Multiple stressor interactions influence embryo development rate in the American horseshoe crab, Limulus polyphemus

Abstract

Fertilized eggs of the American horseshoe crab, Limulus polyphemus, are buried in shallow nests above the high tide line, where they are exposed to variations in abiotic conditions during early development. Using a multiple stressors approach we examined whether the rate of embryonic development is affected by exposure to combinations of three factors: temperature (T; 25, 30 and 35°C), salinity (S; 5, 15 and 34 ppt), and ambient O2 (O2; 5%, 13% and 21% O2). Newly fertilized eggs were incubated under 27 fully-factorial stressor combinations for 14 d, then allowed to recover in control conditions (30°C, 34 ppt, 21% O2) for an additional 14 d. Growth rate was measured every 2 d throughout the experiment (n=1296). We found that the effect of isolated stressors (high T, low S or low O2) reduced developmental success by up to 72% (low S), and that stressor combinations showed stronger effects and evidence of complex interactions. For example, low O2 had little effect individually but was lethal in combination with high T, and low T in isolation slightly decreased the rate of development but reduced the negative effects of low S and low O2. Development was delayed under exposure to low O2 but resumed upon return to control conditions after a 10 d lag. These data demonstrate that complex, synergistic interactions among abiotic stressors can substantially alter the development of a coastal invertebrate in ways that may not be predicted from the effects of the stressors in isolation.