Nitrogen uptake and internal recycling in Zostera marina exposed to oyster farming: eelgrass potential as a natural biofilter

Oyster farming in estuaries and coastal lagoons frequently overlaps with the distribution of seagrass meadows, yet there are few studies on how this aquaculture practice affects seagrass physiology. We compared in situ nitrogen uptake and the productivity of Zostera marina shoots growing near off-bottom longlines and at a site not affected by oyster farming in San Quintin Bay, a coastal lagoon in Baja California, Mexico. We used benthic chambers to measure leaf NH4 (+) uptake capacities by pulse labeling with (NH4)-N-15 (+) and plant photosynthesis and respiration. The internal N-15 resorption/recycling was measured in shoots 2 weeks after incubations. The natural isotopic composition of eelgrass tissues and vegetative descriptors were also examined. Plants growing at the oyster farming site showed a higher leaf NH4 (+) uptake rate (33.1 mmol NH4 (+) m(-2) day(-1)) relative to those not exposed to oyster cultures (25.6 mmol NH4 (+) m(-2) day(-1)). We calculated that an eelgrass meadow of 15-16 ha (which represents only about 3-4 % of the subtidal eelgrass meadow cover in the western arm of the lagoon) can potentially incorporate the total amount of NH4 (+) excreted by oysters (similar to 5.2 x 10(6) mmol NH4 (+) day(-1)). This highlights the potential of eelgrass to act as a natural biofilter for the NH4 (+) produced by oyster farming. Shoots exposed to oysters were more efficient in re-utilizing the internal N-15 into the growth of new leaf tissues or to translocate it to belowground tissues. Photosynthetic rates were greater in shoots exposed to oysters, which is consistent with higher NH4 (+) uptake and less negative delta C-13 values. Vegetative production (shoot size, leaf growth) was also higher in these shoots. Aboveground/belowground biomass ratio was lower in eelgrass beds not directly influenced by oyster farms, likely related to the higher investment in belowground biomass to incorporate sedimentary nutrients

pH-density relationships in seawater

 In surface waters from the Southern Ocean and from the west coast of Baja California, a relationship was found between pH and water column density. In the Southern Ocean, pH was found to correlate well with density and salinity but not with temperature because water column stability was due to salinity. The opposite was found on the west coast of Baja California, where density was controlled by temperature. This demonstrates that pH follows density independently of what controls it. According to the results of this work, we suggest that pH-density correlations may be an important option in the development of algorithms for monitoring CO2 from satellite imagery

The effect of El Niño on the nutrients and total organic cabon of a coastal lagoon of northwestern Baja California

Nutrients (NO3 + NO2, PO4) and total organic carbon (TOC) from Estero de Punta Banda, a coastal lagoon of Baja California (Mexico), were studied during the 1992–93 El Niño. Samples were collected at four sites distributed along the main channel of the lagoon, during four different tidal stages. According to reports in the literature, this coastal lagoon behaves as an antiestuary most of the time, with salinity increasing significantly from the mouth inwards. Greater input of fresh water due to a larger rainfall, well above the annual mean (393 mm), caused the Estero to behave as an estuary, with salinity values of <25 and with an increase of NO3 + NO2, PO4 and TOC. PO4 values fluctuated between 0.5 and 3.5 µM, and those of TOC between 2.3 and 9.8 mg L–1, with a clear tendency to increase from the entrance to the interior of the lagoon. NO3 values fluctuated between 0.2 and 2.3 µM in September 1992, and between 1.4 and 6.8 µM in March 1993, also with a clear tendency to increase towards the lagoon´ s interior in the latter case. PO4 had a significant negative correlation (P < 0.05) with salinity in March 1993. The change of this lagoon from antiestuary to estuary for long periods, of almost up to one year, is related to meteorological phenomena influenced by large scale events like El Niño

Temporal variation in the abundance of postlarval and juvenile blue shrimp (Litopenaeus stylirostris) and brown shrimp (Farfantepenaeus californiensis) in the Colorado River estuary

The temporal variation in the abundance and species composition of penaeid shrimp postlarvae and juveniles was studied in a tidal channel of the Colorado River estuary. Biweekly sampling during flood and ebb tide was conducted from March through November 2000. Postlarvae of the blue shrimp, Litopenaeus stylirostris, were observed beginning in May, with highest densities in early June during flood tide. A much smaller peak in densities occurred in late September, with few postlarvae found in October and November. Juvenile L. stylirostris were present in highest densities during ebb tide in mid-June, with smaller peaks in mid-July and late September. Densities of postlarval and juvenile brown shrimp, Farfantepenaeus californiensis, were much lower than those of L. stylirostris and without clearly defined peaks. The growth rate of juvenile L. stylirostris appeared similar to rates (30–60 mm month–1) reported for penaeid shrimp from the Pacific Ocean, Gulf of Mexico, and Australia. Management decisions affecting the Upper Gulf of California and Colorado River Delta Biosphere Reserve need to be cognizant of the importance of May and June as critical months in the use of the estuarine tidal channels by these commercially important species

