Connectivities of estuarine fishes to the coastal realm

Connectivity is an important concept in landscape ecology, but has several meanings. Here, I treat this term generically, including interactions among land- and seascape elements, transfers of nutrients among them, and interactions among closely related species comprising guilds. Complex relationships between the natural histories of estuary-dependent fishes are best understood in the context of the “coastal realm”, the heterogeneous and diverse portion of Earth where land, sea, and atmosphere interact with great intensity through exchanges of energy and materials. Especially for anadromous fishes, estuaries form especially important conduits between terrestrial watersheds and the coastal ocean. For this reason, these species may be termed “estuary-dependent”. However, for many species that use estuaries, dependency may be difficult to define. I illustrate coastal-realm connectivities for two groups of closely related estuarine species from different latitudes: (1) clupeids of the US east coast, and (2) salmonids of the Bering Sea. These groups inhabit coastal-ocean waters as adults and use estuaries and/or freshwaters for reproduction or as nursery areas. Both groups have evolved metapopulation structures, perhaps also contingent patterns of behavior, that indicate hierarchical interactions within metaestuarine or metafluvial systems. Their natural histories suggest an estuary-dependent adaptive complex involving opportunistic life histories and redundancies within species guilds, which offer resiliency for these guilds under conditions of ecological and/or environmental change. I conclude that: (1) estuarine connectivities are best illustrated for fishes that can be shown to be estuary dependent at some life-history stage; (2) resiliency for functionally important guilds may also offer resiliency to their ecosystems; and (3) further understanding connectivities among coastal fishes and their changing environments depends on the fusion of natural history with land-seascape ecology on multiple scales.