The Value of Long‐Term Assessment of Restoration: Support from a Seagrass Investigation

The importance of judging success of restoration studies over extended time periods has been repeatedly voiced but convincing information to justify increased monitoring is generally unavailable. Building on Bell et al. (2008), we investigated the development of areal coverage of the seagrass, Halodule wrightii, as a metric for assessing the outcome of a restoration effort conducted near Tampa Bay, Florida, U.S.A., over 7 years, thereby expanding the timescale over which a subtropical seagrass restoration project was evaluated for success. In each of 12 plots, 500 planting units of H. wrightii were introduced in 2002, and the seagrass cover level documented annually through 2009. Although only low‐moderate levels of H. wrightii cover were recorded after 3 years, a rapid increase to high coverage levels was evident in many plots after 2006 and sustained through 2009. Plots that supported only low levels of seagrass cover initially remained poor performers, 4–7 years post‐planting. By 2008, substantial seagrass spillover, contiguous with over 75% of plots, was recorded. When both within‐plot coverage and spillover were considered, seagrass restoration success was attained 6 years after initiation. Our findings provide an example of comparatively longer‐term monitoring of a restoration effort leading to reversal of an earlier evaluation of project success. Moreover, unique information on H. wrightii temporal dynamics emerged from the 7 year study, further illustrating the value of long‐term assessment of restoration. Extending the duration of post‐planting surveys of seagrass coverage may address multiple needs as it advances the field of seagrass restoration .     

Innovative Techniques for Large‐scale Seagrass Restoration Using Zostera marina (eelgrass) Seeds

The use of Zostera marina (eelgrass) seeds for seagrass restoration is increasingly recognized as an alternative to transplanting shoots as losses of seagrass habitat generate interest in large‐scale restoration. We explored new techniques for efficient large‐scale restoration of Z. marina using seeds by addressing the factors limiting seed collection, processing, survival, and distribution. We tested an existing mechanical harvesting system for expanding the scale of seed collections, and developed and evaluated two new experimental systems. A seeding technique using buoys holding reproductive shoots at restoration sites to eliminate seed storage was tested along with new techniques for reducing seed‐processing labor. A series of experiments evaluated storage conditions that maintain viability of seeds during summer storage for fall planting. Finally, a new mechanical seed‐planting technique appropriate for large scales was developed and tested. Mechanical harvesting was an effective approach for collecting seeds, and impacts on donor beds were low. Deploying seed‐bearing shoots in buoys produced fewer seedlings and required more effort than isolating, storing, and hand‐broadcasting seeds in the fall. We show that viable seeds can be separated from grass wrack based on seed fall velocity and that seed survival during storage can be high (92–95% survival over 3 months). Mechanical seed‐planting did not enhance seedling establishment at our sites, but may be a useful tool for evaluating restoration sites. Our work demonstrates the potential for expanding the scale of seed‐based Z. marina restoration but the limiting factor remains the low rate of initial seedling establishment from broadcast seeds.     

Habitat preference of three common fishes for seagrass, <Emphasis Type="Italic">Caulerpa taxifolia</Emphasis>, and unvegetated substrate in Moreton Bay,Australia

A decrease in seagrass cover and a commensurate increase in Caulerpa taxifolia distribution in Moreton Bay have prompted concern for the impact that habitat change may have on faunal communities. Therefore, it is important to understand the patterns of habitat use. We examined habitat selection of three common seagrass species: double-ended pipefish (Syngnathoides biaculeatus), eastern trumpeter (Pelates quadrilineatus), and fan-bellied leatherjacket (Monacanthus chinensis) using a mesocosm experiment. Fish were given three possible habitat pairings (1) seagrass and C. taxifolia, (2) seagrass and unvegetated, and (3) C. taxifolia and unvegetated. Observation trials were conducted during the day and night over two days. In all trials, fish preferred vegetated habitat (seagrass or C. taxifolia) over unvegetated habitat (sand). In seagrass and C. taxifolia trials, all species preferred seagrass significantly over C. taxifolia. Habitat use patterns did not differ between day and night trials. Caulerpa taxifolia provides a valuable structured habitat in the absence of seagrass; however, it is unclear if C. taxifolia meadows provide other resource benefits to fishes beyond that of shelter.     

