Quantifying fish and mobile invertebrate production from a threatened nursery habitat

Abstract

Summary Quantification of ecosystem services is increasingly valuable for conservation and restoration decision‐making. Structured habitats serve as nursery grounds by enhancing juvenile fish and mobile crustacean survival and abundance. This service is challenging to quantify due to ontogenetic shifts in habitat use by many species. We reviewed available literature on the increased abundance of juvenile fish and mobile crustaceans in a key nursery habitat – Crassostrea virginica reefs in the USA. We modelled the growth and mortality of the enhanced species using three different natural mortality (M) estimates to provide estimates of the gross and net lifetime production and uncertainty that can be attributed to the habitat. Recruitment of nineteen and twelve species were found to be enhanced by the addition of C. virginica reefs to previously unstructured habitat in the Gulf of Mexico and the South Atlantic and Mid‐Atlantic USA, respectively. This increased recruitment is estimated to result in a mean lifetime enhancement in production of 397 ± 115 (1 SD) g m−2 year−1 in the Gulf of Mexico and 281 ± 56 g m−2 year−1 in the South Atlantic and Mid‐Atlantic. The two regions differed with regard to the identity of the enhanced species and their degree of augmentation. Thus, our results highlight the inadequacy of applying regional estimates of ecosystem services to global scales. Furthermore, estimates of total enhancement varied by up to a factor of 2·8 across the three methods of M estimation. Our estimates are quantitative predictions of the ecological benefits derived from the restoration or conservation of a threatened habitat, and advance the field of restoration science beyond qualitative statements that just predict direction of benefit (e.g. increased or decreased). Quantification of the uncertainty in the production estimates further increases their utility for decision‐makers. Synthesis and applications. Our results can be applied to the restoration or conservation of nursery habitats where habitat is limiting the recruitment of fish species. Quantitative estimates of fisheries productivity enhancement by habitats can be used by managers to determine the expected return on investment in restoration activities, provide testable predictions for monitoring programs and communicate the value of restoring or conserving habitat.