Posts Tagged 'crustaceans'

Integrity of crustacean predator defenses under ocean acidification and warming conditions

Crustaceans are a diverse group of species, but all rely on an exoskeleton that is shed and formed anew throughout their lifetime. Exoskeletons perform a wide range of functions, sometimes acting as armor, a means to produce sound, a tool to crush hard prey, or even a window to facilitate transparency. The exoskeleton and its functions, however, are likely vulnerable to ocean acidification and ocean warming, which may alter its composition and the energy allocated towards its production. I investigated the effects of these future ocean conditions on two southern Californian crustaceans, the California spiny lobster Panulirus interruptus and the grass shrimp Hippolyte californiensis, which rely on their exoskeleton for different predator defenses. P. interruptus is an iconic feature of southern California’s kelp forest ecosystem but also a potential prey item for many of its large predators. Spiny lobsters use their antennae, mandibles, carapace, and horns to avoid predation. Each of these structures is specialized for a certain defense, displaying differences in composition, structure, and material properties that allow the antennae, for example, to remain flexible to avoid breaking when pushing predators away while imbuing hardness in crushing structures like the mandible (Chapter 1). Juvenile lobsters exposed to ocean acidification-like conditions largely maintained their predator defenses, displaying some differences in the composition across the exoskeleton but no strong effects to defense functionality, including the non-exoskeletal defenses of detecting chemical cues and the tail-flip escape response (Chapter 3). Additionally, larval P. interruptus, exposed to both ocean acidification and warming conditions, grew slightly smaller in reduced pH but maintained their transparency in both conditions (Chapter 2). In contrast, H. californiensis resides in eelgrass meadows where a primary defense strategy is cryptic colouration, accomplished via a transparent exoskeleton with underlying pigment. When exposed to both ocean acidification and ocean warming-like conditions, shrimp maintained their transparency and did not respond negatively to either condition (Chapter 4). Together, this work on both species demonstrates that a diversity of predator defenses in temperate crustaceans, included those afforded by the exoskeleton, appear to be relatively resilient to both future ocean acidification and ocean warming conditions.

Continue reading ‘Integrity of crustacean predator defenses under ocean acidification and warming conditions’

Ocean acidification influences plant-animal interactions: the effect of Cocconeis scutellum parva on the sex reversal of Hippolyte inermis

Ocean acidification (O.A.) influences the ecology of oceans and it may impact plant-animal interactions at various levels. Seagrass meadows located at acidified vents in the Bay of Naples (Italy) are considered an open window to forecast the effects of global-changes on aquatic communities. Epiphytic diatoms of the genus Cocconeis are abundant in seagrass meadows, including acidified environments, where they play key ecological roles. A still-unknown apoptogenic compound produced by Cocconeis triggers the suicide of the androgenic gland of Hippolyte inermis Leach 1816, a protandric hermaphroditic shrimp distributed in P. oceanica meadows located both at normal pH and in acidified vents. Feeding on Cocconeis sp. was proven important for the stability of the shrimp’s natural populations. Since O.A. affects the physiology of diatoms, we investigated if, in future scenarios of O.A., Cocconeis scutellum parva will still produce an effect on shrimp’s physiology. Cell densities of Cocconeis scutellum parva cultivated in custom-designed photobioreactors at two pH conditions (pH 7.7 and 8.2) were compared. In addition, we determined the effects of the ingestion of diatoms on the process of sex reversal of H. inermis and we calculated the % female on the total of mature individuals-1 (F/mat). We observed significant differences in cell densities of C. scutellum parva at the two pH conditions. In fact, the highest cell densities (148,808 ±13,935 cells. mm-2) was obtained at day 13 (pH 7.7) and it is higher than the highest cell densities (38,066 (±4,166) cells. mm-2, day 13) produced at pH 8.2. Diatoms cultured at acidified conditions changed their metabolism. In fact, diatoms grown in acidified conditions produced in H. inermis a proportion of females (F/mat 36.3 ±5.9%) significantly lower than diatoms produced at normal pH (68.5 ±2.8), and it was not significantly different from that elicited by negative controls (31.7 ±5.6%).

Continue reading ‘Ocean acidification influences plant-animal interactions: the effect of Cocconeis scutellum parva on the sex reversal of Hippolyte inermis’

Impact of climate change on the American lobster (Homarus americanus): Physiological responses to combined exposure of elevated temperature and pCO2

Highlights
• Climate Change (2300 scenario) has a significant impact on the acid-base status in H. americanus.

• Climate Change causes retention of ammonia in hemolymph.

• Under Climate Change conditions hemolymph pCO2 does NOT exceed environmental pCO2.

• Climate Change causes increase in MO2 and ammonia excretion.

