Increased sea-surface temperatures linked to warming climate threaten coral reef ecosystems globally. To better understand how corals and their endosymbiotic dinoflagellates (Symbiodinium spp.) respond to environmental change, tissue biomass and Symbiodinium density of seven coral species were measured on various reefs approximately every four months for up to thirteen years in the Upper Florida Keys, United States (1994–2007), eleven years in the Exuma Cays, Bahamas (1995–2006), and four years in Puerto Morelos, Mexico (2003–2007). For six out of seven coral species, tissue biomass correlated with Symbiodinium density. Within a particular coral species, tissue biomasses and Symbiodinium densities varied regionally according to the following trends: Mexico≥Florida Keys≥Bahamas. Average tissue biomasses and symbiont cell densities were generally higher in shallow habitats (1–4 m) compared to deeper-dwelling conspecifics (12–15 m). Most colonies that were sampled displayed seasonal fluctuations in biomass and endosymbiont density related to annual temperature variations. During the bleaching episodes of 1998 and 2005, five out of seven species that were exposed to unusually high temperatures exhibited significant decreases in symbiotic algae that, in certain cases, preceded further decreases in tissue biomass. Following bleaching, Montastraea spp. colonies with low relative biomass levels died, whereas colonies with higher biomass levels survived. Bleaching- or disease-associated mortality was also observed in Acropora cervicornis colonies; compared to A. palmata, all A. cervicornis colonies experienced low biomass values. Such patterns suggest that Montastraea spp. and possibly other coral species with relatively low biomass experience increased susceptibility to death following bleaching or other stressors than do conspecifics with higher tissue biomass levels.
Groundwater-surface water (GW-SW) interactions represent an important, but less visible, linkage in lake ecosystems. Periphyton is most abundant at the GW-SW interface and can rapidly assimilate nutrients from the water column. Despite the importance of periphyton in regulating whole-lake metabolism, they are less well studied or monitored in comparison with planktonic taxa and pelagic systems. This is in stark contrast to studies of flowing waters and wetlands, where variability in GW-SW connectivity and periphyton productivity is more often incorporated into study designs. To bridge the gap between groundwater's influence on lake benthic communities, this synthesis aims to prime researchers with information necessary to incorporate groundwater and periphyton sampling into lake studies and equip investigators with tools that will facilitate crossdisciplinary collaboration. Specifically, we (1) propose how to overcome barriers associated with studying littoral ecological-hydrological dynamics; (2) summarize field, laboratory, and modeling techniques for assessing spatiotemporal periphyton patterns and benthic hydrological fluxes; and (3) identify paths for hydrological techniques to be incorporated into ecological studies, deepening our understanding of whole-lake ecosystem function. We argue that coupling hydrological and periphyton measurements can yield dualistic insights into lake ecosystem functioning: how benthic periphyton modulate constituents within groundwater, and conversely, the extent to which constituents in groundwater modulate the productivity of periphyton assemblages. We assert that priming ecologists and hydrologists alike with a shared understanding of how each discipline studies the nearshore zone presents a tangible path forward for both integrating these disciplines and further contextualizing lake processes within the limnological landscape.
Road salt application is a necessary component of winter road maintenance but comes with an environmental cost. Salts are transported via stormwater drainage or overland and soil throughflow to surface waterbodies, where excess ions create unfavorable or even uninhabitable conditions for freshwater organisms. Soils may retain salts during the process of overland and subsurface flow, thus acting as reservoirs that slow the transport of salt into freshwaters. Understanding the capacity and consistency of anthropogenic salt storage in urban soils may allow us to discover when and where deicing salt applications are most harmful. This article investigates the degree to which soils across a heterogeneous urban landscape retain salts. We measured the electrical conductivity (EC) of soils in an urban setting. Land covers included forests, grasslands, open spaces, low- and medium-density developments and along roadsides. We found that across land-cover types, soil carbon and porosity were correlated to EC in late summer, which suggests that pore space is an important and long-lasting reservoir for salt. In addition, more developed areas, had higher mean soil EC and greater EC variability within and between sites, with 75% of overall variance occurring within individual sites. We hypothesize that this within-site heterogeneity is driven by anthropogenic modifications to salt inputs and soil characteristics. The high EC variance in highly developed urban soils is a previously undiscussed phenomenon and highlights the fine-scale complexity of heterogeneous urban landscapes and the need for high-resolution sampling to accurately characterize urban ecosystems.
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