Effects of habitat heterogeneity at multiple spatial scales on fish community assembly

Habitat variability at multiple spatial scales may affect community structure within a given habitat patch, even within seemingly homogenous landscapes. In this context, we tested the importance of habitat variables at two spatial scales (patch and landscape) in driving fish community assembly using experimental artificial reefs constructed across a gradient of seagrass cover in a coastal bay of The Bahamas. We found that species richness and benthic fish abundance increased over time, but eventually reached an asymptote. The correlation between habitat variables and community structure strengthened over time, suggesting deterministic processes were detectable in community assembly. Abundance of benthic fishes, as well as overall community structure, were predicted by both patch- and landscape-scale variables, with the cover of seagrass at the landscape-scale emerging as the most important explanatory variable. Results of this study indicate that landscape features can drive differences in community assembly even within a general habitat type (i.e., within seagrass beds). A primary implication of this finding is that human activities driving changes in seagrass cover may cause significant shifts in faunal community structure well before complete losses of seagrass habitat.     

Rapid restoration of belowground structure and fauna of a seagrass habitat

Seagrass meadows are habitat for an abundance and diversity of animal life, and their continuing global loss has focused effort on their restoration. This restoration not only aims to re‐establish the structure of the seagrass, but also to restore its function, particularly as habitat. The success of seagrass restoration is typically measured by the recovery of aboveground structure, but this ignores the important role of the belowground component of seagrass ecosystems, which may not recover at the same rate, and is equally important for faunal communities. We quantify infaunal communities (abundance, richness, and composition) within expanding plots of restored seagrass, and relate their change to the recovery of belowground seagrass biomass and sediment properties. We found that infaunal abundance and composition converged on that found in natural seagrass within 2 years, while the overall infaunal richness was not affected by habitat. The carbon content of surface sediments also recovered within 2 years, although recovery of belowground biomass and sediment grain size took 4 to 6 years. These results suggest that the structure of recovering seagrass habitats may not need to attain that of natural meadows before they support infauna that is comparable to natural communities. This pace and effectiveness of recovery provides some optimism for future seagrass restoration.     

Integrating biology and economics in seagrass restoration: How much is enough and why?

Although success criteria for seagrass restoration have been in place for some time, there has been little consistency regarding how much habitat should be restored for every unit area lost (the replacement ratio). Extant success criteria focus on persistence, area, and habitat quality (shoot density). These metrics, while conservative, remain largely accepted for the seagrass ecosystem. Computation of the replacement ratio using economic tools has recently been integrated with seagrass restoration and is based on the intrinsic recovery rate of the injured seagrass beds themselves as compared with the efficacy of the restoration itself. In this application, field surveys of injured seagrass beds in the Florida Keys National Marine Sanctuary (FKNMS) were conducted over several years and provide the basis for computing the intrinsic recovery rate and thus, the replacement ratio. This computation is performed using the Habitat Equivalency Analysis (HEA) and determines the lost on-site services pertaining to the ecological function of an area as the result of an injury and sets this against the difference between intrinsic recovery and recovery afforded by restoration. Joining empirical field data with economic theory has produced a reasonable and typically conservative means of determining the level of restoration and this has been fully supported in Federal Court rulings. Having clearly defined project goals allows application of the success criteria in a predictable, consistent, reasonable, and fair manner.     

