Posts Tagged 'crustaceans'

Short-term effects of hypoxia are more important than effects of ocean acidification on grazing interactions with juvenile giant kelp (Macrocystis pyrifera)

Species interactions are crucial for the persistence of ecosystems. Within vegetated habitats, early life stages of plants and algae must survive factors such as grazing to recover from disturbances. However, grazing impacts on early stages, especially under the context of a rapidly changing climate, are largely unknown. Here we examine interaction strengths between juvenile giant kelp (Macrocystis pyrifera) and four common grazers under hypoxia and ocean acidification using short-term laboratory experiments and field data of grazer abundances to estimate population-level grazing impacts. We found that grazing is a significant source of mortality for juvenile kelp and, using field abundances, estimate grazers can remove on average 15.4% and a maximum of 73.9% of juveniles per m2 per day. Short-term exposure to low oxygen, not acidification, weakened interaction strengths across the four species and decreased estimated population-level impacts of grazing threefold, from 15.4% to 4.0% of juvenile kelp removed, on average, per m2 per day. This study highlights potentially high juvenile kelp mortality from grazing. We also show that the effects of hypoxia are stronger than the effects of acidification in weakening these grazing interactions over short timescales, with possible future consequences for the persistence of giant kelp and energy flow through these highly productive food webs.

Continue reading ‘Short-term effects of hypoxia are more important than effects of ocean acidification on grazing interactions with juvenile giant kelp (Macrocystis pyrifera)’

The importance of environmental exposure history in forecasting Dungeness crab megalopae occurrence using J-SCOPE, a high-resolution model for the US Pacific Northwest

The Dungeness crab (Metacarcinus magister) fishery is one of the highest value fisheries in the US Pacific Northwest, but its catch size fluctuates widely across years. Although the underlying causes of this wide variability are not well understood, the abundance of M. magister megalopae has been linked to recruitment into the adult fishery 4 years later. These pelagic megalopae are exposed to a range of ocean conditions during their dispersal period, which may drive their occurrence patterns. Environmental exposure history has been found to be important for some pelagic organisms, so we hypothesized that inclusion of recent environmental exposure history would improve our ability to predict inter-annual variability in M. magister megalopae occurrence patterns compared to using “in situ” conditions alone. We combined 8 years of local observations of M. magister megalopae and regional simulations of ocean conditions to model megalopae occurrence using a generalized linear model (GLM) framework. The modeled ocean conditions were extracted from JISAO’s Seasonal Coastal Ocean Prediction of the Ecosystem (J-SCOPE), a high-resolution coupled physical-biogeochemical model. The analysis included variables from J-SCOPE identified in the literature as important for larval crab occurrence: temperature, salinity, dissolved oxygen concentration, nitrate concentration, phytoplankton concentration, pH, aragonite, and calcite saturation state. GLMs were developed with either in situ ocean conditions or environmental exposure histories generated using particle tracking experiments. We found that inclusion of exposure history improved the ability of the GLMs to predict megalopae occurrence 98% of the time. Of the six swimming behaviors used to simulate megalopae dispersal, five behaviors generated GLMs with superior fits to the observations, so a biological ensemble of these models was constructed. When the biological ensemble was used for forecasting, the model showed skill in predicting megalopae occurrence (AUC = 0.94). Our results highlight the importance of including exposure history in larval occurrence modeling and help provide a method for predicting pelagic megalopae occurrence. This work is a step toward developing a forecast product to support management of the fishery.

Continue reading ‘The importance of environmental exposure history in forecasting Dungeness crab megalopae occurrence using J-SCOPE, a high-resolution model for the US Pacific Northwest’

Can ocean acidification interfere with the ability of mud snails (Tritia obsoleta) to sense predators?


