Shining Light on Photosynthesis in the Harmful Dinoflagellate Karenia mikimotoi–Responses to Short-Term Changes in Temperature, Nitrogen Form, and Availability

Karenia mikimotoi is a toxic bloom-forming dinoflagellate that sometimes co-blooms with Karenia brevis in the Gulf of Mexico, especially on the West Florida Shelf where strong vertical temperature gradients and rapid changes in nitrogen (N) can be found. Here, the short-term interactions of temperature, N form, and availability on photosynthesis–irradiance responses were examined using rapid light curves and PAM fluorometry in order to understand their interactions, and how they may affect photosynthetic yields. Cultures of K. mikimotoi were enriched with either nitrate (NO3−), ammonium (NH4+), or urea with varying amounts (1, 5, 10, 20, 50 µM-N) and then incubated at temperatures of 15, 20, 25, 30 °C for 1 h. At 15–25 °C, fluorescence parameters (Fv/Fm, rETR) when averaged for all N treatments were comparable. Within a given light intensity, increasing all forms of N concentrations generally led to higher photosynthetic yields. Cells appeared to dynamically balance the “push” due to photon flux pressure and reductant generation, with consumption in overall metabolism (“pull” due to demand). However, at 30 °C, all fluorescence parameters declined precipitously, but differential responses were observed depending on N form. Cells enriched with urea at 30 °C showed a smaller decline in fluorescence parameters than cells treated with NO3− or NH4+, implying that urea might induce a photoprotective mechanism by increasing metabolic “pull”.

Postnesting migration routes and fidelity to foraging sites among loggerhead turtles in the western North Atlantic

Although the western North Atlantic hosts the largest nesting assemblage of loggerhead turtles (Caretta caretta) in the world, their fine-scale habitat use beyond the nesting beach and how it effects reproductive output is still poorly understood. To characterize internesting and postnesting habitats used by loggerheads in the region, we satellite tracked 32 individual mature female turtles from a nesting beach in the southeastern Gulf of Mexico from 2009 to 2016. Thirteen of these turtles were tagged and tracked for two or more nesting seasons to assess fidelity to internesting movements, migratory pathway, and foraging site. Internesting movements for all turtles occurred over the West Florida Shelf in relatively close proximity to the nesting beach. Migratory pathways along the continental shelf led to foraging areas in four distinct regions: the southeastern Gulf of Mexico (n = 16 turtles), northeastern Gulf of Mexico (n = 8), Bahama Banks (n = 7), and Campeche Bank (n = 1). Individual turtles exhibited high fidelity to foraging sites across seasons, and 22 of the 32 tracked turtles shared overlapping foraging area utilization with at least one other individual during the tracking period. Loggerheads foraging closest to the nesting beach in the southeastern Gulf of Mexico were generally smaller than those foraging in other regions. This work highlights the importance of the West Florida Shelf for eastern Gulf of Mexico sea turtle rookeries. Identifying and managing the multiple in-water habitats used within and between nesting seasons will help sustain loggerhead turtle population recovery and maintenance.