ALBERT

Description: Increasing amounts of atmospheric carbon dioxide (CO2) from human industrial activities are causing changes in global ocean carbonate chemistry, resulting in a reduction in pH, a process termed "ocean acidification." It is important to determine which species are sensitive to elevated levels of CO2 because of potential impacts to ecosystems, marine resources, biodiversity, food webs, populations, and effects on economies. Previous studies with marine fish have documented that exposure to elevated levels of CO2 caused increased growth and larger otoliths in some species. This study was conducted to determine whether the elevated partial pressure of CO2 (pCO2) would have an effect on growth, otolith (ear bone) condition, survival, or the skeleton of juvenile scup, Stenotomus chrysops, a species that supports both important commercial and recreational fisheries. Elevated levels of pCO2 (1200-2600 µatm) had no statistically significant effect on growth, survival, or otolith condition after 8 weeks of rearing. Field data show that in Long Island Sound, where scup spawn, in situ levels of pCO2 are already at levels ranging from 689 to 1828 µatm due to primary productivity, microbial activity, and anthropogenic inputs. These results demonstrate that ocean acidification is not likely to cause adverse effects on the growth and survivability of every species of marine fish. X-ray analysis of the fish revealed a slightly higher incidence of hyperossification in the vertebrae of a few scup from the highest treatments compared to fish from the control treatments. Our results show that juvenile scup are tolerant to increases in seawater pCO2, possibly due to conditions this species encounters in their naturally variable environment and their well-developed pH control mechanisms.

Description: After a decade of research on how embryonic fish will respond to the increased dissolved carbon dioxide (ρCO2) levels predicted for the next century, no uniform response to near future acidification has been observed among marine species. We exposed Black Sea Bass Centropristis striata (BSB) embryos to varied levels of ρCO2 (microatmospheres [μatm]) for 48 h during seasonal experiments conducted in 2013–2015 to compare embryonic response among multiple broodstocks. The relationship between ρCO2 concentration and hatching success was inconsistent among years, with a nonlinear, inverse relationship noted in 2014 only, explaining 13% of observed variance. Conversely, ρCO2 was a good predictor of unhatched BSB embryos after 48 h for all years combined (39%) and for 2013 (38%). The ρCO2 concentration was a good predictor of the frequency of vertebral column anomalies for individual years (2013: 40%; 2014: 12%; 2015: 38%) but not when data were pooled for all years. In 2013 and 2015, vertebral column anomalies were relatively consistent below 1,000 μatm and were elevated above that threshold. Preliminary results suggest that BSB embryos may demonstrate resilience to future ρCO2 levels, but the results also highlight the challenges associated with drawing broad conclusions given observed variability in results obtained from different broodstocks and study years.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 1987

Description: A group of thecate heterotrophic dinoflagellates (THDs), principally in the diverse and ubiquitous genus Protoperidinium, was investigated both from an ecological and an organismal perspective. When this study was initiated, nothing was known about their feeding mechanisms, rates or food preferences. The population dynamics of these microheterotrophs were studied in a temperate estuary over a 13 month period, along with co-occurring diatoms, ciliates and pigmented (photosynthetic) dinoflagellates. The timing of several peaks in Protoperidinium abundance coincided with those of diatom blooms, suggesting a possible trophic dependance. During such peaks the biovolume or biomass of the THD community exceeded that of both pigmented dinoflagellates and ciliates. Occurrence patterns of individual THD species were closely related to water temperature; this may indicate the involvement of benthic resting cysts in population succession. Small-scale vertical distributional patterns of THDs were also studied in an embayment with an average depth of 5 m. While two autotrophic dinoflagellate species displayed distinct daily vertical migration patterns, THD species did not; most species maintained a constant 2-5 m depth of maximum abundance, while two others had surface maxima. Feeding behavior, as observed in 19 THD species (Oblea rotunda, Zygabikodinium lenticulatum and 17 species of Protoperidinium) fits the following pattern: a THD cell attaches a slender filament to a prey item (usually a diatom) while it is engaged in a characteristic, spiralling "dance". Subsequently, a pseudopod or "pallium" (a term defined here) emerges from the flagellar pore and envelops the prey within a minute. Ten to sixty minutes later the pallium is retracted and the prey (now a nearly-empty frustule) is discarded. Most species feed only on diatoms, but O. rotunda, Z. lenticulatum (both diplopsaloid species) and P. pyriforme also preyed upon dinoflagellates. Ingestion and growth rates were determined in the laboratory where cultures of Protoperidinium hirobis were fed the diatom Leptocylindrus danicus. Feeding cycles were repeated as often as every 1.5 to 2 hours. Maximal ingestion rates of 23 diatoms*day-1 supported unexpectedly high specific growth rates of up to 1.1*day-1 (1.7 divisions*day-1). Half-maximal growth and grazing rates occurred at approximately 1000 diatoms cells*ml- 1. Peak division frequencies occurred at night, although feeding rate was nearly constant on a diel basis. The ultrastructure of the feeding apparatus was studied in Protoperidinium spinulosum. The pallium, when deployed, is composed of a complex system of membranous channels, vesicles, and a few microtubular ribbons radiating from the flagellar pore. Inside this pore, the pallium is continuous with the contents of an elongate microtubular basket that extends towards the nucleus. The apical end of this basket opens adjacent to the nucleus; at this point its contents become continuous with the central cytoplasmic region. This region is distinguished from the relatively dense, peripheral cytoplasm by the presence of either large electron-lucent vesicles (containing, perhaps, digestive enzymes) or numerous small lipid droplets. Examination of a pre-feeding cell has revealed the likely source of the pallium membranes: dense membranous whorls lie within the microtubular basket. A narrow pseudopodal appendage in two non-feeding cells may constitute the tow filament used in prey capture. A complex myonemaI system, including osmiophilic ring, striated collars and connecting bands is described. The microtubular basket and osmiophilic ring structures were also found in Protoperidinium hirobis, Protoperidinium punctulatum and Oblea rotunda. This thesis has done much to further the understanding of a prevalent component of the protozooplankton, the thecate heterotrophic dinoflagellates. This progress, which was due in a large part to the culture success reported herein, includes new insights into the abundance, feeding behavior, food preferences, feeding rates, and ultrastructural basis of feeding in this preeminent group of the thecate heterotrophic dinoflagellates, the genus Protoperidinium.

Description: My research was supported in part by a NSF graduate fellowship, a graduate research grant through the WHOI Coastal Research Center, and two NSF grants, OCE-8400292 and DCB-8520605.