Seawater and shellfish (Geukensia demissa) quality along the Western Coast of Assateague Island National Seashore, Maryland: an area impacted by feral horses and agricultural runoff.

This research focuses on assessing the quality of seawater and ribbed mussels in Assateague Island National Seashore, an area affected by feral horses and agricultural runoff. Findings indicate high nutrient loads and poor water quality, suggesting the need for better environmental stewardship and intervention strategies for preserving marine resources.

Evaluation of Seawater and Shellfish Quality

• The study evaluated the seawater and ribbed mussels (Geukensia demissa) at six sites along Assateague Island National Seashore. The parameters analyzed for seawater included temperature, pH, salinity, dissolved oxygen, total phosphorus, total ammonia nitrogen, and nitrite levels during the summer. On the other hand, total heterotrophic plate counts (a measure of microbial contamination) and total Vibrionaceae (a family of bacteria) levels were examined in the mussels.

Causes of Nutrient Loads

• The study found that nutrient loads, which affect water and shellfish quality, resulted from various sources, including about 150 feral horses (Equus caballus) located on Assateague Island National Seashore. Additionally, local wildlife, agricultural runoff from livestock and croplands, as well as anthropogenic inputs also added to the nutrient loads.

Poor Quality of Seawater and Shellfish

• The research revealed a below-acceptable minimum of average monthly dissolved oxygen for June, which is 2.65 mg L(-1) as compared to the threshold of 3.0 mg L(-1). Moreover, along Chincoteague Bay, the total phosphorus generally exceeded its maximum level set by the Maryland Coastal Bays Program management. During June, the value was around 50 times higher than the recommended threshold.
• The total ammonia nitrogen levels were also alarmingly high, nearing the harmful levels for fish. Furthermore, in August, the total heterotrophic bacteria levels in the mussels from Sinepuxent Bay spiked to exceed acceptable standards for edible bivalves by 19-fold. Approximately 76% of the bacterial isolates belonged to the Vibrionaceae family, indicating a high degree of bacterial pollution.

Need for Improved Stewardship and Interventions

• The study emphasizes the poor management of the coastal environment, as evidenced by the poor seawater and shellfish quality. The excessive nutrient loads and the presence of harmful bacteria suggest a critical need for new intervention strategies. These measures are necessary to reduce chemical and biological contamination and ensure the preservation of marine resources for future generations.