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\begin{document}

\title{CO2 Emission from Epigeal Mounds of Non-Fungus Growing Termites in a
Seasonal Tropical Forest, Thailand}



\author[1]{Warin Boonriam}%
\author[2]{Pongthep Suwanwaree}%
\author[3]{Sasitorn Hasin}%
\author[4]{Akinori Yamada}%
\affil[1]{Mahidol University}%
\affil[2]{Suranaree University of Technology}%
\affil[3]{Valaya Alongkorn Rajabhat University under the Royal Patronage}%
\affil[4]{Nagasaki University Faculty of Environmental Studies Graduate School of Fisheries Science and Environmental Studies}%


\vspace{-1em}



  
  \date{June 14, 2024}


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\selectlanguage{english}
\begin{abstract}
Termites, as main decomposers, are major contributors driving carbon
cycle by litter decomposition. Termites were emphasized as one of high
CO2 emission sources of spatial variation in soil respiration. The aim
of this study was to compare CO2 emissions from the epigeal mounds of
non-fungus growing termites in dry evergreen forest of Thailand. CO2
emission was directly measured on mounds and surrounding soils of five
termite species (n = 5) with a portable infrared gas analyzer connected
to PVC pipes during the wet season (October 2015) and the dry season
(January 2016). The CO2 emissions were significantly different between
termite species. Globitermes sulphureus had the highest nest CO2
emission (37.7 \selectlanguage{ngerman}± 14.7 \selectlanguage{greek}µ\selectlanguage{english}mol m-2 s-1 Mean \selectlanguage{ngerman}± SD), followed by
Microcerotermes crassus, Termes comis, Termes propinquus and
Dicuspiditermes makhamensis, respectively. CO2 emissions in termite
mounds and their surrounding soil were significantly higher in wet
season than dry season. Globitermes sulphureus and M. crassus mounds
produced significantly more CO2 than surrounding soils but T. propinquus
and D. makhamensis produced significantly less CO2 than surrounding
soils. Therefore, G. sulphureus and M. crassus are major CO2 producers
among non-fungus growing termites in a tropical forest.%
\end{abstract}\selectlanguage{ngerman}%



\sloppy


\textbf{Introduction}

Tropical forests significantly impact global climate by regulating
greenhouse gas and storing 45-50\% of global terrestrial carbon stocks
(IPCC, 2007). Soil CO\textsubscript{2} emission (soil respiration) plays
an important role in global carbon cycling with contributing more than
50\% of the total ecosystem respiration (Janssens et al., 2001; Xu et
al., 2001; Chambers et al., 2004). Soil CO\textsubscript{2} emission
from tropical forests could strongly influence future concentrations of
atmospheric carbon dioxide. However, soil respiration considerably
varied with space and time (Boonriam et al., 2021a). Spatial variability
in soil respiration from tropical forests remains difficult to assess
and it may lead to inaccurate soil respiration estimates at ecosystem
level. Consequently, understanding of above and belowground soil
activities on carbon cycle in tropical forest is necessary.

Soil respiration comes from CO\textsubscript{2} production of all living
organisms in the soil, including plant roots, soil microbes, and animals
(Lavelle et al., 2001; Luo and Zhou, 2006. Soil microorganisms and roots
are thought to dominate most soil respiration. However, soil respiration
rate has been shown to fluctuate unexpectedly (10-90\%) at large scales
(Hanson et al., 2000). The known environmental factors: soil, water
content, and temperature are unable to completely explain this
variation. According to Ohashi et al. (2007; 2017), certain areas
displayed extremely higher rates of soil respiration (hot spots) and
soil macrofauna were focused as a predominant driver in tropical
forests. Events were attributed to the undisclosed activities of soil
animals, particularly social insects such as termites. Because it is
widely known that termites are superabundant soil insects in seasonal
tropical forests (Yamada et al., 2003, 2005; Inoue et al., 2006).

