South aci c Studies ol.

, o. ,

asonan an oa ro ati a ( r sta a so o a)from Sandy Beaches in Okinawa-jima Island, Japan
Mottaghi Arezoo 1*, Shimomura Michitaka 2, Reimer James a is ,a ua e S hoo onginee ing an S ien e ni e si o he uk us Sen a u
ishiha a kina a
Ja an
De a men o a u a is oi ak ushu useum o a u a is o an umanis oigashi a Yaha ahigashi ku i ak ushu
Ja an
o i a ios he e esea h en e ni e si o he uk us Sen a u ishiha akina aJa ano es on ing au ho
mai a e oomo aghi ahoo om

Abstract
Isopods are an important part of the marine food we and of many ecosystems, ut often theirecolo y is poorly studied. In this study, isopods were collected at si sandy eaches around su tropical
Okinawa-jima Island etween May

and e ruary, spannin four seasons. Seasonal patternsof isopods were revealed via comparison of the numbers of Sphaeromatidae (Crustacea: Isopoda)
collected each season. The highest and lowest numbers of Sphaeromatidae were observed in spring
and winter, respecti ely. hese results are ery similar to studies in other re ions that ha ealso seen isopod num ers peak in sprin . In eneral, these results are important when comparinen ironmental assessments across di erent seasons, particularly as isopods and other small crustaceans
are often used as bioindicators in environmental assessments.
Key words: ecolo y, Okinawa, reproduction, seasonal ariation, Sphaeromatidae

Introduction
Isopoda elon s to the crustacean superorder eracarida, and their lar ae rood in amarsupium. Isopod crustaceans are identi a le y the presence of one pair of uropods thatare attached to the pleotelson, and pereopods with only one ranch. Isopods are present in awide ariety of oth marine and terrestrial ha itats, and it is estimated that there are reaterthan ,
formally descri ed species ( oore and Bru e). Isopods species may ha e
one or more feedin patterns (includin predators, sca en ers, detriti ores, lter feeders orparasites) and throu h their recyclin and decomposition a ilities, isopods play an importantrole in the food web ( ar urg).
――――――――――――――――――――――――――――――――――――――――――――――
Recei ed:ecem er,
Accepted:o em er

24South aci c Studies ol.

, o. ,As stated by oore and Bru e () more thanof isopods are a uatic (marine
or estuarine). ithin Isopoda, family Sphaeromatidae s mem ers ha e a dorso entrally or
almost completely flattened ody. Additionally, ornamentation and se ual dimorphism iscommon in this family. Most species of Sphaeromatidae are found in depths of less than ,m. owe er, the ecolo y of isopods in eneral and Sphaeromatidae in particular is poorly
studied ( oore and Bru e).
Additionally, isopods can act as potential natural ioindicators (Cortet e a .
,ao eti and assa
, ongo e a .
). e oso e a . () reported that theendemic isopod
i o ana a i iensis (Richardson, 1912) could be used as a potential
human impact bioindicator on Brazilian sandy beaches. As the main island of Okinawajima faces similar human impact pro lems as Bra il, includin o er-e ploitation ofcoastal shorelines, increasin ur ani ation, and coastal construction, which all threaten theecological integrity of coastal systems (Reimer e a .
, Mottaghi e a .
), usinisopods as ioindicators could e a potentially prudent and wise decision, as they are often
abundant and easy to collect ( oore and Bru e). In this study, isopods were collectedfrom intertidal coral rubble and sand samples at paired disturbed (n=3) and non-disturbed(n ) sites around Okinawa-jima Island, Japan, o er a period of four seasons. e counted
the numbers and genera of sphaeromatid isopods from our collections and compared themto examine how the numbers and diversity of sphaeromatids changed over seasons.

Materials and Methods
Isopods in this study were collected
as part of a previous study (Mottaghi eta.
) comparin infaunal crustacean
di ersity across locations all raw data
analyzed in this study were generated
from this previous study. Six sandy
eaches were in esti ated, two each on
the west ( inowan (
.
,
.
) and
inowan(.
,.
)),
south (Odo(.
,.
) and Odo (.
,.
)) and east (A ama
(
.
,
.
) and
A ama (.
,.
))
coasts of Okinawa-jima Island ( i . ).
or the two eaches within each coastline,
one was considered as distur ed, andthe other as non-distur ed, as detailed in
Mottaghi e a . (). At each site fori. Map of samplin locations around Okinawajima Island, Japan, in this study.

