Magnus L. Johnson

Satiation gives krill that sinking feeling.

Document S1. Supplemental Experimental Procedures and Supplemental AnalysisxDownload (.05 MB ) Document S1. Supplemental Experimental Procedures and Supplemental Analysis

Regional scale speciation reveals multiple invasions of freshwater in Palaemoninae (Decapoda)

Ashelby, C.W., Page, T.J., De Grave, S., Hughes, J.M. & Johnson, M.L. (2012) Regional scale speciation reveals multiple invasions of freshwater in Palaemoninae (Decapoda). —Zoologica Scripta, 41, 293–306.

Spectral sensitivities of five marine decapod crustaceans and a review of spectral sensitivity variation in relation to habitat

The spectral sensitivities of five species of decapod crustaceans have been determined by electroretinogram measurements. Their spectral sensitivities conform to the general picture for marine crustacea with high sensitivity to blue-green wavelengths and some showing sensitivity to violet/near ultraviolet. Two deep-water species ( Paromola cuvieri and Chaceon ( Geryon ) affinis ) have spectral sensitivity maxima below 500 nm, whereas the three coastal species examined ( Crangon allmani , Pandalus montagui and Nephrops norvegicus ) are maximally sensitive to light of longer wavelengths (510 to 525 nm).

Size and stripes: how fish clients recognize cleaners

Little is known of how individuals find each other in interspecific mutualisms involving free-living partners. We tested the importance of two factors, namely body size and the presence of a lateral body stripe, in the recognition of cleanerfish by their fish clients. Clients on an Indonesian reef flat readily approached wooden models of the bluestreak cleaner wrasse, Labroides dimidiatus, which varied in size and stripe characteristics. The composition of the clientele of models was not significantly different from that of natural cleaning stations, suggesting that fish visiting the models were seeking to be cleaned. Normal-sized models of cleaner wrasses attracted significantly more clients, which showed more intense interest and stayed with the models for significantly longer, than super-sized models. For normal-sized models, the number of clients increased as the length of the cleaners lateral stripe increased (from 0, to 44, 67 and 100% of body length). However, there was no effect of stripe length on client numbers for super-sized models. Client interest also did not vary with stripe length for models of either size. Small body size and the presence of a lateral stripe therefore appear to be long-distance signals that their bearer may be a cleaner, but after initial attraction, client interest is maintained by other cues. Alternative short-distance signals may include colour, other visual signals such as cleanerfish dances, or physical contact between cleaner and client.

Nephrops fisheries in European waters.

This review focuses on the Norway lobster (Nephrops norvegicus) as a resource, describing how the fishery has developed from the 1960s to the present day to become one of the most economically important fisheries in Europe. In 2010, the total landings were 66,500 tonnes, of which UK fishers landed a significant part (58.1%). The Nephrops fishery is also important for countries such as Ireland (11.7% of the total) and Sweden (1.9%) where it is of regional importance. Some are also taken in the Mediterranean, where Italian, Spanish and Greek fishers together take approximately 7% of the total landing. More than 95% of Nephrops are taken using single- or multi-rig trawlers targeting Nephrops or in mixed species fisheries. In regions such as Western Scotland and the Swedish West Coast, creel fisheries account for up to a quarter of the total landings. Across the range, a small proportion (<5%) is taken using traps in a fishery characterised by larger sized animals that gain a higher price and have lower discard and by-catches of ground fish with low mortalities. The trawling sector, however, is reducing the by-catches of ground fish with the aid of technical measures, such as square-mesh panels and grids and national systems of incentives. Assessments for Nephrops are operated via the 34 functional units (FUs) regarded as stocks. Changes in management procedures have arisen as a result of the advisory input from underwater TV fishery-independent stock surveys. The total allowable catch does not follow FUs but is agreed upon per management area.

Fighting behaviour and the role of urinary signals in dominance assessment of Norway lobsters, Nephrops norvegicus

Norway lobsters, Nephrops norvegicus, live on the bottom of the continental shelf where they construct and defend burrows. Little is known about their agonistic behaviour and potential mechanisms of dominance. This paper investigates fighting behaviour of size-matched male Norway lobsters with a particular emphasis on the role of urinary chemical signals in the assessment of dominance. Norway lobsters were paired in dyadic encounters on two consecutive days. A decrease in fight duration from first to second encounters indicates that N. norvegicus are able to maintain dominance in sequential contests. The main difference between the two encounters is in the behaviour of the loser. Losers strongly reduce their aggression level from first to second encounters. Olfactory sampling behaviour (antennule flicking) of eventual losers is higher than that of the winner indicating that the loser assesses chemical signals of the dominant male. When urine release is blocked for the second encounter, there is no difference in fight duration between first and second encounter. The results suggest that Norway lobsters develop lasting dominance relationships. The study also provides preliminary evidence that urine-borne chemical signals play an important role in mediating dominance.

