Science Philosophy (PPs 702)

Graduate Program / S3

Institut Pertanian Bogor

September 2003

Instructors:

Prof Dr Ir Rudy C Tarumingkeng (Principal)

Prof Dr Ir Zahrial Coto

Can artificial sea grass mimics natural sea grass?

Khusnul Yaqin

P062030151

E-mail: kyaqini@plasa.com

Introduction

Sea grass plays important role in coastal habitat. The presence of sea grasses may increase the abundance of organisms by increasing (i) the amount of physical structure usable as living space;(ii) the number of microhabitats; (iii) sediment deposition and stabilization;(iv) food resources and (v) protection from predators. Sea grass may also reduce hydrodynamic forces. The ability of sea grass beds to fulfill the majority of these roles is well documented, through both biological (e.g. food resources) and physical (e.g. protection offered by canopy structure). (Lee, et al., 2001).

Despite the importance of sea grass in the coastal zone is well recognized, declines in sea grass meadows are global (Walker and McComb, 1992). These declines may result from natural events such as ‘wasting disease’ (Den Hartog, 1987) or high-energy storms (Patriquin, 1972). Most sea grasses loss, however, have resulted from human activities such as eutrophication (Buithuis and Woelkerling, 1983; Cambridge and McComb, 1984; Neverauskas, 1987), sedimentation (Kirkman, 1978; Buithuis et al., 1984; Lee, 1997), land reclamation and changes in land use (Kemp et al., 1983).

Rehabilitation by using artificial sea grass is one of possibility method to recover destroyed sea grass bed in coastal habitat. As rehabilitation instrument the artificial sea grass has to have some similarities to natural sea grass in order to substitute the role of natural sea grass in the marine environment. In fact, it is impossible that artificial sea grass able to substitute natural sea grass completely. However, up to certain point artificial sea grass fill in existence of natural sea grass. Therefore, it can act as natural sea grass does.

Artificial sea grass is usually used in ecological and behavioral sea grass experiment as imitating or collecting instrument. This instrument is also often used in field experiments to investigate the relationship between associated fauna and the physical structure of the sea grass.

The aim of this essay is to briefly discuss at what extent an artificial sea grass can mimic natural sea grass.

Artificial sea grass

Many types of artificial sea grass are used as research or rehabilitation device. In principle, the construction is simulated similar with natural sea grass, which is consisting of leaf, erect shoot and rhizome. One of example of this construction is the laboratory studies instrument that are using wooden dowels, strips of plastic, rubber bands and a 66-foot-long flume to make model beds that mimic different types of natural sea grass and conditions (figure 1.).

rhizome

root

erect shoot

Fig. 1. Comparison between artificial sea grass construction and natural sea grass morphology. (a) Artificial sea grass construction as laboratory study instrument (Nept, 1999). (b) Natural sea grass morphology, Cymodocea serrulata (Anonym, 1997).

Physical Aspects

The construction of artificial sea grass is created for imitating the function of natural sea grass in water column. Physically, artificial sea grass can imitate what natural sea grass act as a baffle for the incoming water flow, which decrease the current velocities and allow deposition surround it. Almasi et al. (1987) studied the effect of natural and artificial sea grass on sedimentation rates. They observed that the mean flow velocity in the grass-free area was higher than in the sea grass area. Consequently, the increase depositional rate of sediment within the sea grass was due to slowing of water current by the sea grass blades. Bostrom and Bonsdorff (2000) demonstrated that density-dependent effect of Zotera-like and Ruppia-like of artificial sea grass not only act as current-baffling, particle-trapping and sediment-binding, but also minimize possibility of in fauna dislodgement. In addition, Kenyon et al. (1999) observed that fine detritus particles were visibly accumulated on artificial sea grass with 24 h of deployment. A gentle environment due to these actions probably produce biological advantages for many types of marine biota namely, sheltering, feeding and nursery ground and epiphyte substrate.

Biological Aspects

As food resources natural sea grass leaves play unimportant role. Only few animals appear directly to use sea grass production as food; some fish, turtles, sirenians and a few sea urchins with ruminant-like cultures of cellulose-splitting bacteria in theirs

guts are notable exception. Bamess and Hughes (1999) estimated only 5% of sea grass production is consumed directly.