Mottaghi et al.: Seasonal Abundance of Sphaeromatidae

each samplin , threemeter ( m2) quadrats were placed randomly in water of depthsof less than meter. n ironmental data ( O, p , salinity, seawater temperature, tur idity,
and conductivity) were recorded and infaunal crustacean sampling was performed frominside each quadrat as described in Mottaghi e a . ().
Sur eys were conducted once per season at each site, on sunny or partly cloudy andnon-rainy days at low tide ( etween . m and . m hei ht) durin daytime etweenMay
to e ruary(Maysprin , Julysummer, o em erfall and e ruary
winter seasons decided ased on sea surface temperature chan es)( i . ).
Isopods were collected from sediment and coral rubble samples from each site withineach each (ntotal samplin e ents
sites,
uadrats, seasons). ollowin themethods of hite (), a -liter ucket was lled one-fourth full with sediment fromeach uadrat, one fourth full with seawater from the sample site and nally at each uadrat,
coral rubble was added to bucket as well to be full.
Immediately after collection, appro imately
ml of formalin was added to eachucket and after e minutes rest, the ucket s contents were thorou hly mi ed and sie edthrou h am mesh sie e. his procedure was repeated se en times per ucket.
he sie es contents were transferred to samplin jars containin.
tO .
The following day samples were roughly sorted and all isopods were separated from thecollection, identi ed to the enus le el, and counted ( a le ).
O, p , salinity, seawater temperature, tur idity, and conducti ity were measured
within each uadrat with a multi-parameter water uality meter (- OA, modelC, okyo), as detailed in Mottaghi e a . (). hese measurements were recorded fromall six sites on the same day as each seasonal survey (Table 1).
Table 1. Sphaeromatidae isopod numbers and seawater environmental parameters of sites examined inthis study around Okinawa-jima Island, Japan.
Seawater environmental parameter
DO
Con.
Tur.
Temp.
Sal.
(Mg/L)(S/m)(Mg/L)
(C)
(PPT)
G1S
36
0
0
36
8.4
7.4
4.8
12.2
25.4
31.5
G2S
42
0
0
42
8.6
12.5
4.6
19.4
24.3
29.9
O1S
0
13
0
13
8.5
9.7
4.9
9.0
26.8
32.3
O2S
0
12
0
12
8.6
9.6
4.9
8.0
25.3
32.3
A1S
0
14
1
15
8.6
9.8
4.9
10.0
25.7
32.1
A2S
0
12
0
12
8.6
9.7
4.9
11.2
26.1
31.7
G1U
7
0
0
7
8.4
7.0
4.8
9.2
29.9
32.4
G2U
13
0
0
13
8.4
7.0
4.9
9.4
30.6
32.9
O1U
10
0
0
10
8.4
7.2
4.8
7.3
34.1
32.9
O2U
5
2
0
7
8.4
6.4
4.8
6.4
33.7
32.9
A1U
5
0
0
5
8.4
6.1
4.8
7.8
32.8
32.7
A2U
6
0
0
6
8.4
7.0
4.9
6.9
34.6
33.1
G1F
1
0
0
1
8.5
7.0
4.8
9.2
27.9
31.5
G2F
7
1
0
8
8.5
7.0
4.6
9.4
27.6
31.9
O1F
2
0
0
2
8.6
7.2
4.9
7.3
28.1
32.3
O2F
1
0
0
1
8.5
6.8
4.9
6.4
27.7
32.3
A1F
5
0
0
5
8.4
6.9
4.9
7.8
28.5
32.1
A2F
5
0
1
6
8.6
7.1
4.9
6.9
28.7
31.7
G1W
0
0
0
0
8.4
7.5
4.8
9.2
18.7
30.7
G2W
3
0
0
3
8.3
7.7
4.8
9.4
18.6
29.8
O1W
0
0
0
0
8.3
7.4
4.8
7.3
19.1
31.0
O2W
2
0
0
2
8.4
7.6
4.9
6.4
19.0
30.8
A1W
2
0
0
2
8.4
6.4
4.8
7.8
19.6
30.5
A2W
5
0
0
5
8.4
7.0
4.9
6.9
19.8
29.9
In the “Site and season” column, the first letter stands for sites (Ginowan, Odo or Azama), the second letter indicates the site number and the third letter theseason (S = spring, U = summer, F = fall, W = winter). Abbreviations of seawater environmental parameters ; DO = dissolved oxygen, Con. = conductivity,
Tur. = turbidity, Temp. = temperature, Sal. = salinity.
Site and season

Holotelson sp. 1

Dynamenella sp.1

Cymodoce sp.1

total

pH

 South aci c Studies ol.

