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Defining the Dynamics and Restoration Potential of Seagrass Resources in Kachemak Bay, Alaska
Issue: Seagrasses are an essential habitat downstream of many coastal development pressures and are uniquely poised to act as a barometer of stressors and habitat quality
Communities
surrounding Kachemak Bay and the larger Cook Inlet are growing rapidly,
increasing the exploitation of marine and terrestrial resources. This
is making it critically important to collect baseline evaluations
of seagrass resources in Kachemak Bay prior to large effects of these
anthropogenic changes. The effects of such anthropogenic
influences on seagrass communities have been documented elsewhere. Their
effects on high latitude seagrass beds that experience large tidal amplitudes
(5 meters) remain largely unstudied. As global climate continues
to warm, sub–Arctic environments may be an early indicator area for effects
on seagrasses. As glacial input to Alaskan waters declines
with warming, significant new territory may become available to eelgrass
as water clarity increases in areas near retreating glaciers. Given its
current relative pristine condition in lieu of growing pressures
of coastal development, Kachemak Bay, including the Kachemak
Bay National Estuarine Research Reserve (NERR), is an ideal study
site to examine the effects from expanding coastal exploitation and global
warming.
Objectives:
- Describe the extent of the large, existing eelgrass (Zostera marina) resources in and around the NERR,
- Identify its spatial and temporal variation, and
- Build predictive models of eelgrass occurrence and change.
Once we are able to define and model the seagrass ecology within the NERR and
adjacent environments, we will
- Translate them into a forecast of restoration potential and
- Predict seagrass responses to global climate change and local scale environmental influences.
Approach:
We collected eelgrass shoot densities and noted vegetative states from
transects run across tidal gradients in seagrass beds throughout Kachemak
Bay. In–depth examination of eelgrass rhizome internodes and leaf lengths
provided detailed information on the seasonal growth as it varied by
site and elevation. To further classify eelgrass growth rates and substrate
colonization, plastochrone intervals (a way of measuring the age of a plant by morphological traits rather than chronological) were determined at select sites
during peak light period (June, +20hrs per day) and waning light period
(August, <10hrs per day). Aerial photography was flown and is being
classified to more comprehensively map the extent and complexity of eelgrass
beds within Kachemak Bay and Port Graham.
Outcome:
We are in the process of completing our sample analysis. Preliminary
results show a strong variation of eelgrass growth by tidal elevation.
Plant growth and health appears to be stabilized with depth, thus reducing
the period of dormancy during dark winter months. Understanding the variation
within sites and among sites is important when formulating an effective
method of restoration. Classification of aerial photography is currently
underway. Our goal is to overlay our eelgrass distribution and production
information with aerial imagery to produce a publicly available, georeferenced
digital map of eelgrass resources in Kachemak Bay and adjoining areas.