Sedimentation and Water Circulation in Green Mussel Farms of Samar, Philippines

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1. Introduction

Marine sediments in shallow waters are often products of seafloor’s destructive processes of biogenic remains (Reid, et al., 2008) and of other rocks or minerals in the area. Coastal zones, on the other hand, may receive deposits of sediments derived from rock and soil particles which were carried into the sea by various agents such as water runoff and wind as well as chemical

precipitates (Balasubramanian, 2017, UPRM, nd). It is also produced by marine organisms like filter-feeding bivalves in form of feces and pseudofeces. These organisms remove large quantities of

suspended matters then transform it into soft sediment (Dankers & Zuidema, 1995; Dame 1993). This means that when the density of filter feeder bivalves is high, the amount of excreted matter is also high which may exceed the passive physical sedimentation of the area (Dame 1993; Verway, 1952).

The global food demand has increased rapidly over the years as the global population quadrupled over the last century (Elfrink & Schierhorn, 2016). Food demand is estimated to grow between 59 to 98% by 2050 (ibid). This increase in demand will require vast spaces for agricultural production which has a

detrimental environmental impact. It was in the early seventies that great need to farm marine resources came about due to the oil crisis that has made traditional fishing highly uneconomical (FAO, nd). Farming of fish was seen as the best option to produce more food for the masses, provide livelihood and many other benefits (ibid). In 2016, total aquaculture production reached 170.9

million tonnes versus 90.9 million tonnes in capture fisheries (FAO, 2018).

Increase in aquaculture activity also means increased impact to the environment surrounding the aquaculture activities (Gallardi, 2014; Martinez-Porchas &

Abstract: In 2009, Samar mussel industry suffered a massive decline in its production due to mass mortality. There were many speculations, varying research results and differing experts' opinion on what is the leading cause of the mass kill of green mussel. One particular reason that is now widely accepted by the community is that the staking method was the culprit as it traps sediments, restricts water circulation and retains wastes on the seabed floor. Two of the identified factor will be examined in this paper, the volume of sediments produced and the water current in the different green mussel farms in various bays and sea of Samar. Results of the study showed that the volume of sediments produced is significantly higher for mussel farms that are more productive (tray module farms) versus other farms (Wigwam and staking methods) and those without farms. Data, however, reveals that water current inside the farms is significantly different except for that using tray module. Results suggest that the higher the mussel farm productivity the likely higher sediments produced.

Keywords: bivalves, aquaculture, carrying capacity of mussel farms, staking method, tahong

Sedimentation and Water Circulation in Green Mussel Farms of Samar, Philippines

Emilio H. Cebu, Ronald L. Orale

Samar State University, Catbalogan City, Philippines [email protected]

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Martinez-Cordova, 2012; Dosdat, 2009;

Hargrave, 2003; Eng et al., 1989). The degree of aquaculture’s contribution to degrading environmental parameters is dependent on the type of marine resource farmed. Bivalve aquaculture such as mussel culture is known to have a lesser

environmental impact as compared to finfish culture because it has lesser addition to the environment like feeds (Gallardi, 2014). In a review of literature conducted by Cranford et al. (2003), they pointed out that dense bivalve farms result into a strong influence on suspended sediments due to its very high capacity to clear particles in the surrounding water. For example, mussel biomass was found to have the ability to remove food particles at a much faster rate than tidal processes. In short, intensive bivalve aquaculture can alter the matter and energy flow of the coastal ecosystem. The intense bivalve production in France and Japan has resulted in changes in food abundance and quality which has led into the mass

mortalities of bivalves (ibid).

The impact of rock mounds along coastal zones used in the production of rock oyster is influenced by the shape and configuration of the mounds (Orale &

Racuyal, 2017; Bendicio, et al., 2017).

Different mound shape and placement produced a separate volume of sediments trapped, affected water circulation and different level of resilience against

inclement weather. This idea of the type of aquaculture affecting sediments

accumulation and water circulation

corroborates with the authorities findings in 2009 explaining the probable cause of green mussel mass mortality in Jiabong, Samar Philippines (Hardy, 2008).

Many authorities have shared that the cause of mass mortality was the kind of farming (staking method) and unknown

virus (Diocton & Brazas, 2017) but not the intensive farming and the area’s carrying capacity. The Bureau of Fisheries and Aquatic Resources was quoted saying that the cause of the problem was due to the excess in phosphates and nitrates on the sea bed (Docdocan, 2009). A total of about 37 truckloads of pollutants were collected from 67 hectares of mussel farm area in Jiabong, Samar, the Philippines in a clean-up activity in 2008 (Hardy 2008). According to

authorities, the lack of regulation on the proper farm establishments resulted into unsustainable farming practices such as building farms so close to each other that impeded water circulation affecting the amount of dissolved oxygen in the water column (ibid). As a solution, they have introduced a new farming method that uses fewer stakes and are more efficient in terms of quantity of green mussel per area.

