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Observations on the biology of a rare British marine amphipod: Monoculodes gibbosus (Crustacea: Amphipoda: Oedicerotidae)
Abstract
To date, the oedicerotid amphipod Monoculodes gibbosus Chevreux, 1888 is known in British seas from only two individuals collected from Loch Fyne and lodged in the Robertson Collection at Millport (Moore, 1984). Recent intensive research on other species in this family in the Clyde Sea area by one of us (D.J.B.) has resulted in the sporadic capture of further individuals of M. gibbosus (128 individuals in total) from Inchmarnock Water, southern Loch Fyne. This material allows us to expand our knowledge of the species' morphology, live colour, population structure, fecundity, egg size, breeding season, diet and behaviour. Notes on these topics are presented below.(Received May 12 1993)(Accepted August 26 1993)
... As concerns Synchelidium species, S. maculatum Stebbing, 1906 seems to be mainly carnivore, feeding on little crustaceans, apart from detritus (Greze, 1968a), as recently observed for some congeneric species (Yu et al., 2003). The heterogeneity in mandibular forms within the family (Watling, 1993) might be at the base of dietary differences between genera, such as active predators on harpacticoids or feeding diatoms from sand grains (Beare & Moore, 1994). ...
Amphipod crustaceans are able to colonise different micro-habitats of coastal marine benthos due to a multiplicity of trophic and morpho-functional adaptations, and may be considered a key taxon in describing the structure of assemblages. Literature concerning amphipod feeding behaviour and way of life showed that studies on functional groups (FGs) started only in the 1980s. A short review about the state of the art of the knowledge is presented here. Aiming at investigating the functional role of amphipods and to ascertain to what extent their adaptations could be a response to different biotic and abiotic conditions, some examples of studies conducted in the Mediterranean Sea on various plant substrata (Posidonia oceanica, Cymodocea nodosa, Zostera marina, Caulerpa racemosa var. cylindracea), at different spatial and temporal scales, were given. Despite many doubts about some species, due to the lack of information and their opportunistic behaviour, the identified taxa were grouped in the main categories of suspension feeders, deposit feeders, carnivores, commensals, herbivores, plant detritus feeders, omnivores, and in the mixed categories of deposit-suspension feeders, deposit feeders-carnivores, herbivores-deposit feeders, according to the food ingested and their feeding strategies; and, according to their life-habits, in epifaunal free-living and domicolous, and infaunal free-burrowing and tube-building. FGs might be considered good descriptors of zonation patterns, mainly against gradients such as depth, where strong environmental factors play a role. FG composition was differentiated according to the structural complexity and the stability of the host plant. Changes observed on a long-term scale, due to regression phenomena in P. oceanica meadows or to the spread of the invasive species C. racemosa var. cylindracea, were well described by FGs. In the first case the trophic diversity was maintained and in the latter the lack of herbivorous forms pointed out the poor role as structuring plant of the seaweed. Although caution is suggested in studies on FGs, they can give further insight in comprehending structural and functional processes in amphipod ecology.
... On the other hand, the molars of Monoculodes sp. are weakly developed (Moore 1984). Beare & Moore (1994) examined the gut contents of M. gibbosus Chevreux collected from the bottom at 35 m depth off Loch Fyne in Scotland and determined that the species was a specialist predator on harpacticoid copepods. The high d 15 N value for Monoculodes sp. ...
We measured stable carbon and nitrogen isotope ratios (13C/12C and 15N/14N) of organic matter sources and consumers, including fishery resources, along the Okhotsk coast of northern Hokkaido, Japan, in early spring to characterize the food web. Phytoplankton and benthic detritus, including ice algae, fecal pellets, and benthic microalgae, constituted the main food sources for primary consumers (zooplankton and small benthic invertebrates, respectively); seagrass and terrestrial plant debris served no trophic function for consumers. Planktivorous and benthivorous fish species could be differentiated using stable carbon isotope ratios. Differences in stable nitrogen isotope ratios revealed species-specific feeding habits of crustacean groups: copepods were separated into three groups as herbivorous, omnivorous, or omnivorous-carnivorous, and benthic amphipods were divided into two groups as either omnivorous or omnivorous-carnivorous. We distinguished four levels of both pelagic and benthic trophic linkages. The δ13C values were enriched by 0.9–1.3‰ at the linkage between each pelagic trophic level except between the 1st and 2nd levels; δ15N values were enriched by 2.2–2.9‰ at each level. For benthic trophic linkages, the enrichment for δ13C and δ15N values between each level ranged from 0.6‰ to 1.0‰ and from 1.6‰ to 2.6‰, respectively. Trophic positions of copepod, mysids, and sand lance appeared between pelagic and benthic linkages. This suggests that those species have fed on both pelagic and benthic diets.
