Jang K. Kim

Emersion Induces Nitrogen Release and Alteration of Nitrogen Metabolism in the Intertidal Genus Porphyra

We investigated emersion-induced nitrogen (N) release from Porphyra umbilicalis Kütz. Thallus N concentration decreased during 4 h of emersion. Tissue N and soluble protein contents of P. umbilicalis were positively correlated and decreased during emersion. Growth of P. umbilicalis did not simply dilute the pre-emersion tissue N concentration. Rather, N was lost from tissues during emersion. We hypothesize that emersion-induced N release occurs when proteins are catabolized. While the δ15N value of tissues exposed to emersion was higher than that of continuously submerged tissues, further discrimination of stable N isotopes did not occur during the 4 h emersion. We conclude that N release from Porphyra during emersion did not result from bacterial denitrification, but possibly as a consequence of photorespiration. The release of N by P. umbilicalis into the environment during emersion suggests a novel role of intertidal seaweeds in the global N cycle. Emersion also altered the physiological function (nitrate uptake, nitrate reductase and glutamine synthetase activity, growth rate) of P. umbilicalis and the co-occurring upper intertidal species P. linearis Grev., though in a seasonally influenced manner. Individuals of the year round perennial species P. umbilicalis were more tolerant of emersion than ephemeral, cold temperate P. linearis in early winter. However, the mid-winter populations of both P. linearis and P. umbilicalis, had similar temporal physiological patterns during emersion.

Comparison of growth and nitrate uptake by New England Porphyra species from different tidal elevations in relation to desiccation

Desiccation stress can determine the upper distribution limits and may enhance the uptake of nitrate and ammonium of eulittoral algal species. Upper shore species may exhibit greater stimulation of nitrate uptake following desiccation and achieve maximum uptake at higher desiccation levels. The objective of this study was to determine whether Porphyra species from different vertical elevations respond differently to the desiccation stress, in terms of growth and nitrate uptake. A eulittoral species (Porphyra umbilicalis) and a sublittoral species (P. amplissima) were compared in the present study. Samples were exposed to air for 0, 30 min (40 ± 10% water loss) and 2 h (90 ± 5% water loss), after an initial 4 h light period every day. Desiccation was more stressful to the sublittoral species, Porphyra amplissima, than to the eulittoral species, P. umbilicalis. When tissues were exposed for 2 h daily, P. amplissima lost weight over a 24 h day, while the growth rate of P. umbilicalis dropped by only 30% compared with that of continuously submerged blades. Nitrate uptake rate of sublittoral P. amplissima was only 73% (40 ± 10% water loss) and 62% (90 ± 5% water loss) of that of continuously submerged tissue. Nitrate uptake rates of P. umbilicalis were not significantly affected by desiccation. These results suggest that species in the eulittoral zone, which have longer exposure times, have a higher time‐use efficiency than the sublittoral species in terms of nitrate uptake. This indicates a possible correlation between nitrate uptake and observed vertical distribution patterns.

Potential applications of nuisance microalgae blooms

Algal blooms have become a major concern in coastal areas and the great lakes of the world. Because of their various consequences for aquatic ecosystems and resources, algal blooms are called “harmful algal blooms” (HABs). HABs often become severely detrimental when they involve one or more toxin-producing microalgae of various taxonomic origins. The accumulation of algal biomass also has deleterious effects on the ecological status of water. However, appropriate management strategies can allow the beneficial utilization of these events by consuming the biomass feedstock in the production of valuable biocommodities, including biofuels, functional food ingredients, UV-absorbing compounds, pharmaceutical products, etc. However, if the algal biomass can be harvested prior to the onset of their death phase, nutrients (carbon, nitrogen, and phosphorus) can also be removed from the ecosystem by harvesting the algal blooms. Great progress has been made in the last decade in monitoring and predicting HABs, and a demand is emerging for persuasive postevent management policies that focus on the potential utilization of these blooms as natural renewable bioresources. This review summarizes various potential applications of nuisance algal blooms and the need for scientific research into their economic and industrial potential. Major algal products with great ecological and economic significance and their contemporary global utilization are analyzed.

