The Function of Marine Critical Transition Zones and the Importance of Sediment Biodiversity

Abstract

Estuaries and coastal wetlands are critical transition zones (CTZs) that link land, freshwater habitats, and the sea. CTZs provide essential ecological functions, including decomposition, nutrient cycling, and nutrient production, as well as regulation of fluxes of nutrients, water, particles, and organisms to and from land, rivers, and the ocean. Sedimentassociated biota are integral to these functions. Functional groups considered essential to CTZ processes include heterotrophic bacteria and fungi, as well as many benthic invertebrates. Key invertebrate functions include shredding, which breaks down and recycles organic matter; suspension feeding, which collects and transports sediments across the sediment-water interface; and bioturbating, which moves sediment into or out of the seabed. In addition, macrophytes regulate many aspects of nutrient, particle, and organism dynamics above-and belowground. Animals moving within or through CTZs are vectors that transport nutrients and organic matter across terrestrial, freshwater, and marine interfaces. Significant threats to biodiversity within CTZs are posed by anthropogenic influences; eutrophication, nonnutrient pollutants, species invasions, overfishing, habitat alteration, and climate change affect species richness or composition in many coastal environments. Because biotic diversity in marine CTZ sediments is inherently low whereas their functional significance is great, shifts in diversity are likely to be particularly important. Species introductions (from invasion) or loss (from overfishing or habitat alteration) provide evidence that single-species changes can have overt, sweeping effects on CTZ structure and function. Certain species may be critically important to the maintenance of ecosystem functions in CTZs even though at present there is limited empirical evidence that the number of species in CTZ sediments is critical. We hypothesized that diversity is indeed important to ecosystem function in marine CTZs because high diversity maintains positive interactions among species (facilitation and mutualism), promoting stability and resistance to invasion or other forms of disturbance. The complexity of interactions among species and feedbacks with ecosystem functions suggests that comparative (mensurative) and ma- 430nipulative approaches will be required to elucidate the role of diversity in sustaining CTZ functions.

Bridging Ridge-to-Reef Patches: Seamless Classification of the Coast Using Very High Resolution Satellite

“…Spatial interfaces lying between land and marine areas are critical zones, which provide ecological functions crucial to human populations, such as disturbance regulation, water supply, nutrient cycling and waste treatment [1]. Coral reefs and mangroves, consisting of the tropical part of the transitional land-to-sea area, are assessed to be the most valuable ecosystems worldwide that ensure recreation and waste treatment services, respectively [2].…”

“…The specific goals were: (1) to demonstrate that the spectral signatures of nine terrestrial and twelve marine classes are discernible using the WV2 and support vector machine (SVM) algorithm, (2) to assess what effect the addition of WV2 novel bands and associated spectral indices have on the classification accuracy of a reliable coastal zone map, (3) to evaluate mapping the seamless coastal zone at a very high spatial resolution using Pan-sharpened WV2 imagery and (4) to analyze whether examining the coast integrity at various levels alters the classification accuracy.…”

Aquatic macrophytes as biological indicators of environmental conditions of rivers in north-eastern Spain

“…Aquatic macrophytes can obtain nutrients from the sediment as well as directly from the water itself (Denny 1972, Chambers et al 1989, Levin et al 2001, Schulz et al 2003, Thiébaut & Muller 2003. Consequently, the availability of sediment nutrients may limit the growth and distribution of macrophytes (Spencer & Ksander 2003), thus complicating interpretation of the data concerning them (Kelly & Whitton 1998).…”

Variation in hierarchical guild structure between two bird assemblages of a wetland in the Mexican Pacific

“…However, most frugivorous birds also consume invertebrates and the observed pattern may reflect forest frugivores foraging for invertebrates in the structurally similar mangrove canopy. In Tonameca, the high abundance in shore-line and wading insectivores was probably associated with tidal sediments containing Oligochaeta, Polychaeta, Bivalvia and Crustacea (Stoner & Acevedo, 1990;Levin et al, 2001). Granivore abundance was likely linked to marsh vegetation of early successional stages in estuarine environments (Gill, 2012), whereas halophytic seed-bearing ground flora is shaded out in mangroves (Snedaker & Lahmann, 1988).…”