Environmental monitoring through the shallow marine ostracods of Phetchaburi area (NW Gulf of Thailand)

INTRODUCTIONIn their previous and preliminary study of the shal-low water ostracod fauna of the coastal area in frontof Mae Khlong mouth (north of Phetchaburi, Gulf ofThailand), Montenegro et al. (in press) identified anostracod fauna consisting of 34 species which areable to tolerate differently variations of salinity, dis-solved oxygen and a generally low pH.

The presence of the ostracods in the investigatedcoastal area was evidently influenced by MaeKhlong, other minor rivers and channels, that drainpollutants (industry) and nutrients, and by the pro-ximity of mangroves. Moreover, through the appli-cation of Shannon Weaver (H') biotic index, theostracod fauna evidenced sampling stations charac-terized by stressing-to-equitable environmentalconditions.

This allowed the identification of species able toindicate these conditions and suggested the possibi-

lity to perform a precise list of ostracod species sho-wing the most/least tolerant taxa versus the envi-ronmental variations.

The present work plans to complete this investi-gation enlarging the ostracod analysis to the coastalarea south of Phetchaburi which denotes highersalinity than the northern part. Moreover, it plans tocomplete the taxonomic and ecological data obtai-ned by Montenegro et al. (in press), focusing on theidentication of ostracod species or assemblages ableto evidence the stressing-to-equitable conditions inthe area.

PREVIOUS STUDIESUntil now ostracods have been poorly investigatedin Thailand. Basic source for the Indo-Pacific Regionis due to Carbonel & Hoibian (1988), Hussain(1998), Hussain & Mohan (2000), Shreeyansh (1978),Titterton et al. (2001), Zhao & Wang (1988), Yassini et

85

Environmental monitoring through the shallow marine ostracodsof Phetchaburi area (NW Gulf of Thailand)

NEVIO PUGLIESE1, MARIA EUGENIA MONTENEGRO1, FRANCESCO SCIUTO2 andNIRAM CHAIMANEE3

1. Dipartimento di Scienze Geologiche, Ambientali e Marine, via Weiss 2, 34127 Trieste (Italy), e-mail: [email protected]. Dipartimento di Scienze Geologiche, sez. Oceanologia e Paleoecologia, Corso Italia 55, 95129 Catania (Italy)3. Geological Survey Division, Department of Mineral Resources, Rama VI Road, Bangkok, Thailand.

ABSTRACT________________________________________________________________________________________The study of the shallow water ostracod fauna of the coastal area near Phetchaburi allows the iden-tification of 38 species. Taking into account the data of some environmental factors, it has been pos-sible to recognize some ostracod groups which indicate relationships with depth and substrate. Theapplication of Shannon Weaver (H') index demonstrates that the best conditions of species richnessand equitability and, then, equitable environmental conditions are present in the central-southernsector of the investigated area. Conversely, stressing conditions occur in the northern sector in frontof the Mae Khlong river mouth, which drains seaward pollutants and nutrients. The sampling stations are included by us in categories corresponding to H' values. Except for thosewithout ostracods (category 1 with H' not calculated), the sampling stations characterize other fourcategories. It is assumed by us that the environmental conditions improve from 1 to 5 category. Whenpresent, the ostracod species evidence in these categories some observations concerning their highor reduced capability to tolerate the variations of the environmental conditions. Species occurring inseveral categories are more tolerant than those present in a reduced number of categories. The for-mer species can be labeled as opportunistic; the latter species can be considered "in equilibrium", orless opportunistic, at least. Thus, this work evidences that the ostracods can be good markers of theenvironmental variability, so becoming useful tools for the monitoring of a coastal area showing par-ticular conditions linked to strong river influence and human activity.

keywords. Ostracods, Phetchaburi area, Gulf of Thailand.

