Trends in estuarine fish assemblages facing different environmental conditions: combining diversity with functional attributes

Abstract

Changes in the Mondego estuary (Portugal) fish assemblage were documented with a long-term monitoring program between June 2003 and March 2010, during which several extreme environmental events occurred, including severe droughts and heavy precipitation. The structure and composition of the fish assemblage was analyzed based on a set of indicators: dominance, diversity, evenness, and composition in functional groups (ecological and feeding guilds). Higher species number, diversity, and evenness were observed in the dry periods. Variations in the relative abundance of the ecological guilds were also observed: in dry years, estuarine residents were the most abundant group, while in typical and rainy years, the marine estuarine-dependent species increased in abundance. Among the feeding guilds, the most abundant group was the invertebrate and fish feeders. Planktivorous and invertebrate feeders occurred in higher abundance in dry years, while the opposite was verified for omnivorous species. The mean trophic level of the fish assemblage increased during the drought period, constantly decreasing afterward, which could be attributed to an increase in predators in dry years. The cumulative responses of estuarine fish assemblages to ongoing climate changes and discrete extreme weather events confirm their importance as indicators of environmental changes.

Early summer near-shore fish assemblage and environmental correlates in an Arctic estuary

“…Monitoring the assemblage of fish species provides a means to examine changes in the ecosystem because fish act as tractable links to the surrounding catchment, freshwater, marine and fluvial environments. Fish community structure has often been used to illustrate changes in environmental conditions (Whitfield, 1996;Elliott and Hemingway, 2002;Griffiths et al, 1998;Nyitrai et al, 2012), with fish species acting as 'sentinels' through their responses to changes and variation in the environment.…”

“…Estuarine fish communities integrate environmental information from marine, freshwater and terrestrial (catchment) environments (Khlebovich, 1997;Whitfield and Harrison, 2008), and are thus excellent candidates for monitoring environmental change (Whitfield and Elliot, 2002). Compared to lacustrine or marine ecosystems, estuaries are likely to exhibit earlier responses to changes such as loss of native Journal of Great Lakes Research xxx (2015) xxx-xxx species, proliferation of exotic species and episodic or discrete extreme weather events (Roessig et al, 2004;Gillson, 2011;Nyitrai et al, 2012).…”

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“…It is obvious that in the coastal waters of northern BOB, salinity was very low in winter compared to other parts of the bay. Variations in salinity, runoff and precipitation regions seemed the most dominant factors for changes in fish assemblage, mainly by the displacement of estuarine habitats and by influencing the migration and recruitment of several species (Nyitrai et al, 2012). The CPUE was high in the PFZ than non-PFZ.…”

The use of an Estuarine System (Mondego estuary, Portugal) as Didactic Tool to incorporate Education for Sustainable Development into School Curricula

“…In addition to the anthropogenic pressures, the estuary has also been affected by the occurrence of natural extreme climatic events in the last years (Marques et al, 2007b;Martinho et al, 2007;Cardoso et al, 2008;Grilo et al, 2010;Dolbeth et al, 2011). As result there were recorded changes in the species distribution, dynamics, and changes in its structure and composition (Marques et al, 2007b;Baptista et al, 2010;Grilo et al, 2011;Nyitrai et al, 2012).…”

“…It has been intensely demonstrated the role of estuaries for life in the oceans, especially coastal platforms, serving as local of breeding, spawning and growth of many marine species Martinho et al, 2007Martinho et al, , 2012, migratory routes of avifauna (Lourenço et al, 2008;Burton et al, 2010) and habitat use for resident species (Baptista et al, 2010;Nyitrai et al, 2012). The estuaries were always areas of high human occupation.…”