The families and genera of marine gammaridean Amphipoda (except marine gammaroids). Part 1
30 Aug 1991-Records of The Australian Museum, Supplement (The Australian Museum)-Vol. 13, Iss: 1, pp 419-866
TL;DR: A handbook for the identification of gammaridean amphipods to generic level through the use of artificial (non-phylogenetic) keys at the family-group level which lead to subsidiary keys to the genera of families or family groups.
Abstract: Keys, diagnoses and lists of species are presented for the marine families and genera of Gammaridea except those marinegammaroids treated by Barrtard& Barnard (1983). This work is a handbook for the identification of gammaridean amphipods to generic level through the use of artificial (non-phylogenetic) keys at the family-group level which lead to subsidiary keys to the genera of families or family groups. Genera in polytypic families are diagnosed and described sufficiently to fit the taxonomic complications within each group. Diagnoses of families are limited to those characters departing from a·gammaridean model which is diagnosed in words and illustrations; hence some families may have identical diagnoses. Therefore, cross-comparisons to similar families are made an organic part of each diagnosis. Family descriptions amplify the generalities of family characters. Relationships are identified not at phylogenetic level but in terms.of possible confusion in making identifications. The reader must cross-compare relationships among the several families that might be mentioned as part of the diagnoses because, to save space, all possible combinations are not replicated at every possible node. The same comparative method is generally but not exclusively used for the genera of each family. Multiple keys are provided for some of the more difficult families; taxa are often cited more tha, once in a key. A pictorial key to families operates with the same proviso that only the deviations from the model gammaridean are depicted. The pictorial key is arranged in reverse order so that the most anomalous taxa appear first and those closest to the model diagnosis are placed· at the end. This progression follows the idea that the most deviant taxa are the easiest to identify to family. level. The master key to families has the endpoints necessary to identify marine gammaroids by reference to Barnard & Barnard (1983); the two works are constructed .inparallel·fashion~·Families,andgenefawithin~families,areOfganisedalphabetically~ ·An index provides the principal reference for each genus and species. Where necessary, each taxon is supplied with notes on removals or major changes since 1965 which have not become common 2 Records of the Australian Museum (1991) Supplement 13 (Part 1) knowledge, or which are implemented herein. Each genus is supplied with a list of species and selected references. A geographic code, applied to each species, can be identified in the lists and maps of Bamard & Bamard (1983). A bibliography includes many publications not cited in the text but omits the marine gammaroids except for items published since 1980 which were not included in Bamard & Bamard (1983). Effective use of this handbook requires memorisation of a gammaridean model, skill in dissection following directions supplied herein, familiarity with the glossary, and acceptance of the idea that keys and diagnoses are only aids, not absolute endpoints.
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TL;DR: It appears, through the use of algal mimics, that the spatial component (space between fronds) is an important factor in determining amphipod demographic patterns in algae.
Abstract: Field and laboratory experiments were conducted on the effect of habitat architecture (the number, size, shape, and arrangement of habitable spaces and structures) created by benthic algae on the habitat selection of an abundant mobile amphipod, Gam- marellus angulosus, on the central coast of Maine. Amphipod population density and body size were determined in algae of different morphologies that provided amphipods with different habitat architectures. The two primary components of habitat architecture in this system were spatial (the number and size of spaces between fronds) and structural (the number, length, and width of fronds). These were measured for algae of specific mor- phologies and for artificial plants that mimicked these morphologies. Field experiments using algae and algal mimic counterparts showed that there were significantly higher den- sities of amphipods in algae with branched and filamentous morphologies than in those algae with foliose and leathery macrophyte morphologies. There was also a significant correspondence between the body size of amphipods and both components of habitat architecture. Laboratory experiments using algae and algal mimics excluded food value, predation, competition, and physical disruption in experimental treatments. When these processes were excluded, patterns of abundance and body-size scaling to habitat dimensions were the same as those in the field. It appears, through the use of algal mimics, that the spatial component (space between fronds) is an important factor in determining amphipod demographic patterns in algae. Algal mimics of different surface rugosity and color indicate that tenacity and crypsis are also important components in habitat selection of amphipods.
344 citations
TL;DR: Freshwater amphipods are greatly polyphyletic, continental invasions have taken place repeatedly in different time frames and regions of the world, and have had great impacts on European fluvial ecosystems.
