Cameron Kmetzsch and Professor Russell B Rader, Integrative Biology
Rock pools are one of the most unique and threatened aquatic habitats in the world. Changes in global climate could alter precipitation patterns and disrupt the annual cycle of filling and drying to which this community has evolved. Previous misconceptions assume that all rock pools are temporary habitats. Over a period of two years we have shown that at least 20 pools in three drainages have maintained constant wetted conditions with moderate seasonal fluctuations in water levels, despite air temperatures near 50º C (120º F) on the open hardpan. These “permanent” pools (Tinajas) are shaded within deeply incised channels. Tinajas are cut into the sandstone bedrock by torrential flows during summertime cloudbursts. Our study site was located six miles northwest of Moab, Utah, near the Canyonlands Airport. This area is on a slight slope, which has produced three separate and secluded drainages each with hardpan pools and pools within Tinajas. There are also many temporary pools located on the sandstone hardpan between channels in a drainage. (See Figure 1)
Metacommunities are a group of communities sufficiently close across geographical space to allow for some degree of dispersal between communities. In this case, individual rock pools are our individual communities. The objectives of our study were to first to study and identify the species within this metacommunity and then to test the following hypotheses: 1) summer monsoons will scour the Tinajas, but re-fill/rejuvenate the hardpan rock pools, and 2) invertebrates inhabiting scoured pools will disperse in a general upstream direction during re-colonization (Müller’s Re-colonization hypothesis 1982, Oecologia 52: 202-207).
In order to identify the species in this community we needed to sample species from each part of the water column. We used a core sampler (5.0 cm2) to collect benthic samples in the sandy substrate. Plankton samples were collected by filtering 1 liter of water through a 63 µm sieve. Nekton or the top of the water column was collected with a standard sweep net with 1 mm mesh. Each sample was placed in a Whirl Pack and then filled with ethanol to preserve the sample. Samples were collected in July 2006, October 2006, May 2007, July 2007 and October 2007. Each sample was sorted under the microscope and each taxa was identified to the lowest feasible level. (See Table 1)
In order to measure the dispersal of the flying taxa we developed a sticky trap. The trap was 3ft wide and 2.5ft tall. The trap was wrapped in shrink wrap and then coated with Tangle Foot, a sticky insect spray. We positioned 25 sticky traps across drainage #2 during July and October 2006. These were directional traps indicating the number of organisms flying upstream, downstream, and left or right across the drainage. We found that there is a significant movement of taxa in the upstream direction consistent with our hypothesis. (See Figure 2)
During the October 2006 trip we were fortunate enough to witness a scouring event in which all of the rock pools, permanent and temporary were scoured out. We discovered that after scouring events almost all of the species in a rock pool are displaced leaving the rock pool virtually empty of life.
Long term rainfall and temperature records were obtained from the weather station at Canyonlands Airport approximately 1 mile from our study site. By examining rain events for the last ten years, we found that temporary pools are filled, on average, 7.4 times a year. Interestingly, we also found that there are approximately 1.5 rain events per year that completely scour all species from the permanent pools.
Climate models project an increase in both summer precipitation and summer temperatures on the Colorado Plateau as a result of global warming. An increase in precipitation will increase the frequency of flash-floods and rates of disturbance. Because of their devastating effects, an increase in the frequency of flooding may compromise the ability of this community to recover. This unusual assemblage of organisms found in rock pools across the Colorado Plateau may be unable to persist as global temperatures increase.
This research was presented at the Desert Fishes Council meetings in Nov 2006 and received the Best Student Poster Award.