Seasonal influence of surface and underground continental runoff over a reef system in a tropical marine protected area

11 pages, 8 figures, 2 tablesContinental runoff is an important source of solutes and nutrients to coastal coral reefs. Nevertheless, they can also act as local stressors due to high coastal urbanization and the associated release of untreated effluents. Here we aimed to qualitatively evaluate the effects of seasonality over reefs from the Costa dos Corais Marine Protected Area (Brazil) and to identify the influence of rivers and submarine groundwater discharge (SGD) on the reefs' environmental status. Surface waters from the reef lagoon, local rivers and shoreline porewaters were sampled monthly during a year and abiotic parameters were determined. The results showed that the reef lagoon is oligotrophic throughout most of the year, with conditions that generally favor biological activities, such as calcification. Chlorophyll-a, with an average of 0.78 ± 0.43 mg m−3, was significantly correlated with salinity and radon in excess. This indicates the influence of rivers and SGD over the reefs, especially during the rainy season. These are important sources of nutrients, regulating primary production. However, signs of anthropogenic pressure were found in the local rivers. In addition, porewaters had a N:P ratio (27.68 ± 24.45) which could potentially impact surface waters through SGD by increasing the local trophic status. In summary, the studied reefs still present good water quality conditions, although continental runoff is a significant transport vector of anthropogenic solutes to the areaThis work is part of the Long-Term Ecological Research – Brazil site PELD-CCAL (Projeto Ecológico de Longa Duração - Costa dos Corais Alagoas) funded by the Brazilian National Council for Scientific and Technological Development – CNPq (grant number #441657/2016-8), the Brazilian Coordination for the Improvement of Higher Education Personnel PELD/CAPES (grant number #23038.000452/2017-16) and the Research Support Foundation of the State of Alagoas – FAPEAL (grant number #60030.1564/2016). This paper is also a contribution of the DICAM project, grant CM II #23038.001423/2014-29 (CAPES)Peer reviewe