• Mud snails respond differently to threat cues from crushed conspecifics and crabs

• Ocean acidification disrupted mud snail predator avoidance behavior

• Snails in acidified tanks crawled towards threat cues instead of away

• Acidification reduced snail crawling distance and climbing escape from threat cues

• Acidification may interfere with cue sensing and alter predator-prey relationships


Nonlethal predator-prey interaction between Dyspanopeus sayi (northern mud crab) and Tritia obsoleta (mud snail) under ocean acidification conditions (OA) were investigated. Nonlethal interactions can influence predator-prey relationships and magnify the ecological impact of predators in marine habitats. Future increases in OA necessitate an understanding of how prey perceive the threat of predation and how this may be impacted by ocean acidification. In baseline experiments at pH 8.1, mud snails responded differently to crab cues compared to crushed conspecifics, burying in the presence of crushed conspecifics and fleeing in the presence of a mud crab. While many predator cue experiments combine these two types of cues, these results suggest that mud snails not only discern between threat cues but also have a nuanced response that is tailored to specific threats. Mud snail responses to predator-prey relationships were delayed under lower pH conditions, as snails in acidified treatments did not exhibit any of the escape responses that they commonly displayed under control conditions. Thus, acidification could shift predator-prey relationships and significantly alter food webs under acidified conditions.

Continue reading ‘Can ocean acidification interfere with the ability of mud snails (Tritia obsoleta) to sense predators?’

Model simulation of seasonal growth of Fucus vesiculosus in its benthic community

Numerical models are a suitable tool to quantify impacts of predicted climate change on complex ecosystems but are rarely used to study effects on benthic macroalgal communities. Fucus vesiculosus L. is a habitat‐forming macroalga in the Baltic Sea and alarming shifts from the perennial Fucus community to annual filamentous algae are reported. We developed a box model able to simulate the seasonal growth of the Baltic Fucus–grazer–epiphyte system. This required the implementation of two state variables for Fucus biomass in units of carbon (C) and nitrogen (N). Model equations describe relevant physiological and ecological processes, such as storage of C and N assimilates by Fucus, shading effects of epiphytes or grazing by herbivores on both Fucus and epiphytes, but with species‐specific rates and preferences. Parametrizations of the model equations and required initial conditions were based on measured parameters and process rates in the near‐natural Kiel Outdoor Benthocosm (KOB) experiments during the Biological Impacts of Ocean Acidification project. To validate the model, we compared simulation results with observations in the KOB experiment that lasted from April 2013 until March 2014 under ambient and climate‐change scenarios, that is, increased atmospheric temperature and partial pressure of carbon dioxide. The model reproduced the magnitude and seasonal cycles of Fucus growth and other processes in the KOBs over 1 yr under different scenarios. Now having established the Fucus model, it will be possible to better highlight the actual threat of climate change to the Fucus community in the shallow nearshore waters of the Baltic Sea.

Continue reading ‘Model simulation of seasonal growth of Fucus vesiculosus in its benthic community’

The challenge of scaling up from individual physiology to population level effects: using the Dynamic Energy Budget to describe and predict crustacean responses to climate variability

