Fungal Diversity

Straminipilous organisms from fallen mangrove leaves fromPanay Island, Philippines

Eduardo M. Leaiio

Aquaculture Department, Southeast Asian Fisheries Development Center, Tigbauan, 5021Hoilo, Philippines; e-mail: edleano@aqd.seafdec.org.ph

Leafio, E.M. (2001). Straminipilous organisms from fallen mangrove leaves from Panay Island,Philippines. Fungal Diversity 6: 75-81.

Fallen senescent mangrove leaves from three marine mangrove sites in Panay island,Philippines were collected for observation and isolation of straminipilous organisms. A total of11 mangrove species were sampled. Halophytophthora species were observed on 7 out of 11mangrove species sampled, with H. vesicula as the most abundant species observed.Halophytophthora epistomium also occurred abundantly on fallen leaves of Rhizophoraapiculata and Sonneratia sp. Thraustochytrids, on the other hand, were observed on allmangrove leaf samples except Aegiceras corniculatum. Schizochytrium mangrovei was themost abundant species observed. Their association and ecological role on the degradation offallen mangrove leaves is discussed.

Key words: Halophytophthora, mangrove, thraustochytrids.

IntroductionMarine straminipilous organisms (oomycetes and thraustochytrids) are

associated with decomposition of leaf materials in the aquatic habitats. In themangrove environment, fallen leaves are colonised by microorganisms, andrelease abundant organic matter upon degradation. Oomycetes andthraustochytrids are common colonizers of fallen mangrove leaves, and areassociated from early to late stages of decay (Bremer, 1995; Nakagiri et al.,1989; Leaiio et al., ]998). They are also reported to play an important role inthe food web of estuarine ecosystem (Nakagiri, ]993) being secondaryproducers in coastal zones where there is high productivity by vascular plants(Newell, 1996). These straminipilous organisms are ubiquitous in marine andestuarine environments, in tropical and sub-tropical areas (Newell and Fell,1992). This study was conducted to determine the abundance of oomycetes andthraustochytrids on fallen mangrove leaves from Panay island in thePhilippines.

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Materials and methods

Sample collectionFallen senescent leaves of 11 mangrove species (Table 1) were collected

from three marine (salinity range: 28-32 %0) mangrove sites in Panay Island:Ibajay and Dumaguit, Aklan; and Banate, Hoilo. At least 10 leaf samples werecollected for each mangrove species per sampling (three samplings in Ibajay;two in Banate; and one in Dumaguit). The leaves were placed in plastic bagsupon collection and returned to the laboratory for observation and isolation ofstraminipilous organisms.

Table 1. Mangrove species sampled at different sampling sites in Panay island, Philippines.

Mangrove species

Aegiceras corniculatum (L.) BlancoAvicennia lanata L.

A. officinalis L.Bruguiera cylindrica (L.) BI.Camptostemon philippinense (Vidal) Becc.Ceriops decandra (Griff.) Ding HouHeritiera littora/is Dryand. Ex. W. Ait.Rhizophora apicu/ata BI.Sonneratia sp.Xylocarpus granatum Roem.X. mekonfIensis Pierre

Ib~xxxxxxxx

xxx

Mangrove sitesDumaguit

x

x

x

Banate

x

xx

Isolation

The leaves were cut into 1 cm2 pieces (5-10 pieces/leaf sample) andwashed three times (lh/wash) in sterile natural seawater (NSW) supplementedwith antibiotics (ab: 1000 U/mT. of Penicillin G and 500 Jlg/mL Streptomycinsulfate). For thraustochytrids, four leaf pieces were inoculated onto yeastextract-peptone (YEP) agar [composed of 1 gyeast extract (BBL), 1 gmycological peptone (Oxoid), 15 g agar (BBL), 1 L NSW] with ab, andflooded with thin layer of sterile NSW with ab. Two YEP plates were preparedper leaf sample. The plates were incubated at room temperature (ca. 30-32 QC)for 2-3 d. Growth of thraustochytrids were monitored daily and selectedcolonies were picked with fine-tipped forceps. The isolates were purified onYEP agar.

