Variation in a host-epiphyte relationship along a wave exposure gradient

The red alga Polysiphonia lanosa (L ) Tandy is an obligate epiphyte that primarily occurs on the fucoid brown algal basiphyte Ascophyllum nodosum (L) Le Jolis In the present study we examine how epiphytic interactions between P lanosa and A nodosum vary along a wave exposure gradient within the southern Gulf of Maine, USA P lanosa was most dense on protected shores, however because the stature of P lanosa was greater on exposed than on sheltered shores, greater biomass occurred In exposed habitats Epiphytlc P lanosa pnmanly attached to inlured vegetative bssue at exposed sites, while ~ t osc currence was primarily receptacular at sheltered sites A significantly stronger correlation was found between host receptacle abundance and epiphyte abundance at a protected low than an exposed site As a result, the distribution of epiphytes along the host S stlpe vanes at different sites We suggest that changes in the distribution and abundance of P lanosa across this wave exposure gradient are highly influenced by vanations in the distribution and persistence of suitable attachment sites on the host plant Because both the quantity and quality of attachment sites vanes w t h exposure, we hypothesize that d~fferenpt rocesses limit or de t e rm~neP lanosa populations in different locations In protected sites P lanosa may be limited by the presence of adequate substrata (inlured bssue and lateral pits) where successful recruitment may occur By contrast at exposed sites the supply of P lanosa sporelings, rather than quantity of appropnate substrata, may limlt population size

A multi-scale analysis of the population ecology of a temperate reef fish

Using field experiments and descriptive analyses this study investigated the significance of larval settlement and post-settlement processes to populations of cunner, Tautogolabrus adspersus. At small spatial scales there was no relationship between the density of new recruits and the percent cover of kelp, foliose algae and branching algae. Crustaceans and mussels were preferred found items of juvenile cunner, and significantly greater numbers of isopods, amphipods and newly settled mussels were present in patches where fish were present than in randomly selected patches. Experimental and correlative analyses demonstrated that variation in recruitment could not be explained by the presence of conspecifics. Manipulations of macroalgal structure showed that the distribution of fish was influenced by the algal habitat. The dispersion of macroalgae influenced the demography of cunner. Settlement was greater to randomly placed than to clumped habitats; however, no differences in recruitment between random and clumped habitat were detected. The magnitude of the change in recruit number between sampling dates did not differ between clumped and random habitats. There was no evidence of either density-dependent mortality or settlement. A larger scale study was conducted comparing the demography of cunner in Newfoundland and the Gulf of Maine. Greater numbers of adult fish were observed in Newfoundland, but higher numbers of juveniles and recruits were found in the Gulf of Maine. In the Gulf of Maine variation was pronounced at the site scale, while in Newfoundland variation was pronounced at both the site and location scales. Variation in recruitment was not expressed as subsequent variation in older age classes. There was no effect of topographic complexity on variation of densities of recruits or juveniles, but in Newfoundland a negative relationship between adults and topography was observed. Algal cover was not important in Newfoundland, but was important in the Gulf of Maine. Although there was consistently greater than 2 orders of magnitude difference in densities of pre-settlement fish between two locations, the location that received fewer pre-settlement fish actually had higher recruitment

Changes in the structure of a New England (USA) kelp bed: the effect of an introduced species?

Since its first observation in the Gulf of Maine (Northwest Atlantic) in 1987, the epiphytic bryozoan Membranipora membranacea has become the dominant epiphyte on laminarian kelps. This note describes changes in the structure of a kelp bed at Cape Neddick (Mane, USA) after the coincident increase of M. membranacea, evaluates the potential causes of the observed changes, and documents the shortterm recovery of the kelp bed. Percent cover, length and density of kelps decreased significantly during 1989 through 1991 The dispersion of Laminaria spp. within the kelp bed was clumped on each sampling date at a large spatial scale (meters), while the distribution of Laminana spp. changed from a random pattern to a clumped d~stribut~on on a smaller spatial scale (0.25 m\u27). There were no consistent differences in storm intensity between years; densities of herbivores within the kelp bed were low and also have not changed between years. The coverage of M. membranacea on laminarian kelps increased 3-fold from 1989 to 1990, and the total coverage of other epiphytes decreased. It appears that the presence of M. membranacea on kelps has contributed to the defoliation of the kelp bed at Cape Neddick. This phenomenon may have important consequences to organisms that utilize kelps as habitat and shelter

