Understanding Environmental Changes in Temperate Coastal Seas: Linking Models of Benthic Fauna to Carbon and Nutrient Fluxes

Abstract

Coastal seas are highly productive systems, providing an array of ecosystem services to humankind, such as processing of nutrient effluents from land and climate regulation. However, coastal ecosystems are threatened by human-induced pressures such as climate change and eutrophication. In the coastal zone, the fluxes and transformations of nutrients and carbon sustaining coastal ecosystem functions and services are strongly regulated by benthic biological and chemical processes. Thus, to understand and quantify how coastal ecosystems respond to environmental change, mechanistic modeling of benthic biogeochemical processes is required. Here, we discuss the present model capabilities to quantitatively describe how benthic fauna drives nutrient and carbon processing in the coastal zone. There are a multitude of modeling approaches of different complexity, but a thorough mechanistic description of benthic-pelagic processes is still hampered by a fundamental lack of scientific understanding of the diverse interactions between the physical, chemical and biological processes that drive biogeochemical fluxes in the coastal zone. Especially shallow systems with long water residence times are sensitive to the activities of benthic organisms. Hence, including and improving the description of benthic biomass and metabolism in sediment diagenetic as well as ecosystem models for such systems is essential to increase our understanding of their response to environmental changes and the role of coastal sediments in nutrient and carbon cycling. Major challenges and research priorities are (1) to couple the dynamics of zoobenthic biomass and metabolism to sediment reactive-transport in models, (2) to test and validate model formulations against real-world data to better incorporate the context-dependency of processes in heterogeneous coastal areas in models and (3) to capture the role of stochastic events.

What global biogeochemical consequences will marine animal–sediment interactions have during climate change?

“…Direct human disturbance can also interact with and exacerbate climate change effects on benthic ecosystems (Bindoff et al, 2019). In the coastal zone, these disturbances can take the form of pollution, trawling and dredging, coastal development leading to habitat squeeze and altered hydrography, and excess delivery of nutrients that cause eutrophication and lead to harmful algal blooms and hypoxia (Middelburg and Levin, 2009;Bindoff et al, 2019;Ravaglioli et al, 2019;Ehrnsten et al, 2020). Overfishing and species invasions can also change the composition of benthic species and their interactions with the seafloor (Bindoff et al, 2019).…”

“…Benthic ecology has a long history of studies on seafloor communities and animal-sediment relationships, from Petersen's (1913) initial efforts to understand variation in fisheries to Sanders's (1958) classic paper on feeding modes and sediments and many hundreds of related studies that have attempted to understand the complex relationships between biota and their sedimentary habitats (e.g., Gray, 1974;Rhoads, 1974;Snelgrove and Butman, 1994). More recently, researchers have begun to consider such relationships in the context of climate change (e.g., Smith et al, 2008;Snelgrove et al, 2018;Ehrnsten et al, 2020;Moore and Smale, 2020). Although several studies have documented benthic community response(s) to changing environmental conditions (e.g., warming, acidification, deoxygenation, food availability) in multiple seabed environments (Smith et al, 2008;McClain et al, 2012;Jessen et al, 2017;Sweetman et al, 2017), hereafter referred to as climate change, the implications of these responses for global-scale elemental cycling and OC storage remain underexplored in the study of seafloor sediments, Earth's largest biome.…”

Large-scale effects of benthic fauna on carbon, nitrogen, and phosphorus dynamics in the Baltic Sea

“…The BALTSEM model was neither improved nor worsened by the addition of benthic fauna, according to the performance analyses comparing pelagic variables to observations (Appendix B). This shows that increasing model complexity does not necessarily increase accuracy, especially when the functions and/or variables added are not well known (Ehrnsten et al, 2020b ;Levins, 1966). In general, though, the previous assessments of model performance showing that the model is able to reproduce seasonal and long-term variations in biogeochemical variables and performs well in comparison to other Baltic Sea models, remain valid (Eilola et al, 2011;Gustafsson et al, 2012Gustafsson et al, , 2014Meier et al, 2018;Savchuk et al, 2012).…”

“…Ev en though the importance of benthic fauna for sediment biogeochemistry and benthic -pelagic fluxes has long been recognized (Rhoads, 1974), the combined effects of animal bioturbation and metabolism have seldom been studied together (Ehrnsten et al, 2020b;Middelburg, 2018;Snelgrove et al, 2018). Further, empirical studies of faunal effects often focus on temporally and spatially limited parts of the system, omitting important interactions and variability occurring in natural ecosystems (Snelgrove et al, 2014).…”

Often Overlooked: Understanding and Meeting the Current Challenges of Marine Invertebrate Conservation

“…In the ocean, the major nutrients of carbon, nitrogen, phosphorous, and silicon are moved through biological and physical processes. Nutrient cycling is essential to keeping the balance in marine ecosystems, but many nutrient models and subsequent budget quantification don't include key invertebrates that effectively cycle nutrients (Pitt et al, 2009;Ehrnsten et al, 2020). Relatively understudied, sponges (phylum Porifera) are ubiquitous in the ocean and as suspension feeders, they constitute an important trophic link between benthos and the water column (Maldonado et al, 2011(Maldonado et al, , 2012.…”