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Study on the Quantitative Evaluation of Performance of Artificial
Timber Reefs in Structuring New Habitats for Marine Life
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                  Jamaluddin Fitrah AlamJapan is known as a country playing an important role in the world’s fisheries. Withstrong fish-rich food culture with advanced fisheries management system, Japan wasleading the fisheries production. However, the national fisheries production has
declined sharply for these 30 years, and the production may drop even more in nearfuture. This situation required the central government to fulfil domestic needs withimported products. Various measures have been taken to alleviate this serious
problem, including deployment of ARs. Japan has a long history of developing ARs. Of
them, artificial timber reefs (ATRs) that use timbers from forest thinning has beenused more recently. In Japan where forest occupying one-third of the total land area,a regular forest thinning is required to maintain the forest in a healthy condition.
Most of the logs from the forest thinning left behind in the forest for no use, becauseof expensive labour cost to collect them. Therefore, the use of timbers as AR material
has a potential regarding its high availability. Thus, I studied how ATRs deployment
is effective in terms of shaping a new ecosystem and performing an increase of fishproduction in Mitsu Bay, Japan.
Objectives of this study, as mentioned in Chapter 1, are (1) to understand thecommunity composition of organisms associated at ATRs which are feed for fish
community, (2) to illustrate the processes of food web creation in the ATRs and thecomparison to other types of ARs (concrete) and area without ARs (Control), and (3) toelucidate the nutrient cycling processes enhanced by the deployment of ATRs. To
perform the above objectives, in Chapter 2, species composition of animals associatedwith the deployed ATRs were described, which is also used for discussion as importantcomponent in the food web in Chapter 3. Then, in Chapter 3, based on the results ofnumerical calculations, functions of the newly formed ecosystem were discussed. In
Chapter 4, the model was integrated with the processes in lower trophic levels, andthe characteristics of ATRs were described in terms of nitrogen and phosphorus cycles.
The model constructed in the present study consists of both pelagic and benthic
systems and being interactive each other in and around of the ATRs areas in Mitsu
Bay. The equations used in the model are those representing the biogeochemical
processes occurring in the ATRs and Mitsu Bay system.
In Chapter 2, 272 taxa were identified for the associated animals from theretypes of ATRs (ATRs, ATRsOS and ATRsLB) in two deployment sites during 20162018. Arthropods dominated followed by molluscans and annelids. Individual numberof those organisms was high in summer and low in winter. The individual number washigh in the first year after the ATRs deployment, and it decreased in the second year
and after, suggesting the animal community may have matured by balancing thegrowth and feeding by fish. All three types of ATRs were commonly large in individual
number and small in species number, resulting a low diversity index. Of the threedifferent types of ATRs, ATRsLB and ATRsOS showed the highest individual number
and highest species number, respectively. The diversity index for simple ATRs waslowest compared to those for ATRsOS and ATRsLB. This result suggests that ATRs
with additional materials can provide a wide range of feed animals which may attract
more fish.
Several feed organisms growing at ATRs are staple for gathering fish and may
be an important factor to determine the structure of fish community. The model usedin Chapter 3 investigated the relative efficacies of the different types of ATRs andcompared them with the conventional ACRs and Control area without ARs. Observed
data were used to validate the model calculations, and the model outputs fit to thetemporal variations of the observed biomass of both feed animals and fish. Here, fish
behavior is taken into account by analyzing a series of video camera recordings. The
feeding selectivity of dominant fish was also incorporated in the model referring to thevast published reports. Both ATRs and ACRs revealed to support far greater fishbiomass compared to Control. Other than provision of feed, this may be coming fromthe function of ATRs that provides shelters particularly for juvenile and smaller-sizedfish. Regarding ACRs, they are likely to host larger-sized fish by their larger room in
the frame. The numerical model revealed that the newly created ecosystem in ATRs
was productive judging from material flows through predator-prey relationships
between feed animals and fish. Despite, as natural products, the decomposed timbers
may act as source for organic matter in the deployment area as discussed in Chapter
4.
The simulation outputs for phosphorus and nitrogen cycles after thedeployment of ATRs with integration of the food web model developed in Chapter 3
reproduced well the seasonal changes of nutrient concentrations in Mitsu Bay. Alongwith a background of the biomass increase in wintertime, it was detected theenhancement of nutrient regeneration in winter season through the processes ofexcretion, egestion and dead matter from mortality. Meanwhile these inputs werecalculated low in spring and summer. This indicates that internal regeneration ofnutrients is playing a key role in the nutrient cycling in ATRs system particularly inwinter.
The higher nutrient concentration in the ATRs deployment area is due toincreased input of organic matter from the ecosystem that was created at the ATRs.
Evidently, the input of DIP and NH due to excretion by organisms were double andtriple higher than those in the surrounding water. Further, the model calculation also
revealed that nutrient produced by regeneration process in the ATRs deployed area
are transferred to the surrounding water by physical exchange of water. Thus, we cansay that ATRs can act as a nutrient source to the surrounding water not only toenhance the biogeochemical processed in the ATRs area. Particularly, this is animportant process in areas like Mitsu Bay where the other nutrient sources were quite
small such as inputs from land, precipitation and benthic flux.
The results obtained by the application of numerical model in this study would
have much improved our understandings on the enhancement of the biogeochemical
processes in material cycles after the deployment of ATRs through created food web
there. It is necessary to replace the ATRs regularly because of their longevity. As
mentioned in Chapter 3, the materials, Japanese Cypress, used for ATR in this study,
is comparatively harder and slowly decomposed to the other tree species, but thelongevity is proved 5 years or so in the present study. Since the project here was a pilot
study, in order to achieve more successful enhancement of fishery production inpractical scale, much greater number of ATRs deployments with expansion ofdeploying area will be needed, in addition to increases of river and sewer discharges.
To perform this kind of activity, it is necessary to collaborate with fishermen,
forest keepers, local government, NPOs, NGOs and volunteers. Deployment of ATRs
using byproducts such as thinning timbers with leaves and branches and oyster shells
may enhance not only the fish stock in the sea but also help fasten the people’sconnectivity by fostering the activity to establish a recycling-oriented society.