Spatial Variation in Stable Isotopes ( 13C and 15N) in Marine Fish Along
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Journal of Coastal Research 24 5 1281–1288 West Palm Beach, Florida September 2008 Spatial Variation in Stable Isotopes (␦13C and ␦15N) 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 ‡Canadian Rivers Institute Universidad de La Habana University of New Brunswick 16 No. 114 Biology Department Playa 1300, Ciudad Habana, Cuba Fredericton, New Brunswick, Canada E3B 6E1 [email protected] ABSTRACT AGUILAR, C.; GONZA´ LEZ-SANSO´ N, G.; FALOH, I., and CURRY, R.A., 2008. Spatial variation in stable isotopes (␦13C and ␦15N) 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 (␦13C and ␦15N) 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., ␦15N 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 (ARECES and TOLEDO, 1985; BELTRA´ N,RUIZ, and VEGA, 1998; GONZA´ LEZ, 1991). Marine eutrophication is one of the most significant im- Recent research by AGUILAR (2005) on bicolor damselfish pacts of humans in coastal zones (ÆRTEBJERG et al., 2001; (Stegastes partitus, Poey), bluehead wrasse (Thalassoma bi- COGNETTI, 2001). The impact of nutrient enrichment and fasciatum, Bloch), slippery dick (H. bivittatus, Bloch), and yel- eventually eutrophication depends on the balance between lowhead wrasse (H. garnoti, Valenciennes) indicated they are the positive (more food) and the negative (e.g., hypoxia and heavier and longer at sites near Havana Harbor and the Al- increase of suspended solids) consequences of adding organic mendares River (Havana City), two major sources of coastal material, e.g., urban, agricultural, or industrial runoff, into pollution. These findings suggest an increased food supply the coastal zone (BREITBURG, 2002). Untreated sewage is a resulting from the eutrophication of these coastal waters. major cause of eutrophication in coastal zones and can be a Stable isotope analyses can elucidate trophic relationships source of toxic substances that affect fish health (e.g., ALBER- in aquatic animals (CONOLLY, 2003; LEE, 2000; PETERSON TO et al., 2004; AMISAH and COWX, 2000; SCHMIDT et al., and FRY, 1987; VOB and STRUCK, 1997) because ␦13Cisan 1999). effective indicator of food source and ␦15N is an indicator of The nearshore marine environment along the coast of Ha- trophic level (e.g., MINAGAWA and WADA, 1984; VANDER ZAN- vana City, Cuba, is impacted by many human activities, in- DEN et al., 1999; YAMAMURO,KAYANNE, and MINAGAWA, cluding overfishing and pollution from wastewater (sewage 1995; but see also MCCUTCHAN et al., 2003). PETERSON and industrial) and land activity runoff (urban and agricul- (1999) observed that human sewage in the marine environ- tural). Significant changes in fish assemblages of fringe coral ment creates an isotopic signature that may be useful for reefs off Havana City have been recently reported (AGUILAR tracking impacts. Research has demonstrated that stable iso- et al., 2004). Changes were associated with distance from Ha- tope ratios can help to trace inputs of carbon and nitrogen vana Harbor, which is the largest pollution source in the area from land-based activities, including sewage discharge in that includes organic matter and nutrients from sewage, crude oil from a refinery, heavy metals, and fine sediments 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- DOI: 10.2112/07-0832.1 received 12 February 2007; accepted in re- 15 vision 11 July 2007. ment of nitrogen ( N) could provide a means of assessing the * Corresponding author. degree of exposure of aquatic organisms to municipal sewage 1282 Aguilar et al. MATERIALS AND METHODS Study Areas The main study area was the northern coast of Cuba, west of Havana City (Figure 1). In this region, the upper subtidal zone is a submarine terrace with a gentle slope to 8 m deep. The slope increases significantly until 12–15 m, where a sandy plain begins. The terrace is about 300 m wide and di- vided into four distinct biotopes existing as bands running parallel to the coastline (AGUILAR et al., 2004): ● Echinometra: The most shoreward and shallowest biotope. The main feature of this zone is the huge population of the sea urchin, Echinometra