Mangrove & Fungi

In particular, the trees of the eastern mangrove have not been examined for the occurrence of marine fungi. Mangrove vegetation contributes to the primary production in the aquatic environment in the form of leaf and litter fall. Decomposition of this organic material by bacteria and fungi results in protein enriched fragments of detritus.

 Fungi rather than bacteria have been considered to be principal sources of this increase in nitrogen (Odum and Heald, 1972). Despite better understanding of the importance of mangroves, they continue to be destroyed at an alarming rate (Ong, 1995). Therefore, it is imperative to record and quantify the abundance of marine fungi in the mangrove ecosystem and to isolate them to ensure their conservation for future biochemical, genetic and molecular studies (Jones and Mitchell, 1996). In recent years, mycologists have documented the fungi on tropical and subtropical mangrove substrata. Apart from isolating several interesting fungi, information was also gathered on the ecology of these fungi. Although mangroves are dominant on the Indian coasts providing niches and habitats for many marine and estuarine organisms, few attempts have been made to investigate the fungi associated with decaying substrata of these plants. This is especially true with mangroves of the east coast of India which covers approximately 33% of the total Indian mangroves (Untawale, 1987).

Early studies on marine fungi on mangroves have focused on taxonomy of marine fungi including descriptions of new species and new genera, lists of fungi and surveys. This includes the marine fungi occurring in mangrove environments. The dead and damaged stems, prop roots, seedlings and leaves of the mangroves which fall on the ground are exposed during low tide and submerged in the water during high tide. The period of exposure depends on the tidal amplitude and place where the materials accumulate. This environment crutches a unique habitat for a certain group of fungi called 'manglicolous fungi' which are well adapted to this type of environment. First review on manglicolous fungi recognised 42 species of higher marine fungi which included 23 Ascomycetes, 2 Basidiomycetes and 17 Deuteromycetes (Kohlmeyer and Kohlmeyer, 1979). Hyde (1990a) listed 120 species from 29 mangroves from all over the WorldThe roots and fallen seedlings provide a unique habitat for fungi as the substrata are wetted daily by intertidal waters. These substrata may be submerged for as little as one hour each day, or permanently submerged except for short periods during spring tides. Mangrove trees are fascinating study objects for the mycologist because the bases of their trunks and aerating roots are permanently or intermittently submerged. whereas the upper parts of roots and trunks rarely or never reached by the salt water, although they sometime may be subjected to saline spray. Thus, terrestrial fungi and lichens occupy the upper part of the trees and marine species occupy the lower part. At the interface there is an overlap between marine and terrestrial fungi (Kohlmeyer, 1969b).

Among the different geographical locations; South East Asia has been sampled most thoroughly (Hyde and Lee, 1995; Jones and Alias, 1997). There seem to be no discernible difference between mangrove fungi reported in the subtropics as compared to those found in tropical areas. This is also true for frequently recorded fungi. The majority of the species reported by Vrijmoed et al. (1994) from Hong Kong and Macau (subtropical climate). However, seasonal occurrence of fungal communities colonizing mangrove wood have not been seriously investigated. The seasonal occurrence of mangrove fungi can be studied in the warm/wet season and dry/cold seasons by maintaining the uniformity in the number of samples collected and examined. We recommend a multiple-year study for seasonality of mangrove fungi.

Depending on the site from which samples of mangrove plants are collected in a horizontal plane with salinity gradient, the frequency of occurrence of fungi varies. Very few reports are available on the effect of salinity on the mycota in mangrove forests. Rhizophora and Avicennia, for instance, are able to grow in salinities ranging from full sea water (about 35%0) to fresh water. A different mycota can therefore be expected from woody substrata in salt water as compared to those in brackish water. Kohlmeyer (1969c) made preliminary observations in theHeeia Swamp on Oahu, Hawaii. Roots of mangroves in theHeeia Fishpond (salinity near 35%0) contained the marine fungi Kallichromatethys, Leptosphaeriaaustraliensis and Lignincolalaevis. Further inland, between stations 4 and 5, where the salinity varied at high tide between 10 and 35%0, the marine ascomycetes Helicas cuskanaloanus and Verruculinaenalia were found on the dead roots of Rhizophora. Some mangrove fungi have to tolerate grthe variation in salinity with respect to seasonal conditions; others tolerate desiccation, and salinity variation in the intertidal zone e.g. arenicolous spores (lones and Jensen, 1999). It would be interesting to conduct physiological studies of the very frequent fungi at different concentrations/regimes of salinity, temperature, pH and other factors in the laboratory and correlate these with the results obtained in the field. A correlation between the factors affecting the frequency of occurrence of fungi discussed so far and the dominance (frequent occurrence) of certain fungi cannot be established if they are not accompanied by the verification of these factors under in vitro conditions. Isolates collected from different places, show different responses to temperature. Fungi of the same species vary grthely in the extracellular enzymes they produce even from one stream to another (Yuen et al., 1998). These species may have geographical races, which are adapted to the conditions prevailing at their site of collection (Yuen et al., 1998). Panebianco (1994) investigated marine fungi and found that the temperature requirements for growth of marine fungi are related to their geographical distribution. Tropical and temperate fungi have an optimum growth at 20-25 C. Tropical freshwater fungi do not grow well at low temperatures and so are absent in temperate regions (Yuen et al., 1998). Although temperate species grow best at 25 C, they are not able to grow as rapidly as tropical species and this probably accounts for their absence in tropical streams (Yuen et al., 1998; Zare-Maivan and Shearer, 1988). It would be interesting to conduct similar studies on marine fungi and correlate the results with frequency of occurrence of the fungi tested. According to Volkmann-Kohlmeyer and Kohlmeyer (1993) it is difficult, for the following reasons, to determine the frequencies of marine fungi. (a) It has to be kept in mind that we are able to count only those fungi that can be identified from their fruiting stage, not those that are possibly present in the substratum in the vegetative (hyphal) state (This problem can be overcome partly by dividing into different pieces horizontally and incubated to allow sporulation). (b) substrata (driftwood, intertidal wood, mangrove roots and branches) are usually not uniform, consisting of uneven lengths and diameters of wood, with and without bark.

