[Back to Meeting 2005]

To Everything There is a Season...
Life in Temporary Aquatic Habitats


Symposium organized by Marie Simovich, University of San Diego; Judith Williams, University of Southern Mississippi on the Gulf Coast and Andrew Bohonak, San Diego State University

[Click on start button to animate; right click on animation for controls]

Ephemeral pools and other temporary wetlands are common worldwide. Ephemeral pools can range in size from small rock basins holding no more than 1-2 liters to large vernal lakes covering hundreds of hectares. They occur at high elevations, below sea level, on bedrock, and on well-developed soils. Depending on climatic patterns, ephemeral pools may have a single annual wet phase, or fill and dry many times each year. Many pools are heterotrophic, depending on detritus for much of their energy input rather than direct photosynthetic production. However, in areas such as the southwestern United States, considerable primary production may be attributed to phytoplankton or seasonally inundated vascular plants.

A diverse array of ephemeral wetlands are distributed across a similarly diverse range of upland habitats. These range from desert playas to wet mountain meadows, and from vernal pools to Carolina Bays. The uniting feature is that all ephemeral wetlands are inherently bi-phasic, with a terrestrial phase in the dry season followed by an aquatic phase driven by rain or snowmelt.

Ephemeral pools typically hold water for only a few days to a few months, yet the evolutionary age of many species inhabiting them suggest that these habitats are quite ancient. For example, fossils of Triops (Crustacea) tadpole shrimps have been found in Cambrian fossil rocks, and the living species Triops cancriformis can be found in the lower Triassic.

Because ephemeral pools form under a variety of climatic regimes, environmental conditions in pools can vary considerably. Some Mediterranean climate pools facilitate relatively cool, long-lasting environments, while short-lived, warm water pools can be found in summer monsoonal climates. Even in arid climates, ephemeral pools can range in hydroperiod from weeks to months. Desert playas contain closed basins that fill and dry slowly, where a long history of mineral accumulation exerts a major influence on pond biogeochemistry. Predictability of inundation also varies considerably across climatic patterns, substrates, and geologic/geomorphic history. It is clear that organisms inhabiting each pool type must be well adapted to persist across the entire distribution of pool inundation lengths.

The unique conditions found in ephemeral wetlands have resulted in the evolution of an exceptional array of plants and animals. Crustaceans in these wetlands have been particularly well studied. Crustacean communities in temporary pools can be extremely diverse, often more so than in comparable permanent waters. Many species are narrowly endemic and exhibit a high degree of genetic structure, presumably due to the patchy nature of the habitat, abiotic habitat differences and restricted gene flow. Recent research efforts have focused on the unique adaptations that allow these species to avoid or tolerate two extremely different sets of environmental conditions as pools fill and dry.

Crustaceans in both ephemeral and permanent waters have developed survival strategies to cope with variable environments. This variability may be driven by annual cycles of drying, freezing, overcrowding or predation. Most species with terrestrial mobility (such as insects) will leave a wetland during its dry phase. In contrast, crustaceans, rotifers and many other invertebrate taxa possess a dormant stage that can withstand the adverse environmental conditions.

Despite the wide range of environmental conditions found in ephemeral pools globally, some "universal" patterns in macroinvertebrate community structuring are apparent. Pool inhabitants are either aquatic opportunists (occupying both temporary and permanent waters), or specialists with precise adaptations for living in temporary aquatic environments. Ostracods are probably the most ubiquitous group in ephemeral pools, and small planktonic crustaceans including Copepods (click on photo) and Cladocera may be present as well. Branchiopods (Click on photo) are one of the quintessential ephemeral pool groups, limited almost entirely to temporary bodies of water. Up to eight species of branchiopods spanning three orders have been found in a single pool. Copepods too can have numerous species within the same temporary pond. Typically, one or more large branchiopod crustacean species (fairy shrimp, tadpole shrimp or clam shrimp) may be present. Of these, fairy shrimp are the most common in the majority of areas. Aquatic insects can be represented by many orders, depending on pool longevity, proximity to permanent water, and abundance of other invertebrates for prey. Insect taxa include diving beetles, backswimmers, water boatmen, and a variety of midges and other flies.

