Pak Phanang Research Articles

Molluscan associations from the Pak Phanang Bay (SW Gulf of Thailand) as a record of natural and anthropogenic changes

Recent environmental changes in the Pak Phanang Bay (SW Gulf of Thailand) are investigated by means of mollusc assemblages. The present-day water depth within the bay slightly exceeds 2m at low tide and the seafloor is almost entirely muddy, except for the outermost part of the embayment which is directly influenced by the longshore drift that is building the Laem Talumpuk sand spit. A multivariate analysis of the molluscan fauna recovered at 16 sampling stations within the bay delineates three thanatofacies and two biofacies. The Bay Mouth thanatofacies, including several infralittoral species, is distributed around the bay entrance; the Tidal Flat thanatofacies, characterized by few brackish and freshwater taxa, occurs in the inner part of the bay; the Channel thanatofacies includes a mixed fauna and is found along the long axis of the bay. All thanatofacies are not older than a few decades. The two biofacies are significantly less diverse than their dead counterparts, and are simply identified as Bay Mouth biofacies and Inner Bay biofacies.The faunal evolution, combined with bathymetric and sedimentological data, confirms that the embayment is undergoing a confinement process. The inner bay has evolved into an undifferentiated tidal flat hosting an oligospecific fauna. The confinement trend and the consequent siltation of the bay, mainly due to natural geomorphologic processes acting since centuries, are likely to have sped up in recent years by interaction with some human activities; among these, the deforestation in the upper Pak Phanang basin and the construction of Uthokaviphatprasit Watergate.

Gonad development and size at maturity of the male mud crab Scylla paramamosain (Forsskål, 1755) in a tropical mangrove swamp

The reproductive traits and size at sexual maturity of the male mud crab Scylla paramamosain were investigated in Pak Phanang mangrove swamps, Thailand. Samples were taken seven times from the local middlemen mud crab traders during June 2006 to January 2008. Gonad development was determined based on histological appearance that was classified into three stages: 1) Immature (Spermatogonia), 2) Maturing (Spermatocytes) and 3) Mature (Spermatids and Spermatozoa). Among the sample population, the highest 72% was under gonad development stage I, whereas mature stage III was only 12%. The size at first maturity was estimated by the external allometric growth and histological observation of gonad. The size at which 50% of individuals attain sexual maturity was estimated by the two mathematical models such as probit analysis and logistic curve. The mean size at first sexual maturity and 50% maturation of male S. paramamosain were 96 mm and 109 mm internal carapace width (ICW) which revealed that 88% individuals were immature. The present result suggested that the minimum legal size of male S. paramamosain capture should be >110 mm ICW.

Gonad development and size at maturity of the male mud crab Scylla paramamosain (Forsskål, 1755) in a tropical mangrove swamp

The reproductive traits and size at sexual maturity of the male mud crab Scylla paramamosain were investigated in Pak Phanang mangrove swamps, Thailand. Samples were taken seven times from the local middlemen mud crab traders during June 2006 to January 2008. Gonad development was determined based on histological appearance that was classified into three stages: 1) Immature (Spermatogonia), 2) Maturing (Spermatocytes) and 3) Mature (Spermatids and Spermatozoa). Among the sample population, the highest 72% was under gonad development stage I, whereas mature stage III was only 12%. The size at first maturity was estimated by the external allometric growth and histological observation of gonad. The size at which 50% of individuals attain sexual maturity was estimated by the two mathematical models such as probit analysis and logistic curve. The mean size at first sexual maturity and 50% maturation of male S. paramamosain were 96 mm and 109 mm internal carapace width (ICW) which revealed that 88% individuals were immature. The present result suggested that the minimum legal size of male S. paramamosain capture should be >110 mm ICW.

Sustainability Indicators for Assessing and Monitoring the Resource Management of Pak Phanang River Basin, Thailand

Abstract Pak Phanang river basin, one of the most important river basins in Thailand, is located in the middle of the southern peninsular. It has diverse resources and land use, and complex and dynamic ecosystem in terms of water use, flooding, and physical change. The construction of the water gate in 1999 has caused drastic changes in the ecosystem of the basin and has led to subsequent effects on the livelihood of the people in the basin. The objectives of this study, hence, was to identify the appropriate sustainability indicators for assessing and monitoring the basin land use through the reviews of historical perspectives, together with the natural and socio-economic impacts on natural resource degradation and challenges. The relationship between causes, problems, and symptoms of different ecological zones were analyzed and used as the basis of identifying sustainability indicators for further in-depth study.

