Monday, March 29, 2010

#4 Wading into Belize's mangroves

Guest post by Dr. Daniel Gruner, University of Maryland, from the Belize Expedition

This week, along with graduate student Alexander Forde, I found myself working in a new system: the tropical mangrove cays off the coast of Belize. Ordinarily I study the ecology of a range of organisms (plants, nematodes, insects, birds ...) on dry land. Mangrove forests differ from most forests in that the trees thrive with their toes constantly wet, usually in salt water that is toxic to most land plants. So, Alex and I would need to adapt to perpetually submerged toes--and legs, and most everything else--to study this ecosystem.

Probably derived from the roots "mangle" and "grove," this name is apt. These forests are a tangle of aerial roots and branches, peat and mud that make them challenging to navigate. Hip waders would be hopelessly hot and restrictive, so we simply splashed into the swamp wearing only surf booties on our feet, our typical terrestrial field clothes and gear and plenty of sunscreen. In the murky waters it can be difficult to judge the depth of the muddy bottom with each step. Many times we found ourselves sinking to the waist (or deeper!) before climbing out the other side. At first tentative, we quickly overcame any hesitation to perfect a shuffling tap dance, first testing the solidity of the substrate with a toe tap before plunging forward. We were soon making rapid progress in our explorations through this fascinating habitat.

Alex in the mud

Mangrove landscapes are frequent casualties to human development, and their extent is in rapid decline worldwide. Coastal land is valuable for housing or tourist activities, for shrimp farms, aquaculture and other commercial uses. The mangrove trees are harvested locally for building materials, for firewood and for many other uses. Knowledge of the biodiversity and ecosystem function of mangroves, through scientific study, is helping to slow this tide. Research demonstrates that mangroves are critical buffers between land and sea.

Mangrove habitat

Mangroves protect the sea through microbial processing of effluent and runoff of chemicals, excess nutrients and sediments coursing in from land. And mangroves buffer the land from severe storm surge and tsunamis while providing a nursery ground for numerous commercially important fisheries. In Belize alone, mangroves provide habitat for more than 70 fish species, 175 birds, 10 amphibians, 30 reptiles (including crocodiles and boa constrictors) and 40 mammals. In light of these findings, the good news is that the Belize government now regulates any proposed development of mangrove areas.

And speaking of the animals in mangroves, we were not the only organisms splashing through the habitat. Splashing sounds are commonplace, from the small to very large--and often very surprising. At these times it is impossible to forget that we share the habitat with crocodiles. We also hear their grunting calls from time to time, but crocodiles are rarely seen and we take comfort in our numbers. Most often the splashing noises can be explained by large fish chasing schools of smaller fish, whose escape behavior is to leap right out of the water en masse. A few great splashes remain unexplained...

As we travel through the habitat, we are fascinated by gardens of 'upside-down' Cassiopeia jellies carpeting the shallow seabed, displaying their frilly undersides to the sun. Partnering with symbiotic photosynthetic algae, these jellies capture their food and energy from sunlight. They display a stunning, colorful morphological diversity captured only in part here.

Cassiopeia morphs

The water in these mangrove lagoons is too warm and too rich in nutrients and sediments to support corals, but we find it amazing how other organisms have adapted their strategies such that no space on the seabed is wasted.

Our research goal this week is to extend collaborative work with Drs. John Parker and Ilka (Candy) Feller of the Smithsonian Environmental Research Center in Edgewater, Maryland. We are interested in how herbivorous insects affect the productivity and shape the structure of these communities, and in turn how birds and crabs affect these outcomes through predation on insects. By feeding on the actively growing meristems of these slow growing trees, attacking the vascular cambia of their trunks, or ravaging the establishing propagules (fruits), insects and crabs can be surprisingly important to the growth, productivity and reproduction of these forests. Alex Forde next will share his observations from designing and carrying out this research.



  1. Wow. That's some deep mud. So where do you run if there's a crocodile coming?

  2. Belize does have excellent laws for the protection of mangroves. However, the sad thing is, the moment there is money to be made, they are ignored, or at least not enforced. Take a look at the development at the mouth of the Sittee River, for example.