**1. Introduction**

Nigeria has the largest mangrove forest in Africa and the third largest contiguous mangrove forest in the world. The mangrove region is widest on the sides of the Niger Delta, 35–45 km and narrows towards the centre to a width of 15 km except for the channel of the Brass River, which has extensive mangroves far upstream [1].

The mangrove forests of Nigeria comprise principally only three families and six species as follows: Family, *Rhizophoraceae* (the red mangrove): *Rhizophora racemosa*, *R. harrisonii* and *R. mangle.* Of these *R. racemosa* is the most abundant covering about 90% of the mangrove forest. *Avicenniaceae* (white mangrove), *Avicennia africana* and *Combretaceae* (*Laguncularia racemosa* and *Conocarpus erectus* [1] and alike have been reported in most parts of the West African coast [2]. The Ijala-Ikeren

wetland is situated in the Niger Delta region of Nigeria. The Niger Delta region of Nigeria has four main ecological zones: Coastal Barrier Islands, Mangrove swamp forests, freshwater swamp and lowland rainforest. The mangrove swamp forest among these four ecological zones is the most affected by anthropogenic influences, as it has very poor regeneration potential [3].

Anthropogenic disturbances in the Niger Delta include oil spills which has been extensive, difficult to assess and often underreported. According to [3], oil spillages in the Niger Delta most especially in the mangrove wetlands are never reported or merely branded minor without minimum post-spill containment, recovery and remediation responses. Also, the World Commission on Environment and Development (WCED) as cited by [4] had reported that the mangrove deforestation and degradation are some of the greatest factors that would cause species extinction in the Niger Delta region in the next 50 years. Consequently, it is frightening that depletion of the mangrove forest could eliminate 5–15% of species by 2020 [5]. The Niger Delta biodiversity, including the Ijala-Ikeren wetland is very important for the concomitant presence of rainforests, mangroves, and many endemic flora and fauna, which are affected by oil pollution from oil spills, usually from bunkering and pipeline vandalisation of the petroleum refinery facilities situated less than 2 km to the East of the Ijala-Ikeren Wetland as well as solid waste pollution.

Oil pollution and its attendant impact on the creek ecology and the community are highly visible in the mangrove swamps due to proximity of the communities to refinery and oil pipelines criss-crossing the environment. The Ijala-Ikeren wetland has been affected by industrial activities, and pollution and this has affected the water quality in the community, and arthropods (insects) and amphibians [6]. Reported that the physical and sanitary quality of hand-dug well waters from communities around the Warri refinery including Ijala-Ikeren wetland was found slightly acidic at 6.04 and may be attributed to emissions from gas flaring and petroleum refining activities, which is common in the area. They also stated that the water quality from the community's surface water bodies and aquatic insect indicators are believed to be gradually deteriorating.

The Ijala-Ikeren wetland is well watered all the year round although the level of water in the creeks drops to about two meters during the dry season and varies daily owing to tides. The current ecological regime in the wetland is the amount of water in creeks and creeklets. This water is determined by tidal flow of sea water from the Atlantic Ocean at high tide and fresh water from the mainland into the Ocean at low tide. The continuous mixing of fresh and sea water gives rise to the brackish nature of water in the creeks and creeklets and in the mangrove swamp. Any change in the water regime either through the stoppage of sea water flowing into the wetland or fresh water flowing into the Ocean, will certainly change the ecology of the wetland and its current composition. The potential route of off-site contaminants to the ecosystem is by Ijala-Ikeren creeks and creeklets. The discharge of water from the creeks to the mangrove ecosystem is constant and runs all through the year but quantity and volume of water available in the mangrove and creeks are unstable [7]. Higher volumes of water are available in the rainy season due to runoffs and inter-tidal nature of the Warri River especially during high tide (personal communication).

Aquatic insects play very important role in food webs, and particularly in wetlands, the larval and adult stages provide a wholesome meal to fish [7], shorebirds [8] and other creatures in the Niger Delta mangroves. They are essential elements in food webs, essentially in energy flow and nutrient cycling [9]. This food source is key to the survival strategy of some fishes, amphibians and other animals. Selected aquatic insects are predators and in consuming their watery prey they help keep the insect population stable and functioning. Many species of aquatic insects are very

### *Impact of Disturbances on the Biodiversity of Ijala-Ikeren Wetland Ecosystem in Niger Delta DOI: http://dx.doi.org/10.5772/intechopen.82604*

sensitive to pollution and other environmental hazards, thus they reflect environmental changes and as a result are often used as indicators of the effects of human activity on water system and provide information on habitat and water quality [10]. Also some aquatic insects help keep the water clear by filtering it, others support in breaking down fallen dead leaves, while yet others clear the algae, allowing the water to produce more oxygen [11, 12].

Amphibians have important roles within nature and their sensitivity to changing environmental conditions may help determine the health of an ecosystem. They constitute an important part of food chain and contain important pharmaceutical compounds on their skin [13]. The International Union of Conservation of Nature (IUCN) Red List of threatened species has identified amphibians as being the most threatened vertebrate group, with about 40% at risk of extinction. The extinction and decline have been variously attributed to habitat loss, pollution, climate change, wild fire and over-exploitation [14].

Recent studies have documented the incidence and severity of sediment contamination by heavy metals in mangrove ecosystems [15, 16]. Contaminants are released via industrial activities and ultimately enter aquatic ecosystems [16, 17].

Industrial effluent is a common anthropogenic impact on aquatic ecosystems including mangroves and this kind of pollution changes physical and chemical characteristics of aquatic systems, thus affecting the assemblage of aquatic fauna [17, 18].

The mangrove forests and salt marshes control the tidal wetland ecosystem dynamics and contribute to the development and condition of the tidal saline wetland ecological communities [19]. Mangrove forests and salt marshes are highly valued ecosystems; however, mangrove forests and salt marshes maintain divergent ecological communities and a different suite of goods and services [20]. Climate change, environmental stress and anthropogenic activities can cause the conversion of mangrove forest to salt marshes, with positive and negative expected and unexpected consequences (e.g., effects upon fish and wildlife populations, ecosystem resilience, nutrient cycling, and variation of texture and soil geochemistry). The physicochemical conditions and ecological implications of these mangrove forests to salt marshes conversions are poorly understood, but would likely include changes in soil, water, associated wildlife populations and supply of some ecosystem goods and services [21, 22].

The lack of publications on the biodiversity (particularly on the indicator species)—such as the insects and amphibians in Ijala-Ikeren wetlands of the Niger Delta, necessitated this study. Hence, this preliminary study was aimed at evaluating the abundance, community structure and diversity of biodiversity therein coupled with temperature, salinity and the pH levels of the ecosystem. We therefore, welcome future collaboration with available funding for a robust study.
