Organotin compounds in marine water and sediments from the port of Ensenada, Baja California, Mexico

 During September and October 1995, samples of surface sediments and water were collected to develop an analytical set-up to determine the concentrations of the organic compounds known as tributyltins (TBTs), including tributyl-, dibutyl- and monobutyltin. The method was then used to measure the levels of these contaminants in the port of Ensenada, Baja California. The method is based on hydride generation with atomic absorption detection. The concentrations determined were found to be relatively high (33 to 1021 ng g–1 of Sn in sediments and 66 to 469 ng L–1 in water samples), when compared to those obtained in similar works at San Diego Bay in California, USA. Comparisons are also made with other geographical locations. These results suggest that the port of Ensenada is an area that is receiving substantial amounts of these chemicals and might already be affecting the health of local biota. Two sources of these chemicals were identified: the activities associated with painting and cleaning of both commercial and sport boats, and the presence, at the time of the sampling, of an old platform near the entrance to the port facilities. The presence of the three compounds suggests that there is a permanent entry of these pollutants; furthermore, the presence of decreasing concentrations, starting with the more butylated compounds, suggests a recent introduction. Thc higher concentrations found in the sediment samples indicates the existence of an eflicient method of removal from the water column to the sediments of these compounds. The removal mechanism is associated with the presente of organic matter in the port area. In the sediments, the distribution of TBTs was partially dictated by the organic content, as a significant correlation (α = 0.05) between TBT concentration and organic content was found

Effects of sulfide concentration, pH, and anoxia on photosynthesis and respiration of Zostera marina

Sulfide produced in marine sediments by sulfate reduction is toxic for several macrophytes, and high sediment sulfide concentrations have been associated with seagrass die-off events. Sulfide has been shown to reduce growth in a number of seagrasses, but little is known about its effect on the photosynthetic and respiratory metabolism. Consequently, the aim of this research was to evaluate the effect of sulfide on photosynthesis and respiration of the seagrass Zostera marina. Photosynthetic oxygen evolution and respiration were determined polarographically, while the optimum quantum yield was used as a measure of the photosynthetic performance of photosystem II in the leaves of Z. marina. The results showed that sulfide concentrations of approximately 1000 uM could be considered an upper threshold limit for the survival of Z. marina in the coastal lagoons of Baja California (Mexico) studied. Respiration was not inhibited by sulfide concentrations up to 1000 ?M during 48-h incubations, while photosynthetic performance was reduced by short exposure to sulfide concentrations of 25 uM but also by long exposure to concentrations as low as 50 uM. This is the first study that shows that the photosynthetic capacity of Z. marina is not recovered once the sulfide-free conditions have been re-established

Combined effects of marine heatwaves and reduced light on the physiology and growth of the surfgrass Phyllospadix torreyi from Baja California, Mexico

This study aimed to elucidate for the first time the combined effects of marine heatwaves (MHWs) and light limitation simulated in mesocosm on critical physiological descriptors of the surfgrass Phyllospadix torreyi, which constitutes highly productive meadows along the intertidal and subtidal rocky shores of the Pacific coast of North America. Our results revealed that short-term exposure (~7 days) to extreme thermal anomalies of + 9 ◦C had positive effects on the photosynthetic capacities of P. torreyi, as indicated by increments in maximum photosynthetic rates, photosynthetic efficiency (α), maximum electron transport rate, and effective quantum yield. Despite that its photosynthetic performance was enhanced, exposure to warming caused a decrease in its internal carbon reserves (i.e. energy status), likely as a consequence of carbon mobilization/utilization to activate heatstress responses. Plants exposed to light limitation generally exhibited an increase in α and/or a decrease in respiration, which ultimately allowed for a reduction in plant compensation irradiance. The combination of low light and seawater warming resulted in a decrease in non-structural carbohydrates content, daily net-productivity, and leaf growth rates. Gross photosynthetic rates at control saturating irradiance exhibited higher activation energy and, thus, greater responsiveness to seawater warming than plants kept under light limitation. While our results indicated that unusual warming events might favor the photosynthetic performance of P. torreyi, combining this condition with a drastic light reduction can lead to internal carbon depletion and potentially compromise plant survival in the long term.1,51