HARVESTING METHOD AND AMOUNT OF MYTILUS GALLOPROVINCIALIS AS BIOMASS RESOURCE FROM SEA

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1 HARVESTING METHOD AND AMOUNT OF MYTILUS GALLOPROVINCIALIS AS BIOMASS RESOURCE FROM SEA Machi Miyoshi 1, Yasunori Kozuki 1, Takuro Kimura 2, Tatsunori Ishida 1, Yusuke Mori 1, Yuki Miyachi 3 and Hitoshi Murakami 1 1 Department of Ecosystem Engineering The University of Tokushima Tokushima, Tokushima, JAPAN haseda@fe.bunri-u.ac.jp 2 Graduate School of Agriculture Kochi University Kouchi, Kouchi, JAPAN 3 Sohgoh Kagaku Inc. Chuo-ku, Osaka, JAPAN ABSTRACT The Blue mussel, Mytilus galloprovincialis, a marine product resource, is collected from seawalls and used effectively on land regions to prevent a deteriorating coastal environment and to get rid of nonnative species. In this study, we estimated the M. galloprovincialis biomass that could be collected for a year. The organic carbon per width of seawall where the macrobenthic attaches is 1.4 kgc/m in July when the M. galloprovincialis reaches maximum growth. Collecting M. galloprovincialis twice a year is considered to be most effective. We recommend harvesting M. galloprovincialis for the first time in May when their biomass is large and a second time the day before it drops out in August. INTRODUCTION Due to the inflow of polluted water from land, the inner bay experiences some problems with eutrophication and decrease of oxygen. Almost the entire coastline of the bay is surrounded by a seawall and a large volume of the mussel, Mytilus galloprovincialis, attaches to the surface of the seawall. When a large volume of excrement and mussels drop to the bottom they cause a decrease of oxygen. An experiment for restoring environmental conditions of the coastal area, Bay of Dokai, Kitakyu-shu, Japan, has been carried out with a plan to culture M. galloprovincialis to purify the water column (Onitsuka et al., 2). Recently, a potential usage of M. galloprovincialis is found as compost because M. galloprovincialis may contain a large proportion of nitrogen, phosphorus, potassium and magnesium (main components of compost). If M. galloprovincialis which are abundantly attached to existing vertical walls can be effectively used on land after harvesting from the wall, these operations may lead to avoidance of environmental degradation in harbor, removal of harmful non-native species from coastal area, and effective use of marine resources. 237

2 In this study, M. galloprovincialis was taken during January 5 and March 6 to estimate potential amounts of resource recovery. Characteristics of this work are as follows: 1) to see existing vertical wall as useful space for taking biomass resources, 2) to construct new route of material cycle from seawater to land soil. Study site METHODS This experiment was conducted at Amagasaki port, located in the innermost part of Osaka Bay. Figure 1 shows the location of Amagasaki port. There are vertical seawalls all the way around Amagasaki port. Except for the waves caused by ships, the water is calm. The amount of suspended matter in Amagasaki port is comparatively more than other areas. Additionally, water transparency decreases, especially in summer, with a decrease of dissolved oxygen at the bottom (Tsujino amd Tamai, 1996). 135ºE 135º E Osaka Bay 34º4 N 1 km Amagasaki port 5 1 m Figure 1. Map of the Amagasaki port in Osaka Bay Measurements of the water quality The water samples from Amagasaki Port were tested for temperature, salinity and dissolved oxygen, from surface to bottom-water at interval of.5m (DL+1., +.5, ±., -.5, -1., -1.5, -2., -2.5, -3., -3.5, and -4. m) for once every month from October 5 to September

