Understanding how a crab's complex life cycle will respond to climate change

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Many marine animals like the Dungeness crab have complex life cycles that include seasonality and timing. If these are disrupted, it can have severe consequences for the population. It is not easy to understand how climate change will affect each stage of life, given all the variables and moving parts that are involved in changing environments. These challenges aside, it is crucial for sustainable fishery management as well as to inform new conservation strategies.

UConn Marine Science researchers, including Halle Berger, Ph.D. student, Assistant Professor Catherine Matassa and Samantha Siedlecki examined the Pacific Northwest section of the Dungeness crab fishing industry. This area stretches from Alaska to Southern California. They determined which life stages were most at risk and what stressors in a paper published in AGU Advances this week.

This research is part a regional vulnerability assessment, and collaboration funded by NOAA Ocean Acidification Program. Siedlecki also says that the research focuses on environmental justice issues.

"Tribal communities of the Pacific Northwest consider Dungeness to be both culturally and economically significant species for their wayof life. Tribal communities are not able to move their land because species are changing. Tribal communities are keen to find ways to sustain the fishery.

The assessment considered three possible stressors resulting from future carbon emission: ocean acidification, low oxygen levels (hypoxia), or warming temperatures. Berger explained that the model was based on multiple layers of information and allowed them to examine the effects of stressors at various times in the life cycle, from eggs to larvae to juveniles to adults.

The Intergovernmental Panel on Climate Change has representative carbon pathways (RCP), which are scenarios that consider different degrees of carbon emission mitigation, when modeling future conditions.

Berger says that RCP8.5 was the highest and was considered the worst case scenario if there's no climate change mitigation. "Then, we added the habitat maps and ocean conditions for each life stage to the framework. To give a more realistic representation of what they would experience, we added a new layer to the framework. We created a model of larval transport to simulate their movement in the water column.

The researchers then reviewed data from previous studies on Dungeness crabs. This helped them to assign scores for vulnerability at each stage of life to better understand the individual responses to stressors. Berger said that vulnerability at the population level was calculated using a weighted means. This is used to determine which life stage contributes most to the population's growth and vulnerability.

Berger states, "It turned out the adult life stage was the most crucial in driving the overall population vulnerability." "All three stressors will cause increased vulnerability to the population in the future. Hypoxia is the most serious. Low oxygen events occur only in spring and summer, which affects adults. Ocean acidification, however, will be more prevalent all year round, impacting all life stages.

Researchers say that these data can be easily integrated into decision-making processes in order to preserve the vital life stages under particularly stressful conditions and to maintain sustainable fisheries.

Berger says, "An example would include monitoring low oxygen events during the summer and possibly pulling the crab traps sooner." This would reduce the chance of the crabs dying inside the trap.

These measures would ensure that fisheries protect the adults, which are the most vulnerable and vital stage of the population for the survival of the species.

Berger notes that the study highlights how important it is to look at species vulnerability using a similar approach.

"This study demonstrates a lot about how important seasonality and life history complexity are in this framework. This framework could be used to capture losses in other vulnerability assessments. Although each stressor was examined in isolation, the laboratory experiments were unable to capture them all together. To better assess cumulative vulnerability, it is important to conduct multi-stressor impact experiments.

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Additional information: Halle M. Berger and colleagues, Seasonality & Life History Complexity Determine Vulnerability to Dungeness crab to Multiple Climate Stressors. AGU Advances (2021). Information from the Journal: AGU Advances Halle M. Berger and colleagues, Seasonality & Life History Complexity Determine Vulnerability to Dungeness crab to Multiple Climate Stressors (2021). doi.org/10.1029/2021AV000456