By Holly Mehl
In November, I laid out the classification hierarchy – the planning regions and assessment units – used by MoRAP and our environmental assessment staff to identify areas on which to focus conservation efforts in aquatic ecosystems of Missouri (download here). I explained how the Missouri analysis defined these areas at a more refined geographic scale (smaller areas) than for our other three states due to better data availability. In the end, separate conservation plans were completed for Missouri’s 17 Ecological Drainage Units (EDUs) within which 158 Conservation Focus Areas were identified. Our modeling showed these areas represent the broad diversity of stream ecosystems and riverine assemblages of species that exist within the state. To give an exciting example, if each of the 158 areas were adequately protected, 95-100% of targeted species within the state would be protected as well. Collectively, these areas represent occurrences of all native fish, mussel, and crayfish species in Missouri. This is very important when you consider that Missouri is home to numerous species that live nowhere else (see pictures below).
Without going into too much detail, for this blog I’ll talk specifically about what we were attempting to achieve with each component of our conservation strategy:
First, we wanted a separate conservation plan for each Ecological Drainage Unit (EDU). Learn more about EDU’s from Missouri Department of Conservation here. Endeavoring to conserve all EDUs is a holistic ecosystem approach to conservation since each one represents an interacting biophysical system and also because no single EDU contains the full range of species found within the state. Second, we wanted to represent two separate occurrences or populations of each target species within each EDU. Redundancy in the account of species that together determine each EDU’s distinct biological composition provides a safeguard for their long term persistence. Our next objective was to conserve an individual example of each Aquatic Ecological System Type (AES-Type) within each EDU. This helps ensure the wide spectrum of the diversity of distinct watershed types within each EDU are accounted for, including the varying successional patterns within ecosystems and dispersal capabilities of different species.
With each type of AES represented in our conservation strategy, and therefore hopefully protected, we next wanted at least one kilometer of the dominant Valley Segment Types (VSTs) for each size class (headwater, creek, small river, and large river) to be represented as an interconnected complex within each selected AES. The assumption here is that environmental conditions will be represented to which species have evolved adaptations for maximizing growth, reproduction and survival. It also represents a wide spectrum of the diversity of stream types within each EDU since the dominant stream types vary among AES-Types. Further, it accounts for source-sink dynamics which is science of how variation in habitat quality may affect the population growth or decline of organisms. Attempting to conserve an interconnected complex of dominant VSTs accounts for seasonal changes in habitat brought on by disturbances like droughts or floods. For example, a headwater species during a prolonged drought may have to seek refuge in larger streams in order to find suitable habitat.
Darters, crayfish, and mussels have limited dispersal capabilities; they cannot move long distances. We decided that three separate headwater VSTs should be represented within each Conservation Focus Area. Including multiple headwater segments should account for multiple distinct spatial occurrences of headwater species as well as preserve several high-quality examples of key nursery habitats.
Lastly, many species require multiple habitats for foraging, reproducing, over-wintering, or for disturbance avoidance. We wanted to conserve at least a one kilometer of each priority VST and ensure connectivity of a wide spectrum of diverse habitats (riffles, pools, runs, and backwaters) so that critters could reach their choice habitat.
My next blog entry in this series will cover the main steps we took to meet these objectives. Stay tuned for that one.
About the Author: Holly Mehl is an ecologist for EPA Region 7 who helps with water monitoring in the field and performs mapping for EPA Region 7’s program offices when in the office.