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Food Availability for Particle-Feeding Bivalves, Anadara spp., inFijiAuthor(s): Yousef A. E. S. M. Buhadi, Toru Kobari, Kei Kawai, TomokoYamamoto, Hiroshi Suzuki, Satoru Nishimura, Takashi Torii, and Joeli VeitayakiSource: Pacific Science, 67(4):539-551. 2013.Published By: University of Hawai'i PressDOI: http://dx.doi.org/10.2984/67.4.5URL: http://www.bioone.org/doi/full/10.2984/67.4.5

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Pacific Science (2013), vol. 67, no. 4:539 – 551 doi:10.2984/67.4.5 © 2013 by University of Hawai‘i Press All rights reserved

539

Particle-feeding bivalves occur abun-dantly in coastal areas. They feed not only on phytoplankton, but also on zooplankton, small benthic organisms, and suspended par-ticles ( Jørgensen 1996, Richard 1996, Lehane and Davenport 2002, Gosling 2003). They are also a major food source for fish, birds, and mammals (Richard 1996). Thus, particle-feeding bivalves directly link energy flow be-tween lower and higher trophic levels in the coastal ecosystems. This short-cut linkage of energy flow results in high ecological effi-

ciency and thus high productivity for the bi-valves (Lalli and Persons 1993). Because of their high productivity and easy collection, particle-feeding bivalves are a major fishery resource. According to the Food and Agricul-ture Organization (FAO), 0.7 million tons of clams, cockles, and ark shells were collected around the world during 2005, and they com-posed 0.7% of total fishery captured produc-tion (93.2 million tons).

There is increasing information on im-provement of water quality by bivalve filtering

Food Availability for Particle-Feeding Bivalves, Anadara spp., in Fiji1

Yousef A. E. S. M. Buhadi,2 Toru Kobari,3,8 Kei Kawai,4 Tomoko Yamamoto,3 Hiroshi Suzuki,3 Satoru Nishimura,5 Takashi Torii,6 and Joeli Veitayaki 7

Abstract: We compared food availability of filter-feeding bivalves, Anadara spp., between two Fijian sites of different mangrove richness to evaluate impacts of environmental variables on Anadara spp. abundance and body size. Suspended particles including planktonic organisms and detritus were more abundant in the fishery grounds of the mangrove-rich site (MR) than in the mangrove-poor site (MP). Although no substantial difference was observed in abundance of Anadara spp., dry weights of soft tissue were heavier for animals at MR than those at MP. Respiration rates (i.e., minimum metabolic requirements) of Anadara spp. decreased with increasing animal weight. Unicellular planktonic biomass was estimated to support the Anadara community metabolic requirements (i.e., min-imum food requirement) for 9.2 to 85.7 days at MR and 1.4 to 67.4 days at MP, indicating that the planktonic biomass cannot support sufficient growth of the bivalve population at some locations. These results suggest that suspended par-ticles support increased shell sizes of Anadara spp. and that resuspended detritus is a supplement or alternative food resource for these bivalves in mangrove- coral associated ecosystems.

1 Part of this study was supported by the Japan Soci-ety for the Promotion of Science ( JSPS) (21401013, 24402005) and the Nikki-Saneyoshi Scholarship Foun-dation. Manuscript accepted 16 November 2012.

2 Fisheries Biology and Oceanography, Graduate School of Fisheries, Kagoshima University, Shimoarata 4-50-20, Kagoshima 890-0056, Japan.

3 Fisheries Biology and Oceanography, Faculty of

Fisheries, Kagoshima University, Shimoarata 4-50-20, Kagoshima 890-0056, Japan.

4 Research Center for the Pacific Islands, Kagoshima University, Korimoto 1-21-24, Kagoshima 890-8580, Japan.

5 Department of Economics, Faculty of Law, Eco-nomics, and Humanities, Graduate School of Fisheries, Kagoshima University, Shimoarata 1-21-30, Kagoshima 890-0065, Japan.

