Network


Latest external collaboration on country level. Dive into details by clicking on the dots.

Hotspot


Dive into the research topics where Roman N. Zajac is active.

Publication


Featured researches published by Roman N. Zajac.


Hydrobiologia | 1998

Recolonization and succession in soft-sediment infaunal communities: the spatial scale of controlling factors

Roman N. Zajac; Robert B. Whitlatch; Simon F. Thrush

Succession in marine soft-sediment habitats has been studied extensively and several general models of successional dynamics have been developed. However, few researchers have addressed how successional dynamics may change over different spatial scales. Here we extend a model that focuses on the factors that control recolonization and succession. These factors comprise three levels of a hierarchy which include environmental conditions, life history and population processes and biotic interactions. Using this hierarchical framework, we consider the spatial scales at which different factors operate, and argue that the relative mix and intensity of factors controlling succession change at different spatial scales. As a result, successional dynamics may vary considerably as the spatial scale of disturbance increases. At small scales, factors at each level of the hierarchy are important. The greater potential for biotic interactions at this scale may be particularly critical. At meso- to large scales, population processes and environmental conditions have the most influence on successional dynamics. Due to these differences, responses to small-scale (≳1 m2) as well as large-scale (≳1 hectare) disturbances may be quite variable. Within this range (≳1 m2 lsim;1 hectare), short- and long-term responses to disturbance may be relatively more predictable and conform to current models of succession in soft-sediment habitats.


Hydrobiologia | 1998

Scale-dependent benthic recolonization dynamics: life stage-based dispersal and demographic consequences

Robert B. Whitlatch; Andrew M. Lohrer; Simon F. Thrush; R. D. Pridmore; Judi E. Hewitt; Vonda J. Cummings; Roman N. Zajac

Soft-sediment recruitment dynamics are dependent upon two sources of colonists; larvae transported from the water column and post-settlement movement of juvenile and/or adult life-stages across the seabed. Differences in the relative dispersal ability of the different life-stages into disturbed patches of habitat should vary predictably with the spatial scale of the disturbance. Smaller patches with a greater edge:surface area ratio should be more influenced by the post-settlement colonist pool than larger patches possessing a smaller edge:surface area ratio. A life stage-based recolonization model, using a Polydora cornuta life table, has been developed to describe how differences in the immigration rates of larvae, juveniles and adults can influence within-patch recovery times. Model results indicate that immigration of adult stages into disturbed patches has the least influence on patch recovery time. In contrast, post-settlement juvenile stages generally has a pronounced effect on patch population dynamics. Experimental evidence of scale-dependent migration of different life-stages to disturbed patches is also presented for the spionid polychaete Boccardia syrtis. Future research on scale-dependent recolonization dynamics in soft-sediment habitats should focus on acquisition of within-patch demographic data in order to more fully understand the importance of post-settlement life-stage movement in regulating population and community dynamics.


Landscape Ecology | 2008

Challenges in marine, soft-sediment benthoscape ecology

Roman N. Zajac

In this paper I address three sets of challenges that face ecologists who are studying soft-sediment benthic landscapes (or benthoscapes). These include (a) development of technology and analytical approaches for sea floor mapping and quantifying benthoscape structure, (b) development of benthoscape ecology theory that integrates ideas from terrestrial and other marine systems, but focuses on the unique aspects of these environments, and (c) making empirical headway. Coordinated efforts in all three areas are needed to make progress in understanding soft-sediment systems, which arguably comprise the largest set of landscapes on the earth. In particular, much more work is needed in relating biotic patterns to the actual spatial structural aspects of soft-sediment benthoscapes.


Landscape Ecology | 2008

Preface: Marine and coastal applications in landscape ecology

Elizabeth K. Hinchey; Matthew C. Nicholson; Roman N. Zajac; Elizabeth Irlandi

Landscape ecology traditionally has been limited to the study of terrestrial systems; however, the questions and methods defining the science are equally relevant for marine and coastal systems. The reciprocal relationship between spatial pattern and ecological processes and the overarching effect of scale on this relationship was being explored in some marine and coastal settings as the general discipline of landscape ecology was evolving throughout the latter two decades of the last century. As with all components of the biosphere, an understanding of these relationships is critical for successful management of marine and coastal systems. In these systems, widely dispersed field or ship-based observations and lack of broad scale data have historically precluded quantification of large-scale patterns and processes and hindered management efforts. However, relatively recent advances in geographic information systems, remote sensing and computer technologies have begun to address these issues and are now permitting assessments of pattern and process in oceans. The intent of this special issue is to highlight research that is adapting the tools of landscape ecology to answer ecological questions within marine and coastal systems, to address the unique challenges faced in these landscapes, and to stimulate an exchange of ideas and solutions to common problems. Inspiration for this special issue of Landscape Ecology began with a special session on “Marine and Coastal Applications in Landscape Ecology” that was held at the 19th Annual Symposium of the United States Regional Association of the International Association for Landscape Ecology, March 31–April 2, 2004 in Las Vegas, Nevada.


