Examining Water Quality and Blue Crab Gut Content in Blackbird Creek

Abstract

Examining Water Quality and Blue Crabs (Callinectes sapidus) Gut Content in Blackbird Creek, Delaware State University Kayla McKinley, Jackie Maina, and and Gulnihal Ozbay, Ph.D. Department of Agriculture and Natural Resources, Dover, DE Department of Agriculture and Natural Resources, Delaware State University, Dover, DE, 19901 Blue crabs are an important part of the Delmarva local economy. They bring in revenues amounting to 4 to 6 million dollars annually. Blue crab habitat use is dependent on life cycle stage. Marsh habitats are especially essential for juvenile blue crabs as they provide shelter from predators. Marsh dynamics are influenced by nutrient input, affecting their ability to support crab populations. The objective of this study was to examine water quality conditions and investigate blue crab feeding behavior in Blackbird Creek, Delaware. Five sites were identified based on dominant vegetation. Site 1: Sporobolus alterniflora and Phragmites australis. Site 2: S. alterniflora and Sporobolus cynosuroides. Site 3:S. alterniflora, S. cynosuroides and P. australis. Site 4: S. alterniflora.Site 5: P. australis. As 51% of the land surrounding Blackbird creek is agricultural land, water quality monitoring targeting nitrogen and phosphorus nutrients was conducted in 2017 and 2020 to determine the creek’s suitability as a blue crab habitat. Fifty-two crabs in total were collected using crab traps. Percentage gut fullness and volume were determined. The preliminary results indicate that the highest mean nitrate, nitrite, ammonia and orthophosphates were from sites 5 (0.44 mg/L) site 2 (0.0136 mg/ L), site 5 (0.068 mg/ L) and site 1 (0.498 mg/ L) respectively. All the nutrients were within Delaware’s regulatory ranges for surface water quality. The crab gut content analysis indicates that the highest percentage fullness mean (75%), and the highest gut volume mean (4.57 mL) were from site 5. The water quality values are almost similar across sites, and they are unlikely to influence blue crab feeding habits in Blackbird Creek. The vegetation is therefore the most likely determinant of food availability in this habitat meaning that although P. australis is an invasive species, it provides a better feeding environment for the blue crabs. Keywords: Blue crab, Gut content, Blackbird Creek, Water quality, Marsh grass Acknowledgements: We acknowledge USDA NIFA Capacity Building Grant Awards# 2016-06642 and 2016-06476 for funding my internship and the project as part of the student experiential learning goal and the Project Director, Dr. Gulnihal Ozbay, and the Project Director, Dr. Shobha Sriharan, respectively for providing this internship opportunity.