Natural variations in estuarine fish, fish odor, and zooplankton photobehavior

Fish odor induces predator avoidance behaviors in zooplankton, like vertical migration, by making zooplankton more responsive to light. Odor cues that alter behavior in marine crustacean zooplankton in the laboratory include sulfated glycosaminoglycans (sGAGs) derived from fish body mucus. Few studies quantify these cues in estuarine/marine environments or assess whether laboratory studies reflect natural scenarios. We collected fish and water samples weekly in Broadkill River, Delaware, USA. We used field-collected water in colorimetric assays to determine the concentration of sGAG-equivalent molecules and in behavioral assays with a zooplankton model, brine shrimp (Artemia spp.) nauplii, which only descend in response to downwelling light after fish odor exposure. Fish quantity was positively related to sGAG-equivalents and zooplankton photosensitivity, indicated by descent responses at lower light levels and across a broad intensity range. Our results support that fish odor concentrations used in previous laboratory assays are consistent with levels found in an estuary.