Microalgal communities on mangrove forest sediments of East Java, Indonesia

概要

Doctoral Thesis

Microalgal communities on mangrove forest sediments of
East Java, Indonesia
࢖ࣥࢻࢿࢩ࢔ᮾࢪࣕ࣡ࡢ࣐ࣥࢢ࣮ࣟࣈᯘᗏἾ࡟⏕ᜥࡍࡿᚤ⣽⸴ࢥ࣑ࣗࢽࢸ࢕



(Summary)

Ayu Lana Nafisyah

Graduate School of Biosphere Science
Hiroshima University
September 2020

CHAPTER 1: General introduction
Indonesia is known as an archipelagic country that has been attributed as the third
longest coastline globally. Diverse coastal ecosystems of Indonesia are considered to be rich
in biodiversity, and one of the vital ecosystems is the mangrove forests, those accounting for
23% (3 million ha) of the worldwide mangrove areas. In this ecosystem, benthic or epiphytic
microalgae (herein abbreviated as MPB) have been regarded as the second largest carbon
stocks after the litterfall of mangrove trees; however, there has been still scanty knowledge
about MPB flora especially in the Indonesian waters. While MPB in mangrove ecosystems
were primarily composed of diatoms, other algal taxa occasionally occur in specific area or
season. Dinoflagellates blooming were found at mangrove estuary in Thailand during a period
of scant occurrence of diatoms in dry season. Actually, during the survey for MPBs in East
Java coasts in this study, a harmful raphydophycean alga was found on the mangrove
sediments at Probolinggo.
This study was conducted aiming to increase an awareness and to provide new insights
on the importance of mangrove ecosystems in Indonesia, at where the highest annual
deforestation rate of mangrove forests in the world has been reported. For this general
purpose, the investigation on MPB in the sediment of mangroves are of interests because their
compositions are expected to be indices of fertility. Also, there has been no research
particularly for harmful algal species in the Indonesian mangrove areas.

CHAPTER 2: Cryptic occurrence of Chattonella marina var. marina in mangrove
sediments in Probolinggo, East Java, Indonesia
During the MPB flora investigation on mangrove swamps of Probolinggo, a mud
sample unexpectedly included large numbers of a notorious fish killer, Chattonella-like
motile cells, and its resting cysts. These motile cells were established as clonal cultures for
further identification and physiological tests. The cysts were examined through palynological
and molecular biological techniques. Based on light microscopy and ribosomal RNA gene
sequences, these cells and cysts were identified as Chattonella marina var. marina. While the
strains were genetically identical to the temperate strains isolated from Japan and China,
temperature experiments showed that the Indonesian strains possessed a high maximum
quantum yield of photosystem II even after exposure to 34 °C, a temperature at which the
Japanese strain could not survive. Salinity experiments showed adaptation of the strains to a
salinity of 15. These findings, together with the discovery of populations of cysts in the
mangrove sediment, highlight the tough and unique nature of the Indonesian strains, which
are likely adapted to wide fluctuations of temperature and salinity in mangrove swamps, and
pose a potential risk to fisheries in Indonesia.
CHAPTER 3: Microphytobenthos florae in different mangrove sediments along the East
Java coast; Probolinggo, Situbondo, Banyuwangi

It has been reported that MPB composition tends to exhibit unique locality and unique
to adjacent environments. If so, those in the Indonesian mangrove forests could be an indicator
of the forests’ status, those now suffering intensive activities by human. Therefore, for the
first time in Indonesia, this study aims to determine the taxonomic composition of MPB in
the sediment of mangrove forests those ranging in geographically and environmentally
variations in the East Java. The study locations were stretch along the northern coast of East
Java, Probolinggo, Situbondo and Banyuwangi, each representing artificially replanted forest,
well-conserved forest and adjacent to shrimp ponds, respectively.
A total of 27 species were identified morphologically in the sediment samples. The
cell density and biovolume based on the cell length, width and height measured under the
microscope revealed the highest biovolume (183,495 x 103 ± 66,965 x 103 μm3 cm−3) at
Situbondo, followed by the replanted site, Probolinggo (107,092 x 103 ± 26,021 x 103 μm3
cm−3) and the nearby shrimp pond site, Banyuwangi (66,962 x 103 ± 19,920 x 103 μm3 cm−3),
insisting MPB assemblages and their biomass might differ depend on the fertility status of
mangrove ecosystems.

