Louisiana Natural Communities: Intertidal Shell Beach Bar

This post is a continuation of the Louisiana Natural Communities series mention in this post and this introduction to the series post.

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

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.

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.

Fiddler Crabs (Uca sp.) were encountered on the shell 

beach for the first time. Later, we would also observe 

them on the cheniers.

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.

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.