... 0,48rhythm (Sheader 1978, Fish & Mills 1979, Moore 1981. So probably the Ampithoe valida population 2 used by Borowsky (1983) Like other amphipod species, Ampithoe valida is a semi-annual with short-lived spring and summer generations (7 to 8 mo) and long-lived autumn and winter generations (9 mo) (Moore 1981, Powell & Moore 1991, Beare & Moore 1994, Sudo & Azeta 1996. Ampithoe valida appeared as an r strategist, with iteroparous females (except summer generation), a multivoltine cycle, high individual fecundity and recruitment throughout the year. ...
The life cycle, population dynamics and production of Ampithoe valida was studied from an intertidal mudflat in central Portugal, close to the northern limit of the species' distributional range in the eastern Atlantic Ocean. Sampling was carried out in eutrophicated areas, where macroalgae blooms of Enteromorpha spp. occur usually from January to early summer, and also in non-eutrophicated areas, with Zostera noltii meadows. A. valida showed a contagious distribution and the population density clearly changed during the study period along the eutrophication gradient. No migratory patterns were detected between the estuary and the sea, but migrations inside the estuary might have occurred. Females were morphologically recognisable at smaller sizes than males. Females reached sexual maturity before males, but males may live slightly longer than females. Females are iteroparous, producing 2, perhaps 3, broods. A 2-generation life cycle involving a short-lived (7 mo), fast-growing summer generation and a longer-lived (9 mo), slower-growing generation that overwinters is hypothesised. Ovigerous females were present year-round. Eggs, depending on the season, increase differently in volume during marsupial development. No correlations were found between fecundity (number of eggs) and the size of females. Along the eutrophication gradient no differences were found regarding the biology of the species. Besides these features, differences were observed between eutrophicated and non-eutrophicated areas with regard to productivity. Growth production (P) of A. valida in the most eutrophicated area was 0.098 g m(-2) 18 mo(-1) and 0.64 g m(-2) 18 mo(-1) in the Z. noltii meadows. P/(B) over bar and E/(B) over bar ratios (where E is the elimination production and (B) over bar is the average population biomass) ranged from 1.42 and 3.06 in the most eutrophicated area to 5.98 and 12.41 in the Z. noltii beds. To a certain extent, the increase of macroalgae biomass may favour A. valida populations, but extensive blooms affecting the whole area of distribution of this species will determine its disappearance.
Results are presented of a comparative study on seasonal variations in population density, population structure and reproductive bionomics of two species of offshore benthic oedicerotid amphipod, Westwoodilla caecula (from 35 m depth) and Monoculodes packardi (from 190 m) in Loch Fyne (Scotland). Observations on live coloration and behaviour of these species in laboratory aquaria are also included. Male W. caecula were, on average, smaller than females. In M. packardi (atypically among Oedicerotidae) the reverse was true. Population densities of both species, calculated from sledge net tows (1-mm mesh), fluctuated erratically over one year (1992). Ovigerous W. caecula were recorded virtually year-round, but were commonest from midsummer to early autumn. Ovigerous M. packardi were noted in spring and early autumn. Monoculodes packardi had a semi-annual life cycle, but the pattern for W. caecula was less clear. The two generations of M. packardi grew at broadly similar rates, presumably associated with the damped seasonal fluctuations in physical environmental factors at 190 m. Female W. caecula possibly moult eight or nine times, and may produce three successive broods in a lifetime (M. packardi may only produce two). A positive correlation was found between fecundity (stage I eggs) and body length in W. caecula but, although a similar trend was apparent in the data for M. packardi, relevant data were too few for significance to be achieved. Ovoid eggs increased in volume by x2 from stage I-W in W. caecula, or x 1.5 from stage I-III in M. packardi. Brood sizes were much smaller in W. caecula than in M. packardi, although apparent brood mortality was higher in the latter. There was no significant relationship between the proportion of ovigerous females in the populations of either species and seasonal variation in physical environmental factors considered (temperature, salinity, daylength).