3 Macrobenthic fauna survey We conducted the macrobenthic fauna survey on the surface of the vertical seawall once every month from October 5 to September 6. The macrobenthic fauna on the vertical seawall were collected in a quadrate (3 3 cm) by a scraper at a depth of DL+.3~±.m, -.2~-.5m, -.7~-1. m. Moreover, the macrobenthic fauna were directly observed by a diver. The collected macrobenthic was analyzed for species construction, total biomass, a range of dominant species shells, total organic carbon (TOC). TOC was used to estimate a potential amount of recovery. They were analyzed with an elemental analyzer after removal of carbonates with 1N HCl solution (Thermo Finnigan, NC Soil Analyzer). The growth rate was calculated with a cohort observation program (PROGEAN, Ver. 4.J). Harvest number was assumed once a year (May), twice a year (November and May), three times a year (January, May and September) and four times a year (November, February, May and August) to consider the relationship between frequency of harvest and potential amounts of resource. The macrobenthic organisms which joined at the harvested site were measured for a fauna, a number of species and weight of each macrobenthic organize. We considered that the biodiversity is increased when new species replaced the non-native species after removal of M. galloprovincialis. In this study, the index of biodiversity was a number of Japanese species which were living there. Seasonal variation of macrobenthic fauna RESULTS AND DISCUSSION Figure 2 shows the changes in macrobenthic fauna and biomass amount. From October 5 to March 6, the barnacle Balanus eburneus was dominant and the biomass ranged from.2 to1. kg/.27m 2 (.74 ~3.7 kg/m 2 ), the dominance was 59~87% among the organisms on the seawall. From April to August, the biomass of M. galloprovincialis made up.5 ~ 7.8 kg/.27m 2 (1.85 ~ 28.9 kg/m 2 ), and the dominance was over 9% of the total biomass. After M. galloprovincialis dropped and died, a void space occurred where the pygmy mussels, Xenostrobus secures and two barnacles, Balanus eburneus and Balanus improvisus made up 57% and 22% of the total biomass, respectively. From the watching observation, M. galloprovincialis was checked at the depth of DL+.5 ~ -4. m. After April 6, their density on seawall increased. In June, there is the mark at the seawall from which M. galloprovincialis dropped to the bottom. It was confirmed that the starfish, such as Asterias amurensis descended the dropped M. galloprovincialis at the bottom (Photo 1). However, A. amurensis wasn t checked in August. The bottom was covered by white veil like anaerobic bacteria. 239

4 DL (m) year month ~. (711) (887) (63) (326) (214) (312) (375) (1384) (84) (244) (45) (28) -.2 ~ -.5 (146) (154) (195) (96) (23) (19) (93) (1483) (171) (289) (55) (46) -.7~ -1. (197) (87) (7) (27) (12) (35) (91) (15) (1792) (255) (727) (7) X. secures Ptericola. sp. cf. lithophaga P. viridis M. galloprovincialis B. eburneus, B. improvisus others Figure 2. A total of three zones biomass Photo 1. Asterias amurensis descended the dropped M. galloprovincialis at the bottom Figure 3 shows the TOC of M. galloprovincialis per 9 m 2 at each depth. M. galloprovincialis appeared at the shallow depth of DL+.3 ~ ±. m in January. Afterwards, TOC increased continuously and reached the maximum value in July. At the middle depth of DL-.2 ~ -.5m, 24

5 TOC increased from February to July 6. At DL-.7 ~ -1. m where M. galloprovincialis could occur was the deepest position, they appeared in March, and in July was peak. When each zone was compared the maximum of TOC is 26 g/9cm 2 at the shallower depth of DL+.3 ~ ±. m. The amount M. galloprovincialis at this zone was smaller than other zones. Therefore, M. galloprovincialis started to attach to the seawall from the shallower depth as well as to drop to the bottom. In contrast, there is a lot of remaining M. galloprovincialis at the deep depth in which M. galloprovincialis was 19 g/9cm 2 in August. Figure 4 shows TOC of the dominant shells species and their proportion. In July, TOC of M. galloprovincialis at the shallower zone was 26g and smaller than that of other zones. In April when M. galloprovincialis starts to appear, TOC obtained from the shallower zone accounted for 69% of the total, but in August when M. galloprovincialis starts to drop and die, it decreased to 3 percent. Therefore, M. galloprovincialis adhesion tends to start from the shallow depth but it tends to drop early too. In contrast, M. galloprovincialis starts to attach later at the deep depth and they survive relatively until late season. There are two individual groups of M. galloprovincialis from January to May (Fig. 5) and these individuals attached at different times to each other. Their average growth rate was.9 mm/day between January and August, but they grew slower after July. Kajiwara (1978) reported that the growth rate of one year old M. galloprovincialis is about.11 mm/day at Yokohama port. The growth rate had similar value obtained of this investigation. TOC (g/9cm 2 ) DL+.3 ~ ±. m DL-.2 ~ -.5 m DL-.7 ~ -1. m month 5 6 Figure 3. Changes of mussels TOC at each depth 241

