Bioenergetic and landscape considerations for scaling expectations of nekton production from intertidal marshes

TLDR: In this paper, the authors consider both bioenergetic and landscape constraints on direct flows of marsh-derived produc- tion to populations of resident and migrant nekton, and find that there is a strong sigmoid relationship between fishery production and the amount of intertidal marsh/creek edge within a 200 m radius of a site.

Abstract: The connection between fishery production and vegetated intertidal habitats is often a key consideration in the rationale for protecting and restoring estuarine salt marshes. Evaluating the contribution of marsh habitats to estuarine nekton production requires an understanding of the mechanisms and constraints controlling production flows to nekton populations; this is especially important for setting and judging success criteria associated with restoration projects. This contribu- tion considers both bioenergetic and landscape constraints on direct flows of marsh-derived produc- tion to populations of resident and migrant nekton. Nekton access to marsh resources is defined in terms of trophic (bioenergetic) and physical (landscape) constraints that determine the amount of nekton production that can be expected. Production to biomass (P:B) ratios applied to measurements of nekton standing stock from multiple marsh sites around Sapelo Island, Georgia, USA provided an example of the spatial variation in nekton production that can be expected from natural marshes. When P:B ratios of 2, 5, and 3 were applied to standing stocks of fishes, caridean shrimps and penaeid shrimps, respectively, annual net production of nekton from 12 intertidal marsh sites ranged from 0.12 to 2.88 g dry weight (dw) m -2 and averaged ca. 1.50 g dw m -2 ; other scenarios using different sets of P:B ratios yielded production ranges of 0.11 to 2.25 and 0.17 to 4.57 g dw m -2 . There was a strong sigmoid relationship between nekton production and the amount of intertidal marsh/creek edge within a 200 m radius of a site for both resident and migrant species. Production was lowest at sites with relatively little marsh/creek edge, and increased rapidly with increasing drainage density until reaching an asymptote, after which even large changes in the amount of marsh/creek edge had no effect on nekton production. The findings suggest that bioenergetic constraints determine the ulti- mate capacity of intertidal marsh systems to produce nekton, but nekton production may be enhanced by relatively small additions of marsh/creek edge up to a threshold level above which no additional enhancement should be expected. Site-specific bioenergetic and landscape constraints should be considered when developing realistic expectations and success criteria for marsh restora- tion efforts aimed at enhancing estuarine nekton production.