The Department of Science and Technology through the Philippine Council for Agriculture and Aquatic Resources Research and Development (DOST- PCAARD) promotes the use of more efficient farming methods such as the longline and the bamboo tray modules (Diocton, 2016). The methods have shown better growth and survival rate and claimed to have reduced sediments between bamboo poles that make growing areas narrow (ibid).

In the study of Cebu & Gomba (2015), a mussel farm using Wigwam, Staking and Bamboo Tray produces 3,305, 3774 and 5,881 kg of green mussel respectively. Tray module is almost 50% better than staking and wigwam method (Cebu, 2016).

In many studies conducted, it was pointed out that an intensive production of bivalve can cause mass mortality (Gallardi, 2014; Martinez-Porchas & Martinez- Cordova, 2012; Cranford, et al., 2003;

Dame, 1996; Heral et al., 1986; Aoyama,

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1989; Heral, 1993). Bivalve farms

environmental effects include water column and nutrients, sediment and benthic habitat and effects on other marine species

(Gallardi, 2014). The higher the volume of bivalves means a higher volume of

sediments deposited which will result into the production of anaerobic sediment, increased bacteria and meiofauna, decreased suspended-feeders, increased in deposit feeders. The removal of calcium carbonate can lead to an increase in acidification and decreased positive feedback (ibid).

2. Objectives

The study determines the sedimentation and water circulation velocities in different bays of Samar specifically inside the green mussel farms using staking, wigwam and bamboo tray module methods.

3. Methodology 3.1 Research Design:

The study employed quantitative approaches to present the current status of mussel belt areas in Samar and the effects of various green mussel farming methods to the marine environment specifically on

sedimentation and water circulation.

3.2 Research Environment:

The study was conducted in Samar Philippines, specifically in Cambatutay Bay, Maqueda Bay and Villareal Bay in 2014.

This means that the data presented here is five years after the 2009 mass mortality of green mussel in the study area. A total of 27 observations stations were considered in this study; four for Cambatutay Bay, seven for Maqueda Bay and 16 for Villareal Bay. The observation sites specifically Villareal Bay

is surrounded by land masses such as the Mainland Samar, Zumarraga Island, and Daram Island. On the other hand, Maqueda Bay is partly protected by smaller islands while Cambatutay Bay is a bit open. There are several water tributaries in these bays contributing heavily to the production of sediments in the area (Cebu & Orale, 2017).

Cambatutay Bay is the lowest covering only around 1,246 hectares more or less while Maqueda and Villareal Bays are about 15,149 and 15,011 hectares respectively.

Every after heavy precipitation, the river delta and the surrounding waters are brown in color, indicating heavy erosion.

Table 1. Observation sites coordinates Bay Stations Coordinates

Latitude Longitude

Camba- tutay Bay Sed.

1 11° 53’ 15” N 124° 45’ 38” E 2 11° 53’ 59” N 124° 46’ 45” E 3 11° 54’ 33” N 124° 47’ 42” E Others 11° 54’ 15” N 124° 46’ 51” E

Maqueda Bay area Sedimentation

1 11° 43’ 55” N 124° 55’ 06” E 2 11° 44’ 30” N 124° 57’ 09” E 3 11° 45’ 17” N 124° 58’ 24” E 4 11° 42’ 11” N 124° 57’ 24” E 5 11° 42’ 17” N 124° 55’ 06” E 6 11° 40’ 24” N 124° 56’ 03” E Others 11° 43’ 45” N 124° 57’ 10” E

Villareal Bay area Sedimentation Stations

1 11° 39’ 25” N 124° 57’ 11” E 2 11° 39’ 20” N 124° 55’ 56” E 3 11° 39’ 18” N 124° 54’ 27” E 4 11° 37’ 56” N 124° 54’ 00” E 5 11° 38’ 03” N 124° 55’ 45” E 6 11° 38’ 12” N 124° 57’ 11” E 7 11° 36’ 54” N 124° 57’ 11” E 8 11° 36’ 54” N 124° 55’ 18” E 9 11° 35’ 45” N 124° 56’ 06” E 10 11° 35’ 00” N 124° 53’ 42” E 11 11° 35’ 41” N 124° 54’ 00” E 12 11° 36’ 56” N 124° 53’ 00” E 13 11° 35’ 49” N 124° 51’ 57” E 14 11° 34’ 26” N 124° 51’ 42” E 15 11° 33’ 07” N 124° 52’ 12” E Others 11° 37’ 10” N 124° 55’ 12” E Others (Seawater Physicochemical Parameters and Water Current Observation sites coordinates)

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3.3 Data gathering and tools:

Improvised sediment traps, drifter, Global Positioning System (GPS), and nautical chart No. 4420 from the National Mapping and Resources Information Administration (NAMRIA) were used in gathering data for this study.

