Aggregation of Lepidostomatidae in small mesh sizelitter-bags: implication to the leaf litter decompositionprocess

Aung Nanda Æ Takashi Asaeda Æ Takeshi Fujino ÆKian Siong Æ Takashi Nakajima

Received: 17 July 2008 / Accepted: 8 August 2008 / Published online: 24 August 2008

� Springer Science+Business Media B.V. 2008

Abstract Invertebrate colonization during leaf litter

decomposition was studied at the 2nd order of Yanase

River, Iruma city, Saitama, Japan from November 13,

2002 to May 20, 2003. Two different mesh sizes (1 and

5 mm) of litter-bags were used to evaluate the decom-

position of leaf litter of Sakura (Prunus lannesiana),

bags were placed equally in riffle (water flow velocity:

0.2–0.6 m s-1) and pool (water flow velocity: 0.04–

0.06 m s-1). Mass loss and invertebrates in the litter-

bags were monitored at interval between 1 and

3 weeks, and the invertebrates were classified based

on their functional feeding group. Among the inverte-

brates found inside the litter-bags, the case-bearing

shredder Lepidostomatidae was the most dominant

invertebrates and they were the early colonizer that

appeared about 3 months after the litter-bags immer-

sion. In absence or low number of leaf-shredders, the

decomposition rates in 1 and 5 mm litter mesh bags

followed the exponential (or first-order) decay kinetic

(R2: 0.72–0.92). However, the presence of a large

number of leaf-shredders in 1 mm litter-bags caused an

acceleration of decomposition process; that even

resulted faster mass loss than the loss from the

5 mm mesh bags placed in riffle area (0.030 day-1

vs. 0.011 day-1). Our results shows the importance of

using different mesh sizes of litter-bags in decompo-

sition study, which is applicable to the experiment in

lotic or lentic ecosystem. Using smaller mesh size of

litter-bags can provide information on how significant

the effect of detritus feeders on the decomposition

process, while the bigger mesh size can represent better

the natural decomposition process when a large

number detritus feeders is present in the smaller mesh

size of litter-bags.

Keywords Detritivore � Decomposition �Litter-bag � Lepidostomatidae � Shredder assemblage

Introduction

The decomposition of detritus (i.e. leaves, twigs, and

woody parts) plays important role in the processes of

energy flow and nutrient cycling (Giller and Malmq-

vist 1998). Litter-bag decomposition studies in lotic

and lentic ecosystem usually employ mesh bags with

0.8–10 mm mesh size, the use of smaller-mesh bags

universally results in reports of slower decomposition

rates for the same material and this has been

attributed both to exclusion of detritus feeders from

the smaller mesh and to greater loss by fragmentation

in larger-mesh bags (Brinson et al. 1981). Several

ecologists have also used few mesh sizes of litter

mesh bag in order to achieve their research objec-

tives. For example, Watts et al. (2008) used 0.1 mm

A. Nanda � T. Asaeda (&) � T. Fujino �K. Siong � T. Nakajima

Department of Environmental Science,

Saitama University, 255 Shimo-okubo,

Sakura-ku, Saitama 338-8570, Japan

e-mail: asaeda@mail.saitama-u.ac.jp

123

Wetlands Ecol Manage (2009) 17:417–421

DOI 10.1007/s11273-008-9114-6

and 2 mm mesh bags for the determination of peat

bog restoration techniques, and Bradford et al. (2002)

used three mesh sizes of litter-bags to evaluate the

importance of micro-, meso- and macro-fauna on

decomposition process.

