Seagrass ecosystem multifunctionality under the rise of a flagship marine megaherbivore

Abstract

Large grazers (megaherbivores) have a profound impact on ecosystem functioning. However, how ecosystem multifunctionality is affected by changes in megaherbivore populations remains poorly understood. Understanding the total impact on ecosystem multifunctionality requires an integrative ecosystem approach, which is especially challenging to obtain in marine systems. We assessed the effects of experimentally simulated grazing intensity scenarios on ecosystem functions and multifunctionality in a tropical Caribbean seagrass ecosystem. As a model, we selected a key marine megaherbivore, the green turtle, whose ecological role is rapidly unfolding in numerous foraging areas where populations are recovering through conservation after centuries of decline, with an increase in recorded overgrazing episodes. To quantify the effects, we employed a novel integrated index of seagrass ecosystem multifunctionality based upon multiple, well-recognized measures of seagrass ecosystem functions that reflect ecosystem services. Experiments revealed that intermediate turtle

Individual variation in home‐range across an ocean basin and links to habitat quality and management

“…This finding adds to the growing evidence of the importance of safe resting areas and more generally for the important role of the risk of predation in shaping animal movements, not just with sea turtles (e.g. Christianen et al., 2023; Heithaus et al., 2007) but more broadly across marine taxa (Lubitz et al., 2022).…”

“…Home-ranges for individual turtles were calculated for 50% and 95% probability contours (hereafter UD50 and UD95), representing core and whole home-ranges respectively, using the biased random bridge (BRB) method (Benhamou, 2011) in R version 3.5.1 (R Development Core Team, Vienna, Austria) with package adehabitatHR v0.4.18 (Calenge, 2023). The BRB method assumes an advective-diffusive movement process between locations where movement direction is biased towards preferred areas, thereby incorporating the ability for preferential selection by individuals of more attractive areas within home-ranges.…”

“…By accounting for the dynamic nature of successive locations, the BRB approach provides a reliable way of estimating home-range utilisation distributions given the often serially correlated nature of location data (Benhamou, 2011). The diffusion parameter D for foraging locations was estimated using a maximumlikelihood function (Calenge, 2023), with the maximum time threshold for inclusion of path segments between successive locations set to 12 h, based on the rate at which locations were obtained.…”

“…Green turtles ( Chelonia mydas ) are a predominantly marine herbivore that are a keystone species, often feeding on seagrass and shaping seagrass ecosystems through their grazing (Christianen et al., 2023; Fourqurean et al., 2019; Gangal et al., 2021). Recently a conservation concern has been highlighted in marine environments with green turtles overgrazing and hence destroying seagrass meadows, which they then abandon (Christianen et al., 2021).…”

Multifunctional redundancy: Impossible or undetected?

“…Gamfeldt & Roger, 2017 ; Hector & Bagchi, 2007 who used maxima from the BIODEPTH experiment; Spehn et al, 2005 ). Still others are ambiguous about their methods (Christianen et al, 2023 ; Moi et al, 2021 ). To progress, Byrnes et al ( 2014 ) suggested that maximum functioning should be measured as an average of the highest performing communities (e.g.…”