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Shallow water seagrass meadows are frequently damaged by recreational and commercial vessels. Severe injury occurs where propeller scarring, hull groundings and mooring anchors uproot entire plants, excavate sediments, and modify the biophysical properties of the substrate. In climax tropical seagrass communities dominated by Thalassia testudinum (turtlegrass), natural recovery in these disturbances can take several years to decades, and in some environmental conditions may not occur at all. During the recovery period, important ecological services provided by seagrasses are absent or substantially diminished and injured meadows can degrade further in response to natural disturbances, e.g. strong currents and severe storms. To determine if we could accelerate rehabilitation and prevent further degradation of injured turtlegrass meadows, we evaluated a restoration method called “modified compressed succession” using the fast-growing, opportunistic species Halodule wrightii to temporarily substitute ecological services for the slower-growing, climax species T. testudinum. In three experiments we showed statistically significant increases in density and coverage rates of H. wrightii transplants fertilized by wild bird feces as compared to unfertilized treatments. In one experiment, we further demonstrated that regrading excavated injuries with sediment-filled biodegradable tubes in combination with wild bird fertilization and H. wrightii transplants also accelerated seagrass recovery. Specific recommendations are presented for the best practical application of this restoration method in the calcium carbonate-based sediments of south Florida and the wider Caribbean region.

Carrion in the form of dead seal pups and algal mats placed on soft bottom habitats at Explorers Cove and Salmon Bay, McMurdo Sound, attract scavenging invertebrates that are driven away by hydrogen sulphide produced by sulphate-reducing bacteria sequestered below a layer of Beggiatoa/Thioploca-like filamentous bacteria. This system is usually found for lipid-rich marine mammal carrion, but also occurred with natural algal mats.

Sponges are the most conspicuous component of the Antarctic benthic ecosystem, a system under stress both from climate change and fishing activities. Observations over four decades are compiled and reveal extremely episodic sponge recruitment and growth. Recruitment occurred under different oceanographic conditions on both sides of McMurdo Sound. Most of the sponges appear to have recruited in the late 1990s–2000. Observations from 2000 to 2010 follow thirty years of relative stasis with very little sponge recruitment or growth followed by a general pattern of recruitment by some forty species of sponges. That there was almost no recruitment observed on natural substrata emphasizes the contrast between potential and realized recruitment. This unique data set was derived from a region noted for physical stasis, but the episodic ecological phenomena highlight the importance of rare events. Against a background of intermittent food resources and the low metabolic costs of stasis, understanding the causes of irregular larval supply, dispersal processes, recruitment success and survivorship becomes critical to predicting ecosystem dynamics and resilience in response to increasing environmental change. Our time-series emphasizes that long-term data collection is essential for meaningful forecasts about environmental change in the unique benthic ecosystems of the Antarctic shelf.

Polar ecosystems are bellwether indicators of climate change and offer insights into ecological resilience. In this study, we describe contrasting responses to an apparent regime shift of two very different benthic communities in McMurdo Sound, Antarctica. We compared species‐specific patterns of benthic invertebrate abundance and size between the west (low productivity) and east (higher productivity) sides of McMurdo Sound across multiple decades (1960s–2010) to depths of 60 m. We present possible factors associated with the observed changes. A massive and unprecedented shift in sponge recruitment and growth on artificial substrata observed between the 1980s and 2010 contrasts with lack of dramatic sponge settlement and growth on natural substrata, emphasizing poorly understood sponge recruitment biology. We present observations of changes in populations of sponges, bryozoans, bivalves, and deposit‐feeding invertebrates in the natural communities on both sides of the sound. Scientific data for Antarctic benthic ecosystems are scant, but we gather multiple lines of evidence to examine possible processes in regional‐scale oceanography during the eight years in which the sea ice did not clear out of the southern portion of McMurdo Sound. We suggest that large icebergs blocked currents and advected plankton, allowed thicker multi‐year ice, and reduced light to the benthos. This, in addition to a possible increase in iron released from rapidly melting glaciers, fundamentally shifted the quantity and quality of primary production in McMurdo Sound. A hypothesized shift from large to small food particles is consistent with increased recruitment and growth of sponges on artificial substrata, filter‐feeding polychaetes, and some bryozoans, as well as reduced populations of bivalves and crinoids that favor large particles, and echinoderms Sterechinus neumayeri and Odontaster validus that predominantly feed on benthic diatoms and large phytoplankton mats that drape the seafloor after spring blooms. This response of different guilds of filter feeders to a hypothesized shift from large to small phytoplankton points to the enormous need for and potential value of holistic monitoring programs, particularly in pristine ecosystems, that could yield both fundamental ecological insights and knowledge that can be applied to critical conservation concerns as climate change continues.

