Descrição
Avoidance response is a well-known mechanism for escaping environmental stress. For organisms with reduced
active movement, such as benthic microalgae, drifting could be a specifically selected mean of avoiding less
favorable environments. To test this hypothesis, a system was developed to assess if hypo-saline stress triggers drift
in the estuarine benthic diatom Cylindrotheca closterium. Concurrently, the effects of salinity on growth inhibition
were also investigated in order to compare the sensitivity of this endpoint with the drift response, and to estimate the
immediate population decline caused by both drift and population growth responses. It was verified that the salinity
value that inhibited the algal population growth by 50% (IGS50) was 19, while the salinity value that triggered the drift
response by 50% of the population (TDS50) was 15. These results indicate that drift is an identifiable response
triggered to escape stressful environments. The combination of the two responses (population growth and drift)
showed that population decline based exclusively on the inhibition of population growth may result in an
underestimation of the risk, compared with the decline when drifting to avoid stress is also taken into account. This study was partially funded by the “Fundação para a Ciência e a Tecnologia” (FCT, Portugal) through a postdoctoral fellowship (reference
SFRH/BPD/74044/2010) to C.V.M. Araújo, through the SALTFREE project (contract PTDC/AAC-CLI/111706/2009) and through “Ciência 2007 - Human
Potential Operational Program” (POPH) and “Quadro de Referência Estratégico Nacional” (QREN) through the European Social Fund (ESF) and the
Spanish Ministry of Education and Science (MEC) funds.
; Romero-Romero, Sonia 