Termites are major structural components of soil partition up to 95\% of
the total soil insect biomass (Jones and Eggleton 2000) and population
density in the tropics could reaches up to 1000 termites per
m\textsuperscript{2} (Eggleton et al., 1996). Termites are widely
distributed along an altitudinal gradient from lowland to mountain
(Kayani et al., 1979; Akhtar et al. 1992). Termites are significantly
important to drive carbon cycle by litter decomposition as much as half
of the primary litter production (e.g. Matsumoto and Abe, 1979; Bignell
and Eggleton, 2000; Coleman et al., 2004). Termites can be divided into
two major feeding groups, wood/litter feeders (fungus and non-fungus
growers) and soil feeders (non-fungus growers) (Wood, 1976; Collins,
1989; Bignell et al., 1997; Bignell and Eggleton, 2000). Fungus growing
termites cultivate symbiotic fungi on fungus gardens (fungus combs)
consisting of plant litter materials built with partially digested
termite faeces (Korb, 2003). Termite CO\textsubscript{2} emissions were
estimated to contribute up to 2\% of global terrestrial emissions
(Sugimoto et al., 2000). Several studies considered epigeal termite
mounds as high CO\textsubscript{2} emission point sources. As the
epigeal termite mounds in tropical savanna emitted higher
CO\textsubscript{2} than surrounding soils with emphasis on fungus
growing termite (Macrotermitinae) (Konate et al., 2003; Br\selectlanguage{ngerman}ümmer et al.,
2009; Risch et al., 2012), except in seasonal tropical forest (Boonriam
et al., 2021b). Besides, De Gerenyu et al. (2015) reported that termite
mounds contributed up to 10\% of the total soil respiration in a
tropical monsoon forest in Vietnam. Thai-tropical forests also contain
various epigeal termite mounds, especially non-fungus growing termites
(Termitidae) due to the number of species and nests were higher than
fungus growing termites (Yamada et al., 2003). According to Korb (2003),
epigeal termite mounds have a different complex architecture to maintain
a constant temperature and humidity. While the seasonal tropical forests
have sometimes a fluctuation of the climate. Consequently, determining
epigeal mound CO\textsubscript{2} emission in terms of non-fungus
growing termites is one of the best approaches for evaluating soil
biological activities in relation to carbon and energy flow in
terrestrial ecosystems.

This study aimed to 1) compare CO\textsubscript{2} emission from epigeal
mounds of different non-fungus growing termites in a seasonal tropical
forest, 2) compare CO\textsubscript{2} emission from the mounds and
their surrounding soils, and 3) determine the relationship between the
surrounding soil CO\textsubscript{2} emissions and soil environmental
factors in the dry and wet seasons.

\textbf{Materials and Methods}

\emph{Study site}

A field study was performed in the dry evergreen forest (DEF) at
Sakaerat Environmental Research Station (SERS) (14°30´N, 101°56´E; about
500 m above sea level) in Nakhon Ratchasima Province, northeastern
Thailand (Fig 1). According to SERS meteorological stations from 2005 to
2015, the mean annual rainfall was 1,084 mm with monthly rainfall less
than 40 mm during the dry season from November to April and the wet
season started from May to October. The average annual relative humidity
and temperature were 83.8\% and 26.7°C (9.1-38.9°C), respectively.
During the study, the monthly rainfall, temperature, and relative
humidity were 189 mm, 25.1°C, and 74.4\%, respectively in October 2015
(wet season) and 12.1 mm, 23.7°C, and 71.0\%, respectively in January
2016 (dry season). The DEF covers an area of 29.5 km\textsuperscript{2},
where the dominant tree species are \emph{Hopea ferrea} and \emph{Hopea
odorata} with canopy trees reach generally 23 to 40 m (Lamotte et al.,
1998).

\emph{Field experiments}

Five dominant species of the epigeal mound-building of non-fungus
growing termites were selected for this study,
namely\emph{Dicuspiditermes makhamensis, Globitermes sulphureus,
Microcerotermes crassus, Termes comis,} and \emph{Termes propinquus} .
Mound characteristic (e.g. population colony) of the non-fungus growing
termites in each species had been preliminarily observed by a
cross-section. Morphological characters of termite soldiers and the
shape of their mounds were observed (Fig 2).

The five mounds of each termite species were randomly selected with a
distance greater than 5 m between each mound. The mound sizes were
measured for the height (base to the top) and circular length of the
bottom. Three to five PVC collars (10 cm in diameter and ca. 3 cm in
height) were placed at the mound and surrounding soils 10 to 30 cm from
the mound at least one day before the measurement to avoid the
disturbance of soil activities (Fig 3). The CO\textsubscript{2}emissions
of each mound was measured by using a portable infrared gas analyzer
(IRGA, EGM-4, PP Systems, Hitchin, UK) with a closed soil
CO\textsubscript{2} efflux chamber (SRC-1, PP Systems) (10 cm diameter)
one time in October 2015 (wet season) and January 2016 (dry season).

