Marine protected areas increase temporal stability of community structure, but not density or diversity, of tropical seagrass fish communities

Abstract

Marine protected areas (MPAs) have been shown to increase long-term temporal stability of fish communities and enhance ecosystem resilience to anthropogenic disturbance. Yet, the potential ability of MPAs to buffer effects of environmental variability at shorter time scales remains widely unknown. In the tropics, the yearly monsoon cycle is a major natural force affecting marine organisms in tropical regions, and its timing and severity are predicted to change over the coming century, with potentially severe effects on marine organisms, ecosystems and ecosystem services. Here, we assessed the ability of MPAs to buffer effects of monsoon seasonality on seagrass-associated fish communities, using a field survey in two MPAs (no-take zones) and two unprotected (open-access) sites around Zanzibar (Tanzania). We assessed the temporal stability of fish density and community structure within and outside MPAs during three monsoon seasons in 2014–2015, and investigated several possible mechanisms that could regulate temporal stability. Our results show that MPAs did not affect fish density and diversity, but that juvenile fish densities were temporally more stable within MPAs. Second, fish community structure was more stable within MPAs for juvenile and adult fish, but not for subadult fish or the total fish community. Third, the observed effects may be due to a combination of direct and indirect (seagrass-mediated) effects of seasonality and, potentially, fluctuating fishing pressure outside MPAs. In summary, these MPAs may not have the ability to enhance fish density and diversity and to buffer effects of monsoon seasonality on the whole fish community. However, they may increase the temporal stability of certain groups, such as juvenile fish. Consequently, our results question whether MPAs play a general role in the maintenance of biodiversity and ecosystem functioning under changing environmental conditions in tropical seagrass fish communities.

The Tropical Seagrass Halophila stipulacea: Reviewing What We Know From Its Native and Invasive Habitats, Alongside Identifying Knowledge Gaps

“…While protecting native seagrasses from global warming is difficult, they can be protected from local stressors such as physical damage (e.g., anchoring), and more importantly from eutrophication. While setting up marine protected areas (MPAs) has become a fundamental strategy in marine conservation, their effectiveness on seagrass meadows has been relatively less studied (reviewed by Alonso Aller et al, 2017). Seagrass MPAs in tropical areas were shown to increase the temporal stability of seagrass-associated fish communities, which in turn enhanced herbivory followed by enhanced seagrass growth rates (Alonso Aller, 2018).…”

Seagrass cover reduction in Zanzibar from 2006 to 2019

“…The coastlines alternate between rocky terrain, sandy beaches, and mangrove forests, and the coastal marine environments often include dense seagrass meadows, algae, and fringing coral reefs. Most seagrass beds and meadows are located in shallow water depths of less than 5 m, and meadows are typically comprised of two or more seagrass species (Aller et al, 2017;Belshe et al, 2018;Ochieng and Erftemeijer, 2003). The dominant seagrass species in Zanzibar include T. ciliatum, T. hemprichi, Cymodocea rotundata, Cymodocea serrulata, and Enhalus acoroides (Lyimo et al, 2008).…”

β‐diversity reveals ecological connectivity patterns underlying marine community recovery: Implications for conservation

“…Yet, ecological spatial connectivity enables a collection of MPAs to function as a network that can bolster the persistence of marine communities at a larger spatial scale given local‐scale natural and anthropogenic disturbances and environmental changes (Carr et al, 2017; Robert et al, 2021). Although MPAs have been recognized to promote the resilience (here referred to as the ability of a system to maintain and/or restore its structure and functions in the face of disturbance; Côté & Darling, 2010; Hodgson et al, 2015) of protected communities by either increasing their resistance to environmental instability or enhancing their recovery after disturbance (e.g., Aller et al, 2017; Babcock et al, 2010; Baskett & Barnett, 2015; Bevilacqua et al, 2006; Bevilacqua, Vellani, et al, 2022; Fraschetti et al, 2013; Roberts et al, 2017), the potential of these effects to extend beyond the reserve boundaries might, indeed, strongly depend on their spatial arrangement (Boero et al, 2016; Steneck et al, 2009). The spatial architecture and connectivity patterns among spatial units underlie the vulnerability of ecosystems in the face of external sources of perturbation (Scheffer et al, 2012), and our understanding of these dynamics is essential to inform conservation and mitigation strategies (Grorud‐Colvert et al, 2014).…”