Selection of Estuarine Habitats by Juvenile Gags in Experimental Mesocosms

© 2003 by the American Fisheries SocietyThe degradation and destruction of estuarine habitats threaten the organisms that depend on these habitats for food and shelter. Gags Mycteroperca microlepis reside on rocky reefs for most of their lives but initially settle and rear in estuarine habitats before moving to offshore reefs. Gag populations have declined to the point where some consider them vulnerable to extinction, and the recovery of the species requires an understanding of what habitats these fish use and why they use them. We examined the habitat selection of juvenile gags in North Carolina using experimental mesocosms.We manipulated the shelter characteristics of habitats and compared the foraging rates of gags to determine the specific attributes of habitats that influence habitat selection. Gags selected structured seagrass or oyster reefs over sand and shell hash habitats. While gags did not show a preference between eelgrass Zostera marina and oyster reefs, they did choose oyster reefs over shoal grass Halodule wrightii and selected seagrass habitats with high shoot densities over those with lower densities. The addition of a small shelter to the habitat that the gags did not choose dramatically increased their use of that habitat. Finally, when we provided pinfish Lagodon rhomboides as prey, gag foraging rate did not vary among seagrass habitats with different shoot densities. However, gags consumed penaeid shrimp at much lower rates in seagrass habitats of high shoot density. Our results agree with those of other studies suggesting that seagrass habitats are important to gags. However, our results also emphasize that gags select specific attributes within seagrass landscapes and suggest that oyster reefs may be important habitats for them

Identifying Thresholds for Ecosystem-Based Management

Background One of the greatest obstacles to moving ecosystem-based management (EBM) from concept to practice is the lack of a systematic approach to defining ecosystem-level decision criteria, or reference points that trigger management action. Methodology/Principal Findings To assist resource managers and policymakers in developing EBM decision criteria, we introduce a quantitative, transferable method for identifying utility thresholds. A utility threshold is the level of human-induced pressure (e.g., pollution) at which small changes produce substantial improvements toward the EBM goal of protecting an ecosystem\u27s structural (e.g., diversity) and functional (e.g., resilience) attributes. The analytical approach is based on the detection of nonlinearities in relationships between ecosystem attributes and pressures. We illustrate the method with a hypothetical case study of (1) fishing and (2) nearshore habitat pressure using an empirically-validated marine ecosystem model for British Columbia, Canada, and derive numerical threshold values in terms of the density of two empirically-tractable indicator groups, sablefish and jellyfish. We also describe how to incorporate uncertainty into the estimation of utility thresholds and highlight their value in the context of understanding EBM trade-offs. Conclusions/Significance For any policy scenario, an understanding of utility thresholds provides insight into the amount and type of management intervention required to make significant progress toward improved ecosystem structure and function. The approach outlined in this paper can be applied in the context of single or multiple human-induced pressures, to any marine, freshwater, or terrestrial ecosystem, and should facilitate more effective management

Is hypoxia’s influence restricted to the deep? Evaluation of nearshore community composition in Hood Canal, Washington, a seasonally hypoxic estuary

Hypoxia [dissolved oxygen (DO) \u3c 2 mg L-1] has been identified as a key threat to the Puget Sound ecosystem, particularly in Hood Canal. Hood Canal is subject to seasonal hypoxia in its southern reaches, and prior work has demonstrated avoidance patterns of demersal species from the deep, offshore hypoxia-impacted waters. However, the non-lethal impact of low DO conditions on the nearshore community is not well understood, despite its importance to the estuary (e.g., nursery habitat). We evaluated the nature and extent of the sub-lethal influence of hypoxia on the nearshore community using underwater video monitoring techniques. Within two regions of Hood Canal, a southern highly impacted region and a northern reference region, we recorded weekly underwater video of the benthos via transects at three depths (10, 20, 30m) to measure species density and composition. Weekly monitoring of water quality revealed strong differences in DO over time and space, with the vertical extent of low DO waters increasing markedly at the end of summer in the south. While we were unable to detect acute shifts in nearshore densities, the community composition was significantly different between the two study regions; the south was primarily composed of hypoxia tolerant invertebrates and fewer fish species compared to the north. Moreover, the tolerant invertebrates displayed a three-fold increase in presence below a specific DO threshold (mean threshold ± SE = 3.95 mg L-1 ± 0.22), while the more sensitive species (e.g., fish) declined. Post-hoc comparisons of our findings to long-term DO trends in Hood Canal revealed the potential for a more persistent low DO state in the southern reaches. As a result, this study provides further insight into the complex regional differences in community structure and potential sensitivity of the nearshore community to other perturbations in Hood Canal

