Connectivity, or the exchange of individuals among marine populations, is a central topic in marine ecology. For most benthic marine species with complex life cycles, this exchange occurs primarily during the pelagic larval stage. The small size of larvae coupled with the vast and complex fluid environment they occupy hamper our ability to quantify dispersal and connectivity. Evidence from direct and indirect approaches using geochemical and genetic techniques suggests that populations range from fully open to fully closed. Understanding the biophysical processes that contribute to observed dispersal patterns requires integrated interdisciplinary approaches that incorporate high-resolution biophysical modeling and empirical data. Further, differential postsettlement survival of larvae may add complexity to measurements of connectivity. The degree to which populations self recruit or receive subsidy from other populations has consequences for a number of fundamental ecological processes that affect population regulation and persistence. Finally, a full understanding of population connectivity has important applications for management and conservation.

Larval Dispersal and Marine Population Connectivity

Relationships among food choice, compensatory feeding, and the consequences for consumer fitness rarely have been quantified. We created foods of varying nutritional quality and evaluated the consequences of compensatory feeding for three sympatric species of amphipods by analyzing food choices, feeding rates, and long-term effects on fitness. Nutritional quality was manipulated by creating low-quality diets from algae (low in protein, nitrogen, and total organic carbon), high-quality diets from commercial fish food (high in protein, nitrogen, and total organic carbon), and intermediate-quality diets from mixtures of those two foods. When high- and low-quality diets were simultaneously offered, the more mobile, non-tube-building amphipods, Gammarus mucronatus and Elasmopus levis, both fed preferentially on the high-quality diet. The more sedentary, tube-building amphipod Ampithoe longimana did not discriminate between these foods. When confined to a single food type, all three species exhibited compensato...

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Can quantity replace quality? food choice, compensatory feeding, and fitness of marine mesograzers

1. The chemistry of algal secondary metabolism by J. Alan Maschek and Bill J. Baker* 2. Macroalgal chemical defenses and their roles in structuring tropical marine communities by Renato Crespo Pereira* and Bernardo Antonio Perez da Gama 3. Macroalgal chemical defenses and their roles in structuring temperate marine communities by Veijo Jormalainen* and Tuija Honkanen 4. Macroalgal chemical defenses in polar marine communities by Charles D. Amsler*, James B. McClintock, and Bill J. Baker 5. Macroalgal and cyanobacterial chemical defenses in freshwater communities by Frank A. Camacho 6. New perspectives for addressing patterns of secondary metabolites in marine macroalgae by Karen N. Pelletreau and Nancy M. Targett* 7. Macroalgal models in testing and extending defense theories by Henrik Pavia* and Gunilla B. Toth 8. Ecological and physiological roles of dimethylsulfoniopropionate (DMSP) and DMSP cleavage in marine macroalgae by Kathryn L. Van Alstyne 9. Influence of algal secondary metabolites on plankton community structure by Georg Pohnert 10. Herbivore offense in the sea: the detoxification and transport of secondary metabolites by Erik E. Sotka* and Kristen E. Whalen 11. Secondary metabolite defenses against pathogens and biofoulers by Amy L. Lane and Julia Kubanek* 12. Oxidative burst and related responses in biotic interactions of algae by Philippe Potin 13. Defense strategies of algae and cyanobacteria against solar ultraviolet radiation by Ulf Karsten 14. Algal sensory chemical ecology by Charles D. Amsler

Algal Chemical Ecology

Studies examining population structure and genetic diversity of benthic marine invertebrates in the Southern Ocean have emerged in recent years. However, many taxonomic groups remain largely unstudied, echinoderms being one conspicuous example. The brittle star Astrotoma agassizii is distributed widely throughout Antarctica and southern South America. This species is a brooding echinoderm and therefore may have limited dispersal capacity. In order to determine the effect of hypothesized isolating barriers in the Southern Ocean, such as depth, geographic distance, and the polar front, 2 mitochondrial DNA markers were used to compare populations from the South American and Antarctic continental shelves. Astrotoma agassizii was shown to be genetically discontinuous across the polar front. In fact, populations previously assumed to be panmictic instead represent 3 separate lineages that lack morphological distinction. However, within lineages, genetic continuity was displayed across a large geographic range (>500 km). Therefore, despite lacking a pelagic larval stage, A. agassizii can disperse across substantial geographic distance within continental shelf regions. These results indicate that geographic distance alone may not be a barrier to dispersal, but rather the combined effects of distance, depth, and the polar front act to prevent gene flow between A. agassizii populations in the Southern Ocean.

