What it all means

Conceptual synthesis diagram that was compiled from the information obtained in the CART trees.

In the downstream, brackish to saline areas of the river deltas sampled, Halodule wrightii was found in sandier sediments along marine coastlines, with Spartina alterniflora the dominant fringing emergent marsh species. Ruppia maritima often co-occurred with H. wrightii, but was also found by itself in lower salinity waters further from the coastline, and those sites had sediments that tended to be more organic matter rich, with shorelines that also had lower energy exposure (protected from wave fetch, or slower currents); often these conditions tended to be found in side channels from the main river channel and often with saline or brackish marsh fringing emergent plants such as Spartina alterniflora or Juncus roemerianus. H. wrightii tended to be more abundant in the eastern sample sites, primarily Grand Bay, whereas R. maritima was pervasive across all five river systems sampled. Vallisneria americana was sometimes found in areas that were expected to be dominated by the two SAVa species (e.g., Mobile Bay).

Vallisneria americana was the major species that dominated the SAVb grouping. The co-dominant species found alongside V. americana differed, however, with Mississippi sites, including the lower Pearl River, St. Louis Bay, Biloxi Back Bay, and Pascagoula River having more “delicate” species such as Najas spp, Zannichellia spp, and Potamogeton pusillus. The habitats where these communities occurred had sediments that tended to be organic matter rich, in narrower and more branched and protected side channels with low energy exposure to either currents or waves. The shoreline at these locations was dominated by emergent brackish to freshwater marsh plants including J. roemerianus, Schoenoplectus tabernaemontani (syn. Scirpus validus), Zizania aquatica, Sagittaria lancifolia, and Cladium jamaicense. In contrast, the V. americana dominated sites in Mobile Bay to the east tended to have Myriophyllum spicatum as the co-dominant SAV species, and habitat that was characterized by sandier sediments and more open coastlines with higher wave energy. (Suggests the delicate spp may be excluded due to energy?). Emergent shoreline vegetation found in the Mobile Bay sites was dominated by Phragmites australis.

The SAVc group had the highest diversity with 14 species (66% of the total), and continued the spatial trend established by the SAVb group, with western sites tending to have different species than eastern sites. Green algae like Chara and Nitella, along with submerged species like Eleocharis spp and Ceratophyllum demersum were found occasionally in association with V. americana in the freshwater upper reaches of the river delta, where habitats had muddy sediments, narrow stream widths, with the shoreline dominated by emergent marsh plants like C. jamaicense or wooded banks with Taxodium distichum. In the eastern sites, particularly Mobile Bay, floating leaved plants like Nuphar luteum were more common in the freshwater reaches of the river delta, where open lagoonal habitats were fringed by a high diversity of emergent plant species such as Orontium sp., Saururus sp., Calstygia sapium, Osmunda regalis, Cephalanthus sp., Anthemis sp., Hibiscus sp., Campsis radicans, Serenoa repens, and Ptillium sp.