Michael N Dawson

Questioning the Rise of Gelatinous Zooplankton in the World's Oceans

During the past several decades, high numbers of gelatinous Zooplankton species have been reported in many estuarine and coastal ecosystems. Coupled with media-driven public perception, a paradigm has evolved in which the global ocean ecosystems are thought to he heading toward being dominated by “nuisance” jellyfish. We question this current paradigm by presenting a broad overview of gelatinous Zooplankton in a historical context to develop the hypothesis that population changes reflect the human-mediated alteration of global ocean ecosystems. To this end, we synthesize information related to the evolutionary context of contemporary gelatinous Zooplankton blooms, the human frame of reference for changes in gelatinous Zooplankton populations, and whether sufficient data are available to have established the paradigm. We conclude that the current paradigm in which it is believed that there has been a global increase in gelatinous Zooplankton is unsubstantiated, and we develop a strategy for addressing the critical questions about long-term, human-related changes in the sea as they relate to gelatinous Zooplankton blooms.

Comparative phylogeography of sympatric sister species, Clevelandia ios and Eucyclogobius newberryi (Teleostei, Gobiidae), across the California Transition Zone

It is paradigmatic in marine species that greater dispersal ability often, but not always, results in greater gene flow and less population structure. Some of the exceptions may be attributable to studies confounded by comparison of species with dissimilar evolutionary histories, i.e. co‐occurring species that are not closely related or species that are closely related but allopatric. Investigation of sympatric sister species, in contrast, should allow differences in phylogeographic structure to be attributed reliably to recently derived differences in dispersal ability. Here, using mitochondrial DNA control region sequence, we first confirm that Clevelandia ios and Eucyclogobius newberryi are sympatric sister taxa, then demonstrate considerably shallower phylogeographic structure in C. ios than in E. newberryi. This shallower phylogeographic structure is consistent with the higher dispersal ability of C. ios, which most likely results from the interaction of habitat and life‐history differences between the species. We suggest that the paradigm will be investigated most rigorously by similar studies of other sympatric sister species, appended by thorough ecological studies, and by extending this sister‐taxon approach to comparative phylogeographic studies of monophyletic clades of sympatric species.

Geographic variation and ecological adaptation in Aurelia (Scyphozoa, Semaeostomeae): some implications from molecular phylogenetics

Mitochondrial and nuclear DNA sequence data indicate considerable phylogeographic structure and at least five sibling species of Aurelia in the Pacific Ocean. At least a sixth sibling species can be found in the northwest Atlantic Ocean. These data suggest long histories of geographic and ecological sub-division and divergence of populations, which are inconsistent with current descriptions of Aurelia as a tri-typic genus in which most populations belong to one almost ubiquitous ecological generalist, A. aurita Linnaeus. Existing ecological and systematic descriptions of Aurelia, therefore, should be re-evaluated in light of these molecular data. Reciprocally, such re-evaluations should facilitate interpretation of the molecular data. Here, we introduce new DNA sequence data from Pacific and Black Sea Aurelia and novel ecological data describing tropical Aurelia inhabiting a marine lake in Palau, Micronesia. Despite large genetic distances between temperate and tropical Aurelia and the different environments inhabited by these populations, their rates of feeding, growth, respiration and swimming are similar. We discuss this result in terms of geographic variation and ecological adaptation in Aurelia and also comment on population dynamics, blooms, exotic species and the systematics of Aurelia. Finally, we consider briefly the implications of these findings for other scyphozoan species.

A review and synthesis on the systematics and evolution of jellyfish blooms: advantageous aggregations and adaptive assemblages