Seasonal precipitation patterns and temperature regimes, the predictability of precipitation (intra- and inter-annual variation), chemical and physical properties of the substrate, and the presence of overland flow all affect the temporary pool environment. Unlike permanent bodies of water, ephemeral wetlands posses little capacity to dampen out climatic or geochemical fluctuations. For example, the survival of aquatic species through extended droughts is not facilitated by water storage in years with high precipitation. Dramatic changes to filling and drying patterns (driven, for example, by long-term climate changes) will likely result in a different habitat, and significant changes in community and ecosystem properties.

Wetlands are disappearing globally at an alarming rate. Due to a terrestrial phase that can last months (or years, during times of low precipitation), ephemeral wetlands are particularly vulnerable to agricultural and other types of development. In California, it is estimated that 80% of vernal pool wetlands have been lost, and loss estimates for San Diego County (site of the 2005 SICB meetings) are a staggering 97%. These habitats are inhabited by an abundance of endemic plants and animals, many of which are undescribed species. As a result of habitat loss, many of these organisms are endangered or threatened. Because the loss of more species is a nearly inevitable consequence of population growth, it is imperative that we learn more about these organisms as quickly as possible.

Below are a series of scanning electron micrographs of Branchiopod diapause eggs, primarily from African ephemeral pools. (Compliments of Dr. Luc Brendonck).

Jan. 8, 2005

8:40 am Welcome, Introduction to Symposium, Announcements - Marie Simovich, University of San Diego
9:00 amWhy are there so many species of calanoid copepods in southeastern temporary ponds? Barbara Taylor, Savanna River Ecology Lab, Univ. of Georgia
9:20 am Spatial and temporal genetic structure in an endangered anostracan. Andrew Bohonak, San Diego State University
9:40 amPopulation genetic structure of large branchiopod crustaceans inhabiting temporary ponds in Florida. Trisha Spears, Florida State University
10:00 am Coffee Break
10:20 am Magnitude of environmental variation and mechanisms of hatching in ephemeral pool crustaceans. Bonnie Ripley, Andrew Bohanak and Marie Simovich, USD
10:40 amThe average shrimp versus the average plant: addressing spatial and temporal unpredictability with ephemeral pool crustaceans. Tom Philippi, Florida International University
11:00 amEffect of methyl farnesoate on reproduction in the tadpole shrimp, Triops longicaudatus. Brian Tsukimura, California State University, Fresno
11:20 amWhat determines lipid content in copepods preparing for long-term dormancy? Judith Williams, University of Southern Miss Gulf Coast
12:00 Noon Board tram for lunch reception and tour at USD's new Shiley Center for Science and Technology

*Anyone that would like to donate money for student travel and registration should contact Dr. Marie Simovich, University of San Diego. All donors will receive a ticket for lunch, a tour of USD's Shiley Center for Science and Technology and grateful acknowledgements in the poster (and on line) at the SICB meeting.
There is a fee for lunch and tour of the facilities of $12.00. This can be paid directly to Dr. Simovich the first day of the meeting or at the Symposium. Please let Dr. Simovich or Williams know that you are attending the lunch and tour.

We would like to thank any and all individuals and groups that have already donated money for student travel.

A special thanks to our contributors who have provided money for the luncheon and session: The Crustacean Society, The Vernal Pool Society and the BRG Environmental Co.

We ask all individuals that are interested in ephemeral water crustacean and diapause to submit a poster presentation at the meetings and provide us with your name and poster number. We will try to have a special section of posters devoted to this area of research.

The text and photos used in this web design were taken from a variety of sources: particular thanks is given to Marie Simovich, Diolinda Parsick, Judith Williams, Luc Brendonck, Tim Graham, Brian Tsukimura, Andy Bohonak, who provided one or both of the media used in this. Web page designed by Judith Williams.