Stakeholder Analysis for Sustainable Land Management of Pak Phanang River Basin, Thailand

Pak Phanang river basin, one of the most important river basins, is situated in the middle of the southern peninsula of Thailand. The construction of a water gate in 1999 to prevent salt water intrusion and separate freshwater from salt water zones has resulted in changes of the natural ecosystem and the locals’ livelihood. The study aimed to identify important stakeholder groups and assess their relationships, relative power and importance for the sustainable resources use of the area. The data of this study were collected through literature reviews, focus group discussions with local stakeholders and individual interviews, using the techniques of Participatory Rapid Appraisal and conceptual content analysis. The study revealed that the most advantageous stakeholders in the coastal saltwater zone were shrimp farmers and stakeholders of related industries characterized by their relatively high input, technology and knowledge. For the coastal plain area with irrigation facilities, the majority of rice farmers benefited from increasing paddy production by intensive farming of up to 2-3 crops per year. These stakeholders’ interest was conformed to the national and regional development strategies and the implementations driven by the government ministers/officials, and the royal project committees. The disadvantageous stakeholders were small-scale shrimp and rice farmers, local fishers and nypa palm harvesters, with limited investment in farming facilities to meet the changing ecosystem and the degrading of natural resources and mangrove forest. This problem was also interested by external stakeholders such as academics in the local and regional educational institutions and NGOs in identifying the needs of these disadvantageous stakeholders for sustainable land use and prevention of the critical ecosystem.

Effect of salinity on adsorption and desorption of paraquat in Pak Phanang river sediment, Thailand

Batch experiments were conducted to study the effect of salinity (0–30 g L−1) on adsorption and desorption of paraquat (1, 1′-dimethyl-4, 4′-dipyridylium dichloride), one of the most widely used herbicides in the world, in sediment of Pak Phanang River Basin, Thailand. Sediments from five locations were used in the studies (two from freshwater sites and three sites under saline environment). The adsorption capacity (Kf) of the sediments was positively correlated with CEC (r = 0.81**) and clay content (r = 0.70*). Paraquat adsorption by sediment was faster under fresh water (0 g L−1) versus saline conditions (10 and 20 g L−1). The adsorption coefficient (Kf) at low salinity (0 g L−1) was 17,302 whereas the Kf at 10 and 20 g L−1 were 5,344 and 4,263, respectively. Paraquat desorption was greater at higher salinity, which is similar to the salinity of estuarine or seawater. Approximately 12–31 % of sorbed paraquat in fresh water and saline sediment (7.67 and 7.98 mg kg−1) were released when leaching with 20 g L−1 salinity. The amount of paraquat released was in proportion to the amount sorbed. Results show that increases in salinity resulting from salt water intrusion from the lower estuary into the Pak Phanang River Basin would result in release of adsorbed paraquat from sediment into the water column.

Physicochemical conditions and biodiversity in the freshwater fishing area of Pak Phanang River Basin, Thailand

This study was conducted to assess the health of the aquatic environment, particularly its physicochemical variables and the diversity of phytoplankton, zooplankton, macrobenthos and nekton in the freshwater fishing area of the Pak Phanang River Basin (PPRB) of Nakhon Si Thammarat Province, southern Thailand, at three different sites (upstream, midstream and downstream) and seasons (dry, early rainy and heavy rainy seasons), 7 years after dam construction by applying standard methods. Results showed that physicochemical variables changed among sites and seasons, but remained consistent with regulations for inland fisheries of the region. Cluster and multidimensional scaling analyses indicated that the physicochemical variables, macrobenthos and nekton communities primarily changed between study sites, while plankton communities predominantly varied with season. The correlation between physicochemical variables and biotic communities confirmed the relevance of these variables listed in the water quality standard for maintaining aquatic diversity. However, the relevance of some variables (e.g. conductivity, salinity) not listed among the standard variables was also confirmed, which implies that those variables should also be regularly monitored in estuaries like the PPRB. The comparison of nekton diversity figures before and after dam construction revealed a decrease, particularly in brackish and marine species, but, on the other hand, there was an increase among freshwater fish species which was reflected in diversity indices when comparing the most recent indices to those of 2003 (4 years after dam construction). These results indicate an improvement in the biodiversity of freshwater species that was consistent with findings on the suitability of the physicochemical conditions of the freshwater fishing area of the PPRB.

