Tuesday, March 30, 2010

#5 Birds, moths and mangroves in Belize

Guest post by Alexander J. Forde, University of Maryland, from the Belize Expedition

It is hot. I wipe droplets of sweat from my forehead and squint as I feel the burn of sunscreen in the corners of my eyes. I am standing knee deep in clear water surrounded by tiny mangrove trees about a meter high. In the distance, large mangroves rise up and block my view of the ocean, obscuring the fact that I am on a small, remote island in the Caribbean.

As I trudge across the flooded peat swamp, I am distracted for a moment by the "chirp chirp, tweet tweet" of the Yucatan Vireo, a gray bird about the shape and size of a robin. As usual, the bird is invisible in the foliage and my weak attempts to coax it out with my own rendition of its call are unsuccessful. I continue my shuffle across the soft peat and, off to my left, an entire school of fry suddenly leap out of the water, having been disturbed by a hungry pack of larger fish. Later, I hear a huge splash followed by the screaming and flapping of birds, which I chalk up to the foraging of a crocodile (as mentioned in Daniel's previous post).


Most people could guess that the latter two sounds were death-knells of predation, but few would associate bird song with mortal attacks on prey. Interestingly, it is exactly the association between birds and predation that is motivating my work on the island. Predation by birds can have very important effects on herbivorous arthropods, such as driving the evolution of warning colors, or decreasing damage to plants and consequently increasing plant productivity.

The mangrove forest is quiet when I reach my destination: a pair of cubic frames made out of PVC pipe that are built around small mangrove trees. One frame has netting over it to keep out birds and the other has no net so that the birds can enter. I measure how much the trees have grown since the frames were built and record the arthropods and damage present on the leaves. I notice serpentine leaf-damage, which indicates the presence of a tiny leaf-mining caterpillar, irregularly shaped areas scraped by tree-crabs, and circular areas chewed by free-living caterpillars. The tree inside the frame with netting even has a borehole into one of its branches through which a wood-eating larva recently entered.


With help from my collaborators I had established 20 pairs of these frames on the island 3 months previously. This simple experimental design involving bird "exclosures" has a rich history of detecting long-term impacts of bird predation in other habitats and after this study is completed, it will help us understand the ecosystem function of birds in mangroves. If birds do have strong ecological effects on arthropod assemblages and on mangrove growth, then they will need to receive more attention from land managers who seek to conserve and restore mangrove forests.

As I set out in the motorboat that takes me from the Carrie Bow field station to my field site, I make a mental check list of activities for the day. I have finished surveying the bird-exclusion frames for this trip, so now I can shift my attention to side-projects. Today all I need are plastic bags, water and a lunch, because I am going to be collecting the pupal cases of a caterpillar that eats mangrove leaves. The last time I was on the island, I found that all sorts of insects invade these cases, sometimes killing the developing moth inside and sometimes setting up shop after the moth has already left.

I tie up the boat to the trunk of a mangrove on the edge of the forest and work my way through the dense stand of large trees that extends along the exterior periphery of the island. I finally enter the more open central domain of the island with a few new scratches on my arms and legs, and begin to search the undersides of twigs for pupal cases. As I scan for suspicious irregularities on the branches from a distance I notice a bump on one nearby branch. I walk over to get a closer look and, sure enough, I have found one of my targets. The oblong case is 2cm in length and is rounded, with the exception of the flattened trap door at the top, which allows the adult moth to emerge. I carefully remove the case from the branch with some difficulty, as the adhesive silk that the caterpillars use to anchor themselves to the branches is extremely tough and strong. Into a bag the case goes, and later I will dissect it and try to reconstruct the history of invasion that has taken place.


I am concerned with these pupae because it is possible that the population dynamics of certain mangrove herbivores are affected to an equal or greater extent by invertebrate predation, compared to bird predation. Pupal dissections have revealed that the pupae are often attacked by parasitoids and ants, so invertebrate predation is likely to be important for this species. My goal is to quantify the relative effects of different predatory taxa on this focal herbivore, and to test whether the extreme patchiness of its spatial and temporal distribution results from the effects of one or all of its natural enemies. Predation on this species may be important for mangrove productivity, as the caterpillars can remove large amounts of biomass during periodic outbreaks.