Seagrass bed patchiness: effects on epifaunal communities in San Diego Bay, USA

Seagrass habitat structure influences epifaunal density, diversity, community composition and survival, but covariation of structural elements at multiple scales (e.g., shoot density or biomass per unit area, patch size, and patch configuration) can confound studies attempting to correlate habitat structure with ecological patterns and processes. In this study, we standardized simulated seagrass shoot density and bed area among artificial seagrass beds in San Diego Bay, California, USA to evaluate the singular effect of seagrass bed configuration (“patchiness”) on the density and diversity of seagrass epifauna. Artificial seagrass beds all were 1 m², but were composed of a single large patch (“continuous” treatment), four smaller patches (“patchy” treatment), or 16 very small patches (“very patchy” treatment). We allowed epifauna to colonize beds for 1 month, and then sampled beds monthly over the next 3 months. Effects of seagrass bed patchiness on total epifaunal density and species-specific densities were highly variable among sampling dates, and there was no general trend for the effects of fragmentation on epifaunal densities to be positive or negative. Epifaunal diversity (measured as Simpson's index of diversity) was highest in very patchy or patchy beds on two out of the three sampling dates. Very patchy beds exhibited the highest dissimilarity in community composition in the first two sampling periods (August and September), but patchy beds exhibited the highest dissimilarity in the third sampling period (October). Our results indicate that seagrass patch configuration affects patterns of epifaunal density, diversity, and community composition in the absence of covarying bed area or structural complexity, and that patchy seagrass beds may be no less valuable as a habitat than are continuous seagrass beds. The spatial pattern employed when harvesting or planting seagrass may influence epifaunal habitat use and should be a key consideration in restoration plans.     

If you build it,will they come? Use of restored dunes by beach mice

Restoration of coastal habitat fragmented, degraded, or destroyed by development and climate‐related processes such as sea level rise and storm surge usually involves planting native plants to restore habitat structure, but whether and how restored areas benefit taxa other than plants is rarely reported. Installing restoration plantings is one method used to build habitat such as beach dunes where dunes have been lost, potentially creating habitat for dune‐dependent species. We compared use of natural vegetated dunes, open sand gaps, and restoration plantings (habitat treatment) by Perdido Key beach mice (Peromyscus polionotus trissyllepsis) over 3 years using tracking tubes to assess the value of restoration plantings for beach mice. Tubes were monitored in two seasons (early and mid‐summer), and under new and full moon conditions. Mice used restoration plantings less than natural vegetated dunes but more than open sand gaps, which suggests restoration plantings may facilitate movement of mice across fragmented areas. Both season and moon phase influenced the effect of habitat treatment, interactions which may be attributable to perceived risk associated with movement under a combination of different conditions of ambient light, vegetation cover, and habitat novelty. Our results show restoration plantings provide habitat for movement and foraging, and may ameliorate some consequences of sea level rise and storms for beach mice and potentially other dune‐dependent species into the future.     

Information costs of reduced-effort habitat monitoring in a butterfly recovery program

Habitat monitoring typically requires a large amount of effort and resources. Project managers are likely to consider cost-cutting options but they may not critically review the information costs of implementing those options. An effort recently began in New York State to monitor critical habitat and restoration progress aimed at recovering the federally endangered Karner blue butterfly (Lycaeides melissa samuelis). Specific strategies were proposed to increase efficiency of fieldwork: (1) estimate larval host plant (wild blue lupine, Lupinus perennis) abundance from cover data, (2) area-based standardization of sample size for nectar sampling, (3) use a minimum cover threshold to trigger nectar species counts, (4) use multiple observers. I quantitatively reviewed these time savers for effects on raw data quality, and for potential effects on interpreting habitat quality as part of recovery criteria. Cover-based models of lupine abundance differed between metapopulation recovery areas, area-based sampling was sufficient to detect over 80% of priority nectar species in most sites, nectar information loss was high due to the minimum cover threshold, and overall results from different observers were similar with one exception. Direct lupine stem counting is recommended over cover estimation, statistical interpolation (rarefaction) and extrapolation (asymptotic estimators) is recommended over area-based nectar sampling, use of minimum cover criteria is strongly discouraged, and field crews need botanical expertise and careful instructions. This example highlights why strategies to save time and money with monitoring fieldwork should be ‘put to the test’.     

