73 Vol. 46, N��1, 2011 Revista de Biolog��a Marina y Oceanograf��a Revista de Biolog��a Marina y Oceanograf��a Vol. 46, N��1: 73-77, abril 2011 Article Metabolic rates and primary productivity of the marine macroalgae Dictyopteris delicatula in Taganga Bay, Colombian Caribbean Tasas metab��licas y productividad primaria de la macroalga marina Dictyopteris delicatula en la Bah��a de Taganga, Caribe Colombiano Juan Diego Gait��n-Espitia1,2 1Instituto de Ecolog��a y Evoluci��n, Facultad de Ciencias, Universidad Austral de Chile, Casilla 567 Valdivia, Chile. juadiegaitan@gmail.com 2Centro de Investigaciones en Zoolog��a y Ecolog��a Marina (CIZEM), Santa Marta, Colombia Abstract.- Metabolic rates and photosynthetic performance of Dictyopteris delicatula were measured in the south of Taganga Bay and on Inca-Inca beach, Colombia, during September and November 2007, as part of a monitoring program of water quality and pollution associated with the stormwater system of the city of Santa Marta. Concentrations of chlorophyll-a of D. delicatula did not show significant differences between both areas but the average rates of net primary productivity and respiration differed significantly, likely due to the effect of the nutrient loadings from the stormwater outlet in Taganga Bay, altering the physiological processes of the macroalgal community. Key words: Phaeophyta, photosynthesis, respiration, metabolism, Colombia INTRODUCTION Primary productivity is the rate at which energy is stored as organic matter in plants per unit area (Fahey & Knapp 2007). Oceans cover the greater part (70%) of the Earth���s surface, but total oceanic net primary production is less (45%) than terrestrial primary production (55%), principally due to the limitation of nutrients in the illuminated surface waters of most open ocean areas (Mackenzie 2005). Although phytoplankton contributes substantially towards the primary productivity of coastal areas, there are certain areas along the coastal belt where production of benthic macrophytes exceeds that of phytoplankton (Dhargalkar & Shaikh 2000). Most coastal areas provide both autochthonous and allochthonous sources of nutrients which result in high primary productivity supporting secondary production. Calculations of primary and secondary productivity in marine communities to estimate metabolic rates are essential to the understanding of trophic web structure and energy and material transfer in marine environments (Carpenter et al. 1991). In many coastal areas along the north coast of the Colombian Caribbean, abundant rocky substrata support a variety of benthic macroalgae communities. In particular, within the Atlantic region of Colombia, the class Phaeophyceae is represented by 71 species, with Dictyopteris accounting for roughly 5.6% of total diversity (D��az-Pulido & D��az-Ru��z 2003). According to Taylor (1960), one of the most common species of the genus in the Caribbean is Dictyopteris delicatula, where it is widely distributed throughout a variety of habitats. The alga commonly grows epiphytically in shallow waters but can also occur down to 30 m depth (Allender & Kraft 1983). This study was undertaken to investigate metabolism in terms of primary productivity, respiration and photosynthesis of a dominant macroalgal population, Dictyopertis delicatula, from the rocky intertidal shore in the south of Taganga Bay following the installation of stormwater culvert drainage system for the city of Santa Marta. There is abundant evidence of the suitability of benthic macrophytes as biological indicators of the effects of pollution gradients (Juanes et al. 2008). There is also evidence that the nutrient loadings from coastal watersheds, stormwater outlets, septic tanks and others sources, are the most widespread factor that alters structure and function of receiving aquatic ecosystems (Valiela et al. 1992). According to this approach, the hypothesis tested was that D. delicatula exhibits higher metabolic rates near Taganga Bay than in coastal areas far away from the city (i.e., Inca-Inca beach) as a result of the influence of the stormwater culvert drainage and the increase in the nutrient input caused by it, where the effect of the run-offs have a direct impact on the macroalgal community.

74 Gait��n-Espitia Primary productivity of Dictyopteris delicatula MATERIAL AND METHODS The study site was located on a rocky intertidal shore near the exit of the stormwater culvert drainage system in the south of Taganga Bay (11��15���27"N 74��12���15"W). A control area (11��12���44"N 74��14���02"W) was located at Inca-Inca Beach (Fig. 1), at a sufficient distance so as not to be under the influence of run-offs from the stormwater culvert drainage system of Santa Marta City. Dictyopteris delicatula displays high percentage cover (35%) in both areas. The algae were collected and incubated (6 hours) once during the rainy season (September- November) of 2007, at both sites of collections at the same time (i.e., between 10 a.m. and 4 p.m.) under natural conditions (i.e., 28��C and 35 psu) at 1 m depth, utilizing the light and dark bottle method, to estimate primary productivity and respiration according to Howarth & Michaels (2000). Incubations were conducted in Falcon tubes of 50 ml with filtered natural seawater, carefully sealed to avoid air bubbles. Ten individuals (each thallus of 2.3 �� 0.04 g wet weight) and two sets of light and dark bottles were used for each location while a set of dark and light bottles incubated without algae served as control. The initial oxygen content was measured before and after each set of experimental bottles was filled with sea water. The oxygen values in light and dark bottles used as control remained constant, so blank corrections need not be applied. Variables such as dissolved oxygen (DO), water temperature, electrical conductivity, and pH were measured at the water column and tubes using digital portable equipments (oximeter YSI model 55 and potentiometer Hatch). Chlorophyll a extraction was obtained by the immersion of the thallus in acetone neutralized with MgCO3 and stored in dark conditions during 24 h at 4��C. In order to eliminate turbidity, the extracts were centrifuged at 5500 g for 20 min. Chlorophyll a concentration was determined using a Hach DR 2010 spectrophotometer and applying the Inskeep & Bloom (1985) equation. Metabolic rates of Dictyopteris delicatula in both sites of study were compared using the Mann-Whitney U test with a level of significance of 5%. Two-way ANOVA was used to compare the pigment content using sampled sites (i.e., Taganga Bay and Inca-Inca beach) and bottles (i.e., light and dark bottle) as fixed factors. For all data, Shapiro-Wilks test for normality and Levene���s test for homogeneity of variance were made. Differences were considered significant at P 0.05. All statistical analyses were performed using STATISTICA 7.0 software (StatSoft, Inc.). RESULTS AND DISCUSSION The macroalgae community composition of the rocky intertidal shore in the Taganga Bay was mostly dominated, in percentage cover, by the brown seaweed Dictyopteris delicatula, followed by Centroceras micracanthum, Padina gymnospora and Jania adhaerens. It is a prerequisite to understand the metabolism of the macrophytic community in order to determine the photosynthetic rates of the dominant (in terms of cover) populations (Littler & Murray 1975). The average rate of Gross Primary Production (GPP) for individuals collected near the fluvial exit of the culvert was 24.7 mgC g dry wt-1 h-1, while at Inca-Inca Beach average GPP was 12.3 mgC g dry wt-1 h-1 (Table 1). Average rates of Net Primary Productivity (NPP) and Respiration (R) differed significantly between the two populations sampled (Mann- Whitney U test, Z = 3.78, P 0.005). On the other hand, the analysis of chlorophyll a (Chl a) concentration (Fig. 2) did Figure 1. Map of the North Coast area in the Colombian Caribbean, showing the two sampling sites, A) Taganga Bay and B) Inca-Inca Beach / Mapa de la Costa Norte del Caribe colombiano se��alando dos lugares de muestreo, A) Bah��a de Taganga y B) Playa Inca- Inca