Ovarian development and size at maturity of the mud crab Scylla olivacea in Pak Phanang mangrove swamps, Thailand

Ovarian development and size at maturity of the mud crab Scylla olivacea from Pak Phanang mangrove swamps, Thailand, were investigated. Samples were taken from local traders between June 2006 and January 2008. Ovarian development was determined based on both external appearance and histological observation and was classified into five stages: immature (stage I), previtellogenesis (II), primary vitellogenesis (III), secondary vitellogenesis (IV) and tertiary vitellogenesis (V). Size of oocytes and volume of ovary increased as ovarian developmental stage progressed. External and histological observation of the ovaries revealed that initiation of vitellogenesis could be identified by external observation of the ovary. However, ovarian maturity could not be determined precisely by morphological observation of the abdomen. Absence of post-spawned females and small sample size of mature females in near-shore mangroves implies the occurrence of spawning migration toward offshore regions. The minimum size at which females attain ovarian maturity was 89.8 mm internal carapace width (ICW), and ICW at which 50% of females attain ovarian maturity was estimated to be 99.1 mm.

Ovarian Development of the Mud Crab <i>Scylla paramamosain</i> in a Tropical Mangrove Swamps, Thailand

The present study describes the ovarian development stages of the mud crab, Scylla paramamosain from Pak Phanang mangrove swamps, Thailand. Samples were taken from local fishermen between June 2006 and December 2007. Ovarian development was determined based on both morphological appearance and histological observation. Ovarian development was classified into five stages: proliferation (stage I), previtellogenesis (II), primary vitellogenesis (III), secondary vitellogenesis (IV) and tertiary vitellogenesis (V). The formation of vacuolated globules is the initiation of primary vitellogenesis and primary growth. The follicle cells were found around the periphery of the lobes, among the groups of oogonia and oocytes. The follicle cells were hardly visible at the secondary and tertiary vitellogenesis stages. Yolk granules occurred in the primary vitellogenesis stage and are first initiated in the inner part of the oocytes, then gradually concentrated to the periphery of the cytoplasm. The study revealed that the initiation of vitellogenesis could be identified by external observation of the ovary but could not indicate precisely. Keywords: Ovarian maturation; Ovarian histology; Mud crab; Scylla paramamosain. © 2010 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved. DOI: 10.3329/jsr.v2i2.3543 J. Sci. Res. 2 (2), 380-389 (2010)

Gear type, species composition and economic value of fisheries in the mangroves of Pak Phanang, Thailand

Fishing gear and methods, catch composition, annual catch numbers and the monetary value of fisheries based in the mangroves of Pak Phanang, Nakhon Si Thamarat province, Thailand, were studied from September 2004 to February 2005. The fishing gear and methods were surveyed by visual observation and interviews. Sample catches were taken for each type of fishing gear and method. Semi-closed questionnaire surveys were conducted among fishers, local traders, local administrative officers and related organizations to derive information on utilized species, gear and methods, fisher and fishery status, and trading and catch price. The Pak Phanang mangrove fishery has three types of multi-species capture gear: channel traps, gill nets and lift nets. It also has three kinds of single-species (group) gear/methods: crab traps, catfish hooks and hand capture using a long tail fishing boat. A total of 57 fish species in 27 families, and 23 shell fish species in 8 families were recorded from the catch samples. Penaeid shrimp (25%), and ambassid (31%) and mugilid (24%) fishes were the abundant groups in the channel traps, while ariid (36%) and mugilid (19%) fishes were abundant in the lift net catches. Ambassid (42%) fish dominated the gill net catches. Species richness (number of species) varied depending on sampling month and type of fishing gear. The total annual catch and its monetary value were estimated to be 442–551 tons and US $368,038–733,973, respectively. The estimated annual catch per unit area of mangrove was 63–79 kg ha−1, which generated a market value of US $52–105.

