2005 Program
(Student name highlighted)
Testing rapid bio-assessment protocols for aquatic habitats in a tropical urban stream
Carmen De Jesús and Jorge Ortiz
University of Puerto Rico, Rio Piedras campus
Rapidly developing tropical countries, like Puerto Rico, lack formal mechanisms to evaluate river conditions. This leads to improper and inconsistent environmental impact evaluations of project proposals that could impact rivers such as: dams, water intakes, road bridges, canalizations, river diversions, urbanizations, etc. In some developed countries, the use of rapid bioassessment protocols (RBP’s) have proven useful in providing consistent basic information on river conditions and in evaluating river restoration actions. The applicability of RBP’s to tropical streams, however, remains unknown. Given the rapid pace of land use changes and increase water demands in tropical developing regions, RBP’s may become a valuable river management tool in these regions. In this study, two widely used RBP’s were tested in 27 stream reaches located in the Río Piedras basin, a highly urbanized basin in the San Juan Metropolitan Area of Puerto Rico. The tested protocols were developed by the US Environmental Protection Agency and by the Natural Resources Conservation Service of the US Department of Agriculture. Both protocols provided similar results and provided a clear representation of river conditions in this watershed. We encountered a high degree of human alteration and a variety of pollutants sources in most of the evaluated reaches. These protocols had worked relatively well and with some modifications they could become a valuable river management tool in Puerto Rico and in other tropical developing countries.
Differential decomposition rates across two arthropod communities and three leaf litter types in the Luquillo Experimental Forest
Laura Hartz and Paul Klawinski
Hamilton College
William Jewell College
This study examined the differential effect of two arthropod decomposer functional groups, shredders and grazers, on the decomposition rate of Cecropia schreberiana, Dacryodes excelsa, and Prestoea acuminata in the Luquillo Experimental Forest, Puerto Rico, USA. We constructed 60 mesocosms imitating the forest floor and stocked the boxes with one of the three types of litter, microbes and bacteria (the control), and either: both shredders and grazers, shredders and no grazers, grazers and no shredders, or neither shredders nor grazers. Per treatment, we used 60 millipedes to represent the shredders, and 600 mites and 250 collembola to represent the grazers. Within each treatment we placed leaf disks of a known mass, and then removed them chronologically to determine the rate of decomposition per box. We hypothesized that the treatment containing both grazers and shredders would have the fastest rate of decomposition due to the increased diversity of arthropod decomposer functional groups. In the first two weeks of data collection there was a significant interaction between leaf species and time: D. excelsa decomposed the fastest in all of the decomposer treatments, followed by P. acuminata and C. schreberiana. There was also a significant interaction between leaf species and grazers, and leaf species and shredders. There was no significant interaction between species, shredders, and grazers. At this stage, there appears to be no interaction among the decomposer functional groups which was our original prediction.
Influence of human recreational activities on populations of
Neritina virginea in Espíritu Santo River
Enrique Marrero and J. Felipe Blanco
University of Puerto Rico, Cayey campus
University of Puerto Rico, Rio Piedras campus
As a result of the increment of human population, infrastructures, like roads and bridges, also increased. Bridges increase recreational activities by providing a more easy access to the streams. Streams support many diadromous fauna like fish, shrimp and snails. One of them is Neritina virginea, a diadromous snail found in mid to lower elevations. The migration patterns, growth and distribution of N. virginea have been studied, but the effects of human recreational activities on the population of this species are relatively unknown. The principal mechanisms that affect N. virginea are: modification of the habitat/microhabitat, harvesting, trampling and increase in water turbidity. Total people were statistical significant differences between site and day of the week (site: p= 0.08, day: p= 0.003) but there was no significant interaction. The geomorphologic characteristics were statistical different, mainly between pools but not between sites. Snail size was significantly different between pools (p= 0.000), location (p= 0.013) and bridge (p= 0.000). As a result, we preferred the density ratio. In Jimenez the density ratio was very close to 1, meaning that the snails observed were close to the expected; while in El Verde was higher than 2, meaning that snails were crowed. There was a significant difference of density ratio among sites (p= 0.000) and day of the week (p= 0.001), but there was no interaction. People densities were higher on Monday than in the other days. In term of population variation over time we found that the population on pools is lower on weekends and Mondays. We also found that the bridge does not affect the population densities. In the control pool, the snails move up to 25% in and out of the quadrant, naturally. In the trampled pool the snails move outside from 25 to 100%. This means that they are directly affected by recreational activities, as soon as 30 minutes of trampling.