6 Fisheries Economics, Faculty of Fisheries, Ka-goshima University, Shimoarata 4-50-20, Kagoshima 890-0056, Japan.

7 School of Marine Studies, Faculty of Science, Tech-nology, and Environment, University of the South Pa-cific, Laucala Bay Road, Suva, Fiji.

8 Corresponding author (e-mail: kobari@fish.kagoshima-u.ac.jp).

540 PACIFIC SCIENCE · October 2013

of excess phytoplankton and suspended matter in eutrophic environments ( Nakamura and Kerciku 2000, Dumbauld et al. 2009). For example, Grizzle et al. (2008) demonstrated that restored shellfish reefs should provide water-quality improvements soon after con-struction. They also mentioned that the over-all impact is probably determined by the size and density of the resident filter-feeder popu-lations relative to water flow characteristics over the reef. Therefore, particle-feeding bivalves have important functional roles in coastal ecosystems.

The Fiji Islands are located in the tropical South Pacific Ocean. The coastal areas are characterized by two different coexisting eco-systems, coral reefs and mangrove forests (El-lison 2010). Although both ecosystems show high biodiversity and productivity (Hogarth 1999, Sheppard et al. 2009), coral reefs are sensitive to different stimuli caused by adja-cent environments due to their narrow physi-ological tolerance range (Pastorok and Bil-yard 1985). Even though Fijian coral reefs are exposed to suspended substances released from mangrove forests (Bouillon et al. 2003), some corals are known to utilize them as major food items in turbid nearshore areas (Anthony 2000). These facts suggest impor-tant linkages between coral reefs and man-grove forests.

Ark shells are particle-feeding bivalve mol-lusks of the family Arcidae. Anadara spp. ( local Fijian name: Kaikoso) is one group of the subtropical ark shells (Okutani 2000, Ha-rasewych and Moretzsohn 2010). They are often found at mudflats in front of mangrove forests and live either submerged in mud or stationed on rocks. Seawater is pumped by nondirected suction, and suspending particles are filtered through the gills; suspended par-ticles released from mangrove forests are ma-jor food items for these species. Thus, their feeding activity would have some impacts on suspended particles at mudflats between man-grove forests and coral reefs.

On average, 193.7 tons per year of Anadara spp. were collected from 2003 to 2004 in Fiji, and they composed 8.8% of the total fishery production (2,205.2 tons per year) (Fiji Fisheries Department 2003, 2004). It is

known that these species are one of the im-portant income sources supporting local vil-lages (Davis et al. 1999). Also, they are a major proteinaceous food item for local vil-lages (Fay et al. 2007). Because of their easy col lection, high production, and stable selling price, high fishery impacts have been evident for Anadara spp. In recent years, Fiji’s lo-cally managed marine area (LMMA) net-work was established for fishery resources including this species (LMMA 2012). Al-though the social and economic importance of Anadara spp. are well appreciated, few ecological studies on Anadara spp. have been done in Fiji.

In this study, we investigated abundance and size of Anadara spp. and environmental variables, including their food resources at the two coastal sites where richness of mangrove forests was different. We discuss food avail-ability for Anadara spp. in coastal ecosystems consisting of coexisting coral reefs and man-grove forests.

materials and methods

Study Site and Period

Viti Levu is the largest island (10,389 km2) in Fiji, located at 17° 48′ S, 178° 0′ E (Figure 1). Seventy percent of the Fijian population (ca. 600,000) lives on this island. The study site is located in the Kumi and Waiqanake Villages, southeastern Viti Levu. Relative coverage of mangrove forests to land around the village is 6.5% at the Kumi study site (MR [mangrove-rich site]) and 1.1% at Waiqanake study site (MP [mangrove-poor site]).

For spatial field surveys, environmental variable measurements and collection of plankton samples and bivalves were carried out at seven stations at MR in August 2010 (dry season) and at five stations at MP in Au-gust 2011 (dry season). Environmental vari-able measurements and plankton samplings were carried out within 2 hr during high tide, and bivalve samplings were done within 2 hr during low tide (Table 1).