After CO\textsubscript{2} measurement, soil temperature and soil
moisture content of the surrounding soils were measured immediately
around each PVC collar at about 10 cm depth with a digital thermometer
waterproof probe (type H-1 and H-2, Shinwa Co., Ltd., Japan) and soil
moisture sensor (SM150, Delta-T Devices Ltd., Cambridge, UK),
respectively. However, soil temperature and soil moisture content of the
mounds were not measured because to avoid disturbing mound and termite
activity. All measurements began from 9:00 am to 6:00 pm (3 to 5 minutes
per location) in the day without rain.

\emph{Statistical analysis}

All the analysis was performed on log-transformed data to transform the
skewed data to approximately conform to normality. The Kolmogorov --
Smirnov test was used to test for normality. Then, an analysis of
CO\textsubscript{2} emission rates for detecting significant differences
among the termite mound species was tested by the analysis of variance
ANOVA as well as their surrounding soils during the dry and wet seasons.
Mean for groups in homogeneous subset among species were evaluated by
Tukey HSD's post hoc test. The difference of CO\textsubscript{2}emission
from the nest and surrounding soil in each species was tested by t-test.
The relationship between CO\textsubscript{2} emission from surrounding
soil and the soil environmental factors (i.e. soil temperature and soil
moisture content) was determined with the Pearson correlation analysis.
All statistical calculations were performed in SPSS ver. 20.0.0 for
Windows.

\textbf{Results}

Rate of CO\textsubscript{2} emissions were directly detected on the
mounds of 5 dominant termite species (n = 5) during the dry and wet
seasons in the DEF at SERS. The characteristic of the selected termite
mounds was described as the size, feeding group, and physical and
environmental factors (Table 1). The mound CO\textsubscript{2} emissions
were widely variable ranging from 0.17 to 55.15 \selectlanguage{greek}µ\selectlanguage{english}mol
CO\textsubscript{2}m\textsuperscript{-2} s\textsuperscript{-1}, while
the range of CO\textsubscript{2} emissions from their surrounding soil
was considerably narrower from 0.68 to 14.86 \selectlanguage{greek}µ\selectlanguage{english}mol
CO\textsubscript{2}m\textsuperscript{-2} s\textsuperscript{-1}. The
results showed that the mean of the CO\textsubscript{2} emission rate
was significantly different between the termite species (\emph{F=}
49.174 \emph{P}\textless{} 0.001) (Table 2).

The highest average of the mound CO\textsubscript{2} emission was
from\emph{G. sulphureus} that reached up to 37.7 \selectlanguage{ngerman}± 14.7 \selectlanguage{greek}µ\selectlanguage{english}mol
m\textsuperscript{-2} s\textsuperscript{-1} mean\selectlanguage{ngerman}± SD, followed
by\emph{M. crassus} , \emph{T. comis} , \emph{T. propinquus} and
\emph{D. makhamensis} which were 15.50 ± 7.84, 6.45 ± 2.35, 1.98 ± 1.78,
and 1.79 ± 0.99 \selectlanguage{greek}µ\selectlanguage{english}mol m\textsuperscript{-2} s\textsuperscript{-1} mean \selectlanguage{ngerman}±
SD, respectively. In both locations, CO\textsubscript{2} emission rate
was significantly different between the mound and surrounding soil
(\emph{F} =35.2.10, \emph{P} \textless{} 0.001) (Table 2) (Fig 4). While
CO\textsubscript{2} emission from the surrounding soil alone was not
different between species (\emph{P} = 0.657) (Fig 4).

The mean of the total CO\textsubscript{2} emission from the mounds
(12.68 ± 15.41 \selectlanguage{greek}µ\selectlanguage{english}mol m\textsuperscript{-2} s\textsuperscript{-1} mean\selectlanguage{ngerman}±
SD) was 2.5 times higher than surrounding soils (5.06 ± 3.29 \selectlanguage{greek}µ\selectlanguage{english}mol
m\textsuperscript{-2} s\textsuperscript{-1} mean\selectlanguage{ngerman}± SD). The overall mean
of CO\textsubscript{2} emissions from the mounds was 3.9 and 2.1 times
higher than surrounding soils in the dry and wet seasons, respectively
(Fig 5). There was a significant difference for both mounds and
surrounding soils between the dry season and wet season (\emph{F} =
14.957 \emph{P} \textless{} 0.001) (Table 2). In each season, mound
CO\textsubscript{2} emissions were significantly different among the
species and surrounding soils in the dry season and wet season (\emph{P}
\textless{} 0.001). The mound CO\textsubscript{2} emissions from
\emph{G. sulphureus} and \emph{M. crassus} mounds were significantly
higher than surrounding soils in both dry and wet seasons. In contrast,
\emph{T. propinquus} and \emph{D. makhamensis} emitted significantly
CO\textsubscript{2} less than the surrounding soils (Fig 6).