CHAPTER 4: Microphytobenthos florae in mangrove sediments of Pang-Pang Bay; a
comparison between a conserved mangrove area and human-affected swamps of the bay
Further field survey was conducted in the unique areas that is Pang-Pang Bay, where
the human-affected swamps and the well-conserved national forest are coexisting. At this bay,
we aimed to clarify MPB communities of both sides and further proof the above hypothesis
stating MPB assemblages might differ depend on the fertility status of mangrove ecosystems.
Also, in this study, the water columns during high tide were observed to further estimating
the primary production rate of the bay that could be driven by suspended MPB. A total of 56
species of MPB were observed in the sediment samples. The highest cell density (448,380
cells cm−3), as well as biovolume (1,666 x 106 μm3 cm−3) was found at St 1 that located in the
conserved side at the east. A dendrogram using the cell density data of each station showed
an interesting result where two major clusters determined with ca. 48−50% similarities
separated the west (human-affected swamps) and east side (well-conserved swamps). During
high tide sampling, about half of microalgal community in the water was consisted of MPB
species, including Navicula agnita (124 x 106 μm3 cm−3) that was also dominant in sediment
samples during low tide sampling. An estimation of primary production in Pang-Pang Bay
resulting the highest value of 1.28 gC m−2 day−1 at the offshore waters (St E).
CHAPTER 5: Physiological responses of microphytobenthos towards environmental
changes
Benthic communities of intertidal area, including mangrove swamps, usually suffered
to harsh environmental drifts, e.g. drastic salinity and temperature changes within a single
day, exposure to direct sunlight at low tide, etc. The unique physiological responses of MPB

have been reported to enable them to tolerate these harsh environmental conditions. In this
study, the physiological characters of the candidate MPB species were tested against some
environmental fluctuations; i.e. extremely high temperature, wide fluctuation of salinity and
intensive light exposure those are characteristic environments of the sites. Tryblionella
cocconeiformis, Navicula gregaria, N. agnita and Nitzschia sigma were selected as the
candidate Indonesian strains. For the comparison, two planktonic strains were subjected,
Biddulphia sp. (Myanmar strain) and Melosira sp. (Japan strain). Against the rises of
temperature, Fv/Fm values of N. sigma was recognized to be highest even under the highest
temperature (36 °C). Among other strains, Indonesian strains was also able to grow in the
broader range of salinity (10 to 30 PSU) with N. sigma as the most tolerate species with 1.43
± 0.14 division day⁻1 at the lowest salinity of 10. The photosynthetic parameters, ΦPSII, NPQ,
and qP, were measured to investigate the tolerances on repeated alteration between low light
and high light. During the exposure of high light, the ability to quench an excess energy as
heat (NPQ) was limiting among the Indonesian strains, especially in T. cocconeiformis and
Navicula species. Even without this dissipating function, these Indonesian strains could utilize
high light without photoinhibition, as indicated by higher photochemical quenching (qP)
during high light, indicating the species could adapt high light exposure on the sediments.
CHAPTER 6: General discussion
The ultimate goal of this study is to provide new insights on the importance of
mangrove ecosystems, particularly in Indonesia, where the wide mangrove forest is existing
but at the same time facing the highest annual deforestation rate. For this purpose,
investigation of microalgal communities on mangrove forest sediments was done revealing
their abundance and diversity which was indicating the fertility of mangrove forests in East
Java, Indonesia. Beside MPB that primarily consisted of diatoms, Chattonella marina var.
marina was also found in this study, wherein when they bloom, it can cause severe economic
losses in fisheries production for adjacent waters.
This study reported a linear regression between the chlorophyll a of sediment surface
and biovolume of the MPB which showed almost all MPB florae consisted of benthic diatom
species. Such linear regression was also obtained in Chapter 4 (Fig. 4-13) which further
showed the Fv/Fm values and the species diversity index were correlated, which implied
environments suitable for the diatoms’ photosynthetic performance led high MPB diversity
and biomass. The physiology of candidate MPB species were evaluated against some
environmental parameters, revealing their high abilities in adapting to temperature increase
and wide salinity range, and also their unique mechanisms to respond high light exposure.
MPB also played an important role in the primary production in the water columns because
of their high occurrence among other planktonic species. The occurrence of dense MPB may
contribute as an important primary producer for the swamps as well as the adjacent coastal
waters. In the future, these secret function of secret garden in the mangrove forest should be
clarified to elucidate high biological production of mangrove forest.