Figure 1. Observation Sites in Maqueda Bay and Villareal Bay

Figure 2. Observation sites in Cambatutay Bay

Sediment traps which were upward facing funnels (Buesseler et al., 2007) were used to observe the sedimentation processes in the study sites. For this study, cylindrical glasses measuring 25 cm high x 9 cm

diameter mouth opening (see Figure 3) were

the instrument set in the water column to collect minute particles and other matters settling to the seabed (Callier et al., 2006;

Walker et al., 2008, WHOI, nd). These traps were deployed in mussel-belts (see Figure 1 and 2 and Table 1) based upon the direct interception of sinking material caught into the tube of a known area and over a known length of time.

Bamboo poles were driven into the seabed in pre-identified strategic sites with coordinates shown in Table 1 guided with GPS. Each sediment trap was tied with polyethylene rope No. 4 and was hung on the staked bamboo elevated approximately at 0.5 m from the seabed. The number of sediment traps deployed varied with the expanses of the study sites. The sediment traps were deployed in such a manner to catch its spatial and temporal variability of the sedimentation processes in mussel-belts, inside the farms and outside it.

The sediments collected by the sediment traps were monitored every after 3- days in 45 days (15 observations). The heights of the sediments accumulated in the glass jars were measured using the

measuring tape and subsequently recorded.

The periodically recorded heights of sediment were transformed into sedimentation rates.

Figure 3. The sediment traps used in this study

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To measure water current, the Eularian method using the drifter (drogue) was used. This method requires the observer to stand at one point, a drifter, and a timer.

A time series can be generated at a given point in order to obtain trends. The set-up shown in Figure 4 was used to measure the water current in the area.

Figure 4. Set-up used in measuring water current

Data collection at each mussel-belt was measured on a stationary motorboat anchored at the sites with coordinates indicated in table 1 and Figures 1 and 2.

3.4 Data Analysis and presentation:

Differences in the observed data were analyzed using One-way ANOVA and post-hoc Turkey HSD Test. Data was presented in tables, bar graphs, and maps.

Data collected per station passed the normality test.

4. Results and Discussion

Seawater circulation and the presence of sediments affect many aspects of the coastal water ecology together with other physico-chemical parameters. Its geographical characteristics generally

influence water circulation while

sedimentation in similar environments is affected by sediments entering the bays through drainage systems (both natural and manmade) and by the water current itself (Sanchez & Hernandez, 2013; Verny R. et al, 2013). In a process of called

biopackaging, all suspension-feeding bivalves which includes green mussel filter various particulates such as organic and inorganic matters from the water column and discharge biodeposits a process that clarifies the water and transfer organic-and nutrient rich particulates to the sea bed (NAP, 2010; ECU, nd).

4.1 Sedimentation characteristics

Sedimentation process in the marine environment is one phenomenon that is not known to many, but this has a significant impact on the water quality in the major mussel-belt area. Suspended sediments can ultimately reduce visibility in the water column. During heavy precipitation in the study area, water changes color to brown contributed by the runoff waters specifically from rivers of Samar which are very rich in sediments (Cebu & Orale, 2017). The data shown on table 2 to 4 are estimated temporal volume of sediments which settled per square meter every three days.

4.1.1 Sedimentation characteristics in Cambatutay Bay

It was noted that these sediments which settled in Cambatutay Bay were primarily organic matters like feces of mussels and few amounts of very fine grain silt. Due to their very fine size, they remain suspended in the water column drifting with the water currents and settled down at some period of the day. Settling rate of suspended particulate is increased through the help of bivalves (Norkko, 2001).

