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2011
Carson, HS, Cook GS, Lopez-Duarte PC, Levin LA.  2011.  Evaluating the importance of demographic connectivity in a marine metapopulation. Ecology. 92:1972-1984. AbstractWebsite

Recently researchers have gone to great lengths to measure marine metapopulation connectivity via tagging, genetic, and trace-elemental fingerprinting studies. These empirical estimates of larval dispersal are key to assessing the significance of metapopulation connectivity within a demographic context, but the life-history data required to do this are rarely available. To evaluate the demographic consequences of connectivity we constructed seasonal, size-structured metapopulation matrix models for two species of mytilid mussel in San Diego County, California, USA. The self-recruitment and larval exchange terms were produced from a time series of realized connectivities derived from trace-elemental fingerprinting of larval shells during spring and fall from 2003 to 2008. Both species exhibited a strong seasonal pattern of southward movement of recruits in spring and northward movement in fall. Growth and mortality terms were estimated using mark recapture data from representative sites for each species and subpopulation, and literature estimates of juvenile mortality. Fecundity terms were estimated using county-wide settlement data from 2006-2008; these data reveal peak reproduction and recruitment in fall for Mytilus californianus, and spring for M. galloprovincialis. Elasticity and life-stage simulation analyses were employed to identify the season- and subpopulation-specific vital rates and connectivity terms to which the metapopulation growth rate (lambda) was most sensitive. For both species, metapopulation growth was most sensitive to proportional changes in adult fecundity, survival and growth of juvenile stages, and population connectivity, in order of importance, but relatively insensitive to adult growth or survival. The metapopulation concept was deemed appropriate for both Mytilus species as exchange between the subpopulations was necessary for subpopulation persistence. However, highest metapopulation growth occurred in years when a greater proportion of recruits was retained within the predominant source subpopulation. Despite differences in habitat and planktonic duration, both species exhibited similar overall metapopulation dynamics with respect to key life stages and processes. However, different peak reproductive periods in an environment of seasonal current reversals led to different regional (subpopulation) contributions to metapopulation maintenance; this result emphasizes the importance of connectivity analysis for spatial, management of coastal resources.

2007
Levin, LA, Mendoza GF.  2007.  Community structure and nutrition of deep methane-seep macrobenthos from the North Pacific (Aleutian) Margin and the Gulf of Mexico (Florida Escarpment). Marine Ecology-an Evolutionary Perspective. 28:131-151.   10.1111/j.1439-0485.2006.00131.x   AbstractWebsite

Methane seeps occur at depths extending to over 7000 m along the world's continental margins, but there is little information about the infaunal communities inhabiting sediments of seeps deeper than 3000 m. Biological sampling was carried out off Unimak Island (3200-3300 m) and Kodiak Island (4500 m) on the Aleutian margin, Pacific Ocean and along the Florida Escarpment (3300 m) in the Gulf of Mexico to investigate the community structure and nutrition of macrofauna at these sites. We addressed whether there are characteristic infaunal communities common to the deep-water seeps or to the specific habitats (clam beds, pogonophoran fields, and microbial mats) studied here, and ask how these differ from background communities or from shallow-seep settings sampled previously. We also investigated, using stable isotopic signatures, the utilization of chemosynthetically fixed and methane-derived organic matter by macrofauna from different regions and habitats. Within seep sites, macrofaunal densities were the greatest in the Florida microbial mats (20,961 +/- 11,618 ind(.)m(2)), the lowest in the Florida pogonophoran fields (926 +/- 132 ind(.)m(2)), and intermediate in the Unimak and Kodiak seep habitats. Seep macrofaunal densities differed from those in nearby non-seep sediments only in Florida mat habitats, where a single, abundant species of hesionid polychaete comprised 70% of the macrofauna. Annelids were the dominant taxon (> 60%) at all sites and habitats except in Florida background sediments (33%) and Unimak pogonophoran fields (27%). Macrofaunal diversity (H') was lower at the Florida than the Alaska seeps, with a trend toward reduced richness in clam bed relative to pogonophoran field or non-seep sediments. Community composition differences between seep and non-seep sediments were evident in each region except for the Unimak margin, but pogonophoran and clam bed macrofaunal communities did not differ from one another in Alaska. Seep VC and delta N-15 signatures were lighter for seep than non-seep macrofauna in all regions, indicating use of chemosynthetically derived carbon. The lightest delta C-13 values (average of species' means) were observed at the Florida escarpment (-42.87 parts per thousand). We estimated that on average animal tissues had up to 55% methane-derived carbon in Florida mats, 3144% in Florida clam beds and Kodiak clam beds and pogonophoran fields, and 9-23% in Unimak seep habitats. However, some taxa such as hesionid and capitellid polychaetes exhibited tremendous intraspecific 613C variation (> 307.0) between patch types. Overall we found few characteristic communities or features common to the three deep-water seeps (> 3000 m), but common properties across habitats (mat, clam bed, pogonophorans), independent of location or water depth. In general, macrofaunal densities were lower (except at Florida microbial mats), community structure was similar, and reliance on chemosynthesis was greater than observed in shallower seeps off California and Oregon.

2001
Ewel, KC, Cressa C, Kneib RT, Lake PS, Levin LA, Palmer MA, Snelgrove P, Wall DH.  2001.  Managing critical transition zones. Ecosystems. 4:452-460.   10.1007/s10021-001-0106-0   AbstractWebsite

Ecosystems that function as critical transition zones (CTZs) among terrestrial, freshwater, and marine habitats are closely connected to the ecosystems adjacent to them and are characterized by a rapid flux of materials and organisms. CTZs play various roles, including mediating water flows, accumulating sediments and organic matter, processing nutrients, and providing opportunities for recreation. They are particularly difficult to manage because they tend to be small, albeit important, components of large watersheds, and managers may not have control over the entire landscape. Moreover, they are often the focus of intensive human activity. Consequently, CTZs are critically important zones, and their preservation and protection are likely to require unique collaboration among scientists, managers, and stakeholders. Scientists can learn a great deal from the study of these ecosystems, taking advantage of small size and the importance of fluxes, but a good understanding of adaptive management strategies is needed to establish a dialogue with managers and stakeholders on technical and management issues. An understanding of risk analysis is also important to help set meaningful goals and establish logical strategies that include all of the interested parties. Successful restoration of a CTZ is the best test of the quality of knowledge about its structure and function. Much has already been learned about coastal CTZs through restoration projects, and the large number of such projects involving riparian CTZs in particular suggests that there is considerable opportunity for fruitful collaborations between scientists and managers.