In: Coccioni R. & Marsili A., (eds), 2006. Proceedings of the Second and Third Italian Meetings on EnvironmentalMicropaleontology. Grzybowski Foundation Special Publication, 11, 85-90.

al. (1993). Focusing on the Indo-Chinese area, a fewpapers essentially deal with the southernmost partof the Malay Peninsula and the Malacca Straits fromthe shallowest depth to about one hundred meters(Whatley & Zhao, 1987, 1988; Zhao & Whatley, 1989,1993). Only the paper by Montenegro et al. (in press)recently reported about ostracods from the northernsector of the Thailand Gulf, where 34 taxa, out ofwhich 11 living, have been found in very shallowwaters from the tidal flat to about 15 meters ofdepth.

MATERIALS AND METHODSThis work analyses 27 grab-samples collected in thedepth range 1-18m on May 2002 (Fig. 1). The sam-pling stations are located in the tidal flat (channel),nearshore and offshore bottoms. For each sample, astandard volume 25 cc was washed through a 63 µmmesh. Subsequently, the ostracods of a half samplewere picked taking into account the adult and thepresence of young specimens, belonging to biocoe-nosis and thanatocoenosis.

Moreover, the adult specimens were counted,while the juveniles were only signaled. Particularattention was made to the recognition of autochtho-nous and displaced forms. The species, which areconsidered autochthonous, are those represented ina sample by the contemporarily presence of adultsand juveniles, males and females and eventuallyliving specimens. The displaced species are charac-terized by the exclusive presence of juveniles and/orbad-preserved specimens. Data concerning depthand substrate sediment come from Chaimanee et al.(1999) and Di Geronimo et al. (in progress) andreported in Tab. 1.

OSTRACOD FAUNAThe ostracod fauna consists of 38 species (Tab.1);among them 21 species are considered autochtho-nous at least in one sampling station. In the sametable, the living species are reported. The ostracodfauna varies from the qualitative and quantitativepoint of view. In general, the samples characterizedby a high or reduced number of species presentabundant or scarce specimens, respectively. Mostspecies occur in all the area. Among them, the mostabundant species are Kejiella gonia, Kejiella multisul-cus, Neomonoceratina iniqua, Sinocytheridea impressaand Stigmatocythere bona. Other species (Cytherellahemipuncta, Gerdocypris sp., Hemicytheridea cancellata,Hemikrithe orientalis and Hemikrithe peterseni) occurin scattered way and are represented by a reducednumber of specimens. Neocyprideis sp. 1 and Tanellagracilis are mostly represented in sampling stationslocated along the coast-line. Few species(Phlyctenophora orientalis, Pseudopsammocythere sp.)are present in the central-southern part of the inve-stigated area, only.

OSTRACODS AND ENVIRONMENTAL PARA-METERSThe ostracod distribution in the littoral area nearPhetchaburi evidences species more or less tolerantto changes of depth and substrate; moreover, someinformation may be performed in relation with sali-nity, pH and dissolved oxygen, although the valuesof these factors correspond to only one season mea-surement (Chaimanee et al., 1999; Di Geronimo etal., in progress). The discussion concerns the specieswhich are considered autochthonous in two sam-ples, at least.

OSTRACODS AND DEPTHExcept for two sampling stations without autochth-nous ostracods (TH 134 and 135), all the investiga-ted coastal area can be considered infralittoral.Conversely, the above mentioned stations are meso-littoral and characterized by a high tidal range (2-3m). Although the investigated area shows shallowsettings, some depth (D) groups of species can beevidenced in relation with their depth distribution(Tab. 2):

Groups with a wide depth range:D1 (<18m) - Cytherella hemipuncta, Copytus postero-

sulcus, Gerdocypris sp., Hemikrithe orientalis,Hemikrithe peterseni, Keijella gonia, Keijella multisul-

86 N. Pugliese, M.E. Montenegro, F. Sciuto & N. Chaimanee

Figure 1. Location map of the sampling stations nearPhetchaburi

cus, Neomonoceratina iniqua, Neosinocythere elongata,Sinocytheridea impressa, Stigmatocythere bona andStigmatocythere indica.

