UNIVERSIDAD DE PUERTO RICO
RECINTO DE RÍO PIEDRAS
PROGRAMA DE CIENCIAS AMBIENTALES
INFLUENCE OF HABITAT MORPHOLOGY ON SHRIMP COMMUNITIES IN
A HEADWATER STREAM:
QUEBRADA PRIETA, LUQUILLO FOREST
Coralys Ortiz Maldonado
Research project submitted
in partial fulfillment
of the requirements for the
Bachelor Sciences degree on
Environmental Sciences
December 2005
A abuela
ii
Acknowledgements
Special thanks to Enrique Marrero and María Ocasio for all their work and support
during this project. Thanks to Dr. Fred Scatena, advisor for this project and without
whom this work could not have been possible; Katie Hein, for her guidance; Dr. Alonso
Ramirez for suggestions and review; and to Dr. Wyatt Cross for his input and
encouragement. Also thanks to Rahiza De Thomas, Andrew Pike, and the El Verde Field
Station Staff for facilitating resources for this project.
Funding for this project was obtained through the REU Site Program at El Verde Field
Station, University of Puerto Rico. NSF Grant # DBI-0243750. Additional funding was
provided by the NSF Luquillo Biocomplexity Project and the USDA International
Institute of Tropical Forestry
iii
Abstract
The purpose of this project is to determine how geomorphological features of pools
in headwater streams affect the abundance and composition of resident shrimp
communities. This study is part of an ongoing effort to determine the biological
interactions of freshwater species in high-elevation streams for the development of
healthy management practices in tropical forests. We focused on developing predictive
relationships between habitat features- such as depth, active channel width, substrate
composition - and shrimp abundance and distribution. Different physical parameters of
55 consecutive pools were measured at Quebrada Prieta, in the Luquillo Experimental
Forest during the summer of 2005. The abundance of shrimp (Atya lanipes, Xiphocaris
elongata and Macrobrachium spp.) was then determined by overnight trapping, and
regression analysis was used to relate shrimp species population and distribution with the
physical parameters of the pools. Relationships between population size and pool area,
volume and distance upstream were found to be significant for Atya and Xiphocaris, but
not for Macrobrachium spp. A trend was observed in pools sampled on a regular basis for
LTER studies, in these pools shrimp densities were low, further studies are needed to
understand this pattern.
This project provides basic information on the habitat requirements needed to
maintain freshwater shrimp populations in headwater streams in the region. It also
develops a detailed profile of the morphological and biotic characteristics of a section of
headwater stream to help establish predictive relationships between habitat features and
stream dynamics in similar settings.
iv
Contents
Page
Title
i
Acknowledgments
iii
Abstract
iv
Contents
v
List of Tables
vi
List of Figures
vi
Introduction
Morphology and habitat dynamics
Freshwater shrimp in Luquillo Mountains
Purpose and scope
1
2
4
5
Methods
Study site
Field sampling
Statistical analysis
6
6
8
9
Results
Geomorphological profile
Atya lanipes
Xiphocaris elongate
Macrobrachium ssp.
11
11
12
12
13
Discussion
19
References
24
Appendix
A1
v
List of Tables
Table 1. Pool morphology measurements.
8
Table 2. Average pool morphology and shrimp abundances for
pools smaller than 20 m2 in Quebrada Prieta.
11
Table 3. Pearson correlation coefficients for shrimp
abundance, pool area and volume for pools smaller
than 20 m2 in Quebrada Prieta.
13
Table 4. Stepwise regression model results by species for
shrimps in Quebrada Prieta.
13
List of Figures
Figure 1. Study site.
7
Figure 2. Abundance of shrimp per pool area in 55 consecutive
pools in Quebrada Prieta.
14
Figure 3. Shrimp abundance vs. pool area for pools smaller than
20 m2 in Quebrada Prieta.
15
Figure 4. Shrimp abundance vs. pool volume for pools smaller
than 20 m2 in Quebrada Prieta.
16
Figure 5. Abundance of Xiphocaris elongata vs. abundance of
Atya lanipes for pools smaller than 20 m2 in Q. Prieta.
17
Figure 6. Average number of individuals and average dry mass
weight for shrimp species in Quebrada Prieta.
18
Figure 7. Rows of Atya lanipes filtering detritus from flowing
water at a pool mouth.
23
Figure 8. Wire trap with bait.
23
Figure 9. Rostral length measurement for Atya lanipes.
23
vi
Introduction