6 TOC (g/9cm 2 ) DL+.3 ~ ±. m -.2 ~ ~ -1. Proportion (%) month 5 6 DL+.3 ~ ±. m -.2 ~ ~ -1. Figure 4. Changes TOC of mussels on three zones Width (mm) month 6 (ind./m 2 ) 1~ 1~ 1~ 1~ 1~ Figure 5. Two individual groups of M. galloprovincialis from January to May The causes of dropout M. galloprovincialis Figure 6 shows the changes in water quality at the depth of M. galloprovincialis adhesion and precipitation. Temperature is high 25 C in the shallower depth (DL+.3 ~ -1. m). Salinity in July is psu according to the rainfall. Poor oxygen concentration was observed even at the shallower depth in October, November 5, and August, September 6. As for the death of M. galloprovincialis, it is reported that the cause is a high water temperature which lead to drop and die at low tide in the summer (Yamochi et al., 1995); the growth must be controlled at more 26 C (Kajiwara et al., 1978). The death and the dropout of M. galloprovincialis took the influence of amount of the oxygen demand loss. There is a report about it is difficult to live when Salinity is decreased (Onitsuka et al., 2). Therefore, it is considered that the condition near the seawall was severe for M. galloprovincialis. It seems that the combination of these severe conditions resulted in a large amount of dropout. 242

7 Temperature ( C) Salinity (psu) DO (mg/l) Precipitation (mm) month month Figure 6. The changes in water quality at the depth of M. galloprovincialis adhesion and precipitation Harvesting amount of resource with M. galloprovincialis Figure 7 shows the variation of TOC per an individual from June to August. For example, TOC with 3 mm width of an individual had 7.38 mgc/ind. in June, 38.6 mgc/ind. in July, and 56.3 mgc/ind. in August, and it tended to that TOC with an individual increased when the width grew. It is considered that the mussel of ripening effects to develop the generative organs and to emit a spermatozoon and an ovum. The maximum is summer, the minimum is winter (Shiraishi et al. 1986). TOC (mgc/ind.) June July Auguest Width (mm) Figure 7. The variation of TOC per individual from June to August There were four species, Ptericola. sp. cf. lithophaga, X. securis, P. viridis, M. galloprovincialis, that make up the fauna on seawall in this reserch. The dominant species was M. galloprovincialis. The biomass of M. galloprovincialis was.4 kgc of pier length in April. The amount began to increase too much. The largest biomass was 1.4 kgc of pier length in July (Fig. 8). The time of maximum growth is May because TOC of M. galloprovincialis is small as well as the width is small. 243

8 Number of mussel (1 4 ind./m) TOC Biomass (kgc/m) month 5 6 Ptericola. sp. cf. lithophaga P. viridis X. secures M. galloprovincialis Figure 8. The changes TOC of M. galloprovincialis and the individual The relationship between the amount of resource recovery and the number of harvests per year of the macrobenthic attached on the wall is shown in Table 1. The amount of resource recovery was 67.5 kg (wet weight)/year per 1 meter of pier length, in the case of one time (May) of harvest per year. While the amount of recovery was 49.7, 23.1 and 29.4 kg (wet weight)/year per 1 meter of pier length, for two times (November and May) of harvest per year, three times (May, September and January) and four times (November February May, and August,), respectively. Among these investigations, one time per year of recovery resulted to be the largest collection. Assuming four harvests a year, on May, in the harvest, M. galloprovincialis was a dominant species on vertical wall whose standing stock was 8.5 kg (14 gc/m) per 1 meter of pier length. After harvest, M. galloprovincialis re-attached and grew on the cleaned wall. On August, the fourth harvest, M. galloprovincialis which also dominated the wall surface among attached organisms, was taken by 11.5 kg (19 gc/m) per 1 meter of pier length. 244

