Sensory biology and behaviour of Nephrops norvegicus

Effects of pile driving sound playbacks and cadmium co-exposure on the early life stage development of the Norway lobster, Nephrops norvegicus

There is an urgent need to understand how organisms respond to multiple, potentially interacting drivers in today's world. The effects of the pollutants anthropogenic sound (pile driving sound playbacks) and waterborne cadmium were investigated across multiple levels of biology in larval and juvenile Norway lobster, Nephrops norvegicus under controlled laboratory conditions. The combination of pile driving playbacks (170 dB_pk-pk re 1 μPa) and cadmium combined synergistically at concentrations >9.62 μg_[Cd] L^-1 resulting in increased larval mortality, with sound playbacks otherwise being antagonistic to cadmium toxicity. Exposure to 63.52 μg_[Cd] L^-1 caused significant delays in larval development, dropping to 6.48 μg_[Cd] L^-1 in the presence of piling playbacks. Pre-exposure to the combination of piling playbacks and 6.48 μg_[Cd] L^-1 led to significant differences in the swimming behaviour of the first juvenile stage. Biomarker analysis suggested oxidative stress as the mechanism resultant deleterious effects, with cellular metallothionein (MT) being the predominant protective mechanism.

Distinct mechanoreceptor pezo-1 isoforms modulate food intake in the nematode Caenorhabditis elegans

Two PIEZO mechanosensitive cation channels, PIEZO1 and PIEZO2, have been identified in mammals, where they are involved in numerous sensory processes. While structurally similar, PIEZO channels are expressed in distinct tissues and exhibit unique properties. How different PIEZOs transduce force, how their transduction mechanism varies, and how their unique properties match the functional needs of the tissues they are expressed in remain all-important unanswered questions. The nematode Caenorhabditis elegans has a single PIEZO ortholog (pezo-1) predicted to have 12 isoforms. These isoforms share many transmembrane domains but differ in those that distinguish PIEZO1 and PIEZO2 in mammals. We used transcriptional and translational reporters to show that putative promoter sequences immediately upstream of the start codon of long pezo-1 isoforms predominantly drive green fluorescent protein (GFP) expression in mesodermally derived tissues (such as muscle and glands). In contrast, sequences upstream of shorter pezo-1 isoforms resulted in GFP expression primarily in neurons. Putative promoters upstream of different isoforms drove GFP expression in different cells of the same organs of the digestive system. The observed unique pattern of complementary expression suggests that different isoforms could possess distinct functions within these organs. We used mutant analysis to show that pharyngeal muscles and glands require long pezo-1 isoforms to respond appropriately to the presence of food. The number of pezo-1 isoforms in C. elegans, their putative differential pattern of expression, and roles in experimentally tractable processes make this an attractive system to investigate the molecular basis for functional differences between members of the PIEZO family of mechanoreceptors.

Burrow emergence rhythms of Nephrops norvegicus by UWTV and surveying biases

Underwater Television (UWTV) surveys provide fishery-independent stock size estimations of the Norway lobster (Nephrops norvegicus), based directly on burrow counting using the survey assumption of “one animal = one burrow”. However, stock size may be uncertain depending on true rates of burrow occupation. For the first time, 3055 video transects carried out in several Functional Units (FUs) around Ireland were used to investigate this uncertainty. This paper deals with the discrimination of burrow emergence and door-keeping diel behaviour in Nephrops norvegicus, which is one of the most commercially important fisheries in Europe. Comparisons of burrow densities with densities of visible animals engaged in door-keeping (i.e. animals waiting at the tunnel entrance) behaviour and animals in full emergence, were analysed at time windows of expected maximum population emergence. Timing of maximum emergence was determined using wave-form analysis and GAM modelling. The results showed an average level of 1 visible Nephrops individual per 10 burrow systems, depending on sampling time and depth. This calls into question the current burrow occupancy assumption which may not hold true in all FUs. This is discussed in relation to limitations of sampling methodologies and new autonomous robotic technological solutions for monitoring.

