First GB records of the invasive Asian shore crab, Hemigrapsus sanguineus from Glamorgan, Wales and Kent, England.

The present contribution reports on the capture of two adult male specimens of the Asian/Japanese shore crab, Hemigrapsus sanguineus (de Haan, 1835) from Glamorgan, south Wales and Kent, southern England. These represent the first records of this species from mainland Great Britain.

Feeding rates and prey selectivity of planktonic decapod larvae in the Western English Channel

Meroplankton are seasonally important contributors to the zooplankton, particularly at inshore sites, yet their feeding ecology is poorly known relative to holoplankton. While several studies have measured feeding in decapod larvae, few studies have examined the feeding rates of decapod larvae on natural prey assemblages throughout the reproductive season. We conducted 8 feeding experiments with Necora puber, Liocarcinus spp. and Upogebia spp. zoea larvae collected from the L4 monitoring site off Plymouth (50°15.00′N, 4°13.02′W) during spring–summer 2009 and 2010. This period spanned moderate-to-high food availability (0.5–1.6 µg chl-a L−1), but a great range in food composition with small cells <20 µm dominating in 2010. Daily rations averaged 17, 60 and 22 % of body C for the 3 respective decapod species. Clearance rates differed according to prey type, and all 3 decapod genera showed evidence of selection of dinoflagellates. Importantly, small cells including nano- and pico-plankton were ingested, this being demonstrated independently by flow cytometric analysis of the feeding experiments and molecular analysis. PCR-based analysis of the haptophyte portion of the diet revealed ingestion of Isochrysis galbana by decapod larvae in the bottle incubations and Isochrysis galbana and Phaeocystis globosa by decapod larvae collected directly from the field. This study has shown that pico- and nano-sized plankton form an important supplement to the diverse and variable diet of decapod larvae.

Feeding selectivity of bivalve larvae on natural plankton assemblages in the Western English Channel

Meroplankton, including bivalve larvae, are an important and yet understudied component of coastal marine food webs. Understanding the baseline of meroplankton ecology is imperative to establish and predict their sensitivity to local and global marine stressors. Over an annual cycle (October 2009–September 2010), bivalve larvae were collected from the Western Channel Observatory time series station L4 (50°15.00′N, 4°13.02′W). The morphologically similar larvae were identified by analysis of the 18S nuclear small subunit ribosomal RNA gene, and a series of incubation experiments were conducted to determine larval ingestion rates on natural plankton assemblages. Complementary gut content analysis was performed using a PCR-based method for detecting prey DNA both from field-collected larvae and those from the feeding experiments. Molecular identification of bivalve larvae showed the community composition to change over the course of the sampling period with domination by Phaxas in winter and higher diversity in autumn. The larvae selected for nanoeukaryotes (2–20 µm) including coccolithophores (<20 µm) which together comprised >75 % of the bivalve larvae diet. Additionally, a small percentage of carbon ingested originated from heterotrophic ciliates (<30 µm). The molecular analysis of bivalve larvae gut content provided increased resolution of identification of prey consumed and demonstrated that the composition of prey consumed established through bottle incubations conferred with that established from in situ larvae. Despite changes in bivalve larvae community structure, clearance rates of each prey type did not change significantly over the course of the experiment, suggesting different bivalve larvae species may consume similar prey.

Horizontal and vertical distribution of cirripede cyprid larvae in an upwelling system off the Portuguese coast

The distribution of cirripede cyprids in relation to associated oceanographic conditions was obtained from a grid survey and intensive vertical sampling at a fixed station located 21 km off the northwest Portuguese coast in May 2002. Analysis of cyprid length composition allowed separation of 3 species groups. Chthamalus montagui, Pollicipes pollicipes and Balanus perforatus were largely restricted to the neuston layer and showed only low-amplitude vertical migration. Most C. stellatus cyprids only appeared in the upper 20 m at night, a migration which did not appear to be affected by physical conditions in the water column, but some differences in the vertical migration pattern between days were probably related to varying light penetration. C. montagui is the most abundant adult species found along the Portuguese coast, but C. stellatus cyprids, at densities of up to 8.7 ind. m–3, were the most common sampled in all depth strata at the fixed station. Cyprid horizontal distribution was mainly restricted to an offshore band along the inner shelf, where highest densities were 11 to 15 ind. m–3. This distribution pattern was considered to result from upwelling-favourable wind conditions, creating fronts along the shelf in which the cyprids become concentrated. Cyprid vertical migration, in association with current vertical shear and onshore movement of fronts during upwelling-relaxation periods, may be the mechanisms returning cyprids to the coast to settle. The regularity of these events in the region falls within the period of cyprid viability.

Commercial oyster stocks as a potential source of larvae in the regeneration of Ostrea edulis in Strangford Lough, Northern Ireland.

