Roy L. Caldwell

Ecological Effects of a Major Oil Spill on Panamanian Coastal Marine Communities

In 1986 more than 8 million liters of crude oil spilled into a complex region of mangroves, seagrasses, and coral reefs just east of the Caribbean entrance to the Panama Canal. This was the largest recorded spill into coastal habitats in the tropical Americas. Many population of plants and animals in both oiled and unoiled sites had been studied previously, thereby providing an unprecedented measure of ecological variation before the spill. Documenation of the spread of oil and its biological begun immediately. Intertidal mangroves, algae, and associated invertebrates were covered by oil and died soon after. More surprisingly, there was also extensive mortality of shallow subtidal reef corals and infauna of seagrass beds. After 1.5 years only some organisms in areas exposed to the open sea have recovered.

Circular polarization vision in a stomatopod crustacean.

We describe the addition of a fourth visual modality in the animal kingdom, the perception of circular polarized light. Animals are sensitive to various characteristics of light, such as intensity, color, and linear polarization [1, 2]. This latter capability can be used for object identification, contrast enhancement, navigation, and communication through polarizing reflections [2-4]. Circularly polarized reflections from a few animal species have also been known for some time [5, 6]. Although optically interesting [7, 8], their signal function or use (if any) was obscure because no visual system was known to detect circularly polarized light. Here, in stomatopod crustaceans, we describe for the first time a visual system capable of detecting and analyzing circularly polarized light. Four lines of evidence-behavior, electrophysiology, optical anatomy, and details of signal design-are presented to describe this new visual function. We suggest that this remarkable ability mediates sexual signaling and mate choice, although other potential functions of circular polarization vision, such as enhanced contrast in turbid environments, are also possible [7, 8]. The ability to differentiate the handedness of circularly polarized light, a visual feat never expected in the animal kingdom, is demonstrated behaviorally here for the first time.

Polarization Vision and Its Role in Biological Signaling

Abstract Visual pigments, the molecules in photoreceptors that initiate the process of vision, are inherently dichroic, differentially absorbing light according to its axis of polarization. Many animals have taken advantage of this property to build receptor systems capable of analyzing the polarization of incoming light, as polarized light is abundant in natural scenes (commonly being produced by scattering or reflection). Such polarization sensitivity has long been associated with behavioral tasks like orientation or navigation. However, only recently have we become aware that it can be incorporated into a high-level visual perception akin to color vision, permitting segmentation of a viewed scene into regions that differ in their polarization. By analogy to color vision, we call this capacity polarization vision. It is apparently used for tasks like those that color vision specializes in: contrast enhancement, camouflage breaking, object recognition, and signal detection and discrimination. While color is very useful in terrestrial or shallow-water environments, it is an unreliable cue deeper in water due to the spectral modification of light as it travels through water of various depths or of varying optical quality. Here, polarization vision has special utility and consequently has evolved in numerous marine species, as well as at least one terrestrial animal. In this review, we consider recent findings concerning polarization vision and its significance in biological signaling.

Ecology and evolution of agonistic behavior in stomatopods

Stomatopods are marine crustacea which occupy cavities and burrows on most of the worlds tropical reefs and beaches. They are highly aggressive and defend their burrows using a raptorial appendage capable of inflicting lethal blows. Morphologically, the raptorial appendages of stomatopods can be divided into two types, spearing and smashing. Those species possessing the smashing appendage, which is the more potent of the two forms, show heavier telson armor, agonistic repertoires which are more intense and complex, and tend to occupy homesites such as cavities in rock or coral which are scarce as compared to the availability of burrow sites for spearers. Within a group of species from one habitat, the most aggressive is usually the most abundant, suggesting contest competition.

Biomechanics: Deadly strike mechanism of a mantis shrimp

Stomatopods (mantis shrimp) are well known for the feeding appendages they use to smash shells and impale fish. Here we show that the peacock mantis shrimp (Odontodactylus scyllarus) generates an extremely fast strike that requires major energy storage and release, which we explain in terms of a saddle-shaped exoskeletal spring mechanism. High-speed images reveal the formation and collapse of vapour bubbles next to the prey due to swift movement of the appendage towards it, indicating that O. scyllarus may use destructive cavitation forces to damage its prey.