River systems in islands throughout the Caribbean have recently been a focus of
renewed study and the implementation of management policies for two main reasons:
they supply most of the population’s water needs, and they provide spaces for a wide
range of activities such as fishing, recreation and small industries that rely on the wealth
and integrity of the natural system. These two concepts might seem mutually exclusive,
but ecologically sustainable water management programs have been recognized as the
most effective – and profitable in the long-term – approach to resource managing (Richter
et al. 2003).
Population growth and resulting landscape modification for social use have been a
matter of concern regarding river management, and tropical ecosystems in general (Lugo,
1995). Rivers and streams along the Luquillo Mountains in North-Eastern Puerto Rico
have been actively used for water supply, recreation and research in the last decades. The
recognition of an ever-growing strain in those resources, especially from water
withdrawal practices, has fueled initiatives to encompass human population necessities
and ecosystem integrity. One of such initiatives is the HELP project for the Luquillo
Mountains watersheds (Ortiz-Zayas & Scatena, 2004), aimed to promote water
management practices that are beneficial for humans as well as the ecosystem. The need
to achieve this balance has generated many questions about habitat requirements and the
extent to which our use and modification of the morphological features of streams affect
ecosystem dynamics (Pringle & Scatena 1999).
Two main approaches dealing with stream habitat research have been put forward
(Newson & Newson, 2000). One emphasizes the physical aspect of habitat hydraulics,
1
and the development of habitat models such as PHABSIM (Newson & Newson, 2000;
Scatena & Johnson, 2001) intended to identify optimal habitat features. The other
approach is focused on understanding the interactions among certain species (i.e.,
bioindicators) and their response to stress in different environments (Covich et al., 1996;
Crowl et al., 2002).
Both approaches are relevant in adopting management programs to the particular
needs of those sites where they are implemented. In this regard, Hodkinson and Jackson
(2005) stress the importance of basic guidelines when selecting suitable bioindicators for
specific sites. It is important that the selected species is abundant, easily surveyed and
manipulated, and that their biology and responses to stress are well documented. By
identifying species that fit this criteria and studying their life histories on different
settings it would be possible to determine the condition of the system.
Morphology and habitat dynamics
In any freshwater setting, substrate composition, food availability and predation are
the most significant parameters that shape an environment (Williams, 1984). The extent
at which each of them influence different life stages of the system is still a subject of
debate (Newson & Newson, 2000).
For instance, formations along the Luquillo Experimental Forest are mostly
composed of volcanic rocks and sedimentary deposits rising as steep sloped mountains
(Seiders, 1971). River networks that drain these mountains are of steep gradients and
connect montane, lowland and marine environments over relatively short distances,
creating a range of habitat settings were stream dynamics and productivity are influenced
2
on different levels by the interaction of the species present as well as the physical
features.
Understanding the individual and collective effects of the factors that influence
these organisms is essential in developing effective management policies for this area.
Habitat estimate models are one approach to developing this understanding. However,
most habitat models have been developed for fish in temperate, cold water streams;
therefore they are not accurate predictors for organisms in tropical communities (Scatena
& Johnson, 2001).
The Luquillo Mountains have been a site for various projects regarding habitat
management and stream channel restoration efforts, aimed to identify habitat features that
would allow a more effective use of the available resources (Scatena & Johnson, 2001).
Research conducted in headwater streams in the region regarding these relationships is
advantageous for several reasons:

