The purpose of a biotic survey is to identify the different organisms found in a mangrove estuary, examine their behavior, and delve into their interactions and roles in the ecosystem. Students should be able to place organisms in a food web and recognize the intricate relations that define ecosystems. Below are listed a handful of organisms typically found in a mangrove estuary including behavioral aspects and key roles in the ecosystem.
- Red Mangrove – Defining characteristic are its prop roots, propagules, and thick waxy leaves. Prop roots play an important role in stabilizing the mangrove allowing them to live in deeper water and deal with currents, as well as provide habitat for aquatic organisms. Propagules are the reproductive structure of the plant. They are viable up to a year after being dropped and can travel on currents to new locations. This characteristic is what makes the Red Mangrove a pioneer species, or a colonizer of new or disrupted areas. Thick waxy leaves help conserve plant moisture during exposure to the hot tropical sun. The Red Mangrove is a cornerstone species of the estuary, as many aquatic organisms depend on its photosynthetic processes and function.
- Swimming Crabs – Characterized by a pair of paddle shaped back legs, mottled brownish coloration, aggressive behavior, sharp pair of claws. The crabs cryptic coloration allows it to blend in with the substrate where it lives aiding in ambush predation, and camouflaging it from predators. Sharp claws aid in securing prey and are effective in defending against predators. The paddle like back legs are efficient aids in rapid swimming, as well as effective at helping the crab burrow into sediments. The swimming crab is considered an intermediary species on the food pyramid, it is an active predator as well as decomposer that moves energy up from the lower levels of the pyramid. The crab itself is a primary prey item for fish and birds, which allows for energy to continue its flow to the upper reaches of the pyramid.
- Roseate Spoonbill – This mid-sized wading bird is characterized by its large feet, long legs, spatula shaped bill, and pink plumage. The large feet of the Spoonbill increase its surface area helping it not sink in the soft substrates where it wades. The long legs aid in wading in deeper water. One of the more interesting characteristics is the spatula shaped bill the is swung back and forth in the water to filter planktonic animals out of the water. The roseate coloration of the Spoonbills plumage is due to the pigments of the shrimp that it feeds on. The Spoonbill is in the upper part of the pyramid feeding on primary and secondary consumers.
- Crocodile – The crocodile is a top-level predator and is characterized by its scaly-plated skin, elongated snout, large teeth, and long tail. Evolutionarily speaking the crocodile is a successful, long-lived species. Its characteristics have helped it become a top level ambush predator. Take care in its presence.
- Students will understand the role that biotic factors play in the system’s function.
- Students will identify and observe organisms that inhabit mangrove estuaries.
- Students will also specify the role and place of the organism within a food pyramid and ecosystem.
The exploration of the biotic factors of an estuary starts with an introductory lecture of common organism found in an estuary, a visit to an estuary for organism identification and observation, and a conclusion that examines interrelationships within the ecosystem. Below is a sample observation sheet, and a series of questions that examines organism relationships.
Vocabulary: Primary producer, Consumer (primary, secondary, tertiary), Herbivore, Omnivore, Carnivore, Adaptation
Google search for organism identification and characteristics.
- The crocodile is considered an ambush predator, identify three characteristics or behaviors and explain how they aid the crocodile.
- Where are the greatest population numbers within the pyramid; top, bottom, or middle? Support and explain.
- Why is the Red Mangrove considered to be a pioneer species? Support and explain.
- Dark coloration helps the crocodile blend in with its dark surroundings. Raised eyes and nostrils allow the crocodile remain submerged while stalking prey. And finally, speed and strength for a quick killing attack.
- Greatest population numbers are typically found at the base of the pyramid due to greater availability of energy at the lower levels.
- A pioneer species is one that can reach and colonize new or disturbed areas. Characteristics of the Red Mangrove that define it as a pioneering organism are
- Drifting nature and longevity of the mangrove propagule that allow it to seek new areas
- Prop roots allow the mangrove to establish itself in marginal areas with deeper water and stronger currents by providing elevation and anchoring capacity.