Mangroves: A World of Diversity

Mangroves are extremely adept at living life. Along costal regions, mangroves occupy a zone of high salinity, scorching temperature and thicken mud.  These amphibian-like vegetations are complex organisms that have adapted to living on the edge, half way between water and terrestrial surface. On the National Mangrove Conservation Site in Pranburi, Thailand, two types of mangroves, Grey mangroves (Avicennia marina) and Red mangroves (Rizophora mangle), and their surrounding environments were studied. Both of these mangroves are capable of growing up to fourteen meters in tropical regions, have aerial roots, which allows them to absorb the oxygen lacking in its habitat and can tolerate high salinity by excreting salt through its leaves. A variety of abiotic factors was found to be inhibiting both region surrounding the two types of mangroves. The presence of the mangroves, which provides a food source and physical protection for biotic factors, allows a tremendous diversity of organisms to thrive in the area. However, the distribution of each species of organisms vary between the two types of mangroves due to the differing abiotic factors that surround each habitat. The purpose of this study was to investigate how the different types of mangroves affect the distribution and diversity of the variety of organisms that inhabit the area. 

Red Mangroves (Rizophora mangle) at the Mangrove conservation, Pranburi, Thailand. 

Grey Mangroves (Avicennia marina) along the cost of the Mangrove Conservation

Grey mangroves occupy the intertial zones of estuarine areas, which are costal regions with one or more rivers flowing into the area. In order to study the organisms along the site, the belt transect method was used. This method comprises of lining a continuous transect line from the walking path up to the stream where the population of grey mangroves begin to recede. Once two transect lines were laid out one meters apart, all organisms within the two lines were accounted for. The only organisms that were accounted for were those than could be seen without having to harm the the organism's habitat or the organisms themselves. The biotic factors along this site, which included pH, salinity, turbidity, light intensity and substrate were also measured, in order to examine whether a correlation exists between the abiotic factors of two sites and the distribution of different species. 

Because the red mangroves were situated in another area of the conservation, quadrat sampling was a more suitable method to collect results for that particular site. Quadrat sampling consists of constructing a 1 meter squared (1m x 1m) quadrat using a piece of string. This quadrat was set up around the edge of the mangrove in order to reduce any risk of harming the organisms that inhabit the area. Each team (A and B) took a sample from different quadrats and averaged out the results at a later time. Much like the method used to study grey mangrove area, the abiotic factors (pH, salinity, turbidity, etc. were also measured for red mangroves site. In order to test the different abiotic factors, various probes and sensors were used. However, because there was no available equipments that were needed to measure light intensity, the amount of light at the moment of measurement was measured with an arbitrary scale (high, medium or low). Below is a table which shows the average of the different biotic factors that were accounted for along each site. Mangrove site A represents the site of the red mangroves while site B was the site along the cost where grey mangroves grew. 

Mangrove A		Mangrove B
Species	Average	Species	Average
A	1.5	A	69.5
B	3.5	B	45.5
C	3.0	C	27.5
D	4.0	D	40.0
E	68.5	E	42.0
F	1.0	F	10.0
G	31.5	G	1.0
H	0.5	H	12.0
I	4.0
J	4.5

The table below displays the key of the organisms that were found on each site. 

Site A	Name	Site B	Name
A	Spider	A	Seeding
B	Red mangrove	B	Intermedate
C	Snail	C	Mature
D	Scallop	D	Moss
E	Lichen green	E	Lichens
F	Flies	F	Snails
G	Lichen (yellow)	G	Flies
H	Ant	H	Mud Crab
I	Mud Crab
J	Water spider

These data results were processed using the Simpson's Diversity Index, which accounts for the number of species and the abundance of each species present in each habitat. The two different factors that are considered when calculating diversity is richness, the number of species per sample, and evenness,the relative abundance of each species. The higher the calculated number, the more diverse a certain habitat is considered to be. The diversity of red and gray mangroves site for the samples that were accounted for were calculated by using the Simpson's Diversity formula as presented in the link above and the results are shown in the graph below. 

Bar graph showing the diversity of the two different mangrove sites.

As seen from the bar graph in the image above, which displays the Simpson's diversity index calculation, the site for Red mangroves (Mangrove A) can relatively be classified as more diverse than the site for grey mangroves (Mangrove B). Even though these two types of mangroves exists in the same conservation site, their difference is as prominent as if they'd existed in different parts of the world. The diversity that existed within the conservation itself was astonishing. This goes to show that mangroves are very adaptably remarkable organisms that can sustain their own lives and the lives of other species. Mangrove plants provide the surrounding organisms with protection from the high salinity and a food source. There are various biotic and abiotic factors that can influence the diversity of different species of animals living in a particular community and ecosystem. The biggest different between the environment which surrounds the two mangroves seems to be the substrate that make up the surrounding. Red mangroves, which were established in the conservation for a longer time period, are surrounded by muddy, rich soil which can sustain a variety of organisms. On the other hand, the substrate that surrounds the grey mangroves are more corse, sandy and dried. The grey mangroves which grow along this site are shorter in height and have shorter aerial roots compared to red mangroves. The difference between the quality of the substrate which surrounds each type of mangrove could be a plausible reason for the diversity found in both the habitats. 

Bio HL 2013 Seniors :)