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Table 3. Sedimentation Rates in Different Sites of Maqueda bay

Sta. T-test comparing sedimentation rate between stations

Stn 1 Stn 2 Stn 3 Stn 4 Stn 5 Stn 6 Stn 7

Sta 1 **0.0010 *0.0119 0.1441 0.8999 **0.0087 0.1017

Sta 2 0.1098 **0.0081 **0.0010 0.1364 *0.0132

Sta 3 0.8999 *0.0458 0.8999 0.8999

Sta 4 *0.0358 0.8999 0.8999

Sta 5 *0.0352 0.2697

Sta 6 0.8999

Volume (cu.m./m²/day) of Sediment in Observation Sites

Mean 0.0058 0.0090 0.0075 0.0071 0.0061 0.0077 0.0072

SD 0.0015 0.0014 0.0019 0.0016 0.0015 0.0001 0.0009

Sta1-Waters off Cal-Apog Pt. Sta2-Waters off Jiabong Sta3-Watersoff Malobago Sta. Waters off Hita-asan Sebastian Sta5-Central Waters of Maqueda Bay Sta6-Southern Waters of Maqueda Bay Sta7-Maqueda Bay-wide

** significant (p<0.01) *significant (p<0.05)

Collected data has shown that the sediments closer to the Cambatutay River received the highest accumulated sediments totaling to about 0.4270 m in 45 days. This amount is about 11.3% higher than the bay- wide average and 23.4% higher than that of station 1, the farthest observation site from the river. Stress at the sea floor is stronger nearby the mouth of big rivers (Dalyander &

Butman, 2012). Suspended particulates can quickly be moved away through water current but when it settles at the bay floor, the stress needed on the sea floor for the sediments to move is larger (ibid).

Table 2. Sedimentation Rates in Different Sites of Cambatutay bay

Sta.

T-test comparing sedimentation rate between stations

Stn 1 Stn 2 Stn 3 Sta 4

Sta 1 0.2929 0.0010** 0.1661

Sta 2 0.0411* 0.9000

Sta 3 0.0867

Vol. (m³/m²/day) of Sediment in Observation Sites Mean 0.0077 0.0084 0.0095 0.0085 SD 0.0011 0.0013 0.0012 0.0008 Sta1-Mouth of Cambatutay Bay Sta2-Middle Waters Sta3-Off Cambatutay River Sta4-Cambatutay Bay-wide

The total sediments that settle in the Cambatutay Bay area are estimated to reach 3,252,199 m³ in a month or at a rate of 85.26 mt per hectare per day. Statistical tests shown in Table 2 reveals that the station near the Cambatutay River (Sta. 3) is significantly different compared to other stations specifically stations 1 and 2.

4.1.2 Sedimentation characteristics in Maqueda Bay

Table 3 reflects the differences in the sedimentation rates in various sites of the Maqueda Bay area. The sediments were composed mainly of organic matters comprising of feces and algae which remained in suspension drifting with the water movements in the area and settled down after some time during the observation period.

Among the sites in the bay, Station 1 (the waters off Cal-apog Point, the boundary between Catbalogan City and Jiabong, Samar) had the least sedimentation rates amounting to only 0.0058 cu.m./square meters per day compared with other sites.

On the other hand Station, 2 has the highest sedimentation rate with an average of 0.0090 cu.m per square meter per day.

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Table 4. Sedimentation Rates in Different Sites of Villareal Bay

Sta. T-test comparing sedimentation rate between stations

Stn 1 Stn 2 Stn 3 Stn 4 Stn 5 Stn 6 Stn 7 Stn 8

Sta 1 **0.001 **0.001 **0.001 **0.001 0.312 0.171 *0.029

Sta 2 0.900 0.900 0.454 *0.045 0.100 0.404

Sta 3 0.900 0.144 0.200 0.356 0.768

Sta 4 *0.029 0.545 0.723 0.900

Sta 5 **0.001 **0.001 **0.001

Sta 6 0.900 0.900

Sta 7 0.900

Mean 0.0108 0.0091 0.00927 0.00944 0.0084 0.0101 0.0100 0.0098 SD 0.0009 0.0006 0.00079 0.00083 0.0080 0.0008 0.008 0.0010

Station T-test comparing sedimentation rate between stations

Stn 8 Stn 9 Stn 10 Stn 11 Stn 12 Stn 13 Stn 14 Stn 15 Sta 1 *0.029 **0.007 **0.001 **0.001 **0.001 **0.001 **0.001 **0.001

