The influence of dietary elemental contents on consumer stoichiometry was investigated in selected and combined soft tissues (as a proxy of the whole individual) of the omnivorous sea urchin, ...Lytechinus variegatus. We raised urchins for 4 months in controlled seawater tanks using three different diets with different nutritional contents (from lower to higher: seagrass, red macroalgae, and a formulated diet). Individuals fed the different diets varied an average of 19.7, 19.4, and 38 % in C:N, C:P, and N:P ratios, respectively, with stronger temporal variability for C:P and N:P ratios across tissues and whole individuals. This resulted in homeostasis parameters (1/H) of −0.45, 0.09, and 0.38, respectively, for C:N, C:P, and N:P, indicative of homeostatic to weakly homeostatic organisms, at least for C:P and N:P ratios. Individuals fed the nutrient-rich formulated diet had higher growth rates (14 ± 0.83 g WW month⁻¹) than those fed macroalgae or seagrass (9.3 ± 0.57 and 3.4 ± 0.33 g WW month⁻¹, respectively). However, rapid body increments in more nutritional diets caused both a decrease in the %N and an increase in the %P of soft tissues, which resulted in significant but opposite effects of diet stoichiometry and growth in sea urchin C:N (R = −0.74 and R = 0.93, for diet and growth effects, respectively) and N:P ratios (R = 0.60 and R = −0.63, also, respectively, for diet and growth effects). Among potential compensatory mechanisms helping to preserve certain levels of homeostasis, ingestion rates (g WW diet per g WW of urchin) were higher for seagrass and macroalgae diets than for the nutrient-rich formulated diet. In contrast, absorption and growth efficiencies displayed significant negative associations with nutrient contents in diets and did not exhibit nutritional compensation. Overall, our results suggest that resource stoichiometry strongly determines the growth rate of individuals (R = 0.88, P < 0.01), and moderate variability in C:N:P ratios of sea urchins possibly arise from differences in the allocation of proteins and RNA to body components, similarly to what has been proposed by the growth rate hypothesis.
A decade since coastal restoration began across U.S. Gulf of Mexico states after the Deepwater Horizon oil spill, it is timely to examine its collective effects relative to intended outcomes. Through ...2021, allocated funds for 570 projects by state, federal, non-profit, and other entities approached half the unprecedented recovery settlements. The need for synthesis of restoration results to inform further expenditures is urgent. Yet, unlike the western and eastern U.S. coasts, this region lacks an entity charged with conducting environmental synthesis. Synthesis of the cumulative effects of large-scale restoration will encompass three challenging components: (1) understanding and accounting for synergistic and antagonistic effects; (2) incorporating long-term environmental trends and acute events; and (3) addressing the relative scale of restoration effects.
Quantifying the nursery role of habitats or locations in supporting fisheries is central to understanding population-scale animal−habitat relationships, and in guiding ecosystem-based management. We ...assessed the nursery role of northern Gulf of Mexico seagrass meadows for gray snapper, lane snapper, and gag recruiting to Alabama’s extensive offshore reef complex. We accomplished this using broadscale juvenile trawl surveys and geochemical tags—indicative of past habitat use—stored in the otoliths of > 2200 fishes. These natural tags revealed that 47−61% of snapper and gag recruits to Alabama reefs originated in Florida panhandle seagrass nurseries. Seagrass meadows in Alabama and Mississippi were also important nurseries for snappers and gag, contributing 26−46% of recruits. Despite high juvenile snapper and gag catches along the extensive Chandeleur Islands, Louisiana, relatively few of those fishes recruited to Alabama’s reefs (< 13% of total recruits, across species), although they may have recruited to populations outside our sampling domain. Beyond the applied value of these data for resource management (i.e. interstate connectivity), our findings highlight broadscale drivers of the nursery role of juvenile habitats for coastal marine populations. These factors include: (1) juvenile habitat extent (i.e. extensive Florida panhandle meadows sourced the most recruits for Alabama fisheries); (2) proximity between juvenile and adult habitats (i.e. highest unit-area contribution from Alabama− Mississippi meadows); and (3) unidirectional, alongshore migration of egressing juveniles (i.e. primarily east-to-west movement, enhancing connectivity with Florida panhandle nurseries, and dampening connectivity with Chandeleur nurseries).
Four decades of research findings on the ecology of seagrasses and their animal and plant associates are described here, along with some of the major changes and advances that have taken place in our ...understanding of the inner workings of these amazingly productive and diverse ecosystems. Of primary importance are shifts in the recognition of: 1) the importance of the nursery role of seagrasses and how it can be quantified; 2) the importance of direct herbivory in the trophic ecology of seagrass-dominated ecosystems; and 3) the primacy of consumer effects in determining the abundance of algal epiphytes that colonize leaves and other aboveground seagrass tissues. Exciting new areas of investigation include elucidating rhizosphere interactions, including developing a deeper understanding of the importance of nutrient foraging by seagrass roots, and of the microbes in the sediments that fix nitrogen and reduce toxic hydrogen sulfide concentrations. Increased understanding of the roles of genetic diversity and the size and integration of seagrass clones, as well as additional and better evaluations of the relative value of different seagrass meadows as finfish nurseries are also needed. Of great importance for seagrass researchers of the future is spending large amounts of time in the field developing a thorough understanding of the natural history of the many and varied inhabitants of seagrass meadows. The knowledge gained by this investment of time will be essential for the development of meaningful, new hypotheses and the means for testing them.