Error,Power, and Blind Sentinels: The Statistics of Seagrass Monitoring

We derive statistical properties of standard methods for monitoring of habitat cover worldwide, and criticize them in the context of mandated seagrass monitoring programs, as exemplified by Posidonia oceanica in the Mediterranean Sea. We report the novel result that cartographic methods with non-trivial classification errors are generally incapable of reliably detecting habitat cover losses less than about 30 to 50%, and the field labor required to increase their precision can be orders of magnitude higher than that required to estimate habitat loss directly in a field campaign. We derive a universal utility threshold of classification error in habitat maps that represents the minimum habitat map accuracy above which direct methods are superior. Widespread government reliance on blind-sentinel methods for monitoring seafloor can obscure the gradual and currently ongoing losses of benthic resources until the time has long passed for meaningful management intervention. We find two classes of methods with very high statistical power for detecting small habitat cover losses: 1) fixed-plot direct methods, which are over 100 times as efficient as direct random-plot methods in a variable habitat mosaic; and 2) remote methods with very low classification error such as geospatial underwater videography, which is an emerging, low-cost, non-destructive method for documenting small changes at millimeter visual resolution. General adoption of these methods and their further development will require a fundamental cultural change in conservation and management bodies towards the recognition and promotion of requirements of minimal statistical power and precision in the development of international goals for monitoring these valuable resources and the ecological services they provide.     

The effectiveness of different planting frameworks for recruitment of tropical rainforest species on ex‐rainforest land

A long‐term rainforest restoration experiment was established on abandoned pasture in northeastern Queensland in 1993 to examine the effectiveness of five different restoration planting methods: (T1) control (no plantings); (T2) pioneer monoculture (planting seedlings of one pioneer species, Homalanthus novoguineensis, Euphorbiaceae); (T3) Homalanthus group framework method (H. novoguineensis and eight other pioneer species); (T4) Alphitonia group framework method (Alphitonia petriei, Rhamnaceae, with eight other pioneer species); and (T5) maximum diversity method (planting pioneers, middle‐phase species, and mature‐phase species). We investigated temporal patterns in the (1) fate of seedlings originally planted in 1993; (2) natural recruitment of native plant species; and (3) current habitat structure (canopy cover and ground cover of grasses and invasive plants) within each restoration treatment. A total of 97% of seedlings planted in T2 died within the first 13 years and all had died by 2014. A total of 72% of seedlings planted in T3, 55.5% of seedlings planted in T4, and 55% of seedlings planted in T5 also died by 2014. By 2014, 42 species from 21 families had recruited across the experimental site, and the abundance of recruits was almost twice that recorded in 2001 and 2006. Overall, T3, T4, and T5 had the greatest diversity and abundance of recruits. By 2014, canopy cover was greatest in T3, T4, and T5 but grass cover was least in T5. It is concluded that some restoration success measures increase with planting diversity, but overall the rate of recovery is similar in framework species and maximum diversity method.     

A genetic assessment of a successful seagrass meadow (Posidonia australis) restoration trial

Seagrass meadows are in decline globally. Although numerous experimental methods have been implemented to restore meadows, few have been successful in the long term. Poor decisions on the sourcing of transplants from donor sites, including poor genetic integration and/or low genetic diversity, may impact on restoration success. However, despite evidence to suggest a positive association between genetic diversity and ecological resilience, there is usually little or no input from genetic data to inform on the genetic management of ecological restoration. Cockburn Sound has seen a 77% decline in seagrass cover since 1967. A transplant trial was conducted between 2004 and 2008 with sprigs of Posidonia australis being planted into a bare sand area. Survival was monitored annually, and in 2012, we compared genetic diversity in this transplant area with the original donor site. Genetic diversity in the restored meadow was very high and comparable to the donor site, with no genetic differentiation detected. The high level of genetic diversity and choice of site may have played an important role in the success of this restoration trial. The observed natural recruits around the site after establishment of transplants suggest that local restoration efforts may improve seafloor habitat and facilitate natural expansion of the meadow.     