The relationship between diver experience levels and perceptions of attractiveness of artificial reefs - examination of a potential management tool.

Artificial reefs are increasingly used worldwide as a method for managing recreational diving since they have the potential to satisfy both conservation goals and economic interests. In order to help maximize their utility, further information is needed to drive the design of stimulating resources for scuba divers. We used a questionnaire survey to explore divers’ perceptions of artificial reefs in Barbados. In addition, we examined reef resource substitution behaviour among scuba divers. Divers expressed a clear preference for large shipwrecks or sunken vessels that provided a themed diving experience. Motives for diving on artificial reefs were varied, but were dominated by the chance of viewing concentrated marine life, increased photographic opportunities, and the guarantee of a ‘good dive’. Satisfaction with artificial reef diving was high amongst novices and declined with increasing experience. Experienced divers had an overwhelming preference for natural reefs. As a management strategy, our results emphasize the capacity of well designed artificial reefs to contribute towards the management of coral reef diving sites and highlight a number of important areas for future research. Suggested work should validate the present findings in different marine tourism settings and ascertain support of artificial reefs in relationship to level of diver specialization.

The global invader Palaemon macrodactylus (Decapoda, Palaemonidae): an interrogation of records and a synthesis of data

In the latter half of the 20th Century and the early part of the 21st the Asian shrimp species Palaemon macrodactylus began being reported from several world-wide locations. Literature records of Palaemon macrodactylus are herein collated, corroborated through examination of material where possible. Material from each main occupied region has been verified as P. macrodactylus, but records from Taiwan and Darwin do not refer to P. macrodactylus. Some records still require verification in the absence of material examined. The data show that, in most cases, the first occurrence of P. macrodactylus in a region is several years prior to the detection of the species. Biological, ecological and physiological aspects of the species are summarised to gain an understanding of why the species is such a successful invader. However, the factors favouring the introduction of P. macrodactylus over other species of Palaemon remain unclear as many traits are shared with other species of the genus. Information on larval tolerances may provide further clues for the success of P. macrodactylus. We hypothesise that the global distribution of the species has been achieved through a combination of at least three primary introductions from Asia and three secondary introductions, but the origin of the Argentinean population remains unclear. Small-scale secondary introductions have likely aided spread within a region. Regions at risk of invasion by P. macrodactylus include the Baltic Sea, southern Norway and South Africa, whilst further spread within occupied, broad regions should be expected.

Experience matters: females use smell to select experienced males for paternal care.

Mate choice and mating preferences often rely on the information content of signals exchanged between potential partners. In species where a females reproduction is the terminal event in life it is to be expected that females choose high quality males and assess males using some honest indicator of male quality. The Nereidid polychaete, Neanthes acuminata, exhibits monogamous pairing and the release of eggs by females terminates her life and larval success relies entirely on a males ability to provide paternal care. As such females should have developed reliable, condition-dependent criteria to choose mates to guarantee survival and care for offspring. We show that females actively chose males experienced in fatherhood over others. In the absence of experienced males dominance, as evident from male-male fights, is utilized for mate selection. The preference for experienced males is not affected by previous social interactions between the individuals. We show that the choice of the partner is based on chemical signals demonstrating a ‘scent of experience’ to females providing evidence for the role of chemical signals in sexual selection for paternal care adding to our understanding of the mechanisms regulating condition-dependent mate choice.

Linking Eye Design with Host Symbiont Relationships in Pontoniine Shrimps (Crustacea, Decapoda, Palaemonidae)

Symbiosis is prevalent in the marine environment with many studies examining the effects of such interactions between host and symbiont. Pontoniine shrimps are a group whose ecology is characterised by symbiotic interactions. This investigation examines the gross morphology of Pontoniinae compound eyes and superficial optical parameters with reference to their symbiotic relationship or lifestyle category; free-living, ectosymbiont, endosymbiont (bivalves) or endosymbiont (non-bivalves). The eye morphologies of free-living and ectosymbiotic species are very similar, yet differ from both forms of endosymbiotic species. Endosymbionts have significantly smaller and simpler eyes with larger facets and bigger interommatidial angles and eye parameters for increased sensitivity levels. However bivalve endosymbionts form an intermediary group between non-bivalve endosymbionts and ectosymbionts as a result of their more active lifestyle. The accessory eye or “nebenauge”, although of uncertain function, commonly occurs in free-living Pontoniinae species but rarely in endosymbionts apart from in more primitive species. The variation in morphology reflects tensions between functional requirements and ecological pressures that have strongly influenced eye design in Pontoniinae.