Ocean acidification significantly alters the trace element content of the kelp, Saccharina latissima.

Seaweeds are ecosystem engineers that can serve as habitat, sequester carbon, buffer ecosystems against acidification, and, in an aquaculture setting, represent an important food source. One health issue regarding the consumption of seaweeds and specifically, kelp, is the accumulation of some trace elements of concern within tissues. As atmospheric CO2 concentrations rise, and global oceans acidify, the concentrations of elements in seawater and kelp may change. Here, we cultivated the sugar kelp, Saccharina latissima under ambient (~400 µatm) and elevated pCO2 (600-2400 µatm) conditions and examined the accumulation of trace elements using x-ray powder diffraction, sub-micron resolution x-ray imaging, and inductively coupled plasma mass spectrometry. Exposure of S. latissima to higher concentrations of pCO2 and lower pH caused a significant increase (p < 0.05) in the iodine and arsenic content of kelp along with increased subcellular heterogeneity of these two elements as well as bromine. The iodine-to­calcium and bromine-to­calcium ratios of kelp also increased significantly under high CO2/low pH (p < 0.05). In contrast, high CO2/low pH significantly reduced levels of copper and cadmium in kelp tissue (p < 0.05) and there were significant inverse correlations between concentrations of pCO2 and concentrations of cadmium and copper in kelp (p < 0.05). Changes in copper and cadmium levels in kelp were counter to expected changes in their free ionic concentrations in seawater, suggesting that the influence of low pH on algal physiology was an important control on the elemental content of kelp. Collectively, these findings reveal the complex effects of ocean acidification on the elemental composition of seaweeds and indicate that the elemental content of seaweeds used as food must be carefully monitored as climate change accelerates this century.

A survey of Dinophysis spp. and their potential to cause diarrhetic shellfish poisoning in coastal waters of the United States.

Multiple species of the genus Dinophysis produce diarrhetic shellfish toxins (okadaic acid and Dinophysis toxins, OA/DTXs analogs) and/or pectenotoxins (PTXs). Only since 2008 have DSP events (illnesses and/or shellfish harvesting closures) become recognized as a threat to human health in the United States. This study characterized 20 strains representing five species of Dinophysis spp. isolated from three US coastal regions that have experienced DSP events: the Northeast/Mid-Atlantic, the Gulf of Mexico, and the Pacific Northwest. Using a combination of morphometric and DNA-based evidence, seven Northeast/Mid-Atlantic isolates and four Pacific Northwest isolates were classified as D. acuminata, a total of four isolates from two coasts were classified as D. norvegica, two isolates from the Pacific Northwest coast were identified as D. fortii, and three isolates from the Gulf of Mexico were identified as D. ovum and D. caudata. Toxin profiles of D. acuminata and D. norvegica varied by their geographical origin within the United States. Cross-regional comparison of toxin profiles was not possible with the other three species; however, within each region, distinct species-conserved profiles for isolates of D. fortii, D. ovum, and D. caudata were observed. Historical and recent data from various State and Tribal monitoring programs were compiled and compared, including maximum recorded cell abundances of Dinophysis spp., maximum concentrations of OA/DTXs recorded in commercial shellfish species, and durations of harvesting closures, to provide perspective regarding potential for DSP impacts to regional public health and shellfish industry.

The invasive red seaweed, Dasysiphonia japonica, forms harmful algal blooms: Mortality in early life stage fish and bivalves and identification of putative toxins.