Dynamic processes taking place in numerous small streams throughout the
watershed have a significant collective effect on the entire system.

Headwater streams are relatively simple systems with less confounding
variables that can be isolated from the influence of watershed scale processes
in large rivers.

There is a lower number of species which can be studied without the influence
of active predation or other influences such as land use and water withdrawal.

The food-webs in headwater streams tend to be simpler, thus enabling the
studies on distribution and habitat preference of freshwater shrimp without the
influence of different food sources.
3
Freshwater Shrimp in Luquillo Streams
Shrimp communities are considered among the most important components of
freshwater ecosystems because they account for a significant portion of the total biomass,
influence nutrient cycles, and affect in-stream decomposition rates (Crowl et al., 2001).
These amphidromous organisms drift to the coast as planktonic larvae, return to
freshwaters as juveniles and live to adulthood in headwater streams, using the entire
watershed during their life cycle. This behavior of continuous upstream migration makes
their abundance and size distribution excellent long-term indicators of the health of the
whole river system. Population composition at high elevations (e.g., shrimp species
diversity and abundance) can be related to conditions downstream.
This study focuses on the abundance and distribution of some of the most
commonly found species of shrimp in the Luquillo Mountains streams at elevations
greater than 300m, specifically Atya lanipes, Xiphocaris elongata (Family Atydae), and
four species of Macrobrachium: M. carcinus, M. heterochirus, M. crenulatum, M.
faustinum (Family Palaemonidae).
While resident Atya lanipes spend most of the time near the substrate, Xiphocaris
elongata is mostly found in the water column. This difference in preferred habitat is
explained by their respective feeding mechanisms. Atyas are considered scrapers, feeding
on conditioned leaf litter, algae and microbes from the bottom rocks, or filter feeders,
using modified chelae to filter the water and feed on suspended particles in water flowing
at 5 cm/s or more (fig. 7). In contrast, Xiphocaris uses small pinchers to shred pieces of
leaves, these are very active swimmers and can be seen searching for small seeds and
4
insects that fall into the surface of the pool (Covich & Johnson, 1996). This behavior also
makes them more prone to predation by Macrobrachium than the bottom dwelling Atya.
Macrobrachium species are omnivorous; usually feeding on detritus and on smaller
shrimps. They are also known to be very aggressive and territorial. Studies have shown
that they can release chemical signals to discourage other Macrobrachium from getting
near them. These signals also alert small shrimp of the presence of these predators,
encouraging them to move forward upstream (Crowl & Covich, 1994).
Purpose and scope
The goal of this project is to develop predictive relationships between physical
habitat features and shrimp abundance in Puerto Rican streams. This would allow us to
relate the physical parameters of the stream channel to the life histories of organisms in
headwater streams. We hypothesize that:
H1: Shrimp abundance can be predicted on the basis of the physical morphology of
the channel.
H2: The abundance of shrimp is inversely related to the morphological complexity
of habitats in stream channels, resulting in more shrimp in simple habitats due
to the amount of energy required to reach the more complex habitats upstream.
5
Methods
Study site
This study was conducted in one stream within the Luquillo Experimental Forest,
near El Verde (18˚18´N, 65˚47´W). Quebrada Prieta is a second-order tributary that runs
through the Luquillo LTER1 Forest Dynamics Plot, and flows into Quebrada Sonadora at
approximately 250m above sea level. The drainage area is covered by subtropical wet
forest dominated by Tabonuco trees (Dacryodes excelsa) and sierra palms (Prestoea
