details
on research interests
Current
work emphasizes experimental investigations of the mechanisms
of intertidal zonation. My collaborators and I (Robles and Desharnais
2002, Donalson et al. 2004) proposed that the lower boundary
of a mussel bed falls at a shore level corresponding to an abrupt
shift in equilibria -- from an equilibrium maintaining a sparse
population of small individuals below to a second maintaining
a dense population of larger individuals above. The equilibria
are a dynamic balance between rates of size-dependant predation
and prey production (recruitment and growth). The shift from
one equilibrium to another is "forced" by spatial
variation in tidal submergence and wave energy, and as a result
prey population structure (boundaries and size structure) varies
greatly over large spatial scales in the intertidal landscape.
This "adjusted equilibrium hypothesis" was expressed
in a cellular automaton (computer simulation model) which allows
us to consider other spatially structured mechanisms, such as
the shielding of smaller, vulnerable mussels by a phalanx of
larger mussels. The model stands as an alternative to the widely-held
"refuge theory", which maintains that dense zones
of invertebrate prey form only on shore levels above the effective
foraging range of the predators.
My on-going projects are field studies that address either the
testing or further development (parameterization) of spatially
explicit population models. The projects are listed below.
C.
Robles, C. Garza (Dr. Garza is my former student) and R. Desharnais.
Experimental test of prey regulation in the Mytilus-Pisaster
system. While both the long established verbal theory and the
adjusted equilibrium hypothesis predict that sea star removal
will incur downward extension of a mussel bed, the latter uniquely
predicts upward recession of the boundary following experimental
augmentation of the sea stars population. It also predicts relative
rates of boundary movement and certain changes in boundary intensity
(sharp or "fuzzy"). My research group is testing the
predictions in Barkley Sound, British Columbia. Topographically
isolated mussel beds 20 to 40 meters long each receive one of
three treatments: seas stars removed, sea stars added, and control.
Six replicates comprising 18 sites have been set up over a 12
km2 area of the Sound. Changes in the detailed spatial patterns
of the beds are captured with a photo mosaic technique developed
in my lab (see below). The work should provide a critical test
of benthic population regulation and pattern formation that
is unprecedented in its detail and scale.
C.
Robles and J. Shima. Sea star foraging in intertidal landscapes:
agents in spatially structured dynamics. This monograph in progress
describes eighteen years of surveys of the population structures
of Pisaster and Mytilus in Barkley Sound. The surveys include
studies of sea star growth and movement in landscapes with different
prey distributions and abundances. I developed a technique of
tagging the mussels with Passive Internal Transponders, which
allows one to follow individual sea stars. Examining sea star
responses to changing prey abundances suggests that sea stars
are capable of effecting stabilizing regulation of their prey,
a central premise of the adjusted equilibria hypothesis.
C.
Robles, R. Desharnais and C. Garza. Photo mosaic studies of
mussel bed pattern: observational tests of the adjusted equilibria
hypothesis. The cellular automaton (Robles and Desharnais 2002)
makes explicit predictions about the location and intensity
of prey boundaries in the intertidal landscape. These aspects
of pattern cannot be easily analyzed with tradition quadrat
sampling techniques. My research group (Blakeway et al. 2004)
developed a method for quickly capturing photo mosaics, which
are overhead views of mussel coverage hundreds of square meters
in extent, yet with a resolution in millimeters. Spatial statistics
describing the location and intensity of boundaries are compared
between the mosaics and schematic maps of mussel bed structure
output by the models. Fieldwork for this project is complete,
and data analysis is in progress.
C.
Robles, B. Chesney (former student) P. Moya (former student)
and C. Hernandez (former student). Settlement patterns of Mytilus
spp. in intertidal landscapes. My research group is amassing
a GIS database for the mussel bed problem. Layers in the database
include a site's topography, wave velocity surfaces drawn from
dense arrays of wave dynamometers, mussel bed distribution and
size structure, and mussel settlement rates (primary and secondary).
A comparison among the layers suggests hypotheses about the
adaptive significance of differences in settlement among Mytilus
spp over the wave exposure gradient. The data are also used
to parameterize the simulation models.
K.
