The mangroves not only give us ecosystem services (provisional, regulating, supporting, cultural) but also help for Global Peace. This is because mangrove forests around the world sequester quite large amount of carbon in soil every year and thus help mitigating climate change. International bodies have recognized that climate change is a threat to global peace and security. So, mangroves conservation is important for World Peace.
It is said that mangroves are deteriorating in many places due to several anthropogenic stresses and these are need to be addressed properly especially in integrated way. The knowledge on mangrove invertebrates has great values for conservation since they are the main drivers of mangrove ecosystem. Unfortunately, despite the tremendous importance of invertebrates in the mangrove ecosystem, vertebrates (mainly mammals, birds and reptiles) get priorities in most conservation efforts.
In fact, vertebrate animals, especially the big ones attract more public attention and sympathy than invertebrates for conservation. But in reality, invertebrates make up about 80% of all species, where as vertebrates make up less than 4%. Ecosystem services provide by the invertebrates are far greater than the vertebrates. Even then, scientific research on animal biodiversity is very much biased on vertebrates.
This is also true for mangrove ecosystem, although few commercially important invertebrate species (mainly shrimps, prawns and crabs) in mangrove forests have very high demand. However, the species and ecological diversities of all mangrove invertebrates are very high in comparison to these few commercially important species. Moreover, people are generally interested to harvest these commercially important species often ignoring their ecological values. In fact, common people are mainly fascinated with big mammals, birds and reptiles like in other type of forests. Media are also happy to give big coverage on big animals, i.e. on mangrove vertebrates. Tourism departments focus on attracting tourists to view charismatic megafauna, such as birds and tigers of mangrove forests. It is true that silvicultural management of mangrove forests usually neglects the invertebrates. In fact, invertebrates in the mangrove forests are badly neglected not only by the general public but also by the policy makers.
Mangrove invertebrates consist of as many as 19 phyla, viz. Protozoa, Porifera, Cnidaria, Ctenophora, Platyhelminthes, Rotifera, Gastrotricha, Kinorhyncha, Nematoda, Sipuncula, Annelida, Arthropoda, Bryozoa, Entoprocta, Brachiopoda, Chaetognatha, Mollusca, Nemertea, Echinodermata. The members of these phyla in the mangrove forests can further be classified into four general trophic groups: (1) direct grazers such as insects and mangrove tree crabs; (2) filter feeders such as sessile invertebrates, which feed on phytoplankton and detritus; (3) deposit feeders such as mobile invertebrates that consume detritus, algae, and small organisms from the sediment surface; and (4) carnivores such as highly mobile invertebrates that feed upon all the other group.
Mangrove invertebrates play great roles in nutrient cycling, filtration and also in biochemical processes. Among the mangrove invertebrates, the benthic group (epifauna and infauna) performs vital ecological roles by burrowing the sediment. Through this process they actually help in flushing toxic substances, and ultimately modify the oxidation status of the surrounding sediment. They feed plant matters (detritivory) and help in recycling organic substances thus produces animal biomass. This biomass is a source of food for several vertebrate predators and inshore fishes, which come during the high tide.
In mangrove forests, the benthic fauna is dominated by crabs (sesarmid, Grapsidae and fiddler crabs, Ocypodidae), which are known as ecosystem engineers. This is because these groups of invertebrate animals construct and maintain burrows and change the physical structure and transport conditions. The engineering impacts of burrowing are evident through the change of sediment fatty acids profile, higher percentages of bacteria, vascular plants, macroalgal etc. in the burrow compartments and crab habitats than sediments without crabs. Burrowing and feeding activities as well as faecal deposition by the crabs have a significant effect on the total lipids and fatty acid distributions in mangrove sediments. In fact, crabs have positive effects on the growth and success of mangroves.
Numerous species of insects and arachnids live in mangrove forests, although their diversities and ecological roles are not evaluated properly in the various mangrove forests of the world. Some insects act as herbivores, i.e. consume plant parts, viz. leaves, twigs, stems and thus cause harms to the mangrove plants. However, many of them play beneficial roles as mangrove pollinators, predators or parasitoids and as food source of other animals in the forests. Arachnids in the mangrove forest also play role as predators or as prey of various predators in the mangrove forests. Thus, insects and arachnids have also enormous roles in the balancing of mangrove ecosystem. But till to date their diversities and ecological interactions in the world’s mangrove forests are not known satisfactorily.
Experiences show that people give importance only to the few species of honey bees among the vast number of insect species present in the mangrove forests. It can be pointed out that there are more than 200000 invertebrate species, which act as pollinators on this planet. Thus, there might be numerous invertebrate species in the mangrove forests, which are responsible for pollination. But works on this aspect is poor throughout the world.
A number of factors can be identified for this invertebrate negligence. First of all, research proposals on tetrapods (mammals, birds, reptiles and amphibians) of mangrove forests generally get preference over invertebrates for funding in many countries. Secondly, there are shortages of experts on mangrove invertebrates in many countries and for this reason a beginner from such country faces problems and ultimately at a stage, sometimes is forced to leave his/her interests. Thirdly, the media (including social) prefer to uphold big animals of mangrove forests especially in many developing or poor countries. They publish stories on large animals of mangrove forests and advocate for their conservation where as they seem to be reluctant in the case of invertebrates. Fourthly, many countries are lack of proper institutions to study the mangrove invertebrates.
We have to overcome all these aforesaid limitations by keeping in mind that invertebrates are the integral part of mangrove forests. Small invertebrates live in sediments with mangrove roots and rootlets, decomposed leaves and several other detritus, and also arboreal insects and arachnids are generally overlooked by researchers. As a result, in spite of their great numbers and ecological importance, the mangrove invertebrates are generally neglected by the conservation practitioners.
Accordingly, the time has come to change our attitudes towards mangrove conservation. Precise information on invertebrates can enhance the scientific ecological knowledge. Integration of inputs from scientific ecological knowledge, local ecological knowledge and other stakeholders are necessary for sustainable mangrove conservation.
Bidhan Chandra Das
Department of Zoology, University of Rajshahi, Bangladesh
Professor (Rajshahi University) and Conservation Biologist, several citations to his credits, writer (newspaper) and talker (radio) on environment related issues.