Groups with a reduced depth range:D2 (<6m) - Hemicytheridea cancellata, Neocyprideis

sp.1, Neocytheretta murilineata, Phlyctenophora orien-talis and Tanella gracilis (from 1-1.5m to 5-6m).

D3 - Propontocypris spp. (from 12 to 16m).

OSTRACODS AND SUBSTRATEThe ostracods occur on bottoms characterized bysandy gravel, silty sand, sandy silt, slightly sandysilt and silty, but they avoid sandy bottoms. Theyare more abundant on sandy silts than other textu-ral classes. Tab. 3 show the link between ostracodspecies and type of substrate. The following sub-strate (S) groups are recognized:

S1 - Cytherella hemipuncta, Neonoceratina iniqua,Sinocytheridea impressa and Stigmatocythere indica,which tolerate several substrates except sand;

S2 - Copytus posterosulcus, Hemicytheridea cancella-ta, Hemikrithe orientalis, Keijella gonia, Keijella multi-sulcus, Neocyprideis sp.1, Neosinocythere elongata,Phlyctenophora orientalis, Stigmatocythere bona andTanella gracilis (silty sand to silt), and Gerdocypris sp.,Hemikrithe peterseni (slightly sandy silt to silt);

S3 - Neocytheretta murilineata (sandy silt orslightly sandy silt).

OSTRACODS VERSUS SHANNON WEAVER(H') INDEXIn agreement with Shannon & Weaver (1949), the H'index can be an useful tool to evaluate the quality ofthe ostracod fauna and environmental conditions.In the formula pi corresponds to ni/N, i.e. the pro-

portion of the ith species in the samples, and Srepresents the number of species in the sample.

In the study area, the H' index is not calculatedin the stations without ostracods, while in the otherones its values vary up to 3.17 (tab.4). Thus, fivecategories of sampling stations are proposed:

- category 1 (H' not calculated) corresponds to thesampling stations without ostracods - it denotesstressing conditions;

- category 2 (H'<1.8) - it identifies stressing-inter-mediate conditions;

- category 3 (1.8<H'< 2.1) - it evidences interme-diate conditions;

- category 4 (2.1<H'<2.8) - it records intermediate-equitable conditions;

- category 5 (H'> 2.8) - it testifies equitable condi-tions.

Figure 2 evidences the H' categories for the sam-pling stations of the investigated area.

Category 1 corresponds to the sampling stationsTH 134 and TH 135, which are without ostracods. Itcorresponds to shallow waters, from 1m to 4mdepth, in sandy sediments, at salinity values bet-ween 20 and 22‰, at values of dissolved oxygenfrom 3 to 3.2 ml/l and at pH values ranging between5.7 and 5.8. This situation corresponds to the chan-nel flowing across the tidal flat in front of MaeKhlong river mouth. There, the ostracods are repre-sented by displaced forms. Among them,Neocyprideis sp. 1 is the most common species.

Category 2 is represented in the sampling sta-

87Environmental monitoring through the shallow marine ostracods of Phetchaburi area

Table 1. Ostracods of Phetchaburi coastal area (legend: 1 - number of adult specimens of the thanatocoenosis; 1b - num-ber of specimens of the biocoenosis; x - presence of juvenals) . The table also reports data on depth and sediment grain-size.

tions TH 150, TH 129 and TH 133. These stationscorrespond to a depth range 1-16m, bottoms cha-racterized by sandy gravel, 32‰ of salinity, dissol-ved oxygen and pH ranging from 3.2 to 4 ml/l andfrom 5.7 to 8, respectively.

This category is represented off the tidal flat inthe northern sector and, locally, in the southern oneof the investigated area. The most common speciesare: Cytherella hemipuncta, Keijella gonia, Keijella mul-tisulcus (sometimes dominant in the assemblage),Neocyprideis sp.1, Neonoceratina iniqua,Neosinocythere elongata, Sinocytheridea impressa,Stigmatocythere bona, Stigmatocythere indica andTanella gracilis.

