Effect of Salinity and Dissolved Oxygen on Blue Crab (Callinectes sapidus) Size in Blackbird Creek, Delaware

Abstract

Effect of Salinity and Dissolved Oxygen on Blue Crab (Callinectes sapidus) Size in Blackbird Creek, Delaware Daivik Arora1, Jackie Maina2, and and Gulnihal Ozbay2, Ph.D. 1The Charter School of Wilmington1, Wilmington, DE 2Department of Agriculture and Natural Resources, Delaware State University, Dover, DE Blue crabs are a keystone species in the Delaware bay and are an important source of revenue. However, due to overfishing and water pollution, the crab population has declined significantly, going from 800 million in 1990 to 200 million in 2008 in the Mid-Atlantic region. Water quality changes can be linked to the development of low oxygen areas called dead zones in the feeding areas of the crabs, diminishing their food sources. Higher salinity levels in crab habitat has been associated with larger crabs due to its significance in shell development where calcium carbonate is the main component of the exoskeletons. In this research project, the effect of salinity and dissolved oxygen on crab size was determined using monthly water monitoring data from 2017 and 2020. The study was carried out in Blackbird Creek, Delaware, and 5 sites were identified based on dominant marsh vegetation and salinity gradient. The water quality testing was carried out using the YSI 556 multiprobe sensor and crab sampling was conducted using crab traps and trawling method. 108 crabs were used in this study. Carapace width was determined using calipers. The highest salinity average was recorded in site 1 (5.8 ppt) and the lowest average in site 5 (3.6 ppt). Dissolved oxygen had the highest mean in site 1 (6.6 mg/L) and the lowest mean in site 3 (5.6 mg/L). The largest carapace width average was at site 1 (113.1 mm), while the smallest width average was found in site 4 (94.2 mm). The preliminary results indicate that the largest crabs were from site 1, suggesting a positive relationship between salinity and crab size. These results contribute to the existing knowledge base on salinity and dissolved oxygen influence on blue crabs. Continued monitoring would provide more conclusive insight regarding applicability to blue crab management. Keywords: Dissolved oxygen, Salinity, Blue crab, Carapace, Blackbird Creek 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.