Pablo P. Leal

Distribution, abundance and diversity of modern dinoflagellate cyst assemblages from southern Chile (43–54° S)

The distribution, abundance and diversity of modern dinoflagellate cyst assemblages were investigated in sediments from the inshore seas of southern Chile (438089–548559 S) at eight sites from April 2004 to January 2005. A total of 24 cyst types were recorded, of which 12 and five were identified at the species and genus levels, respectively. Dinoflagellate cysts were recorded from all sampling sites, but they differed in total abundance (15–270 cysts ml-1) and diversity index (H9 0.88–2.40). Heterotrophic dinoflagellate cysts assigned to heterotrophic species were the most abundant trophic form, with 418 cysts ml -1 , representing 55% of the total cyst abundance. Cluster analysis based on the abundance of dinoflagellate cyst species indicated that sampling sites were segregated into three groups likely to be related to the proportion of autotrophic vs. heterotrophic species cysts and the total abundance of cysts at each site. Distinctive cyst species composition differences among sampling sites may allow inferences about local nutrient and feeding dynamics within the water column.

Meiospores produced in sori of nonsporophyllous laminae of Macrocystis pyrifera (Laminariales, Phaeophyceae) may enhance reproductive output

Different lamina of Macrocystis pyrifera sporophytes (i.e., sporophylls, pneumatocyst‐bearing blades, and apical scimitars) in a wave‐sheltered site were found to be fertile. We quantified their sorus surface area, reproductive output (number of spores released) and the viability of released spores (germination rate). Sorus area was greatest on the sporophylls, with sporangia developing on >57% of the total area and smallest on the pneumatocyst‐bearing blades with 21% of the total area bearing sporangia. The apical scimitar released the greatest number of meiospores (cells · mL−1 · cm−2) and the sporophylls the least. Meiospores produced from all types of fertile laminae were equally viable. This reproductive plasticity may enhance reproductive output, and contribute to short and long‐distance spore dispersal and the cryptic gametophyte propagule bank for the next generation of sporophytes.

Ocean acidification and kelp development: reduced pH has no negative effects on meiospore germination and gametophyte development of Macrocystis pyrifera and Undaria pinnatifida

The absorption of anthropogenic CO2 by the oceans is causing a reduction in the pH of the surface waters termed ocean acidification (OA). This could have substantial effects on marine coastal environments where fleshy (non‐calcareous) macroalgae are dominant primary producers and ecosystem engineers. Few OA studies have focused on the early life stages of large macroalgae such as kelps. This study evaluated the effects of seawater pH on the ontogenic development of meiospores of the native kelp Macrocystis pyrifera and the invasive kelp Undaria pinnatifida, in south‐eastern New Zealand. Meiospores of both kelps were released into four seawater pH treatments (pHT 7.20, extreme OA predicted for 2300; pHT 7.65, OA predicted for 2100; pHT 8.01, ambient pH; and pHT 8.40, pre‐industrial pH) and cultured for 15 d. Meiospore germination, germling growth rate, and gametophyte size and sex ratio were monitored and measured. Exposure to reduced pHT (7.20 and 7.65) had positive effects on germling growth rate and gametophyte size in both M. pyrifera and U. pinnatifida, whereas, higher pHT (8.01 and 8.40) reduced the gametophyte size in both kelps. Sex ratio of gametophytes of both kelps was biased toward females under all pHT treatments, except for U. pinnatifida at pHT 7.65. Germling growth rate under OA was significantly higher in M. pyrifera compared to U. pinnatifida but gametophyte development was equal for both kelps under all seawater pHT treatments, indicating that the microscopic stages of the native M. pyrifera and the invasive U. pinnatifida will respond similarly to OA.