Species density of macrofaunal invertebrates living in marine soft sediments was highest at the shelf-slope break (100‐150 m) in Monterey Bay (449 m )2 ). There were 337 species m )2 in the mid-shelf mud zone (80 m). There were fewer species along the slope: 205 m )2 from the lower slope (950-2000 m) and 335 m )2 on the upper slope (250-750 m). Species density was highest inside the bay (328-446 m )2 ) compared to outside (336-339 m )2 ), when examining samples at selected water depths (60-1000 m). There was little difference in local species density from 1 km of shoreline compared to regional species density along 1000 km of shoreline at both shelf and slope depths. The highest species densities worldwide in the literature are recorded along the Carolina slope in the Atlantic Ocean, where peak species density (436/0.81 m 2 ) at 800 m and values at the largest sample areas are similar to those on the Monterey Bay shelf. We speculate that the highest species densities occur where ocean water exchanges energy with shoaling topography at the continental margin, bringing more food to the benthos ‐ areas such as the very productive waters in the upwelling system of Monterey Bay.

Despite widespread degradation, some coastal ecosystems display remarkable resilience. For seagrasses, a century-old paradigm has implicated macroalgal blooms stimulated by anthropogenic nutrient, loading as a primary driver of seagrass decline, yet relatively little attention has been given to drivers of seagrass resilience. In Elkhorn Slough, CA, an estuarine system characterized by extreme anthropogenic nutrient loading and macroalgal (Ulva spp.) blooms, seagrass (Zostera marina) beds have recovered concurrent with colonization of the estuary by top predators, sea otters (Enhydra lutris). Here, we follow up on the results of a previous experiment at the seagrass interior, showing how sea otters can generate a trophic cascade that promotes seagrass. We conducted an experiment and constructed structural equation models to determine how sea otters, through a trophic cascade, might affect the edge of seagrass beds where expansion occurs. We found that at the edge, sea otters promoted both seagrass and ephemeral macroalgae, with the latter contributing beneficial grazers to the seagrass. The surprising results that sea otters promote two potentially competing vegetation types, and a grazer assemblage at their boundary provides a mechanism by which seagrasses can expand in eutrophic environments, and contributes to a growing body of literature demonstrating that ephemeral macroalgae are not always negatively associated with seagrass. Our results highlight the potential for top predator recovery to enhance ecosystem resilience to anthropogenic alterations through several cascading mechanisms.

One of the largest contiguous seagrass ecosystems in the world is located on the shallow continental shelf adjacent to the west coast of Florida, USA and is comprised of seasonally ephemeral Halophila decipiens meadows. Little is known about the demography of the west Florida shelf H. decipiens , which may produce 4.56 × 10 8 g C day −1 or more during the peak growing season. We documented seagrass distribution, biomass, and productivity, and density of sediment seed reserves, seedlings, flowers and fruits on the southeastern portion of the west Florida shelf by sampling along a transect at three stations in 10, 15, and 20 m water depth. Biomass, flower, fruit, seedling, and seed bank densities tended to be highest at stations in 10–15 m water depth and lowest at 20 m. Flowers and fruit were most prevalent during summer cruises (June and August 1999, July 2000). Seedling germination occurred during summer, fall (October 1999), and winter (January 2000) sampling events, with the highest seedling densities present during the winter. Seed bank density remained consistent through time. A Category I hurricane with sustained winds of 120 km h −1 passed over the stations, but only limited impact on H. decipiens biomass was observed. The presence of a persistent seed bank provides for recovery after storm disturbance, annual reestablishment of populations, and continual maintenance of the 20,000 km 2 of deep water seagrass habitat present on the west Florida shelf.

