Histological evidence of accumulation of iron in postlarvae of red abalone, Haliotis rufescens Loreto Andrea Pino Chandia 1 , Andrea C Alfaro 2 , Roberto Flores Aguilar 1 , Marcos Godoy 3 & Alfonso Gutierrez Venegas 1 1 Centro de Investigacio´n y Desarrollo i-mar, Universidad de Los Lagos, Puerto Montt, Chile 2 School of Applied Sciences, Faculty of Health and Environmental Sciences, Auckland University of Technology, Auckland, New Zealand 3 Panamericana Sur 581, Puerto Montt, Chile Correspondence: A C Alfaro, Faculty of Health and Environmental Sciences, School of Applied Sciences, Auckland University of Technology, Private Bag 92006, Auckland 1020 New Zealand. E-mail: andrea.alfaro@aut.ac.nz Abstract The effect of iron on abalone postlarvae (Haliotis rufescens) was investigated in a controlled-cultur- ing system. Three iron concentrations (0.15, 1.5 and 15 mg L 1 of Fe) and a control (no iron added) were used to culture H. rufescens postlar- vae while being fed the diatom Navicula inserta over 10 days. Results indicate that H. rufescens postlarvae accumulate iron granules in the stom- ach, digestive gland and mantle, but not in the gills or other tissues. The number and diameter of iron granules in tissues increased with increas- ing iron concentration in the culturing environ- ment. The iron accumulation is assumed to have been acquired in the digestive system through the iron-enriched diatom feed and in the mantle through subcutaneous iron transfer. The lack of iron granules in the gills suggests that iron is not absorbed through the respiratory system, as is the case for many filter feeding bivalves. Exposure to the highest iron concentration (15 mg L 1 ) resulted in tissue abnormalities where granules accumulated, and may have significantly affected the health of H. rufescens postlarvae. These find- ings provide valuable information for the regula- tion of appropriate iron levels within aquaculture settings and highlights the importance of moni- toring iron levels within abalone larval culturing environments. Keywords: abalone postlarvae, Haliotis rufes- cens, iron granules, histological sections, heavy metal exposure, tissue disintegration Introduction For most marine invertebrates, such as abalone, the larval stage is one of the most vulnerable times in their life cycle. After the first week in the water column, abalone larvae undergo initial settlement and metamorphosis. Once in their benthonic life stage, postlarvae begin to feed on microalgae, until they complete the development of the radula and digestive system to consume macroalgae. The post-larval period is a critical step in their develop- ment, and requires a good supply of biofilms with diatoms and bacteria (Searcy-Bernal 1996). How- ever, during the first few weeks after settlement, massive mortalities (>90%) often are observed, especially if the complex of bacteria and diatom biofilms are too dense (Hahn 1989; Searcy-Bernal, Salas-Garza & Flores-Aguilar 1992a; Searcy-Ber- nal, Salas-Garza, Flores-Aguilar & Hinojosa-Rivera 1992b). This density-dependent mortality appears to be related to increased susceptibility to post- larval stresses, such as oxygen saturation and boundary layer conditions (Searcy-Bernal 1996). Postlarvae also may be exposed to high concentra- tions of environmental contaminants (e.g., heavy metals, pathogens), and chemical fluctuations in their surroundings, which often cause high mor- talities. Within these stressful environments, heavy metals are particularly dangerous for marine invertebrate larvae and early juveniles, since these chemicals are easily incorporated and accumulated in soft tissues (Chang & Reinfelder 2002; Viant, Walton, TenBrook & Tjeerdema 2002; Ferrer, And- rade, Asteasuain & Marcovecchio 2006; Gorski & © 2011 Blackwell Publishing Ltd 1 Aquaculture Research, 2011, 1–8 doi: 10.1111/j.1365-2109.2011.02969.x