Abstract: Amphipods are brooding peracaridan crustaceans whose young undergo direct development, with no independent larval dispersal stage. Most species are epibenthic, benthic, or subterranean. There are some 1,870 amphipod species and subspecies recognized from fresh or inland waters worldwide at the end of 2005. This accounts for 20% of the total known amphipod diversity. The actual diversity may still be several-fold. Amphipods are most abundant in cool and temperate environments; they are particularly diversified in subterranean environments and in running waters (fragmented habitats), and in temperate ancient lakes, but are notably rare in the tropics. Of the described freshwater taxa 70% are Palearctic, 13% Nearctic, 7% Neotropical, 6% Australasian and 3% Afrotropical. Approximately 45% of the taxa are subterranean; subterranean diversity is highest in the karst landscapes of Central and Southern Europe (e.g., Niphargidae), North America (Crangonyctidae), and Australia (Paramelitidae). The majority of Palearctic epigean amphipods are in the superfamily Gammaroidea, whereas talitroid amphipods (Hyalella) account for all Neotropic and much of the Nearctic epigean fauna. Major concentrations of endemic species diversity occur in Southern Europe, Lake Baikal, the Ponto-Caspian basin, Southern Australia (including Tasmania), and the south-eastern USA. Endemic family diversity is similarly centered in the Western Palearctic and Lake Baikal. Freshwater amphipods are greatly polyphyletic, continental invasions have taken place repeatedly in different time frames and regions of the world. In the recent decades, human mediated invasions of Ponto-Caspian amphipods have had great impacts on European fluvial ecosystems.
309 citations
TL;DR: It is confirmed that association with chemically defended plants can reduce predation on generalist, as well as specialist, herbivores and suggested that preferential feeding on chemically defending plants is most likely for sedentary mesograzers because low mobility enhances the ability to exploit chemically defended seaweeds as refuges from fish predation.
Abstract: Numerous small sedentary herbivores (mesograzers such as amphipods, small crabs, and gastropods) are resistant to seaweed secondary metabolites that deter larger, more mobile herbivorous fishes. In addition, specialist mesograzers experience reduced predation from fishes when living on seaweeds that produce these compounds. In this study we tested the hypothesis that generalist, as opposed to specialist, mesograzers can also benefit from reduced predation when they occupy chemically defended plants. Secondly, we assessed the hypothesis that low herbivore mobility, unconfounded by herbivore size or specialized feeding, selects for tolerance of seaweed chemical defenses, by comparing responses to the chemically defended brown seaweed Dictyota menstrualis of three sym- patric, generalist amphipods that differ in mobility (A mpithoe longimana, Ampithoe valida, and Gammarus mucronatus). Responses to Dictyota's chemical defenses varied as much among these three amphipods as among the phylogenetically distant fishes and mesograzers studied previously and sup- ported the hypothesis that less mobile herbivores should be most tolerant of plant chemical defenses. In laboratory experiments, A. longimana moved little, preferentially consumed Dictyota over other seaweeds, and was unaffected by all Dictyota secondary metabolites tested. In contrast, G. mucronatus was active, it did not feed on Dictyota, and two of three Dictyota secondary metabolites deterred its grazing. Distribution of amphipods in the field suggested that these feeding patterns affected amphipod risk of predation. A. longimana reached its highest abundance on Dictyota, which is unpalatable to omnivorous fish pred- ators, during the season when fish are most abundant. At the same time, the highly active G. mucronatus decreased to near extinction. Like G. mucronatus, A. valida was deterred by two Dictyota secondary metabolites, did not eat Dictyota, and disappeared when fishes were abundant. Experiments confirmed that A. longimana was less vulnerable to fish predation when occupying a chemically defended seaweed than when occupying a palatable seaweed. This decreased predation resulted primarily from a decreased frequency of encounter with pred- ators when amphipods were on chemically defended plants. When we experimentally equalized encounter rates between omnivorous pinfish (Lagodon rhomboides) and the seaweeds Dictyota menstrualis and Ulva curvata (unpalatable and palatable, respectively, to pinfish) in the laboratory, amphipods occupying these two plants were eaten at similar rates. In contrast, when live amphipods were affixed to Ulva and Dictyota and deployed in the field, amphipods survived only on Dictyota. Heavy fish grazing on Ulva in the latter experiment suggests that poor survival of amphipods on U/va may have resulted from greater detection and/or incidental ingestion of amphipods on this plant, due to frequent visitation by fishes. Infrequent visitation of Dictyota by foraging fish also may explain A. /ongimana's persistence through the summer on this chemically defended seaweed while the two Ulva-associated amphipods declined precipitously. These results (1) confirm that association with chemically defended plants can reduce predation on generalist, as well as specialist, herbivores and (2) suggest that preferential feeding on chemically defended plants is most likely for sedentary mesograzers because low mobility enhances the ability to exploit chemically defended seaweeds as refuges from fish predation.
