|Environment and development
in coastal regions and in small islands
Insect Biodiversity in Southern Mozambique as an
Indicator for Sustainable Coastal Management
P. N. Rubuluza, M. R. Jury, and P. Reavell University of Zululand Dept. of Environmental Studies UNESCO
Progress Report December 2004
The natural world around us is extremely rich and variable in forms, colours, odours, behaviors, movements etc. To be able to understand this richness and variability it is necessary to aggregate these entities into classes, types and categories. This being a way to create some order in the vast biotic complexity. Biodiversity deals with biological and geographical entities such as genes, chromosomes, species, families, and habitats or biogeographic regions. This means that in order to understand nature it is essential that we have both distinction and description of these biological and biogeographical entities (de Valk, 1999).
At the beginning of the 21st century scientists around the world are conscious of the increasing threat that our biodiversity is being put under. There have been many studies that have been conducted with regards to species diversity and numbers. The results suggest that the world's diversity is on the decrease, what the investigators often refer to as "the sixth extinction" (Leakey & Lewin, 1995), which is worse than the Cretacean era that wiped out most of the earth's fauna. This time the destruction of this earthly life is by human beings and is not a result of natural occurrences, with the result that many species face the danger of being wiped out from earth forever (de Valk, 1999).
Due to the reality of the rapid disappearance of species, this problem has come to be regarded as the worst situation that the earth's environment has had to face thus far. Species loss is currently rated as being more serious than pollution and global warming. This is according to the Worldwatch Report (Ayres, 1998) that surveyed various scientists in America. Many biologists are of the opinion that up to a fifth of all species existing in 2000 could disappear within the next 30 years if human settlement patterns continue to encroach on plant and animal habitats (Warrick, 1998; Ayren, 1998).
Although the scientific community has a lot of information about the state of affairs of our earth environment, the non-scientific community is largely 'unaware'. According to a survey that was conducted in America, sixty percent of the people interviewed ranged from knowing a little about the subject to not being bothered by the issue at all. Amongst the remaining percentage only a few believed that species loss is an import issue that puts earth's diversity under threat (Warrick, 1998).
The biodiversity of Mozambique is not well known. There have been a few studies conducted and these have revealed various areas that, from a biological diversity viewpoint, have been classified as being important (Munguambe et al. 1997). This is still the case, according to a recently published report on Mozambique's Red Data List. Mozambique has a high endemism of plant species which would imply endemism of fauna as well. Of the known species, 38% are threatened with extinction (Samira et al. 2004). This obviously brings to mind the issue of education to bring about environmental awareness amongst the larger part of the population, so as to promote the idea of biodiversity conservation and consequently sustainability. As Morris (In Arnold & Scott, 2004) explained, the future of the next generation will be in some ways influenced by the current one, as it is the one that 'sets the priorities'. In the process, biodiversity be conserved, to account for the unpredictability of the future, and to provide sustainability. The study reported here will use insects as an indicator of diversity. The main reason for using insects is because of their abundance, and biodiversity can be represented in snapshot surveys. Also, insects are highly sensitive to environmental instability.
Ecology looks at the interaction between organisms and their environment. An insect's environment may be described by physical factors such as temperature, wind, humidity, light, and biological factors such as the other members of the species, food sources, natural enemies, and competition (intra-specific and inter-specific). Although insects are highly adaptable (Bevis, 1964), over the long term, it may be of importance to have an understanding of how physical and biological factors relate to insect diversity, activity and abundance, as a contribution towards the maintenance of the environment to suit present insect diversity, and possibly prevent zoological extinction in a wider sense, despite developments (Hoffman & Frodsham, 1993).
The area studied is Ponta do Ouro in Mozambique. It is a coastal village at the southern border of the country. It is a mere 3 km north, of South Africa's Kosi Bay. The area is fringed by sea, sand dunes, forests, wetlands and grasslands, with a resident community of about 10 000 people. Ponta do Ouro is a scenic location with a warm climate that offers a wonderful opportunity for outdoor activities e.g. camping, hiking, and water sports. Ponta do Ouro is world reknown for scuba diving and ski boating. For these reasons, it is classified as a major tourist destination, with an excess of 50,000 people visiting the area over the Christmas festive season.