Ostrea edulis was extremely rare in the wild in Strangford Lough from the early 1900s until renewed spatfall was observed at a number of sites in the 1990s. A monitoring programme was undertaken to investigate the presence and distribution of planktonic oyster larvae at nine sites around the lough between June and September in 1997 and 1998 as a precursor to studies of spatfall patterns. Larval densities at sites in the northern basin of the lough were significantly higher than those in the southern basin where larvae were lacking or in low numbers. Densities and sizes of oyster larvae showed significant temporal variation suggesting pulsed larval release. Larval densities also showed significant spatial variation with higher densities at sites closer to commercial stocks pointing to these as the main source of oyster larvae. This hypothesis was supported during a larval flux study over a complete tidal cycle which indicated a 90% net tidal movement of O. edulis larvae from the entrance of the bay where commercial stocks were held to the main body of the lough. Thus the maintenance of dense commercial stocks of flat oysters may provide the key to the redevelopment of native oyster beds in Strangford Lough and elsewhere by providing an initial broodstock nucleus from which larvae can be exported.

Physiological stress responses in the edible crab, Cancer pagurus, to the fishery practice of de-clawing

We examined physiological stress responses in the edible crab, Cancer pagurus, subjected to the commercial fishery practice of manual de-clawing. We measured haemolymph glucose and lactate, plus muscular glycogen and glycogen mobilisation, in three experiments where the crabs had one claw removed. In the first, crabs showed physiological stress responses when 'de-clawed' as compared to 'handled only over the short term of 1-10 min. In the second, de-clawing and the presence of a conspecific both increased the physiological stress responses over the longer term of 24 h. In the third, de-clawing was shown to be more stressful than 'induced autotomy' of claws. Further, the former practice caused larger wounds to the body and significantly higher mortality than the latter. Since the fishery practice is to remove both claws, the stress response observed and mortality data reported are conservative.

Fighting for shells: how private information about resource value changes hermit crab pre-fight displays and escalated fight behaviour

Pre-fight displays typically provide honest, but sometimes dishonest, information about resource holding potential and may be influenced by assessment of resource value and hence motivation to acquire the resource. These assessments of potential costs and benefits are also predicted to influence escalated fight behaviour. This is examined in shell exchange contests of hermit crabs in which we establish an information asymmetry about a particularly poor quality shell. The poor shell was created by gluing sand to the interior whereas control shells lacked sand and the low value of the poor shell could not be accurately assessed by the opponent. Crabs in the poor shell showed changes in the use of pre-fight displays, apparently to increase the chances of swapping shells. When the fights escalated, crabs in poor shells fought harder if they took the role of attacker but gave up quickly if in the defender role. These tactics appear to be adaptive but do not result in a major shift in the roles taken or outcome. We thus link resource assessment with pre-fight displays, the roles taken, tactics used during escalation and the outcome of these contests.

Monoamines and decision making during contests in the hermit crab Pagurus bernhardus

During fights animals are expected to make a series of strategic decisions that involve interactions between information about the contest and the individual's nervous system that produce a change in behaviour. Biogenic monoamines such as serotonin ('5-HT') and dopamine are thought to prime decision-making centres for appropriate responses during aggressive interactions in crustaceans, and circulating levels vary both between individuals and during agonistic encounters. Aminergenic systems operate in diverse animal taxa and in this study we assayed circulating levels of S-HT and dopamine following shell fights in the common European hermit crab, Pagurus bernhardus. The two roles in these fights, attacker and defender, perform different activities but, in both, S-HT increased and dopamine declined in response to engaging in a fight. In defenders but not attackers, giving up was correlated with low 5-HT and dopamine. In attackers, motivation to initiate a fight was positively correlated with dopamine levels. Circulating monoamines are therefore involved in decision making during these aggressive encounters. (c) 2007 The Association for the Study of Animal Behaviour Published by Elsevier Ltd. All rights reserved.

Honest and dishonest displays, motivational state and subsequent decisions in hermit crab shell fights

Animal fights are typically preceded by displays and there is debate whether these are always honest. We investigated the prefight period in hermit crabs, Pagurus bernhardus, during which up to four types of display plus other activities that might provide information are performed. We determined how each display influences or predicts various fight decisions, and related these displays to the motivational state of the attacker, as determined by a startle response, and of the motivational state of the defender, as determined by the duration for which it resisted eviction from its shell. Two displays appeared to have consistent but different effects. Cheliped presentation, where the claws were held in a stationary position, often by both crabs but for longer by the larger, seemed to be honest, and allowed for mutual size assessment. This display enhanced the motivation and the success of the larger crab. In contrast, cheliped extension, involving the rapid thrust of the open chelae towards the opponent, did not seem to allow for mutual size assessment and may contain an element of bluff. It was performed more by the smaller crab and enhanced its success. The complexity of displays in this species appears to allow for both honesty and manipulation.

Motivational change during shell fights in the hermit crab Pagurus bernhardus

During agonistic interactions the motivation of each contestant is expected to vary because of increased information and changes in fighting ability. In shell fights between hermit crabs over gastropod shells, attackers rap their shell in a series of bouts against that of the defender whereas defenders remain withdrawn into their shells until the encounter is resolved; either the defender is evicted from its shell or the attacker 'gives up' and the defender retains its shell. We assessed the motivational state of attackers for performing rapping by measuring the duration of startle responses elicited by a novel stimulus. We staged fights between pairs of crabs in six different groups defined by the potential gain in shell quality available to attackers (high or low) and by the point at which the novel stimulus was applied (prior to rapping, after one bout or after four bouts). Startle response duration decreased during the first four bouts of fighting and showed a U-shaped relationship with the relative difference in size between the crabs. There was, no difference in startle response duration between high- and low-gain groups. Individuals showing short startle responses were likely to be victorious and we conclude that the relationship between the relative size difference of the opponents and. startle duration reflects that between size difference and the cost of gaining an eviction. (C) 2001 The Association for the Study of Animal Behaviour.