Orchomene nanus (Krøyer) was captured in funnel traps baited with crushed crabs [Carcinus maenas (L.)]. Monthly field samples were collected for population analysis over one year. Male Orchomene nanus can be distinguished most effectively from females and juveniles on the basis of the number of articles in antenna 2 flagellum. This flagellum becomes more elongate at each moult after sexual differentiation. The acquisition of calceoli reflects sexual maturation in males, as does a setose brood pouch in females. Analysis of the amalgamated size-frequency data for all seasons, allowed recognition of putative moult stages and calculation of moult-to-moult growth factors throughout the life of an individual (estimated to be 13 instars). Sexual differentiation occurred at instar 5 and maturity at instar 8. Males may live slightly longer than females. Females are iteroparous, producing three, perhaps four, broods. A two-generation life cycle involving a short-lived (7mo), fast growing summer generation and a longer-lived (12 months), slower growing generation that overwinters is hypothesized. Ovigerous females were present virtually year-round (none was recorded in October or January), resulting in domination of the population by juveniles for most of the year. Fecundity was related to female body size. Maximum clutch size was 26; with a lifetime potential fecundity calculated to be 27–52 eggs. Eggs doubled in volume during marsupial development. That hatchlings were under-represented in the collections could be due to sampler deficiencies (mesh size), or to behavioural differences, cf. adults. In most samples, the sex ratio was not significantly different from 1:1. However, a tendency toward female dominance was apparent overall (with the proviso that inaccuracies associated with recognition of the smallest males may have contributed to this finding).
Reproduction in peracarid crustaceans is characterized by direct development with the young carried by the female in a ventral brood pouch made from overlapping oostegites. The major exception occurs in thermosbaenaceans where the young develop under a posterior extension of the carapace. Sexual reproduction is the norm, as is standard genetic development of males and females, but intersexes, males with unusual chromosome numbers and hermaphrodites occur in some species.General anatomy of the female reproductive tract is similar for all orders, differing only in the specific details. Asellote isopods develop a unique spermathecal duct for sperm storage. The male reproductive system is much more variable. In some orders it consists of paired tubes, and in others it is unpaired; sperm may be stored in the posterior region of the testes or in vas deferens; and the external genitalia may be located on the coxae or the sternites, with or without penes or other sperm transfer appendages.Sperm morphology has been considered a unifying trait for the Peracarida but, in fact, there are some significant differences among the orders. Peracaridan sperm are aflagellate. Most consist of a head piece and a rigid, non-motile, fibrillar tail of varying design by which the sperm are bundled in spermatophores. Tanaid sperm are round and tailless, and spermatophores are absent. Oögenesis follows a common pattern in those peracarids that have been studied. A period of previtellogenic growth is followed by slow primary vitellogenesis with endogenous yolk synthesis Prior to molting and fertilization, rapid secondary vitellogenesis, utilizing exogenous yolk synthesis, occurs.Life cycles in the more diverse peracaridan orders can be compared. Temperate species often have long overwintering generations interspersed with several shorter summer generations. Polar and deep-sea pericaridans have much longer generations whereas tropical species may produce broods year-round in rapid succession. Mating usually occurs when the mature oöstegites appear, with copulation occurring shortly after the female molts. Precopulatory pairing and mate guarding by males using specially modified appendages is common, but some males cruise from one female to another. Sperm is generally deposited into the marsupium where fertilization occurs, but some isopods store sperm for later use.Development follows the general crustacean pattern of superficial cleavage, with the details of organ and appendage formation varying from order to order. Some special brood pouch structures exist, primarily in isopods, and in some tube-dwelling tanaids the young develop in the female's tube rather than in the marsupium. Peracarids generally hatch in the brood pouch as fully developed juveniles or as mancas (without the last pair of thoracic legs).With a few exceptions, brood size is a function of female marsupial volume. The trade-off between egg size and egg number varies with both habitat and, in some cases, with season. Since egg size affects incubation time, these complex interrelationships and the adaptive value of specific reproductive strategies are still unresolved.
