Invertebrate mobile

Chapters 9 and 10 while in this chapter we concentrate on cell-cell structures and their organic chemical communication and the very simple nerve networks between senses and muscles. At the same time a complicated series of organs became involved in intake, synthesis, distribution of material and waste excretion so as to supply suitable material with energy to the whole body and remove excess chemicals. Probably to protect and strengthen the structures, the invertebrates developed external shells but it is only with the arrival of vertebrates, animals with bones, that great internal structural strength with mobility evolved (see Figure 8.6 and Table 8.3). 

BaP was not detectable in muscle and gut, indicating that BaP on sediments may be mobilized and made available to benthic invertebrates and fish but that the process was highly inefficient with minor biomagnification a similar case is made for fluoranthene... 

Equation 3.56 indicates that the biofilm essentially behaves like an immobilized water layer, with a resistance that is independent of the biofilm-water partition coefficient. Evidently, when the growth rate of the biofilm and the diffusion rate of the contaminants are of similar magnitude, this highly idealized model breaks down, and it can be expected in those cases that highly hydrophobic compounds will have more difficulty in reaching the membrane than less hydrophobic (more mobile) compounds. Also, Eq. 3.56 will likely fail to predict solute transport in biofilms with sizable populations of invertebrates because of bioturbation. 

The divergence of plastic metabolism between mobile and sluggish fish can also be found in other animals, including marine invertebrates, with similar structural-metabolic changes underlying it. A comparison between large taxa of molluscs, cephalopods and lamellibranchs, in particular, reveals that their content of docosohexaenoic acid is directly proportional to their degree of mobility. 

Chemical Ecology of Mobile Benthic Invertebrates Predators and Prey,... 

III. Chemical Mediation of Competition Among Mobile Invertebrates.173... 

Several excellent reviews currently exist on particular aspects of marine chemical ecology,1-6 so this chapter does not attempt to provide a comprehensive or historic overview, but rather tries to provide a sound conceptual discussion of the diversity and importance of chemically mediated interactions involving mobile invertebrates. Due to space constraints, not all relevant studies can be included, and recent studies are sometimes cited in favor of more classical work, as these provide similar conceptual information but often use more advanced methodologies and provide greater access to other literature on the topic. Where possible, this chapter highlights studies that assess the importance of chemically mediated interactions within the broader context of ecology and evolutionary biology. 

Although relatively few mobile invertebrates produce their own defensive compounds, many more use the defensive compounds produced by other organisms, either by physiologically sequestering them from their prey, or by developing commensal or mutualistic associations with other chemically unpalatable organisms (see Section IV.B). Additionally, some animals use waterborne cues to detect the presence of predators and adjust their behavior and use of refuges to minimize the risk of detection. 

As with sessile animals and plants (see other chapters, this volume), the chemical deterrence of mobile invertebrates is best assessed using an approach in which ecologically relevant consumers are offered palatable food items with chemical extracts coated on, or embedded within, them.7 Assays in which the toxicity of compounds is assessed by dissolving them in the water containing the assay organisms have been repeatedly shown to bear no relation to the effects of compounds when ingested with prey.1 8,9 Most feeding deterrents of mobile invertebrates appear to be lipid-soluble, thus these... 

Chemical defenses are less commonly reported in other groups of mobile marine invertebrates, but they may exist. Heine et al.21 showed that a common Antarctic nemertean worm is rejected as prey by co-occurring fishes despite the lack of obvious structural defenses. The unpalatability has been attributed to a highly acidic mucus coating (pH 3.5), although toxic peptides were also present22... 

This type of correlative approach is widespread, as only a few marine studies involving inducible defenses (and none with mobile invertebrates) have directly demonstrated that the induction results in a decrease in the susceptibility of the organism to predation.71,72 Statistically significant differences in shell thickness or concentrations of defensive chemicals may or may not meaningfully affect predator preferences in ecologically relevant field situations. For chemical defenses, compound dose-response relationships may be nonlinear, and threshold levels of defense could be sufficient to deter predators so that further induction has little additional benefit. Thus, future studies should focus on directly demonstrating whether an induced response reduces predation on prey organisms. 

An emerging generalization from studies of the susceptibility of consumers to prey chemical defense is that many small, low-mobility invertebrates such as amphipods, polychaetes, shell-less gastropods, and crabs readily consume seaweeds that produce chemicals that deter feeding by larger, mobile grazers like fishes and urchins.30,38,39,84-87 From most of these studies it is unclear whether... 

Knowledge of the variability in the susceptibility of different guilds and species of mobile invertebrates to chemical defenses produced by sessile invertebrates and seaweeds is critical for a mechanistic understanding of the distribution of the sessile benthos in the sea. Large mobile invertebrates like sea urchins commonly alter benthic community composition from palatable to unpalatable species.92,93 Most notably, chemical defenses produced by tropical seaweeds have been widely implicated in the persistence of these species in areas of intense herbivory like coral reefs1,3 (also see Chapter 6 in this volume). 

Thus far, this section has focused primarily on ways in which mobile invertebrates use chemicals to defend themselves against predators and the consequences of these defenses for the behavior and fitness of predators. However, predators also employ chemicals in all phases of their search for prey, including prey location, capture, and initiation of feeding. 

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