Detritus feeders affect decomposition of litter

through changes in particle size due to mechanical

fragmentation, production of feces, and assimilation of

detritus for growth and respiratory work (Cragg 1961;

Cummins et al. 1989). Furthermore, Boulton and Boon

(1991) reported that the results of litter-mesh bags

experiments would be bias if the number of inverte-

brates contained in the mesh bags is more than twice

the number found in natural leaf pack. In upstream of

river ecosystem, shredder is the main group of

invertebrate responsible for the conversion of coarse

particulate organic matter to fine particulate organic

matter (Cummins et al. 1989). Meanwhile the litter

processing in wetlands ecosystem can be significantly

affected by the amphipods (Saenger 2002). Middleton

and McKee (2001) showed that the decay rates due to

macro-fauna (e.g. crabs and amphipods) that fed on the

detritus in litter-bag was three times faster than the

decay rates due to microbial activities.

Nakajima et al. (2006) reported that leaf of Sakura

(Prunus lannesiana) had higher breakdown rates in

the riffle habitat than the leaf placed in the pool area.

The authors suggested that water flow velocity and

transported silt particle enhanced the breakdown rates

of leaf in riffle zone. The authors used both 1 and

5 mm size of litter-bags; however, the percentage of

mass remaining after certain time period was reported

as the average measurements from both mesh sizes of

the litter-bags, this gave a large standard deviation of

mass loss, particularly the measurement after three

months of the litter-bags immersion. Furthermore,

although invertebrates were separated and identified

from each litter-bag before obtaining the final mass

remaining, the interactions between detritus feeder

activities and rates of mass loss were not discussed.

Therefore, the aim of this study was to evaluate the

importance of detritus feeder on leaf litter decompo-

sition performed using litter mesh bags.

Materials and methods

The leaf litter decomposition experiment was carried

out at the 2nd order Yanase River in Iruma city,

Saitama, Japan from November 13, 2002 to May 20,

2003. This stream flows through a dense deciduous

forest, in which Sakura (P. lannesiana Wils.) is one

of the dominant tree species. We used 1 and 5 mm

litter-mash bags to evaluate the decomposition of

Sakura leaf litters, litter-bags were filled with about

2.0 g of oven-dried (50�C) leaf, bags were placed

equally in riffle (water flow velocity: 0.2–0.6 m s-1)

and pool (water flow velocity: 0.04–0.06 m s-1).

Mass loss and invertebrates in the litter-bags were

monitored at 1–3 weeks interval, the invertebrates

were classified based on their functional feeding

group (i.e. collector filterer, collector gatherer, shred-

der and predator) (Hauer and Resh 1996; Giller and

Malmqvist 1998).

The breakdown rates (k) were calculated by using

an exponential decay model, Wt = Wo exp(-kt), in

which Wt is the mass remaining after t (day), Wo is

the initial mass of the sample, and t is the time

measured in days. The Zellner’s seemingly unrelated

regression (SUR) model (STATA Ver.10, StataCorp

LP, TX, USA) was used to examine the difference of

k values. In each SUR model, two regression slopes

(i.e. k) were obtained simultaneously and the slopes

differences were compared using Wald-test.

Results and discussion

Overall, the average percentage mass loss of

P. lannesiana was faster in the riffle than the pool

regardless the litter-bag mesh size (Table 1). How-

ever, mass loss in the first two months, presumably

due to the passive leaching and microbial processes,

was relatively slow and comparable among the litter-

bags (Figs. 1 and 2), slightly higher mass loss in riffle

than the pool sites was likely due to mechanical

fragmentation by faster water current. The break-

down rates in riffle, however, became distinctly

different after the invertebrate colonization in 1 mm

litter-bag (Fig. 1). The invertebrates colonization was

observed mostly in 1 mm mesh bags from both riffle

and pool locations about three months after the

immersion of litter-bags (Fig. 1). A total of nine

insect families (i.e. shredder (Lepidostomatidae,

Nemouridae and Sericostomatidae), collector

gatherer (Baetidae and Chironomidae), collector

filterer (Hydropsychidae and Simulidae), predator

(Corydalidae and Perlidae)) were found inside the

418 Wetlands Ecol Manage (2009) 17:417–421

123

litter-bag. And the case-bearing shredder Lepidostom-

atidae was the most dominant invertebrate and they

were early colonizers. The abundance of shredders

(e.g. Lepidostomatidae, casing size: 6–12 mm long,

diameter: 1–2 mm, drymass: 6–9 mg) in 1 mm mesh

bags was the highest at the beginning of the inverte-

brate colonization stage (Fig. 1) and then decreased in

the later samplings, with only abandoned body casings

(diameter [1 mm) left inside the litter-bag (Fig. 1b).

