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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.

We observed high diversity (species density) of infaunal invertebrates from the mid-shelf (50 m) to the upper slope (325 m) with high abundance and low dominance along 4 depth transects ranging from 10 to 2000 m. The highest shallow water diversity recorded worldwide was at the shelf-slope break (109–150 m) with a peak of 185 species 0.1 m-2 (449 m-2, this work and Oliver JS, Hammerstrom K, McPhee-Shaw E, Slattery P, Oakden J, Kim S, Hartwell SI, Mar Ecol 32:278–288, 2011). The peak included a large number of species and individuals of small nestling amphipods. The most abundant genera were Photis, Aoroides, and Gammaropsis. The percentages of crustacean species (40%) and individuals (60%) were extremely high as well. A large caprellid amphipod, Tritella tenuissima, was the most abundant animal found in our survey (387 individuals 0.1 m-2), and characterized the mixed gravel bottoms on the upper slope. We discovered a dense tube mat of relatively large ampeliscid amphipods at the upper margin of the oxygen minimum zone (700 m). This was the most distinct community cluster and was dominated by Ampelisca unsocalae and Byblis barbarensis. The percentage of crustacean species (40%) and individuals (67%) were also highest here. This is the only ampeliscid tube mat known from deep water and is ecologically similar to extensive shallow-water ampeliscid mats in the Bering and Chukchi Seas, the primary feeding grounds of gray whales. The diverse and abundant continental margin communities occurred in a dynamic, current-swept upwelling center with complex topography. Diversity decreased below the upper slope and on the wave-swept inner shelf, where there was another dramatic crustacean pattern. These shifting sands were dominated by burrowing amphipods (phoxocephalids and haustoriids) and small ostracods in the 1970s that were rare in the present survey. In total, we collected 938 invertebrate species, including 431 polychaetes, 270 crustaceans, 171 mollusks, and 38 echinoderms in 123 samples. More than any other taxa, the crustaceans characterized the most unique and interesting community patterns along the continental margin of the Monterey Bay area.

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.

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.

Few studies have addressed the spatial and temporal variability in seagrass seed banks. For small-seeded species in particular, seed banks are hard to sample quantitatively because of the difficulty in separating small seeds from sediment. Halophila decipiens is a highly fecund and cosmopolitan seagrass species, occupying niches which other larger-sized perennial species cannot utilize. Although many studies have suggested H. decipiens meadows are annual and depend on seed banks to re-establish, none have quantitatively examined this necessary life history component. To process the number of samples required to adequately address questions of spatial and temporal variability in H. decipiens seed banks, we developed a density separation technique which removes seeds from sediment and allows easier enumeration. Sediment samples were treated with refrigerated Ludox, a colloidal silica. The colloidal silica supernatant and two surface sediment rinses were examined for the presence of seeds. Our protocol removed between 78 and 100% of seeds from sediment, with a mean removal efficiency of 89%. Use of this method increased our sample processing capability from 4 to 20 samples per day.

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.

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.