Estuarine fish communities respond to climate variability over both river and ocean basins

Abstract

Estuaries are dynamic environments at the land-sea interface that are strongly affected by interannual climate variability. Ocean-atmosphere processes propagate into estuaries from the sea, and atmospheric processes over land propagate into estuaries from watersheds. We examined the effects of these two separate climate-driven processes on pelagic and demersal fish community structure along the salinity gradient in the San Francisco Estuary, California, USA. A 33-year data set (1980-2012) on pelagic and demersal fishes spanning the freshwater to marine regions of the estuary suggested the existence of five estuarine salinity fish guilds: limnetic (salinity = 0-1), oligohaline (salinity = 1-12), mesohaline (salinity = 6-19), polyhaline (salinity = 19-28), and euhaline (salinity = 29-32). Climatic effects propagating from the adjacent Pacific Ocean, indexed by the North Pacific Gyre Oscillation (NPGO), affected demersal and pelagic fish community structure in the euhaline and polyhaline guilds. Climatic effects propagating over land, indexed as freshwater outflow from the watershed (OUT), affected demersal and pelagic fish community structure in the oligohaline, mesohaline, polyhaline, and euhaline guilds. The effects of OUT propagated further down the estuary salinity gradient than the effects of NPGO that propagated up the estuary salinity gradient, exemplifying the role of variable freshwater outflow as an important driver of biotic communities in river-dominated estuaries. These results illustrate how unique sources of climate variability interact to drive biotic communities and, therefore, that climate change is likely to be an important driver in shaping the future trajectory of biotic communities in estuaries and other transitional habitats.

Evidence of a Shift in the Littoral Fish Community of the Sacramento-San Joaquin Delta

“…Some of these annual differences in fish community composition appear to be driven by the interannual variability of freshwater inflow into the Delta, a pattern reflected in the second NMDS axis (Fig 3). This result is not surprising given that numerous studies have demonstrated a strong relationship between fish community and hydrologic variability in California [72,73,74,75]. Yet, the largest differentiation between years, as captured by the first NMDS axis, seems to follow a pattern of continuous change over time.…”

“…Particularly, some of the substantial changes that occurred around the time of the POD included abrupt changes in sediment supply [23,76], alterations in pesticide use [77], nutrient inputs [78], species introductions [21], an expansion in aquatic weeds [23], and hydrologic and operational changes [29,79]. As noted by Feyrer et al [75], these anthropogenic disturbances can be powerful enough to overwhelm natural processes driving estuarine variability. Hence, ecosystem shifts are often extremely difficult or impractical to reverse [1].…”

Ecosystem variability along the estuarine salinity gradient: Examples from long‐term study of San Francisco Bay

“…Other biological communities are similarly structured by the salinity gradient. The fish community of San Francisco Bay includes 137 species that group into guilds based on their salinity ranges (Feyrer et al ), including: marine species found only at high salinity (e.g., yellowtail rockfish Sebastes flavidus , Dover sole Microstomus pacificus , white seabass Atractoscion nobilis ); freshwater species confined to low salinity (e.g., juvenile Western brook lamprey Lampetra richardsoni , spotted bass Micropterus punctulatus , tule perch Hysterocarpus traskii ); and generalists found across a wide salinity range (e.g., adult American shad Alosa sapidissima , starry flounder Platichthys stellatus , longfin smelt Spirinchus thaleichthys ). The phytoplankton community also includes freshwater taxa found only at salinity < 5 ( Anabaena affinis , Chlorella vulgaris , Cryptomonas ovata , Fragilaria crotonensis ), marine taxa found only at salinity > 25 ( Ceratium furca , Biddulphia pulchella , Pyramimonas parkeaea ), and others found across a wide salinity range (1–25) such as Gyrosigma acuminatum , Plagioselmis prolonga , and Cyclotella striata (Cloern and Dufford ).…”

Human activities and climate variability drive fast‐paced change across the world's estuarine–coastal ecosystems

“…Our purpose here is to synthesize the information contained in time series of measurements made in coastal marine ecosystems influenced by connectivity to landestuaries, bays, lagoons, inland seas and nearshore shelf waters receiving river runoff. These are highly complex transitional ecosystems between land and sea, so the signals of human disturbance can be confounded by variability of the climate system through its separate influences over watersheds and ocean basins (Feyrer et al, 2015). However, clear signals can emerge when time series are extended long enough and include measurements of key drivers of change both on land and in the coastal ocean.…”