Kagoshima University Research Center for the Pacific Islands Occasional Papers No.39, 59-64, 2003
Section 2, Report 5. The Progress Report of the 2000 and 2001 Survey of the Research Project“Social Homeostasis of Small Islands in an Island-zone”

59

INFLUENCES OF WAVE ACTION ON SHELL SHAPE OF MARINE SNAILNERITA PLICATA AND OIL SPILL ON MARINE COASTALENVIRONMENTS
KAWAI Kei＊

Abstract
Influences of wave action on shell shape of marine intertidal snail Nerita plicata and oil spill onmarine coastal environments were investigated in Ulithi Atoll, Yap State, Federation of States ofMicronesia. Twenty species of marine snails were observed in the intertidal areas in Ulithi Atoll.
Aperture mouth size of N. plicata, which was the most common snail in Ulithi Atoll was significantly
different between smaller and larger snails but not between wave exposed area and sheltered area.
However shell shape was significantly different between smaller and larger snails and between exposed area and sheltered area. These results suggested that shell shape and aperture size of N. plicata
were affected by different factors.
Six Polycyclic Aromatic Hydrocarbons (PAHs) components (fluorine, phenanthrene, anthracene,fluoranthene, pyrene and chrysene) in surface seawater, sand and marine snails N. plicata in Ulithi
Atoll where oil spill had happened from a sunken ship in August 2001 showed lower value. Althoughconcentration of benzo (a) pyren in surface seawater and sand showed lower value, that of marine
snails showed about six times higher concentration than snails in not-polluted area. I discussed the possibility of the influences by oil spill to the lives in coastal area.
Keywords: benzo (a) pyren, Micronesia, Nerita plicata, oil spill, Ulithi Atoll, wave action

Introduction
Many environmental conditions in intertidal area are rapidly changing in a short period.
Therefore, this is one of harsh area for animals and plants to inhabit. However, many animals
and plants adapted to these environmental conditions very much and much number of them inhabited in this area. Many researchers have studied the mechanisms and systems of their adaptation on these environment conditions such as wave action, predator, temperature, desiccation,light, etc (ex. LITTLE and K ITCHING 1996; RAFFAELLI and HAWKINS 1996). Wave action was
one of the important factors to influence on shell shape of the snails and shell shape was highly
correlated to strength of wave force (ex. ETTER 1988).
Recently environmental pollution by oil spill became a big problem in the world (ex.
PETERSON 1993). Oil spill has happened from a sunken oil tanker in August 2001 near Falalop
Island, Ulithi Atoll, Micronesia (SALAS 2001). The ship was sunken by Japanese submarine“Kaiten” in World War Ⅱ. The leaking point of sunken ship was soon filled up but some amountof oil was leaking to Atoll. Two weeks later, most of the oil spill from the ship was gone throughto open sea beside Asor and Falalop Islands. But there is not any research about influence of oil＊Kagoshima University Research Center for the Pacific Islands. Kagoshima 890-8580, Japan.

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KAWAI Kei

leaking on the animals.
There are three purposes on this paper: 1) to investigate species of marine snails in intertidal
area in Ulithi Atoll, 2) to study the influence of wave action on the shell shape and aperturemouth of N. plicata, which is the most common species in the intertidal areas, and 3) to investigate the concentration of oil in the seawater, sand, and marine snail N. plicata.

Materials and Methods
The research was carried out in intertidal areas in Ulithi Atoll, Yap State, Federation ofStates of Micronesia from 18 October to 24 October 2001. To study sort of marine snails in theintertidal areas, I walked along seaside in Mogmog, Asor, Falalop, and Fassarai Islands, to record the species name of all kind of the observed snails and take unknown species into laboratory
to know species name.
I decided that Nerita plicata was a target species to study, because this was the most common snail in these areas (see Result). Thirty smaller (shell length < 15 mm) and 30 larger (shelllength > 15 mm) N. plicata were collected from wave exposed and sheltered areas of Mogmog,Asor, Falalop, and Fassarai Islands, respectively. I assumed that the open seaside of atoll was exposed area and inside of atoll was sheltered area. In the laboratory, I measured the shell length,
shell width, aperture length, and aperture width of the all snails (Fig. 1) and calculate following
2 indices: 1) Relative Aperture Index (RAI) = (aperture length) × (aperture width) / (shelllength) 2, and 2) Relative Shell Shape Index (RSSI) = (shell length) / (shell width). RAI is anindex of size of aperture mouth and higher value of the index means that size of the aperture isbigger. RSSI is an index showing shell shape.