Nutrient dynamics in the west arm of San Quintín Bay, Baja California, Mexico, during and after El Niño 1997/1998

 Time series of 8 h (May, September and November 1997, and March 1998) and 24 h (June and September 1999, and February 2000) were carried out at two (1997–1998) or three sites (1999–2000) of the west arm (Falsa Bay, FB) of San Quintín Bay, in order to assess the nutrient dynamics during and after the 1997/1998 El Niño event. Chlorophyll a concentrations were also determined during each time series. Non-conservative fluxes of dissolved inorganic phosphorus (∆DIP), dissolved inorganic nitrogen (∆DIN), nitrates (NO3–) and ammonium (∆NH4+) were estimated using a nutrient budget model. High NH4+ peaks (18–45 µM) were detected during El Niño 1997/1998, and the mean concentration values were higher than those of 1999–2000. Ammonium concentration was consistently less than 8 µM during 1999–2000. Significant correlations (r = 0.60 to 0.80) were found between tidal height and NO3– concentration in 1999–2000, as well as an inverse relationship between nitrates and salinity, thus reflecting the input of new DIN from the ocean. Chlorophyll a concentration was up to two times higher in 1999–2000 than during El Niño. There were no significant correlations between tidal height and nutrient concentration during 1997–1998, suggesting that: (a) the high NH4+ concentrations found in 1997–1998 were due to in situ remineralization of the organic matter and, possibly, the excretion by cultured mollusc bivalves in FB, and (b) the increase of chlorophyll a and NO3– during 1999–2000 was mainly due to new inputs from the adjacent ocean. The positive ∆DIP values (0.1 to 0.57) and negative values of the net ecosystem metabolism (NEM = –1 to –60 mmol m–2 d–1) observed throughout 1997–2000 indicate that FB permanently exported DIP towards the ocean and behaved as a net heterotrophic system, with or without the presence of El Niño

Phosphate balance and spatial variability on the continental shelf off the western US-Mexico border region

 A cruise was conducted along the northwestern coast of Baja California, off the US-Mexico border region, to determine the physical, biological and anthropogenic factors affecting the concentration and distribution of phosphates (PO43–). The vertical distribution of temperature and PO43– showed isograms (13ºC and 0.75 µM, respectively) rising towards the shore. Although this phenomenon was observed in all the study area, it was more abrupt in the southern part than in the northern, resulting in lower phosphate concentrations in the north (0.50 µM) associated with high chlorophyll a concentrations (10.0 mg m–3). A principal components analysis indicated that the PO43– concentrations were related to upwelling (51%) and phytoplankton biomass (23%). A PO43– mass balance indicated that sewage discharge had a very local effect, contributing 3.0 ± 0.12 t d–1 (5%), while horizontal advection contributed 20.0 ± 2.2 t d–1 (32%) and upwelling supply was 41.1 ± 2.3 t d–1 (63%). If the PO43– sewage contribution trend does not change, we predict that in 2035 the anthropogenic contribution will be as high as the amount delivered to the area by the Californian Current. Conversely, if Mexico´ s sewage treatment systems improve to a level similar to that in the USA, we estimate that by 2012 the anthropogenic sources will be insignificant

Seasonal and inter-annual variability in alkalinity in Liverpool Bay (53.5° N, 3.5° W) and in major river inputs to the North Sea

A critical factor controlling changes in the acidity of coastal waters is the alkalinity of the water. Concentrations of alkalinity are determined by supply from rivers and by in situ processes such as biological production and denitrification. A 2-year study based on 15 cruises in Liverpool Bay followed the seasonal cycles of changing concentrations of total alkalinity (TA) and total dissolved inorganic carbon (DIC) in relation to changes caused by the annual cycle of biological production during the mixing of river water into the Bay. Consistent annual cycles in concentrations of nutrients, TA and DIC were observed in both years. At a salinity of 31.5, the locus of primary production during the spring bloom, concentrations of NO x decreased by 25?±?4 ?mol kg?1 and DIC by 106?±?16 ?mol kg?1. Observed changes in TA were consistent with the uptake of protons during primary biological production. Concentrations of TA increased by 33?±?8 ?mol kg?1 (2009) and 33?±?15 ?mol kg?1 (2010). The impact of changes in organic matter on the measured TA appears likely to be small in this area. Thomas et al. (2009) suggested that denitrification may enhance the CO2 uptake of the North Sea by 25%, in contrast we find that although denitrification is a significant process in itself, it does not increase concentrations of TA relative to those of DIC and so does not increase buffer capacity and potential uptake of CO2 into shelf seawaters. For Liverpool Bay historical data suggest that higher concentrations of TA during periods of low flow are likely to contribute in part to the observed change in TA between winter and summer but the appropriate pattern cannot be identified in recent low-frequency river data. On a wider scale, data for the rivers Mersey, Rhine, Elbe and Weser show that patterns of seasonal change in concentrations of TA in river inputs differ between river systems