Journal of Coastal Research 24 5 1281–1288 West Palm Beach, Florida September 2008 Spatial Variation in Stable Isotopes ( 13 C and  15 N) in Marine Fish along the Coast of Havana City: Evidence of Human Impacts from Harbor and River Waters Consuelo Aguilar † , Gaspar Gonza ´lez-Sanso ´n † , Isabel Faloh † , and R. Allen Curry ‡ * † Centro de Investigaciones Marinas Universidad de La Habana 16 No. 114 Playa 1300, Ciudad Habana, Cuba ‡ Canadian Rivers Institute University of New Brunswick Biology Department Fredericton, New Brunswick, Canada E3B 6E1 racurry@unb.ca ABSTRACT AGUILAR, C.; GONZA ´ LEZ-SANSO ´ N, G.; FALOH, I., and CURRY, R.A., 2008. Spatial variation in stable isotopes ( 13 C and  15 N) in marine fish along the coast of Havana City: evidence of human impacts from harbor and river waters. Journal of Coastal Research, 24(5), 1281–1288. West Palm Beach (Florida), ISSN 0749-0208. We examined the hypothesis that nutrients from land sources are enhancing the food supply for fish in coastal reefs of northwestern Cuba. Spatial variation in stable isotope ratios ( 13 C and  15 N) was investigated at two sites heavily impacted by mixed pollution sources in Havana City, Cuba, and two reference sites. Significant differences in isotope signatures were found among sites for territorial species, e.g.,  15 N was consistently enriched at impacted sites. The most plausible explanation is enriched nitrogen and carbon sources in the food web derived from organic pollution of the coastal zone by human wastewaters. This supports earlier findings that fish were larger in the vicinity of the harbor because of nutrient additions due to sewage that can increase ecosystem productivity and enhance growth of fish. It is also evidence of the direct land-to-water linkage in coastal zone food webs and illustrates how additional nutrients may affect marine food web functions. ADDITIONAL INDEX WORDS: Human impacts, Caribbean reefs, bicolor damselfish, bluehead wrasse, slippery dick, yellowhead wrasse, Chromis. INTRODUCTION Marine eutrophication is one of the most significant im- pacts of humans in coastal zones (ÆRTEBJERG et al., 2001; COGNETTI, 2001). The impact of nutrient enrichment and eventually eutrophication depends on the balance between the positive (more food) and the negative (e.g., hypoxia and increase of suspended solids) consequences of adding organic material, e.g., urban, agricultural, or industrial runoff, into the coastal zone (BREITBURG, 2002). Untreated sewage is a major cause of eutrophication in coastal zones and can be a source of toxic substances that affect fish health ( e.g., ALBER- TO et al., 2004; AMISAH and COWX, 2000; SCHMIDT et al., 1999). The nearshore marine environment along the coast of Ha- vana City, Cuba, is impacted by many human activities, in- cluding overfishing and pollution from wastewater (sewage and industrial) and land activity runoff (urban and agricul- tural). Significant changes in fish assemblages of fringe coral reefs off Havana City have been recently reported (AGUILAR et al., 2004). Changes were associated with distance from Ha- vana Harbor, which is the largest pollution source in the area that includes organic matter and nutrients from sewage, crude oil from a refinery, heavy metals, and fine sediments DOI: 10.2112/07-0832.1 received 12 February 2007; accepted in re- vision 11 July 2007. * Corresponding author. (ARECES and TOLEDO, 1985; BELTRA ´ N,RUIZ, and VEGA, 1998; GONZA ´ LEZ, 1991). Recent research by AGUILAR (2005) on bicolor damselfish (Stegastes partitus, Poey), bluehead wrasse (Thalassoma bi- fasciatum, Bloch), slippery dick (H. bivittatus, Bloch), and yel- lowhead wrasse (H. garnoti, Valenciennes) indicated they are heavier and longer at sites near Havana Harbor and the Al- mendares River (Havana City), two major sources of coastal pollution. These findings suggest an increased food supply resulting from the eutrophication of these coastal waters. Stable isotope analyses can elucidate trophic relationships in aquatic animals (CONOLLY, 2003; LEE, 2000; PETERSON and FRY, 1987; VOB and STRUCK, 1997) because  13 C is an effective indicator of food source and  15 N is an indicator of trophic level (e.g., MINAGAWA and WADA, 1984; VANDER ZAN- DEN et al., 1999; YAMAMURO,KAYANNE, and MINAGAWA, 1995; but see also MCCUTCHAN et al., 2003). PETERSON (1999) observed that human sewage in the marine environ- ment creates an isotopic signature that may be useful for tracking impacts. Research has demonstrated that stable iso- tope ratios can help to trace inputs of carbon and nitrogen from land-based activities, including sewage discharge in aquatic ecosystems (DARNAUDE,SALEN-PICARD, and HAR- MELIN-VIVIEN, 2003; RAU et al., 1981; VAN DOVER et al., 1992; VIZZINI and MAZZOLA, 2004). For example, the enrich- ment of nitrogen ( 15 N) could provide a means of assessing the degree of exposure of aquatic organisms to municipal sewage