Toward Reversal of Eutrophic Conditions in a Subtropical Estuary: Water Quality and Seagrass Response to Nitrogen Loading Reductions in Tampa Bay, Florida, USA

Coastal waters have been significantly influenced by increased inputs of nutrients that have accompanied population growth in adjacent drainage basins. In Tampa Bay, Florida, USA, the population has quadrupled since 1950. By the late 1970s, eutrophic conditions including phytoplankton and macroalgal blooms and seagrass losses were evident. The focus of improving Tampa Bay is centered on obtaining sufficient water quality necessary for restoring seagrass habitat, estimated to have been 16,400 ha in 1950 but reduced to 8800 ha by 1982. To address these problems, targets for nutrient load reductions along with seagrass restoration goals were developed and actions were implemented to reach adopted targets. Empirical regression models were developed to determine relationships between chlorophyll a concentrations and light attenuation adequate for sustainable seagrass growth. Additional empirical relationships between nitrogen loading and chlorophyll a concentrations were developed to determine how Tampa Bay responds to changes in loads. Data show that when nitrogen load reduction and chlorophyll a targets are met, seagrass cover increases. After nitrogen load reductions and maintenance of chlorophyll a at target levels, seagrass acreage has increased 25% since 1982, although more than 5000 ha of seagrass still require recovery. The cooperation of scientists, managers, and decision makers participating in the Tampa Bay Estuary Program’s Nitrogen Management Strategy allows the Tampa Bay estuary to continue to show progress towards reversing many of the problems that once plagued its waters. These results also highlight the importance of a multi-entity watershed management process in maintaining progress towards science-based natural resource goals.     

Underwater video as a monitoring tool to detect change in seagrass cover

To date seagrass monitoring has involved the removal of seagrass from its environment. In fragile or highly disturbed systems, monitoring using destructive techniques may interfere with the environment or add to the burden of disturbance. Video photography is a form of non-destructive monitoring that does not require the removal of seagrass or interference with the environment and has the potential to be a valuable tool in monitoring seagrass systems. This study investigated the efficacy of video photography as a tool for detecting change in seagrass cover, using the temperate Australian species Amphibolis antarctica (Labill.) Sonder ex Aschers. Using visual and random point estimates of seagrass cover from video footage, it was possible to determine the minimum sample size (number of random video frames) needed to detect change in seagrass cover, the minimum detectable change in cover and the probability of the monitoring design committing a Type II error. Video footage was examined at three scales: transects (m apart), sites (km apart) and regions (tens of km apart). Using visual and random point estimation techniques, a minimum sample size of ten quadrats per transect was required to detect change in uniform and variable seagrass cover. With ten quadrats it was possible to identify a minimum detectable change in cover of 15% for uniform and 30% for variable seagrass cover. Power analysis was used to determine the probability of committing a Type II error from the data. Region level data had low power, corresponding to a high risk of committing a Type II error. Site and transect level data had high power corresponding to a low risk of committing a Type II error. Based on this study's data, managers using video to monitor for change in seagrass cover are advised to use data from the smaller scale, for example, site and transect level data. By using data from the smaller scale, managers will have a low risk of incorrectly concluding there has not been a disturbance when one has actually occurred.     

Characterization of the benthic vegetation in the Farwà Lagoon (Libya)

This study forms part of the Action Plan for the Conservation of Marine Vegetation in the Mediterranean SEa (United Nation Environmental Program). It was carried out in June 2000 in the Farwà Lagoon, Libya. The mapping of the main benthic vegetation was achieved by compiling the field observations (transect method), and remote sensing of SPOT satellite images. The phytobenthos in the Farwà lagoon covers an area of 1820 ha (65%). Three benthic macrophyte species dominate, namely the marine phanerogamsCymodocea nodosa andPosidonia oceanica, and the algaCaulerpa prolifera. DeadPosidonia oceanica leaves (litter) form veritable mounds in the vicinity of the openings leading to open sea. These leaves, which come from the coastal sea, are brought into the lagoon by currents and tides; their decomposition will lead to high oxygen consumption and the release of hydrogen sulphide. The phenological data ofPosidonia oceanica shoots sampled in the lagoon are similar to those from other stations in the Mediterranean. Conversely, the lepidochronological parameters of shoots sampled in the central part of the lagoon exhibit values that are substantially higher than those generally recorded in the Mediterranean. The mean number of leaves produced annually is 9.9 (mean value for the Mediterranean: 7.5) and the rhizome growth rate is of 35.7 mm.yr⁻¹ (mean value for the Mediterranean: 7.5 mm.yr⁻¹). This hypersaline environment would seem to provide optimum growth conditions for the speciesPosidonia oceanica.     