montana). The headwaters of this stream are located in a wooded area managed by the
USDA Forest Service; downstream sections are subject to rapidly growing urban
developments and water extraction schedules (Lugo et al. 2004). Mean annual
precipitation is 360 cm yr -1 evenly distributed throughout the year, with slightly more
rainfall in the months from May to December (Covich et al., 2000).
This perennial stream is lined with igneous rock boulders and cobbles, as well as
sand and silt in some areas. Stream sections in higher elevations are frequently impacted
by landslides and mud accumulation. The slope within the reach and throughout the
stream is predominantly steep (25%). The section of stream studied in this project ranges
in elevation from about 320m to 470m above sea level (fig. 1).
Atya lanipes and Xiphocaris elongata are the most common species of decapods
found in Quebrada Prieta. However, four species of Macrobrachium (M. heterochirus, M.
crenulatum, M. faustinum, M. carcinus) are also found. There is an absence of predatory
fish due to waterfalls and other natural barriers downstream. Only one species of grazing
gobiid fish (Sicydium plumieri) and one species of amphibious crab (Epilobocera
sinuatifrons) have been reported in Prieta (Covich & Johnson, 1996).
1
Long-Term Ecological Research program for the National Science Foundation.
6
7
Field sampling
Geomorphological measurements:
Fifty-five consecutive pools (including pools regularly sampled by the Luquillo
LTER program), in a section of approximately one kilometer along Quebrada Prieta were
surveyed. Sampling locations were limited by the trapping method; neither riffles nor
pools smaller than 0.5m2 or shallower than 0.20m were used for this study as those areas
cannot hold the traps used for shrimp sampling.
One pool, with an area of nearly 75m2 was excluded from the analysis because of
its unique size (see below). Data regarding pool size, substrate composition and flow
direction was collected at each survey (Table 1). Depth measurements were adjusted
comparing the water level at the time of each survey to a previously recorded water level
(0.442m)2. This was done to account for stream flow variations on different dates
throughout the survey. Pool substrate was characterized as silt, sand, gravel ( < 5cm),
cobble ( > 5cm), boulder ( > 30cm) or bedrock. Estimates of percent substrate covered by
leaves, and other organic matter such as branches, bark, logs and roots were also made.
Table 1. Pool morphology measurements.
Measurement
Max pool depth
Max pool width
Active channel
Pool length
Distance between pools
Average pool depth
Grain size
% substrate cover
Flow direction
2
Equipment
Ruler measurements,
adjusted for stage
Tape
Tape
Tape
Tape
Average of 25 random
depth measurements
25 random point counts
25 random point counts
Compass
Precision
1 cm
10 cm
10 cm
1 cm
10 cm
1 cm
6 classes
2 classes
5˚
Water levels were measured from a USGS gage at Quebrada Prieta.
8
Shrimp abundance:
Shrimp abundance was measured once on each pool between June and July of
2005. Shrimps are known to be resident of specific pools and do not move greatly
between pools (Scatena & Johnson, 2001). Therefore, a single sampling was considered
adequate to characterize pool populations. We used baited funnel traps of 20 cm in
diameter, with one 3.5 cm entrance located on each side, at approximately 8 cm from the
substrate (fig. 8). About 4.5 grams of soft cat food was used as bait in each trap. Traps
were distributed within the pools to accommodate 0.5 traps per square meter of surface
area to equalize sampling efforts among pools. Shrimps captured overnight, in addition to
fish or crabs that might have entered the traps, were recorded, measured and identified to
species the next morning and released into the same pools. One measurement from the
back of the carapace to the tip of the rostrum of each individual (rostral length) was
recorded to estimate their average length and biomass (fig. 9). Biomass calculations were
made for the most abundant species A. lanipes and X. elongata using equations developed
from LTER projects (Cross, unpublished):