The role of predators in structuring tropical stream communities in Puerto Rico
María Ocasio and Todd Crowl
University of Puerto Rico, Humacao campus
Utah State University
This investigation was made to determine whether biological or physical processes are the major structuring forces of shrimp communities. We expected fish predation to have a greater influence on shrimp communities than stream morphology and shrimp density to be higher in the absence of fish. We measured the physical aspects of two streams, one with fish (Ikaika) and one without fish (La Prieta), and set traps overnight to estimate shrimp density. We counted shrimp by species and measured their carapace lengths. We electrofished to learn what species of predators were present in the Ikaika Stream. We found the mountain mullet or Taja’o (Agonostomus monticola) and the American eels (Anguilla rostrata). The physical aspects of both streams turned out to be very similar. On the other hand, fish predation limited the density of shrimp in Ikaika since Atya and Xiphocaris, filter feeders and scrapers, were significantly more abundant in La Prieta while Microbrachium had more number of organisms in Ikaika. Nevertheless, experimental manipulation is needed to determine if predation is the major cause for the shrimps’ density.
Influence of habitat morphology on shrimp abundance in the Quebrada Prieta
Coralys Ortíz and Fred Scatena
University of Puerto Rico, Rio Piedras campus
University of Pennsylvania
The purpose of this project is to determine how morphological features of stream pools affect the abundance and composition of shrimp communities. This study is part of an ongoing effort to determine the biological interactions of freshwater species in high-elevation streams. Our study focused on developing predictive relationships between habitat features- such as depth, active channel width, water velocity, substrate composition, etc. - and shrimp abundance and distribution. The hypothesis for this project was that biotic abundance is inversely related to the morphological complexity of habitats in stream pools. We measured different physical features of 55 consecutive pools in Quebrada Prieta (a high-elevation stream); then estimated the population and distribution of various species of shrimp (Atya lanipes, Xyphocaris elongata and Macrobrachium) to look for correlations between physical parameters and biotic complexity. Correlations of area, volume and distance upstream were found to be significant for A. lanipes and X. elongata, but not for Macrobrachium species.
Examining the importance of tropical freshwater shrimps in the cycling of fine particulate organic matter
Alexandra Santana and Wyatt Cross
Universidad Metropolitana
University of Georgia
We examined the contribution of tropical freshwater shrimps in the cycling of fine particulate organic matter (FPOM) in two small streams (Quebrada Prieta and Quebrada Bisley) within the Luquillo Mountains at El Verde Field Station, Puerto Rico. We predicted that 1) shrimps would consume and egest a significant proportion of the available FPOM and 2) ingestion and egestion rates would be related to body size and food quality (i.e., algae vs. leaves). We found that body size was negatively related to field-estimated egestion rates (r2 = 0.52, p < 0.0001). There was no difference in egestion rate between shrimp species or between streams. Interestingly, we found that the organic matter content of shrimp feces was higher in Quebrada Prieta than in Quebrada Bisley, reflecting differences in the quality of fine particulate matter between these streams. Laboratory estimates of consumption and egestion rates on different food types revealed that food quality had a significant influence on FPOM turnover. While algae and stream FPOM were utilized rapidly, leaf-based FPOM was consumed very slowly. We used our estimates of FPOM consumption rates and standing stocks of FPOM in streams at El Verde, to estimate whether shrimps consume a large proportion of the available FPOM. Our results indicate that shrimps may consume up to 60% of available FPOM in key habitats (i.e., rock substrates). This study will aid in understanding the importance of freshwater shrimps in whole-ecosystem turnover of FPOM. In addition, our results will be useful for predicting the consequences of shrimp extirpation due to human activities.