The occurence of an invasive alien mussel Mytilopsis adamsi Morrison, 1946 (Bivalvia: Dreissenidae) in estuaries and lagoons of the lower south of the Gulf of Thailand with comments on their establishment

The invasive false mussel, Mytilopsis adamsi Morrison, 1946 (Bivalvia: Dreissenidae), is a brackish water bivalve, native to tropical West Pacific coast of central America. The species has now become established in East Asian, South Asian and Southeast Asian countries. Species spread has been especially rapid with its distribution now including the lower part of the Gulf of Thailand. This is the first report of the establishment of this species in the lower part of the Gulf of Thailand, in Haad-kaew Lagoon and Thale Sap Songkhla, in Songkhla province, and the Pak Phanang Estuary in Nakhon Si Thammarat province, south Thailand. Descriptions of its morphology are consistent with previous descriptions from other areas as M. adamsi. Based on the available evidence, it is postulated that the species was transported to the areas between the year 1990 and 2000 via international commercial cargo ships. These findings indicate that the spread of M. adamsi is still in progress and that this invasive mussel continues to colonize the Songkhla Lagoon System.

Impact of solid shrimp pond waste materials on mangrove growth and mortality: a case study from Pak Phanang, Thailand

One of the most serious threats to tropical mangrove ecosystems caused by shrimp farming activities is the poor management of pond waste materials. We hypothesise that mangroves can tolerate chemical residues discharged from shrimp farms and can be used as biofilters, but the capability of mangroves to cope with solid sediments dredged from shrimp ponds is limited. Our study in Pak Phanang, Thailand, confirmed that the excess sediments discharged from nearby shrimp ponds reduced mangrove growth rates and increased mortality rates. A series of transformed multi-temporal satellite images was used in combination with the field data to support this claim. In addition, a comparison between four dominant mangrove species revealed that Avicennia marina could tolerate sedimentation rates of >6 cm year−1, while Bruguiera cylindrica tolerated sedimentation rates of 5 cm year−1 (total sediment depth = 25 cm) before dying, while Excoecaria agallocha and Lumnitzera racemosa performed intermediate. This outcome implied that in our situation A. marina and to lesser extent E. agallocha and L. racemosa could be more effective as biofilters than B. cylindrica, as they may survive the sedimentation longer in the disposal areas. Further studies on the impact of sedimentation and chemical pollution of shrimp farm wastes on mangrove mortality and growth are required.

Effects of mangrove deforestation on fish assemblage at Pak Phanang Bay, southern Thailand

Daytime sampling using a seine net was conducted at Pak Phanang Bay (Nakhon Si Thammarat Province, Thailand) in February and July 2006, to determine differences in fish assemblage structures between a mangrove site and an adjacent site completely cleared of mangroves. The overall numbers of fish species and individuals were significantly higher at the mangrove site than the cleared site in both months. Although benthic crustacean feeders showed more species and individual numbers at the mangrove site in both months, the opposite was found for zooplankton feeders. A cluster analysis, based on the abundance of each species, demonstrated that the fish assemblage structures were distinctly different between the two sites. In addition, significant differences in length frequency distributions for each of the four most abundant species were found between the sites in February and/or July. Small individuals of Scatophagus argus, Ambassis nalua, and Tetraodon nigroviridis were more common at the mangrove site, and of Chelon subviridis at the cleared site. These results suggest that mangrove deforestation exerts marked effects on fish assemblages.

Production of Sugar-Beating Sap from Nipa Palm in Pak Phanang Basin, Southern Thailand

Production of Sugar-Beating Sap from Nipa Palm in Pak Phanang Basin, Southern Thailand

The study on maritime transport along the southern coast of Thailand on the Gulf of Thailand: a summary

This paper examines the potential of developing coastal ports and channels along the Southern coast on the Gulf of Thailand. There were 18 channels included in the study area, ranging from Ban Don Channel to Pattani Channel. The study approach was based on the analysis of the data on cargo movement to and from the study area by coastal shipping and truck, in terms of quantity and types of cargo. The study found that there are three potential areas to be developed for coastal shipping in Thailand (along the southern part on the Gulf of Thailand), namely Songkhla (Songkhla channel), Surat Thani (Ban Don and/or Ta Thong) and Nakhon Sri Thammarat (Sichon and/or Pak Phanang). This paper, however, suggests that further study on the technical part for support of the precise channels to be developed is needed.