Sta 2 0.404 0.679 0.900 0.900 0.900 0.405 0.900 0.900

Sta 3 0.768 0.900 0.900 0.900 0.900 0.900 0.642 0.734

Sta 4 0.900 0.900 0.900 0.900 0.900 0.826 0.268 0.355

Sta 5 **0.001 **0.003 0.634 0.138 0.355 0.642 0.900 0.900

Sta 6 0.900 0.900 *0.016 0.158 *0.049 *0.012 **0.001 **0.001

Sta 7 0.900 0.900 0.045 0.295 0.110 *0.032 **0.001 **0.002

Sta 8 0.900 0.234 0.710 0.435 0.186 *0.016 *0.025

Sta 9 0.501 0.900 0.710 0.435 0.064 0.091

Sta 10 0.900 0.900 0.900 0.900 0.900

Sta 11 0.900 0.900 0.688 0.780

Sta 12 0.900 0.900 0.900

Sta 13 0.900 0.900

Sta 14 0.900

Mean 0.0098 0.0096 0.0090 0.0092 0.0091 0.0090 0.0087 0.0088 SD 0.0010 0.0008 0.0007 0.0010 0.0008 0.0008 0.0007 0.0006 Please see Table 1 and Figure 1 for location of observation stations Sta. 1 to 15

The average sedimentation rate in the bay was pegged at 0.0072 cu.m/sq.m/day where only station 2 appears to be different from it significantly. Stations 1 and five which is near the mouth of the bay has lower sedimentation rates compared to inner stations. The sediments collected from these stations are probably from the streams exiting into the bay.

The sediments near the mouth of the bay are lower than those in the inner waters.

This is likely because these areas are

shallower and therefore scouring the bottom of the bay results into the disturbed sea bed.

Also, the sediments carried by water runoff specifically during heavy rains affect the volume of suspended sediments in the water column. The total sediments that settle in the Maqueda Bay area are estimated to reach 53,576,405 m³ in a month or 115.26 mt per hectare per day.

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4.1.2 Sedimentation characteristics in Villareal Bay

The data in Table 4 shows that Stn 1 (the northeast waters of the Bay) had high sedimentation rates compared with the rest of the sites. The magnitude of the daily sediment depositions in the area ranges from 0.0087 to 0.0108 cu.m/sq.m./day. Like in Maqueda and Cambatutay Bays,

sedimentation rates closer to the coastal zones having river deltas have higher sediments than those in the middle portion of the bay.

The volume of sediments which settled in this site is about 0.0090 ± 0.0007 cu.m. per sqm per day was found at 0.405 cu.m.per m². In Stn 11 (the waters between Barangay Himyangan and Lamingao, Villareal, Samar), the volume of sediments had slightly increased to 0.416 mt per m² in (Stn 11) where it settled at the rate of 0.0092

± 0.0010 mt per m² per day. The sediment deposition rates in this site ranged from 0.0077 to 0.0107 mt per m² per day.

The total sediment volume of 0.410 mt per m² had deposited in the seabed of Stn 12 (Buad Channel). The daily sedimentation rates in this site ranged from 0.0097 to 0.0103 mt per m² with a mean deposition rate of 0.0091 ± 0.0008 mt per m² per day. Slightly reduced range of sediment deposition rates were noted Stn 12 (waters off Barangay Guintacan, Villareal) where the volume of sediment that had deposited in the site had slightly increased to 0.404 mt per m². The same volume had settled at the rate of 0.0090 ± 0.0008 mt per m² per day.

The sediment depositions in the Stn 14 (SW central waters of the Bay) and in the Stn 15 (waters at the entrance of Laguimit Bay) further slightly reduced in volume to 0.392 and 0.34 mt per m², respectively. The

daily sedimentation rates in these areas ranged from 0.0077 to 0.0103 mt per m² in the former site and 0.0080 to 0.0100 mt per m² in the latter site. These volumes of sediments had settled at the rate of 0.0090 ± 0.0008 mt per m² per day and 0.0087 ± 0.0007 mt per m² per day in their respective sites. Total sediments accumulated in Villareal Bay is estimated to reach 93.53 mt per hectare per day.

4.1.3 Sedimentation characteristics in different Green Mussel Farms

Sediments in the bay come from various sources, one which are aquaculture farms of green mussel, a filter feeder bivalve. In Cambatutay Bay, only the Wigwam and Staking method of green mussel farming was used. Sediment traps was gathered covering a total of about 200 m² mussel farms and in areas without farming activity. Mean daily particulates collected in the sediment traps based on 45 days monitored every 3 days for the three bays is estimated to be 294.05 mt per hectare per day.