Category 3 occurs in the sampling stations TH152, TH 151, TH 142, TH 147, TH 136, TH 132 andTH 128. These stations correspond to a depth range1-15m, bottoms characterised by silty sand to silt,32‰ of salinity (with an local exception of 22‰),dissolved oxygen and pH ranging from 3.4 to 4.1ml/l and from 6.4 to 8, respectively.

This category is well represented in all the inve-stigated area. The most common species are: Bairdiasp., Cytherella hemipuncta, Gerdocypris sp.,Hemicytheridea cancellata (sometimes dominant inthe assemblage), Keijella gonia, Keijella multisulcus(sometimes dominant in the assemblage) ,Neocyprideis sp.1 (sometimes dominanat in theassemblage), Neomonoceratina iniqua, Neosinocythereelongata, Pontocypris attenuata, Propontocypris spp.,Sinocytheridea impressa, Stigmatocythere bona,Stigmatocythere indica and Tanella gracilis.

Category 4 characterizes the sampling stationsTH 149, TH 130, TH 143, TH 141, TH 145, TH 153,TH 146, TH 144 and TH 148. These stations show adepth range 3.5-17m, bottoms characterized bysandy silt to silt, 18-32‰ of salinity, dissolved oxy-gen and pH ranging from 3.2 to 4.5 ml/l and from 6to 8, respectively.

This situation is scarcely represented in the nor-thern sector of the investigated area. On the con-trary, this category corresponds to the southernsampling stations. The species occurring in thiscategory are: Copytus posterosulcus, Cytherella hemi-

puncta, Gerdocypris sp., Hemicytheridea cancellata,Hemikrithe orientalis, Hemikrithe peterseni, Keijellagonia, Keijella multisulcus, Neocytheretta murilineata,Neocyprideis sp. 1, Neonoceratina iniqua,Neosinocythere elongata, Phlyctenophora orientalis,Propontocypris spp., Pseudopsammocythere sp.,Sinocytheridea impressa, Stigmatocythere bona,Stigmatocythere indica and Tanella gracilis.

Category 5 is present in the sampling stations TH131, TH 154, TH 137, TH 140, TH 138 and TH 139.These sampling stations present a depth range 1.5-15m, bottoms characterized by sandy silt to silt, 25-32‰ of salinity, dissolved oxygen and pH rangingfrom 3.2 to 4.2 ml/l and from 5.9 to 8, respectively.

This situation is scarcely represented in the nor-thern sector of the investigated area. On the con-trary, this category corresponds to the central-sou-thern sampling stations and, particularly, in the cen-tral ones. The species represented in this categoryare: Copytus posterosulcus, Cytherella hemipuncta,Gerdocypris sp., Hemicytheridea cancellata, Hemikritheorientalis, Hemikrithe peterseni, Keijella gonia, Keijellamultisulcus, Neocytheretta murilineata, Neocyprideissp.1, Neomonoceratina iniqua, Neosinocythere elongata,Phlyctenophora orientalis, Sinocytheridea impressa,Stigmatocythere bona, Stigmatocythere indica andTanella gracilis.

It appears evident that in the investigated area

88 N. Pugliese, M.E. Montenegro, F. Sciuto & N. Chaimanee

Table 2. Ostracods and depth.

Figure 2. Categories of sampling stations and their envi-ronmental conditions.

two sectors can be recognised: the northern sector ismostly characterised by H' categories indicatingenvironmental conditions which are not favourablefor the benthic life; the southern sector generallypresents sampling stations with equitable environ-mental conditions.

OSTRACODS: OPPORTUNISM AND "EQUILI-BRIUM" SPECIESTab. 4 summarises the links between ostracod spe-cies and H' categories. The following species occurin all the categories (2, 3, 4 and 5): Cytherella hemi-puncta, Keijella gonia, Keijella multisulcus,Neocyprideis sp.1, Neomonoceratina iniqua,Neosinocythere elongata, Sinocytheridea impressa,Stigmatocythere bona, Stigmatocythere indica andTanella gracilis. Following Dodd & Stanton (1991),these species can be considered opportunistic sincethey are generalists and adapted to a wide range ofenvironmental conditions.

