Feeding Ecology of the Sesarmid Crab Neosarmatium trispinosum Davie (Crustacea: Brachyura) from the

Mangroves of the Ryukyu Islands, Japan

MS ISLAM, T UEHARA, S SHOKITA AND MA RAHMANMS ISLAM, T UEHARA, S SHOKITA AND MA RAHMAN

Faculty of Science, University of the Ryukyus, Okinawa, Japan

General aims

Specific aims

Investigate the feeding habits of Neosarmatium trispinosum in the mangrove ecosystems of the Ryukyu Islands, Japan.

1. Stomach contents analysis

2. Consumption of mangrove leaves

3. Leaf preference based on colors

4. C/N ratio in leaves, sediments and faces

5. Nutritional analysis of mangrove leaves

Aims and Background

Methodology

Nutritional analysis

Mangrove leaves

Crab tissues

C/N ratio analysis

Leaves andsediments

Crab faeces

Feedingexperiment

Leafconsumption

Leaf preference

Stomachanalysis

Stomachfullness

Stomachcontents

Sampling

Statistical Analysis

Stat View 5.0

Map of samples collection sites on the Ryukyu Islands, Japan.Map of samples collection sites on the Ryukyu Islands, Japan.

Overview of Shira mangroves on Iriomote Island, Okinawa, Japan

Shira River on Iriomote Island, during low tide

Shira River on Iriomote Island, during high tide

Sampling station of Shira mangroves, during low tide

Sampling station of Shira mangroves, during high tide

Study species, the mangrove sesarmid crab Neosarmatium trispinosum Davie

Three different types of Bruguiera gymnorrhiza mangrove leaves used for feeding experiments, C/N ratio and nutritional analysis. Scale = 5 cm.

Green leaves Yellow leaves

Brown leaves

Sto

ma

ch

fu

llne

ss

(%)

Seasons Sexes Islands

Stomach fullness of N. trispinosum. SS, Miyako Island; SR, Iriomote Island; NR, Okinawa Island. Bars with different letters

are significantly different (P<0.0001, Statview ANOVA).

Pe

rce

nta

ge

occ

urr

en

ce

(%)

Food categories Food categoriesP

erce

nta

ge

occ

urr

ence

(%

)

Stomach content analysis of N. trispinosum. NF, not found; SS, Shimajiri swamp on Miyako Island; SR, Shira River on

Iriomote Island; NR, Nuha River on Okinawa Island.

IslandsSeasons

Sexes

Supplied mangrove leaves Supplied mangrove leaves

Co

ns

um

pti

on

ra

te (

%)

Gro

wth

by

bo

dy

wei

gh

t (%

)

Consumption rate and growth by body weight of N. trispinosum. Data indicate mean (±SD), N=24. Bars with different letters are

significantly different (P<0.0001, Fisher’s PLSD).

A-C: Before processA1-C1: After processABB1C1GreenYellowBrownGreenYellowBrownCA1Supplied Together

Changes in appearance of B. gymnorrhiza mangrove leaves by N. trispinosum.

Mode of Processing and ConsumptionMode of Processing and Consumption

Supplied separatelySupplied separately Supplied togetherSupplied together

Changes in appearance of B. gymnorrhiza leaves by Neosarmatium trispinosumABB1C1A, A15 cmB, B15 cmC, C15 cmGreenYellowBrownGreenYellowBrownCA1A-C: Before processA1-C1: After processMode of Processing and ConsumptionsSupplied SeparatelyABB1C1GreenYellowBrownGreenYellowBrownCA1Supplied Together

Changes in appearance of B. gymnorrhiza leaves by Neosarmatium trispinosumABB1C1A, A15 cmB, B15 cmC, C15 cmGreenYellowBrownGreenYellowBrownCA1A-C: Before processA1-C1: After processMode of Processing and ConsumptionsSupplied SeparatelyABB1C1GreenYellowBrownGreenYellowBrownCA1Supplied Together

Preference of B. gymnorrhiza mangrove leaves by N. trispinosum.

Leaf Preference Based on Colors and QualityLeaf Preference Based on Colors and Quality

Brown

First choice

Yellow

Second choice

Green

Third choice

TC

(m

g/g

dry

wt.

)T

OM

(m

g/g

dry

wt.

)

TN

(m

g/g

dry

wt.

)C

/N r

ati

os

Burrow leaves

TC, TN and TOM contents, and C/N ratio in burrow leaves. Bars with different letters are significantly different (P<0.0001, Fisher’s PLSD).TC, TN and TOM contents, and C/N ratio in burrow leaves. Bars with different letters are significantly different (P<0.0001, Fisher’s PLSD).

NR=Nuha RiverSR=Shira River

TC

(m

g/g

dry

wt.

)T

OM

(m

g/g

dry

wt.

)

TN

(m

g/g

dry

wt.

)C

/N r

ati

os

Burrow sediments

TC, TN and TOM contents, and C/N ratio in burrow sediments. Bars with different letters are significantly different (P<0.0001, Fisher’s PLSD).

TC, TN and TOM contents, and C/N ratio in burrow sediments. Bars with different letters are significantly different (P<0.0001, Fisher’s PLSD).

NR=Nuha RiverSR=Shira River

Comparison of C/N ratio in burrow leaves and sediments. Comparison of C/N ratio in burrow leaves and sediments.