For Halophytophthora species, the 2-4 leaf pieces (per leaf sample) wereinoculated on sterile NSW at room temperature for 5 d. Zoosporangialproduction was monitored daily. Individual zoosporangium of selected isolateswere picked and inoculated onto peptone-yeast extract-glucose-seawater

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Fungal Diversity

(PYGS) agar [composed of 1.25 g mycological peptone, 1.25 g yeast extract, 3g glucose (Ajax), 12 g agar, IL NSW] supplemented with ab. The isolates werepurified on fresh PYGS agar.

IdentificationThraustochytrid isolates were identified using the pine-pollen culture and

based on cell and zoosporangial characteristics described by Booth and Miller(1968), Raghukumar (1988), and Honda et al. (1998). Halophytophthoraspecies were identified based on zoosporangial characteristics using theidentification scheme by Ho et al. (1991).

Results and discussion

Straminipilous oomycetes and thraustochytrids are widely distributed inmany mangrove habitats in tropical and sub-tropical areas. This include Japan(Nakagiri et al., 1989), Bahama islands (Newell and Fell, 1992), Taiwan (Ho etal., 1991), India (Raghukumar, 1988), Malaysia (Bremer, 1995), and HongKong (Leafio et al., 1998) among others. This study is the first report on theoccurrence of Halophytophthora species and thraustochytrids from thePhilippines. Table 2 shows the abundance of Halophytophthora species andthraustochytrids observed on fallen leaves from Panay island mangroves.Halophytophthora species were observed on 7 out of 11 mangrove speciessampled. Halophytophthora vesicula (Anast. and Church!.) H.H. Ho and Jong(Figure 1) was the most dominant species observed with frequencies ofoccurrence from 85 to 100%. Halophytophthora epistomium (Fell and Master)H.R Ho and Jong was observed abundantly on fallen leaves of Rhizophoraapiculata (77%) and Sonneratia sp. (60%). Other species observed were H.kandeliae H.H. Ho, RS. Chang and S.Y. Hsieh on leaves of Avicennia lanata,R. apiculata and Sonneratia sp., H. spinosa var. lobata (Fell and Master) H.H.Ho and Jong on Xylocarpus mekongensis, and H. bahamensis (Fell and Master)RH. Ho and Jong and an unidentified species on A.lanata.

Halophytophthora species are pythiaceous oomycetes that inhabit marineand brackish water environments (Nakagiri, 1998). They are the primary groupinvolved in the colonization of detached and submerged mangrove leaves(Newell and Fell, 1992). Several reports show that H. vesicula is the mostdominant species observed on several mangrove species (Nakagiri et al., 1989;Newell and Fell, 1992). The dominance of this species over other fungalspecies was attributed to: (i) abundant zoospore production (Nakagiri et al.,1989); (ii) wide tolerance to salinity and temperature (Nakagiri, 1993; Leafio,et al., 1998); (iii) ability to compete against higher fungi in colonizingmangrove leaves (Newell and Fell, 1997); and, (iv) the ability of the zoospores

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to attach firmly on the substrata surface for successful germination andcolonization (Leafio et al., 2000). Moreoever, H. vesicula was found toproduce enzymes (e.g. cellulase, pectic lyase, polygalacturonase) necessary forthe degradation of a wide variety of organic compounds present in mangroveleaves (Raghukumar et al., 1994).

Among the thraustochytrids, all leaf samples collected except Aegicerascorniculatum yielded few to abundant colonies (Table 2). Schizochytriummangrovei Raghuk. (Figure 2) was the most abundant species observed withfrequencies of occurrence ranging from 40 to 100%. Thraustochytrium sp. wasalso observed on leaves of X. granatum (abundant) and R. apiculata (few).

Table 2. Abundance of Halophytophthora and thraustochytrids on fallen mangrove leavesfrom Panay island, Philippines.