• Climate Change causes decrease in citrate synthase in tail muscle.

Abstract
The physiological consequences of exposing marine organisms to predicted future ocean scenarios, i.e. simultaneous increase in temperature and pCO2, have only recently begun to be investigated. Adult American lobster (Homarus americanus) were exposed to either current (16 °C, 47 Pa pCO2, pH 8.10) or predicted year 2300 (20 °C, 948 Pa pCO2, pH 7.10) ocean parameters for 14–16 days prior to assessing physiological changes in their hemolymph parameters as well as whole animal ammonia excretion and resting metabolic rate. Acclimation of lobster simultaneously to elevated pCO2 and temperature induced a prolonged respiratory acidosis that was only partially compensated for via accumulation of extracellular HCO3– and ammonia. Furthermore, acclimated animals possessed significantly higher ammonia excretion and oxygen consumption rates suggesting that future ocean scenarios may increase basal energetic demands on H. americanus. Enzyme activity related to protein metabolism (glutamine dehydrogenase, alanine aminotransferase, and aspartate aminotransferase) in hepatopancreas and muscle tissue were unaltered in future ocean scenario exposed animals; however, muscular citrate synthase activity was reduced suggesting that, while protein catabolism may be unchanged, the net energetic output of muscle may be compromised in future scenarios. Overall, H. americanus acclimated to ocean conditions predicted for the year 2300 appear to be incapable of fully compensating against climate change-related acid-base challenges and experience an increase in metabolic waste excretion and oxygen consumption. Combining our study with past literature on H. americanus suggests that the whole lifecycle from larvae to adult stages is at risk of severe growth, survival and reproductive consequences due to climate change.

Continue reading ‘Impact of climate change on the American lobster (Homarus americanus): Physiological responses to combined exposure of elevated temperature and pCO2’

The impact of climate change on intertidal species, camouflage and predation

To understand the impact of climate change on ecosystems we need to know not only how individual species will be affected, but also the relationships between them. Predator-prey relationships determine the structure and function of ecosystems worldwide, governing the abundance of populations, the distribution of different species within habitats and, ultimately, the composition of communities. Many predator-prey relationships are shifting as a result of environmental change, with climate change causing both mismatches in the abundance and distribution of species and changes in predator and prey behaviour. However, few studies have addressed how climate change might impact the interactions between species, particularly the development of anti-predator defences, which enable prey to limit their predation risk. One of the most widespread defences in nature is camouflage, with many species capable of changing colour to match their background to avoid being seen and eaten. The impact of climate change on this process is largely unknown, save for studies on species that exhibit seasonal changes in coloration. Using behavioural assays with predatory rock gobies (Gobius paganellus) and chameleon prawn prey (Hippolyte varians), I first demonstrate how background matching affects survival, shedding light on the fitness benefits of camouflage. Building on this fundamental understanding, this project explores how defensive coloration may be affected by anthropogenic climate change. Through a series of laboratory studies I test what impact ocean warming and ocean acidification have on the development of camouflage in intertidal crustaceans (chameleon prawns and common shore crabs, Carcinus maenas). Camouflage is modelled according to the visual systems of relevant predators, allowing us to understand what implications their coloration has for detectability, predation risk, and associated trophic links. Finally, this project investigates how camouflage can be applied to conservation and aquaculture. By rearing juvenile European lobster (Homarus gammarus) on different backgrounds, I show that they are capable of colour change for camouflage, as well as colour change throughout ontogeny. This capacity could be harnessed to help improve survival on release into the wild. As such, this thesis explores the fundamental science of camouflage, anthropogenic impacts on this process and its applications for conservation.

Continue reading ‘The impact of climate change on intertidal species, camouflage and predation’

Effects of chronic hypercapnia and elevated temperature on the immune response of the spiny lobster, Jasus lalandii

Highlights

• Lobsters are very efficient at rendering an injected dose of bacteria non-culturable.
• There is an interactive effects of temperature and pH on lobster immunity.
• Haemocyte numbers are reduced following chronic exposure to hypercapnia/high temperature.
• Chronic exposure to hypercapnia/high temperature does not affect the ability of J. lalandii to defend itself against bacterial infection.