Fig. 1. Measuring method of two indices: 1) Relative Aperture Index (RAI) = (aperture length)
x (aperture width) / (shell length)2, and 2) Relative Shell Shape Index (RSSI) = (shelllength) / (shell width).

To study state of the pollution, I studied 7 Polycyclic Aromatic Hydrocarbons (PAHs) components (fluorine, phenanthrene, anthracene, fluoranthene, pyrene, benzo (a) pyren and chrysene)in seawater, sand, and marine snail N. plicata in Asor Islands. Three litter of surface seawater

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Marine Research in Ulthi Atoll3

was sampled near the shore. Two thousands and seven hundred cm of sand was collected form
5 cm depth under the ground surface. Ten N. plicata were collected from sheltered shore. I commissioned Japan Frozen Foods Inspection Corporation to analysis these samples.

Results and Discussion
Shell ShapeTwenty species of marine snails were observed in the intertidal areas in Ulithi Atoll (Table1). Nerita plicata and Littorina undulata were the two most common snails in this area. I adopted
N. plicata as a target species of the study, because the density was higher than the other snails(personal observation).
Table 1. Species name which observed in intertidal area in Mogmog Island, AsorIsland, Falalap Island, and Fassarai Island. ○ indicates that the snail wasobserved in the island.
Species
Nerita plicata
Cerithium nodulosum
Littoraria undulata
Cypraea tigris
Cypraea moneta
Thais marginatra
Thais savignyi
Drupa ricinus
Drupa ebraeus
Drupa grossularia
Mancinella hippocastanus
Coralliophila neritoides
Vasum ceramicum
Eugina mendicaria
Strigatella paupercula
Conus ebraeus
Muricidae A
Muricidae B
Muricidae CMitridae AMogmog
○
○
○
○

Asor
○

Falalap○

Fassarai
○

○

○

○
○

○
○
○

○
○
○
○

○

○
○
○
○
○

○
○
○
○

Average RSSI of larger snails was significantly lower than that of smaller snails (two way
ANOVA, P < 0.001) and average RSSI of snails in exposed area was significantly higher thanthat in sheltered area (two way ANOVA, P < 0.001) (Fig. 2, Table 2). There was an interaction
effect between snail size and shore type on RSSI (two way ANOVA, P < 0.05). These suggested
that there was significantly difference between exposed and sheltered area in smaller snail andno significant difference in larger snail. Larger and smaller snails inhabited in same area (personal observation), therefore both group received the same strength of wave force but shell shape
showed different. There are two possible explanations on this. Firstly, sensitivity for selection
force by wave force might be different between smaller and larger snails. Secondly, this was

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KAWAI Kei

result of interaction between environmental factor and genetics.
Average RAI of larger snails showed significantly lower than that of smaller snail (two way
ANOVA, P < 0.001) (Fig.3, Table 3). But there was no significant difference between shoreFig. 2. Mean (± SE) relative aperture index (RSSI) of larger and smaller snails
in exposed and sheltered areas
Table 2. Results of ANOVA on the effects of shore type and size of snail on RSSISource
Shore type
Snail size
Interaction
Residual

d.f
1
11
331

SS
0.027
0.086
0.006
0.515

MS
0.027
0.086
0.006
0.002

F
17.10555.447
3.961

P
0.001
0.001
0.047

Fig. 3. Mean (± SE) relative shell shape index (RAI) of larger and smaller snails in
exposed and sheltered areas
Table 3. Results of ANOVA on the effects of shore type and size of snail on RAISource
Shore type
Snail size
Interaction
Residuald.f
1
11331