Table 5. Sedimentation Rates in Different Farms of Cambatutay Bay

Stations T-test comparing sedimentation rate between stations

Control Staking Wigwam

Control **0.0010 **0.0010

Staking 0.1255

Mean 0.0051 0.0095 0.0109

SD 0.0014 0.0017 0.0023

Mean daily sediments collected in the open waters of the bay is lesser than those under the farms. This suggests that there are more sediments under the mussel

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farms than not. The amount of sediment in the farms using Wigwam is larger by 14.7%

versus those collected inside farms using staking method. The statistical test, however, showed the difference to be not significant. Daily sedimentation rate at the mouth of the Cambatutay River is 0.0285 cubic meter per day which is significantly higher than the sedimentation rate inside the mussel farms.

Table 6. Sedimentation Rates in Different Farms of Maqueda Bay

Stations

A t-test comparing sedimentation rate between stations

Control Staking Wigwam Tray

Control *0.0481 0.5642 0.8999

Staking 0.6544 0.1245

Wigwam 0.7898

Mean 0.0115 0.0094 0.0104 0.0019 SD 0.0015 0.0016 0.0019 0.0019

Mean daily volume of sediments collected in the open waters of the bay is significantly different that of the sediments collected inside green mussel farms. Bay- wide average is 0.0220 cubic meter/day while those in the farm are relatively lower.

Except for the farms using staking method which is significantly lower than the control station, the rest of the stations are not significantly different. However, looking at the data, it appears that there are more sediments collected inside the farms with those collected under Wigwam farms.

Like in other bays, there is more sediment in other parts of the bay than in the farms. For Villareal Bay, the amount of sediments collected totaled to 0.028a cubic meter/day which is near twice in terms of volume. It is also apparent that the amount of sediments gathered under a farm using

tray module is significantly higher than other stations as shown on Table 7.

Table 7. Sedimentation Rates in Different Farms of Villareal Bay

Stations T-test comparing sedimentation rate between stations

Control 0.8999 0.2928 **0.0010

Staking 0.2672 **0.0010

Wigwam *0.0220

Mean 0.0092 0.0092 0.0102 0.0117 SD 0.0004 0.0017 0.0013 0.0019

Table 8. Total Sediments Collected From Different Farms in Samar in (45 Days Observation)

Stations

T-test comparing sedimentation rate between stations

Staking Wigwam Tray

Staking 0.1203 **0.0010

Wigwam **0.0045

Volume (cu.m) of Sediment in Observation Sites

Mean 6.380 7.010 8.155

SD 1.486 1.463 1.591

Shown on Table 8 are the estimated total accumulated sediments in the

observation area. It was very evident that the Tray Module Farm produced more

sediments than farms using staking and Wigwam method. In the study of Cebu and Gomba (2015), farms using bamboo tray module outperform the other two methods in many aspects especially in terms of weight of green mussel produced. This means that the high sedimentation in the tray module mussel farm is likely one of the reason. It was emphasized in many pieces of literature that filter-feeders like green mussel ingest suspended particulates in the water and

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packages it into their feces that easily settle, faster than the suspended solids in the area (Reid, et al., 2008; Cranford, et al., 2003;

Dame, 1993; Eng, et al., 1989; ECU, nd.).

The organic sediments accumulate at the seafloor and later moved through water current.

4.2 Water Current in the Bays.

Water movement is an essential physical parameter of mussel-belts for it influences the transport of food (like plankton) for mussels from one place to the other. This is generally termed as water current which is the magnitude of

continuous movement of certain water mass from one point to the other as directed by various natural phenomena like tides and the prevalent wind flow. It was hypothesized by some experts in the field that one cause of the mass mortality of green mussel in the area is due to the reduced water current due to uncontrolled farming (Hardy 2008).

4.2.1 Water Current in Cambatutay Bay

The movements of the waters in the bay changed temporally which was mainly influenced by the diurnal tidal fluctuations.

Directions of the water were on its eastward movement at the onset of flood tides and reverse to westwards at the onset of ebb tides. The bi-hourly magnitude of water currents observed within 48-h in

Cambatutay Bay is shown in Figure 7.

Generally, the direction of the water flow in the area was going in and out during the flood (rising state) and ebb (lowering state) of tides, respectively. On the first monitoring period (Jan. 22-24, 2014), the water currents in the area had a minimum magnitude of 9.71 cm per second noted at 0930H in the last period. This was

associated with the very movement of the

ebb tide. On the other hand, the strongest water current in the Bay had the magnitude of 75.91 cm per second (1.43 Knots) recorded at 0330H associated to the flood tide on the early period of on 23 Jan 2014.

Within 48-h observation, the water

movements behaved at the mean of 34.47 ± 19.54 cm per sec (0.65 ± 0.37 Knots).