Survival and growth of transplants of laboratory raised axenic seedlings of Enhalus acoroides (L.f.) Royle and field-collected plants of Syringodium isoetifolium (Aschers.) Dandy, Thalassia hemprichii (Ehrenb.) Aschers. and Halodule pinifolia (Miki) den Hartog

Experimental transplantation investigations, using laboratory raised axenic seedlings of Enhalus acoroides and natural populations of Syringodium isoetifolium, Thalassia hemprichii and Halodule pinifolia in the Gulf of Mannar Marine Biosphere Reserve, found that the denuded seagrass ecosystem of this Gulf can effectively be restored with plug and turfs methods of seagrass transplantation. Axenically developed E. acoroides, transplanted by the staples method, established by adapting to the prevailing environmental conditions. 0% seedlings “washed ashore” when the staples method was adopted using ‘L’ shaped bamboo sticks for transplanting E. acoroides and S. isoetifolium seedlings. This suggests that the seagrass transplantation using “L” shaped bamboo sticks, as staples will be technically feasible and eco-friendly for future seagrass transplantation programmes. Substratum type, duration of low tide exposure and environmental parameters like surface water temperature and turbidity are key parameters determining the success of the transplantation attempts.     

An ecosystem perspective on potential impacts of drilling fluid discharges on seagrasses

Potential effects of oil drilling fluid discharges uponThalassia seagrass ecosystems were examined using seagrass core microcosms. Observed experimental effects, summarized in this article, included changes in both autotrophic (Thalassia and epiphyte) and heterotrophic (dominant benthic macroinvertebrates) species, and the processes of primary productivity and decomposition. The physical disturbance related to greater turbidity and sedimentation caused some effects, while others seemed a direct response to the toxic constituents of drilling fluids. Using these experimental results and the case ofThalassia and drilling fluids as a case study, we explore general methodological and philosophical issues for ecotoxicology and, furthermore, focus upon the challenge of providing a scientific basis for judging acceptability of environmental changes likely to ensue from human activities.     

Ecological research for integrated coastal zone management: Introduction

Two Special Features on integrated coastal zone management, especially along the Mediterranean Sea, result from a MeDCOAST conference held in Hammamet (Tunisia). 20–25 October 2001. In this first Special Feature some papers are presented on ecological and biological research related to integrated coastal zone management. All over Europe coastal environments are threatened by human activities such as urbanization, industrial development, fisheries, aquaculture, recreation and tourism. Research has to be developed that can be applied to similar case studies in different countries. Methods of monitoring are necessary and baseline data have to be available in order to judge the significance of changes in the abjotic and biotic environment. Examples of studies included in this Special Feature are mainly from southern banks of the Mediterranean Sea but there is also an example from Estonia and one from the Canary Islands.     

Metal contamination of Posidonia oceanica meadows along the Corsican coastline (Mediterranean)

The aim of this study is to determine metal (Cd, Co, Cr, Hg, Ni, Pb) concentrations in Posidonia oceanica tissues along the Corsican coastline. The results show that except for Cr, all the metals are preferentially accumulated in the blades; this is particularly interesting as it means that future metal analyses may be carried out only on the blades avoiding thus the removal of the shoots. Moreover, they show that metal concentrations may reflect the "background noise" of the Mediterranean Sea. Station 15 (Canari) can however be distinguished from the others due to its high Co, Cr and Ni concentrations. This result may be related to the presence of a previous asbestos mine, located near this station. Therefore, this study reinforces the usefulness and the relevance of Posidonia oceanica as a tracer of spatial metal contamination and as an interesting tool for water quality evaluation.