Genetic diversity and gene flow in collapsed and healthy abalone fisheries.

Overexploitation of marine species invariably results in population decline but can also have indirect effects on ecological processes such as larval dispersal and recruitment that ultimately affect genetic diversity and population resilience. We compared microsatellite DNA variation among depleted and healthy populations of the black-lip abalone Haliotis rubra from Tasmania, Australia, to determine if over-fishing had affected genetic diversity. We also used genetic data to assess whether variation in the scale and frequency of larval dispersal was linked to greater population decline in some regions than in others, and if larval dispersal was sufficient to facilitate natural recovery of depleted populations. Surprisingly, allelic diversity was higher in depleted populations than in healthy populations (P < 0.05). Significant subdivision across hundreds of metres among our sampling sites (F(ST) = 0.026, P < 0.01), coupled with assignment tests, indicated that larval dispersal is restricted in all regions studied, and that abalone populations across Tasmania are largely self-recruiting. Low levels of larval exchange appear to occur at the meso-scale (7-20 km), but age estimates based on shell size indicated that successful migration of larvae between any two sites may happen only once every few years. We suggest that genetic diversity may be higher in depleted populations due to the higher relative ratio of migrant to self-recruiting larvae. In addition, we expect that recovery of depleted abalone populations will be reliant on sources of larvae at the meso-scale (tens of km), but that natural recovery is only likely to occur on a timescale unacceptable to fishers and resource managers.

Posttraumatic stress two years after the Oklahoma City bombing in youths geographically distant from the explosion.

This article describes Posttraumatic Stress Disorder (PTSD) symptomatology in 69 sixth-grade youths who resided within 100 miles of Oklahoma City at the time of the 1995 bombing of the Alfred P. Murrah Federal Building. These youths neither had any direct physical exposure nor personally knew anyone killed or injured in the explosion. A survey conducted two years after the bombing assessed exposure, PTSD symptoms, and functioning. PTSD symptom frequency was measured with the Impact of Event Scale--Revised. Our BCD criteria for defining PTSD caseness was modeled after DSM-IV B, C, and D criteria requiring one reexperiencing, three avoidance/numbing, and two arousal symptoms for diagnosis. Those who met our BCD criteria had significantly higher PTSD symptom scores than those who did not. Both increased mean PTSD symptom score and meeting our caseness definition were associated with increased functioning difficulties. Media exposure and indirect interpersonal exposure (having a friend who knew someone killed or injured) were significant predictors of symptomatology. These findings suggest that children geographically distant from disaster who have not directly experienced an interpersonal loss report PTSD symptoms and functional impairment associated with increased media exposure and indirect loss.

The role of exposure in posttraumatic stress in youths following the 1995 bombing.

This study investigated the relative impact of various forms of exposure to the 1995 Oklahoma City bombing in middle and high school students seven weeks after the incident. We assessed 3210 youths with an instrument that probed for physical, television, and emotional exposure to the bombing and subsequent posttraumatic stress symptomatology and television reactivity. The majority of youths were exposed through physical proximity--hearing and/or feeling the blast--and through television viewing. These types of exposure, as well as emotional exposure, constituted important variables in the development of posttraumatic stress symptoms and television reactivity. Youths with immediate family casualties were more symptomatic than those without.