Respiration experiments were done at the aquarium of the University of the South Pa-cific during August 2010 and 2011. Animals

Food Availability for Bivalves in Fiji · Buhadi et al. 541

for experiments were collected in the fishery grounds including our sampling stations and taken to the aquarium.

Field Survey

For the spatial field survey, water tempera-ture, salinity, and dissolved oxygen were re-corded at sea surface using a YSI 556 MPS (Multiprobe System), and in situ chloro-phyll a concentrations were measured with a handheld fluorometer (Aquafluor by Turner Designs). Water samples for weight mea-surement and Coulter counter analysis of sus-pended particles were collected at sea surface with a plastic mess cylinder. Water samples (500 ml) were filtered through a Whatman

GF/ F filter (∼0.7 μm nominal pore size) under low vacuum pressure (<20 kPa) and rinsed with filtered tap water. Thereafter, the filters were dried at 60°C for more than 24 hr, and dry weight of the suspended particles on the filter was measured with a microbalance (Shi-madzu Libror ARX-200G). Water samples for the Coulter counter analysis (15 ml) were transferred into plastic tubes and fixed with the borax-buffered formaldehyde (1% final concentration) which was filtered by What-man GF/ F. The density and size spectrum of suspended particles from 5 to 15 μm were de-termined with a Coulter counter (Beckman-Coulter Z2).

The abundance of Anadara spp. was esti-mated using a quadrat with an area of 0.25 m2

Figure 1. Study sites around Viti Levu island, Fiji (center). Triangle and square indicate the location of Kumi (MR, right) and Waiqanake Villages (MP, left), respectively. A – G, stations of field surveys.

TABLE 1

Sampling Periods at Each Station at Kumi (MR) and Waiqanake Villages (MP)

Location Station Sampling Date Sampling Time DTa (min)

MR A 2010/8/17 13:55 – 14:35 +833 – +874B 2010/8/16 16:14 – 16:30 +278 – +294C 2010/8/17 – 18 13:25 – 13:45 +804/+731 – +824/+751D 2010/8/17 – 18 13:50 – 14:30 +829/+756 – +869/+796E 2010/8/18 14:36 – 15:02 +802 – +828F 2010/8/18 15:05 – 15:35 +831 – +861G 2010/8/18 15:00 – 15:20 +826 – +846

MP A — — — B 2011/8/17 10:35 – 11:05 +118 – +148C 2011/8/18 09:15 – 09:45 −2 – +28D 2011/8/18 09:50 – 10:20 +33 – +63E — — — F 2011/8/18 10:45 – 11:15 +88 – +118G 2011/8/17 09:30 – 10:02 +53 – +85

a DT, Difference of sampling time from high tide in the morning (min).

542 PACIFIC SCIENCE · October 2013

(0.5 m × 0.5 m). At each station, the quadrat was randomly placed on the ground, and Anadara spp. in the mud within 10 cm depth were counted. Shell lengths of all animals were then measured with a slide caliper. Al-though A. anomala, A. antiquata, A. maculosa, and A. scapha were found around the study site (Tebano 2002), we did not identify Anadara spp. into species due to difficulty of morpho-logical identification.

Plankton Sampling and Enumeration

Water samples (500 ml) for microsized plank-ton were collected at sea surface and fixed with buffered formaldehyde (1% final con-centration). Microsized plankton were identi-fied and classified into four groups (DIAT, diatoms; DINO, dinoflagellates; CILI, cili-ates; NAUP, copepod and barnacle nauplii [Table 2]). At least 100 cells or cells at 100 sights were enumerated under an inverted microscope after allowing samples to settle overnight. Although some marine planktonic ciliates and dinoflagellates are known to be mixotrophs (Gaines and Elebrešchter 1987, Pierce and Turner 1992, Jones 1994), diatoms and dinoflagellates were considered as auto-trophs and ciliates and nauplii as heterotrophs in this study.