The average rate of CO\textsubscript{2} emission from surrounding soils
was 3.4 times higher in the wet season (7.83 ± 2.33 \selectlanguage{greek}µ\selectlanguage{english}mol
CO\textsubscript{2} m\textsuperscript{-2} s\textsuperscript{-1} mean \selectlanguage{ngerman}±
SD) than the dry season (2.29 ± 0.89 \selectlanguage{greek}µ\selectlanguage{english}mol
CO\textsubscript{2}m\textsuperscript{-2} s\textsuperscript{-1} mean \selectlanguage{ngerman}±
SD). The relationship between the soil CO\textsubscript{2} emissions,
soil temperature, and soil moisture content aids in distinguishing
seasonal variations. The CO\textsubscript{2} emission rates from
surrounding soils were positively correlated with soil moisture
contents. (Pearson correlation,\emph{r} = 0.804, \emph{P} \textless{}
0.001) (Fig 7). The highest CO\textsubscript{2} emission rates (more
than 10 \selectlanguage{greek}µ\selectlanguage{english}mol CO\textsubscript{2} m\textsuperscript{-2}
s\textsuperscript{-1}) were found at around 10 to 19\% of the soil
moisture content. While the relationship between soil temperature and
surrounding soil CO\textsubscript{2} emission was not significant
(Pearson correlation\emph{, r} = -0.024, \emph{P} = 0.768). The soil
temperature had limited variation from 21.8 to 27.5 \selectlanguage{ngerman}°C.

\textbf{Discussions}

This study found that the CO\textsubscript{2} emission from the mounds
of non-fungus growing termites were different between species and their
surrounding soils during both dry and wet seasons in a tropical seasonal
forest. The mean annual mound CO\textsubscript{2} emission was 2.5 times
higher than surrounding soils. In particular,
CO\textsubscript{2}emissions from the mounds of \emph{G. sulphureus} and
\emph{M. crassus}were much higher than other termite species and greater
than their surrounding soils in both seasons. The high
CO\textsubscript{2}emissions were from the mounds from these species
because their populations were found ubiquitously in the nest or mound
with a thin wall, whereas the other species were found in some part of
the nest. Also, most of the nest materials are mixed from the macerated
wood and their faeces (Bignell and Eggleton, 2000). Moreover, \emph{G.
sulphureus} and \emph{M. crassus} are a group of wood/litter feeders
that these species may be consumed directly to organic carbon much more
than the soil feeders. Although respiratory rate varied inversely with
body weight, the substrates for all feeding groups have an effect on the
variations in metabolic rate (Jeeva et al., 1999). In the same forest,
these two species were found in high abundance and biomass,
especially\emph{M. crassus} was 46\% and 36\% of the termite abundance
and biomass, respectively (Yamada et al., 2003). Therefore, the mounds
of\emph{G. sulphureus} and \emph{M. crassus} could potentially drive the
high spatial variation in soil CO\textsubscript{2} emission in the
tropical seasonal forests.

As a result, the mean CO\textsubscript{2} emission rate from the mound
of \emph{G. sulphureus} was higher than the mound of other species in
this study. This emission rate was also higher than the mound from the
other studies in both non -- fungus grower (Brümmer et al., 2009; Jamali
et al., 2013; De Gerenyu et al., 2015; Konemann and Kard, 2016) and
fungus -- grower termites (Konate´ et al., 2003; Nyamadzawo et al.,
2012; Sawadogo et al., 2012; Ohashi et al., 2017) from the different
topography, except for some rates of CO\textsubscript{2} emissions from
the subterranean nest of termites (e.g. \emph{Hospitalitermes
hospitalis} ) in a tropical rainforest (Ohashi et al., 2017) (Table 3).

