Recent studies show that ocean acidification impairs sensory functions and alters the behavior of teleost fishes. If sharks and other elasmobranchs are similarly affected, this could have significant ...consequences for marine ecosystems globally. Here, we show that projected future CO₂levels impair odor tracking behavior of the smooth dogfish (Mustelus canis). Adult M. canis were held for 5 days in a current‐day control (405 ± 26 μatm) and mid (741 ± 22 μatm) or high CO₂(1064 ± 17 μatm) treatments consistent with the projections for the year 2100 on a ‘business as usual’ scenario. Both control and mid CO₂‐treated individuals maintained normal odor tracking behavior, whereas high CO₂‐treated sharks significantly avoided the odor cues indicative of food. Control sharks spent >60% of their time in the water stream containing the food stimulus, but this value fell below 15% in high CO₂‐treated sharks. In addition, sharks treated under mid and high CO₂conditions reduced attack behavior compared to the control individuals. Our findings show that shark feeding could be affected by changes in seawater chemistry projected for the end of this century. Understanding the effects of ocean acidification on critical behaviors, such as prey tracking in large predators, can help determine the potential impacts of future ocean acidification on ecosystem function.
The direction of an odor signal source can be estimated from bilateral differences in signal intensity and/or arrival time. The best-known examples of the use of arrival time differences are in ...acoustic orientation 1. For chemoreception, animals are believed to orient by comparing bilateral odor concentration differences, turning toward higher concentrations 2–4. However, time differences should not be ignored, because odor plumes show chaotic intermittency, with the concentration variance several orders of magnitude greater than the concentration mean (e.g., 5). We presented a small shark species, Mustelus canis, with carefully timed and measured odor pulses directly into their nares. They turned toward the side stimulated first, even with delayed pulses of higher concentration. This is the first conclusive evidence that under seminatural conditions and without training, bilateral time differences trump odor concentration differences. This response would steer the shark into an odor patch each time and thereby enhance its contact with the plume, i.e., a stream of patches. Animals with more widely spaced nares would be able to resolve smaller angles of attack at higher swimming speeds, a feature that may have contributed to the evolution of hammerhead sharks. This constitutes a novel steering algorithm for tracking odor plumes.
► To steer, sharks use bilateral odor arrival-time differences, not concentration ► New navigation algorithm for chemical plume tracking underwater ► New evolutionary selection mechanism for spacing of nares in hammerhead sharks
A major goal of the aquaculture industry is to reduce collection pressure on wild populations by developing captive breeding techniques for marine ornamental species, particularly coral reef fishes. ...The objective of this study was to develop a rearing protocol for two recently described species of neon gobies that are endemic to the Mesoamerican Barrier Reef: 1) Elacatinus lori; and 2) Elacatinus colini. First, the current study describes the reproductive behavior and larval development of both species. Second, it evaluates the effects of different rotifer and Artemia densities on the survival and growth of E. lori and E. colini larvae. Third, it compares the survival and growth of E. colini larvae fed wild plankton to those fed a combination of rotifers and Artemia. Once acclimated, pairs of E. lori began spawning in 53.2±12.4 d (mean±sd), while pairs of E. colini took only 12.2±10.3 d. E. lori produced more embryos per clutch (1009±477) than E. colini (168±83). E. lori larvae hatched 8.18±0.4days after initial observation with a notochord length of 3.67±0.2mm. In comparison, E. colini larvae hatched 6.8±0.4days after initial observation with a notochord length of 3.51±2.3mm. Both species settled as early as 28days post hatch at 9–9.5mm standard length, following the fusion of the pelvic fins to form a pelvic disc. During rotifer density trials, from 0 to 6days post hatch, there was no significant difference in survival or standard length between treatments fed 10, 15 or 20rotifersml−1 for either species. During Artemia density trials, from 6 to 14days post hatch, control treatments fed solely on 15rotifersml−1 had significantly higher survival than treatments that were fed rotifers in combination with 3, 6 or 9Artemiaml−1. Finally, E. colini larvae that were fed wild plankton had significantly higher survival and growth than those fed with a combination of 15rotifersml−1 and 3Artemiaml−1. The results of this study suggest that Artemia nauplii are not a suitable prey for E. lori or E. colini larvae. Our results demonstrate the feasibility of rearing E. lori and E. colini to settlement, and suggest that 10–20rotifersml−1 and wild plankton provide a viable starting point for optimizing the survival and growth of Elacatinus spp. larvae.