Pelagic gelatinous invertebrates in many diverse phyla aggregate, bloom, or swarm. Although typically portrayed as annoying to humans, such accumulations probably are evolutionary adaptations to the environments of pelagic gelatinous zooplankton. We explore this proposition by systematic analysis completed in three steps. First, using the current morphological taxonomic framework for Scyphozoa, we summarize relevant information on species that aggregate, bloom, and swarm and on those species that do not. Second, we establish a molecular phylogenetic framework for assessing evolutionary relationships among classes and many orders of Medusozoa and among most families of Scyphozoa (particularly Discomedusae). Third, we interpret the phylogenetic distribution of taxa and of characteristics of jellyfish that aggregate, bloom, or swarm, in terms of species diversity—a proxy for evolutionary success. We found that: (1) Medusae that occur en masse are not randomly distributed within the Phylum Cnidaria but instead they are found primarily within the Scyphozoa which have a metagenic life history. (2) Midwater and deep-sea medusae rarely bloom or swarm. (3) Epibenthic medusae do not swarm. (4) Large carnivores that feed on large prey do not bloom strongly. (5) Large medusae that feed exclusively on small prey both bloom and swarm. (6) Pelagia, the only holoplanktonic, epipelagic scyphomedusan, both blooms and swarms, demonstrating that a metagenic life cycle is not required for blooming or swarming at sea. (7) Environmental change (overfishing, species introductions, and eutrophication) may induce or inhibit blooms. (8) Taxa that bloom or swarm are often more diverse than taxa that do not. (9) Speciation in scyphozoans can occur rapidly. (10) Morphological stasis in holozooplankton masks genetic variability. (11) Selection for convergent evolution in the sea is strong because mass occurrence has evolved multiple times in independent evolutionary lineages under similar circumstances. Thus, attributes possessed by many taxa that occur en masse appear to be evolutionarily advantageous, i.e., adaptations.

Domestic waste and TBT pollution in coastal areas of Ambon Island (Eastern Indonesia)

Coastal areas of the island of Ambon (eastern Indonesia), but especially Ambon Bay, were polluted by domestic waste. There was severe beach litter pollution and contamination of inshore waters. High incidences of the isopod ectoparasite Renocila sp. on the coral reef fish Abudefduf saxatilis were probably indirect consequences of pollution stress. Symptoms of imposex, presumably caused by tributyltin compounds leaching from the anti-fouling paints used on boat hulls, were severe in some whelk populations in Ambon Bay but were mild or absent from populations elsewhere on the island. Coastal pollution, and the over-exploitation of natural resources, are global problems but are particularly severe in areas of high population density and those adjacent to semi-enclosed and shallow seas. There are, for example, serious problems along much of the north coast of Java. The island has an enormously dense population accounting for only 6.9% of the land area of Indonesia but supporting 60% of its total population of 176 million people. The most acute problems are in Jakarta Bay which receives pollutants from the city of Jakarta. It suffers from heavy metal and sewage pollution (Sutamihardja, 1988; Thayib & Razak, 1988),

Phylogeography of the tidewater goby, Eucyclogobius newberryi (Teleostei Gobiidae) in coastal California

Abstract.— The tidewater goby, Eucyclogobius newberryi, inhabits discrete, seasonally closed estuaries and lagoons along approximately 1500 km of California coastline. This species is euryhaline but has no explicit marine stage, yet population extirpation and recolonization data suggest tidewater gobies disperse intermittently via the sea. Analyses of mitochondrial control region and cytochrome b sequences demonstrate a deep evolutionary bifurcation in the vicinity of Los Angeles that separates southern California populations from all more northerly populations. Shallower phylogeographic breaks, in the vicinities of Seacliff, Point Buchon, Big Sur, and Point Arena segregate the northerly populations into five groups in three geographic clusters: the Point Conception and Ventura groups between Los Angeles and Point Buchon, a lone Estero Bay group from central California, and San Francisco and Cape Mendocino groups from northern California. The phylogenetic relationships between and patterns of molecular diversity within the six groups are consistent with repeated, and sometimes rapid, northward and southward range expansions out of central California caused by Quaternary climate change. Plio‐Pleistocene tectonism, Quaternary coastal geography and hydrography, and historical human activities probably also influenced the modern geographic and genetic structure of E. newberryi. The phylogeography of E. newberryi is concordant with phylogeographic patterns in several other coastal California taxa, suggesting common extrinsic factors have had similar effects on different species. However, there is no evidence of a phylogeographic break coincident with a biogeographic boundary at Point Conception.

A biophysical perspective on dispersal and the geography of evolution in marine and terrestrial systems.

The fluid mechanics of marine and terrestrial systems are surprisingly similar at many spatial and temporal scales. Not surprisingly, the dispersal of organisms that float, swim or fly is influenced by the fluid environments of air and seawater. Nonetheless, it has been argued repeatedly that the geography of evolution differs fundamentally between marine and terrestrial taxa. Might this view emanate from qualitative contrasts between the pelagic ocean and terrestrial land conflated by anthropocentric perception of within- and between-realm variation? We draw on recent advances in biogeography to identify two pairs of biophysically similar marine and terrestrial settings—(i) aerial and marine microplankton and (ii) true islands and brackish seawater lakes—which have similar geographies of evolution. Commonalities at these scales, the largest and smallest biogeographic scales, delimit the geographical extents that can possibly characterize evolution in the remaining majority of species. The geographies of evolution therefore differ statistically, not fundamentally, between marine and terrestrial systems. Comparing the geography of evolution in diverse non-microplanktonic and non-island species from a biophysical perspective is an essential next step for quantifying precisely how marine and terrestrial systems differ and is an important yet under-explored avenue of macroecology.