NR=Nuha River SR=Shira River

Leaves

C/N

ra

tio

s

NR SR

C/N

ra

tio

s

SedimentsNR SR

C/N = 22C/N = 52

C/N = 17-20, a value suggested as a general maximum for sustainable animal nutrition by Russel-Hunter

(1970).

C/N = 17-20, a value suggested as a general maximum for sustainable animal nutrition by Russel-Hunter

(1970).

C/N

ra

tio

s

Leaf processing

C/N ratio in mangrove leaves, processed by N. trispinosum. Bars with different letters are significantly different (P<0.0001, Fisher’s PLSD).

C/N ratio in mangrove leaves, processed by N. trispinosum. Bars with different letters are significantly different (P<0.0001, Fisher’s PLSD).

C/N

ra

tio

s

Crab faeces

C/N ratio in faeces of N. trispinosum. Bars with different letters are significantly different (P<0.0001, Fisher’s PLSD).

C/N ratio in faeces of N. trispinosum. Bars with different letters are significantly different (P<0.0001, Fisher’s PLSD).

Present study and literature records of C/N ratio in leaves and sediments from mangroves- a habitat of sesarmid crabs.

MaterialsMaterials C/N ratioC/N ratio LocationLocation ReferenceReference

LeavesLeaves 7474 South AfricaSouth Africa Steinke et al. (1983)Steinke et al. (1983)

9292 AustraliaAustralia Micheli (1993)Micheli (1993)

115115 JapanJapan Present studyPresent study

SedimentsSediments 1919 MalaysiaMalaysia Tanaka and Choo (2000)Tanaka and Choo (2000)

2020 TanzaniaTanzania Skov and Hartnoll (2002)Skov and Hartnoll (2002)

2222 JapanJapan Present studyPresent study

Nutritional composition of mangrove leaves at wet conditions (g/100g).

Ca

rbo

hyd

rate

(g

/100

g)

En

erg

y (

kca

l/10

0g

)

1

2

3

CONCLUSIONS

Stomach content showed that the diet of Stomach content showed that the diet of Neosarmatium trispinosumNeosarmatium trispinosum mainly consisted of mainly consisted of mangrove leaves, complemented with little mangrove leaves, complemented with little amount of sediments, indicating as a primarily amount of sediments, indicating as a primarily detritivorous species.detritivorous species.

Consumption rates of the brown leaves was Consumption rates of the brown leaves was significantly higher than those of yellow or green significantly higher than those of yellow or green leaves, indicating that brown leaves are highly leaves, indicating that brown leaves are highly nutritious for the mangrove sesarmid crabs.nutritious for the mangrove sesarmid crabs.

Burrow sediments of Burrow sediments of N. trispinosumN. trispinosum had C/N had C/N ratio 2-3 times lower than that of burrow leaves, ratio 2-3 times lower than that of burrow leaves, indicating that the sediments could have higher indicating that the sediments could have higher nutritional value than the burrow leaves.nutritional value than the burrow leaves.

HYPOTHESES

Why do mangrove crabs eat brown (aged) leaves?Why do mangrove crabs eat brown (aged) leaves? Mangrove leaves are unlikely to fulfill the N Mangrove leaves are unlikely to fulfill the N requirements of crabs, which they plaster onto burrow requirements of crabs, which they plaster onto burrow wall to increase the edibility, where N content increase wall to increase the edibility, where N content increase and C/N ratio decrease through microbial activities. and C/N ratio decrease through microbial activities. Thus by not eating leaves immediately, leaving them to Thus by not eating leaves immediately, leaving them to age on burrow wall. Therefore, crabs might not only age on burrow wall. Therefore, crabs might not only improve the digestibility of leaves, but also decrease improve the digestibility of leaves, but also decrease the C/N ratio in their diets.the C/N ratio in their diets.

Might sediment be an important source of N for crabs?Might sediment be an important source of N for crabs? Mangrove sediment detritus could be a richer source Mangrove sediment detritus could be a richer source of N, as shown by lower C/N ratio, and regular of N, as shown by lower C/N ratio, and regular ingestion of crabs. Mangrove sediment detritus had ingestion of crabs. Mangrove sediment detritus had C/N ratio 2-3 times lower than mangrove leaves, C/N ratio 2-3 times lower than mangrove leaves, indicating higher nutritional value than leaves. indicating higher nutritional value than leaves. Bacteria may certainly reach high densities in Bacteria may certainly reach high densities in mangrove mud and are highly digestible by mangrove mangrove mud and are highly digestible by mangrove sesarmid crabs. sesarmid crabs.

THANK YOU ALL FOR KIND ATTENTION

We are greatly acknowledged to:We are greatly acknowledged to:

1. the Japanese Society for the Promotion of Science for financial support

2. the University of the Ryukyus, Okinawa, Japan for technological support

3. Prof. Gustav Paulay, University of Florida, USA, for scientific support

4. Prof. Chang-Po Chen, Institute of Zoology, Taiwan, encourage to join ISISA

5. the Organizing Committee of ISISA-2004 in Taiwan for inviting us

6. Mr. Hiratsuka, Mr. Obuchi and Mr. NI Khan, University of Ryukyus for technical support