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Background: Recent studies using batch-fermentation suggest that the red macroalgae Asparagopsis taxiformis has the potential to reduce methane (CH4) production from beef cattle by up to ~ 99% when added to Rhodes grass hay; a common feed in the Australian beef industry. These experiments have shown significant reductions in CH4 without compromising other fermentation parameters (i.e. volatile fatty acid production) with A. taxiformis organic matter (OM) inclusion rates of up to 5%. In the study presented here, A. taxiformis was evaluated for its ability to reduce methane production from dairy cattle fed a mixed ration widely utilized in California, the largest milk producing state in the US. 

Results: Fermentation in a semi-continuous in-vitro rumen system suggests that A. taxiformis can reduce methane production from enteric fermentation in dairy cattle by 95% when added at a 5% OM inclusion rate without any obvious negative impacts on volatile fatty acid production. High-throughput 16S ribosomal RNA (rRNA) gene amplicon sequencing showed that seaweed amendment effects rumen microbiome consistent with the Anna Karenina hypothesis, with increased β-diversity, over time scales of approximately 3 days. The relative abundance of methanogens in the fermentation vessels amended with A. taxiformis decreased significantly compared to control vessels, but this reduction in methanogen abundance was only significant when averaged over the course of the experiment. Alternatively, significant reductions of CH4 in the A. taxiformis amended vessels was measured in the early stages of the experiment. This suggests that A. taxiformis has an immediate effect on the metabolic functionality of rumen methanogens whereas its impact on microbiome assemblage, specifically methanogen abundance, is delayed. 

Conclusions: The methane reducing effect of A. taxiformis during rumen fermentation makes this macroalgae a promising candidate as a biotic methane mitigation strategy for dairy cattle. But its effect in-vivo (i.e. in dairy cattle) remains to be investigated in animal trials. Furthermore, to obtain a holistic understanding of the biochemistry responsible for the significant reduction of methane, gene expression profiles of the rumen microbiome and the host animal are warranted. 

A cage culture system was previously developed for the red alga Gracilaria parvispora Abbott on Molokai, HI; however, yields have shown marked variation, even among cages with identical stocking rates and fertilization treatments. Water motion, which can be affected by location and arrangement of the cages in the grow-out area, was hypothesized to be a factor contributing to the variation in yield. To examine this, the growth rates of thalli and the development of sporelings in relation to water motion were determined in replicated trials both in tanks and in small-scale field experiments.Generally, water motion had a substantial effect on both thallus growth rate and spore development. In the tank cultures of thalli, water velocities ranged up to 13.7 cm s−1, and relative growth rates (RGRs) ranged from 2.8% to 8.9% day−1. In the lagoon, water velocities ranged between 3.6 and 11.6 cm s−1. Relative growth rates of the thalli in the lagoon trials were 0.02–10.3% day−1. Sporeling density, a measure of spore development, was also significantly affected by water motion. In the tank trials, water motion ranged from near 0 to 6.50 cm s−1, and sporeling densities ranged from 1.4 cm−2 at lower water motion levels to 11.6 sporelings cm−2 at higher levels. Similar results were obtained in lagoon trials, with sporeling densities ranging from 0.2 to 6.7 cm−2. However, sporeling length was not significantly correlated with water motion. In previous trials, we have been able to achieve high sporeling densities, but elongation of sporelings has been inhibited. In the present trials, we were able to break the apparent sporeling dormancy by incubating the sporelings in tanks enriched in nutrients supplied by fish cultures. Consideration of the effects of water motion is important in designing culture systems for species of Gracilaria and other marine algae. The results also suggest that nutrients play a key role in regulating the early development of G. parvispora sporelings.

Experiments were conducted in Mayagüez, Puerto Rico, to assess the effects of a commercially available extract of the brown alga Ascophyllum nodosum on ‘Palmer’ and ‘Parvin’ mangos grown for transplants. The extract was soil-applied biweekly at 0 to 5 ml/L, using 150 ml of aqueous solution per plant per application. Both varieties responded similarly to the alga extract. Increasing the extract rate resulted in increased leaf chlorophyll content (up to 25% higher) and accelerated scion shoot height gain (up to 22%). These results indicate that Ascophyllum alga extracts can be used to reduce the time necessary to grow mango transplants.

Seaweeds are ecologically important primary producers, competitors, and ecosystem engineers that play a central role in coastal habitats ranging from kelp forests to coral reefs. Although seaweeds are known to be vulnerable to physical and chemical changes in the marine environment, the impacts of ongoing and future anthropogenic climate change in seaweed- dominated ecosystems remain poorly understood. In this review, we describe the ways in which changes in the environment directly affect seaweeds in terms of their physiology, growth, reproduction, and survival. We consider the extent to which seaweed species may be able to respond to these changes via adaptation or migration. We also examine the extensive reshuffling of communities that is occurring as the ecological balance between competing species changes, and as top-down control by herbivores becomes stronger or weaker. Finally, we delve into some of the ecosystem- level responses to these changes, including changes in primary productivity, diversity, and resilience. Although there are several key areas in which ecological insight is lacking, we suggest that reasonable climate-related hypotheses can be developed and tested based on current information. By strategically prioritizing research in the areas of complex environmental variation, multiple stressor effects, evolutionary adaptation, and population, community, and ecosystem-level responses, we can rapidly build upon our current understanding of seaweed biology and climate change ecology to more effectively conserve and manage coastal ecosystems.