An oyster hatchery at Gwynn’s Island reported unusual larval mortality problems this spring, but researchers could not conclusively identify the source of the problem, according to a recently issued Virginia Institute of Marine Science report.

Refurbishment work at the Gwynn’s Island bridge, which carries Route 223 connecting the island to the Mathews mainland near Hudgins, “may have contributed to feeding and mortality problems observed in larval oysters at the nearby Oyster Seed Holdings hatchery,” the report said. The hatchery is located about 2,500 feet from the bridge.

“There is substantial evidence that toxicants associated with the bridge coating material, most likely Zn (zinc), can have a deleterious effect on larval oysters,” said Professor Kimberly Reece of the VIMS team which compiled the report.

Such larval oyster mortality most often occurs in mid to late summer, the report said, as water quality deteriorates due to unidentified facto...