Frequency of Occurrence (%)*Halophytophthora Thraustochytrids

Mangrove species

Aegiceras corniculatumAvicennia lanata

A. officinalis

Bruguiera cylindricaCamptostemon philippinenseCeriops decandraHeritiera littoralis

Rhizophora apiculata

Sonneratia sp.

Xylocarpus granatum

X. moluccensis

H. vesicula (94)H. kandeliae (28)H. bahamensis (12)Halophytophthora sp. (5)H. vesicula (lOO)

H. vesicula (95)

H. vesicula (100)H. epistomium (77)H. kandeliae (15)H. vesicula (85)H. epistomium (60)H. kandeliae (25)H. vesicula (lOO)

H. epistomium (20)H. vesicula (100)H. spinosa var. lobata (5)

Schizochytrium mangrovei(100)

S. mangrovei (83)Schizochytrium sp. (l0)Schizochytrium sp. (15)S. mangrovei (75)S. mangrovei (lOO)Schizochytrium sp. (7)Thraustochytrium sp. (15)Schizochytrium sp. (5)

S. mangrovei (90)Schizochytrium sp. (20)

Thraustochytrium sp. (70)S. mangrovei (65)S. mangrovei (40)

* Number of specific straminipilous organism observedTotal number ofleaf samples collected (per mangrove species)

x 100%

Thraustochytrids are widely distributed in saline lakes, as well as marineand estuarine waters (Naganuma et al., 1998). They are reported to beassociated with mangrove swamps (Ulken, 1981), seawater (Honda et al.,1998), marine sediments (Raghukumar, 1980), and littoral algae and seaweeds

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Fungal Diversity

Figs. 1-2. Dominant species ofstraminipilous organisms from fallen mangrove leaves in Panayisland, Philippines. 1. Halophytophthora vesicula. 2. Schizochytrium mangrovei (c = maturecell; t = tetrad; 0 = octad). Bars: 1 = 20 IJm, 2 = 10 IJm.

(Miller and lones, 1983). Unlike Halophytophthora species, however, fewreports are available on their association on fallen mangrove leaves.Raghukumar (1988) reported the presence of S. mangrovei on fallen leaves ofR. mucronata Lam. and A. officinalis. Thraustochytrids were also foundcolonizing fallen senescent leaves of Sonneratia and Rhizophora (Bremer,1995). Results from this study show that thraustochytrid species can alsocolonize a wide variety of mangrove leaf species once fallen into the water(Table 2).

Thraustochytrids play an important role in the aquatic food web throughtheir degradative activities (Ulken, 1981). Raghukumar et al. (1994) reportedthat S. mangrovei secretes high amounts of degradative enzymes includingamylase, cellulase and polygalacturonase. In addition, many species ofSchizochytrium and Thraustochytrium are efficient producers ofpolyunsaturated fatty acids including decosahexaenoic acid (DHA) andeicosapentaenoic acid (EPA) (Yaguchi et al., 1997).

In general, oomycetes and thraustochytrids as detrital microbes, play amajor role in altering the chemistry of detritus (Raghukumar et al., 1994)especially fallen leaves in mangrove environments. As early colonizers, theydegrade a wide variety of organic compounds (Raghukumar et al., 1994) thus

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enriching the nutrient of the leaves with their biomass (Nakagiri, 1998). Thisprocess changes the plant debris into a nutritious form for consumption oforganisms in higher trophic levels. Therefore, the degradation and enrichmentof fallen mangrove leaves by these microorganisms contribute significantly onthe nutrition of many bottom-feeding and filter-feeding organisms, makingmangroves as excellent nursery grounds for many fish and crustacean species.

AcknowledgementsThis study was funded by SEAFDEC/AQD under study code Nr-05-F99T. The author

wishes to thank K.W. Fan of City University of Hong Kong for assistance in the identificationof thraustochytrid isolates.

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(Received 1 July 2000, accepted 1 October 2000)

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