Population genetic analysis of a recent range expansion: mechanisms regulating the poleward range limit in the volcano barnacle Tetraclita rubescens

As range shifts coincident with climate change have become increasingly well documented, efforts to describe the causes of range boundaries have increased. Three mechanisms—genetic impoverishment, migration load, or a physical barrier to dispersal—are well described theoretically, but the data needed to distinguish among them have rarely been collected. We describe the distribution, abundance, genetic variation, and environment of Tetraclita rubescens, an intertidal barnacle that expanded its northern range limit by several hundreds of kilometres from San Francisco, CA, USA, since the 1970s. We compare geographic variation in abundance with abiotic and biotic patterns, including sea surface temperatures and the distributions of 387 co‐occurring species, and describe genetic variation in cytochrome c oxidase subunit I, mitochondrial noncoding region, and nine microsatellite loci from 27 locations between Bahia Magdalena (California Baja Sur, Mexico) and Cape Mendocino (CA, USA). We find very high gene flow, high genetic diversity, and a gradient in physical environmental variation coincident with the range limit. We infer that the primary cause of the northern range boundary in T. rubescens is migration load arising from flow of maladapted alleles into peripheral locations and that environmental change, which could have reduced selection against genotypes immigrating into the newly colonized portion of the range, is the most likely cause of the observed range expansion. Because environmental change could similarly affect all taxa in a region whose distributional limits are established by migration load, these mechanisms may be common causes of range boundaries and largely synchronous multi‐species range expansions.

Cyanea capillata is not a cosmopolitan jellyfish: morphological and molecular evidence for C. annaskala and C. rosea (Scyphozoa : Semaeostomeae : Cyaneidae) in south-eastern Australia

The taxonomic status of the lions mane jellyfish, Cyanea, of south-eastern Australia has been unsettled since 1884 when medusae from Port Jackson were described as a new variety of C. annaskala von Lendenfeld rather than assigned to C. rosea Quoy & Gaimard described previously from the same location. Cyanea annaskala was later combined with C. mullerianthe Haacke then synonymised with C. capillata (Linnaeus), which is now considered a circumglobal species, before being resurrected as a subspecies, C. capillata annaskala, in 1986. Here I demonstrate that Cyanea in southern New South Wales and Cyanea in Tasmania and Victoria constitute two distinct morphological groups separated by >10% sequence difference in both cytochrome c oxidase subunit I and internal transcribed spacer 1. Moreover, these clades are molecularly distinct (>6%) from C. capillata collected in its North Sea type locality. Analyses of medusae from another type locality, Port Philip Bay, Victoria, demonstrate that Cyanea annaskala von Lendenfeld is a valid species. Cyanea rosea is tentatively resurrected for medusae from New South Wales, pending confirmation by analyses of medusae from the vicinity of Sydney. Assigning other south-eastern Australian Cyanea specimens from museum collections to species is difficult in the absence of molecular analyses because biogeographic and morphological inferences sometimes conflict. Integrative molecular and morphological analyses of medusae from type localities may offer the most robust approach to straightening out the often convoluted systematics of scyphomedusae.

Identification of genetically and oceanographically distinct blooms of jellyfish

Reports of nuisance jellyfish blooms have increased worldwide during the last half-century, but the possible causes remain unclear. A persistent difficulty lies in identifying whether blooms occur owing to local or regional processes. This issue can be resolved, in part, by establishing the geographical scales of connectivity among locations, which may be addressed using genetic analyses and oceanographic modelling. We used landscape genetics and Lagrangian modelling of oceanographic dispersal to explore patterns of connectivity in the scyphozoan jellyfish Rhizostoma octopus, which occurs en masse at locations in the Irish Sea and northeastern Atlantic. We found significant genetic structure distinguishing three populations, with both consistencies and inconsistencies with prevailing physical oceanographic patterns. Our analyses identify locations where blooms occur in apparently geographically isolated populations, locations where blooms may be the source or result of migrants, and a location where blooms do not occur consistently and jellyfish are mostly immigrant. Our interdisciplinary approach thus provides a means to ascertain the geographical origins of jellyfish in outbreaks, which may have wide utility as increased international efforts investigate jellyfish blooms.