In addition, the other soil organism was proposed as the
CO\textsubscript{2} point source such as ants and earthworm (Khalil et
al., 1990; Stoyan et al., 2000; Risch et al., 2005; Ohashi et al.,
2007). According to Ohashi et al. (2017) reported that the
CO\textsubscript{2} emission rate from the subterranean nest of
ant\emph{Dinomyrmex gigas} (45.5 \selectlanguage{greek}µ\selectlanguage{english}mol
CO\textsubscript{2}m\textsuperscript{-2} s\textsuperscript{-1}) was
higher than the rate in this study. However, the CO\textsubscript{2}
emission rate from \emph{G. sulphureus} mound in this study that was
higher than soil CO\textsubscript{2} emission which affected by the
other ants (Sousa-Souto et al., 2012; Hasin et al., 2014; Fernandez-Bou
et al., 2019) and earthworms (\selectlanguage{polish}Š\selectlanguage{english}imek and Pi\selectlanguage{polish}ž\selectlanguage{english}l, 2010) (Table 3). In term
of earthworms, although there were no effect on the emission of
CO\textsubscript{2} from soil (Guo et al., 2019), earthworms have
increased the carbon content and other nutrients (Lavelle et al., 2001)
for enhancing soil respiration by microbial activities.

Meanwhile, the CO\textsubscript{2} emissions from \emph{T. propinquus}
,\emph{D. makhamensis} , and \emph{T. comis} mounds were both much lower
than \emph{G. sulphureus} and \emph{M. crassus} and were significantly
lower than surrounding soils in both seasons (except for \emph{T.
comis}which did not differ between surrounding soils in the wet season).
However, these three species are categorized as soil-feeder,
while\emph{G. sulphureus} and \emph{M. crassus} are wood/litter-feeder
(Wood, 1976; Collins, 1989; Bignell et al., 1997; Bignell and Eggleton,
2000). This was probably due to the respiration rate from termite
populations of soil-feeders was lower than wood/litter-feeders.
According to Yamada et al. (2005) Termite individual contributions to
carbon mineralization by the respiration from wood/litter-feeders and
soil-feeders were 2.8\% and 1.2\% of the annual aboveground litterfall
in the DEF at SERS, respectively.

Mound structure differences between species may also contribute to
variation in mound CO\textsubscript{2} emissions. Nest construction
material as the wood carton (a mixture of faeces and macerated wood) is
used for the most wood/litter-feeding group, while many soil-feeders use
faeces mixed with topsoil (Bignell and Eggleton, 2000). In addition, the
soil feeder epigeal mounds may not contain the entire colony population
above the mound because most individuals move below the soil for
foraging and to avoid adverse environmental conditions (Fig 8).
Moreover, the mound CO\textsubscript{2} emission rates of \emph{T.
propinquus} , and \emph{D. makhamensis} were similar to those reported
by Song et al. (2013) who reported that the range of
CO\textsubscript{2}emission from termite mounds (species: not given) was
from 1.63 to 3.71 \selectlanguage{greek}µ\selectlanguage{english}mol CO\textsubscript{2} m\textsuperscript{-2}
s\textsuperscript{-1} and these species did not affect soil
CO\textsubscript{2} emission in the tropical rainforest. As the result
of Song et al. (2013), mounds were either typical soil-feeding group
mounds or similar to the fungus growing termites that build a
dome-shaped mound with thick walls (20-40 cm thickness) and several
branching underground passages (Inoue et al., 2001).