260 citations
TL;DR: In this article, the break-up of Gondwana during the Tertiary indicates that shallow water marine habitats may have been present continuously, and on occasions were considerably more extensive than at present.
Abstract: Abstract Current knowledge of the break-up of Gondwana during the Tertiary indicates that shallow water marine habitats may have been present continuously, and on occasions were considerably more extensive than at present. Although direct fossil evidence is sparse after the Eocene, geophysical evidence suggests that shallow waters have been present since the late Mesozoic, and possibly much longer. The break-up of Gondwana was accompanied by a more or less steady lowering of both surface and bottom temperatures in the Southern Ocean from about 15°C in the Late Cretaceous to the present range of roughly +2 to −1.8°C. Microfossils in deep-sea drilling cores indicate that temperature drops were particularly sharp in the early Oligocene (c. 38 Ma), mid-Miocene (10–14 Ma) and Pliocene (c. 4 Ma BP). Geological evidence suggests that the Drake Passage opened, and the present oceanographic regime established, about 25–30 Ma BP. This is now known to be about the time of full-scale development of the East Antarctic ice cap. Subsequently ice sheets extended across, and deeply eroded, the continental shelves but the effects of these glacial maxima on the marine biota are not fully understood. Late Cretaceous/early Tertiary marine fossils from the James Ross Island group indicate a diverse shallow water marine fauna, including two groups notably lacking in diversity in the living fauna: decapods and teleost fish. In several genera occurrences in this fauna predate first occurrences in lower latitudes by as much as 40 Ma, suggesting the possibility that a number of groups originated at high southern latitudes. The living fauna exhibits a high biomass in many areas, and within-site diversity can be as high as anywhere in the world. Some individual taxonomic groups, however, (notably bivalves and gastropods) have a lower diversity than in the tropics, supporting the concept of a latitudinal cline in diversity. Studies of physiological adaptation to temperature suggest that the decline in seawater temperature during the Cenozoic has not presented a particularly severe evolutionary problem. The reasons for the absence of large decapods and the low diversity of fish in the present fauna are unclear. Most of the biological features of the modern fauna are more likely a response to the seasonality of the ecosystem rather than low temperature per se. Overall the evidence suggests that the present Southern Ocean shallow water marine fauna largely evolved in situ, having been present since at least the Late Cretaceous, and possibly much longer. Some groups have invaded, for example along the Scotia arc, but the isolation of the Southern Ocean by the present oceanographic regime and the limited dispersal ability of many forms means that exchange with lower latitudes is very slow.
248 citations
TL;DR: The results show that seaweed-associated amphipods are a trophically diverse group that could either increase or decrease host fitness depending on their feeding preferences, and the species composition of the amphipod fauna can determine whether these animals increase or decreases seaweed fitness.
Abstract: Herbivorous marine amphipods have been implicated as important grazers on filamentous and ephemeral algae, and thus as beneficial to macrophytes in reducing overgrowth by epiphytic competitors. In North Carolina, USA, amphipods comprise 97% of all macroscopic animals inhabiting the abundant brown seaweed Sargassum filipendula, and peak in abundance between late winter and early summer. I used outdoor tank experiments to test the species-specific impact of common phytal amphipods on the growth of Sargassum and its epiphytes. The results show that seaweed-associated amphipods are a trophically diverse group that could either increase or decrease host fitness depending on their feeding preferences. The amphipods Ampithoe marcuzii, Caprella penantis, and Jassa falcata each significantly reduced growth of epiphytes on Sargassum plants relative to amphipod-free controls, while Ericthonius brasiliensis had no significant effect on Sargassum or its epiphytes. However, amphipod grazing was not necessarily beneficial to Sargassum. A. marcuzii consumed Sargassum in one outdoor tank experiment, reducing its mass by 11%, while Sargassum plants without amphipods grew by 81%. Epiphytes (mostly diatoms and the filamentous brown alga Ectocarpus siliculosus) and detritus remained abundant on these plants suggesting that A. marcuzii preferred the host to its epiphytes. Similarly, when given simultaneous access to Sargassum and to several common foliose and filamentous epiphytes in the lab, A. marcuzii ate Sargassum almost exclusively. The other three amphipods ate no macroalgae. In contrast to A. marcuzii, C. penantis consistently reduced epiphytes with no negative effect on Sargassum. Thus the species composition of the amphipod fauna can determine whether these animals increase or decrease seaweed fitness.
200 citations