The Establishment of Macrobenthic Faunal Communities in Planted Mangroves of Increasing Age

Abstract

The mangrove ecosystem is a tropical coastal community inhabited by organisms adapted to the stressful environment of the tidal zone. Mangrove ecosystems has in recent years been noted for the important ecosystem services they offer. Still, they are threatened by anthropogenic activities and it has been estimated that a third of the world’s natural mangrove cover has already been lost. Efforts have been made to conserve and to introduce new mangrove areas in many countries.
The macrobenthic faunal community structure in the mangrove forest has a close association to environmental factors such as the age of the mangrove stand. It may therefore be used as an indicator of environmental quality.
For this study, I sampled and identified macrobenthic fauna in planted mangroves of ages 18, 31 and 54 years, as well as a bare mudflat site in the Jiulongjiang Estuary, Fujian Province China. The sampled organisms were used to investigate the establishment and potential increase of diversity in macrobenthic faunal communities as a planted mangrove area develops with age.
In total, 1871 individuals from 52 taxa belonging to 7 phyla were found, Crustacea and Polychaeta being the two most dominant groups. The species richness increased with mangrove age, and a linear regression on the Shannon-diversity based on biomass also showed a significant increase (p=0.0135, R2=0.6059), while the Shannon-diversity based on abundance did not. Only the 54-year old mangrove showed any significant difference to the mudflat site, and only in terms of a higher abundance (p=0.0016) and barely in a higher Shannon-diversity based on biomass (p=0.0509).
The few replicates and sampled sites are probable explanations for the non-significant results. Future studies should increase the number of replicates, be conducted over several seasons, and include other physical parameters in the analysis, to get a better overview and comprehension of the macrobenthic faunal community.

Abstract (Swedish)

Mangroveskogens ekosystem är ett tropiskt kustsamhälle bebott av organismer anpassade till den stressfulla miljön i tidvattenszonen. Mangroveskogen har på senare år blivit erkänd för de viktiga ekosystemtjänsterna den erbjuder. Trotts detta hotas den av mänskliga aktiviteter, och en tredjedel av världens naturliga mangroveskog uppskattas redan ha gått förlorad. Ansträngningar har gjorts för att bevara, samt introducera nya mangroveskogar i många länder.
Strukturen av det makrobentiska faunasamhället i mangroveskogen har en nära association med faktorer i den kringliggande miljön, så som åldern av mangroveskogen själv. Därmed kan den användas som en indikator av kvaliteten på miljön.
I denna studien identifierade jag makrobentisk fauna från prover jag tagit i planterade mangroveskogar av åldern 18, 31 och 54 år, samt i ett kalt strandområde, vid Jiulongjiangs flodmynning, Fujian provinsen, Kina. Organismerna funna i proverna användes för att undersöka etableringen av och den eventuella ökningen av diversitet i makrobentiska faunasamhällen efterhand som en planterad mangroveskog utvecklas med åldern.
Totalt 1871 individer från 52 taxa tillhörande 7 fyla fanns i proverna, varav Crustacea och Polychaeta var de två mest dominanta grupperna. Artrikedomen ökade med åldern av mangroveskogen, och en linjär regression med Shannon.diversiteten baserad på biomassa visade en signifikant ökning (p=0.0135, R2=0.6059), medan Shannon.diversiteten baserad på individantal inte visade något signifikant resultat. Endast den 54 år gamla mangroveskogen visade någon signifikant skillnad från det kala strandområdet, och då endast när det kom till ett högre individantal (p=0.0016) och knappt när det kom till en högre Shannon-diversitet baserad på biomassa (p=0.0509).
De få replikaten och provtagna områdena är troliga förklaringar till de icke-signifikanta resultaten. Framtida studier bör öka antalet replikat, genomföras under flera årstider, samt inkludera andra fysiska parametrar i analysen för att få en bättre översikt och förståelse av det makrobentiska faunasamhället.

Popular Abstract

The Healthy Mangrove Forest and its Fauna
Much of the worlds mangroves have been lost to the shrimp farm industry, but lately mangroves have been noticed for their true value. Replanting efforts are now stepping up in China. But are just replanting mangroves enough? What is a healthy mangrove ecosystem?
Mangroves are a type of trees that grow in the tropics along coastal regions. Despite being a unique habitat for many animals, they also provide us humans with significant benefits. Their roots will stabilize the soil and minimize coastal erosion. Their physical presence will better hinder the progress of a tsunami compared to a deforested area. They also have a positive effect on the fish industry. During high tide, the forest becomes a safe haven for young fish. Among the trees they can hide from predators and feast on the abundance of small animals that are part of the mangrove ecosystem. In the past, mangroves have been deforested to make room for short sighted gains, such as luxury shrimp farms. By replanting mangroves, we hope to regain their benefits.
But there is a lot more to a healthy forest than just it’s trees. For this ecosystem to fully function, it also needs its fauna, the small animals living in the soil of the mangrove forest. Is just planting trees enough to establish a whole ecosystem? To find out, I set out to the Jiulongjiang Estuary in the Fujian Province of China were replanting efforts have been made during the past half century.
Many different animals burrow and live in the mangrove forest floor, such as marine worms, snails, crabs and insects. There is even a fish called the Mudskipper, which burrow in the soil where it keeps its eggs. During low tide, it actually crawls through the mud, foraging and breathing through its skin out in the open air. Different animals play different roles in the ecosystem. Some burrow deep, some shallow. Some feed on other organisms, some on each other. An ecosystem with a high diversity of organisms is recognized as a more stable one.
The mangroves and these animals exist in a mutualistic relationship. In the mangrove forests, the stabilized soil will provide a more suitable habitat for mangrove associated fauna. In turn, the burrowing of these animals increases the oxygen in the soil, which is crucial for the trees. To have a healthy mangrove forest, it is therefore important to understand the relationship with its faunal diversity.
I wanted to see how mangrove soil fauna establish over time after plantation. I therefore sampled the soil of three planted mangroves of increasing age, including a mudflat as a comparison. All found animals bigger than 1 mm were identified, counted and weighed. This information could then be used to estimate the faunal diversity at each site.
In total I found 1871 individuals from 52 different species groups. Due to time restrictions, I could only take a few samples. These proved too few to draw any true conclusions, and I could only see tendencies. My results did however suggest that the number of animal species increase as the mangrove forest ages. There also seem to be a transformation in habitat types from a mudflat to a mangrove forest when trees are planted on a bare beach. This was seen as the youngest mangrove site didn’t show any increase in species from the mudflat site, but instead an equal number of species, but of very different composition.
Even though I couldn’t draw many conclusions from this study, I did manage to survey the mangrove faunal diversity at mangroves sites often used by Xiamen University as a study area. My results will hopefully improve their understanding of these mangrove sites. I also evaluated the methods used for studying mangrove soil fauna. By doing this, I gave suggestions on what future studies should consider when studying faunal diversity in mangrove forests.

• author: Jacobsen Ellerstrand, Simon
• supervisor: Linus Zhang; Hu Hongyou
• organization: Division of Water Resources Engineering
• alternative title: Etableringen av makrobentiska faunasamhällen i planterade mangroveskogar av ökande ålder
• course: VVRL01 20171
• year: 2017
• type: M2 - Bachelor Degree
• subject: Biology and Life Sciences
• keywords: Benthos, Shannon-diversity, forestation, biodiversity, ecosystem engineers, development issues
• ISSN: 1101-9824
• language: English
• id: 8928714
• date added to LUP: 2017-11-30 13:57:51
• date last changed: 2017-11-30 13:57:51