Previous studies have reported that the mound-builder and subterranean
nest of termites emitted significantly higher CO\textsubscript{2} than
typical soils (e.g. Konate et al., 2003; Br\selectlanguage{ngerman}ümmer et al., 2009; Risch et
al., 2012; De Gerenyu et al., 2015; Ohashi et al., 2017). Not only
CO\textsubscript{2} emission from termite individuals, but their nest
also contributed to soil respiration. According to Hu et al. (2017)
reported that CO\textsubscript{2} emission from termite nest soil was
higher than typical soil, due to termite nest soils had higher dissolved
organic carbon concentration and C/N ratio, accelerating for microbial
activities. In a tropical savanna, the fungus-growing termite was
emitted 10-19 \selectlanguage{greek}µ\selectlanguage{english}mol CO\textsubscript{2}
m\textsuperscript{-2}s\textsuperscript{-1} from the mound which compared
to 5-10 \selectlanguage{greek}µ\selectlanguage{english}mol CO\textsubscript{2} m\textsuperscript{-2}
s\textsuperscript{-1} from surrounding soils (Konate et al., 2003). In a
tropical rain forest, the mean of CO\textsubscript{2} emission from
termite mound was reached up to 27.9 \selectlanguage{greek}µ\selectlanguage{english}mol CO\textsubscript{2}
m\textsuperscript{-2}s\textsuperscript{-1} that much higher than the
surrounding soil (3.96 \selectlanguage{greek}µ\selectlanguage{english}mol CO\textsubscript{2} m\textsuperscript{-2}
s\textsuperscript{-1}) (Ohashi et al., 2017). An earlier study (Ohashi
et al., 2007) indicated that the rate of soil respiration was sometimes
extremely high (\textgreater{}10 \selectlanguage{greek}µ\selectlanguage{english}mol CO\textsubscript{2}
m\textsuperscript{-2}s\textsuperscript{-1}) contributing 10\% to the
total soil respiration in the tropical rainforest. De Gerenyu et al.
(2015) showed that the mound CO\textsubscript{2} emission of
\emph{Odontotermes} termites (fungus grower) and \emph{G. sulphureus}
(non-fungus grower) was 2.0-2.5 times higher than the background soil
during both dry and wet seasons. Also, those termite mounds contributed
up to 10\% of the total soil respiration in a tropical monsoon forest of
southern Vietnam, showing the maximum rates of the mound
CO\textsubscript{2} emissions were 17 and 20 \selectlanguage{greek}µ\selectlanguage{english}mol CO\textsubscript{2}
m\textsuperscript{-2} s\textsuperscript{-1}from \emph{Odontotermes} and
\emph{G. sulphureus} , respectively. On the other hand, mound CO2
emission rate was 2.5 times lower than the surrounding soil that was
affected by termite respiration through their underground passages in
the surrounding soil (Boonriam et al., 2021b).

The relationship between soil CO\textsubscript{2} emission and its
environmental factors was also observed from only soil around each
mound, while soil temperature and soil moisture content were not
measured from the mounds to avoid disturbing termite activity at the
nest. In this study, soil CO\textsubscript{2} emission rate was 3.4
times higher in the wet season than the dry season. Soil
CO\textsubscript{2} emissions showed a consistent relationship with soil
moisture content. In addition, soil CO\textsubscript{2} emission rate
was started to decrease when soil moisture content peaked more than 18\%
(Adachi et al., 2009) and 21\% (Hasin et al., 2014) in diurnal variation
of Thai tropical forest. A previous study reported that the rate started
to drop at 27 \selectlanguage{ngerman}°C soil temperature and 21\% soil moisture content in the
same topographical forest (Boonriam et al., 2021a). Although
precipitation influences soil microbial activities accelerating soil
respiration, high precipitation could inhibit
CO\textsubscript{2}emission by a barrier of high moisture content in the
soil (Sotta et al., 2004; Wood et al., 2013). This inconstancy within
the timing and magnitude of precipitation occasions can influence soil
respiration.

\textbf{Conclusion}

The CO\textsubscript{2} emissions from termite mounds were generally
higher than surrounding soils. The mound CO\textsubscript{2}
emission,\emph{G. sulphureus} and \emph{M. crassus} are major
CO\textsubscript{2}producers among the non-fungus growing termites in
this tropical forest. The difference in CO\textsubscript{2} emissions
among termite mounds may due to the population colony, ventilation, and
thickness of the nests. The rate of soil CO\textsubscript{2} emission
was increased with increasing soil moisture content. Future information
regarding the total soil CO\textsubscript{2} emission and the mound
density on large scale as well as their environmental conditions are
necessary for evaluating the contribution to the total soil respiration
in Thai-tropical forest.

\textbf{Acknowledgments}

This work was mainly supported by the Japan Society for the Promotion of
Science under Grant-in-Aid for Young Scientists (B) 25850104 (to AY).
This study was partly supported by both Suranaree University of
Technology and Thailand Institute of Scientific and Technological
Research (TISTR). We are thankful to SERS staff for their advice and
support with this study.

\textbf{Author contribution}

The experiment was designed by Warin Boonriam, Akinori Yamada, and
Pongthep Suwanwaree. Data collection, sampling, and species
identification were performed by Warin Boonriam. Statistical analysis
and text review were discussed by Warin Boonriam, Pongthep Suwanwaree,
and Sasitorn Hasin. All authors discussed and revised the manuscript.

\textbf{Conflict of interest}

The authors declare that there is no conflict of interest regarding the
publication of this article.

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