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Evaluating Connectivity in the Brooding Brittle Star Astrotoma agassizii across the Drake Passage in the Southern Ocean

The Amphipoda includes a large clade defined by the presence of a previously unrecognised synapomorphy, apical robust setae on the rami of uropods 1–2. We term this clade the Senticaudata subord. nov. (Latin: sentis = thorn). It includes almost all freshwater species as well as a number of marine benthic taxa, formerly part of the ‘Gammaridea’. The phylog-eny of the senticaudates was determined by cladistic analysis of morphological characters and character states. Within the suborder Senticaudata there are six infraorders: Carangoliopsida, Talitrida, Hadziida, Corophiida, Bogidiellida and Gam-marida. A classification is provided and all the senticaudate families are diagnosed. We introduce for the first time in am-phipod classification, the level parvorder between infraorder and superfamily. Four new families are described: Kairosidae; Eriopisidae; Nuuanuidae and Kergueleniolidae.

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A Phylogeny and Classification of the Senticaudata subord. nov. Crustacea: Amphipoda)

Effective spatial management of coral reefs including design of marine protected areas requires an understanding of interpopulation genetic connectivity. We assessed gene flow along 355 km of the Florida reef system and between Florida and Belize in three commensal invertebrates occupying the same host sponge ( Callyspongia vaginalis ) but displaying contrasting reproductive dispersal strategies: the broadcast-spawning brittle star Ophiothrix lineata and two brooding amphipods Leucothoe kensleyi and Leucothoe ashleyae. Multiple analytical approaches to sequence variation in the mitochondrial COI gene demonstrated a high degree of overall connectivity for all three species along the Florida reef system. Ophiothrix lineata showed significant genetic structuring between Florida and Belize, and a pattern of isolation by distance but no significant genetic structuring along the Florida coastline. Bayesian estimates of migration detected a strong southerly dispersal bias for O. lineata along the Florida reef system, contrary to the general assumption of northerly gene flow in this region based on the direction of the Florida Current. Both amphipods, despite direct development, also showed high gene flow along the Florida reef system. Multiple inferences of long-distance dispersal from a nested clade analysis support the hypothesis that amphipod transport, possibly in detached sponge fragments, could generate the high levels of overall gene flow observed. However, this transport mechanism appears much less effective across deep water as connectivity between Florida and Belize (1072 km) is highly restricted.

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Genetic connectivity in the Florida reef system: comparative phylogeography of commensal invertebrates with contrasting reproductive strategies.

Studies of factors aAecting host plant spe- cialization by herbivores commonly highlight the value of the plant as both food and habitat, but often cannot distinguish the relative importance of these plant traits. A diAerent approach is to study non-herbivorous ani- mals that specialize on particular plants but do not feed on tissue from these plants. Such animals will not be aAected directly by the nutritional, chemical, or mor- phological traits that determine the value of the plant as a food. This study reports on a filter-feeding amphipod, Ericthonius brasiliensis, that lives in domiciles it con- structs by curling terminal segments of the green, cal- cified, and chemically defended seaweed Halimeda tuna. We examined the temporal (1850s-1990s) and spatial (Caribbean, Mediterranean, and Pacific regions) scale of the association, the factors that may select for spe- cialization on H. tuna, and the eAect of the amphipod on growth of its host. Sampling along 125 km of coral reefs in the Florida Keys (USA) indicated that almost all populations of H. tuna had been colonized by this amphipod. Infested plants occurred on nine of ten reefs that supported H. tuna populations, with between 8 and 75% of the plants on those reefs colonized by the am- phipod. For infested plants, 2-23% of all segments on each plant had been curled by the amphipod. Common co-occurring congeners of H. tuna (H. opuntia and H. goreaui) were never used for domicile construction. A survey of 1498 Halimeda specimens collected during the last 140 years and archived in the U.S. National Museum of Natural History (Smithsonian Institution, Washington, D.C.) indicated that the association has existed for >100 years and occurs throughout the Ca- ribbean region, never in the Indo-Pacific or Mediterra- nean, and only on H. tuna. Predation by fishes could select for amphipod specialization on H. tuna. Labo- ratory experiments demonstrated that amphipods in- habiting curled segments of H. tuna were relatively immune from fish predation while those on the exterior surface of the plant or in open water were rapidly eaten. Segments of H. tuna are large enough to provide full protection from predators, while those of the co- occurring congeners H. goreaui and H. opuntia are of a size that may provide only partial protection. Experi- mental addition of E. brasiliensis to H. tuna plants in the field significantly decreased segment accumulation on infested relative to uninfested control plants. Whether this negative eAect was a direct or indirect consequence of amphipod occupancy is unclear. Rolling plant portions into domiciles could directly decrease host growth by increasing shading and decreasing ex- posure of plant surface area to water column nutrient flux. Amphipod occupancy could indirectly slow net host growth if fishes selectively feed on plant sections occupied by amphipods. Underwater video showed that herbivorous fishes did not graze infested plants more than uninfested plants, but small predatory fishes did prefer feeding from infested plants. These non-herbiv- orous fishes may slow host growth by damaging the terminal meristematic tissues of plants during attacks on amphipods. This study demonstrates that habitat specialists can negatively impact hosts without con- suming them and that specialization on a plant can occur due to its habitat value alone (as opposed to its value as a food).