Evaluation of green seaweed Ulva sp. as a replacement of fish meal in plant-based practical diets for Pacific white shrimp, Litopenaeus vannamei

A growth trial and a digestibility trial were conducted to evaluate seaweed Ulva sp. as a substitution for fish meal (FM) in commercial-type feed formulation for Pacific white shrimp, Litopenaeus vannamei. Towards this goal, the 6-week growth trial utilized increasing levels (0, 6.35, 12.7, 19.05, and 25.4%) of the first batch of Ulva meal (UM1) to replace up to 8% FM in a plant-based feed formulation. At the end of the growth trial, shrimp offered diets containing 12.7, 19.05, and 25.4% UM1 exhibited significantly reduced weight gain. Apparent net protein retention (ANPR) was significantly decreased, while feed conversion ratio (FCR) was significantly increased when shrimps were fed with diets containing 19.05 and 25.4% UM1. Crude lipid content of whole shrimp samples were significantly decreased when UM1 was supplemented in the diets. Apparent digestibility coefficients of dry matter, energy, protein, and amino acids of two batches of Ulva meal (UM1 and UM2) were determined using chromic oxide as an inert maker and the 70:30 replacement technique. Energy and protein digestibility of UM1 and UM2 were significantly lower than FM and soybean meal (SBM) which were run at the same time. As a result of relatively low protein availability, individual amino acids digestibility of UM1 and UM2 are also significantly lower than those of FM and SBM. Results of the present study indicate that UM1 can be included in the shrimp diet up to 6.35% to replace 2% fish meal without resulting in growth depression. The low nutrients availability and high mineral contents of Ulva meal may explain a portion of the observed reduction in shrimp growth.

Metabolic plasticity of nitrogen assimilation by Porphyra umbilicalis (Linnaeus) Kützing

The physical stresses associated with emersion have long been considered major factors determining the vertical zonation of intertidal seaweeds. We examined Porphyra umbilicalis (Linnaeus) Kützing thalli from the vertical extremes in elevation of an intertidal population (i.e. upper and lower intertidal zones) to determine whether Porphyra thalli acclimate to different vertical elevations on the shore with different patterns of nitrate uptake and nitrate reductase (NR) and glutamine synthetase (GS) activities in response to different degrees of emersion stress. We found that the nitrate uptake and NR recovery in the emersed tissues took longer in lower intertidal sub-population than in upper intertidal sub-population; and GS activity was also significantly affected by emersion and, interestingly, such an activity was enhanced by emersion of thalli from both upper and lower intertidal zones. These results suggested that intra-population variability in post-emersion recovery of physiological functions such as nutrient uptake and NR activity enables local adaptation and contributes to the wide vertical distribution of P. umbilicalis. The high GS activity during periodic emersion stress may be a protective mechanism enabling P. umbilicalis to assimilate nitrogen quickly when it again becomes available, and may also be an evidence of photorespiration during emersion.

Life history interactions between the red algae Chondrus crispus (Gigartinales) and Grateloupia turuturu (Halymeniales) in a changing global environment

Abstract: The invasive rhodophyte Grateloupia turuturu is a large perennial alga, discovered first in Narragansett Bay (Rhode Island) in 1994 and subsequently in the Long Island Sound estuary. The algas low intertidal to shallow subtidal distribution overlaps that of the native Chondrus crispus. Our field measurements suggest that physical disturbance may promote increased substrate cover by G. turuturu. Molecular quantification of spore abundance suggests G. turuturu produces fewer spores, which also disperse shorter distances than spores of C. crispus. However, sporelings of G. turuturu grew faster than those of C. crispus at all environmentally relevant light levels, salinities and temperatures tested. In addition, the temperature tolerance of G. turuturu sporelings was broader; C. crispus sporelings died just after germination at 30°C; whereas, those of G. turuturu survived. The results have implications for community shifts as coastal waters continue to warm into the future.