Evaluating a Large‐Scale Eelgrass Restoration Project in the Chesapeake Bay

Approximately 90,000 shoots of eelgrass (Zostera marina) were planted over 3 years (2003–2005) at Piney Point (PP) in the lower Potomac River estuary in the Chesapeake Bay (mid‐Atlantic coast of North America) following 3 years of habitat evaluation using a Preliminary Transplant Suitability Index (PTSI) and test plantings. Initial survival was high for the 2003 and 2004 plantings; however, most of the eelgrass died during the summer following the fall planting. Habitat quality and restoration success were monitored for the 2005 plantings and compared to a nearby restoration site (St. George Island [SGI]). Eelgrass planted at PP in the fall of 2005 declined through the summer of 2006 with some recovery in the spring of 2007, but was gone by the end of the summer of 2007. The summer decline from late July to mid‐August of 2006 coincided with water temperatures greater than 30°C, hypoxic oxygen (0–3 mg/L) concentrations, and low percent light at leaf level (PLL < 15%). Epiphyte loads were much heavier at PP than at SGI, despite similar water quality. We suggest that this was the result of higher wave exposure at PP. All of these factors are likely to have contributed to the mortality of the 2005 plantings. Submerged aquatic vegetation habitat quality based on the PTSI, median PLL during the growing season, and test plantings did not explain the decline of the plantings. Restoration site selection criteria should be expanded to include the effects of wave exposure on self‐shading and epiphyte loads, and the potential for both short‐term exposures to stressful conditions and long‐term changes in habitat quality.     

Long-term changes in amphipod population dynamics in a temperate estuary following ecosystem restoration

The Mondego estuary (Portugal) has suffered severe ecological stress over the last two decades, as manifested in the replacement of seagrasses by opportunistic macroalgae, degradation of water quality and increased turbidity. A restoration plan was implemented in 1998, which aimed to reverse the eutrophication effects, and especially to restore the original natural seagrass (Zostera noltii) community. This article explores the long-term changes in Ampithoe valida and Melita palmata (Amphipoda) populations in response to eutrophication (with consequent seagrass loss and macroalgal proliferation) and to the subsequent restoration plan (with progressive seagrass recovery and macroalgal biomass decline). Until the early 1990s, high densities of A. valida and M. palmata were recorded in the Mondego estuary, especially during the occurrence of the macroalgal bloom and during all the periods in which green macroalgae were available. After the implementation of the restoration plan, species abundance, biomass and production levels decreased considerably due to the progressive decline of green macroalgae. This implied the virtual disappearance of the amphipod population, mainly A. valida. Distinct behaviours displayed by the two species could be related to different food strategies and habitat preferences. Ampithoe valida showed feeding preferences for ephemeral softer, filamentous or bladed algae (e.g. Ulva sp.) due to its high caloric content, using the Z. noltii bed only as a habitat for protection against predators or shelter from wave action. On the other hand, M. palmata did not suffer a strong decline in its population density, biomass and production, which may indicate that this species is probably not a primary consumer of green macroalgae and may readily shift to alternative ecological niches. Handling editor: P. Viaroli     

A Comparative Test of Mechanized and Manual Transplanting of Eelgrass, Zostera marina, in Chesapeake Bay

Abstract The laborious process of manual seagrass transplanting has often limited the size of seagrass restoration efforts. This study tested the efficiency of a mechanized planting boat, previously used for transplanting Halodule wrightii, relative to manual transplanting methods for establishing Zostera marina in Chesapeake Bay. Eelgrass planting was conducted at two sites, one each in the Rappahannock and James rivers, in October 2001. The methods were evaluated by three criteria: (1) initial planting success = proportion of attempted planting units (PUs) initially established (number confirmed in sediment by divers/number attempted); (2) survival = proportion of the initially established PUs persisting over 1, 4, and 24 weeks; and (3) efficiency = labor (in person·seconds) invested in each surviving PU. Initial planting success was significantly lower for the planting boat (24 and 56% at the Rappahannock and James sites, respectively) than for manual transplanting (100% at both sites). At the Rappahannock site, survival of initially established PUs declined over time for both methods, but while mean survival was always higher for manually planted rows, differences in survival between methods were not statistically significant. At the James site, survival to 1 and 4 weeks was significantly lower for the machine than for the manual method, but survival to 24 weeks was not significantly different. While the machine was able to attempt PUs faster than the manual method (2.2 s/PU vs. 5.8 s/PU, respectively), this speed was offset by poorer planting success rates, resulting in a much greater total labor investment for each machine‐planted PU that persisted to 24 weeks than for each similarly persisting manually planted PU (40.6 person·seconds/PU and 22.4 person·seconds/PU, respectively, averaged across sites). In summary, those PUs successfully planted by the machine survived similarly to PUs planted by hand, but as a result of poorer initial planting success, the machine required a greater investment of labor and plant donor stock for each PU surviving to 24 weeks. Therefore, in its tested configuration this planting boat is not a significant improvement over the manual method for transplanting eelgrass.     