The composition and structure of the Amphipoda community from the continental shelf adjacent to Baixada Santista coast was studied in relation to the environmental factors. Twenty-one stations were sampled in August and September 2005 (Winter) and February 2006 (Summer), on board of R/V Prof. W. Besnard as part of the interdisciplinary project ECOSAN. The samples were obtained with a 0.09 m2 box corer in duplicate. Species composition and the community variables (density, biomass, diversity and eveness) were determinated. The environmental parameters obtained were depth, temperature, salinity, granulometry, organic matter and carbonate content of the sediment. Cluster, n-MDS, Similarity and BIO-Env analyses were performed to interpret the results. Fourty one species and nineteen morfospecies were found and classified in twenty four families for both campaigns. Summer presented the highest abundance and few species were dominant. Ampelisca paria, Metharpinia sp.n., Microphoxus moaresi, Urothoe sp.n., Gitanopsis sp. and Photis brevipes were dominant in all sampled periods. Diversity and density were low in the stations near to the mouth of Baía de Santos and southwards, in front of Peruíbe. Both ordination and similarity analyses showed the shelf divided in four distinct areas in winter and four in summer, based in the species composition and influenced by depth. It was found a typical community in the coastal zone, other in the outer shelf and another sharing species with both zones. The vertical faunal distribution pointed a decrease in density and diversity with the increase in depth of the sedimentary column. Same stations of the intermediary and deep group showed a less abrupt decrease in density and richness in relation to the shallow stations. In general, each stratum were characterized by a different species. A composição e estrutura da comunidade de Amphipoda da Plataforma Continental adjacente à Baixada Santista foi estudada em relação aos fatores ambientais. Vinte e uma estações foram amostradas em agosto e setembro de 2005 (inverno) e em fevereiro de 2006 (verão), à bordo do N/ Oc. Prof. W. Besnard como parte do projeto interdisciplinar ECOSAN. As amostras foram obtidas com um box corer de 0,09 m2 em duplicata. A composição de espécies e as variáveis da comunidade (densidade, biomassa, diversidade e eqüitatividade) foram determinadas. Os parâmetros ambientais obtidos foram profundidade, temperatura, salinidade, diâmetro dos grãos, matéria orgânica e carbonato contidos no sedimento. Análises de Cluster, n-MDS, similaridade e BIO-Env foram realizadas para interpretar os resultados. Quarenta e uma espécies e dezenove morfoespécies foram encontradas e classificadas em vinte e quatro famílias nas duas campanhas. O verão apresentou os maiores valores de densidade e uma dominância marcante de poucas espécies. Ampelisca paria, Metharpinia sp.n., Microphoxus moaresi, Urothoe sp.n., Gitanopsis sp. e Photis brevipes foram predominantes nos dois períodos amostrados. A diversidade e densidade foram baixas nas estações próximas à desembocadura da Baía de Santos e ao sul, em frente à Peruíbe. Tanto as análises de ordenação quanto as de similaridade mostraram que, em função da fauna de Amphipoda presente, a plataforma esteve dividida em quatro áreas no inverno e quatro no verão, onde a profundidade mostrou ser um fator preponderante nessa repartição. Foi encontrada uma comunidade típica de zona costeira, outra de plataforma externa e uma terceira contendo espécies de ambas. A distribuição vertical da fauna no sedimento mostrou que houve uma diminuição na densidade e diversidade do estrato de superfície em direção ao estrato inferior. Em algumas estações das zonas intermediárias e profunda houve um decréscimo menos abrupto da densidade e da riqueza de espécies em direção aos estratos mais profundos, ocorrendo a dominância de diferentes espécies nos diferentes estratos
While several features of the amphipod body are used both to classify and estimate phylogenetic relationships of species, little is understood of the functional significance of most of these features. The amphipod mandible consists of a compact coxa bearing a toothed incisor orientated to cut in the transverse plane of the body, a row of lifting spines leading dorsally to a molar designed for crushing. The basic pattern is retained in those groups where microphagy is important. Modifications include reduction of the incisor, loss of the lifting spines, reduction or loss of the molar, or all of these. In several families the mandible is maintained unmodified; in others most genera possess mandibles of the basic pattern but one or two modifications can be seen in a small number of genera. In a few families the basic form is retained in only one or two genera, while several different modifications are seen in the majority of the others. Finally, several families have lost all vestige of the basic mandible pattern. In this latter group, however, the number of modifications is low. Most mandible modifications occur in response to predation and/or scavenging as a feeding strategy, although two independent pathways to this end are seen. In the first the reductions occur on a compact coxa, and seem designed for feeding on small prey, while in the second the mandible body (coxa) becomes elongate and the orientation of the incisor changes such that cutting is now in the vertical frontal plane of the animal's body. It is concluded that families with exclusively predatory/scavenging mandibles cannot be considered to be plesiomorphous.