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Host-plant specialization by a non-herbivorous amphipod: advantages for the amphipod and costs for the seaweed

Thomas, James Darwin, and J. Laurens Barnard. The Platyischnopidae of America (Crustacea: Amphipoda). Smithsonian Contributions to Zoology, number 375, 33 pages, 12 figures, 2 tables, 1983.—The known American taxa of this family are divided into genera to complement the oriental taxa. Several unsolved problems remain. The taxa are Eudevenopus (new), with type-species Platyischnopus metagracilis J.L. Barnard, and including newly reanalyzed Platyischnopus gracilipes Schellenberg, Phoxocephalus capuciatus Oliveira (obscure), and a new species, E. honduranus (these three may be synonymous); Tiburonella (new), with type-species Platyischnopus viscana J.L. Barnard; and Skaptopus (new), with type-species S. brychius (new). These species are widespread through the Americas. Skaptopus is a deepwater taxon in depths of 100+ m whereas the other taxa occur in shallow water. They all have a plough-shaped head and are assumed to be fossorial. OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded in the Institution's annual report, Smithsonian Year. SERIES COVER DESIGN: The coral Montastrea cavtmosa (Linnaeus). Library of Congress Cataloging in Publication Data Thomas, James Darwin The Platyischnopidae of America (Crustacea, Amphipoda) (Smithsonian contributions to zoology ; no. 375) Bibliography: p. Supt. of Docs, no.: SI 1.27:375 1. Platyischnopidae—Classification. 2. Crustacea—Classification. 3. Crustacea—America— Classification. I. Barnard, J. Laurens (Jerry Laurens), 1928. II. Title. III. Series. QLI.S54 no. 375 |QL444.M315J 591s |595.3'71] 82-600317

The Platyischnopidae of America (Crustacea, Amphipoda)

The lack of the information on the biology of the commensal amphipod family Anamixidae prompted investigations into mouthpart ultrastructure, feeding biology, and host specificity of Anam;x;s hansen; Stebbing, 1897. Earlier investigators presented conflicting reports on the structural composition of the buccal region and feeding modes in anamixids. Scanning electron microscope analysis of A. han,I'en; showed a complete set of mouthparts to be present, although much modified and reduced, except for the well-developed maxilliped palps, Feeding is not parasitic (piercing and sucking host tissue) as previously believed but is accomplished while A. hansen; rests inside its host. Minute food particles are trapped on a filter net of setal tufts located on the medial carpal lobes of the enlarged second gnathopods, Both pairs of antennae and maxilliped palps are employed in maneuvering the food mass to the mouth. Mucus secretions by the host may aid in agglutination of food particles and could itself be a food source, Findings show that A. hansen; is a highly specialized commensal with closest affinities to the genus Leucothoides of the Leucothoidae, A, hansen; inhabits compound tunicates and small solitary cal-

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Mouthpart Morphology and Feeding Strategies of the Commensal Amphipod, Anamixis hanseni Stebbing

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James Darwin Thomas

Papers

Genetic connectivity in the Florida reef system: comparative phylogeography of commensal invertebrates with contrasting reproductive strategies.

Host-plant specialization by a non-herbivorous amphipod: advantages for the amphipod and costs for the seaweed

The Platyischnopidae of America (Crustacea, Amphipoda)

Mouthpart Morphology and Feeding Strategies of the Commensal Amphipod, Anamixis hanseni Stebbing

Discovery of a majid host for the commensal amphipod Stenothoe symbiotica Shoemaker, 1956