The Mozambique coastal plain, which stretches from the Tugela River to the north of the Mozambique border is of Cretaceous origin (Hobday, 1975). Ponta do Ouro is part of it. The geology, is dominated by dunes of sand colonized by pioneer floral communities (Hobday, 1975). The area has a high rainfall, so water is readily available, although the sands are generally leached. The top and west-facing slopes of the 100m high dunes have been found to have a coastal dune forest as its climax plant community (Bayer & Tinley, 1966; Weisser, 1978). West of the higher dunes (about 1km), are grassland communities, followed by with a high ground water table in which swamps and sedgelands are common (Conlong & van Wyk, 1991). This is the case at Ponta do Ouro, particularly in the sampled ecotones (Fig. 1).
The botanical vegetation in the dune forest ecotone is relatively undisturbed due to the belief that landmines are still present within and among the vegetation. Also, this area is not easily accessible, due to the fact that the dunes are very steep and there is no direct and easily recognizable path to the area.
The grassland ecotone is a mixture of various species of short grasses, with a maximum length of ╝ m. There are also various herbs, which mainly form bushes. The topsoil is observably very thinly layered. The insects in the area are apparent just by observing, with butterflies flying, grasshoppers and ants.
The fringe of the wetland ecotone is of reed and marsh. There was a thin layer of water available in the site during the time of sampling. This is due to the 3-year drought that started in 2001. The water only started 8 m into the wetland, and at the area where Phragmites started. The water had a brown colour, indicating a high iron content, high dissolved organic matter and possibly anoxic conditions. There were helodid surf bugs, alien water snails (invaders from America) and many butterflies observed at the wetland site.
The area has been chosen because it is under pressure from the community. The other reason is that the UNESCO monitoring project is interested in studying cross-border differences in the environment. The habitat is being interfered with to accommodate residential and agricultural use, resulting in habitat destruction, as was found by Naidu (2003).
Plans are currently under way to further develop Ponta do Ouro as a mass tourist destination. This is part of the program that is aimed at developing the Maputaland region by promoting tourism as the principal land use activity. The intention is to address the economic needs of this rural / coastal area. Tourism is ideal for the area with its multitude of environmental spectres such as pristine beaches, a diversity of plants and animals and coastal forests that have a lot to offer to naturalists, both for ecological interest and recreation. With these plans to promote tourism, there is a need for more factual information on the functioning of the ecosystem and the potential impacts that development will have on the biodiversity in the coastal area (Govender, 2001).
This work is a snapshot survey of insect diversity in the study area. The results will form a baseline as part of the UNESCO database of the biological diversity of the area. It will eventually contribute towards the ongoing study of habitat reduction through development, in Ponta do Ouro. There is a lot of unplanned development currently occurring in the area. People just build wherever they want, as little activity is controlled. With the factual information at hand, environmental planners will be able to work towards promoting ecological health and sustainable development.
The hypothesis is that the wetland would have the greatest insect species diversity as wetlands are considered to be the most productive ecosystems in terms of biodiversity. The dune forest should have the second largest species diversity, because the forest environment has various niches to offer, so a variety of species can survive. There were three identifiable layers of vegetation. The grassland region is expected to have the least diversity due to the nature of the ecotone. There is mainly grass and a few herbs in a grassland system, which does not offer much in terms of shelter (protection) to organisms.
The main objective of the investigation is to determine insect diversity in three ecotones, the wetland system, grassland region and dune forest habitat, by making snapshot surveys. This will be in the form of making inventories of biodiversity in prescribed areas, specifically looking at insect diversity. The ultimate objective is to find solutions to preserve biodiversity in the context of development.
Fig. 1: Map showing the Ponta do Ouro coastline and sites
Fig. 2: The Grassland Site
Fig. 3: The Wetland Site - showing proximity of human influence
Fig. 4: The Dune Forest Site
The field data were divided into flying, jumping and crawling insects. This was done to identify the major groups that dominate each site. Afterwards, the total number of species sampled was compared in all ecotones, according to overall species richness, using species, family and order level classifications. The aim behind this was to identify differences and / or similarities between the species composition at species, family and order level. The analysis of the samples included the determination of alpha- and beta- diversity, and the similarity between the sites (Ellenbroek, 1987). Alpha-diversity, also known as intra-community, refers to the number of species within an area e.g. a particular site. Beta-diversity refers to diversity in species composition of each site, otherwise known as the inter-community (Whittaker, 1975).