Sediment Properties along Gradients of Siltation in South-east Asia

Marine sediment properties were quantified along SE Asian siltation gradients and across different habitat types to assess the extent of terrestrial sediment influence and derive indicators of of terrestrial sediment input. Three sites in the Andaman Sea (Ranong, Phuket and Trang; Thailand), one site in the Gulf of Thailand (Pak Phanang; Thailand) and three sites in the South China Sea (Bolinao at the Luzon Island, Puerto Galera at the Mindoro Island and El Nido at the Palawan Island, all in the Philippines) were studied. The following main habitat types were covered: mangroves, seagrass beds, coral reefs, mud flats, river mouths and deep channels.Particularly in Bolinao and El Nido, distinct fronts in siltation were identified at about 7km from the source. Mud (<63μm), water content, organic matter, total nitrogen, total phosphorus and iron co-varied along the first axis of a principal components analysis, which correlated negatively with the pattern in medium to coarse sand (>250μm), total and inorganic carbon as well as calcium. Interstitial ammonia and phosphate varied with the fine sand fraction along the second axis. Two-way analysis of variance showed that water depth, distance from silt source, site and habitat type all contributed to the variance, but site explained most. Linear regressions showed positive correlations between silt and water content, organic matter, total nitrogen, total phosphorus and iron, but negative correlations with calcium suggesting iron and calcium as markers for terrigeneous and marine origin, respectively. The composition of the sediment particulate matter groups the habitat types in two clusters: (1) silty types as river mouths, shallow mud bottoms, deep channels and mangrove stands with high contents of organic matter and nutrients versus (2) non-silty types as seagrass beds and coral reefs with low contents of nutrients and organic matter.Median settling velocities of the silt loads varied from 0·6md−1to 27md−1. Experimentally determined susceptibility to resuspension identified a critical water content of 50%.

Colonization success of common Thai mangrove species as a function of shelter from water movement

Seedling survival and growth of the 3 common SE Asian mangrove species Avicennia alba, Rhizophora mucronata and Sonneratia caseolaris were quantified experimentally along 2 spatial gradients of shelter: (1) between 2 stations, at the inner and outer end of the sheltered Pak Phanang Bay (SW Thailand); and (2) for each station, among plots across a gradient of vegetation density from the mangrove forest edge inwards. Exposure to water movement, quantified as gypsum clod card weight loss, was found to vary more than 5-fold between seasons, which contributed most of the variance accounted for (73%). Variation between plots was higher than that between the 2 sta- tions: clod card loss ranged between 3.0 and 4.6 g d -1 in the plots, whereas the grand means of the 2 stations were 3.4 and 3.7 g d -1 , respectively. These differences between stations and plots were com- parable to the patterns found for mangrove seedling survival. Survival was high (80 to 93%) in most treatments in R. mucronata, with the exception of the most exposed plot (30%). In the other 2 species, overall survival was significantly less but was highest in the outermost plots with the lowest tree den- sity. This pattern confirms the successional status of these 3 mangrove species. Seedling growth, expressed as height increase, was significantly reduced with increasing neighboring tree density for A. alba and S. caseolaris, whereas R. mucronata showed an opposite pattern. Internode production of all 3 species was highest in the most exposed plots. Overall, relative growth rate, expressed as height increase, declined with the age of the seedlings.