Biovolumes or lorica volumes were esti-mated from size measurement of arbitrarily selected organisms (up to 30 cells or animals) at each station, assuming simple geometrical shapes. Digital images were captured by CCD camera ( Nikon CoolPix 995), and each cell size was measured using Motic Image Plus

2.2S. The biovolumes or lorica volumes were converted to carbon values by using reported formulae or conversion factors (Table 2).

Respiration Experiments

Before respiration experiments, Anadara spp. were kept in a 50 liter tank of flow-through sand-filtered seawater with aeration for more than 24 hr. For respiration experiments, 5 liters of sand-filtered seawater was poured into 11.2 liter cubical polyethylene bags ex-cluding air. We added three animals in 2010 or two in 2011 to each experiment bag. To evaluate bacterial respiration, no animal was added to control bags. All bags were floated in 500 liter containers with sand-filtered sea-water and incubated for 2 hr. Three replicate bags were used for each size class of Anadara spp. At the beginning and the end of incuba-tion, we took samples from all experiment bags for dissolved oxygen (i.e., respiration). Dissolved oxygen was measured using a YSI 556 MPS.

Estimation of Respiration Rate

The respiration rate of Anadara spp. (RO: ml O2/mg/ hr) was estimated using the following equation:

RO = [(DOEo − DOEt)

− (DOCo − DOCt)]/T/DW. (1)

DOEo and DOEt are dissolved oxygen content of the bag with animals at the beginning and end of the experiment (ml O2/ liter), respec-

TABLE 2

A Summary List of Conversion Factors or Formulae from Cell Number or Volume to Carbon Mass of Different Taxonomic Groups of the Plankton Community

Taxon Abbreviation Conversion Factors or Formulaa Source

Diatom DIAT Log10 C = 0.811 Log10 V − 0.541 Menden-Deuer and Lessard (2000)Dinoflagellate DINO Log10 C = 0.864 Log10 V − 0.353 Menden-Deuer and Lessard (2000)Ciliate CILI 0.19V Putt and Stoecker (1989)Nauplius NAUP 0.06V Parsons et al. (1984)

Note: Most of the nauplii are composed of copepods and barnacles.a C, carbon (pgC); V, biovolume or lorica volume (μm3).

Food Availability for Bivalves in Fiji · Buhadi et al. 543

tively. DOCo and DOCt are dissolved oxygen content of the bag without animals at the be-ginning and end of the experiment (ml O2/ liter), respectively. T is the experimental du-ration (hr). DW is the individual dry weight of soft tissue for Anadara spp. (mg).

The respiratory requirement of Anadara spp. (RC: mg C/mg/day) was estimated using the following equation:

RC = RO * RQ * 12/22.4 * 24. (2)

RQ is respiratory quotient. In this study, RQ is assumed to be 1 (i.e., the respiratory substrate is a carbohydrate).

results

Environmental Variables

Sea-surface temperatures and salinities in the fishery ground of MR (27.6° – 30.5°C, 37.0 – 37.6 Practical Salinity Units [PSU]) were higher than those of MP (24.4° – 25.6°C, 34.0 – 35.8 PSU ) (Figure 2). Gradual increase toward station G was evident for sea-surface temperature and salinity of MR, but a similar pattern was not clear at MP. Density and dry weight of suspended particles at MR were relatively higher than those at MP. In situ chlorophyll a concentrations at MR were

Figure 2. Spatial variation in water temperature (top, columns: °C), salinity (top, circles: PSU ), dry weight (middle, column: mg/ liter) and density of suspended particles (middle, circles: particles/ml), and in situ chlorophyll a concentra-tion ( bottom, column: μg/ liter) at Kumi (MR: left panels) and Waiqanake Villages (MP: right panels). Bars show ± SD. ND, No data.

