WEEK 1 OVERVIEW
During our first week we visit the coastal marshes of
the Southern West Gulf Coastal Plain, an environment defined by the fluctuating
extremes of tide, fire, wind and weather. These communities belong to the
Texas-Louisiana Coastal Marshes subregion of the Western Gulf Coastal Plains and take the brunt of our subtropical storms coming up the Gulf of Mexico. Historically, Shell Beach Bars were the bastions of a dynamic interior mosaic of salt, brackish and freshwater marshes inscribed with streams. Defined by cycles of erosion and
deposition and experience frequent disturbance, the coast is in a constant tug of war between land and sea. The animals and plants that live here are tough, resilient
Intertidal Shell Beach Bar
Locations:
Unnamed
Shell Beach, Rockefeller Wildlife Refuge, Cameron Parish, LA
Rutherford Beech,
Cameron Parish, LA Coordinates: N 29.759278, S 93.124544 |
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Shell
beaches are dynamic systems. Historically
erosion and heavy deposition
cycles built these communities
out towards the Gulf, later to become Cheniers.
These communities are currently receding
into salt marshes
due to lack of deposition from levied alluvial systems
all
along the coast, especially the Mississippi.
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Intertidal Shell Beach Bar is defined by very recent mineral deposits of shell "hash", debris. Underlying this layer of shell fragments are mucky clay-silt
mineral deposits (at app. 10cm depth) on top of Pleistocene terrace. This terrace is built of sediments much older an more firm than those found in the delta regions surrounding the Mississippi and thus erodes more slowly and slightly more stable. Still this community
is part of a dynamic cycle of deposition and erosion that is typical of all of our coastal environments.
During the erosion phase, marsh is eroded and shell materials are re-deposited
further back along the shore. During the deposition phase, East-to-West long
shore currents carry sediment from eastern plumes delivered by the Mississippi and other outlets, building marsh in front of the shell beach. The relatively large sediment sizes of shell
provide a substrate that is well-drained and thus dry during periods of low
tide, lending itself to low growing, salt tolerant and often succulent plant
communities. Light is abundant. High energy input from coastal winds and storms
as well as particle size of shell hash greatly limits the vertical structure of
the shell beach and the formation of steep dunes.
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Fiddler
Crabs (Uca sp.) were encountered on the shell
beach for the first time. Later,
we would also observe
them on the cheniers.
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We visited this community on May 15, 2013 at an unnamed shell beach which we traveled to by fleet of airboats provided by LDWF staff and then again at
Rutherford Beech (May 16, 2013) with Ceclia Richmond. Dominant vegetation observed include Marsh
Elder (Iva frutescens), Sea Ox-Eye
Daisy (Borrichia frutescens), Seaside
Heliotrope (Heliotropium currasivicum)
and Camphor Daisy (Rayjacksonia
phyllocephala). Some plants typical of highly disturbed environments were
also present, including Poor Man’s Pepper (Lepidium
virginicum), Cuman’s Ragweed (Ambrosia
psilostachya), and Medick (Medicago
sp.). A portion of the beach included a small salt flat fringed with
Saltworts (Batis maritima) and a
tidal pool with some Widgeon Grass (Ruppia
maritima). Invertebrates included Fiddler Crabs (Uca sp.) were observed in the wrack line. Near the shelter of the
vegetation Seaside Dragonlets (Erythrodiplax
berenice), one of our only brackish-saltwater dragonflies, were common. Avifauna observed at this site was Laughing Gulls, nesting
Least Terns (Sterna antillarum), Brown
Pelicans (Pelecanus occidentalis) and
Ruddy Turnstones (Arenaria interpres).
Another species observed as flyover at this site and nowhere else on our
coastal trip was the Whimbrel (Numenus
phaeopus), though this species is most likely be attributed to the nearby
saltmarsh.
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Camphor
Daisy (Rayjacksonia phyllocephala)
was first
encountered on the shell beach with LDWF biologist Will Selman. This
plant, common
to well-drained coastal shell and sand
beaches has remarkably fragrant leaves,
thus “camphor”.
Such secondary compounds are byproduct of the harsh
environment
and can be observed in other coastal plants.
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