The diversity patterns were calculated according to species richness (number of species) at each site. The first analysis was of similarity between species at the order level of classification, and then at the family classification level using the Bray-Curtis similarity measure. The values were transformed to the 4th root to normalize the data and also because the subject being dealt with is species count. The cluster analysis (similarity matrix) was produced using hierarchical agglomeration with group average linkages. The similarity matrix enabled both the determinations of similarities between the species richness at each site at both the order and family level. The order level could be taken to represent the beta-diversity, while the family level represents the alpha-diversity.
The measure that was considered during the analysis of the data is the species richness (d). Species richness is defined as the number of species in a sample. This is calculated with the equation :
d = [S -
1] / Log (N)
where S = total number of species and
N = total number of individuals
This is especially important to calculate in this study, as the main objective was to determine species richness in each site and consequently compare the richness (diversity) in each site in the transect moving inland. In order to determine whether the species richness correlates to the plant diversity at each site, the observations of the plant species identified by Naidu (2003) and the insect species sampled during this study were compared. The aim behind this was to determine whether the amount of available plant species truly does affect insect species diversity as Docherty et al. (1997) believe.
This section provides the results obtained during the sampling and gives a brief interpretation. Looking at the overall species composition in the three ecotones, the wetland has the greatest diversity for all types, with a total of 125 different species of insects. The grassland is a far second in terms of diversity with a total of 41 species. The dune scrub has a total of 20 different species. All ecotones are dominated by flying insects. The dune scrub has the least numbers of jumping insects.
The total number of families sampled is 82 for three different habitats. Govender (2001) obtained 64 in sampling at Mabibi, just 100 km to the south. This could be an indication that Ponta do Ouro is more diverse in terms of insect species, which may be attributed to the slightly more tropical conditions and the presence of wetlands that are currently richer in biotic activity than in the Mabibi area.
The dune scrub area is divided into three layers; the ground layer, herb layer and the tree canopy. The habitat is dominated by ground dwelling species.
The ground layer experiences the most activity and is dominated by cockroaches, making the system a detritivore driven food chain. There was only one type of cockroach species in the dune scrub, possibly an indication that other cocroach species are unable to compete with this particular species. What is important to note is that cockroaches are nocturnal (Bevis, 1964) but here they were found during daytime. Other major invertebrates that were observed are; isopods and crustaceans.
The Isoglossa plant dominates the herb layer. It is in fact, the only plant that was observed at its layer. The plant is known to secrete toxins, so other species would not be able to complete on a fair level with it. Its leaves had holes in them and the suspected feeders are the moths and / or weevils.
One reason for the low numbers of insect species in this ecotone was the presence of rainfall towards the end of the sampling session. Insects that had been swept made the bulk of the sample. Also, before the net sweeping sampling, the traps were first lain out. That may have disturbed some of the insects that otherwise might have been sampled. Hence this site should be re-sampled.
The annual growth rate of grasses is generally much faster than any other plants, which could explain the species richness being greater than that of the dune forest. There were many grasshoppers and ants observed during the sampling. There were very few butterflies, but many more in the wetland habitat, which is about 500m away. This implies that there is a shelter or food in the grassland.
The wetland had many waterborne / detrital insects. There were many butterflies which escaped capture. The wetland had the greatest Hymenopters species, Heteroptera and Coleoptera. This was the only habitat in which Thysanura were found. These insects are known to be active at night, and to be attracted to water (Bevis, 1964). This serves as an explanation why they were not in the dune scrub and grassland samples.
Fig. 5: Graph comparing species diversity within each site at order level classification
Most species found in the other habitats also occurred in the wetland region. Of the total species types collected only ten were not represented in this region = (10/82*100) = 12%. The implication is that the three sampled ecotones have a similar species composition. The main difference comes in the diversity and possibly density as well. The diversity analysis showed that the wetland had the greatest total species number, followed by the grassland ecotone and lastly the dune forest.
Diversity Values for species at order level classification
S - refers to the total
number of species
N - refers to the total number of individuals
d - is the diversity index
At the order level of classification (beta-diversity), the wetland ecotone has the greatest total species, followed by the grassland site and lastly the dune forest. The number of total individuals per site was also greatest for the wetland site, followed by the grassland ecotone and then the dune forest.