lucunter, a species that excavates the rocky bottom for shelter. ● Rocky plain: A biotope whose main feature is the smooth rocky bottom that is covered by seaweed seasonally. ● Terrace edge: The area just before the point where the bot- tom slope becomes steeper. ● Terrace base: The deepest biotope, where the rocky wall of the terrace meets the sandy plain. Figure 1. Location of study sites (black circles) in western Cuba. Sam- pling sites: BR ϭ Havana Harbor, C30 ϭ Miramar, Ca ϭ Cantiles Key, In the vicinity of Havana City, there were three sampling ϭ RIO Almendares River. stations. The entrance of Havana Harbor, site BR, is heavily impacted by the polluted waters from this industrial harbor (23Њ8.864Ј N, 82Њ21.576Ј W; Figure 1). Waters are eutrophic; in the receiving environment (e.g., LAKE et al., 2001; WAY- coral growth is low; sponge density is high; polychaetes are LAND and HOBSON, 2001). numerous (Table 1). Site RIO was the eastern coastal area at We hypothesized that nutrients coming from land-based the mouth of Almendares River (23Њ8.250Ј N, 82Њ24.565Ј W; activities in the area around Havana City are enhancing the Figure 1). A dominant coastal current flowing from SW to food supply for fish in coastal coral reefs. We present results NW directs river discharge to the NW. The river is heavily for stable carbon and nitrogen isotope ratios of selected fish polluted as it flows through the city with organic matter from species and their potential food items at several sites varying sewage, heavy metals, and other sources of unknown nature in sewage inputs along the coast of Havana City. We observed from several industries (AGUILAR and GONZA´ LEZ-SANSO´ N, larger fish than AGUILAR (2005) and predicted that fish were 2002). There is greater coral cover and colony size and num- larger in the vicinity of the harbor because of its enriched ber than BR, but these indicators are still low (Table 1). Algal environment. We predicted that stable isotope levels would cover increases at this site. Site C30 was the area off 30th reflect this proximity to human inputs, e.g., elevated ␦15N and Street in Miramar, Havana City (23Њ7.587Ј N, 82Њ25.793Ј W; lower ␦13C, and thus provide additional evidence that nutri- Figure 1). This site was considered a reference site in the ents from human activities on land are entering coastal reef northern zone. It is an open area with good currents running food webs. parallel to the coast toward the city (AGUILAR et al., 2004). Table 1. Key features of substrate and benthos at the sampling stations of the northern coast; see Figure 1. Sampling Sites Variable BR RIO C30 Comments Complexity index† 1.17 1.05 1.16 The complexity of substrate is very similar in all sites. Number of coral species 3 11 17 Higher number of species, higher density of colonies, bigger colonies, and Density of coral colonies (per m2) 0.4 2.4 6.3 higher cover are indicators of better environmental conditions in coral Coral size (cm) 10.3 15.4 25.8 reefs. Coral cover (%) 0.0 0.6 6.5 Density of sponges (ind/m2) 11.2 2.0 5.9 In general, more sponges and fewer gorgonaceans are predicted at eutro- Density of gorgonaceans (ind/m2) 0.3 0.1 2.1 phic sites. Algal cover (%) 62.8 97.1 45.6 Algal cover is positively correlated with nutrient levels. Polychaete cover (%) 35.2 0.0 0.0 Both are considered good indicators of organic pollution. Cyanobacteria cover (%) 6.8 0.0 0.0 (Unpublished data provided by E. de la Guardia and P. Gonza´lez-Dı´az, Center of Marine Research, University of Havana, Cuba). BR ϭ Havana Harbor, C30 ϭ Miramar, RIO ϭ Almendares River. † Using the chain method. Journal of Coastal Research, Vol. 24, No. 5, 2008 Human Impacts on Cuban Reef Fish 1283 ␦ ϭ Ϫ ϫ No significant pollution sources exist near the shore, except X [(Rsample/Rstandard) 1] 1000 delta, for a small, intermittently flowing drainage pipe receiving where X ϭ 13Cor15N and R ϭ 13C/12Cor15N/14N. illegal sewage effluents. Effects on the subtidal zone are not Replicates of commercially available isotope standards apparent. Benthos is well developed with large corals and a yielded results that were both accurate and precise (Inter- high density of colonies, including gorgonaceans (Table 1).