544 PACIFIC SCIENCE · October 2013

lower than those at MP. A spatial pattern was not evident for density and dry weight of sus-pended particles and in situ chlorophyll a at either site.

Suspended particles were more abundant at MR than at MP (Figure 3). The size distri-bution was also different between the two sites. The most abundant category was 5 to 6 μm in MR and 5 μm in MP. Particles larger than 10 μm were less abundant at MP com-pared with those at MR.

Plankton Community

Carbon-based biomass was relatively higher for the microsized plankton community at MR than that at MP (Figure 4). A spatial pat-tern was not clear due to similar biomass among the stations within MP and MR, but fewer ciliates and dinoflagellates occurred at MP. The spatial pattern of the taxonomic composition was different between the two sites. In MR, the predominant group changed toward the peninsula, from nauplii to dinofla-gellates and then to diatoms. At MP, nauplii were the predominant group, except diatoms at station D.

Anadara spp.

A significant nonlinear regression curve (P < .05) was found between dry weight of soft tissue and shell length of Anadara spp. at

both sites (Figure 5). There was some vari-ance in dry weight at similar shell lengths, probably indicating that the four species were mixed in our samples. Dry weight to shell length was heavier for animals at MR com-pared with those at MP.

Abundance of Anadara spp. ranged from 0 to 52 animals/m2 at MR and from 0 to 44 animals/m2 at MP (Figure 6). On average, the density was similar between the two sites (MR: 9.9 ± 7.3 animals/m2; MP: 9.6 ± 6.3 animals/m2). A spatial pattern was not clear at either site.

Dry tissue weight of Anadara spp. ranged from 0.3 to 4.1 g/animal at MR and from 0.1 to 2.0 g/animal at MP (Figure 6). On the av-erage, the dry weight was heavier at MR (1.5 ± 0.8 g/animal) than at MP (0.6 ± 0.5 g/animal) ( Welch’s t test: t = 5.84; df = 83,22; P < .01). The dry weights were heavier toward station G at MR, but that pattern was not clear at MP.

Because the effects of environmental vari-ables on the abundance and size of Anadara spp. were explored, the Pearson correlation coefficient was determined using data at both sites (Table 3). The dry weight showed a sig-nificantly positive correlation to dry weight of suspended particles (r = 0.620, P < .05) and to concentrations of suspended particles mea-sured by Coulter counter (r = 0.661, P < .05). No significant correlation was evident be-tween the abundance and environmental vari-ables (P > .05).

Figure 3. Spatial variation in size distribution of suspended particles (counts/ml) from 5 to 15 μm counted by Coulter counter at MR ( left) and MP villages (right).

Figure 4. Spatial variation in carbon-based biomass (top: g C/m3) and its taxonomic composition ( bottom: %) of micro-plankton community at Kumi (MR: left panels) and Waiqanake Villages (MP: right panels). Bars show ± SD. DIAT, diatoms; DINO, dinoflagellates; CILI, ciliates; NAUP, nauplii. ND, No data.

Figure 5. Relationships between dry weight of soft tissue of Anadara spp. (animal dry weight [ADW ]: g) and shell length (SL: mm) at Kumi (MR: left panel ) and Waiqanake Villages (MP: right panel ). Regression curve equations are superimposed and both are significant (P < .05).

546 PACIFIC SCIENCE · October 2013

Respiration

Respiration rates (RO) of Anadara spp. ranged from 0.3 to 2.2 ml O2/g/ hr in the experiments conducted in 2010 and 2011 (Figure 7). The resultant respiratory re-quirement (RC ) ranged from 3.7 to 28.2 mg

C /g/ hr. The RC exhibited an exponential decrease with the dry weight of soft tissue. A significant regression curve was found between the respiration rate and the indi-vidual dry weight of soft tissue (ADW ) as follows: RO = 2.330ADW −1.38 (r 2 = 0.673, P < .001).

