Spiny Lobster Survival in a Warming Ocean: The Role of Temperature in Altering Lobster Metabolism and Predation
As temperatures rise, a key predator in temperate reef ecosystems may be primed for a significant change in its future. The California spiny lobster, a staple of the ocean food chain and one of the largest fisheries on the west coast of the United States, is likely to experience major increased energy demands as ocean temperatures rise. For lobsters in in the Santa Barbara Channel, however, their capacity to keep up with the higher energy demands associated with warmer waters were impressive. It’s only at the highest simulated temperatures that lobsters showed high mortality and an inability to keep up with the energy demands of warmer waters. This study, co-funded by the California Ocean Protection Council and the National Science Foundation Santa Barbara Coastal LTER is the first study to explore how spiny lobsters are likely to respond to changes in temperature and offers critical insight into linked bioenergetics and ecology of lobsters and offers key insights into how seasonal and interannual fluctuations in temperature likely alter lobster biology.
A Primer on the California Spiny Lobster
The California spiny lobster is a marine crustacean that belongs to the family Palinuridae. They are typically brown or greenish in color and have large spines on their bodies and legs. Spiny lobsters are nocturnal and primarily feed on mollusks, crustaceans, and other invertebrates. They are found in rocky or sandy bottoms in subtidal and intertidal areas along the coast of California and Mexico and use their large antennae to detect potential food sources and their strong claws to crack open shells. Research has demonstrated that spiny lobsters can play a critical role in the intertidal , as well as on rocky reef communities, sometimes preying on sea urchins.
The California spiny lobster fishery is an important industry for both commercial and recreational fishing. Commercial fishing is primarily done using traps, while recreational fishing is typically done by diving. Harvesting spiny lobsters is subject to regulation by state and federal agencies to ensure sustainable populations and minimize bycatch. The season for commercial and recreational fishing typically runs from October to March, with some variations based on location and local regulations. The commercial fishery for spiny lobster is a significant industry in California, with landings typically worth tens of millions of dollars each year. Fishermen use traps to catch lobsters, which are then sold to dealers and eventually to markets and restaurants, often as an export market. In recent years, there has been some concern about the effects of climate change on the spiny lobster population, but despite this, there has been relatively little work examining the role of temperature in driving variation in lobster biology or ecology.
The link between temperature and metabolism for marine invertebrates
To understand how lobsters might be affected by variation in temperature, one needs an appreciation of how ocean invertebrates might be affected by changes in temperature. Marine invertebrates are ectotherms, also known as "cold-blooded" organisms, which regulate their body temperature through external sources such as the environment. Increases in temperature can greatly affect their metabolism, as their metabolic rate is directly linked to the temperature of their environment. For example, when the water temperature in a marine invertebrate’s habitat increases, its metabolic rate increases as well, causing an increase in demand for food to fuel its metabolic processes. In recent years, there has been growing concern about the potential effects of increasing water temperatures on the metabolism of marine invertebrates, as well as the risk that these animals might not be able to keep up with the energetic demands of a rapidly changing environment caused by global climate change. For lobsters to meet this increased demand for food at higher temperatures they need to have that food readily available, and to be able to catch, manipulate, and digest that food fast enough to keep up with their metabolism. While lots of research has documented that increased temperature drives increases in ocean invertebrate metabolism, few studies have explored whether this increase in metabolism can be met by predators. In this study that’s exactly what the researchers did!
How much variation in temperature do spiny lobster experience?
Spiny lobster have a wide range from Baja Mexico all the way to point conception. This means that they experience an average of x degrees sea surface temperature in Baja while y degrees at the northern edge of their distribution near point conception. But even within a location, they experience wide variability in temperature throughout the year and between years, requiring they are capable of adjusting their behavior and feeding rates to meet variable demands. For example, check out this graph of ocean temperature from thermisters in the Santa Barbara channel. Where you can see that temperatures on any given month in the summer can span as low as 11 degrees C and as high as 22 degrees C.
Temporal Variation in Bottom Temperature. Monthly bottom (4.5 m depth) temperatures at Mohawk Reef (34.396290, -119.731297) in Santa Barbara, CA compiled from 2005-2017. Vertical dashed lines represent three of four treatment temperatures (11, 16, 21°C). Data Source: Santa Barbara Coastal Long-Term Ecological Research group.
Residing in the temperate reef ecosystems, the spiny lobsters are key predators that play a critical role in the dynamics and stability of their ecosystem. But as temperatures rise, the fate of these creatures hangs in the balance. As theory predicts, increases in temperature drive increases in metabolism, and animals respond by ramping up their food consumption to meet the metabolic demand. However, if consumption does not increase as rapidly with temperature as metabolism, increases in temperature can ultimately cause a reduction in consumer fitness and biomass via starvation.
