Predicting ecological changes on benthic estuarine assemblages through decadal climate trends along Brazilian Marine Ecoregions

Highlights

• We reviewed decadal climatic variability from five Brazilian Marine Ecoregions.

• Estuarine benthic assemblages differ among Marine Provinces and Ecoregions.

• Warming and storm events may impact estuarine benthic ecosystems.

Abstract

Estuaries are threatened coastal ecosystems that support relevant ecological functions worldwide. The predicted global climate changes demand actions to understand, anticipate and avoid further damage to estuarine habitats. In this study we reviewed data on polychaete assemblages, as a surrogate for overall benthic communities, from 51 estuaries along five Marine Ecoregions of Brazil (Amazonia, NE Brazil, E Brazil, SE Brazil and Rio Grande). We critically evaluated the adaptive capacity and ultimately the resilience to decadal changes in temperature and rainfall of the polychaete assemblages. As a support for theoretical predictions on changes linked to global warming we compared the variability of benthic assemblages across the ecoregions with a 40-year time series of temperature and rainfall data. We found a significant upward trend in temperature during the last four decades at all marine ecoregions of Brazil, while rainfall increase was restricted to the SE Brazil ecoregion. Benthic assemblages and climate trends varied significantly among and within ecoregions. The high variability in climate patterns in estuaries within the same ecoregion may lead to correspondingly high levels of noise on the expected responses of benthic fauna. Nonetheless, we expect changes in community structure and productivity of benthic species at marine ecoregions under increasing influence of higher temperatures, extreme events and pollution.

Introduction

Benthic estuarine ecosystems are highly productive and mediate biogeophysical and biogeochemical feedbacks to climate change through organic carbon degradation, trophic transfer and nutrient remineralization (Alongi, 1998, McLusky and Elliott, 2004). Estuaries are a major carbon sink in coastal areas worldwide (Duarte et al., 2005, Sanders et al., 2010, Donato et al., 2011, McLeod et al., 2011), but increasing pressure from human activities may compromise their resilience and the ecological services they provide (Lotze et al., 2006).

Estuaries are among the most modified aquatic environments by human activities. Estuarine habitats are under increasing human stress which interact with background gradients of salinity, hydrodynamics and temperature (Nicholls et al., 1999, Elliott and Quintino, 2007, Doney et al., 2012). Thousands of square kilometres of mangrove forests, salt marshes and mudflats are lost yearly due to coastal development or impacted by pollutant inputs. The loss of estuarine wetland areas in Brazil is estimated at 50,000 ha of mangroves over the last 25 years (FAO, 2007) and 50,000 ha of mudflats and sandflats over the last 15 years (MMA, 2010), mainly due to urban development and shrimp farming. The estimated total land conversion in Brazilian marine wetlands is about 1.5–16.5% of the total original area and led to the emission of 1 to up 11% of the total Brazilian yearly CO₂ emissions per year (Pagliosa et al., 2012). Sea level rise impinges further pressures on wetlands (Airoldi and Beck, 2007) and in association with other local and regional threats to estuarine ecosystems, global climate change may severely alter estuarine dynamics over the next decades. As a result of vegetation and habitat loss, wetlands may suffer loss of ecosystem integrity and function, reducing carbon storage and altering food web cycling (Lee, 1995, Hewitt et al., 2008, Sweetman et al., 2010, Pendleton et al., 2012).

Estuaries are preeminent seascapes along the 9200 km of the Brazilian coastal margin and widely differ in their meteorological and oceanographic conditions (Dominguez, 2006, Bernardes et al., 2012). Although the structure and dynamics of their benthic fauna are reasonably known in the southern and southeastern Brazilian regions (Bernardino et al., in press), macroecological approaches and large scale comparisons of major patterns and processes are still missing along this extensive sector of the Southwestern Atlantic.

It is expected that climate change will affect estuarine ecosystems at a global and regional scale due to corresponding changes in physiology (and tolerance), dispersal patterns and species interactions (Doney et al., 2012, Semeniuk, 2013). The capacity of organisms to move and adapt to changing conditions will depend on their life history characteristics, phenotypic plasticity, genetic variability, inheritability of adaptive characteristics. Mobile benthic organisms may respond to changes in estuarine salinity and temperature by changing patterns of population structure, distribution, behaviour and growth (Attrill and Power, 2000, Thurman et al., 2010, Munguia et al., 2013), whereas infaunal species may exhibit changes in productivity and community structure (Cardoso et al., 2008, Dolbeth et al., 2011).

Climate change impacts can be severe when physiological tolerance is exceeded, such as in confined tropical estuaries and lagoons, in nutrient rich coastal areas and during temperature extreme events (Diaz and Rosenberg, 2008, Vaquer-Sunyer and Duarte, 2011, Sunday et al., 2012). Higher temperatures increase the metabolism rate of aquatic organisms and create physiological stress for species with higher aerobic demand (Bishop et al., 2006, Vaquer-Sunyer and Duarte, 2008). Salinity is likely to change due to altered patterns of rainfall and sea level rise, and can potentially affect most marine benthic organisms through changes in osmolarity resulting in loss of functioning of the entire ecosystem (Garcia-Rodriguez et al., 2013). Considering the diversity of estuarine habitats, the variable levels of human impacts that influence the hability of organisms to cope with climate change, and the heterogeneous trends of climatic changes itself, it is very likely that estuarine benthic assemblages will show complex responses to predicted global changes. Therefore, addressing the distribution of benthic assemblages across a number of estuarine habitats in coastal areas of Brazil will provide better support for macroecological and biogeographical studies.

We have herein compiled and interpreted data on decadal trends of rainfall and temperature, and assessed the structure of polychaete assemblages from 51 estuaries from five Marine Ecoregions of Brazil (Spalding et al., 2007), as a proxy for overall benthic communities. Meteorological oscillations and anomalies in temperature and rainfall during the last 40 years were used to evaluate potential climate change effects on polychaete assemblages. As long-term and experimental studies of climate impacts on benthic assemblages are unavailable in Brazil (Bernardino et al., in press), our analysis was based on ad hoc expert knowledge and surveys of published literature that addressed climate effects on assemblage level. Our objectives are to: 1) identify long-term trends and climate anomalies in rainfall and temperature across five Marine Ecoregions of Brazil; 2) identify similarities and dissimilarities among benthic polychaetes assemblages from estuaries in each Marine Ecoregion and make qualitative comparisons of their spatial distribution; and 3) make theoretical predictions on the main threats that these benthic assemblages face as a result of long-term oscillations in rainfall and temperature increases, using the available biological and climatological information available.