Beliefs about Development Versus Environmental Tradeoffs in the Puget Sound Region

Policymakers face difficult decisions as they attempt to balance competing calls for increased developmentand environmental protection. In the Puget Sound region of Washington State, population growth and the needfor housing and energy have brought these types of tradeoffs to the forefront. Using data from a phone survey of 1,980 residents, researchers from the Carsey Institute and the National Oceanic and Atmospheric Administration (NOAA) Fisheries investigated public perceptions of environmental concerns across Puget Sound. This fact sheet outlines residents' views about the importance of environmental protection as well as their opinions about energy development, protection of wild salmon, and land use regulation

A Comparison of Early Juvenile Red Drum Densities Among Various Habitat Types in Galveston

ABSTRACT: Seagrass meadows are often cited as important nursery areas for newly settled red drum even though many estuaries, such as Galveston Bay, Texas, support large numbers of red drum and have limited seagrass cover, suggesting the use of alternate nursery areas. We examined patterns of habitat use for newly settled red drum at six sampling areas in Galveston Bay; two areas had seagrass beds and four areas had no seagrass. We measured densities in different habitat types using epibenthic sleds and enclosure samplers. Peak recruitment of young red drum to the estuary occurred during September through December. Highest densities of new settlers were found in seagrass meadows (primarily Halodule wrightii), but when seagrass was absent, the highest densities of red drum occurred along the Spartina alterniflora marsh edge interface. Densities were relatively low on nonvegetated bottom away from the marsh edge. We also examined density patterns in other habitat types at selected sampling areas and found no red drum within marsh vegetation away from the marsh edge interface (5 and 10 m into the marsh interior). Oyster reef Crassostrea virginica was sampled using lift nets, and we found no red drum using this habitat, although adjacent seagrass and marsh interface habitats were used. Even though red drum densities in marsh edge were low relative to seagrass, the large areal extent of marshes in the bay complex probably makes marsh edge the most important nursery habitat for red drum in Galveston Bay

Integrated Ecosystem Assessments: Developing the Scientific Basis for Ecosystem-Based Management of the Ocean

Integrated ecosystem assessments challenge the broader scientific community to move beyond the important task of tallying insults to marine ecosystems to developing quantitative tools that can support the decisions national and regional resource managers must make

An integrated environmental and human systems modeling framework for Puget Sound restoration planning

Local, state, federal, tribal and private stakeholders have committed significant resources to restoring Puget Sound’s terrestrial-marine ecosystem. Though jurisdictional issues have promoted a fragmented approach to restoration planning, there is growing recognition that a more coordinated systems-based restoration approach is needed to achieve recovery goals. This presentation describes our collaborative effort to develop and apply an integrated environmental and human systems modeling framework for the Puget Sound Basin, inclusive of all marine and land areas (1,020 and 12,680 sq. mi.). Our goal is to establish a whole-basin systems modeling framework that dynamically simulates biophysical interactions and transfers (water, nutrients, contaminants, biota) across terrestrial-marine boundaries. The core environmental models include a terrestrial ecohydrological model (VELMA), an ocean circulation and biogeochemistry model (Salish Sea Model), and an ocean food web model (Atlantis). This environmental subsystem will be linked with an agent-based modeling subsystem (e.g., Envision) that allows human decision-makers to be represented in whole-basin simulations. The integrated environmental and human systems framework aims to facilitate discourse among different stakeholders and decision makers (agents) and enable them play out the ecological, social and economic consequences of alternative ecosystem restoration choices. All of these models are currently being applied in Puget Sound, but they have not yet been integrated. The linked models will better capture the propagation of human impacts throughout the terrestrial-marine ecosystem, and thereby provide a more effective decision support tool for addressing restoration of high priority environmental endpoints, such as the Vital Signs identified by the Puget Sound Partnership (http://www.psp.wa.gov/vitalsigns/). Our overview will include examples of existing stand-alone model applications, and conceptual plans for linking models across terrestrial-marine boundaries. The Puget Sound multi-model framework described here can potentially be expanded to address the entire Salish Sea transboundary ecosystem (https://www.eopugetsound.org/maps/salish-sea-basin-and-water-boundaries)