The importance of aquatic insects in the movement of fine organic matter in rivers
Lizmar Silvestrini and Alonso Ramírez
Universidad Interamericana, Ponce campus
University of Puerto Rico, Rio Piedras campus
The function of aquatic insects in processing leaf litter has been studied in depth, but the function of these individuals in processing fine organic material has not been studied. This study determines the role of aquatic insects in the movement of fine organic matter. More in specific, the study determines the amount of fine organic matter that is ingested by aquatic insects, the amount of time it takes them to do it, and the amount of fecal pellets (egestion rate) produced by aquatic insects. The study site was the Luquillo Experimental Forest, Puerto Rico. We used Quebrada Bisley and Quebrada Prieta, two streams in Tabonuco Forest. Quebrada Bisley is located in the adjacent Mameyes and Quebrada Prieta is a representative first and second-order tributary in the Rio Espíritu Santo. To determined the role of insects in the movement of fine particules, I used ephemeroptera, which are common in the study streams. Consumption was estimated by measuring egestion and ingestion rates. For egestion rate (fecal pellets) production was measured by placing ephemeroptera in plastic bags and determining production over time and igestion rates were mesured in the laboratory by following the displacement of labeled food and using diferent types of food. Results indicated that egestion rate in Organic Matter and Dry Mass were not different between streams but in Organic Matter content in Feces was highest for ephemeroptera in Bisley. Ingestion rates as Gut Passage Time were no differences between food types. The fraction of FPOM processed by ephemeroptera was based on excretion rates. We found that larval ephemeroptera processed 0.04 – 0.50 g daily. Therefore, in one day insects process < 1% of the FPOM available in the stream and amount of FPOM processed. Ephemeroptera can process more FPOM in Prieta than in Bisley. In conclusion insects consumption did not change with FPOM availability. The FPOM quality did not affect insect consumption. Insects consumed a small fraction of FPOM, and the size of this fraction depends on the stream. Insects process fine particules in a mechanical way, unaffected by quality or quantity.
Understanding distribution patterns of the terrestrial orchid Prescottia stachyodes (Swartz) Lindley at the Luquillo Forest Dynamics Plot (LFDP) Puerto Rico, based on land use history, habitat, and ecological relationships
Melissa Whitman and Jim Ackerman
Western Washington University
University of Puerto Rico, Rio Piedras campus
Human land use practices can have a significant and long term impact on species distribution and ecological relationships. However, environmental factors that co-vary with land use may be more influential than the actual land use per se. To address if there is a need for integrated analysis of factors influencing species we used the terrestrial orchid Prescottia stachyodes as a model to test conclusions drawn from using land use history as a distinct and separate factor, compared to the impact of land use as an indication of overall habitat type. We analyzed factors influencing P. stachyodes distribution (abundance and frequency,) leaf morphology, and response to human impact (with and without additional habitat variables) as well comparing it to Wullschlaegelia. calcarata, a terrestrial saprophytic orchid that is found within the same study site but limited to areas with minimal disturbance. The factors included category of historical habitat disturbance, rockiness, slope, and soil type. The first distribution analysis of P. stachyodes and land use history found that the significant majority were in moderately disturbed areas with dense canopy cover. Yet a secondary analysis of land use, combined with a variety of habitat characteristics, determined that the highest density was associated with flat, non-rocky areas regardless of land use history or soil type. In suitable habitat areas orchids were densely clustered with morphological variation between groups. We determined that factors most significant for species distribution (rockiness and slope) did not necessarily influence the vegetative development (such as larger leaves associated with specific soil type) of a species once it was established in an area. Overall P. staychodes’ limited response to land use disturbance was in dramatic contrast to W. calcratata, thus generalizations about Orchidaceae within comparable habitat or history cannot be assumed. We also concluded that a comprehensive understanding of species distribution, especially when relevant to land management, should incorporate as many environmental factors as possible.