Atya
lanipes
:
dry
mass

0
.
0002
0
.
8338
rostral
length

0
.
4668

g


mm
3
.
0625




Xiphocaris
elongata
:
dry
mass

0
.
0003
0
.
7787
rostral
length

0
.
9731

g


mm
2
.
9064
Statistical analyses
Field measurements were entered into Excel worksheets to calculate area, average
depth, volume, median grain size, grain size distribution and percentages of leaf and other
organic matter cover within the pools. After calculating these parameters for each pool,
9
exploratory graphical analyses were conducted to examine relationships between physical
features, relative abundance and shrimp distribution. A Pearson Correlation Coefficient
analysis was used to determine the significance of these relationships. Regression
analyses for abundance, density and biomass were conducted to estimate population
composition and species interactions. Finally, a stepwise multiple regression model was
used to predict abundance and distribution based on specific morphological features.
Initial graphical analysis of the data indicated that almost all pools were
comparable in size and in shrimp abundance. One pool, however, (Pool Zero) was at
least 5 times larger that the other pools and had a noticeable difference in shrimp
densities. Therefore, this pool was excluded from the analysis reported below. This
analysis only pertains to headwater pools less than 20m2 in area.
10
Results
Pool morphology and shrimp population surveys along the study reach showed a
range of habitat availability and preference for each of the three species.
Table 2. Average pool morphology and shrimp abundances for pools smaller than 20m2 in Quebrada Prieta.
Measurement
Active channel width (m)
Pool area (m2)
Pool Volume(m3)
Avg. Depth (m)
% OM coverage
Shrimp per m3
Shrimp per m2
Atya per m3
Atya per m2
Xiphocaris per m3
Xiphocaris per m2
Macrobrachium per m3
Macrobrachium per m2
Average length of Atya (mm)
Average length of Xiphocaris (mm)
Average length of Macrobrachium (mm)
Dry biomass Atya (g/m2)
Dry biomass Xiphocaris (g/m2)
Average
6.69
4.24
1.02
0.22
33.67
182.46
35.84
81.92
15.82
99.61
19.82
0.93
0.20
16.67
14.09
36.27
9.75
4.83
STD
2.03
2.95
0.93
0.08
11.09
136.10
24.35
81.09
14.40
70.31
12.70
1.60
0.32
1.76
0.76
12.50
9.71
3.27
Max
13.50
13.20
4.60
0.57
64.00
635.29
123.86
355.53
69.32
292.22
54.55
6.81
1.30
20.40
17.30
67.10
43.63
13.67
Min
3.30
0.63
0.13
0.11
8.00
15.82
4.30
2.20
0.56
3.16
0.48
0.00
0.00
11.30
13.04
16.50
0.09
0.22
Geomorphological profile
Statistical analysis of the physical features measured showed that the average pool
within the reach has an area of 4.24m2 and a volume of 1.02m3, maximum pool depths
range from 0.19m to 1.04m, and the average width of the stream’s active channel is
6.69m. Pool substrate was predominantly composed of gravel (46%) and boulders (28%),
but cobble (17%) and sand (8%) were also found. Silt substrates (1%) were the least
abundant (fig. A1). On most cases, the pool bottom was covered by leaf litter (42%) and
other organic matter (10%). Water level variation for the entire survey was 0.085m.
11
The accumulation of leaf litter was associated with the channel width (PC = -0.32,
P<0.05). Various parameters were also related to the location of the pools. The presence
of boulders (PC = -0.55, P<0.01), as well as the average pool depth (PC = -0.54, P<0.01)
were distinctly linked to the elevation, which is related here to the distance upstream.
Atya lanipes
Slightly significant correlations were found between the distance upstream and the
number of individuals per pool area (PC = 0.48, P<0.01) and volume (PC = 0.61,
P<0.01). In addition, the number of individuals per pool volume was negatively
correlated with the percentage of boulder substrate in each pool (PC = - 0.45, P<0.01) and
the number of entrances (PC = -0.41, P<0.01). There also was a strong correlation
between number of Atya and number of Xiphocaris trapped in each pool (PC = 0.80,
P<0.01).
Xiphocaris elongata
A slightly significant positive correlation was also found for Xiphocaris between
the distance upstream and the amount of individuals per pool volume (PC = 0.57,
P<0.01). Similar results were found for the amount of biomass (PC = 0.38, P<0.05). A
negative correlation was found between average depth of the pools and individuals per