, o. ,

ResultsAmoncoral ru le sand samples, three enera of sphaeromatid isopods ( o o e son
sp. , nD namene a sp. , n
mo o e sp. 1 n= 2) were collected from all
sampling sites and during all four seasons. All related information is available in Table 1.
enerally, num ers of sphaeromatids were hi hest in sprin(n), and were muchhi her than num ers present in summer(n), fall(n), and winter
(n=12).
In allseasons and sites the dominant genus was o o e son, followed y D namene aand thereafter
mo o e ( i . ).
Spearmanrho
correlations for abundance of Sphaeromatidae versus pH (rs . ),O (rs . ), temperature (rs= . ), salinity (rs= . ), conducti ity (rs= . ), and tur idity(rs= . ) were calculated ut they were all low and not si nificant, and therefore the null
hypothesis (no correlation between isopod numbers and environmental parameters) was
accepted.
140

130

120
100
80
60

78

springsummer

51

46

48

40
20

21

Holotelson sp.1
iwinter

23
12

12
2

0

fall

1

Dynamenella sp.1

0

Total isopods/Season. Seasonal ariation (sprin , summer, fall
and winter) in a undance of three enera of
Sphaeromatidae isopods at si sites around Okinawa-jima Island, Japan. here were only two
individuals of mo o e sp. 1 observed during the study and therefore this species was notincluded here.

Discussion
Accordin to our ndin s, there was a clear seasonal distri ution pattern with a peakin sprin
for sphaeromatid isopods in Okinawa. Similar to our results, in erte rate
species inhabiting different marine environments have been reported as being most andleast a undant in sprin and winter months, respecti ely, includin isopod species fromseveral other families ( e ter, Jarami o e a .
). Additional similar e amples
include Jones (), who reported the a undance of the isopod enus Jaera ( each,)Mottaghi et al.: Seasonal Abundance of Sphaeromatidae

in Castletown stuary, Isle of Man, with hi hest a undances durin sprin (with a peak inMay, similar to our results) and lowest a undances durin winter months and ang andun (), who documented that Sphaeromatidae at Busan, orea, in the ast China Sea
showed hi hest and lowest num ers of indi iduals in April (indi iduals) and e ruary(only
indi iduals), respecti ely, ery similar to our o ser ed results.
owe er, there are many other studies that ha e shown ery different seasonality
a undance patterns for crustaceans from many locations. or e ample, Bushe andBoyd () reported on the marine isopod S ni o ea ae i o sa is (Miers,) fromelaware Bay, SA, and found that the hi hest and lowest a undances were durin
summer and winter, respecti ely. Another study conducted in man ro e estuaries alon
the northeastern coast (Cape York Peninsula) of tropical Australia showed that meiofaunadensities were highest during autumn (A ongi). ay or () reported on seasonalvariation in densities of mobile epifauna over a 2 to 3 year period in northeastern New
ealand, and durin the rst two years, hi hest a undances were o ser ed durin autumn
winter. owe er, for third year of the study the a undance patterns chan ed and thehi hest a undance was o ser ed durin sprin . hus, our o ser ed pattern of hi h isopod
a undances in sprin and low a undances in winter may not e the same e ery year, andlon er-term studies may help clarify these trends. owe er, it is clear that isopods and othermeiofauna often ha e clear seasonal chan es in num ers, and this needs to e taken into
account during surveys.
Interestin ly, another family ( nathiidae, spon e-dwellers with a parasitic lar alphase) from the northern part of Okinawa-jima Island have been reported to have lowest
and hi hest a undances durin summer and late winter to early sprin , respecti ely (Otae a.
). Althou h nathiids ha e di erent life cycles and ha itats from sphaeromatids,
this pre ious sur ey can ser e as another e ample for of seasonal uctuations in isopods in
Okinawa.
In our results the highest numbers of isopods were those of o o e son sp. , whichwere found in all four samplin seasons, su estin that at least some species of this enus
reproduce year round in the sandy intertidal beaches around Okinawa-jima Island. On theother hand, mo o e sp. indi iduals were present only on the east coast, and only once
each durin sprin
and fall, and D namene a sp. 1 was not present at any site
durin winter.
O erall, these results demonstrated that there is seasonal pattern for enera of
Sphaeromatidae in the sands around Okinawa-jima Island. owe er, as such sur eys
ha e not een performed in the Ryukyu Archipela o efore, with the closest pre ious
example from Korea ( ang and un), and as the population dynamics, ecolo y, andiodi ersity of this family are enerally poorly known, further studies on lar er scales, suchas includin more samplin sites o er lon er time spans, are hi hly recommended.

South aci c Studies ol.

, o. ,

Acknowledgements
We wish to give special thanks to all who assisted us with this study. The senior author
was supported y a JS S uno-Junkan rant entitled Studies on ori in and maintenanceof marine biodiversity and systematic conservation planning”. Comments from the editor
and three reviewers greatly improved an earlier version of this manuscript.

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