Kim Withers

Shorebird Use of Coastal Wetland and Barrier Island Habitat in the Gulf of Mexico

The Gulf Coast contains some of the most important shorebird habitats in North America. This area encompasses a diverse mixture of estuarine and barrier island habitats with varying amounts of freshwater swamps and marshes, bottomland hardwood forests, and coastal prairie that has been largely altered for rice and crawfish production, temporary ponds, and river floodplain habitat. For the purposes of this review, discussion is confined to general patterns of shorebird abundance, distribution, and macro- and microhabitat use in natural coastal, estuarine, and barrier island habitats on the Gulf of Mexico Coast. The following geographic regions are considered: Northwestern Gulf (Rio Grande to Louisiana-Mississippi border), Northeastern Gulf (Mississippi to Florida Keys), and Mexico (Rio Grande to Cabo Catoche [Yucatan Strait]). Wintering and migrating shorebirds are most abundant along the Gulf Coast in Texas and Tamaulipas, particularly the Laguna Madre ecosystem. Other important areas are the Southwest Coast region of Florida and the area between Laguna Terminos and Puerto Progresso in Mexico. In general, relative abundances of shorebirds increase from north to south, and decrease south of the Tropic of Cancer (23° 27’ N). Based on bimonthly maximum counts within 5° latitudinal bands, the region between 25–30° N is used most heavily by wintering and spring migrating birds. Non-vegetated coastal wetland habitats associated with bays, inlets and lagoons, particularly tidal flats, and sandy beaches are the habitats that appear to be favored by wintering and migrating shorebirds. In general, these habitats tend to occur as habitat complexes that allow for movement between them in relation to tidal flooding of bay-shore habitats. This relationship is particularly important to Piping Plover and may be important to others. Although vegetated habitats are used by some species, they do not appear to attract large numbers of birds. This habitat is most widespread between the Texas-Louisiana border and the Florida Panhandle region, but it has not been studied extensively. Shorebird abundance and habitat use in this area need to be addressed.

Benthic microalgae serve as the major food resource for porcelain crabs (Petrolisthes spp.) in oyster reefs: Digestive track content and pigment evidence

Suspension-feeding porcelain crabs (Petrolisthes spp.) are often the most abundant decapod crustaceans in oyster reef habitat. Analysis of water column and subtidal algal biomass from three Texas estuaries suggests that planktonic food resources are insufficient for porcelain crab growth. Pigment composition of porcelain crab muscle and digestive track contents included the diatom pigment fucoxanthin and cyanobacterial pigment canthaxanthin with digestive track samples containing attached (adnate) benthic diatoms as well as benthic cyanobacteria not found in the water column. Feeding appendages on porcelain crabs include numerous cirri with serrated edges as well as fewer more brush-like longer units. Benthic food resources are in sufficient supply to support porcelain crab biomass.

Toxicity of Three Dispersants Alone and in Combination with Crude Oil on Blue Crab Callinectes sapidus Megalopae

Abstract During the Deepwater Horizon incident in 2010, ∼1.8 million gallons of Corexit® dispersants were approved for use directly onto the released oil. Callinectes sapidus (Blue Crab) megalopae are pelagic and, therefore, likely to be one of the first organisms exposed to spilled oil and applied dispersants in open-ocean and nearshore waters. In this study, we examined acute toxicity of Corexit 9500, Corexit 9527, and MicroBlaze® (a microbial surfactant) alone and in combination with crude oil. We adapted methods from the established 48-h copepod toxicological assay and exposed Blue Crab megalopae for 48 h to varying dosages of each treatment. Oil treated with dispersant was more toxic than either oil or dispersant alone (48-h LC50 = 29.8 mg/L vs. 55.9 mg/L and 37.5–59.1 mg/L, respectively), and MicroBlaze was essentially non-toxic (48-h LC50: 7643 mg/L). Corexit 9527 was more toxic than Corexit 9500 both in solutions with oil and alone (48-h LC50 = 37.5 mg/L vs. 51.8 mg/L and 59.1 mg/L, respectively). Exposure to these toxicants not only induced mortality at certain dosage levels, but life-stage transitioning also seemed to be effected. The decreased ability to metamorphose, however, was not affected in a typical gradient manner, as with mortality; those that were exposed to a toxicant, overall, exhibited a decreased occurrence of metamorphosis (37% average decrease). This study provides essential baseline data needed for further investigations to determine optimal dosing of dispersants and balancing of dispersant use and dosage with anticipated crab-fishery impacts.