area (PC = -0.42, P<0.01). There was also a negative correlation between individuals per
volume and the percentage of boulder substrate (PC = - 0.50, P<0.01).
12
Macrobrachium
Considerably less individuals of Macrobrachium (48) were found than of Atya
(3,156) or Xiphocaris (4,257). Number of individuals per area (PC = -0.49, P<0.01) and
volume (PC = -0.43, P<0.01) were inversely related to the distance upstream. The
percentage of organic matter within the pools had a slightly significant correlation with
the number of Macrobrachiums per area (PC = 0.46, P<0.01) and volume (PC = 0.43,
P<0.01).
Table 3. Pearson correlation coefficients for shrimp abundance and pool area and volume for pools smaller
than 20 m2 in Quebrada Prieta.
Area
0.62**
0.62**
0.35**
0.65**
Atya
Xiphocaris
Macrobrachium
All shrimp species
Volume
0.47**
0.53**
0.44**
0.53**
**Correlation is significant at the 0.01 level or less
Table 4. Stepwise regression model results by species for shrimps in Quebrada Prieta.
Atya
R sq
0.538
Xiphocaris
0.570
Macrobrachium
0.380
All
0.562
Predictors
Area
Pool exits
gravel
Max width
Stdev depth
boulder
OM
Max width
Avg depth
Area
Pool exits
Stdev depth
Partial coefficients
0.650**
-0.265*
0.223*
0.348**
0.454**
-0.360*
-0.446**
0.396**
0.337**
0.598**
-0.355**
0.254*
*Correlation is significant at the 0.05 level or less
**Correlation is significant at the 0.01 level or less
13
14
15
16
17
25.00
average shrimp per m^2
20.00
15.00
10.00
5.00
0.00
atya
xiphocaris
macrobrachium
12.00
10.00
dry mass (g/ m^2)
8.00
6.00
4.00
2.00
0.00
atya
xiphocaris
Figure 6. Average number of individuals (a) and average dry mass weight (b) for shrimp species in
Quebrada Prieta.
18
Discussion
Shrimp abundance and distribution were related to geomorphological differences
among the pools. The surface area of a pool, rather than total pool volume, seems to be
the best predictor of Atya and Xiphocaris abundance. However, predictions of shrimp
abundance based on volume are slightly more significant for Xiphocaris than for Atya.
This is consistent with the observed decrease in Xiphocaris abundance in pools with low
average depths, and suggests that pools with greater volume provide more habitat space
for the swimming Xiphocaris to search for food and escape predators.
In contrast, Atya seem to be more sensitive to substrate composition than
Xiphocaris. This is reasonable since they stay on the pool bottom for long periods of
time feeding on sediment and scraping the rocks. They were also found to be most
abundant in small, shallow pools. This is not surprising considering that their most
efficient feeding mechanism is filtering; the morphology of these pools allows water to
run faster, enabling them to catch more food, with less energy expense.
The strong positive correlation between the abundances of Atya and Xiphocaris in
each pool suggests that these two species do not strongly compete for habitat or food
resources. While average number of Xiphocaris per pool was greater than the average
number of Atya, biomass calculations indicate that Atya is the dominant species in terms
of size (fig.6), and are more likely to have a greater effect on consumption rates and
nutrient cycles for this ecosystem. Similar processes throughout the watershed would be
expected to have a significant influence on lower elevation environments.
An extremely low abundance of the large Macrobrachium was found in this reach
compared to abundances of Atya and Xiphocaris. It is possible that territorialism among
19
adults of these species would result in a scattered population along the reach. Another
possibility is that the number of individuals sampled was not representative of their actual
density due to the small size of the entrance holes in the traps. Nevertheless, most
individuals were found in the lower elevation pools with abundant organic matter. A
similar study indicates that some species of Macrobrachium do prefer boulder substrates
(Iwata et al. 2003) and suggest that the amount of preferred microhabitat play an
important role in the distribution of these organisms.
A slight increase in shrimp density on the higher elevation pools and a decrease of
Atya and Xiphocaris at pools with greater boulder substrate could be linked to the
