Recreational activities trigger changes in meiofauna and free-living nematodes on Amazonian macrotidal sandy beaches

Highlights

• The effect of recreational activities on Amazonian beach fauna were evaluated.

• Physical variables were constant in each area, with exception for compaction.

• Meiofauna and Nematode structure varied from before to vacation period.

• Recreational activities modified the Nematode trophic groups.

• Compaction was the principal variable that influenced the fauna.

Abstract

Sandy beaches are key economic assets worldwide, however, recreational activities are an important source of disturbance in these ecosystems. Intensive human use of beaches has a negative effect on benthic communities as it alters species abundance, diversity, and/or distribution. Here, we report the impacts of recreational activities (trampling and vehicles) on meiobenthic communities and nematode assemblages on Amazonian sandy beaches for the first time. For this purpose, samples were carried out in four consecutive months encompassing a period of high visitation peak (one month Before Vacation, During Vacation, and two months After Vacation) on three contrasting beaches regarding disturbances (Urban: Atalaia; Intermediary: Farol-Velho; and Protected: Corvinas) at seven equidistant sampling stations (50 m apart) from the high tide water mark to the swash zone. At each sampling station, three biological samples and sediments samples were collected haphazardly. Also, in each station, the sediment compaction was determined using a manual penetrometer. Overall, physical sediment variables (grain size, sorting) were constant over time in all beaches, whereas differences in intensity of recreational activities and sediment compaction were found between beaches and months. Sediment compaction was considered the most important factor for the differences observed in meiofauna community structure in the study areas, and it was related to intensity of recreational activities. Variations in density and changes in richness between periods were observed in Atalaia and Farol-Velho beaches. On the other hand, Corvinas beach remained the same throughout the study. In the first month after vacation, density and richness were similar to those in the period before vacation, thus indicating that the beaches had recovered in one month. Furthermore, vulnerabilities of Tardigrada and Copepoda, as well as of the Nematoda genera Daptonema, and Chromadorita, indicate that they might be potential indicators of recreational activities.

Introduction

Sandy beaches occur in nearly all coastal zones in temperate and tropical areas (McLachlan and Turner, 1994), and historically these environments play an important role as locations for recreation upon which tourism development has been based (Orams, 2003). Beach recreation includes a wide array of activities, such as camping (Hockings and Twyford, 1997), use of vehicles (Schlacher and Thompson, 2008), and other recreational pursuits (Fanini et al., 2014). Overall, these activities can dramatically alter the natural physical characteristics of beaches through compaction, rutting, and displacement of the sand matrix (Anders and Leatherman, 1987; Priskin, 2003), which influence benthic communities either directly or indirectly (Brosnan and Crumrine, 1994; Brown and Taylor, 1999).

Meiofauna, and particularly free-living marine nematodes, comprise an important component of the benthic biota in both abundance and biomass. They are also closely related to other organisms, playing multiple roles, such as nutrient recycling and transferring energy and matter into benthic and pelagic trophic food webs (see Giere, 2009 for review). The meiobenthic fauna that inhabits sandy beaches is generally dominated by harpacticoid copepods and nematodes, with the dominance of one group over the other depending on sediment grain size (see Giere, 2009 for review). Although the presence of nematodes is independent of sediment characteristics (e.g. grain size, sorting, shape) (Vanaverbeke et al., 2000), they are generally more abundant in fine sands, while harpacticoid copepods are more important in coarse sediments (McLachlan and Brown, 2006; Giere, 2009).

Benthic organisms on sandy beaches are one of the most effective tools for assessing environmental variations in the habitat (Coull and Chandler, 1992; Giere, 2009; Félix et al., 2016). Meiofauna can particularly be used as a biological indicator of anthropogenic impacts due to their small size, simple body structure, high abundance, rapid generation time, and direct benthic development (Kennedy and Jacoby, 1999; Zeppilli et al., 2015). These characteristics make these organisms more suited to be used as bioindicators on sandy beaches when compared to traditionally studied organisms, such as the macro- and megafauna (Kennedy and Jacoby, 1999). In addition, these organisms provide different responses to different types of impacts, both qualitatively and quantitatively, (e.g. density and richness changes, replacement of organisms) (Giere, 2009; Moreno et al., 2011); therefore, it can be used as a sensitive indicator of several impacts (Coull and Chandler, 1992; Sun et al., 2014).

However, most studies on the effects of recreational activities in sandy beaches refer to macrofauna (both at the community and population levels) (Schlacher et al., 2007; Schlacher and Thompson, 2012; Costa et al., 2020), and little is known about the effects of these activities on meiofauna community in these environments (Johnson et al., 2007). The results of the few studies available showed a general negative effect of recreational activities on abundance, diversity, and composition of the meiobenthic community (e.g. Moellmann and Corbisier, 2003; Gheskiere et al., 2005; Pereira et al., 2017). Also, recreational activities are known to have a negative effect on beach communities as they may increase sediment compactness (Ugolini et al., 2008). The degree of sediment compaction can be affected by the intensity of recreational activities (Schlacher et al., 2007), and it correlates with several sediment physical properties (Hsu et al., 2009). Thus, sites with high compaction, reflecting harder substrates, might be unfavorable to a wide range of organisms and meiofauna is particularly susceptible, as these organisms inhabit the sediment interstitial space (Giere, 2009).

Macrotidal sandy beaches of the Brazilian Amazonian coast, with their natural environments distributed along a coastline of 3900 km (Klein and Short, 2016), have considerable potential for tourism (Pereira et al., 2016a, b). In general, these beaches are overcrowded during vacation (July) and some bank holidays, especially in the second half of the year (Sousa-Felix et al., 2017). Information available on the biodiversity of Brazilian sandy beaches, particularly in northern Brazil (Amazonian coast), is insufficient to ensure their preservation (Amaral et al., 2016). Furthermore, although meiofauna is a powerful tool to assess human-induced impacts (Schratzberger et al., 2009; Netto and Valgas, 2010), studies that aim to evaluate the effect of recreational activities on meiofauna community in macrotidal tropical sandy beaches are scarce (e.g. Martínez et al., 2020).

In this context, the present study assessed the impact of recreational activities on the structure and composition of meiofauna community and nematode assemblages in three Amazonian macrotidal sandy beaches with different levels of tourism (high, intermediary, and low) before, during, and after an episode of high tourist occupancy (vacation in July). The following hypothesis was tested: high intensity of recreational activities (human trampling and vehicle traffic) causes changes in the structure and composition of the meiobenthic community and nematode assemblages by decreasing species richness and density, particularly in the urban beach during vacation.