Biodivocean-Baltimore's Journal

After retrieving and cleaning the racks on July 15th, and redeploying all 6 back on the same platform on July 20th, a lot of colonization has occurred on the top discs. The Inner Harbor is back to the normal, "iced tea" color instead of a pistachio green (sulfur bacterial bloom).

Although the discs still were still dark, they were not black/gray. The dominating organisms found on the discs include the tube bryozoan and stentors. A few entoprocts, colonial ciliates, and mussels were also found around the disc.

General Timeline for July

Before, in the early month of June, older disc racks from January 2026 were highly colonized and very biodiverse.

July 1 - July 4: Heat Wave, Biofilm disc communities' biodiversity peaked.

July 4 - July 8: Back-to-back Thunderstorms

Sulfur bacteria bloom started around July 8th. Extremely low dissolved oxygen and chlorophyll levels, dropping to 0% saturation on some days. For many days, counts were unable to be conducted without some recovery.

July 13: Most recent or last biodiversity count for the discs. Biofilm disc communities' biodiversity was at its lowest.

July 15: Highly anoxic conditions persisted. Racks were retrieved and cleansed.

Blooms prolonged throughout the weeks and started recovering around July 20th with less rainy days and extreme weather. The green, pistachio-like waters started to fade. Racks were redeployed July 20th.

July 28: Thunderstorm occurred right after some progress on recovery.

July 30: A second wave of a sulfur bacteria bloom (or pistachio tide event) is underway.

The Baltimore Inner Harbor is part of the Patapsco River that connects to the Chesapeake Bay in Maryland. Observations of biofilm and invertebrate colonization on a series discs have been studies since the start of the VIRTUE Project in 1997. Over the years, the disc substrate has been changed from plastic(acrylic PMMA) to metal (aluminum) to accommodate investigations of microplastic accumulation in biofilm colonization. Observations recoded this summer (2026) are part of a collaboration between Maryland Sea Grant, the Institute of Marine and Environmental Technology, and the Community Engaged Internship (CEI) Program.