March 2025 Critter of the Month

These evenings, if you gazed upwards, you may be treated to the sight of Osprey in flight returning to nest in the Chesapeake. The return of these charismatic raptors marks one of the most celebrated phenological events in the region and they will soon be enthusiastically building and defending their nests. But, beneath the water’s surface a different territorial display is unfolding. Here, a much less famous and far less raucous resident is beginning his own springtime rituals. Although he is a true homebody, a year-round resident of the oyster reef rather than a revered transcontinental globetrotter, the Striped Blenny (Chasmodes bosquianus) is gearing up to display territorial maneuvers that we find no less charming, and perhaps even worthy of his own nest cam. 

At first glance, this fish which is no larger than 4 inches might seem unremarkable, but a closer look reveals its many adaptations to life on the oyster reef. The Striped Blenny earns its name from the irregular, horizontal tan stripes that run along its olive body. During mating season, males develop a distinctive blue spot and a yellow- orange streak on their dorsal fin. Females and juveniles display additional mottled vertical bars that break up their outline, providing camouflage on an oyster reef. Their laterally compressed body helps them squeeze into empty oyster shells, which serve as not only their homes, but also a stage for courtship and nesting. Unlike many fish, the Striped Blenny lacks a swim bladder, the organ that allows others to balance and orient themselves in the water column. This absence commits them to a benthic lifestyle; these fish sit on the seafloor (or oyster reef) perched upright like tripods on their large pectoral fins. They use their rearward fins to propel themselves forward in fast bursts—usually to confront a trespasser on their territory—rather than for sustained travel.

When spring waters warm and days grow longer, male Striped Blennies rouse from their slow-winter pace to become devoted suitors and fathers. When courting a female, the male Striped Blenny shakes his head and body with an outstretched dorsal fin, flashing his new breeding colors. Unlike fish that invest in producing thousands of small eggs, Stripped Blennies invest in producing fewer (100s) but larger eggs, which are deposited in neat adhesive clusters on the ceiling of the male’s chosen oyster shell. The males then become dedicated guardians, protecting the eggs from predators and gently fanning them to prevent silt accumulation. The male maintains this vigilant watch until the eggs hatch, never straying far from his shell nursery. He’ll continue tending new broods from spring through fall, a successful strategy that has enabled the Striped Blenny to persist and thrive within the complex oyster reef ecosystem.

Keep your eyes on the water as you pass local reefs this month; while you might not spot our solitary and secretive blenny friends, know that they're there, defending their tiny territory in the sheltered spaces between the shells, contributing in their own way to the Bay's grand spring chorus.