The water movements on the second observation period (Feb 21-23, 2014) were relatively weaker compared from that on the first observed data. The data suggest that the heights of the tidal waters during this second observation period had lower fluctuations. Within the 48-h monitoring, the water currents had a minimum

magnitude of 24.69 cm per sec which was noted on the later hours of the first day (21 Feb 2014) which was associated with the ebb tide. The maximum magnitude of the water currents during this period was 51.28 cm per sec which was the recorded data.

The water currents during this second monitoring period varied at its mean of 34.76 ± 6.81 cm per sec.

4.2.2 Water Current in Maqueda Bay

The bi-hourly magnitude of water currents in Maqueda Bay is shown in Figure 8. The data suggest that the water currents in the Bay area had a magnitude which was generally higher compared to that in

Cambatutay Bay. Comparatively, strong water currents were noted during the first observation period (Jan 15-17, 2014). On the first day of the monitoring period (15 Jan 2014), the water currents were relatively slow and only ranged from 10.95 cm per sec to 29.33 cm per sec. Tidal fluctuations influenced the trend of the water currents on this period. Its magnitude varied at its mean of 21.49 ± 6.34 cm per sec.

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The tidal fluctuation further influenced the water movements on the earlier periods from 0000H-0830H of 16 Jan 2014. The winds of typhoon “Agaton"

started to change the magnitude of the water currents when it prevailed on the succeeding periods. The water currents in the Bay became very strong until it reached the maximum quantity of 90.91 cm per second (1.73 Knots) on the later period of the day at about 1900H which was the peak of the typhoon in the Bay area.

As time went by, the water movements slowly declined with the prevailing wind until it reached the magnitude of 42.55 cm per sec on the last day. In the 48-h period, the water currents behaved at 25.09 ± 13.92 cm per sec (0.48 ± 0.26 Knot).

In the second observation period, the direction of water flows in the Bay area did not change as observed in the past. Again, the water flows were at opposite directions due to two water masses that converged in the Bay. At the onset of flood tide (rising water levels), water movements along the northern waters were southeasterly

direction, while at the Southern section were at North Eastward. At ebb tides (lowering sea levels), the north water flowed North Westward, and Southern waters were to South Westward direction.

However, a significant change was noted on the pattern of the water currents.

The trend suggests that tidal fluctuations influenced the magnitude of the water currents in the Bay. The daily trend shows a multimodal pattern of two high and low water current magnitude, suggesting that the water movements were due to a semi-diurnal tidal pattern.

Within 48-h on these periods, the water currents in the Bay ranged from a magnitude of 11.20 cm per sec (≈0.21 Knot) noted before the slack tide on the mid- afternoon of the first day, and the most active water current had a magnitude of 92.59 cm per second (≈1.76 knots). On this second monitoring period, the water currents in the Bay varied at 38.64 ± 23.83 cm per sec (0.37 ± 0.41 Knot).

Maqueda Bay has a unique water dynamics which is associated with the daily tidal and wind patterns, and the movement of external waters entering the Bay. The vertical water movements in the bay were mainly affected by daily tidal fluctuations, while the horizontal movements were associated with the oceanic water

movements that came in and out of the Bay from two sources.

At the onset of flood tides, oceanic waters from Leyte Gulf passed the San Juanico Strait and entered into the Bay through Daram Channel south of the Daram Island and the Villareal Bay. Another mass of water from Samar Sea also entered the Maqueda Bay area at the observed mean water current velocities of 4.07 ± 3.64 cm per second passing through the open channels between Majaba and Darajuay Daco Islands and Darajuay Guti Island and Cugao Point. These water masses

converged at the central section of the Bay forming a gyre. At the onset of ebb tides, the waters in the Bay moved out in opposite directions. The waters at the southern vicinities of the Bay flow at South Westerly direction, while the northern waters flowed at North Westerly direction.

The waters in Maqueda Bay became rough due to Easterly winds (local name:

Dumagsa) which was prevalent at late in the morning or early afternoon (1000H-1500H)

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at velocities of 30-40 km per hour. The South Westerly winds (habagat) that was prevalent from mid-July to mid-September usually cause the waters in Maqueda Bay

moderately rough with wave heights ranging 0.5-1.0-m and even higher with the

enhanced magnitude of wind velocities.