Moreover, Keijella multisulcus, Neocyprideis sp.1and Sinocytheridea impressa are sometimes dominantin the assemblages and, thus, have additional quali-ties for the label of opportunistic species.

Other species (Gerdocypris sp. and Hemicytherideacancellata) are present in three (3, 4 and 5) categories.They show a lower degree of opportunism than theabove mentioned species which occur in four cate-

gories. Moreover, Hemicytheridea cancellata is domi-nant in some assemblages.

Additional species occur in two categories:Propontocypris spp. (3-4); Copytus posterosulcus,Hemikrithe orientalis, Hemikrithe peterseni,Neocytheretta murilineata and Phlyctenophora orienta-lis (4-5). In agreement with Dodd & Stanton (1991),these species can be called equilibrium species,since they occur in a small number of assemblagesand environments; moreover, these species show areduced number of specimens.

Bardia sp. and Pontocypris attenuata andPseudopsammocythere sp. are present in only onecategory, i.e. 3 and 4 respectively. Since they arevery rare, it is opportune to wait for further data inorder to discuss their label.

CONCLUSIONSThe study of the shallow water ostracod fauna ofthe coastal area near Phetchaburi allows the identi-fication of 38 species. The composition of the ostra-cod fauna presents some small differences in rela-tion with different environmental conditions: thenorthern sector presents species able to toleratestrong river inflows; the southern sector presentsostracods characteristic of marine conditions.

Taking into account the data of some environ-mental factors, it has been possible to recognisesome depth (D) and substrate (S) ostracod groups,which are able to indicate more or less precise rela-tionships with depth and substrate, respectively.

The application of H' index demonstrates that thebest conditions of species diversity and, then, equi-table environmental conditions are present in thecentral-southern sector of the investigated area.Conversely, stressing conditions occur in the nor-thern sector in front of the Mae Khlong river mouth,which is the second important river of Thailand andresponsible to drain seaward pollutants andnutrients. Five categories of sampling stations areproposed by us, assuming that the environmentalconditions improve from 1 to 5 category. When pre-sent, the ostracod fauna allows some observationsconcerning their high or reduced capability to tole-

89Environmental monitoring through the shallow marine ostracods of Phetchaburi area

Table 3. Ostracods and sediment grainsize.

Table 4. Ostracods and Shannon Weaver (H') index. The table reports the categories of sampling stations.

rate the variations of the environmental conditions.Species occurring in several categories are moretolerant than those present in a reduced number ofcategories. The former species can be labeled asopportunistic; the latter species can be considered"in equilibrium", or less opportunistic, at least.Moreover, it appears evident that the opportunisticspecies are exclusive and, sometimes, dominant insampling stations characterized by low values of H'index. Thus, this work evidences that the ostracodscan be good markers of the environmental variabi-lity, so becoming useful tools for the monitoring ofa coastal area showing particular conditions linkedto strong river influence and human activity, asalready reported by Montenegro et al. (in press).

ACKNOWLEDGEMENTSThe authors wish to thank: Dr. Niran Chaimanee(Geological Survey, Thailand) for his precious helpin the field activity and the nice hospitality; Prof. I.Di Geronimo and Dr. R. Sanfilippo (University ofCatania), Prof. E. Robba (University of Milan) forthe useful discussions and advice during the prepa-ration of the text; the referees, Prof. D. Danielopol(Limnologisches Institute, Mondsee, Austria) andProf. A. Russo (University of Modena and ReggioEmilia) for their observations which helped us toimprove the text. Research supported by MIURcofin program (2001) " Distribution and ecology ofthe Holocene modern foraminifers and ostracods inthe coastal area near Phetchaburi, Thailand" (Dir. N.Pugliese; National leader: E.Robba).

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