The life cycles of Lembos websleri Bate and Corophium bonnellii Milne Edwards are based on two generations per year. Eight cohorts have been identified in Lembos and nine for Corophium, each of which has a different longevity. In Lembos the summer generation proper lives ≈ 5–7 months whilst cohorts of the overwintering population may live up to 11.5 months. Males do not live as long as females, their longevity being ≈ 11% less in summer and 5% less in winter. C. bonnellii is parthenogenetic. Its summer generation lives ≈ 5 months and its winter generation 8–10 months. Corophium thus has a shorter life span than Lembos. It also grows faster. Growth is severely inhibited overwinter (but less so in Corophium) and picks up in spring. Year to year variations in timing of reproductive events may be related to temperature differences, sea state, and food supply. Population data for 1974 and 1975 were, however, generally very similar. Ovigerous females are present all the year in Lembos websteri but were never found in January in Corophium bonnellii. Egg-laying behaviour is described. Brood size is linearly related to maternal length in both species. A size-independent index of fecundity shows clear seasonal variation, with peak fecundity in summer. Minimum size of egg-bearing females is also a function of temperature in both species. A semi-lunar rhythmicity of brood production at summer temperatures is reported. Brood mortalities of ≈ 25–30% were found in both species which seemed unrelated to maternal size but which may (in Lembos) be seasonally variable (lower in winter). Egg size is similar in both species and egg volume more than doubles during development from Stage I to Stage IV. Corophium bonnellii eggs are bigger and individual female reproductive effort is higher than in other Corophium species. Corophium sometimes carried the ciliate Conidophrys on the basal segments of its antennae. Occasional endoparasites, namely cercariae and encysted metacercariae, were noted. Mortality due to fish predation was established to occur, the clingfish Apletodon microcephalus (Brook) and the sea snail Liparis liparis (L.) being important amphipod consumers.
The life cycles of females of seven species of amphipod were determined from fortnightly sampling of sites in the Clyde Sea area. Three species, Lembos websteri, Corophium bonnellii and Bathyporeia pilosa, exhibited semi-annual life cycles with an overwintering generation producing a shorter-lived summer generation. The deep-water species Stegocephaloides christianiensis exhibited continuous breeding, as did the sublittoral species Gammaropsis nitida. The other deep-water species, Ampelisca macrocephala, exhibited a biennial life cycle. The littoral species Echinogammarus pirloti exhibited a reproductive cycle that was closely correlated with the abundance of its food supply. With the exception of E. pirloti and S. christianiensis, the reproductive cycles of the species studied were closely correlated with photoperiod. Environmental temperature was of secondary importance to seasonal variation in breeding in all species. A female bias in the sex ratio was observed throughout the year in four of the seven species. In E. pirloti there was a significant male bias in the sex ratio. No males were discovered in the populations of C. bonnellii and S. christianiensis. Possible factors contributing to the observed seasonal changes in sex ratio are discussed.
Material from Loch Fyne referable to Monoculodes gibbosus Chevreux (Oedicerotidae) has been discovered in the Reference Collection at Millport originally labelled by David Robertson as M. stimpsoni Bate. This is the first British record of this little known species. A detailed redescription is provided and comparison made with French material (including the holotype). A revised key to the British species is presented. © 1984, Marine Biological Association of the United Kingdom. All rights reserved.