Invertebrate assemblage inside the 5 mm mesh of leaf

litter-bags was rarely found in most of the samplings,

nevertheless this does not mean they were absence in

5 mm mesh bags. The detritus feeders may also have

accessed the leaf litter in 5 mm mesh bag at the same

time, however, because the litter-bags mesh size was

big enough, they were not trapped like the case in

1 mm mesh bags.

The use of smaller-mesh bags results in slower

decomposition due to the exclusion of detritus feeders

from the smaller mesh and to greater loss by

fragmentation in larger-mesh bags (Brinson et al.

1981). In contrary to this general acceptance, Watts

et al. (2008) reported the breakdown rates of litter in

peat bog were higher in the 0.1 mm mesh size than

the 2 mm mesh size, and this have been attributed to

a better moisture retention in 0.1 mm mesh size bags

that favored microbial colonization and subsequently

Table 1 Comparison of decomposition rates of P. Lannesiana in 1 and 5 mm mesh litter-bags, placed at riffle and pool

Mesh size Decay rate (k, day-1) 1 mm 5 mm

Pool (high Sh) Pool (low Sh) Riffle (high Sh) Riffle (low Sh) Pool Riffle

1 mm Pool (high Sh) (0.003, R2 = 0.65) –

Pool (low Sh) (0.002, R2 = 0.72) * –

Riffle (high Sh) (0.030, R2 = 0.66) *** *** –

Riffle (low Sh) (0.016, R2 = 0.82) *** ** ** –

5 mm Pool (0.003, R2 = 0.89) NS *** *** *** –

Riffle (0.011, R2 = 0.92) *** *** *** ** *** –

R2: coefficient of determination, k: decay parameter, Sh: shredder

Significant level: NS, not-significant; * 0.01 \ P \ 0.05, ** 0.001 \ P \ 0.01, *** P \ 0.001

Leave decomposition in 1mm mesh bags (pool)

0

25

50

75

100

0 7 12 21 35 56 70 93 118 146 167 188

Days

mas

s re

mai

ning

(%

)

0

5

10

15

20

25

30

Shr

edde

r (n

umbe

r/ba

g)

no. shredder per bag (high shredder)

no. shredder per bag (low shredder)

% mass remaining (low shredder)

% mass remaining (high shredder)

Leaves decompostion in 1 mm mesh litter bags (riffle)

Abandonedcasings

0

25

50

75

100

0 7 12 21 35 56 70 93 118 146 167 188

Days

mas

s re

mai

ning

(%

)

0

5

10

15

20

25

30

Shr

edde

r (n

umbe

r/ba

g)

no. shredder per bag (high shredder)

no shredder per bag (low shredder)% mass remaining (low shredder bag)

% mass remaining (high shredder bag)

a)

b)

Fig. 1 The average percentage of mass remaining in

1 mm mesh litter-bags, placed in pool (a) and riffle (b). Error

bars before invertebrate colonization (i.e. before 167th (a) and

93rd (b) days) represent standard deviation from three

measurements (n = 3). After the invertebrate colonization,

error bars represent standard deviation of two measurement

results, while result without error bars represent result from

single litter-bag

Leaves decomposition in 5 mm mesh Litter bags (pool and riffle)

0

25

50

75

100

0 7 12 21 35 56 70 93 118 146 167 188

Days

mas

s re

mai

ning

(%

)