Predicting how marine communities will be affected by environmental change is one of the most significant challenges facing researchers today. In order to tackle this challenge, a mechanistic understanding of climate impacts at the individual level is necessary, as variations in species physiological responses are often reflected in patterns at higher organisational levels such as populations and communities. In order to explore the relationship between individual physiology and higher-level dynamics more fully, the swimming crab Liocarcinus depurator (Linnaeus, 1758) was selected as a model species for experimental work in which whole organism responses (growth, respiration and allocation to reproduction) to climate drivers were investigated using a bio-energetic modelling approach. This species was selected as a model organism after analysis of epibenthic time-series from the Western English Channel monitoring Station L4 revealed that decapod crustaceans played a key role in structuring the benthic community, and that L. depurator was one of the most dominant species in the area, in terms of both abundance and biomass. A bio-energetic approach was used as the same time-series analysis identified water temperature and seasonal phytodetrital input (e.g. food) as the predominant drivers of variation in benthic community wet biomass at L4, with the two drivers appearing to primarily influence community biomass at different times of the year. It is possible that warmer water temperatures in the autumn trigger gonad development and a consequent increase in reproductive biomass, while the sedimentation of the spring phytoplankton bloom drives an increase in somatic biomass. This time-series analysis clearly highlighted the role of organism energetics, and the environmental conditions that influence energy allocation, in structuring benthic communities. Further work elucidated the relationship between environmental variables and individual energy budgets. L. depurator responses to climate drivers (temperature, hypoxia and ocean acidification) were tested experimentally, and a mechanistic Dynamic Energy Budget (DEB) model was parameterised to describe the life history characteristics of crustaceans. At an individual level the model was able to accurately describe and predict observed responses to environmental drivers, both in isolation and in multiple stressor scenarios. Experimental results suggested that L. depurator was broadly tolerant of those climate drivers tested in the short term. Over the longer term however, model scenarios suggested that OA and the combined stressors may have an adverse effect on growth. When the multi-stressor model was forced with environmental projections from a coupled hydrodynamic-biogeochemical model (NEMO-ERSEM), it could be used to make predictions regarding ultimate carbon mass, age-at-maturity and cumulative allocation to reproduction, which were used to infer possible population level effects such as species distributions and population viability. Model scenarios suggested that, in the future, the optimum settlement time for juvenile L. depurator would shift forward across the north-west European shelf, and that this crustacean species may be able to expand its range further into the northern North Sea. The DEB model presented here can provide a mechanistic underpinning of observed species responses to climate drivers, and more broadly, the thesis demonstrates how multi-stressor models can be built from data collected in single stressor experiments, thereby providing a way of synthesising single stressor data into a modelling environment. This approach allows us to simulate more complex, ecologically relevant conditions. At a broader scale, the coupled DEB-ERSEM model showed that it can provide insight into why changes in species’ distributions are predicted, as these distributions are an emergent property of the processes being modelled.

Continue reading ‘The challenge of scaling up from individual physiology to population level effects: using the Dynamic Energy Budget to describe and predict crustacean responses to climate variability’

Cascading effects of climate change on plankton community structure

Plankton communities account for at least half of global primary production and play a key role in the global carbon cycle. Warming and acidification may alter the interaction chains in these communities from the bottom and top of the food web. Yet, the relative importance of these potentially complex interactions has not yet been quantified. Here, we examine the isolated and combined effects of warming, acidification, and reductions in phytoplankton and predator abundances in a series of factorial experiments. We find that warming directly impacts the top of the food web, but that the intermediate trophic groups are more strongly influenced by indirect effects mediated by altered top-down interactions. Direct manipulations of predator and phytoplankton abundance reveal similar strong top-down interactions following top predator decline. A meta-analysis of published experiments further supports the conclusion that warming has stronger direct impacts on the top and bottom of the food web rather than the intermediate trophic groups, with important differences between freshwater and marine plankton communities. Our results reveal that the trophic effect of warming cascading down from the top of the plankton food web is a powerful agent of global change.

Continue reading ‘Cascading effects of climate change on plankton community structure’

Ocean acidification does not affect fish ectoparasite survival

The juveniles of gnathiid isopods are one of the most common fish ectoparasites in marine habitats and cause deleterious effects on fish by feeding on host blood and lymph. Reef fishes tend to engage in cooperative interactions with cleaning organisms to reduce their ectoparasite load. Ocean acidification (OA) pose multiple threats to marine life. Recently, OA was found to disrupt cleaner fish behaviour in mutualistic cleaning interactions. However, the potential effects of ocean acidification on this common ectoparasite remains unknown. Here, we test if exposure to an acidification scenario predicted by IPCC to the end of the century (RCP 8.5 – 980 μatm pCO2) affects gnathiid survival. Our results show that ocean acidification did not have any effects on gnathiid survival rate during all three juvenile life stages. Thus, we advocate that the need for cleaning interactions will persist in potentially acidified coral reefs. Nevertheless, to better understand gnathiid resilience to ocean acidification, future studies are needed to evaluate ocean acidification impacts on gnathiid reproduction and physiology as well as host-parasite interactions.

Continue reading ‘Ocean acidification does not affect fish ectoparasite survival’

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Ocean acidification in the IPCC AR5 WG II

OUP book