Salt marshes face chronic anthropogenic impacts such as relative sea level rise and eutrophication, as well as acute disturbances from tropical storms that can affect the productivity of these ...important communities. However, it is not well understood how marshes already subjected to eutrophication and sea level rise will respond to added effects of episodic storms such as hurricanes. We examined the interactive effects of nutrient addition, sea level rise, and a hurricane on the growth, biomass accumulation, and resilience of the saltmarsh cordgrass Spartina alterniflora in the Gulf of Mexico. In a microtidal marsh, we manipulated nutrient levels and submergence using marsh organs in which cordgrasses were planted at differing intertidal elevations and measured the impacts of Hurricane Isaac, which occurred during the experiment. Prior to the hurricane, grasses at intermediate and high elevations increased in abundance. After the hurricane, all treatments lost approximately 50% of their shoots, demonstrating that added nutrients and elevation did not provide resistance to hurricane disturbance. At the end of the experiment, only the highest elevations had been resilient to the hurricane, with increased above- and belowground growth. Added nutrients provided a modest increase in above- and belowground growth, but only at the highest elevations, suggesting that only elevation will enhance resilience to hurricane disturbance. These results empirically demonstrate that S. alterniflora in microtidal locations already subjected to submergence stress is less able to recover from storm disturbance and suggests we may be underestimating the loss of northern Gulf Coast marshes due to relative sea level rise.
Eutrophication is a widespread phenomenon that disrupts natural ecosystems around the globe. Despite the general recognition that ecosystems provide many services and benefits to humans, little ...effort has been made to address how increasing anthropogenic eutrophication affects those services. We conducted a field experiment to determine the effect of nutrient enrichment on five ecological services provided by a model coastal system, a shallow seagrass community near Mobile Bay, Alabama (USA): (1) the provision of shelter for fauna; (2) the quality of food provided to first-order consumers; (3) quantity of food provision to first-order consumers and O
2
/CO
2
exchange; (4) producer carbon and nitrogen storage, and (5) water clarity. The results showed a severe negative impact on seagrass density and biomass, which greatly reduced the structural complexity of the community and provision of shelter to fauna. Water clarity and the standing stock of producer carbon were reduced in the fertilized area in comparison with the control area. In contrast, nutrient addition did not affect in any consistent way the total quantity of food available for first-order consumers, the net exchange of O
2
/CO
2
, or the standing stock of producer nitrogen in the community. The nutritional quality of the food available for first-order consumers increased with fertilization. These results show that the impacts of nutrient enrichment on the services provided by natural systems may be disparate, ranging from negative to positive. These findings suggest that management policies for anthropogenic eutrophication will depend on the specific ecosystem service targeted. In the case of shallow seagrass beds, the loss of biogenic habitat and drastic impacts on commercially important fauna may be sufficiently alarming to warrant rigorous control of coastal eutrophication.
Climate-driven range shifts can result in altered mixtures of foundation species that can affect ecosystem structure and function. Higher diversity mixed assemblages may moderate disturbance impacts, ...yet this prediction has rarely been tested. The
Deepwater Horizon
oil spill provided an opportunity to examine the effects of salt marsh foundation species identity and composition on the response of both plant and faunal communities to oil disturbance. In the northern Gulf of Mexico, salt marshes are typically dominated by the foundation species smooth cordgrass,
Spartina alterniflora
. However, the sub-tropical black mangrove,
Avicennia germinans
, is expanding northward and increasingly growing with, and even replacing,
Spartina
. Based on a series of field surveys in the Chandeleur Islands, Louisiana, we found that oil exposure had few impacts on the plant community 5 yr post-oiling, though oil disturbance shifted the interaction among foundation species, increasing
Avicennia
’s competitive advantage and likely enhancing mangrove expansion. In contrast, abundance of the epibenthic animal community was reduced by ~30% and community composition was altered at oiled sites. Mixed foundation species assemblages provided few reductions in oil impacts within either trophic level. Strong habitat associations of epibenthic taxa, coupled with oil effects on individual foundation species, likely suppressed any advantage of mixed vegetation on the associated fauna. Our survey highlights that plant and epibenthic animal responses to disturbance can be decoupled, emphasizing the importance of examining both simultaneously to better understand and predict long-term responses.
A recent National Academies consensus report addresses monitoring and assessment of cumulative effects of large-scale and multiple restoration projects within the context of long-term environmental ...change. Fines and penalties from the
Deepwater Horizon
oil spill in the Gulf of Mexico (GoM) have supported hundreds of restoration projects at spatial scales not often possible in the past. Here, the report committee members and staff provide personal reflections from our time working on the study. We found that gaps in data collection, issues with data accessibility, and a lack of synthesis and analysis are hindering the ability to answer a basic question: What are the impacts of these many restoration efforts on improving ecosystem health and productivity in the GoM at the regional and Gulf wide scale? Restoration efforts are occurring in environments where many trends are changing and exhibiting higher variability than in the past, suggesting that previously successful restoration practices may no longer be adequate to compensate for the effects of environmental changes and variability. Our proposed approach to these challenges includes employing emerging monitoring technologies; using conceptual models; devising an adaptive management framework; rethinking restoration outcome goals; assessing cumulative effects; and undertaking rigorous synthesis and analysis of existing information on long-term environmental trends and restoration efforts. Restoration scientists and practitioners working in the GoM have an unprecedented opportunity to demonstrate large-scale environmental recovery if advances in monitoring, synthesis, assessment, and action are taken quickly. We are cautiously optimistic that, with mid-course adjustments, continued progress toward large-scale environmental recovery is possible.