Among the three major habitats of the biosphere, the marine realm which covers 70% of the earth’s surface provides the largest inhabitable space for living organisms, particularly microbes. Marine microbes thrive not only in the surface waters of the sea, but also in the lower and abyssal depths from coastal to the offshore regions, and from the general oceanic to the specialized niches.The term ‘microorganism’ encompasses an extensive and diverse assemblage of organisms, such as bacteria, viruses, protists and fungi which exhibit widely different morphological, ecological and physiological characteristics. Oceanic areas in different parts of the world have been shown to be habitats for marine fungi (Johnson and Sparrow, 1961). Investigators, however, have usually concentrated on particular groups of fungi by use of selective isolation methods (Barghoorn and Linder, 1944; Moore and Meyers, 1959; Jones, 1962). Only one extensive analysis of marine waters for a general fungus population is known, and it was made in the northwestern subtropical Atlantic Ocean (Roth et al., 1964). References to the occurrence of fungi in the Pacific Ocean are found (1 ) as incidental to studies of bacteria in marine water (ZoBell, 1946) ; (2) in studies of specialized fungi such as lignicolous fungi (Cribb and Cribb, 1955 , 1956, 1960; Kohlmeyer, 1960; Meyers and Reynolds, 1960) and those on algae (Cribb and Cribb, 1955 , 1956, 1960); and (3) in studies of particular kinds of fungi , e.g., Phycomycetes in Japanese waters (Kobayashi, 1953) and path ogenic species (Van Uden and CasteloBranco, 1961 ) .

Fungi are heterotrophic eukaryotes that play a major role in the decomposition of dead plant tissues (cellulose and lignan) and to a lesser extent animal tissues such as keratin and chitin. The decomposition liberates nutrients back into the ecosystem. Fungi have evolved biologically and biochemically in a diverse manner that has allowed them to utilize various solid substrates. Many of the fungi can be isolated from the air, with their incidence varying according to geographic, environmental or bioclimatic factors such as collection site, time of the years relative air humidity, rainfall, wind speed and proximity to the source where they were produced. Consequently, these factors determine the quality and quantity of the mycobiota existing in aquatic and terrestrial ecosystems Gambale et al., (1983); Meyer et al., (1983); Oliveira et al., (1993); Tan et al., (1992). (Kohlmeyer and Kohlmeyer, 1971) and (Tan, 1985), among others, recorded exclusively marine fungi, but the soil is the typical reservoir of anemophilous fungi (Hawksworth, 1991). Although many ecological roles for fungi in the terrestrial ecosystem have been described and thoroughly studied, the ecology of fungi in the marine environment has been more difficult to study. Marine fungi play an important role in decomposition of organic matter in the sea. Lignicolous marine fungi inhabit various types of woody substrata available in the marine environment. Wood in the sea may originate from sources such as salt marshes and mangroves or it may be terrestrial wood reaching the sea by various means (Pointing et al. 2000).Though the existence of fungi in the marine habitat is known from early times, their significance as active participants in marine ecological processes has been overlooked39. Hughes104 stated that marine fungi cannot be defined strictly only on physiological criteria. They need broad ecological spectrum of definition. He classified them into obligate and facultative forms. Fungi which grow and sporulate exclusively in the marine habitats are considered as obligate, whereas those native in freshwater or terrestrial habitats and are also capable of growing and sporulating in the marine environment are termed facultative. Fungi contribute to the energy flow and productivity of an ecosystem by their presence as a contributory source for meeting the basic requirements of organic carbon of organisms at higher trophic levels. They appear as parasites on algae and animals, as mutualistic symbionts, and as saprotrophs, and play functional roles in nutrient recycling, biogeochemical processes and food web dynamics of the oceans. Most studies of marine fungi to date have been based on morphological characterization of fruitbodies, other structures and isolated cultures. More recently, Sanger sequencing, DNA fingerprinting and high throughput sequencing have provided new insights into the diversity and systematics of marine fungi (Stoeck and Epstein, 2003; Zuccaro et al., 2008; Amend et al., 2012).

With respect to marine fungal diversity, the mangrove is the best-studied habitat and most attention has been devoted to the wood-inhabiting fungi which constitute over 50% of 450 species of obligate marine fungi. Mangrove forests generate considerable amount of detritus such as leaf litter, woody debris and inflorescence and hence constitute an ideal environment for many detritus-dependent microbes. Substantial fungal populations are, therefore, involved in detritus-processing. Studieshave been conducted on filamentous fungi fromthe mangrove woody litters. About 150 species are found exclusively on decaying mangrove wood, aerial roots and seedlings. The mangrove-inhabiting fungi are categorized as ‘manglicolous fungi’, which have a recent report of fossil record from the west coast of India.