Seeing in the sea is a difficult task when the visual conditions can range from crystal clear ocean to muddy tidal estuaries. Light intensities can vary over nine orders of magnitude depending on water clarity and the colour of the light. According to Andrij Horodysky from the College of William and Mary,members of the sciaenid fish family inhabit a wide range of coastal and estuarine environments, and have successfully adjusted to their dramatically different visual worlds. However, it wasn't clear how each individual species'visual systems had adapted to the different light conditions. Teaming up with colleagues from the College of William and Mary, the US National Marine Fisheries Service and Lund University, Horodysky looked at the light sensitivity, colour sensitivity and temporal resolution of five sciaenid species from different visual environments in the Chesapeake Bay to see what adaptations they have made (p. 3601).
The team found that the visual systems of species living at depth were more sensitive than those of species found in shallow waters. Testing the temporal resolution (the fish's responses to flickering light), the team found that the weakfish's responses were much slower than those of other species. Horodysky explains that this allows the weakfish to gather more light in muddy estuary waters, to improve their sensitivity, and adds that `benthic-foraging sciaenids likely possess generalist eyes that balance luminous sensitivity,speed and resolution without excelling at any one task.'
Having found that the adaptations of each sciaenid make the fish well suited to light conditions in their own particular niche, Horodysky sounds a note of warning. He explains that human activity is probably muddying the waters `at a pace faster than the evolution of the visual system of Chesapeake Bay's fauna,' and adds that `Studies that examine the relationships between sensory physiology and behavioural ecology are important... to support the management of aquatic resources.'