Thalassia testudinum seedling recruitment, survival, and growth were examined within physically disturbed seagrass beds in the Florida Keys. Two separate studies were conducted. In the first, a large-scale study, T. testudinum seedlings were surveyed and collected from a large seagrass disturbance (1560 m 2 ), 4.8 yr after the initial impact from a motor-vessel grounding. In the second, a smaller-scale study, T. testudinum seedling recruitment was examined over a 2 yr period within 9 smaller motor-vessel disturbances located within intact T. testudinum beds. In the large-scale study, we reconstructed the age of the seedlings based on shoot production rates from a previous study and from the small-scale study. A total of 79 seedlings were collected that varied in age from young of the year to 4.8 yr old; 6 different seedling cohorts were identified. The average density and rhizome- elongation rate for 1 yr old seedlings were 1 m -2 and 6.6 cm yr -1 , respectively. In the small-scale study, we surveyed and permanently marked all newly recruited seedlings; monitoring was conducted 5 more times over a 2 yr period. The average seedling survival after Year 1 was 42%; after Year 2, average survival dropped to 20%. The average seedling density after Year 1 was 0.071 m -2 ; after Year 2, average density dropped to 0.026 m -2 . The average rhizome-elongation rate and shoot- production rate of 1 yr old seedlings were 6 cm yr -1 and 1.8 shoots yr -1 , respectively. The results of this study suggest that T. testudinum seedlings are a regular and reliable source of new recruits on seagrass banks in the Florida Keys.

International audience; The description of major patterns in beta (β) diversity is important in order to understand changes in community composition and/or richness at different spatial and temporal scales, and can interrogate processes driving species distribution and community dynamics. Human impacts have pushed many estuarine systems far from their historical baseline of rich, diverse, and productive ecosystems. Despite the ecological and social importance of estuaries, there has not yet been an attempt to investigate patterns of β-diversity and its partitioning along estuarine systems of different continents. We aimed to evaluate if benthic assemblages would show higher turnover than nestedness in tropical than in temperate systems, if well-known impacted estuaries would show greater nestedness than less polluted systems, and to propose a conceptual framework for studying benthic macrofauna beta diversity along estuaries. We analyzed subtidal benthic macrofaunal data from estuaries in Brazil, USA and France. We estimated alpha (α), beta (β) and gamma (γ) diversity for each sampling time in each system, investigated patterns of β -diversity as multivariate dispersion and the partitioning (nestedness and replacement) of β-diversity along each estuary. There was a decrease in the α-diversity along marine to freshwater conditions at most of the estuaries and sampling dates. Beta diversity as multivariate dispersion showed high variability. Most of the estuaries showed a greater proportion of the β-diversity driven by replacement than nestedness. We suggest a conceptual framework for estuaries where relatively pristine estuaries would have their β-diversity mostly driven by replacement while impacted estuaries subjected to several anthropogenic stressors would show total nestedness or total replacement, depending on the stress.

Experimental restoration of Halodule wrightii (shoal-grass) to its former range on Galveston Island, Texas, began in April 1994. We tested the effects of site, planting density, water depth, and fertilizer addition on survival and growth through June 1996. Temperature, salinity, light transmittance, turbidity, and sediment properties at two restoration sites, Redfish Cove and Snake Island Cove, were similar to those in naturally occurring grassbeds in nearby Christmas Bay. Halodule survival, coverage, and new shoot densities were affected by site (significantly higher at Redfish Cove than at Snake Island Cove, which eventually failed), by planting density (significantly higher when planted on 0.25-m or 0.5-m centers rather than on 1.0-m centers), and by water depth (significantly higher when planted in relatively shallow water). Propagation (spreading from transplant units) was significantly greater from 0.25-m or 0.5-m center plantings but was not consistently affected by site or water depth. Fertilizer enhanced propagation but not survival. After two years, Redfish Cove produced belowground biomass similar to that observed in Christmas Bay, but above-ground biomass remained significantly less. Snake Island Cove plant mortality in September 1995 may have been presaged by low root-rhizome carbohydrate levels observed in October 1994, but causes remain unknown. Further restoration of Halodule to Galveston Bay is possible at selected sites, but structural equivalency will take longer than two growing seasons to achieve.