Figure: 7. Temporal Water Current in an Observation Station at Cambatutay Bay

Figure: 8. Temporal Water Current in an Observation Station at Maqueda Bay

Figure: 9. Temporal Water Current in an Observation Station at Villareal Bay

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4.2.3 Water Current in Villareal Bay

The trend on the magnitude of the water movements in the Bay area is shown in Figure 9. The data suggest that the water currents in this area had a lesser magnitude compared with other mussel-belts. During the first observation periods (Feb. 7-9, 2014), the water currents ranged from 33.33 to 54.55 cm per sec (≈0.63 to 1.04 Knots).

The tidal fluctuations likewise influenced the water currents in the Bay area. The movement of the waters was directed towards East to Northeast during flood tide and shifted to West to Southwest during ebb tide. The seawater behaved at a current of 9.44 ± 5.62 cm per second (≈0.18

± 0.11 knot).

During the second monitoring period (Feb. 28-Mar 2, 2014), the water currents in the Bay had an extremely low magnitude of 2.10 cm per sec (0.04 Knot) observed prior to the slack tide on the evening of the first day, while the strong water current had a magnitude of 62.56 cm per sec (1.19 Knots), observed at noon on the second day.

During this monitoring period, the water currents in the Bay area varied at the mean magnitude of 21.82 ± 17.36 cm per sec (≈0.41 ± 0.33 Knot).

Villareal Bay had water movements that were also associated with diurnal tidal and wind patterns. Vertical water

movements in the Bay were due to the diurnal tidal fluctuations while the

horizontal water movements were affected by tidal cycles and enhanced by daily wind patterns. During flood tides, the waters in the Bay flowed easterly pushed by the oceanic water coming in through the narrow Daram Channel which was the same water mass that flowed to Maqueda Bay. At the onset of ebb tides, waters in the Bay flowed back at Westerly direction passing through

the same channel. The water movements in the area had a mean water velocity of 2.48 ± 0.67 cm per second during low tidal height fluctuations.

Like in Maqueda Bay, the easterly winds (or Dumagsa) affected the horizontal water movements in Villareal Bay. The wind blows usually caused the Buad channel and its vicinities to very rough conditions inducing waves of 1-2 m high. Such conditions were generally enhanced by the stronger magnitude of water current of 26.26 cm per second especially observed at ebb tides. During these periods, the observed water movement in the area was in South Westerly direction towards the Daram Channel. However, the slight blows of Easterly winds also caused Buad Channel to relatively calm with observed water current of 15.35 cm per second.

4.2.4 Water Current in Different Types of Green Mussel Farms in Samar

Reports suggest that water current is affected by the green mussel farming method in the area. Experts in green mussel farming claim that some farming methods hinder the flow of water (Diocton and Brazas, 2017; Diocton, 2016; Docdocan 2009). This section aimed to show if there are differences in the water current in these farms. As shown on Table 9, there was a significant difference in the water current in Wigwam mussel farms as compared to Tray and area with no farm. There was no

difference in water current in bamboo tray module mussel farms.

Current in the mussel farms specifically on those using wigwam and staking methods were affected. The study, however, was not able to observe if the reduction is enough to prevent sediments from being re-distributed. Current also

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allows aerating the area improving the dissolved oxygen (DO). The DO levels in every farm using different methodologies were not included in this study. Presented in the study of Cebu and Orale (2017) that the DO levels in the study area are significantly different from each other.

Table 9. Sedimentation Rates in Different Farms of Maqueda Bay

Stations

T-test comparing water current between stations

Control 0.1916 **0.0060 0.9000

Staking 0.4661 0.3348

Wigwam **0.0147

Volume (cm/sec) of Sediment in Observation Sites

Mean 22.93 19.90 17.72 22.44

SD 3.66 3.80 2.93 3.50

Table 10. Sedimentation Rates in Different Farms of Villareal Bay

Stations

T-test comparing water current between stations

Control 0.4799 *0.0124 0.9000

Staking 0.2923 0.5706

Wigwam *0.0190

Volume (cm/sec) of Sediment in Observation Sites

Mean 40.00 34.14 26.87 39.34

SD 10.23 9.85 7.71 10.04

5. Conclusion and Recommendation

Authorities identified the type of mussel farming methodology as one of the culprits in the mass kill some time in 2009.

This mass kill was primarily attributed to staking method trapping sediments in its vicinity coupled by the reduced water circulation. However, data from this

publication reveals that sedimentation is not primarily attributed to the type of farming method but more of the number of bivalve in a given area. Most of the sediments in mussel farms are produced by the green mussel itself.

On the other hand, data support the earlier information that water current in the farms is affected by the type of farms. The result showed that the water current impact is bigger in Wigwam mussel farms.

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