Mark S. Fonseca

Faunal response to fragmentation in seagrass habitats: implications for seagrass conservation

Fragmentation in seagrass systems results in changes to landscape features that may have implications for fauna. We examine published studies to identify whether faunal abundance shows any relationship with patch size of seagrass beds, suggesting preferential use of the edge or interior by seagrass associated taxa. In a series of studies in Tampa Bay, FL, we also examined: (1) the relationship between abundance of both fish and amphipod fauna and seagrass patch size in 24 seagrass (Halodule wrightii) beds (5–93 m2) in 1994 and 1995; (2) whether abundance of the infaunal polychaete, Kinbergonuphis simoni, was significantly different within the 1 m edge versus interior of two seagrass (Halodule wrightii ) beds of similar size and age; and (3) compared the spatial distribution of the tube-building polychaete, Spirorbis spirillum, in Thalassia testudinum seagrass beds in two sites in Tampa Bay. Neither review of the published literature on fauna and seagrass patch size nor the data presented from our Tampa Bay studies suggest that habitat fragmentation has any consistent impact on fauna over the spatial scales that have been investigated. Likewise, little evidence exists that identifies any taxonomic group to be fragmentation sensitive in that they differentially utilized edge or core areas of seagrass patches. While we did detect a reduction of both infaunal and epibenthic polychaetes at the 1 m edges of seagrass beds relative to interior areas, the reduction was not similar along all edges. Events such as seagrass die off or a high incidence of boat propeller-damage over an extensive area may be required to detect effects of habitat fragmentation on fauna. Given that patch size alone does not appear to adequately account for variation in faunal abundance, we suggest that restoration efforts might best focus upon locating areas with similarity of landscape context or patch characteristics other than patch size.

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

Abstract 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.

A comparison of threats, vulnerabilities and management approaches in global seagrass bioregions

Global seagrass habitats are threatened by multiple anthropogenic factors. Effective management of seagrasses requires information on the relative impacts of threats; however, this information is rarely available. Our goal was to use the knowledge of experts to assess the relative impacts of anthropogenic activities in six global seagrass bioregions. The activities that threaten seagrasses were identified at an international seagrass workshop and followed with a web-based survey to collect seagrass vulnerability information. There was a global consensus that urban/industrial runoff, urban/port infrastructure development, agricultural runoff and dredging had the greatest impact on seagrasses, though the order of relative impacts varied by bioregion. These activities are largely terrestrially based, highlighting the need for marine planning initiatives to be co-ordinated with adjacent watershed planning. Sea level rise and increases in the severity of cyclones were ranked highest relative to other climate change related activities, but overall the five climate change activities were ranked low and experts were uncertain of their effects on seagrasses. The experts’ preferred mechanism of delivering management outcomes were processes such as policy development, planning and consultation rather than prescriptive management tools. Our approach to collecting expert opinion provides the required data to prioritize seagrass management actions at bioregional scales.

The use of fertilizer to enhance growth of transplanted seagrasses Zostera marina L. and Halodule wrightii Aschers

Abstract The effect of two slow release fertilizers on the survival and growth of transplants of two seagrasses, Zostera marina L. and Halodule wrightii Aschers was examined. The two fertilizers, an unbalanced nitrogen, phosphorus, and potassium formulation (18-0-0) and a balanced (14-14-14) formulation, were applied to bare root transplant units (PU) of each seagrass at three doses, 10, 90, and 170 g per PU. Survival and growth of the transplants, nutrient release from the fertilizers, and several environmental characteristics of the study sites were examined. Nitrogen enrichment vegetative reproduction, the rate of area covered and leaf growth in a fall transplant of Z. marina , but only moderately stimulated growth in the spring, confirming that nitrogen may limit the rate of development of newly established populations of Z. marina . There was no effect of nitrogen on survival of Z. marina nor on the growth and survival of H. wrightit transplants. No phosphorus was released from the balanced fertilizers in the spring and fall experiments and no nitrogen was released from the unbalanced formulation in the spring Z. marina experiment. Therefore, it was not possible to examine the effect of nitrogen and phosphorus interactions on plant growth and vegetative reproduction. Nitrogen enrichment may be used to stimulate shoot growth of Z. marina transplants, and we suggest alternative procedures of fertilizer application to overcome problems of nutrient release.

A Cost-evaluation Technique for Restoration of Seagrass and Other Plant Communities

Coastal habitat loss must be reduced either through conservation or mitigative efforts. Implementation of mitigation depends largely on accurate cost-assessment of the projects that are involved. We centre our discussion here on seagrass transplanting as an exemplary mitigative tool. The technology of restoring seagrass communities has received increasing attention in recent years. However, the methods used have had varying degrees of success, a largely unknown factor being the cost of the technique that is used. In this paper is presented a universal format that includes consideration of the essential factors in our costanalysis, such as planning, planting, and monitoring activities, geographic location, tidal influence, labour, and materials (both expendable and non-expendable). Cost per (successfully established) shoot or seed or fruit is recommended as the best indicator of cost effectiveness for a given technique. Incorporation and presentation of this information is urged in future projects to motivate wider application of seagrass and other essential plantcommunity restoration.