0

5

10

15

20

25

30

Shr

edde

r (n

umbe

r/ba

g)

no. shredder perbag (pool)no. shredder per bag (riffle)% mass remaining (pool)% mass remaining (riffle)

Fig. 2 The average percentage of mass remaining in

5 mm mesh litter-bags, placed in pool and riffle and the

average number of shredder found in each sampled bag. Error

bars represent standard deviation of three samples (n = 3)

Wetlands Ecol Manage (2009) 17:417–421 419

123

decomposition. Likewise, our experiment showed

that P. lannesiana leaf in 1 mm mesh bags decom-

posed faster than the leaf litter in 5 mm mesh bags

placed in riffle (0.016–0.030 day-1 vs. 0.011 day-1)

and the abundance of Lepidostomatidae in

1 mm mesh bags was associated with the accelera-

tion of the mass loss (Fig. 1). Whiles et al. (1993)

showed that the case-bearing shredder, Lepidostom-

atidae was early colonizer and they colonize rapidly

following disturbance, enhancing the restoration of

vital ecosystem processes such as litter decomposi-

tion. Cummins et al. (1989) showed that shredders

were important in leaf litter fragmentation into finer

particle that enhance the rate of decomposition

process.

While shredding insect like Lepidostomatidae is

confined to the headwater ecosystem (Vannote et al.

1980), few studies showed the importance of shrimp

and shrimp like-crustacean (Gammaridea, Amphi-

poda) on leaves litter decomposition in mangrove

ecosystem. For example, Middleton and McKee

(2001) examined the macro-fauna consumption of

leaves litter at Belizean mangrove forest, they

reported that the presence of sandhoppers (Gammari-

dea, Amphipoda) in 1 mm litter mesh bags led to a

greater mass loss of leaves litter. Rajendran and

Kathiresan (2004) showed that the abundance of

juvenile shrimps was the highest inside the litter-bags

(2 mm) of easily decomposed leaves and therefore

the authors proposed this ‘‘vegetation trap’’ technique

to increase the population of juvenile shrimps in

mangrove waters. These results suggest that the small

mesh sizes (1–2 mm) of litter-bags are accessible by

the organisms during their young stage, and they are

likely to exploit the litter-bags environment as

‘‘favorable micro habitats’’, not only to feed on the

leaf litter but also to avoid from predatory effect.

However, a study by Ananda et al. (2008) that used

1 mm mesh size litter bags, showed the decay rates of

both fresh and dried mangrove leaves (Rhizophora

mucronata) were not associated with the invertebrate

abundance as no detritivore was found during the

experiment. The colonization of invertebrate in litter

mesh bags and their influences on the decomposition

rates were therefore, somehow complicated. And yet,

regardless the nature of habitats or ecosystems (i.e.

steams and wetlands), the use of small mesh bags

may create ‘‘favorable micro-habitats’’ to micro-,

meso- and macro-size detritivores, leading to a bias

result in the decomposition experiment if a large

number of detritivores are present inside the litter-

bags.

A direct approach to evaluating the importance of

detritus feeders on decomposition experiment is to

eliminate them selectively and compare rates of

decay in their presence and absence (Brinson et al.

1981). However, such approach would be difficult to

perform in practice, particularly if the experiment is

conducted in aquatic ecosystem, because the removal

of detritus feeders from the litter-bags may also

introduce new error; that is mechanical disturbance.

We suggest using at least two different mesh sizes of

litter-bags for decomposition experiment in streams

or freshwater wetlands; in which the smaller mesh

size can provide information on how significant the

effect of detritus feeders on the decomposition

process, the bigger mesh size can represent better

the natural decomposition process when a large

number detritus feeders is present in smaller mesh

size of litter-bags.

Acknowledgements This research was financially supported

by a Research Grant-in-Aid from the Ministry of Education,

Culture, Sports, Science, and Technology, Japan (No. 15686021

& No. 17760388) and by the Japanese Society of the Promotion

of Science.

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