Seawater carbonate chemistry and brown dottyback (Pseudochromis fuscus) movement and feeding behaviour during experiments, 2011

Changes in olfactory-mediated behaviour caused by elevated CO2 levels in the ocean could affect recruitment to reef fish populations because larval fish become more vulnerable to predation. However, it is currently unclear how elevated CO2 will impact the other key part of the predator-prey interaction - the predators. We investigated the effects of elevated CO2 and reduced pH on olfactory preferences, activity levels and feeding behaviour of a common coral reef meso-predator, the brown dottyback (Pseudochromis fuscus). Predators were exposed to either current-day CO2 levels or one of two elevated CO2 levels (~600 µatm or ~950 µatm) that may occur by 2100 according to climate change predictions. Exposure to elevated CO2 and reduced pH caused a shift from preference to avoidance of the smell of injured prey, with CO2treated predators spending approximately 20% less time in a water stream containing prey odour compared with controls. Furthermore, activity levels of fish was higher in the high CO2 treatment and feeding activity was lower for fish in the mid CO2treatment; indicating that future conditions may potentially reduce the ability of the fish to respond rapidly to fluctuations in food availability. Elevated activity levels of predators in the high CO2 treatment, however, may compensate for reduced olfactory ability, as greater movement facilitated visual detection of food. Our findings show that, at least for the species tested to date, both parties in the predator-prey relationship may be affected by ocean acidification. Although impairment of olfactory-mediated behaviour of predators might reduce the risk of predation for larval fishes, the magnitude of the observed effects of elevated CO2 acidification appear to be more dramatic for prey compared to predators. Thus, it is unlikely that the altered behaviour of predators is sufficient to fully compensate for the effects of ocean acidification on prey mortality.

Transverse drainages of the Susquehanna River basin, Pennsylvania, USA

While large-scale transverse drainages (TDs) such as those of the Susquehanna River above Harrisburg, PA, have been recognized since the 19th century, there have been no systematic surveys done of TDs since that of Ver Steeg's in 1930. Here, the results are presented of a topographic and statistical analysis of TDs in the Susquehanna River basin using Google Earth and associated overlays. 653 TDs were identified in the study area, 95% of which contain streams with discharges of less than 10 m3/s. TD depths ranged from a 23 m deep water gap near Blain, PA, to the 539 m deep gorge of the Juniata River through Jacks Mountain. Although TD depth tended to increase with stream size, many small streams were located in deep gaps, and eight streams with discharges of 10 m3/s or less were found in gorges whose depths matched or exceeded the deepest TD of the Susquehanna, the largest stream in the basin. Streams of less than 10 m3/s made up the majority of TDs regardless of the rock type capping the breached structure. Overall, TDs through sandstone-capped ridges were deeper than those topped by shales, and TDs in both sandstones and shales displayed a lognormal distribution of depths, which may be indicative of a preferred value. Stream flow direction was primarily perpendicular to local structural strike, with 47% of streams flowing NW and 53% flowing SE. 19% of the TDs were found to be in alignment with at least one other TD, with aligned segment lengths ranging from .5 to 14.8 km. The majority of TDs were in rocks of Paleozoic age. The techniques described here allow the frequency and distribution of TDs to be quantified so that they can be integrated into models of basin evolution.