presence Macrobrachium hiding in crevices on these boulder lined, lower elevation
pools. Other physical parameters, such as number of pool exits and distance between
pools, did not have a significant influence in shrimp populations and distribution.
The results described above indicate that the geomorphological features of pools in
Quebrada Prieta influence the abundance of resident shrimp populations. The narrow
width of the stream channel prevents large amounts of direct sunlight from reaching the
stream; leaf litter from surrounding riparian vegetation becomes the main energy source,
and it is continuously replenished throughout the year. Primary production within the
pools is low, with food webs relying mainly on detritus.
Silt and sand accumulations at higher elevation pools can also be linked to physical
erosion processes and landslide events. Sediment yield, although not discussed here, is a
critical parameter in habitat characterization at zones downstream (Larsen, 1999). Still,
pool substrates on this reach were heterogeneous in composition and size.
20
Even though headwater streams are often characterized by low detritus retention
due to frequent flood events (Crowl et al., 2001), leaf and other organic matter quantities
(and subsequent microbial conditioning) are still significant enough to support the shrimp
population. Percentages of leaf cover and organic matter do not seem to have an effect on
the abundance nor the distribution of any of the species, suggesting that food availability
is more than sufficient to sustain the population.
These relationships are consistent for all pools sampled except Pool Zero. This pool
showed significant differences in volume as well as shrimp densities, it also presented
greater sand substrate composition than any other pool in the reach; but the reason for the
unique biotic characteristics of this pool could not be linked to any specific parameter.
An apparent trend was observed in the pools that are sampled on a continual basis
for LTER studies, where shrimp densities were particularly low (fig. 2). There is not
enough information at the moment to relate these lower densities to the trapping
practices. Further studies on these pools as well as analysis of the long-term data would
help understand whether this is in fact a behavioral pattern or it’s due to the limitations of
the sampling method used here.
Overall, hypotheses for this study were true, albeit some of the relationships were
not as strong as expected. Shrimp, at least at the community level, seem to cope better
than expected with the morphological variations, especially at high altitudes. This is
probably because of the abundant food supply characteristic of these habitats.
Furthermore, energy expended in reaching high elevation pool may be compensated by
an abundance of food supply.
21
Future work comparing population estimates with nutrient transport and
consumption rates, and sampling over a greater range of pool types in similar headwater
streams would greatly contribute to a better understanding of the interactions discussed
above. Nevertheless, the equations and relations presented here can be used to compare
shrimp abundances in similar environments in the Luquillo Mountains.
22
Figure 7. Rows of Atya lanipes filtering detritus from
flowing water at a pool mouth.
Photo: Katie Hein
Figure 8. Wire trap with bait.
Photo: Katie Hein
Figure 9. Rostral length measurement for Atya lanipes.
23
References
Covich, A.P., Crowl, T.A., Scatena, F.N. 2000. Linking habitat stability to floods and
droughts: effects on shrimp in montane streams, Puerto Rico. Verh. Internat.
Verein. Limnol. 27: 1-5.
Covich, A.P.; McDowell, W.H. 1996. The Stream community. In: Reagan, D.; Waide,
R.B. (eds.): The food web of a tropical rain forest. Chicago, IL. University of
Chicago Press.
Covich, A.P., Crowl, T.A., Johnson, S.L., Pyron, M. 1996. Distribution and abundance
of tropical freshwater shrimp along a stream corridor: Response to disturbance.
Biotropica, 28(4a): 484-492.
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26
Appendix
Figure A1. Morphological Profile of pools smaller than 20 m2 in Quebrada Prieta.
A1
A2
A3
Table A1. Pool morphology and shrimp population raw data.
A4
A5
A6
A7