海草场生态系统及其修复研究进展

海草场能够提供重要的生态系统服务。自20世纪末以来,由于人类活动和自然灾害的影响,全球范围内的海草场出现了急剧衰退,由此也促进了海草场生态系统的研究以及海草场人工修复技术的发展。近年来,针对海草场生境流失的现状,中国也开始开展海草场修复工作。从以下方面进行论述:(1)海草的种类、分布,海草场生态系统功能及其生态系统服务:与陆地系统相比,全球海草物种多样性较低,了解海草的分布特征有助于通过了解海草如何适应当地环境压力,以揭示海草适应环境的能力;海草场提供重要而广泛的自然生态系统服务,特别是在维护近岸生态系统健康和满足人类需求过程中起到重要的作用;(2)海草场的衰退及其原因:认识并缓解人类压力对海草场的危害是促进海草场生态系统可持续发展的重要一环;(3)国内外海草场修复现状:以此阐明海草场修复原理,为海草场修复提供科学的方法;(4)总结与讨论:基于科学研究背景,为中国海草场生态系统保护和修复提出建议。海草场的修复和保护应当相辅相成,并与我国海岸长远规划相结合,以此推动我国海草场生态系统服务的可持续发展。     

Improving restoration success through microsite selection: an example with planting sagebrush seedlings after wildfire

Post‐fire restoration of foundation plant species, particularly non‐sprouting shrubs, is critically needed in arid and semi‐arid rangeland, but is hampered by low success. Expensive and labor‐intensive methods, including planting seedlings, can improve restoration success. Prioritizing where these more intensive methods are applied may improve restoration efficiency. Shrubs in arid and semi‐arid environments can create resource islands under their canopies that may remain after fire. Seedlings planted post‐fire in former canopy and between canopies (interspace) may have different survival and growth. We compared planting Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle & Young) seedlings post‐fire in former sagebrush canopy and interspace microsites at five locations. Four growing seasons after planting, seedling survival was 46 and 7% in canopy and interspace microsites, respectively. Sagebrush cover was 5.8 times greater in canopy compared to interspace microsites. Sagebrush survival and cover were likely greater because of less competition from herbaceous vegetation as well as benefiting from resource island effects in canopy microsites. Initially, post‐fire abundance of exotic annual grasses was less in canopy microsites, but by the third year post‐fire it was substantially greater in canopy microsites, indicating that resource availability to seedlings was greater, at least initially, in canopy microsites. These results suggest microsites with greater likelihood of success should be identified and then utilized to improve restoration success and efficiency. This is important as the need for restoration greatly exceeds resources available for restoration.     

Large- and small-scale effects of habitat structure on rates of predation: how percent coverage of seagrass affects rates of predation and siphon nipping on an infaunal bivalve