Journal of Experimental Marine Biology and Ecology | 2003

Community and population-level responses to disturbance in a sandflat community

Roman N. Zajac; Robert B. Whitlatch

Abstract The responses of soft sediment infauna were investigated in an intertidal sandflat to determine patterns of recolonization and succession at the community and population level. Experimental disturbance plots, 1 m 2 , were initiated in August and sampled for 4.5 months along with ambient sediments. Sediment grain-size was used as a general indicator of the physical state of the disturbance patches, and grain-size distributions among disturbance and ambient patches became similar after ∼2.5 months. Recolonization varied among the dominant infaunal taxa. Densities of infauna that were most abundant in the habitat, primarily syllid polychaetes, did not recover to ambient levels until 3–4 months after disturbance, when ambient densities were falling to winter lows. Multivariate analysis indicated that community recovery occurred by the end of the study period after 4.5 months. Although community structure recovered by the end of the study, the population structure of the dominant species Parapionosyllis longicirrata remained significantly different among ambient and disturbed patches. On all sampling dates except one, disturbance patches had a higher number of larger individuals than ambient sediments. Previous studies have shown that bedload transport of juveniles and adults, and other processes, can cause recolonization to be relatively rapid on intertidal sandflats. However, our results indicate that recovery times may be on the order of months at large disturbance sizes. Therefore, rapid responses may occur primarily in the case of small-scale ( 2 ) disturbance patches. Secondly, recovery at the community level does not necessarily mean that population-level characteristics of species comprising the community have recovered. Population-level differences may be longer lasting than indicated by community level indicators of recovery.


Estuaries | 2001

Response of macrobenthic communities to restoration efforts in a New England estuary

Roman N. Zajac; Robert B. Whitlatch

Changes in macrobenthic communities were studied over a 3.5 yr period following restoration activities in Alewife Cove, a small estuary located in southeastern Connecticut, U.S. Development around this estuary had resulted in reduced freshwater and tidal inflows, loss of critical habitats such as salt marshes, and eutrophication. Early in 1988 the lower reach of the estuary was dredged to increase tidal flushing and enhance environmental quality. Following dredging, tidal range within the Cove increased from 52 to 83 cm. Due to erosion within the Coves lower channel and sediment migration into the Cove, tidal flows and ranges approached pre-dredge levels by 1991. Despite these changes, the percentage of silt/clay in the surface sediments in the middle and upper basins of the Cove declined by 30–45% over the study period. Changes in infaunal community structure in the lower reach following dredging were not great, primarily comprising shifts in the relative abundances of species typical of sandier versus muddier sediments. Directional changes in community structure were most evident in the middle and upper basins, away from the dredged area. Infaunal species richness increased significantly, with many species previously found only in the sand habitats of the lower reach establishing populations in the middle and upper basins. There was a significant decrease in the summer abundances of the pollution indicator polychaeteCapitella capitata throughout much of the middle and upper basins. Restoration efforts in Alewife Cove centering on altered bydrology resulted in selected positive changes. Increases in tidal flow altered environmental conditons in the middle and upper basins where shifts in infaunal community structure indicated decreases in organic loading of sediments over 2–3 yr. Continued changes in the physical dynamics of the lower reach reduced tidal flow, arresting the positive ecological changes that were beginning to occur. This type of restoration approach of small estuaries can have positive results, but there may be a lag in the ecological response of the system. Macrobenthic communities, in particular summer abundance patterns of selected species, provided an integrated assessment of ecological changes in the Cove.


PLOS ONE | 2013

Spatial and Temporal Patterns in Macrofaunal Diversity Components Relative to Sea Floor Landscape Structure

Roman N. Zajac; Joseph Vozarik; Brittney R. Gibbons

We examined temporal changes in macrofaunal α- and β-diversity over several spatial scales (within patches, among patches, across landscapes and across regions) in Long Island Sound on the northeast USA coast. Regional ε-diversity was estimated at 144 taxa, however γ-diversity fluctuated over time as did α- and β-diversity components. Based on additive partitioning, patch- and region-scale β-diversity components generally had the highest contributions to γ-diversity; lower percentages were found at within-patch and landscape scales. Multiplicative diversity partitioning indicated highest species turnover at within- and among patch scales. For all partition results, within-patch and patch-scale β-diversity increased sharply when hypoxia impacted benthic communities. Spatial variation in diversity components can be attributed to the collection of different patch types at varying spatial scales and their associated habitats across the benthic landscapes, as well as gradients in depth and other estuarine-scale characteristics. Temporal variation in diversity components across spatial scales may be related to seasonal changes in habitat heterogeneity, species population dynamics, and seasonal disturbances. Rare species were significant and temporally consistent components of macrofaunal diversity patterns over different spatial scales. Our findings agree with other marine and terrestrial studies that show diversity components vary significantly over different spatial scales and the importance of habitat/landscape heterogeneity in supporting diversity. However, our results indicate that the relative contributions of scale-specific β-diversity components can also change significantly over time. Thus, studies of diversity patterns across patches and landscapes based on data collected at one time, or assembled into a single data set from different times, may not capture the full suite of diversity patterns that occur over varying spatial scales and any time-specific determinants of those patterns. Many factors that shape and maintain sedimentary communities vary temporally, and appear to play an important role in determining and maintaining macrofaunal diversity over different spatial scales.