The determination of the age and growth of SE Asian mangrove seedlings from internodal counts

The occurrence of periodic changes in the length of the internodes of the seedlings of SE Asian mangrove species (Rhizophora apiculata, Avicennia alba, and Sonneratia caseolaris) growing in the Pak Phanang estuary (Nakhon Si Thammarat, SE Thailand) was confirmed. The annual nature of these periodic changes was verified through comparisons with the observed average number of internodes produced by plants tagged for one year. The cycles in the sequence of internodal length of the seedlings had an average (± SE) period of 16.0 ± 0.78 internodes for Avicennia alba, 25.0 ± 1.2 internodes for Sonneratia caseolaris, and 8.29 ± 0.40 internodes for Rhizophora apiculata. These values are remarkably close to, and not significantly different (t‐test, P > 0.05) from the average (± SE) annual number of internodes of 17.6 ± 0.8 for Avicennia alba, 28.8 ± 2.1 for Sonneratia caseolaris, and 8.03 ± 0.36 for Rhizophora apiculata produced in a year by tagged plants. In addition, the average (± SE) growth of the tagged plants was 0.39 ± 0.018 cm day-1 for Avicennia alba, 0.24 ± 0.015 cm day-1 for Sonneratia caseolaris, and 0.091 ± 0.0036 cm day-1 for Rhizophora apiculata. These estimates were very close to those (0.45 ± 0.06 cm day-1 for Avicennia alba, 0.32 ± 0.01 cm day-1 for Sonneratia caseolaris, and 0.13 ± 0.005 cm day-1 for Rhizophora apiculata) derived as the product of the mean number of internodes produced per day, calculated from the inferred number of internodes produced per year, and the mean length of the internodes of the plants. These findings indicate that the use of regular, annual changes in the length of the internodes of mangrove seedlings can be used reliably to determine their age and to estimate their growth rate.

Mangrove Colonization: Mangrove Progression Over the Growing Pak Phanang (SE Thailand) Mud Flat

A combination of remote sensing techniques andin situmeasurements along a chronosequence was used to elucidate the rate of progression of the mangrove forest in the Pak Phanang Bay (SE Thailand), a large bay with an extended and rapidly accreting mud flat. The examination of black and white aerial photographs of the forest in 1966, 1974, 1989 and 1995, and satellite images in 1985, 1990 and 1994 revealed that the mangrove forest located in the eastern bank of the bay was progressing over the mud flat. The rate of progression was estimated, from examination of changes in the position of the forest edge with time in the series of images, to average 38·6m year−1over the 28-year interval encompassed by the images. Mangrove progression rates were fastest between 1966 and 1974 and slowest between 1974 and 1985, remaining uniform at about 30m year−1thereafter. Thein situexamination of vegetation along transects in the area of fastest mangrove progression showed an average progression rate of 53·12±5·86m year−1, quite similar to the estimate (48·4m year−1) derived from remote sensing techniques for the area where the transects were surveyed.Avicennia albawas found to dominate the vegetation at the progressing edge of the mangrove, followed bySonneratia caseolaris, withRhizophora apiculatabeing present only occasionally. The fast colonization ofA. albaover the mud flat was supported by a large export flux of mangrove propagules from the channels draining the mangrove forest, which averaged 3715±920 and 1900±808 fruits day−1in each of the channels examined. Extrapolation of the long-term mean mangrove progression rate observed along the eastern bank of the Pak Phanang Bay suggested that this mangrove forest will increase by 33ha year−1. These results provide evidence that natural mangrove colonization can be a rapid process if sufficient propagules of the pioneer species (A. albaandS. caseolaris) are available, and point, therefore, to alternative management plans to promote and enhance natural colonization processes.

The Effect of Increased Sediment Accretion on the Survival and Growth ofRhizophora apiculataSeedlings

The effects of experimental sediment accretion on the survival and growth ofRhizophora apiculataseedlings planted on an expanding mud flat in Pak Phanang Bay (south-east Thailand) were assessed. Seedling mortality rates increased linearly (R2=0·87,F=75·9,P<0·0001) with increasing sediment accretion, at a rate of 3% per cm of sediment deposited, and implied a 96% increase in mortality at the highest sediment accretion applied (32cm). Similarly, seedling growth declined linearly with increasing sediment accretion (r=−0·95,P<0·01) with the seedlings receiving 32cm of sediment showing no significant growth. These results clearly show thatRhizophora apiculataseedlings will not be efficient colonizers of coastal areas exposed to sudden events of high (>4cm) sediment accretion and, therefore, afforestation programmes based on this species are unlikely to be successful in such areas.