9 Table 1. The relationship between the amount of resource recovery and the number of harvest per year of the macrobenthic attached on the wall. Number Season Native species Dominant Species Biomass Total Number % *Nonnative species (wet kg/m) (wet kg/m) 1 1 May M. galloprovincialis* Nov B. eburneus * May 9 53 M. galloprovincialis* Jan B. eburneus * May 7 33 M. galloprovincialis* Sep. 1 5 X. secures *.6 1 Nov B. eburneus * Feb. 48 Leptomedusae.2 3 May 9 53 M. galloprovincialis* Aug 1 11 M. galloprovincialis* 11.5 These results suggest that the best approach to take M. galloprovincialis as biomass resources was two times a year, in May when their standing stock reached maximum and in August when organisms would fall, if the attached organisms were seen as biomass resources in this harbor. Potential amount of resource recovery was estimated, assuming to harvest the organisms two times a year (May and August). It was assumed that a water depth was constant in Amagasaki port where M. galloprovincialis attached on the seawall in this research. As a result, the amount of resource recovery was estimated 1,22 kgc in May, and 1,387 kgc in August. The total amount per year was about 2,49 kgc. Further, we must consider the utility of M. galloprovincialis a biomass resource. Effect of improvement on biodiversity Biodiversity was examined by using the index as number of native species when M. galloprovincialis, as nonnative species, was removed. As a result, there was a relationship between the number of species and the number and season of M. galloprovincialis recovery. In autumn and winter when M. galloprovincialis didn t attach to the seawall, the non-native species such as B. eburneus and X. secures made up the fauna. CONCLUSIONS In this study, we investigated the recovery of M. galloprovinciallis attached on the seawall at Amagasaki port in Japan to estimate potential amounts of recovered M. galloprovinciallis as a marine resource. The results are: (1) From October 5 to March 6, the biomass of the barnacle Balanus eburneus was dominant and ranged from.2 ~ 1. kg/.27m 2 (.74 ~3.7 kg/m 2 ), and accounted for 59~87% of total biomass. From April to August, the biomass of M. galloprovincialis made up 245

10 .5~7.8kg/.27m 2 (1.85 ~ 28.9 kg/m 2 ), and over 9% of total biomass. A new space occured after M. galloprovincialis dropped and died. The pygmy mussels, Xenostrobus secures and the barnacles Balanus eburneus and Balanus improvisus made up 57% and 22% of the total biomass, respectively. From the standing stock, M. galloprovinciallis is suggested to be focused as biomass among the attached organisms at the location of this investigation. (2) M. galloprovincialis adhesion starts from the shallower depth (DL+.3~±. m) but they drop early in season. In constant, M. galloprovincialis adhesion starts later at the deep depth (DL-.7~-1. m) and they can survive until late season. (3) The high temperature, low salinity and decreasing oxygen occurred at even relatively shallow depth DL+.3~±. m where M. galloprovincialis attached in summer. It is considered that M. galloprovincialis drop and die by the combination of these influences. (4) The largest biomass was observed in July 6 and the amount reached to1.4 kgc of pier length. (5) These results suggested that it was the best approach to take M. galloprovincialis as biomass resources two times a year, in May when their standing stock reached maximum amount and in August when organisms would fall, if the attached organisms were seen as biomass resources in this harbor. REFERENCES Kajiwara. T., Y. Ura and N. Ito The Settlement, Growth and Mortality of Mussel in the Intertidal Zone of Tokyo Bay, Bulletin of the Japanese Society of Scientific Fisheries, 44(9): (in Japanese with English abstract) Onitsuka. G., T. Yanagi, S. Montani., M. Yamada, N. Ueda and M. Suzuki. 2: An Attempt to Purify Water by Culturing Mussels in Dokai Bay, Japan, Journal of Oceanography, Vol.11, No.3(55) pp (in Japanese with English abstract) Shiraishi A., K. Sakamoto, S. Sumikawa, H. Fujii Seasonal Changes of Biochemical Composition in Various Parts of Blue Mussel, Mytilus Edulis, Journal of home economic of Japan, vol.137, (in Japanese) Tsujino. M. and K. Tamai Sediment Conditions and Meiobenthic Community in Osaka Bay, Japan. Bull. Nansei Natl. Fish. Res. Inst. (29):87-1. (in Japanese with English abstract) Yamochi, S., H. Ariyama, T. Kasukabe, M. Sano, Y. Nabeshima and K. Mutsutani Effect of a Predominant Sedentary Organism of the Coastal Artificial Structure on the Eutrophication of the Coastal Area of Osaka Bay 1. Growth and Elimination of Mytilus edulis galloprovinciallis on the Vertical Wall. Ocean Research. 4(1):9-18. (in Japanese with English abstract) 246