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Climate Change

Tiny lobsters, big problems.

Paper:

Wood, H. L., Eriksson, S. P., Nordborg, M., & Styf, H. K. (2015). The effect of environmental stressors on the early development of the Norway lobster Nephrops norvegicus (L.). Journal of Experimental Marine Biology and Ecology, 473, 35–42. doi:10.1016/j.jembe.2015.08.009

Early stage lobster. Photo credit: Macroscopic

Early stage lobster. Photo credit: MacroscopicSolutions

Introduction

Before delicious crustaceans such as crabs and lobsters make their way to our plates, they go through a larval phase. During this scary stage of life, crabs and lobsters can only float, hoping to survive and become adults. Not only can tiny baby lobsters encounter large fish predators but also they are vulnerable to less than ideal environmental conditions. Changes in temperature or salinity can spell disaster, as well as encountering pollution or areas without adequate food. The ability of larvae to successfully grow into adults determines the future success of the population.

Along with a changing climate, the ocean environment is also changing via increasing temperatures and lowered pH due to excess CO2 in the atmosphere being absorbed into the ocean, causing an increase in acidity. Furthermore, salinity may fluctuate as weather and rain patterns change. Larvae in the open ocean will face these new, changing conditions. This study explores the effect of environmental stressors on the early days of the Norway lobster’s life (Nephrops norvegicus), a popular European commercial fishery species.

 

Methods

Adult lobsters carrying eggs were caught near Gullmarsfjord, Sweden at 40 meter depths and kept in aquaria until the eggs matured. As larvae were released they were collected and moved to experimental conditions including various salinity or pH levels.

Salinity tolerance experiments:

Rainfall patterns are changing and increased bouts of rain add extra freshwater into a system causing lower salinities. Larvae were placed in aquaria with salinities of 4, 9, 13, 17, 23, or 33 ppt ranging from low salinity to near full strength sea water (the current salinity of the research location). Survival was observed and recorded each day. Development through molts stages was also monitored as well as metabolic rate through measuring the amount of consumed oxygen.

Low pH experiments:

Larvae and unhatched eggs were raised in either a control pH environment (the same as current conditions) or a low pH (increased acidity, as predicted by climate change models). Growth and survival were measured as in the salinity experiments. The calcium content was measured to determine the effect of low pH on the calcification of the lobsters’ exoskeletons.

 

Results and Significance

Short term changes in salinity did not affect the survival of lobster larvae, though longer term exposures to different salinities all resulted in different levels of mortality. Lower salinity caused the larvae to have higher metabolic rates, either a good diet plan or a recipe for increased stress. The higher metabolic rate transfers into burning more calories and in fact the larvae at lower salinities weighed less than in the higher salinity.

 Weight (mean mg DW larva− 1 ± 95% C.I.) in Nephrops norvegicus zoea II larvae after post-hatching exposure to salinity treatments (34 control, 21 and 17) at 15 °C for 12 days (n = 30).

Weight in  larvae after post-hatching exposure to salinity treatments (34 control, 21 and 17) at 15 °C for 12 days (n = 30).

fig2_lobster

A. Survival (%) of larvae exposed to a decreasing salinity of 2 (circles), 4 (triangles) and 8 (squares) salinity units over four days, starting at salinity 33 day 1. B. Survival (mean % ± 95% Confidence interval

 

 

 

 

 

 

 

 

 

 

 

The survival of larvae to low pH differed between the young of different mothers showing a genetic predisposition may exist for increased ability to survive a changing ocean pH. The calcium content increased in eggs exposed to low pH, but the larvae showed no difference. Although on average the calcium level in larvae is 25 times the amount found in eggs.

Survival (%) of N. norvegicus larvae at day 18 (Zoea II) in both control pH (light bars) and acidified (− 0.4 pH units, dark bars). Data shown across different broods, each with different parents

Survival (%) of N. norvegicus larvae at day 18  in both control pH (light bars) and acidified (− 0.4 pH units, dark bars). Data shown across different broods, each with different parents.

This paper gives an overview of how larvae might be affected by two important environmental stressors. It also raises question about what is behind the different levels of tolerance to extreme salinities or pH. Working to understand how our favorite seafood will fare with impending climate change can help us be more prepared to better manage those fisheries. This study also reminds us that some effects of changing environments are not obvious, tiny larval creatures are easily overlooked but important for the larger population.

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