SS
0.005
1.162
0.002
0.91

MS
0.005
1.162
0.002
0.003

F
1.938
422.525
0.727

P
0.165
0.001
0.395

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Marine Research in Ulthi Atolltypes (two way ANOVA, P > 0.05). Wave action did not influence aperture size but smallersnails had bigger size of aperture mouth than larger ones. It suggested that aperture size might
be ontogenetically decided.
Both results suggested that shell shape and aperture size were affected by different factors,although I need more studies to confirm on these.
Oil Spill
Results of PAHs components in seawater, sand, and marine snails showed in Table 4. PAHs
components in sands showed lower than these in seawater and snails. Most of PAHs components
in seawater, sand, marine snail, except benzo (a) pyren in marine snail in this research were similar value to not-polluted ordinal beach in Japan but benzo (a) pyren in N. plicata showed about
six times higher concentration than snail in not-polluted area (FUJIMOTO 1998). Another researchsuggested that benzo (a) pyren concentration of snails and mussels showed high in oil-polluted
area (N OREA-BARROSO et al. 1999), suggesting the snails were affected by oil pollution. But
source of the pollution was not clear in this area, although oil spill has happened from a sunken
ship in August 2001 in Ulithi Atoll. There were two possibilities for source of the pollution. First
possibility is oil spill from a sunken ship in August 2001 in Ulithi Atoll. Second one is oil leaking from boats, which were used general life.
Table 4. Results of PAHs analysis of seawater, sand, snails
Fluorene Phenanthrene Anthracene Fluoranthene Pyrene Chrysene Benzo (a) pyrene
Seawater (ng / g)

< 0.1

3.8

< 0.1

1.4

1

< 0.1

< 0.1

Sand (ng / g)

< 0.1

0.5

< 0.1

< 0.1

< 0.1

< 0.1

< 0.1

Snails (ng / g)

315

< 123

< 17Benzo (a) pyren may be a chemical to develop cancer (SMOLAREK 1988) and has negative
effect on mate reproduction in the mouse (REVEL et al. 2001). Concentration of benzo (a) pyrenin snail was high in Asor Island, suggesting a possibility that many coastal animals mightdevelop cancer by benzo (a) pyren. Moreover, many marine animals are food for the localpeople. Therefore, there is a possibility to affect the health of local people by oil pollution.
To find out source(s) of the pollution to the snails and continuous monitoring of the concentration of PAHs are important for conservation of the marine ecosystem and for health of thelocal people in this area.

References
ETTER, R. J. 1988. Physiological stress and color polymorphism in the intertidal snail Nucellalapillus. Evolution 42: 660–680.
FUJIMOTO, K. 1998. Report of influences of oil spill by sunken ship “Nahotoka” on fisheries andecosystem. Department of Fisheries Agency, Japan. 542 pp. (in Japanese)
LITTLE, C. and J. A. K ITCHING. 1996. The Biology of Rocky Shore. 240 pp. Oxford UniversityPress.
N OREA-BARROSO, L., G. GOLD-BOUCHOT, ZAPATA-P EREZ, and J. L. SERICANO. 1999.
Polynuclear aromatic hydrocarbons in American oyster Crassostrea virginica from theTerminos lagoon, campeche, Mexico. Mar. Poll. Bull. 38: 637–645.

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PETERSON, C. H. 1993. Improvement of environmental impact analysis by application of principles derived from manipulative ecology: lessons from coastal marine case histories. J. Aus.
Ecol. 18: 21–52.
RAFFAELLI, D and S. H AWKINS. 1996. Intertidal Ecology. 244 pp. Chapman and Hall.
REVEL, A., H. RAANANI, E. Y OUNGLAI, J. X U, R. HAN, J. F. S AVOURET, and R. F. CASPER .
2001. Resveatrol, a natural aryl hydrocarbon receptor antagonist, protects sperm from DNA
damage and apoptosis caused by benzo (a) pyrene. Repro.Toxi. 15: 479–486.
SALAS, S. 2001. Oil spill in Yap makes international headlines. News 8, 17 August 2002,<http://www.kuam.com/news/story.asp?headline=1773>.
SMOLAREK, T. A. 1988. Temperature-induced alterations in the metabolic activation of benzo-apyrene to DNA biding metabolites in the bluegill fry cell line bf-2. Aqua. Toxi. Ams. 13:
89–97.