Inventory and Monitoring at Padre Island National Seashore

hummingbird visits Ipomoea pes-caprae
Ruby-throated hummingbird visits Ipomoea pes-caprae at Padre Island National Seashore

Chris Adams

Overview

Padre Island National Seashore was established in 1962, and consists of approximately 130,000 acres of land and water. At 70 miles, it is the longest stretch of undeveloped barrier island in the world, and ranges in width from 0.5 to 3 miles. The authorized boundary of the seashore includes not only the barrier island itself, but also portions of the Gulf of Mexico and the Laguna Madre. The Laguna Madre extends the whole length of the South Texas coast, from Corpus Christi Bay to the Mexican border. It is 200 kilometers long and is one of the few hypersaline lagoon systems in the world. The Laguna Madre supports 75% of Texas’s seagrass meadows, which are some of the most productive estuarine systems as well as valuable nursery areas for a variety of wildlife. Due to the pressure from growing development along coastal Texas, the habitat in the park has become an increasingly important resource for many resident and migrating species.

view of the upper laguna madre with water and seagrass beds in the foreground and storm clouds in the distance
Upper Laguna Madre of Padre Island National Seashore with seagrass meadows in the foreground and a storm approaching

Joe Meiman/NPS

Ecosystems at Padre Island National Seashore

There are a number of aquatic and terrestrial ecosystems in this park, although the bulk of the land area falls into one of three categories:

  1. Coastal and near-shore-marine ecosystems, including beaches and dunes, tidal marshes and flats, and seagrass meadows
  2. Grasslands, and
  3. Freshwater wetlands and freshwater aquatic ecosystems


Beginning on the Gulf side and going west to the Gulf Intracoastal Waterway, the park includes the nearshore waters, the beach foreshore (swash zone), the beach backshore (from high-tide line to dunes), foredunes, vegetated grassland flats (dominated by seacoast bluestem [Schizachyrium littorale] and gulfdune paspalum [Paspalum monostachyum]) with some shallow fresh- or brackish-waterbodies, occasional back-island dunes, wind-tidal flats (including algal flats of Lyngbya confervoides), and shallow, hypersaline seagrass beds in the lagoon. The interplay of climate, physiography, and geomorphology results in a landscape that is largely shaped by wind.

Very little surface freshwater is available from terrestrial sources adjacent to the Laguna Madre or on Padre Island. On Padre Island, freshwater sources are limited and generally confined to ponds that form in swales and depressions in the vegetated flats. These ponds are an extremely important source of both drinking water and food for many terrestrial vertebrates and birds. However, most are ephemeral, and many become brackish or dry up, particularly during dry periods.

two field researchers standing in a grassland, reviewing notes and entering data into a handheld device
Field crew in grassland at Padre Island collecting data for vegetation mapping

NPS/GULN

view from above: a field crew member standing in the water and using a sieve to collect data on seagrass
A member of the field crew using a sieve to collect data on seagrass and its related environmental covariates.

GULN NPS

Vital Signs Monitored at Padre Island NS

The Gulf Coast Network monitors five indictors of ecological health --called vital signs-- at this park. They are
Percent cover of seagrass species Halodule wrightii (shoal grass) in monitoring plots from 2011 to 2016
Percent cover of seagrass species Halodule wrightii (shoal grass) in GULN monitoring plots in the Laguna Madre from 2011-2016.  The animation shows that percent cover (0-100%) can fluctuate widely from year to year and among plots.  There is also an overall decline in cover over the pilot period.

A Closer Look at a Selected Vital Sign: Seagrass Monitoring

To monitor seagrass at Padre Island NS, a field crew measures percent cover of all seagrass species in 0.25 x .25 meter plots. The crew also collects data on water depth, salinity, turbidity, as well as other water quality measures. During the pilot phase, the network documented striking plot-to-plot variation in coverage of the dominant seagrass species, shoal grass, within the Laguna Madre, as well as extreme change in individual plots over time. The average across plots from 2011-2016 was 74%, 89%, 81%, 59%, 60%, and 53%, respectively. Given the pilot study's short duration, it is unclear whether this apparent decline is simply random fluctuation, cyclical change or a lasting loss in seagrass coverage for the park.

Changes in seagrass coverage during the project's pilot phase may be indirectly linked to a severe drought in mainland Texas in 2012 and 2013, although many more years of data are essential for unravelling any apparent trends.

Salicornia bigelovii with sea lavender and seablite
Dwarf saltwort (Salicornia bigelovii) with fall colors growing with sea lavender (Limonium carolinianum) and seablite (Suaeda linearis). This saltwort species can be distinguished from its relatives by the sharp tips, rather than rounded tips, on the scales of the stem.

Jane Carlson/NPS

Last updated: May 9, 2018