•A description of reproductive behavior and a larval rearing protocol are provided for two species of Elacatinus gobies.•There was no difference in the survival or standard length of larvae that were fed 10, 15 or 20rotifers ml−1.•Larvae fed Artemia beginning at 6days post hatch had lower survival than controls fed solely with rotifers.•E. colini larvae fed wild plankton had higher survival and growth than those fed a combination of rotifers and Artemia.•A diet of 10 – 20rotifers ml−1 and wild plankton provides a viable starting point for rearing Elacatinus spp. larvae.
Reef fish sustain populations on isolated reefs and show genetic diversity between nearby reefs even though larvae of many species are swept away from the natal site during pelagic dispersal. ...Retention or recruitment to natal reefs requires orientation capabilities that enable larvae to find their way. Although olfactory and acoustically based orientation has been implicated in homing when larvae are in the reef's vicinity, it is still unclear how they cope with greater distances. Here we show evidence for a sun compass mechanism that can bring the larvae to the vicinity of their natal reef. In a circular arena, pre-settlement larvae and early settlers (<24 hours) of the cardinal fish, Ostorhinchus doederleini, showed a strong SSE directional swimming response, which most likely has evolved to compensate for the locally prevailing large scale NNW current drift. When fish were clock-shifted 6 hours, they changed their orientation by ca. 180° as predicted by the tropical sun curve at One Tree Island, i.e. they used a time-compensated sun compass. Furthermore, the fish oriented most consistently at times of the day when the sun azimuth is easy to determine. Microsatellite markers showed that the larvae that had just arrived at One Tree Island genetically belonged to either the local reef population or to Fitzroy Reef located 12 kilometers to the SSE. The use of a sun compass adds a missing long-distance link to the hierarchy of other sensory abilities that can direct larvae to the region of origin, including their natal reef. Predominant local recruitment, in turn, can contribute to genetic isolation and potential speciation.
The behavior of reef fish larvae, equipped with a complex toolbox of sensory apparatus, has become a central issue in understanding their transport in the ocean. In this study pelagic reef fish ...larvae were monitored using an unmanned open-ocean tracking device, the drifting in-situ chamber (DISC), deployed sequentially in oceanic waters and in reef-born odor plumes propagating offshore with the ebb flow. A total of 83 larvae of two taxonomic groups of the families Pomacentridae and Apogonidae were observed in the two water masses around One Tree Island, southern Great Barrier Reef. The study provides the first in-situ evidence that pelagic reef fish larvae discriminate reef odor and respond by changing their swimming speed and direction. It concludes that reef fish larvae smell the presence of coral reefs from several kilometers offshore and this odor is a primary component of their navigational system and activates other directional sensory cues. The two families expressed differences in their response that could be adapted to maintain a position close to the reef. In particular, damselfish larvae embedded in the odor plume detected the location of the reef crest and swam westward and parallel to shore on both sides of the island. This study underlines the critical importance of in situ Lagrangian observations to provide unique information on larval fish behavioral decisions. From an ecological perspective the central role of olfactory signals in marine population connectivity raises concerns about the effects of pollution and acidification of oceans, which can alter chemical cues and olfactory responses.