The researchers from the Ocean Recoveries and Eliason Labs tested the hypothesis that increases in temperature cause more rapid increases in metabolism than increases in consumption using the California spiny lobster as a model system. They acclimated individual lobsters to temperatures they experience across their biogeographic range (11, 16, 21, or 26°C) and measured whether the lobsters' consumption rates were able to meet the increased metabolic demands of rising temperatures. They found positive effects of temperature on metabolism and predation, but in contrast to their hypothesis, rising temperature caused lobster consumption rates to increase at a faster rate than increases in metabolic demand, suggesting that for the mid-range of temperatures, lobsters can readily compensate by eating more to address the increased metabolic demand. But like anything there was a limit. At the extreme ends of the simulated temperatures, lobster biology broke down. At the coldest temperature, lobsters had almost no metabolic activity and at the highest temperature, 33% of lobsters died.
Temperature Effects on Lobster Metabolism. (A) Resting metabolic rates (RMR), (B) maximum metabolic rates (MMR), (C) absolute aerobic scopes (AAS = MMR – RMR), and (D) factorial aerobic scopes (FAS = MMR/RMR) measured for individual lobsters (light gray points) at 11, 16, 21, and 26°C (n = 6 for all treatments except 26°C, where n = 4). Colored points represent treatment means and bars are equal to 95% confidence intervals. Gray dots represent jittered raw data. Lines and gray shading are the mean ± 95% CI’s for fitted models. See Methods for details on the models fit to each rate.
These results show that temperature plays a key role in driving the geographic range of spiny lobsters, constraining their migration northward due to cold temperatures, and limiting their summer distributions when temperatures are warmer. The spatial and temporal shifts in temperature within and among years a critical role in driving the strength of species interactions for this key predator in intertidal and temperate reef ecosystems.
Temperature Effects on Lobster Functional Responses. Type II functional responses fit using a Bayesian hierarchical framework. Gray curves represent individual lobsters and colored curves represent treatment means (left to right: light blue = 11°C, dark blue = 16°C, light red = 21°C, dark red = 26°C). Solid gray regions highlight the 95% credible intervals estimated at the treatment level.
Interestingly however, metabolic demand did not predict feeding rates perfectly. Some lobsters were incredibly capable of feeding at high rates despite low metabolic demand and other lobsters with high metabolic demand did not feed at a high rate. Suggesting that significant variability exists in the population’s capacity to deal with changing temperatures and perhaps offers some hope for lobsters capacity to deal with future warmer ocean conditions.
Metabolism Effects on Foraging Across Temperatures. Median posterior estimates for the maximum consumption rate (Cmax) of each individual lobster plotted as a function of the individuals (A) resting metabolic rate, (B) maximum metabolic rate, (C) absolute aerobic scope and (D) factorial aerobic scope across temperatures. Gray error bars are the 95% CI’s of the median estimate from the posterior distribution. Lines and gray shading are mean linear trends and 95% CI’s from simple linear regressions fit to the median estimates of Cmax. Density plots show the distribution of metabolic traits (x-axis) and Cmax (y-axis) for each treatment. We provide an example of an individual we characterized as an overperformer (IV10; 11°C treatment) and as an underperformer (IV19; 26°C treatment) as compared to treatment means.
Whether temperature-dependence in feeding rates match or mismatch with temperature-dependence in metabolic rates is key to anticipating the impacts of warming on ecosystem stability and dynamics. This research offers one of the few integrative studies that explicitly link temperature-dependence in metabolism with temperature-dependence in predator-prey interactions. Their results indicate that metabolic, and predation rates increase as functions of temperature, but show that predation rates increased at a faster rate with temperature than metabolism. This capacity to maintain high foraging rates as temperatures increased suggests that some species may not immediately suffer from a bioenergetic meltdown caused by declining energy intake and increased energy expenditure. Yet at the coldest temperatures lobsters were barely ate, and at the hottest temperatures lobsters had high mortality, which highlights the existence of thermal limits.
The better we understand why animals experience temperature dependence in their physiology or ecology, the better we will be able to predict how natural and human-induced changes in temperature are likely to affect the stability and function of ecosystems. This study provides evidence that at least some species can maintain high feeding rates to meet the higher energetic demands associated with higher temperatures. This study also show how cold constraints can fully stop predators from functioning physiologically and ecologically, suggesting that the strength of predation is likely highly seasonal. Lastly, while the authors link temperature, metabolism, and predation, this study also demonstrates that, at least for lobsters, a significant amount of temperature-dependence in predation is explained by individual variation driven by other non-metabolic biological processes that are currently unknown. Identifying these unknown forces is critical to evaluate and fully predict how temperature alters the strength of species interactions, drives range shifts, and alters animal bioenergetics.