Jeffrey Alexander

Harmful algal blooms in the Chesapeake and coastal bays of Maryland, USA: Comparison of 1997, 1998, and 1999 events

Harmful algal blooms in the Chesapeake Bay and coastal bays of Maryland, USA, are not a new phenomenon, but may be increasing in frequency and diversity. Outbreaks ofPfiesteria piscicida (Dinophyceae) were observed during 1997 in several Chesapeake Bay tributaries, while in 1998,Pfiesteria-related events were not found but massive blooms ofProrocentrum minimum (Dinophyceae) occurred. In 1999,Aureococcus anophagefferens (Pelagophyceae) developed in the coastal bays in early summer in sufficient densities to cause a brown tide. In 1997, toxicPfiesteria was responsible for fish kills at relatively low cell densities. In 1998 and 1999, the blooms ofP. minimum andA. anophagefferens were not toxic, but reached sufficiently high densities to have ecological consequences. These years differed in the amount and timing of rainfall events and resulting nutrient loading from the largely agricultural watershed. Nutrient loading to the eastern tributaries of Chesapeake Bay has been increasing over the past decade. Much of this nutrient delivery is in organic form. The sites of thePfiesteria outbreaks ranked among those with the highest organic loading of all sites monitored bay-wide. The availability of dissolved organic carbon and phosphorus were also higher at sites experiencingA. anophagefferens blooms than at those without blooms. The ability to supplement photosynthesis with grazing or organic substrates and to use a diversity of organic nutrients may play a role in the development and maintenance of these species. ForP. minimum andA. anophagefferens, urea is used preferentially over nitrate.Pfiesteria is a grazer, but also has the ability to take up nutrients directly. The timing of nutrient delivery may also be of critical importance in determining the success of certain species.

HARMFUL ALGAE POSE ADDITIONAL CHALLENGES FOR OYSTER RESTORATION: IMPACTS OF THE HARMFUL ALGAE KARLODINIUM VENEFICUM AND PROROCENTRUM MINIMUM ON EARLY LIFE STAGES OF THE OYSTERS CRASSOSTREA VIRGINICA AND CRASSOSTREA ARIAKENSIS

Abstract The eastern oyster, Crassostrea virginica (Gmelin, 1791) has been in decline along the eastern seaboard, and especially in Chesapeake Bay, for decades because of over-harvesting, disease and declines in water quality and suitable habitat. Eutrophication has also been increasing over the past half century, leading to increases in hypoxia and harmful algal blooms (HABs). The effects of two common Chesapeake Bay HAB dinoflagellates, Karlodinium veneficum, and Prorocetnrum minimum were tested on larvae of C. virginica and the Asian oyster being considered for introduction to Chesapeake Bay, C. ariakensis. When embryos from freshly spawned C. virginica and C. ariakensis were exposed immediately to K. veneficum at 104 cells mL−1, virtually all of the developed larvae were deformed within 48 h in one experimental trial, but not in a second trial in which algae were at a different growth stage. No deformities, and mortalities of <45%, were observed in controls to which a standard diet of the haptophyte Isochrysis was added. When 2-wk-old larvae of both species were exposed to the same HAB species, the effect was a severe reduction in motility with K. veneficum, but with P. minimum only C. ariakensis was affected and not C. virginica. Comparisons were made of the frequency of these HABs in Chesapeake Bay from long-term data analysis and the temporal period of spawning. Whereas both blooms are more common during the summer months, the frequency of blooms of K. veneficum and the period of oyster spawning, June to September, coincide more strongly. To compare spatial similarity, results of a larval transport model were compared with observational data for K. veneficum. This comparison demonstrated a significant overlap in July, particularly in the northern reaches of the Bay. These eutrophication-related HABs thus have the potential to reduce survival of early life history stages of oysters and hence to reduce oyster recruitment. Any reduction in recruitment either spatially or temporally, combined with an overall reduction in sheer numbers of larvae that survive, will make restoration or establishment of significant, self-sustaining populations of natural or introduced oyster species much more difficult.

Phytoplankton communities from San Francisco Bay Delta respond differently to oxidized and reduced nitrogen substrates—even under conditions that would otherwise suggest nitrogen sufficiency

The effect of equivalent additions of nitrogen (N, 30-40 μM-N) in different forms (ammonium, NH4+, and nitrate, NO3-) under conditions of different light exposure on phytoplankton community composition was studied in a series of four, 5-day enclosure experiments on water collected from the nutrient-rich San Francisco Bay Delta over two years. Overall, proportionately more chlorophyll a and fucoxanthin (generally indicative of diatoms) was produced per unit N taken up in enclosures enriched with NO3- and incubated at reduced (~15% of ambient) light intensity than in treatments with NO3- with high (~60% of ambient) light exposure or with NH4+ under either light condition. In contrast, proportionately more chlorophyll b (generally indicative of chlorophytes) and zeaxanthin (generally indicative of cyanobacteria) was produced in enclosures enriched with NH4+ and incubated under high light intensity than in treatments with low light or with added NO3- at either light level. Rates of maximal velocities (Vmax) of uptake of N substrates, measured using 15N tracer techniques, in all enclosures enriched with NO3- were higher than those enriched with NH4+. Directionality of trends in enclosures were similar to phytoplankton community shifts observed in transects of the Sacramento River to Suisun Bay, a region in which large changes in total N quantity and form occur. These data substantiate the growing body of experimental evidence that dichotomous microbial communities develop when enriched with the same absolute concentration of oxidized vs. reduced N forms, even when sufficient N nutrient was available to the community prior to the N inoculations.

Differential Production of Feces and Pseudofeces by the Oyster Crassostrea ariakensis When Exposed to Diets Containing Harmful Dinoflagellate and Raphidophyte Species

Abstract The Asian oyster, Crassostrea ariakensis, is being evaluated for its potential success in the restoration of oyster populations in Chesapeake Bay. Critical to an understanding of its potential success is knowledge of the impacts of common harmful algae in its diet; blooms of such algae are common in Chesapeake Bay. In these experiments, C. ariakensis were exposed to a standard algal diet, Isochrysis sp., alone, and in combination with the harmful dinoflagallates Prorocentrum minimum and Karlodinium veneficum and the raphidophytes Heterosigma akashiwo and Chattonella subsalsa. Two experiments were run, with varying proportions of Isochrysis to the test algal species. Feces and pseudofeces were examined microscopically and by high-performance liquid chromatography for changes in diagnostic pigments relative to the initial diet and for production of degradation pigments of chlorophyll. All species were cleared from suspension to varying degrees by the oysters. In the Isochrysis control and in the Isochrysis + P. minimum treatment, intact, solid feces were produced, and the highest proportion of chlorophyll degradation pigments were found in the Isochrysis control diet suggesting algal digestion. Thin, “ropey” feces and pseudo-feces were observed in the K. veneficum + Isochrysis treatment. Virtually no degradation pigments were found for oysters fed a diet containing K. veneficum, suggesting lack of digestion and assimilation of algal food. With the raphidophytes, reduced production of feces and pseudofeces was evident, and these contained a lower proportion of recognizable harmful algal cells, and higher proportion of degradation pigments than found with the other test species. Amorphous and cellular material that appears to be partly derived from the oyster digestive system was evident in the feces of oysters exposed to K. veneficum, H. akashiwo, and C. subsalsa; this was particularly pronounced in oysters exposed to H. akashiwo and suggests damage to the oyster gut. The impact of the presence of harmful algae in the diet of the oysters thus varied by algal species, but in all cases oyster digestion was altered relative to the control diet.