Broad-scale impacts of salmon farms on temperate macroalgal assemblages on rocky reefs E.S. Oh a,⇑ , G.J. Edgar a , J.B. Kirkpatrick b , R.D. Stuart-Smith a , N.S. Barrett a a Institute for Marine and Antarctic Studies, University of Tasmania, GPO Box 252-49, Hobart, Tas 7001, Australia b Geography and Environmental Studies, University of Tasmania, GPO Box 252, Hobart, Tas 7001, Australia article info Article history: Received 2 February 2015 Revised 25 June 2015 Accepted 27 June 2015 Available online xxxx Keywords: Aquaculture Fishes Benthic macrofauna Invertebrates Organic pollution Tasmania abstract Intensive fish culture in open sea pens delivers large amounts of nutrients to coastal environments. Relative to particulate waste impacts, the ecological impacts of dissolved wastes are poorly known despite their potential to substantially affect nutrient-assimilating components of surrounding ecosys- tems. Broad-scale enrichment effects of salmonid farms on Tasmanian reef communities were assessed by comparing macroalgal cover at four fixed distances from active fish farm leases across 44 sites. Macroalgal assemblages differed significantly between sites immediately adjacent (100 m) to fish farms and reference sites at 5 km distance, while sites at 400 m and 1 km exhibited intermediate characteris- tics. Epiphyte cover varied consistently with fish farm impacts in both sheltered and exposed locations. The green algae Chaetomorpha spp. predominated near fish farms at swell-exposed sites, whereas fila- mentous green algae showed elevated densities near sheltered farms. Cover of canopy-forming perennial algae appeared unaffected by fish farm impacts. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Nutrient and sediment inputs from anthropogenic activities can cause changes to habitat structure and diversity in temperate reef ecosystems (Airoldi, 2003; Connell et al., 2008; Krause-Jensen et al., 2008; Worm et al., 1999b). These changes may affect delivery of ecosystem services to society, as well as marine conservation objectives for reef areas, which are disproportionately rich in spe- cies compared with other habitats. Whilst much attention has been focussed on terrestrial-derived pollution on reef (Arevalo et al., 2007; Connell et al., 2008; Costanzo et al., 2001; Giordani et al., 2009; Littler and Murray, 1975), eutrophication from marine fish farms may also pose a threat. Most previous monitoring and research programs relating to fish farm aquaculture have focused solely on changes to the soft sediments below and adjacent to farm lease areas, in-water nutrients levels, and phytoplankton popula- tions (Edgar et al., 2010a). Farmed salmon are commonly grown to maturity in net cages, situated in unpolluted sheltered temperate coastal waters. Salmon rely on nutrient-rich compound aquafeeds as an external food source (Tacon and Metian, 2008). Although improved feeding technology has provided a reduction in wasted feed input, Sanderson et al. (2008) suggested that about 70% of the nitrogen and 80% of the phosphorus input to a salmon farm is released to the environment as feed wastage, fish excretion, faeces production and respiration. The majority of these nutrients dissipate in dis- solved form. Approximately 87% of nitrogen released from fish farms in the Huon Estuary, Tasmania, is estimated to be in dis- solved form and 13% as particulate matter (HEST, 2000b, a). The impact of particulate fish farm waste on sediment communities is variable, according to interactions between depth, current speed, current direction, sediment type, and latitude (Kalantzi and Karakassis, 2006). Commonly impacts are found to be relatively localised (Borja et al., 2009; Grego et al., 2009; Ye, 1991), with meta-analyses reporting benthic community change extending 40–70 m on average (Giles, 2008), although instances of impacts to 145 m have also been recorded (Hamoutene et al., 2015). The extent of impact of dissolved wastes is poorly known, but may extend further (HEST, 2000a). The effects of fish farm derived nutrients on the diversity and composition of macroalgal-dominated reef communities are likely to be similar to those already observed in eutrophic systems affected by terrestrial derived organic pollution, such as sewage and runoff from fertilised landscapes. A well-documented conse- quence of excessive nutrients in coastal reef environments is the over-abundant growth of certain types of productive, fast growing macroalgae (Bokn et al., 2003b; Krause-Jensen et al., 2008; http://dx.doi.org/10.1016/j.marpolbul.2015.06.049 0025-326X/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: IMAS-Taroona, Nubeena Cresent, Taroona, Tasmania 7053, Australia. E-mail address: Elizabeth.Oh@utas.edu.au (E.S. Oh). Marine Pollution Bulletin xxx (2015) xxx–xxx Contents lists available at ScienceDirect Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul Please cite this article in press as: Oh, E.S., et al. Broad-scale impacts of salmon farms on temperate macroalgal assemblages on rocky reefs. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.06.049