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Sustainable aquaculture includes the aquaculture of non-fed crops that provide ecosystem services including nutrient extraction and water quality improvement. While shellfish are the most farmed sustainable aquaculture crops in the USA, shellfish farmers in the northeastern US have an interest in diversifying their crops and incorporating seaweeds into their farms. In this study, we worked with oyster farmers to investigate the potential for farming sugar kelp, Saccharina latissima, across different environmental regimes in coastal Rhode Island USA. Kelp seed spools were outplanted at two time points in the fall/winter of 2017 and 2018 at four sites and cultivated until harvest the following spring. Kelp performance (length, width, yield), tissue content, and nutrient extraction were determined for each line in each year; oyster growth was also measured monthly for one year at each site. We found that kelp could successfully grow in both shallow coastal lagoons and estuarine sites, although the timing of planting and placement of sites was important. Lines that were planted earlier (as soon as water temperatures<15°C) grew longer and yielded more biomass at harvest; overall, kelp blade yield ranged from 0.36 ± 0.01 to 11.26 ± 2.18 kg/m long line. We report little variation in the tissue quality (C:N) of kelp among sites, but differences in biomass production led to differences in nutrient extraction, which ranged from 0.28 ± 0.04 to 16.35 ± 4.26 g nitrogen/m long line and 8.93 ± 0.35 to 286.30 ± 74.66 g carbon/m long line. We found extensive variability in kelp growth within and between lines and between years, suggesting that crop consistency is a challenge for kelp farmers in the region. Our results suggest that, as there is a lower barrier in terms of permitting (versus starting a new aquaculture farm), it may be a worthwhile investment to add sugar kelp to existing oyster farms, provided they have suitable conditions. At current market rates of US$0.88-$3.30 per kg, farmers in southern New England have the potential to earn US$2,229 per 60 m longline. While seaweed aquaculture is growing, considerable barriers still exist that prevent wide-scale kelp aquaculture adoption by existing aquafarmers. [ABSTRACT FROM AUTHOR]

We combined field monitoring and laboratory experiments to examine the population ecology of both the microscopic and macroscopic stages of a new invasion of Undaria pinnatifida in California. Over the course of 1 yr, we observed 2 distinct recruitment pulses of individuals in the Santa Barbara harbor; the appearance of these pulses was strongly correlated with a 4degreesC drop in ocean temperature approximately 2 mo prior to recruitment, Cultures of zoospores and successive microscopic stages revealed thermal tolerances consistent with field recruitment data; individuals grown at 13degreesC had significantly higher survivorship than individuals grown at higher temperatures (harbor temperatures annually ranged from 12 to 21degreesC). The 2 cohorts also differed greatly in individual size, growth rate, and survival to maturity. Grazing by herbivores, predominately the native kelp crab Pugettia producta, effectively prevented nearly all individuals in the second cohort from reaching reproductive maturity. Grazer control was effective despite far higher rates of recruitment during the second recruitment pulse. Our results highlight the potential for extreme variability in U. pinnatifida demography mediated by local oceanographic and biotic factors. Understanding controls on U. pinnatifida demography helps to explain variation in the spread and impact of this invader worldwide, and allows better prediction of when and where U. pinnatifida may continue its invasion along the west coast of North America.

Many algal species have life cycles that involve an obligate alternation of generations between nearly identical, free-living haploid and diploid individuals. The percentages of haploids to diploids, and the spatial and temporal scales of variation of these percentages, must be examined before hypotheses about the relative importance of haploid and diploid demographic processes on population dynamics can be evaluated. In this paper, we investigated the spatial and temporal dynamics of the percentage of haploid and diploid stages in 4 congeners of the marine alga Mazzaella (M capensis, M flaccida, M laminarioides, and M splendens) across large portions of their geographical ranges. For the 3 species that were sampled over multiple years (M. flaccida, M. laminarioides, M splendens), the percentage of haploids varied significantly among sites. However, 2 of them (M flaccida, M. splendens) did not exhibit significant temporal (interannual) variation in the percentage of haploids. In addition, more fine-scale temporal studies on M flaccida populations revealed that there were also no significant intra-annual fluctuations in the percentage of haploids, although there was significant population turnover on this timescale. This spatial variability but temporal stability of haploid-diploid ratios (for M flaccida and M splendens) can be used to generate, and subsequently test, hypotheses on the regulation of haploid-diploid ratios and the relative importance of haploid and diploid demographic processes on population dynamics.

Coastal wetlands are known for exceptional productivity, but they also receive intense land-based nitrogen (N) loading. In Narragansett Bay, RI (USA), coastal ecosystems have received anthropogenic N inputs from wastewater for more than two centuries. Greenhouse gas fluxes were studied throughout a growing season (2016) in three coastal wetlands with contrasting histories of nitrogen loading. The wetland with the highest historic N load (Mary’s Creek, Warwick, RI) had significantly greater nitrous oxide (N2O) and methane (CH4) emissions than the other two sites. However, the two marshes with historic N loads (Mary’s Creek and Mary Donovan, Little Compton, RI) also had greater rates of CO2 uptake than the reference site (Nag Marsh, Prudence Island, RI). Their CO2 uptake rates far outpaced their other greenhouse gas emissions. Mary’s Creek had the greatest above- and below-ground plant biomass, vertical accretion rates, and carbon content of soils. Spartina alterniflora height was greatest at Mary’s Creek and Mary Donovan marsh. The following growing season (2017), greenhouse gases were compared across four plant-defined ecological zones in Mary’s Creek. Higher rates of CO2 uptake and CH4 emissions were found in the S. alterniflora-vegetated creekbank compared to high marsh zones or bare mudflats. Potential denitrifying enzyme activity did not significantly differ across the four zones nor between Mary’s Creek and Nag Marsh, suggesting a consistently high capacity to completely reduce N loads. These results support efforts to protect and restore these coastal ecosystems for their carbon sequestration function even despite prevalence of anthropogenic N loading. [ABSTRACT FROM AUTHOR]