Wounding of both terrestrial and marine plants is known to induce chemical responses in the plants; the induced compounds may defend against herbivory or act in wound-healing processes. We demonstrate here, for the first time, induction of phlorotannins in kelps (Phaeophyta, Laminariales). an important and widespread group of marine benthic algae. The rapid response of kelps to mechanical wounding contrasts with previously published work on other marine algae, where response has been slower. In 4 of the 5 species tested, induction (increases of approximately 30 to 9036 of original levels) occurred very rapidly, within 1 to 3 d of wounding, although the magnitude and duration of the induction varied among species and tissue types. Many induced responses persisted for 5 to 7 d and then relaxed. Relaxation times are a critical component in the hypothesized cost-effectiveness of induced versus constitutive defenses, and this is one of the first attempts to measure relaxation times of chemlcal defenses in marine algae. The temporal persistence of the response suggests an antiherb~vory rather than a wound-healing function for induction of phlorotannins, although this needs further testing KEY MiORDS Kelp phlorotannins . Induction Relaxat~on Chemlcal defense . Wound heal~ng Herb~vory

Polar ecosystems are sensitive to climate forcing, and we often lack baselines to evaluate changes. Here we report a nearly 50-year study in which a sudden shift in the population dynamics of an ecologically important, structure-forming hexactinellid sponge, Anoxycalyx joubini was observed. This is the largest Antarctic sponge, with individuals growing over two meters tall. In order to investigate life history characteristics of Antarctic marine invertebrates, artificial substrata were deployed at a number of sites in the southern portion of the Ross Sea between 1967 and 1975. Over a 22-year period, no growth or settlement was recorded for A. joubini on these substrata; however, in 2004 and 2010, A. joubini was observed to have settled and grown to large sizes on some but not all artificial substrata. This single settlement and growth event correlates with a region-wide shift in phytoplankton productivity driven by the calving of a massive iceberg. We also report almost complete mortality of large sponges followed over 40 years. Given our warming global climate, similar system-wide changes are expected in the future.

Benthic macrofauna are used extensively for environmental assessment, but the area sampled and sieve sizes used to capture animals often differ among studies. Here, we sampled 80 sites using 3 different sized sampling areas (0.1, 0.05, 0.0071 m2) and sieved those sediments through each of 2 screen sizes (0.5, 1 mm) to evaluate their effect on number of individuals, number of species, dominance, nonmetric multidimensional scaling (MDS) ordination, and benthic community condition indices that are used to assess sediment quality in California. Sample area had little effect on abundance but substantially affected numbers of species, which are not easily scaled to a standard area. Sieve size had a substantial effect on both measures, with the 1-mm screen capturing only 74% of the species and 68% of the individuals collected in the 0.5-mm screen. These differences, though, had little effect on the ability to differentiate samples along gradients in ordination space. Benthic indices generally ranked sample condition in the same order regardless of gear, although the absolute scoring of condition was affected by gear type. The largest differences in condition assessment were observed for the 0.0071-m2 gear. Benthic indices based on numbers of species were more affected than those based on relative abundance, primarily because we were unable to scale species number to a common area as we did for abundance. Integr Environ Assess Manag 2012; 8: 649–658. © 2010 SETAC

There were highly significant changes in the structure of benthic infaunal communities at the end of the last cold regime (1976) compared to the end of the last warm regime (1999) in the California Current. The warm regime is characterized by much lower plankton production, which we argue is the primary cause of the degraded infaunal community at the end of the warm regime. In 1997-98, we resampled a depth gradient along a subtidal, high-energy sandy beach (6-24m) in Monterey Bay that was sampled for five years at the end of the last cold regime (1971-75). There was a dramatic decline in the total number species, number of individuals, and biomass by the end of the warm period. There was no overlap in benthic assemblages at all water depths between the decades in either non-metric multidimensional scaling ordination or cluster analysis. In the 1970s, the community dominants in the shallow crustacean zone, centered in 9 m, were pericarid crustaceans, including predacious phoxocephilid amphipods, haustoriid amphipods, and ostracods, which all live in the sediment. The amphipods, in particular, are well adapted to burrowing in sand. The numerical dominants in the deeper polychaete zone (18-24m) were large, sedentary polychaete worms. The largest was a tube-dwelling predator (Nothria) accounting for most of the biomass. The other was a suspension and surface deposit feeding polychaete worm, Magelona. By the 1990s, the most abundant crustacean was a small, swimming amphipod; and the most abundant polychaetes were small, relatively mobile, and deposit feeding. This trend from large size, sedentary, and suspension feeding to smaller size, higher mobility, and deposit feeding also characterizes infaunal shifts from the food-rich continental shelf into the food-poor deep sea. The dominant polychaetes had more opportunistic life histories, and shallow faunal zones extended into deeper water in the 1990s. If global warming continues, the ongoing cold regime may be less productive and the sandy bottom communities should not develop the species composition and high diversity, abundance, and biomass observed in the 1970s.