TABLE 3

Summary Results of Pearson Correlation Coefficients for Density (animals/m2) and Animal Dry Weight (g) of Anadara spp. and Environmental Variables

Environmental Variables a

Micro WT SAL CHL SPDW SPCC

r n r n r n r n r n r n

No. −0.074 12 −0.246 12 −0.274 12 0.003 12 −0.046 12 −0.224 12Size 0.399 11 0.593 11 0.529 11 −0.088 11 0.620* 11 0.661* 11

a Micro, microsized plankton biomass (gc/m3); WT, water temperature (°C); SAL, salinity (PSU ); CHL, in situ chlorophyll a (μg/ liter); SPDW, dry weight of suspended particles (mg/ liter); SPCC, concentrations of suspended particles measured by Coulter counter (counts/ml); r, Pearson correlation coefficient; n, number of animals analyzed.

*, P < .05.

Figure 6. Spatial variation in density (top: individuals/m2) and animal dry weight ( bottom: g) of Anadara spp. at Kumi (MR: left panels) and Waiqanake Villages (MP: right panels). Bars show ± SD. ND, No data; NO, no occurrence.

Food Availability for Bivalves in Fiji · Buhadi et al. 547

Food Availability

We estimated food availability to support the community respiratory requirement of Anadara spp. in the fishery ground at MR and MP (Figure 8), based on the following assumptions: (1) Anadara spp. on 1 m2 can feed on microsized plankton community in

the water mass (1 m3) on their habitat. (2) Feeding behavior is continued 12 hr dur-ing high tide in a day. (3) The respiratory quotient is 1. (4) Lateral transport and ver-tical mixing of food resources are ignored. (5) Because spatial and temporal variation of growth rates seem to be lower than those of the standing stock, they are ignored. As a

Figure 7. Relationship of respiration rate (RO: ml O2/g/ hr) and the estimated respiratory requirement of Anadara spp. (RC: mg C/g/day) to animal dry weight (ADW: g). The regression curve equation is super imposed and is significant (P < .05).

Figure 8. Food availability (days) to support commu nity respiratory requirement of Anadara spp. (RC) in the fishery grounds at Kumi (MR: left panel ) and Waiqanake Villages (MP: right panel ). ND, No data; NO, no occurrence.

548 PACIFIC SCIENCE · October 2013

result, the carrying capacity estimated ranged from 9.2 to 85.7 days for the fishery ground at MR and from 1.4 to 67.4 days for that at MP.

discussion

Food Availability for Anadara spp.

To date, mangrove and coral ecosystems have been well examined in many studies (e.g., So-rokin 1993, Hogarth 1999, Luiz 2002, Shep-pard et al. 2009). There is some information on vulnerability of mangrove forests and coral reefs to climate changes and human impacts in Fiji (Ellison 2010), but there is little eco-logical information on the aquatic organisms living in these coastal ecosystems.

Environmental variables revealed that sus-pended particles including plankton at MR were more abundant than at MP (Figures 2, 3, and 4). Contrary to this pattern, phytoplank-ton pigments at MR were lower than those at MP (Figure 2). These results mean that large portions of the suspended particles at MR are composed of detritus-like resuspended parti-cles from the bottom, and these particles are available for the particle-feeding bivalves at MR. Anadara spp. showed larger shell lengths (i.e., heavier dry weights) at MR than those at MP, although there was no substantial dif-ference in their abundance between the two sites (Figure 6). Dry weight was significantly positively correlated with abundance of sus-pended particles. These results suggest that suspended particles, along with planktonic or-ganisms, increase the size of Anadara spp. Ac-cording to our simultaneous research (S.N., K.K., T.K., and T.T., unpubl. data), the fish-ery impacts on Anadara spp. at MR (ca. 40,200 individuals/week) were higher than those at MP (26,520 individuals/week), but apparent abundance was similar at the two sites. These findings mean that abundance, taking into account the fishery impacts, would be much higher for the populations at MR compared with those at MP. Therefore, the abundance of suspended particles is considered to have positive impacts on the abundance and shell size of Anadara spp.

