of the epifauna is debatable (Virstern and Howard 1987), studies have 90 Biodiversity of mollusks using the NaGISA Protocol

shown that mollusk biodiversity is higher in substrates covered by seagrasses in comparison to bare substrates (Miloslavich et al 2005). In the present study, we found a higher density of mollusks at Las Luisas in comparison to Guayacán, as well as a higher number of shoots at Las Luisas (3228 shoots/m2) and biomass (2669 gr/m2 of humid weight) than at Guayacán (48 shoots/m2 and 1436 gr/m2 of humid weight). Our findings support the theory that the abundance of epifauna could be related to plant biomass. Huck (2001) pointed out that other factors to be considered as predictors of epifaunal abundance are the amount of plant dead tissue as well as the organic matter in the sediment. This work reports that the composition and abundance of gastropods at several seagrass locations of Morrocoy National Park, were directly related to particle size, amount of dead tissue of Thalassia testudinum and the amount of organic matter in the sediment suggesting that this gastropod assemblage depended mainly on decaying organic matter due to the fact that most species found had been reported to be detritivorous. Finally, we have to mention the unusual rainy conditions at Guayacán during our field trip in comparison to other years as mentioned earlier. The consequences of this out of season rains, were a very poor visibility due to sedimentation and a very stressed seagrass (the seagrass was very scarce in terms of shoots and a high number of dead leaves were observed floating). In an earlier campaign to this site, we reported a mean mollusk density of 48.58+36.73ind/m2 and an ave ra g e biomass of T h a l a s s i a testudinum of around 500 g/m2 (dry weight) (Miloslavich et al. 2003). Mollusk densities are lower than those found in the present study, however plant biomass was much higher. This decrease in plant biomass could be related to a lower benthic diversity and abundance as a consequence of lack of substrate and lack of food for herbivores, however, this was not observed. Most of the species here reported feed mostly in particulate organic matter. Rocky shores The composition of gastropod species at both rocky shore localities, one of them being a changing ecosystem from a reef to a macroalgal community in tropical conditions, and the second being a non-continuous and patchy environment of rocks, sand and Thalassia testudinum in an upwelling system, was completely different with no species in common. Regarding bivalves, only one species (Barbatia cancellaria) was found at only one of the localities (Cayo Sal). This species was reported to be “rare” at the central coast of Venezuela (Almeida 1973). As well as in seagrasses, the difference in species assemblages could be due to different spatial and temporal variations in species composition at both sites, to local environmental conditions and/or to the low number of samples collected. In rocky shores, particularly, patchiness is considerable, and mostly produced by the main habitat forming species, so predicting along-shore variations in the community structure is even more difficult (Witman and Dayton 2001). As in seagrasses, our results would indicate that these sites have a low abundance and biodiversity of mollusks. Mollusk studies in rocky shores are not very common in Mem. Fund. La Salle de Cienc. Nat. 171 91