Motoring away from the mangrove island for the last time on this expedition, I look back at the edge of the mangrove forest. I wonder to myself what I will find waiting for me in the bird-exclusion frames the next time I return, and I imagine all of the interactions between individual predators and prey that I will never see in person, but that will be collectively captured in statistical patterns in my data. I feel happy that I will be able to return to this fascinating place soon, and that, one day, the bug-bites, scratches, stinging sunscreen-tainted eyes, and sunburns that I acquired as part of my work in the forest will have been suffered for a worthwhile purpose: helping communities better understand and preserve beautiful and beneficial Caribbean mangrove ecosystems.


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.

Thursday, March 25, 2010

#3 Time is a precious commodity.

Peter Gawne, Belize Expedition

Every moment of every day on this island seems to be a race against the clock. We rise with the sun and quickly get to work. While the days are long, they are not without limit and there is much work to do before the sun goes down.

Time in the field is an extremely limited resource for scientists. The daylight hours are spent in parts unknown. Samples must be gathered. Measurements must be taken. All of the data that is going to sustain a scientist's work is to be gathered in the field. Later there will be time, albeit limited, to crunch numbers, analyze samples and work toward the eventual goal of publication (as mentioned in post #2).

When working underwater the issue of time is compounded. Beneath the surface, time is measured in minutes rather than hours. There is a constant struggle between air--supply, decompression limits and the work that must be done. Each failed attempt to capture a fish eats precious minutes that will never be recovered.

Wednesday, March 24, 2010

#2 Now it is time for some science

Peter Gawne, Belize Expedition

The table is set. The pieces are in place. Now it is time for some science.

The attitude of this island centers solely on the pursuit of science, and the full-time staff have that pursuit at the center of their mission. Bonnie and Ed, the field station's managers, are indispensable in aiding the work of the two teams currently on island. Although they come from different backgrounds, each has a wealth of experience and a worldly sense. Their sage council, experience and genuine passion for both the island and the work conducted here is evident in everything they do. I both respect and like each of them immensely.

Saturday, March 20, 2010

#1 Surrounded by people who are very good at what they do

Peter Gawne, Belize Expedition

I find myself surrounded by people who are very good at what they do.

After the customary tedium of traveling within the confines of the United States, Randi and I finally landed in Belize City. During the flight, we had met one of the other researchers, Alex, who was heading to Carrie Bow to conduct experiments surrounding mangroves and their associated insects. Alex was seated directly in the seat in front of me, and overheard a conversation about Carrie Bow Cay, and decided that the odds were in his favor that we were headed there as well. It was funny to be seated so close to someone headed for the same remote destination. In a plane filled with over one hundred passengers, we were seated within earshot of a man headed to the same small island with a maximum population of eight. Alex has an obvious passion for his work, and a quick sense of humor. I liked him instantly.

Traveling with so much scientific equipment (something the Phoenix Islands Expedition is familiar with), it was unsurprising that the prying eyes of officials in the Miami airport could not resist one last look inside our plastic trunk, packed with a tools, nets and chemicals of all varieties. We decided to wait for the entirety of our baggage, and took in some tamales at the airport. Those were some of the best tamales I have ever tasted, worlds beyond typical American airport food.

Friday, March 19, 2010

You'd better Belize it!

Randi Rotjan and Peter Gawne, Belize Expedition

Randi: It's been two years since I've been to Carrie Bow Caye, a small (0.74 acre!) island in Belize where I did all of the work for my doctoral dissertation. Sum total of over a year of my life spent on this tiny island; at one point I could recognize every single coral head and had pet names for the resident turtles. Since then, reefs all over the world have experienced substantial demise. Several hurricanes, storms and development projects have transpired; I'm terrified to go back to one of my favorite places on this planet--will it still be all that it was? Who knows, but I'm going in order to answer that (plus many other!) question(s). Lucky for me, I am bringing along Peter Gawne, one of the New England Aquarium staff from the fishes department, who will be looking at Belize with fresh eyes. I can't wait to experience a place that I know so well through a new perspective.