As estimated for carrying capacity (Figure 8), unicellular phytoplankton and microzoo-plankton biomass can support the minimum metabolic requirement (i.e., minimum feed-ing rate) of Anadara spp. for 9.2 to 85.7 days at MR and for 1.4 to 67.4 days at MP. The minimum metabolic requirement does not in-clude anything else such as mucus production, gonad maturation, and body mass growth for Anadara spp. Because we also ignore competi-tion with other animals (e.g., mesozooplank-ton and particle-feeding crustaceans and mol-lusks) for the unicellular planktonic biomass, the estimation means that the food availability measured in some fishery grounds cannot support sufficient growth for Anadara spp. However, the correlation coefficients suggest that suspended particles can support growth of Anadara spp. If the ratio of carbon to dry weight for suspended particles is assumed to be from 0.04 to 0.26 ( Ismail et al. 2005), the carbon mass is estimated to range from 1.7 to 41.6 g C/m3 at MR and from 0.1 to 6.1 g C/m3 at MP. We suggest that resuspended particles such as detritus are available for Anadara spp., and they supplement food resources to sup-port their population growth in these coastal waters.

In Fiji, Anadara spp. are known to spawn throughout the year, but their gonad mat-uration occurs during September to March (rainy season) (Tawake 2004). Tue et al. (2012) found that particulate organic matters (POMs) declined and phytoplankton in-creased during the rainy season in a Vietnam-ese mangrove estuary. POMs collected dur-ing the dry season were enriched in terrestrial constituents in a Florida mangrove estuary (Xu and Jaffé 2007). These findings suggest that there may be seasonal changes in the food availability and requirement for Anadara spp. in mangrove estuaries. More information on the balance between food availability and food requirements might be obtained from seasonal samplings.

Fishery on Anadara spp. in Fiji

Fay et al. (2007) suggested that Anadara spp. is an important fishery as a household income

Food Availability for Bivalves in Fiji · Buhadi et al. 549

source in villages close to main fish markets. The fishery on ark shells involves villagers ranging from the elder women to younger housewives who seek income for their house-holds. Such heavy reliance on Anadara spp. is due to the difficult economic circumstances in many villages in Fiji. Tawake et al. (2007) also confirmed that the fishery on Anadara spp. is not only a major protein source but is also a source of small financial income for daily needs, because going to mudflats at low tides and collecting the clams by hand is easy and suitable for urban villages. It was also pointed out that some villagers have started programs to preserve the species due to decreasing abundance. In the broader context of sustain-able management of fishery resources with heavy fishery impacts, local management has also been proposed for Anadara spp. (LMMA Network 2012). There are many studies to cover the social aspect of these rural areas and their livelihood. However, we have little knowledge on the ecology of Anadara spp. This study demonstrated that size of Anadara spp. differed between sites with differences in mangrove abundance and associated sus-pended particles. Based on stable isotope studies, some mangrove-derived organic par-ticles were deposited in adjacent sea-grass beds and coral reefs (Hemminga et al. 1994). Kawai et al. (2008) pointed out that local Fijian villagers were dependent on fishery resources captured in coastal ecosystems consisting of coexisting mangrove forests and coral reefs. These findings suggest that proper management of mangrove forests and adjacent waters is important for sustainable fisheries of Anadara spp. Environments were considerably variable among the sites, and they influenced Anadara spp. abundance and shell size. We suggest that resource manage-ment should be site-specific depending on the environmental conditions, apart from the general conservation strategy afforded by Marine Protected Areas (MPAs).

acknowledgments

We are grateful to Biman Prasad, Vina Ram-Bidesi, and William Camargo for the kind co-

operation and assistance with the respiratory experiments and research activities at the University of the South Pacific and Anthony S. Ilano for English correction. We also thank Tareguci Sigarua and the people in both Kumi and Waiqanake Villages for the kind assistance during field observations and sample collections.

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