The underwater sensory world and the sensory systems of aquatic animals have become better understood in recent decades, but typically have been studied one sense at a time. A comprehensive analysis ...of multisensory interactions during complex behavioral tasks has remained a subject of discussion without experimental evidence. We set out to generate a general model of multisensory information extraction by aquatic animals. For our model we chose to analyze the hierarchical, integrative, and sometimes alternate use of various sensory systems during the feeding sequence in three species of sharks that differ in sensory anatomy and behavioral ecology. By blocking senses in different combinations, we show that when some of their normal sensory cues were unavailable, sharks were often still capable of successfully detecting, tracking and capturing prey by switching to alternate sensory modalities. While there were significant species differences, odor was generally the first signal detected, leading to upstream swimming and wake tracking. Closer to the prey, as more sensory cues became available, the preferred sensory modalities varied among species, with vision, hydrodynamic imaging, electroreception, and touch being important for orienting to, striking at, and capturing the prey. Experimental deprivation of senses showed how sharks exploit the many signals that comprise their sensory world, each sense coming into play as they provide more accurate information during the behavioral sequence of hunting. The results may be applicable to aquatic hunting in general and, with appropriate modification, to other types of animal behavior.
In recent years it has become increasingly clear that chemical interactions play a fundamental role in aquatic habitats and have far-reaching evolutionary and ecological consequences. A plethora of ...studies have shown that aquatic organisms from most taxa and functional groups respond to minute concentrations of chemical substances released by other organisms. However, our knowledge of this ‘chemical network’ is still negligible. Chemical interactions can be divided into two larger sub-areas based on the function of the chemical substance. First, there are interactions where chemical substances are toxic to other organisms and are used as a defence against consumers (including both herbivores and predators) or a weapon against competitors (allelopathy). Second, chemical substances may be used as a source for information on the environment; for example: how can I find the optimal habitat, the best food, the nicest partner, and avoid being eaten? Aquatic organisms are able to detect and respond to extremely low concentrations of chemical cues to answer all these questions. The book aims at connecting these intriguing chemical interactions with traditional knowledge of organism interactions. It covers a wide range of studies, both plant and animal, from different geographic regions and habitats — pelagic as well as benthic. Most of the chemical interactions are similar in freshwater and marine habitats and this book therefore strives at integrating work on both systems.
We investigated the possibility that invertebrates recognize conspecific individuals by studying dominance relationships in the long‐clawed hermit crab, Pagurus longicarpus. We conducted three sets ...of laboratory experiments to define the time limits for acquiring and maintaining memory of an individual opponent. The results reveal two characteristics that make individual recognition in this species different from standard associative learning tasks. Firstly, crabs do not require training over many repeated trials; rather, they show evidence of recognition after a single 30‐min exposure to a stimulus animal. Secondly, memory lasts for up to 4 d of isolation without reinforcement. A third interesting feature of individual recognition in this species is that familiar opponents are recognized even before the formation of a stable hierarchical rank. That is, recognition seems to be relatively independent of repeated wins (rewards) or losses (punishments) in a dominance hierarchy. The experimental protocol allowed us to show that this species is able to classify conspecifics into two ‘heterogeneous subgroups’, i.e. familiar vs. unfamiliar individuals, but not to discriminate one individual of a group from every other conspecific from ‘a unique set of cues defining that individual’. In other words, we demonstrated a ‘binary’– and not a ‘true’– individual recognition. However, 1 d of interactions with different crabs did not erase the memory of a former rival, suggesting that P. longicarpus uses a system of social partner discrimination more refined than previously shown.
Lobsters are capable of tracking turbulent plumes to their sources faster than can be accomplished by estimating a spatial gradient from time-averaging the concentration signal. We have used ...RoboLobster, a biomimetic robot lobster to investigate biologically scaled chemotaxis algorithms using two point concentration sampling to track a statistically characterized turbulent plume. Our results identify the range of effectiveness of these algorithms and, with studies of lobster behavior, suggest effective strategies beyond this range. They suggest that a lobster’s chemo-orientation strategy entails an unidentified means of dealing with the intermittency of the concentration signal. Extensions of these algorithms likely to improve are discussed.
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