In recent decades, the rate of introduction of non-indigenous macroalgae has increased. While invasive seaweeds often outcompete native species for substrata, their direct effects on marine life are rarely described. Here, we describe 'red water' events caused by the decay of blooms of the invasive red seaweed, Dasysiphonia japonica, in Great South Bay, NY, USA, and the ability of water from such events to induce rapid and significant mortality in larval and juvenile fish (Menidia beryllina, Menidia menidia, and Cyprinodon variegatus) and larval bivalves (Mercenaria mercenaria and Crassostrea virginica). All species studied experienced significant (p<0.05) reductions in survival when exposed to macroalgae in a state of decay, seawater in which the alga was previously decayed, or both. Both bivalve species experienced 50-60% increases in mortality when exposed to decaying D. japonica for ∼ one week, despite normoxic conditions. Among fish, significant increases (40-80%) in mortality were observed after 24 h exposure to decayed D. japonica and one-week exposures caused, on average, 90% mortality in larval M. beryllina, 50% mortality in juvenile (∼3 cm) M. menidia, and 50% mortality in larval C. variegatus. All fish and bivalve mortality occurred under normoxic conditions (dissolved oxygen (DO) >7 mg L-1) and low ammonium levels (< 20 µM), with the exception of C. variegatus, which expired under conditions of decayed D. japonica coupled with reduced DO caused by the alga. Screening of water with decayed D. japonica using liquid chromatography-mass spectrometry revealed compounds with mass-to-charge ratios matching caulerpin, a known algal toxin that causes fish and shellfish mortality, and several other putative toxicants at elevated levels. Collectively, the high levels of mortality (50-90%) of larval and juvenile fish and bivalves exposed to decaying D. japonica under normoxic conditions coupled with the observation of 'red water' events in estuaries collectively indicate the red seaweed, D. japonica, can create harmful algal blooms (HABs).

The organizing effects of elevated CO2 on competition among estuarine primary producers.

Fossil fuel combustion, eutrophication, and upwelling introduce excess CO2 into coastal zones. The extent to which marine autotrophs may benefit from elevated CO2 will be a function of their carbon limitation and, among other factors, competition with other primary producers. Here, we report on experiments performed with North Atlantic species of Ulva and Gracilaria grown in situ or exposed to ambient (~400 µatm) and elevated pCO2 (~2500 µatm) and/or subjected to competition with each other and/or with natural plankton assemblages. Elevated pCO2 significantly increased the growth rates of Gracilaria and Ulva and yielded significant declines in tissue δ13C, suggesting that increased growth was associated with increased CO2 use relative to HCO3-. Gracilaria growth was unaffected by competition with plankton or Ulva, while Ulva experienced significantly reduced growth when competing with Gracilaria or plankton. Dinoflagellates experienced significantly increased growth when exposed to elevated pCO2 but significantly slower growth when competing with Gracilaria. Elevated carbon-to-nitrogen ratios among macroalgae suggested that competition for nitrogen also shaped interactions among autotrophs, particularly Ulva. While some estuarine autotrophs benefit from elevated pCO2, the benefit can change when direct competition with other primary producers is considered with Gracilaria outcompeting Ulva and dinoflagellates outcompeting diatoms under elevated pCO2.

Ocean Acidification Accelerates the Growth of Two Bloom-Forming Macroalgae.

While there is growing interest in understanding how marine life will respond to future ocean acidification, many coastal ecosystems currently experience intense acidification in response to upwelling, eutrophication, or riverine discharge. Such acidification can be inhibitory to calcifying animals, but less is known regarding how non-calcifying macroalgae may respond to elevated CO2. Here, we report on experiments performed during summer through fall with North Atlantic populations of Gracilaria and Ulva that were grown in situ within a mesotrophic estuary (Shinnecock Bay, NY, USA) or exposed to normal and elevated, but environmentally realistic, levels of pCO2 and/or nutrients (nitrogen and phosphorus). In nearly all experiments, the growth rates of Gracilaria were significantly increased by an average of 70% beyond in situ and control conditions when exposed to elevated levels of pCO2 (p<0.05), but were unaffected by nutrient enrichment. In contrast, the growth response of Ulva was more complex as this alga experienced significantly (p<0.05) increased growth rates in response to both elevated pCO2 and elevated nutrients and, in two cases, pCO2 and nutrients interacted to provide a synergistically enhanced growth rate for Ulva. Across all experiments, elevated pCO2 significantly increased Ulva growth rates by 30% (p<0.05), while the response to nutrients was smaller (p>0.05). The δ13C content of both Gracilaria and Ulva decreased two-to-three fold when grown under elevated pCO2 (p<0.001) and mixing models demonstrated these macroalgae experienced a physiological shift from near exclusive use of HCO3- to primarily CO2 use when exposed to elevated pCO2. This shift in carbon use coupled with significantly increased growth in response to elevated pCO2 suggests that photosynthesis of these algae was limited by their inorganic carbon supply. Given that eutrophication can yield elevated levels of pCO2, this study suggests that the overgrowth of macroalgae in eutrophic estuaries can be directly promoted by acidification, a process that will intensify in the coming decades.