The species richness at the order level classification was greatest in the wetland ecotone, followed by the dune forest and then the grassland ecotone. This means that the dune forest, although with less species numbers and total individuals, had proportionately greater diversity than the grassland ecotone. This is a significant finding for management purposes.
analysis of the insect orders sampled at Ponta do Ouro
The crisis of biodiversity around the world continues at an accelerating rate as a result of habitat loss (Wilson, 1988, 1992; SoulÚ, 1991) with the result that large floral and faunal assemblages are becoming extinct because they are unable to adjust to the rapid and often large-scale habitat alterations. Habitat loss is most pronounced in forest, which are being cleared throughout the world (Winchester, 1997). The fragmentation of these landscapes has greatly increased the awareness for a need to understand the endemic fauna and flora (Scudder, 1994) and apply system-based conservation approaches across a wide range of vegetation types (Murray et al., 1993; Harding & McCullum, 1994).
Currently, there is not enough known about the status of Mozambique's biological diversity in rapidly developing coastal zones. This means that any efforts aimed at describing the state of biodiversity, the species, the habitats and the ecosystems are often suppositions, based on the few studies that have been conducted and from observations The country's Natural History Museum has 3074 identified insect species. The country has an endemic dragonfly Ceriagrion mourne, of which very little is known. (Mabjaia et al. 1997). In contrast, South Africa, just south of Mozambique currently has 175 identified Blattodea species of which there are about 3500 - 4000 that are known world-wide (Robertson, 2004). South Africa also has 3000 known Orthoptera specie (Brock, 2004). This is to illustrate the lack of information about Mozambique, only a few thousand kilometres from the southern most tip from South Africa. Clearly, there is a need for more of these species diversity determination to be conducted on a regular basis and obviously over a long period in order to eventually bridge the information gap that currently exists.
The problem of the non-existence of local governance structures in the face of tourism -oriented development has the potential of robbing the country of its natural biodiversity heritage, as conservation is difficult. As Mozambique is still a developing country, it undoubtedly needs to be developed. But these developments do not have to be at the expense of the environment. There is a need to ensure that any development that takes place incorporates in its plans of operation the issues of conservation of the environment and biodiversity, and the sustainability of the resources.
In Mozambique, limited baseline data means that there is little accurate information with regards to trends in biodiversity and activities or processes that threaten the biodiversity. So it is important that the status quo of the land's biodiversity eventually be assessed and determined so that in the end there can be an appropriate method that can be developed to protect and conserve the biodiversity. This means that more of these surveys will have to be done on an ongoing basis over the years in order to determine the diversity of the area prior and during the development, so as to determine the extent of the disturbance to the environment due to coastal developments.
de Valk (1997), argues that conservation is based on a knowledge of ecology (the science concerned with the relationship between life and the environment) and also on a wide variety of other issues such as human feelings, beliefs, and attitudes as well as science and technology. This means that on top of gathering information about the state of our environment, it is of utmost importance that the wider population be educated and told about such issues. This would help to develop the environmental ethos in people with the result that the protection and conservation of our natural world and the living nature in it will become an everyday occurrence. This could begin at the local schools and introduced as part of the school curriculum. There could also be a community conservation group that could be started to teach about conservation and the importance of balancing development and conservation in our communities.
The main issue with regards to our conservation problems is that multiple decisions concerning the environment are made in isolation of one another such that no consensus is reached between the various user sectors. To deal with this problem there should be an application of an 'ecosystem management' orientated approach that recognizes that the way to avoid or solve the problems is with decisions made in consultation. The goal is the maintenance of biodiversity and ecosystem processes. Here we find that species richness at order level may be a better tool in land management, than the more difficult-to-achieve family and species level classifications.
We hope that after reading this report, the reader feels enlightened on many aspects of the Ponta do Ouro environment and of the importance of preserving its biodiversity. The study as such, encompasses and touches on many aspects that require further investigation, but on a higher level, i.e. over a longer period so as to provide adequate time for the observation and acquiring of all relevant information. Further investigations should involve replicates to gain confidence in the interpretations presented here.
List of all sampled species with their classification
|(stink & shield bugs)|
|(ants, bees, wasps)||(bees)|
|(predatory ground beetle)|
|( diving beetle, water beetle)|
|(toktokkies, darkling beetles)|
|(crickets, locusts, katydids)||(short horn grasshopper)|
|(delphacid plant hopper)|
The numerical values in the table denote the number of morphospecies identified per site.
See other articles related to the UNESCO pilot project on 'Development-conservation strategies for integrated coastal management in Maputaland (South Africa, Mozambique)'