High Levels of Sediment Contamination Have Little Influence on Estuarine Beach Fish Communities

While contaminants are predicted to have measurable impacts on fish assemblages, studies have rarely assessed this potential in the context of natural variability in physico-chemical conditions within and between estuaries. We investigated links between the distribution of sediment contamination (metals and PAHs), physico-chemical variables (pH, salinity, temperature, turbidity) and beach fish assemblages in estuarine environments. Fish communities were sampled using a beach seine within the inner and outer zones of six estuaries that were either heavily modified or relatively unmodified by urbanization and industrial activity. All sampling was replicated over two years with two periods sampled each year. Shannon diversity, biomass and abundance were all significantly higher in the inner zone of estuaries while fish were larger on average in the outer zone. Strong differences in community composition were also detected between the inner and outer zones. Few differences were detected between fish assemblages in heavily modified versus relatively unmodified estuaries despite high concentrations of sediment contaminants in the inner zones of modified estuaries that exceeded recognized sediment quality guidelines. Trends in species distributions, community composition, abundance, Shannon diversity, and average fish weight were strongly correlated to physico-chemical variables and showed a weaker relationship to sediment metal contamination. Sediment PAH concentrations were not significantly related to the fish assemblage. These findings suggest that variation in some physico-chemical factors (salinity, temperature, pH) or variables that co-vary with these factors (e.g., wave activity or grain size) have a much greater influence on this fish assemblage than anthropogenic stressors such as contamination

Managing the impacts of SCUBA divers on Thailand's coral reefs

While dive tourism enjoys continued growth worldwide, concern exists that it is contributing to the degradation of coral communities, biologically and aesthetically. This study examined the effect of SCUBA diver contacts with coral and other substrates. Ninety-three percent of divers made contact with substrata during a 10-minute observation period with an average of 97 contacts per hour of diving. Two-thirds of the divers caused some coral damage by breaking fragments from fragile coral forms with an average of 19 breakages per hour of diving. Fin damage was the major type of damage. Underwater photographers caused less damage per contact than non-photographers; as did male divers, compared with females. Diver-induced damage decreases with increasing number of logged dives and attendance at pre-dive briefings. Park managers can help reduce impact by identifying and directing use to sites that are resistant to damage, matching diver competence and site preferences, and alerting operators to dive conditions. Minimising impact requires dive operators to be proactive in promoting minimal impact diving behaviour. This includes selecting sites that match diver expectations and experience, and providing pre-dive briefings in the context of diver activities and physical capacity, and site susceptibility to impact and current strength