One of food resources that play important role is epiphyte, which attaches on sea grass blades. Artificial sea grass blades that made from strapping band, which have rough surface, are suitable substrate for epiphyte. Yaqin (1998) found that composition of the epiphyte contain 42.2% Bacillariophyceae, 15.8% Cyanophyceae, 15.8% Chromonadea, 10.2% Sarcodina, 5.8% ciliata, and 3.6% Crustacea. Fifteen species of epifauna were recorded by Lee et al.(2001) in the experimental artificial sea grass; nine gastropods, five brachyurans and one bivalve.

Epiphytic structure reveals different composition and abundant between artificial and natural sea grass (Pinckney and Micheli, 1997). Lee, et al. (2001) found Amphipods, microgastropods and polychaetes were common in the Zostera bed, but not in the artificial sea grass. This difference is probably a result of the differences in biological quality between artificial sea grass and Z. japonica. The presence of living rhizomes and spatially complex root system, the ability to release organic carbon (Penhale and Smith, 1977 in Lee et al. 2001) and influence of nutrient fluxes (McRoy and McMilland, 1977 in Lee et al., 2001) by natural sea grass may be contribute to difference in the faunal community between Artificial and natural sea grass.

Epiphytic structure appeared to play only a limited role in determine the density of most mobile fauna, but epiphytic structure appeared to be important in augmenting the settlement of bivalves (Bologna, et al., 1999). These structure increased microstructure on the artificial sea grass blades and might influence settlement by the adhesiveness of the surface. Bologna et al. (1999) found that when epiphytes were abundant on artificial sea grass blades, the densities of small grazers (primarily crustaceans and gastropods) were significantly greater.

Artificial sea grass not only provides epiphyte as food resources, but also provides eligible sheltered habitat for numerous marine fauna. It is because artificial sea grass attract physically a fauna similar to that of natural sea grass (Bell et al., 1985; Virnstein and Curran, 1986;Sogard, 1980 in Sogard and Able, 1994). Liu and Lonerangan (1996) found that large postlarvae (2.7mm CL) and juvenile (4.1 mm CL) of tiger prawn (Penaeus semisulcatus and P. esculentus) both were more abundant on artificial sea grass than bare sand during the day but not at night, which was indicating that they used it as sheltered habitat.

The development of a dial pattern in immigration of marine fauna to artificial sea grass habitat could linked to variability of behavior and/or predation risk. The more active and larger individual colonized artificial sea grass at night and vice versa (Sogard and Able, 1994). Bauer (1985) suggested that reduced predation risk from visual hunters at night allowed caridean shrimp to move up into water column above the sea grass canopy. Similarly, Vance (1992 in Sogard and Able, 1994) proposed that a pattern of higher nighttime activity in three species of penaeids resident in sea grass and mangrove habitat was related to decrease fish and bird predation at night.

Chemical Aspects

Interaction between artificial sea grass blades and the epiphytes create both sediment and contaminant trap. Nept (1999) suggest that sometimes the artificial canopy “captures” contaminants by creating still regions that allow particulate material to accumulate around stems and leaves. In addition, this canopy create little of turbulence, which may improve the uptake of elements like phosphorous and nitrogen, or may accelerate the uptake of chemicals by microbial communities living on the artificial blade surfaces.

Liu and Lonerangan (1996) observed that both larvae and juveniles of Penaaeus semisulcatus were greater numbers on natural than artificial sea grass during the day. Juvenile P semisulcatus were also more abundant on natural than artificial sea grass. This difference is probably due to chemical compounds that produced by natural sea grass. Study on lobster postlarvae (Homarus americantis) indicates that they can detect sea grass extract in seawater and use them for orientation (Boudreu et al. 1993 in Liu and Lonerangan, 1996). The chemical cue emitted from the sea grass might influence the habitat preference of lobster post larvae (Boudreu et al., 1990, 1993, in Liu and Lonerangan 1996). The presence of eelgrass accelerates the molt time of blue crab megalopae (Forward et al., 1994 in Liu and Lonerangan 1996) and it was suggested that eelgrass provide both chemical and natural cue to megalopae. Therefore, it was indicated that chemical cue play important role in biotic interaction which is not occur in artificial sea grass.

Conclusion

It is unavoidable that non-living thing cannot imitate living thing completely. In the case artificial sea grass, it may be able to mimic physical aspect of natural sea grass almost perfectly such as water movement baffling, particle trapping and sediment binding. Although, it depends on how similar the artificial sea grass construction to natural sea grass. On the other hand, in term of chemical and biological aspects, artificial sea grass can imitate fewer aspect of natural sea grass than those on physical aspects. It is because there is no biotic interaction between marine fauna and artificial sea grass.

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