Landscape ecology, predominantly a terrestrial discipline, considers the effect of large-scale (tens of meters to kilometers) spatial patterns of habitats on ecological processes such as competition, predation, and flow of energy. In this study, a landscape-ecology approach was applied to a marine soft-sediment environment to examine rates of predation and transfer of secondary production in and around vegetated habitats. Seagrass beds naturally occur in a variety of spatial configurations from patches 1–10s of meters across with interspersed unvegetated sediments (i.e., patchy coverage) to more continuous coverage with little or no bare sediment. I designed experiments to address how percent coverage of seagrass in a 100-m² area of seafloor, and the spatial arrangement (degree of patchiness or fragmentation) of an equal area (100 m²) of vegetation affected predation (lethal) and siphon nipping (sublethal) intensity on an infaunal bivalve, Mercenaria mercenaria (hard clam). Measures of seagrass density and biomass with different percent coverage of seagrass were also made. When clams were placed in both the vegetated and unvegetated portions of the seafloor nearly twice as many clams were recovered live with 99% seagrass cover than with 23% seagrass cover, while survivorship was intermediate with 70% cover. Cropping of clam siphons from both the vegetated and unvegetated sediments was also affected by the amount of seagrass cover in a 100-m² area of seafloor: mean adjusted siphon weights were approximately 76% heavier from the 99% seagrass cover treatment than from the 70% or 23% cover treatments. Survivorship of clams placed within an equal area of seagrass in very patchy, patchy, and continuous spatial configurations was 40% higher in the continuous seagrass treatment than in either of the two patchy treatments. This study demonstrates that transfer of secondary production in the form of predation and cropping on an infaunal organism is altered as the percent cover of seagrass changes. While large-scale changes in the amount and spatial patterning of vegetation may affect habitat utilization patterns and foraging HGLoopbehavior, increased seagrass density and biomass with increased percent coverage of seagrass limit any conclusions concerning predator foraging behavior and feeding success in response to patch shapes and sizes. Instead, local changes in seagrass characteristics provide the most compelling explanation for the observed results.     

Microhabitat use by a post-settlement stage estuarine fish: evidence from relative abundance and predation among habitats

Seagrass beds provide food and shelter for many fish species. However, the manner in which fishes use seagrass bed habitats often varies with life stage. Juvenile fishes can be especially dependent on seagrass beds because seagrass and associated habitats (drift macroalgae) may provide an effective tradeoff between shelter from predation and availability of prey. This study addressed aspects of habitat use by post-settlement pinfish, Lagodon rhomboides (Linneaus), an abundant and trophically important species in seagrass beds in the western North Atlantic and Gulf of Mexico. Abundance of post-settlement fish in seagrass beds was positively related to volume of drift macroalgae, but not to percent cover of seagrass, indicating a possible shelter advantage of the spatially complex algae. Tethering experiments indicated higher rates of predation in seagrass without drift macroalgae than in seagrass with drift macroalgae. Aquarium experiments showed lower predation with higher habitat complexity, but differences were only significant for the most extreme cases (unvegetated bottom, highest macrophyte cover). Levels of dissolved oxygen did not differ between vegetated and unvegetated habitats, indicating no physiological advantage for any habitat. Seagrass beds with drift macroalgae provide the most advantageous tradeoff between foraging and protection from predation for post-settlement L. rhomboides. The complex three-dimensional shelter of drift macroalgae provides an effective shelter that is embedded in the foraging habitat provided by seagrass. Drift macroalgae in seagrass beds is a beneficial habitat for post-settlement L. rhomboides by reducing the risk of predation, and by providing post-settlement habitat within the mosaic (seagrass beds) of adult habitat, thus reducing risks associated with ontogenetic habitat shifts.     

Community structure of caprellids (Crustacea: Amphipoda: Caprellidae) on seagrasses from southern Spain

The community structure of caprellids inhabiting two species of seagrass (Cymodocea nodosa and Zostera marina) was investigated on the Andalusian coast, southern Spain, using uni and multivariate analyses. Three meadows were selected (Almería, AL; Málaga, MA; Cádiz, CA), and changes in seagrass cover and biomass were measured from 2004 to 2005. Four caprellid species were found; the density of Caprella acanthifera, Phtisica marina and Pseudoprotella phasma was correlated to seagrass biomass. No such correlation was found for Pariambus typicus, probably because this species inhabits sediments and does not cling to the seagrass leaves. We recorded a significant decrease in seagrass cover and biomass in MA due to illegal bottom trawling fisheries. Phtisica marina and P. typicus were favoured by this perturbation and increased their densities after the trawling activities. A survey of reports on caprellids in seagrass meadows around the world showed no clear latitudinal patterns in caprellid densities (ranging from 6 to 1,000 ind/m² per meadow) and species diversity. While caprellid abundances in seagrass meadows are often very high, the number of species per meadow is low (range 1–5).