Abstract

The West Coast rock lobster (WCRL), Jasus lalandii, inhabits highly variable environments frequented by upwelling events, episodes of hypercapnia and large temperature variations. Coupled with the predicted threat of ocean acidification and temperature change for the coming centuries, the immune response in this crustacean will most likely be affected. We therefore tested the hypothesis that chronic exposure to hypercapnia and elevated seawater temperature will alter immune function of the WCRL. The chronic effects of four combinations of two stressors (seawater pCO2 and temperature) on the total number of circulating haemocytes (THC) as well as on the lobsters’ ability to clear (inactivate) an injected dose of Vibrio anguillarum from haemolymph circulation were assessed. Juvenile lobsters were held in normocapnic (pH 8.01) or hypercapnic (pH 7.34) conditions at two temperatures (15.6 and 18.9 °C) for 48 weeks (n = 30 lobster per treatment), after which a subsample of lobsters (n = 8/treatment), all at a similar moult stage, were selected from each treatment for the immune challenge. Baseline levels of haemocytes (THC ml−1) and bacteria (CFU ml−1) in their haemolymph were quantified 24 h prior to bacterial challenge. Lobsters were then challenged by injecting 4 × 104 V. anguillarum per g body weight directly into the cardiac region of each lobster and circulating haemocyte and culturable bacteria were measured at 20 min post challenge. No significant differences in THC ml−1 (p < 0.05) were observed between any of the treatment groups prior to the bacterial challenge. However lobsters chronically exposed to a combination of hypercapnia and low temperature had significantly higher (p < 0.05) THCs post-challenge in comparison with lobsters chronically exposed to hypercapnia and high temperature. A significant interactive effect was recorded between temperature and pH for the post-challenge THC data (two-way ANOVA, p = 0.0025). Lobster were very efficient at rendering an injected dose of bacteria non-culturable, with more than 83% of the theoretical challenge dose (∼1.7 × 105 Vibrio ml−1 haemolymph) inactivated within the first 10 min following injection. Although differences in the inactivation of V. anguillarum were observed between treatment groups, none of these differences were significant. Clearance efficiency was in the following order: Hypercapnia/low temperature > normocapnia/high temperature > normocapnia/low temperature > hypercapnia/high temperature. This study demonstrated that despite chronic exposure to combinations of reduced seawater pH and high temperature, the WCRL was still capable of rapidly rendering an injected dose of bacteria non-culturable.

Continue reading ‘Effects of chronic hypercapnia and elevated temperature on the immune response of the spiny lobster, Jasus lalandii’

Quantifying susceptibility of marine invertebrate biocomposites to dissolution in reduced pH

Ocean acidification threatens many ecologically and economically important marine calcifiers. The increase in shell dissolution under the resulting reduced pH is an important and increasingly recognized threat. The biocomposites that make up calcified hardparts have a range of taxon-specific compositions and microstructures, and it is evident that these may influence susceptibilities to dissolution. Here, we show how dissolution (thickness loss), under both ambient and predicted end-century pH (approx. 7.6), varies between seven different bivalve molluscs and one crustacean biocomposite and investigate how this relates to details of their microstructure and composition. Over 100 days, the dissolution of all microstructures was greater under the lower pH in the end-century conditions. Dissolution of lobster cuticle was greater than that of any bivalve microstructure, despite its calcite mineralogy, showing the importance of other microstructural characteristics besides carbonate polymorph. Organic content had the strongest positive correlation with dissolution when all microstructures were considered, and together with Mg/Ca ratio, explained 80–90% of the variance in dissolution. Organic content, Mg/Ca ratio, crystal density and mineralogy were all required to explain the maximum variance in dissolution within only bivalve microstructures, but still only explained 50–60% of the variation in dissolution.

Continue reading ‘Quantifying susceptibility of marine invertebrate biocomposites to dissolution in reduced pH’

Effects of ocean acidification on the respiration and feeding of juvenile red and blue king crabs (Paralithodes camtschaticus and P. platypus)

Ocean acidification is a decrease in pH resulting from dissolution of anthropogenic CO2 in the oceans that has physiological effects on many marine organisms. Juvenile red and blue king crabs (Paralithodes camtschaticus and P. platypus) exhibit both increased mortality and decreased growth in acidified waters. In this study, we determined how ocean acidification affects oxygen consumption, feeding rates, and growth in both species. Juvenile crab were exposed to three pH levels: ambient (pH 8.1), pH 7.8, and pH 7.5 for 3 weeks. Oxygen consumption and feeding ration were determined immediately after exposure to treatment water and after 3 weeks’ exposure. Growth was calculated as a change in wet mass. Both species exhibited initially increased oxygen consumption at pH 7.5, but not after 3 weeks. Feeding rations did not vary with pH or exposure time. Red king crabs that moulted grew more in ambient water than in pH 7.5. The initial increase in oxygen consumption at pH 7.5 suggests the crab increased metabolism and expended more energy in osmo-/iono-regulation. Without an increase in feeding ration, it is likely the crab reduced energy expenditure in other areas, explaining the reduced growth and increased mortality observed in this and other studies.

Continue reading ‘Effects of ocean acidification on the respiration and feeding of juvenile red and blue king crabs (Paralithodes camtschaticus and P. platypus)’


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