Venezuela, and very few literature is available. Almeida (1973) found at the rocky shores of the central coast of Venezuela about 48 species of mollusks, being the most common species Cittarium pica, Fissurella nodosa, Isognomon radiatus, Littorina mespillum, L. ziczac, Nerita versicolor, Nodilittorina tuberculata and Purpura patula. In the Caribbean, Cittarium pica (“Quigua”) constitutes the second most important exploited gastropod species after the Queen Conch, Strombus gigas (Gómez Gaspar 1999). Rodríguez (2003) points out that the fishing pressure on C. pica in Venezuela is not sustainable and that captures have been decreasing. At the moment, the “Quigua” has been classified as an “insufficiently known” species in the Venezuelan Red Book (Rodríguez and Rojas-Suárez 1999). In the Colombian Caribbean, an extensive study of the reef associated molluskan fauna, reported a total of 201 species collected between 1982 and 1989 at seven localities in the Santa Marta area (Díaz et al. 1989- 1990). Since one of our localities used to be a , it would be interesting to study the replacement of species from one ecosystem to the other and detect changes in biodiversity. Unfortunately, no information about mollusk assemblages was collected at Cayo Sal while it was a coral reef to make comparisons. Finally, we must emphasize on the importance of studying marine biodiversity not only as part of a monitoring program, but also to understand the zoogeographic tendencies of this taxonomic group. In the southern Caribbean (Colombia and Venezuela), Díaz (1995) reported a gastropod fauna with 40% of endemism, enough to consider this region as a separate zoogeographic subregion, and on this basis, he proposed three major discrete subprovinces. Díaz (1995) also suggested that the zoogeographic tendencies found in the distribution patterns of marine gastropods can be explained by a combination of historic biogeographic (links of the present fauna to the Eastern Pacific) and dispersal factors, as well as to regional environmental features such as the trade-wind induced upwelling along the of Colombia and Venezuela. In order to obtain valuable data to compare locally and with the rest of the region, we must refine the NaGISA protocol in the sense of taking more samples at each locality. Since we obtained such high variability between samples (standard deviations were higher than the mean values), and the total sampled area was small in comparison to other studies, we must make an extra effort that will allow us to have a better and more accurate idea of the mollusk community and in general, of the invertebrate assemblages associated to these habitats. Since we are not sampling an intertidal zone as such and the rocky shore habitat does not extend below 1 m depth, we suggest to concentrate all the effort of a complete NaGISA protocol (five samples at five different depths) in the very narrow zone that we have available. 92 Biodiversity of mollusks using the NaGISA Protocol

Acknowledgements. We wish to thank the NaGISA headquarters at the Seto Marine Laboratory, University of Kyoto, Japan, for their support for the NaGISA Workshop in Venezuela as well as to the Decanato de Investigación y Desarrollo, Universidad Simón Bolívar, Venezuela, for additional support. We are also indebted to all the people who helped in collecting and sorting the samples, both participants from the workshop and to the Marine Biology students of 2006: Juan José Cruz (1), Brenda Konar (2), Alberto Martín (1), Maickel Armenteros (3), Andrés Averbuj (4), René Ayala (1), Pelle Boberg (1), Marco Caputo (1), Ana Karinna Carbonini (1), Maximiliano Cledón (4), Erminda Couto (5), Manuel Cruz (6), Omar Defeo (7), Paulo Lana (8), Falk Huettmann (2), Nicida Noriega (1), Manuel Ortiz (3), Norman Quinn (9), Marina Quiñe (10), Martín Rada (11), Pedro Recarte (1), Nadia Santodomingo (12), Jeffrey Sibajas (13), Federico Tapella (14), David Thompson (15), Wilhelm Trujillo (1), Silvina van der Molen (16) and Ana Yranzo (1).

(1)Universidad Simón Bolívar, Venezuela; (2) University of Fairbanks, USA; (3) Universidad de La Habana, Cuba; (4) Universidad de Buenos Aires, Argentina; (5) Universidad Estadal de Santa Cruz, Brazil; (6) Instituto Oceanográfico de la Armada INOCAR, Ecuador; (7) Universidad de la República, Uru g u ay; (8) Un i ve rsidad Fe d e ral do Pa rana, Brazil; (9) Discove ry Bay Laboratory, Jamaica; (10) Instituto del Mar del Perú IMARPE, Perú; (11) Fundación La Salle de Ciencias Naturales, Venezuela; (12) Instituto de Investigaciones Marinas y Costeras INVEMAR, Colombia; (13) Universidad de Costa Rica; (14) CADIC, Argentina; (15) Fundación Huinay, Chile; (16) CENPAT, Argentina.

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Recibido: 27 septiembre 2007 Aceptado: 2 febrero 2009

Patricia Miloslavich and Elizabeth Huck Universidad Simón Bolívar, Departamento de Estudios Ambientales, Caracas, Venezuela. [email protected], [email protected]