Tropical Ecosystem: Estuarine Biodiversity in Iwahig

patzwikiStarred Page By patzwiki, 26th Sep 2012 | Follow this author | RSS Feed | Short URL
Posted in Wikinut>Guides>Nature>Habitats & Ecosystems

There is a dearth of literature published online on the biodiversity of tropical ecosystems particularly the estuarine portion of the coastal zone. This photo-essay on a typical estuarine ecosystem in Palawan Island, one of the places endowed with a rich biodiversity in the Philippines, aims to fulfill this gap.


Many students are unfamiliar with the biodiversity of a mangrove ecosystem in the tropics. But many of the references available in the internet may be too geeky for a beginning marine biologist or too simple for their research needs. Technical terms like scientific names of animals or plants, without any pictures to show how they look like, could dampen the spirit of a beginning researcher.

This photo essay aims to fill this need to allow a better understanding of the estuarine ecosystem which is a highly vulnerable part of the coastal zone. It serves to bridge the gap between a layman's basic understanding of estuarine biodiversity to the much more rigorous and technical treatise of a seasoned marine biologist. Thus, students will be able to appreciate the role of biodiversity living therein to human life.

Herein described are the variety of plants and animals living in the estuarine ecosystem, specifically along the riparian zone. It also features pictures of the particular organism discussed. The scientific names of the animals and plants are supplied based on data or information existing either in the internet or based on previous readings, training and knowledge of the author. Readers may write their comments if there are glaring errors in the identification of the animals and plants featured herein.

The different species of mangroves and animals in this photo essay was documented in about two hours of field exploration on September 22, 2012 in the vicinity of Iwahig River - a typical river traversed by people in the City of Puerto Princesa in Palawan, Philippines. Marine biology students in nearby Palawan State University explored the portion of the river where the river meets the sea - a brackish environment.

Researchers need to secure a permit from concerned government agencies like the Palawan Council for Sustainable Development (PCSD) to collect these animals or any part of the biodiversity of Palawan especially those that are classified as endangered species. Hence, whatever was captured or collected by the group during the field trip was released back to the wild.

Due to the high regard of the people on the integrity of the environment, this portion of the city still serves as a viable habitat to wildlife. Whenever visitors come to enjoy nature still at its best in the Province of Palawan, they get a glimpse of an extensive, verdant growth of mangal in this zone as the airplane prepares to land.

The specific location where this inventory occurred is at 9 deg 44' 8.9" N latitude and 118 deg 41' 49.7" longitude.

Estuarine Biodiversity of Iwahig

The two-hour long inventory of a portion of Iwahig near the mouth of Iwahig River yielded several species of animals and plants. The animals consisted of mudskippers, mud lobster, the common mud crab, a purple-pincered crab which the author failed to identify, fiddler crabs, halfbeaks, and shrimps. There are two species of mangroves identified in the area - Sonneratia alba and Rhizophora apiculata.

More details on the characteristics of these animals and plants as well as photographs are presented below.


Goby - Periophthalmus sp.

Mudskippers are among those animals found along the margins of Iwahig River. They are also referred to as gobies which are ubiquitous species that are easily seen along the shores of the coastal zone. They quickly jump about whenever they are approached.

Mudskippers are called amphibious fishes because they can drag the whole length of their body as if they have legs. But the pair of "legs" are actually pectoral fins that correspond to the forelimbs of higher vertebrates or bony animals. They can stay out of the water for a longer time than their fully aquatic species of fish which have the tendency to escape in tide pools as the tide recedes.

Mud Lobster

Thalassina anomala

The mud lobster builds mounds of mud, similar to that made by the termites, in the mangrove area. Ecologically speaking, the burrowing activity of the mud lobsters help in the cycling of nutrients in the mangrove ecosystem because they bring up the mud from the ground thereby facilitating the transport of nutrients towards the surface. This is also the reason why many fishpond operators want to get rid of these crustaceans because of the damage they cause to fishponds.

The mud lobster is nocturnal in habit, meaning, they are active at night.

Mud Crab

Scylla sp.

Mudcrabs, just like the shrimps, also comprise the biodiversity of the mangrove ecosystem. They can grow to as much as 9 inches. See the big crab below and appreciate how large it can get. The one on the right is a young crab about an inch long which the students gathered, took pictures and released back to the water.

Unidentified Mudcrab

Crustacea - Unidentified species

This unidentified purple-pincered mangrove crab has characteristic blue pincers which appear to be its distinctive feature. This is just among the hundreds of mangrove species found in the brackish environment.

Mangrove crabs are important in the mangrove ecosystem because they dig burrows thus allow aeration and cycling of nutrients. Studies show that they aid in the control of sulphides and ammonia that relate to the productivity of the mangrove forest.

Overextraction of the mangrove crabs may cause imbalance in the ecosystem. For this reason, they are considered as keystone species.

Fiddler Crab

Uca sp.

Fiddler crabs also abound along the margins of Iwahig River, scampering away to the nearest hole they could access. These crustaceans are easily spotted at low tide. A prominent feature of the fiddler crab is that one of their pincers, a cheliped, is larger than the other. But this is true to the males because they use this during their ritual combat of courtship over a female. They usually lift this up and down as if waving or calling giving the impression that they are somewhat playing a fiddle, of course without the fiddle. Hence, the name "fiddler".


Hemiramphus brasiliensis

Halfbeaks, also known as ballyho or bally were observed feeding on organic material. They also feed on small fishes. These fishes have the usual tendency of swimming near the surface of the water in schools.

Fishermen use halfbeaks as bait in their fishing activities.


Penaeus sp.

Shrimps also abound in the mangrove area near the mouth of the river. The one shown in the picture measures approximately 5.7 centimeters from tip of snout to the end of the tail. This size is of good commercial value. Shrimps and bangus are actually cultured by the locals in the surrounding fishponds.

Firefly Mangrove

Sonneratia alba

The mangroves at the mouth of Iwahig River are mainly of the Sonneratia species. This mangrove species is tolerant of high salt conditions so these are frequently observed lying along the margins of the mangrove forest.

About two kilometers inland, a firefly watching tour is offered by a local tourism operator. This attraction is made possible by Sonneratia because its flowers in bloom attracts fireflies. Thus, it is also referred to as the "firefly mangrove".

Bakawan Lalaki

Rhizophora apiculata

Among the most common species long the coastal margins of mangal are the Rhizophora apiculata. Local people call this mangrove "bakawang lalaki", which means male mangrove.


Definitely, there are more species of animals and plants found in the estuarine ecosystem. The above inventory is not exhaustive as the sampling activity took only two hours. More intensive study will be done to document other important biodiversity in the estuarine zone.

©2012 Patrick Regoniel


Estuarine Biodiversity, Estuarine Fish, Estuarine Habitats, Mangrove Biodiversity, Mangrove Ecosystems, Mangroves Biodiversity

Meet the author

author avatar patzwiki
I am essentially an environment specialist who has a leaning on computers, photography, and wildlife. But I could write on almost any topic under the sun. I am a PADI member.

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author avatar April Liao
30th Jun 2014 (#)

I enjoyed reading. Very informative. Can you upload more?

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