Connor (current masters student) and C. Robles. Differential
shell growth of the mussel Mytilus californianus in tidal and
wave exposure gradients. This study uses epiflourescent microscopy
and Calcein dye administered in situ to measure spatial variation
in shell growth. Surprisingly, there are no longitudinal studies
of growth of individual M. californianus across the complete
ranges tidal and wave exposures. Prior studies looked at changes
in mean cohort size or did not include the complete range of
environmental variation. Data will be used for model parameterization.
top
selected
publications
Intertidal
Insects :
Robles,
C. 1984. Coincidence of agonistic larval behavior, uniform dispersion,
and unusual pupa morphology in a genus of marine midge (Chironomidae).
Journal of Natural History (London). 18:897-904. Download
PDF
Robles,
C. 1982. Disturbance and predation in an assemblage of herbivorous
diptera and algae on rocky shores. Oecologia 54:23-31. This
work was featured in the zoological classic Between Pacific
Tides, E.F. Ricketts and J. Calvin, pages 463-465, Fifth Edition,
1988, Stanford University Press, Palo Alto. Download
PDF
Robles,
C.D. and J.D. Cubit. 1981. Influence of biotic factors in an
upper intertidal community: effects of grazing diptera on algae.
Ecology 62:1536-1547. Download
PDF
The
Mytilus-Pisaster Interaction:
Robles,
C. D. and R. A. Desharnais. 2002. History and current development
of a paradigm of predation in rocky intertidal communities.
Special Feature Article, Ecology 82:1521-1536. Download
PDF
Robles,
C., R. Sherwood-Stephens and M. Alvarado. 1995. Responses of
a key intertidal predator to varying recruitment of its prey.
Ecology 76:565-579. Download
PDF
Spiny
Lobsters in the Intertidal Zone:
Robles,
C, D. 2007. Lobsters. In: Encyclopedia of Tide Pools and Rocky
Shores. M.W. Denny and S.D. Gaines (eds), University of California
Press, Berkeley. Pages 333-335. Download
PDF
Robles,
C. D., M. A. Alvarado, and R. A. Desharnais. 2001. The shifting
balance of littoral predator-prey interactions in regimes of
hydrodynamic stress. Oecologia 128:142-152. Download
PDF
Robles,
C., 1997. Changing recruitment in constant species assemblages:
implications for predation theory in intertidal communities.
Ecology 78: 1400-1414. This work is featured in a marine biology
textbook, an instructional CD, and an interactive exhibit in
the new ecology wing of the California Science Center, now under
construction in Exposition Park, CA. Download
PDF
Robles,
C, 1996. Turf battles in the tidal zone. Natural History 105:24-27.
Download
PDF
Robles,
C. and J. Robb. 1993. Varied carnivore effects and the prevalence
of intertidal algal turfs. Journal of Experimental Marine Biology
and Ecology 166:65-91. Download
PDF
Dittman,
D. E. and C. Robles. 1991. Effect of algal epiphytes on the
Mussel Mytilus californianus (Conrad). Ecology 72:286-296.
Download
PDF
Robles,
C., D.A. Sweetnam and J. Eminike. 1990. Lobster predation on
mussels: shore-level differences in prey vulnerability and predator
preference. Ecology 71:1564-1577. Download
PDF
Robles,
C. 1987. Predator foraging characteristics and prey population
structure on a sheltered shore. Ecology 68:1502-1514.
Download
PDF
Modeling
and Methods:
Blakeway,
D., C.D. Robles, D. Fuentes, and H-L. Qiu. 2004. Spatially extensive,
high resolution images of rocky shore communities. Chapter 7
in "Handbook of Scaling in Aquatic Ecology: Measurement,
Analysis and Simulation," edited by P. Strutton and L.
Seuront. CRC Press. Pages 109-124. Download
PDF
Martel,
A., C. D. Robles, K. Bechenback and M. Smith. 1999. Distinguishing
early juveniles stages of Eastern Pacific mussels (Mytilus spp.)
using morphology and genomic DNA. Invertebrate Biology 118:149-164.
Download
PDF
Carlos
Robles, Ph.D.
Professor of Biology.JPG)