Copper ecotoxicology of marine algae: a methodological appraisal

ABSTRACT The production of accurate and reliable data on copper ecotoxicology of marine algae depends on the use of trace metal clean techniques during experimentation. We reviewed the methodologies used in the literature on copper ecotoxicology of marine macro- and microalgae, specifically the use of trace metal clean procedures such as the labware used (glassware vs. plasticware), methods of cleaning the labware (acid soaking and ultrapure water rinsing), stock solution preparation (copper source and acidification), and measurement and reporting of dissolved copper concentrations. In terms of taxonomic classification, the most studied algal groups were the Phyla Ochrophyta, Bacillariophyta, Rhodophyta, and Chlorophyta. In terms of methodology, ∼50% of the articles did not specify the labware, ∼25% used glassware, and ∼25% plasticware; ∼30% of the studies specified cleaning protocols for labware to remove trace metal impurities; the copper form used to prepare the stock solutions was specified in ∼80% of studies but acidification to stabilise the dissolved copper was performed in only ∼20%; and the dissolved copper concentration was measured in only ∼40% of studies. We discuss the importance of following trace metal clean techniques for the comparison and interpretation of data obtained on copper ecotoxicology in algae.

Seawater pH, and not inorganic nitrogen source, affects pH at the blade surface of Macrocystis pyrifera: implications for responses of the giant kelp to future oceanic conditions

Ocean acidification (OA), the ongoing decline in seawater pH, is predicted to have wide-ranging effects on marine organisms and ecosystems. For seaweeds, the pH at the thallus surface, within the diffusion boundary layer (DBL), is one of the factors controlling their response to OA. Surface pH is controlled by both the pH of the bulk seawater and by the seaweeds metabolism: photosynthesis and respiration increase and decrease pH within the DBL (pHDBL ), respectively. However, other metabolic processes, especially the uptake of inorganic nitrogen (Ni ; NO3- and NH4+ ) may also affect the pHDBL . Using Macrocystis pyrifera, we hypothesized that (1) NO3- uptake will increase the pHDBL , whereas NH4+ uptake will decrease it, (2) if NO3- is cotransported with H+ , increases in pHDBL would be greater under an OA treatment (pHu2009=u20097.65) than under an ambient treatment (pHu2009=u20098.00), and (3) decreases in pHDBL will be smaller at pH 7.65 than at pH 8.00, as higher external [H+ ] might affect the strength of the diffusion gradient. Overall, Ni source did not affect the pHDBL . However, increases in pHDBL were greater at pH 7.65 than at pH 8.00. CO2 uptake was higher at pH 7.65 than at pH 8.00, whereas HCO3- uptake was unaffected by pH. Photosynthesis and respiration control pHDBL rather than Ni uptake. We suggest that under future OA, Macrocystis pyrifera will metabolically modify its surface microenvironment such that the physiological processes of photosynthesis and Ni uptake will not be affected by a reduced pH.

Photosynthesis and nitrogen uptake of the giant kelp Macrocystis pyrifera (Ochrophyta) grown close to salmon farms

Finfish aquaculture is an activity that has experienced an explosive global development, but presents several environmental risks, such as high nitrogen outputs with potential eutrophication consequences. Therefore, the integration of seaweed aquaculture with the aim of decreasing nitrogen emissions associated with intensive salmon farming has been proposed as a bioremediation solution. Ecophysiological knowledge about seaweeds cultured close to farming cages is, however, still rudimentary. We experimentally studied the growth and physiological responses of Macrocystis pyrifera (Linnaeus) C. Agardh in a suspended culture system near a commercial salmon farm at three culture depths in order to understand its productivity performance. The results showed maximum growth responses at intermediate depths (3u202fm) as opposed to near the surface (1u202fm) or at a deeper culture level (6u202fm). At 6u202fm depth, light limitations were detected, whereas the sporophytes growing at 1u202fm depth responded to high irradiances, especially in late spring and summer, where they were more intensely exposed to decay of photosynthesis than individuals from other depths. Accordingly, photosynthetic pigment concentrations (chlorophyll a and c, and fucoxonthin) were higher during low-light seasons (winter and early spring) but decreased during the summer. On the other hand, although both nitrogen uptake and Nitrate Reductase (NR) activity varied seasonally, increasing significantly in spring and summer, these variables were not affected by culture depth. Therefore, the optimal culture depth of M. pyrifera near salmon farms appears to be a physiological integration between nitrogen supply and demand, which is modulated by plant acclimation to the seasonal change in light and temperature. The results allow to discuss about the environmental constrains of M. pyrifera in an ecophysiological context to improve the understanding of its aquaculture, and to contribute relevant information on the use of this species in bioremediation.