Ecological Applications | 2011

Changes in habitat heterogeneity alter marine sessile benthic communities.

Pablo Munguia; Richard W. Osman; John Hamilton; Robert B. Whitlatch; Roman N. Zajac

Habitat heterogeneity is considered an important mechanism influencing diversity patterns in spatially structured habitats. However, spatial heterogeneity is not static and it can change along temporal scales. These changes, whether gradual or rapid, have the potential of forcing species extinctions or facilitating the introduction of nonnative species. Here, we present modeling results that show how changes in spatial heterogeneity over several generations can produce strong changes in benthic species composition residing in eastern Long Island Sound, USA. For many benthic species, hard substrate is a limiting resource which can vary in availability among different coastal areas. We modeled gradual changes from a heterogeneous landscape (mimicking patches of natural hard and soft substrate) to a homogenous one (analogous to a fully developed coast with hard, manmade substrate) and followed the abundance and distribution patterns of species possessing four different life histories. We also modeled changes from homogeneous to heterogeneous landscapes. We found that as regions become more homogeneous, species extinctions become more frequent and poor dispersers dominate locally. In contrast, as habitats become more heterogeneous, species distributing across localities leads to regional species coexistence and fewer extinctions. These results suggest that focusing on changing habitat heterogeneity can be a useful management strategy to prevent poor dispersing species, such as invasive ascidians, from driving communities to monocultures.


Archive | 1999

Understanding the Sea Floor Landscape in Relation to Impact Assessment and Environmental Management in Coastal Marine Sediments

Roman N. Zajac

It is becoming increasingly clear that in order to adequately assess both the natural ecological dynamics of soft-sediment communities and their responses to human impacts it is necessary to have detailed knowledge of the spatial structure and dynamics of the sea floor. Benthic landscape structure can be mapped and quantified at different spatial and temporal scales using technologies such as side-scan sonar, in conjunction with conventional bottom sampling methods. Concurrently, it is critical to develop a theoretical and empirical framework to focus research on relationships between sea floor structure and the benthic communities. The elements of a benthic landscape (or benthoscape) ecology are presented, and key areas of research are suggested to include: 1) relationships between physical and biotic patch structure, 2) the interaction of seascape and benthic landscape mosaics, 3) the degree of variation in benthic ecological dynamics at different spatial and temporal scales, 4) how populations interact across the benthic landscape and 5) how benthic communities respond to different scales of disturbance. The increase in the number of studies which focus on issues of spatial and temporal scale in soft-sediment environments over the past decade indicates that a benthoscape ecology is slowly emerging and that it may provide critical information for the management and restoration of coastal environments.


Archive | 2014

Biology and Ecology of Long Island Sound

Glenn R. Lopez; Drew Carey; James T. Carlton; Robert M. Cerrato; Hans G. Dam; Rob DiGiovanni; Chris S. Elphick; Michael G. Frisk; Christopher J. Gobler; Lyndie A. Hice; Penny Howell; Adrian Jordaan; Senjie Lin; Sheng Liu; Darcy J. Lonsdale; Maryann McEnroe; Kim A. McKown; George B. McManus; Rick Orson; Bradley J. Peterson; Chris Pickerell; Ron Rozsa; Sandra E. Shumway; Amy N. S. Siuda; Kelly Streich; Stephanie C. Talmage; Gordon T. Taylor; Ellen Thomas; Margaret Van Patten; Jamie M.P. Vaudrey

Many compelling management issues in Long Island Sound (LIS) focus on how organisms respond to stresses such as commercial and recreational harvesting, eutrophication, hypoxia, habitat degradation, invasion of non-native species, ocean acidification, and climate change. In order to address these complex problems, we must first understand the factors controlling biological processes and how organisms interact ecologically. This chapter provides an overview of the major groups of organisms occupying the dominant habitats of LIS.

Collaboration


Dive into the Roman N. Zajac's collaboration.

Top Co-Authors

Avatar
Top Co-Authors

Avatar

Ralph S. Lewis

University of Connecticut

View shared research outputs
Top Co-Authors

Avatar

Lawrence J. Poppe

United States Geological Survey

View shared research outputs
Top Co-Authors

Avatar

Richard W. Osman

Smithsonian Environmental Research Center

View shared research outputs
Top Co-Authors

Avatar

David C. Twichell

United States Geological Survey

View shared research outputs
Top Co-Authors

Avatar
Top Co-Authors

Avatar

John Hamilton

University of Connecticut

View shared research outputs
Top Co-Authors

Avatar

Drew Carey

Science Applications International Corporation

View shared research outputs
Top Co-Authors

Avatar
Top Co-Authors

Avatar

Michael A. Russello

University of British Columbia

View shared research outputs
Researchain Logo
Decentralizing Knowledge