Deceptive communication in asymmetric fights of the stomatopod crustacean Gonodactylus bredini

When fighting for ownership of cavities, newly moulted stomatopods, Gonodactylus bredini, bluffed opponents by producing meral spread threat displays, even though their soft condition prevented them from delivering or withstanding blows. Newly moulted stomatopods adjusted the frequency of bluffing according to the relative size of their opponent, apparently in response to the risk of probing. Newly moulted residents were more likely to threaten and less likely to flee when facing intruders that were 15% smaller than when facing intruders that were the same size or 15% larger. Bluffs by residents inhibited escalation by intruders and increased the probability of successful cavity defence. This effect was strongest when the intruder was smaller than the resident. When stomatopods fought twice in the laboratory, they often modified their fighting behaviour according to the nature of their first encounter. However, no evidence was found that intruders developed scepticism towards the meral spread threat display after successfully evicting a bluffing resident. Furthermore, newly moulted animals did not decrease their use of the bluff following unsuccessful attempts to deter intruders.

Extreme impact and cavitation forces of a biological hammer: strike forces of the peacock mantis shrimp Odontodactylus scyllarus.

SUMMARY Mantis shrimp are renowned for their unusual method of breaking shells with brief, powerful strikes of their raptorial appendages. Due to the extreme speeds of these strikes underwater, cavitation occurs between their appendages and hard-shelled prey. Here we examine the magnitude and relative contribution of the impact and cavitation forces generated by the peacock mantis shrimp Odontodactylus scyllarus. We present the surprising finding that each strike generates two brief, high-amplitude force peaks, typically 390–480 μs apart. Based on high-speed imaging, force measurements and acoustic analyses, it is evident that the first force peak is caused by the limbs impact and the second force peak is due to the collapse of cavitation bubbles. Peak limb impact forces range from 400 to 1501 N and peak cavitation forces reach 504 N. Despite their small size, O. scyllarus can generate impact forces thousands of times their body weight. Furthermore, on average, cavitation peak forces are 50% of the limbs impact force, although cavitation forces may exceed the limb impact forces by up to 280%. The rapid succession of high peak forces used by mantis shrimp suggests that mantis shrimp use a potent combination of cavitation forces and extraordinarily high impact forces to fracture shells. The stomatopods hammer is fundamentally different from typical shell-crushing mechanisms such as fish jaws and lobster claws, and may have played an important and as yet unexamined role in the evolution of shell form.

Recovery in rubble fields: long-term impacts of blast fishing

This paper presents initial results from a study of factors that inhibit or enhance hard coral recovery in rubble fields created by blast fishing in Komodo National Park and Bunaken National Park, Indonesia. Within nine sites monitored since 1998, there was no significant natural recovery. Levels of potential source coral larvae were assessed with settlement tiles in the rubble fields and in nearby high coral cover sites. Rubble movement was measured and shown to be detrimental to small scleractinians, especially in high current areas. In shallow water (2-6 m deep), rubble is often overgrown by soft corals and corallimorpharians, which inhibit hard coral survival. There is increased scleractinian recruitment in quadrats cleared of soft coral, and Acropora nubbins transplanted into soft coral fields suffer greater mortality than those transplanted above the soft coral canopy. Gaining an understanding of the prognosis for coral recovery is essential not only in order to assess the long-term impacts of blast fishing, but also to improve management decisions about protection of intact reefs and potential restoration of damaged areas.

A test of individual recognition in the stomatopod Gonodactylus festate

Abstract The mantis shrimp Gonodactylus festae lives in rock cavities which it must frequently defend against conspecifics. To determine if individual recognition is used to mediate these aggressive contests, adult intruders were matched sequentially against residents that were larger and smaller than themselves. Intruders were repulsed by large residents, but were able to evict small ones from their cavities. Later, each intruder was exposed once to a cavity containing the odour of the animal that deeated it and once to a cavity containing the odour of the animal it defeated. Intruders rapidly entered cavities containing the odour of the resident they defeated, but were hesitant to enter cavities containing the odour of the animal that had successfully defended against them. This demonstrates that G. festae can distinguish between the odours of two previously encountered opponents and suggests that this species is capable of individual recognition.

Cavity occupation and defensive behaviour in the stomatopod Gonodactylus festai: Evidence for chemically mediated individual recognition

Abstract Pairs of the mantis shrimp Gonodactylus festai fought in an open arena. Later, the dominant individual was placed in a cavity and defended it against the subordinate. Visual, tactile, and acoustical displays used during contents for cavities are here described. Fifteen minutes later the subordinate animal was placed in an arena with a cavity containing water from the aquarium of the animal that had just defeated it, water from the aquarium of a stomatopod it had never met, or water that had never contained a stomatopod. Animals readily entered cavities containing clean water, investigated and entered cavities containing strange stomatopod water, and avoided cavities containing water from the home aquarium of the animal that had previously defeated them.