Genetic and Phenotypic Response of Larval American Lobster to Ocean Warming and Acidification across New England's Steep Thermal Gradient (Regional)
Co-PIs Wahle (UMaine) and Fields (Bigelow Laboratory) join Co-investigator Greenwood (UPEI) in this US-Canadian collaboration. The investigators have a strong, complementary track record of research on the biological effects of ocean acidification, gene expression, and the biology, ecology and culture of the American lobster. The proposed study is designed to fill knowledge gaps in our understanding of the response of lobster larvae to ocean warming and acidification across lobster subpopulations occupying New England’s steep north-south thermal gradient. The research involves a comprehensive assessment of the physiological and behavioral response of lobster larvae to climate model-projected end-century ocean temperature and acidification conditions. We will address the following two primary objectives over the 2-year duration of the proposed study: (1) To determine whether projected end-century warming and acidification impact lobster larval survival, development, respiration rate, behavior and gene expression; and (2) To determine whether larvae from southern subpopulations are more resistant than larvae from northern populations to elevated temperature and pCO2.
The proposed research on lobster larvae is a full factorial experimental design with two temperature and three acidification levels for a total of six treatment combinations to which lobster larvae from three contrasting subpopulations will be exposed. The experimental apparatus and protocol was developed and tested in recent NSF- and NOAA-supported research on OA effects on estuarine zooplankton conducted at Bigelow Laboratory by Co-PI Fields. During the summers of 2016 and 2017, egg-bearing lobsters will be collected from oceanographically contrasting locations: Rhode Island (RI), southwestern Maine (SME) and northeastern Maine (NME), representing a considerable range in summer temperature maxima (RI: ~23ºC; SME ~16ºC; NME ~12ºC). Hatching advances northward as temperatures reach ~12ºC, so the southern subpopulations will be first to hatch and egg-bearing female from each site will be taken in sequence and kept in temperature controlled recirculating tanks at UMaine’s Darling Marine Center.
Lobster larvae hatched within the same 12 h period will be transported to Bigelow Laboratory for larval rearing experiments. They will be divided among the six treatment combinations, comprising two temperatures (16°C and 19°C) and three pCO2 levels ('ambient' 400 ppm) 'projected end-century' (750 ppm), and 'worst case' (1200 ppm). Each tank will be stocked at the beginning of the experiment with 250 stage I larvae. At these temperatures, raising larvae to the postlarval stage (IV) will take approximately 1 mo. Daily water chemistry measurements will include pH, temperature and salinity, and weekly high-precision water chemistry measurements will include spectrophotometric pH and alkalinity. Biological response variables to be measured include:
1. Development, body mass and mortality: Larvae will be raised under ambient and elevated pCO2 and temperature treatments. Developmental stage and mortality rates will be assessed daily. Larvae will be dried, weighed and measured for total C and N at each larval stage.
2. Respiration: Oxygen consumption measurements will be made with a Clark-type O2 electrode during each larval stage. Respiration rate will be used to examine larval physiology and metabolic rates can be calculated through standard crustacean equations.
3. Swimming and Feeding rates: Video records of swimming rates will be made using shadow videography which provides high magnification and depth of field and maximum contrast. The 3-D coordinates of larvae within the field of view are recorded in full HD with 2 synchronized, perpendicular digital cameras. Swimming speed and direction will measured using NIH-Image J software. Prey consumption rates by lobster larvae will be determined in a grazing experiment whereby lobster larvae will be placed in 1L containers with 100 brine shrimp nauplius larvae. At the end of the grazing period the remaining brine shrimp are counted to calculate losses.
4. Gene expression: Subsamples of stage III and IV larvae will be preserved from each treatment to analyze at the University of Prince Edward Island's Atlantic Veterinary College Lobster Science Centre for differences in global gene expression through RNASeq and qPCR. We will look for changes in in the expression of well-studied genes associated with molting and development.
The input of anthropogenic carbon into the atmosphere has caused large scale ocean warming and acidification that has important implications for commercial fisheries in the Northeastern United States. The Northwest Atlantic is experiencing more rapid increases in temperature and acidification than other parts of the world. Consequently, over recent decades the fishing industry has witnessed traditional commercial fish populations receding from the south and expanding to the north. While most of these shifts have been attributed to ocean warming, the impact of acidification has only been examined in a few species and the interactive effects of warming and acidification remain poorly understood. In the present study we focus on the interactive effects of ocean warming and acidification on the iconic American lobster (Homarus americanus), one of New England’s most valuable fisheries.
The proposed project represents a multi-institutional collaboration of investigators with strong track records and complementary skills in crustacean ecology, physiology, and genomics that reinforces an already strong international partnership. Our work directly addresses Sea Grant’s research priority “to support innovative biophysical and social science research that will further the understanding of the effects of ocean acidification on key coastal marine resource species and economies.” This work aligns with Sea Grant’s overarching mission to maintain coastal ecosystems, support coastal communities and promote sustainable fisheries. These data are critical for policy makers and harvesters to manage the future of this fishery. The project also complements the development of forecasting and habitat suitability models being developed in other collaborations supported by NSF's Coastal SEES and NOAA FATE programs. Stock assessment scientists and the fishing industry in the US and Canada, the NECAN, as well as Maine’s Ocean Acidification Commission, have all recognized the urgent need for the information our study will provide.
Taken together, the proposed project will provide unprecedented and much-sought information on the interactive effects of elevated temperature and pCO2 on the American lobster’s most vulnerable early life stages. The study is novel in the following ways:
1. It is the first to examine the joint effects of elevated pCO2 and temperature on lobster larval development. Previous studies on clawed lobster have only examined the effects of one or the other.
2. It is the most comprehensive assessment of temperature and OA effects on decapod larval physiological and behavioral responses to date.
3. It is the first to evaluate gene expression responses to temperature and OA treatments in a decapod crustacean.
4. It is the first to compare the performance of American lobster larvae from different sub-populations along the steep environmental gradient of its geographic range.
5. It is a US-Canadian collaboration taking advantage of world class institutional facilities and expertise available on both sides of the border.
6. It sets the stage with protocols and facilities for further comparative work on physiology, behavior and gene expression in other commercially and ecologically important species.