Chemosensory Basis of Feeding Behavior in Pacific White Shrimp, Litopenaeus vannamei

AbstractThe Pacific white shrimp, Litopenaeus vannamei, is important as the principal species in the worldwide aquaculture of shrimp. It has also become a model in the study of crustacean biology, especially because it is one of the first decapod crustaceans to have its genome sequenced. This study examined an aspect of the sensory biology of this shrimp that is important in its aquaculture, by describing its peripheral chemical sensors and how they are used in acquiring and consuming food pellets. We used scanning electron microscopy to describe the diversity of sensilla on the shrimp's major chemosensory organs: antennules, antennae, mouthparts, and legs. Using behavioral studies on animals with selective sensory ablations, we then explored the roles that these chemosensory organs play in the shrimp's search for, and acquisition and ingestion of, food pellets. We found that the antennules mediate odor-activated searching for pellets, with both the lateral and medial antennular flagella contributing to this behavior and thus demonstrating that both aesthetasc (olfactory) and distributed chemosensors on the antennules can mediate this behavior. Once the shrimp finds and grasps the food pellet, the antennular chemoreceptors no longer play a role, and then the chemoreceptors on the mouthparts and legs control ingestion of the pellets. This sequence of chemosensory control of feeding in L. vannamei, a dendrobranchiate crustacean with small antennules and an ability to live and feed in both benthic and pelagic environments, is generally similar to that of the better-studied, large-antennuled, benthic reptantian crustaceans, including spiny lobsters (Achelata), clawed lobsters and crayfish (Astacidea), and crabs (Meirua).

Importance of suspended particulate organic matter in the diet of Nephrops norvegicus (Linnaeus, 1758)

The extent to which commercially important Nephrops norvegicus lobsters feed on particulates in the wild is unknown, even though this could be an important way for burrow-dwelling females to avoid starvation during the long breeding season. This was investigated using δ¹³C and δ¹⁵N isotopic signatures in tissues with long and short turnover rates to provide diet discrimination and compare this between males and females. Secondary objectives examined size-related differences and calculated the trophic position based on the new results. Almost half the diet (47%) was made up of suspended particulate organic matter (POM_susp) alone. Fish was another important item in the diet, with plankton and invertebrate sources coming much lower down in dietary importance. Significantly more suspension feeding was observed in small or medium sized individuals than large ones in both sexes. However, there were no sex-related patterns, despite females being restricted to burrows for part of the analysis period. Female diet was almost identical to males and POM_susp comprised a large component of the diet in both sexes. The trophic position was estimated at 2.94 ± 0.16 (mean ± SD), which was at the lower end of the range reported in previous studies (2.60 to 4.32).

Density-dependent growth in 'catch-and-wait' fisheries has implications for fisheries management and Marine Protected Areas

Stock enhancement activities provide an opportunity to examine density-dependent suppression of population biomass which is a fundamental issue for resource management and design of no-take-zones. We document 'catch-and-wait' fisheries enhancement where all but the largest lobsters are thrown back, recapturing them later after they have grown to a larger size. The residency, rate of return, and potential negative density-dependent effects of this activity are described using a combination of tagging and v-notching and by relating spatial growth patterns to population density defined with Catch Per Unit Effort. The results successfully demonstrated the concept of catch-and-wait practices. However, a density-dependent suppression of growth (in body size) was observed in male lobsters. This demonstrates a mechanism to explain differences in lobster sizes previously observed across EU fishing grounds with different stock densities. This negative effect of density could also affect individual biomass production in marine reserve or no-take zones.

Fighting over burrows: the emergence of dominance hierarchies in the Norway lobster (Nephrops norvegicus)

Animals fight over resources such as mating partners, territory, food or shelter and repeated contests lead to stable social hierarchies in different phyla. The group dynamics of hierarchy formation are not characterized in the Norway lobster (Nephrops norvegicus). Lobsters spend most of the day in burrows and forage outside of them according to a diel (i.e. 24 h-based) activity rhythm. Here, we use a linear and generalized mixed model approach to analyse, in seven groups of four male lobsters, the formation of dominance hierarchies and rank-related changes in burrowing behaviour. We show that hierarchies emerge within 1-3 days and increase in steepness over a period of 5 days, while rank changes and number of fights gradually decrease over a 5-day period. The rank position determined by open area fights predicts the outcome of fights over burrows, the time spent in burrows, and the locomotor activity levels. Dominant lobsters are more likely to evict subordinate lobsters from their burrows and are more successful in defending their own burrows. They spend more time in burrows and display lower levels of locomotor activity outside the burrow. Lobsters do not change their diel activity rhythms as a result of a change in rank, and all tested individuals showed higher activity at night and dusk compared with dawn and daytime. We discuss how behavioural changes in burrowing behaviour could lead to rank-related benefits such as reduced exposure to predators and energy savings.