Masuda et al.: Fish assemblages associated with three types of artificial reefs 
171 
Deployment of wooden ARs as a tool 
for ecosystem-based fishery management 
The major anthropogenic impacts on coastal ecosys- 
tems include overfishing, loss of physical complexity 
induced by construction or trawling, and eutrophica- 
tion induced by water discharge. ARs made of cedar 
and other materials have the potential to attenuate at 
least some of these problems. ARs are useful in that 
they preclude trawling, protect juveniles in nursery 
grounds, and provide fishing sites for artisanal fisher- 
men (Polovina, 1991). Our study site had also been a 
trawl fishing ground for bivalves and sea cucumbers, 
but fishermen could not trawl at our ARs. The preven- 
tion of trawling resulted in the accumulation of rela- 
tively large individuals of sea cucumber in our ARs 
(R. Masuda, unpubl. data). Habitat complexity, such 
as vertical relief and holes, can be a positive factor 
for the survival of juvenile fish. For instance, Gorham 
and Alevizon (1989) showed that the attachment of 
polypropylene rope to ARs significantly increases the 
abundance of juvenile fish. Wooden ARs not only pro- 
vide vertical relief but also provide a porous substrate 
for boring and attachment by encrusting organisms, 
such as boring sponges, oysters, and wood boring pid- 
dock. Some demersal fishes, such as black rockfish, 
wrasses, and gobies might well use these encrusting 
organisms for both refuge and as prey. 
Most of the encrusting organisms on ARs are 
plankton feeders that can use a wide size range of 
phytoplankton and zooplankton. For example, a sin- 
gle oyster filters several liters of sea water per day 
and produces pseudofeces that contain about half 
of the organic content of that trapped on the gills 
(Deslous-Paoli et al., 1992). Most juvenile and young 
demersal fish feed on benthic organisms in addition 
to relatively large zooplankton. Therefore, encrusting 
organisms on ARs can transform phytoplankton and 
microzooplankton to a usable energy source for fish- 
es. Fabi et al. (2006) demonstrated that ARs provide 
the main food source (e.g., encrusted organisms and 
crustaceans) for the three major fish species ( Sciaena 
umbra, Diplodus annularis, and Lithognathus mor- 
rnyrus) they studied. Furthermore, improved water 
clarity due to the filtering function of the encrusting 
organisms is likely to result in the better growth of 
primary producers, such as macroalgae. The use of fish 
reefs as biofilters for nutrient removal has also been 
proposed by Seaman and Jensen (2000). 
The efficacy of wooden ARs is of a short duration (up 
to 3-5 years) compared to those made of concrete, which 
can last decades (Yabe, 1995). However, fishermen have 
observed that wooden ARs attract fish sooner than other 
types of AR. Although wooden ARs biodegrade sooner 
than concrete ARs, from an ecological point of view of 
providing immediate refuge, habitat, and a source of 
food, they have long-term effects on the marine environ- 
ment. Simple wooden ARs that combine logs and con- 
crete blocks sink easily in a muddy substrate, and their 
life as an effective AR can be as short as one year (R. 
Figure 6 
Seasonal changes in the mean (±standard error) number 
of fish species and individuals per transect in the area 
immediately adjacent to the artificial reefs, and the surface 
and bottom water temperatures measured in those areas 
during the surveys from January 2002 to June 2008, at 
Nagahama, Maizuru, Japan. Vertical arrows represent the 
date (21 May 2004) of artificial reef deployment. 
Masuda, personal observ. ). The shape of wooden ARs 
presented in this article, with a double-cross formation 
(Fig. 1), provides an open and stable vertical relief that 
can attract more fish recruits. This formation can also 
act as a stable substrate for encrusting organisms that 
can function as powerful biofilters, and has a longer 
durability than other wooden constructs. 
The recruitment of reef fishes is often limited by 
the availability of suitable nearshore nursery habitats, 
which tend to be vulnerable to anthropogenic impacts. 
The decrease of reef fish populations is therefore partly 
attributable to the loss of nursery habitats, such as 
natural rocky reefs and seagrass beds. The deployment 
of wooden ARs may provide an opportunity to mitigate 
this trend of decline in nursery quality and because 
they are highly biodegradable, the risks of unexpect- 