Growth, ammonium metabolism, and photosynthetic properties of Ulva australis (Chlorophyta) under decreasing pH and ammonium enrichment

The responses of macroalgae to ocean acidification could be altered by availability of macronutrients, such as ammonium (NH4+). This study determined how the opportunistic macroalga, Ulva australis responded to simultaneous changes in decreasing pH and NH4+ enrichment. This was investigated in a week-long growth experiment across a range of predicted future pHs with ambient and enriched NH4+ treatments followed by measurements of relative growth rates (RGR), NH4+ uptake rates and pools, total chlorophyll, and tissue carbon and nitrogen content. Rapid light curves (RLCs) were used to measure the maximum relative electron transport rate (rETRmax) and maximum quantum yield of photosystem II (PSII) photochemistry (Fv/Fm). Photosynthetic capacity was derived from the RLCs and included the efficiency of light harvesting (α), slope of photoinhibition (β), and the light saturation point (Ek). The results showed that NH4+ enrichment did not modify the effects of pH on RGRs, NH4+ uptake rates and pools, total chlorophyll, rETRmax, α, β, Fv/Fm, tissue C and N, and the C:N ratio. However, Ek was differentially affected by pH under different NH4+ treatments. Ek increased with decreasing pH in the ambient NH4+ treatment, but not in the enriched NH4+ treatment. NH4+ enrichment increased RGRs, NH4+ pools, total chlorophyll, rETRmax, α, β, Fv/Fm, and tissue N, and decreased NH4+ uptake rates and the C:N ratio. Decreased pH increased total chlorophyll content, rETRmax, Fv/Fm, and tissue N content, and decreased the C:N ratio. Therefore, the results indicate that U. australis growth is increased with NH4+ enrichment and not with decreasing pH. While decreasing pH influenced the carbon and nitrogen metabolisms of U. australis, it did not result in changes in growth.

Copper pollution exacerbates the effects of ocean acidification and warming on kelp microscopic early life stages

Ocean warming (OW), ocean acidification (OA) and their interaction with local drivers, e.g., copper pollution, may negatively affect macroalgae and their microscopic life stages. We evaluated meiospore development of the kelps Macrocystis pyrifera and Undaria pinnatifida exposed to a factorial combination of current and 2100-predicted temperature (12 and 16u2009°C, respectively), pH (8.16 and 7.65, respectively), and two copper levels (no-added-copper and species-specific germination Cu-EC50). Meiospore germination for both species declined by 5–18% under OA and ambient temperature/OA conditions, irrespective of copper exposure. Germling growth rate declined by >40%·day−1, and gametophyte development was inhibited under Cu-EC50 exposure, compared to the no-added-copper treatment, irrespective of pH and temperature. Following the removal of copper and 9-day recovery under respective pH and temperature treatments, germling growth rates increased by 8–18%·day−1. The exception was U. pinnatifida under OW/OA, where growth rate remained at 10%·day−1 before and after copper exposure. Copper-binding ligand concentrations were higher in copper-exposed cultures of both species, suggesting that ligands may act as a defence mechanism of kelp early life stages against copper toxicity. Our study demonstrated that copper pollution is more important than global climate drivers in controlling meiospore development in kelps as it disrupts the completion of their life cycle.