Decision rules, energy metabolism and vigour of hermit-crab fights

Aggressive interactions between animals are often settled by the use of repeated signals that reduce the risk of injury from combat but are expected to be costly. The accumulation of lactic acid and the depletion of energy stores may constrain activity rates during and after fights and thus represent significant costs of signalling. We tested this by analysing the concentrations of lactate and glucose in the haemolymph of hermit crabs following agonistic interactions over the ownership of the gastropod shells that they inhabit. Attackers and defenders play distinct roles of sender and receiver that are fixed for the course of the encounter. Attackers perform bouts of 'shell rapping', which vary in vigour between attackers and during the course of the encounter, and are a key predictor of victory. In contrast to the agonistic behaviour of other species, we can quantify the vigour of fighting. We demonstrate, to our knowledge for the first time, an association between the vigour of aggressive activity and a proximate cost of signalling. We show that the lactate concentration in attackers increases with the amount of shell rapping, and that this appears to constrain the vigour of subsequent rapping. Furthermore, attackers, but not defenders, give up when the concentration of lactate is high. Glucose levels in attackers also increase with the amount of rapping they perform, but do not appear to influence their decision to give up. Defenders are more likely to lose when they have particularly low levels of glucose. We conclude that the two roles use different decision rules during these encounters.

Pharmacological characterisation of neuropeptide F (NPF)-induced effects on the motility of Mesocestoides corti (syn. Mesocestoides vogae) larvae

Neuropeptide F is the most abundant neuropeptide in parasitic flatworms and is analogous to vertebrate neuropeptide Y. This paper examines the effects of neuropeptide F on tetrathyridia of the cestode Mesocestoides vogae and provides preliminary data on the signalling mechanisms employed. Neuropeptide F ( greater than or equal to 10 muM) had profound excitatory effects on larval motility in vitro. The effects were insensitive to high concentrations (I mM) of the anaesthetic procame hydrochloride suggesting extraneuronal sites of action. Neuropeptide F activity was not significantly blocked by a FMRFamide-related peptide analog (GNFFRdFamide) that was found to inhibit GNFFRFamide-induced excitation indicating the occurrence of distinct neuropeptide F and FMRFamide-related peptide receptors. Larval treatment with guanosine 5'-O-(2-thiodiphosphate) trilithium salt prior to the addition of neuropeptide F completely abolished the excitatory effects indicating the involvement of G-proteins and a G-protein coupled receptor in neuropeptide F activity. Addition of guanosine 5'-O-(2-thiodiphosphate) following neuropeptide F had limited inhibitory effects consistent with the activation of a signalling cascade by the neuropeptide. With respect to Ca2+ involvement in neuropeptide F-induced excitation of M. vogae larvae, the L-type Ca2+-channel blockers verapamil and nifedipine both abolished neuropeptide F activity as did high Mg+ concentrations and drugs which blocked sarcoplasmic reticulum Ca2+-activated Ca2+-channels (ryanodine) and sarcoplasmic reticulum Ca2+ pumps (cyclopiazonic acid). Therefore, both extracellular and intracellular Ca2+ is important for neuropeptide F excitation in M. vogae. With resepct to second messengers, the protein kinase C inhibitor chelerythrine chloride and the adenylate cyclase inhibitor MDL-2330A both abolished neuropeptide F-induced excitation. The involvement of a signalling pathway that involves protein kinase C was further supported by the fact that phorbol-12-myristate-13-acetate,known to directly activate protein kinase C, had direct excitatory effects on larval motility. Although neuropeptide F is structurally analogous to neuropeptide Y, its mode-of-action in flatworms appears quite distinct from the common signalling mechanism seen in vertebrates. (C) 2003 on behalf of Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.

Claw removal and feeding ability in the edible crab, Cancer pagurus: Implications for fishery practice

Feeding ability and motivation were assessed in the edible crab, Cancer pagurus, to investigate how the fishery practice of de-clawing may affect live crabs returned to the sea. Crabs were either induced to autotomise one claw, or were only handled, before they were offered food. Initially, autotomised and handled crabs were offered mussels, Mytilis edulis, a large part of their natural diet. After 3 days, both autotomised and handled crabs were then offered fish, a more readily handled food source. Autotomy induced crabs consumed significantly fewer mussels and less mussel mass, but ate significantly more mass of fish. This indicates that the effect of autotomy was a reduction of ability to feed on mussels rather than a general reduction of feeding motivation. The discontinuation of claw removal needs to be considered, both for the sustainability of the fishery and animal welfare concerns. (C) 2008 Elsevier B.V. All rights reserved.