Sampling to differentiate between pulse and press perturbations.

There is great inconsistency in the use of the terms 'pulse' and 'press' when describing types of perturbations. This is due primarily to a failure to distinguish between the cause and the effect of the perturbation in question. The cause and effect may be either short- or long-term and clearly one may be short-term and the other long-term. Distinction between these two types of disturbance is crucial for management to prevent further impact. Thus, it is important to describe separately these two aspects of a perturbation. Here, we define a protocol for sampling perturbations which enables the cause and effect to be distinguished between short- or long-term. Existing (i.e., already established) assemblages and newly-established assemblages are sampled and compared among disturbed and control locations. Existing assemblages may have been affected by past (pulse) disturbances and/or ongoing (press) disturbances, whereas the establishment of new assemblages can only be influenced by ongoing disturbances. We describe the procedures for assessing impacts of estuarine marinas as an illustration of the issues to be considered in any habitat. Settlement plates and defaunated sediment are suggested for sampling the establishment of new assemblages in aquatic environments.