Fish Habitat: Essential Fish Habitat and Rehabilitation

Abstract

<em>Abstract</em> .—Basic research on the settlement and postsettlement ecology of spiny lobster <em>Panulirus argus </em> has led to an application with the potential to replace lost natural refuge with artificial shelters intended for the vulnerable small juvenile stages. We began investigating ecological processes regulating juvenile spiny lobster recruitment in the Florida nursery in the mid-1980s. An unprecedented massive die-off of sponges in the middle Florida Keys followed cyanobacterial blooms in 1991–1993, ultimately affecting about 300 km2 of a region providing approximately one-fifth of total juvenile recruitment. Before 1991, crevices in sponges provided diurnal refuge from predators for about 70% of juveniles <50 mm carapace length. On the basis of sampling done before and after sponge loss, we estimated that juvenile abundance declined by 30–50% on spongeless sites without alternative shelter, resulting in a decrease of annual nurserywide potential of up to 10%. Results of a field experiment evaluating the relative influences of the magnitude of settlement and availability of crevice shelter on juvenile recruitment, fortuitously begun before the sponge die-off, showed that juvenile survival and abundance were sustained on small 0.02- to 0.07-ha test sites provided with supplemental artificial shelters (slotted concrete blocks). In the absence of sponges, survival of microwire-tagged juveniles on the shelter-supplemented sites was about six times higher than that on unsupplemented sites. On the basis of our earlier ecological findings, we devised a feasibility study to test whether the artificial shelters could replace lost sponge shelter for juvenile lobsters on a large scale. It took the form of a field experiment using 240 shelters spread over 1-ha sites located amid hard substrate denuded of sponges. The shelters provided substitute crevices, supporting juvenile lobster recruitment approximating that in areas with good sponge cover. This outcome exemplifies the essential value of initial basic research that provides understanding of the ecological processes regulating individual survival and, ultimately, the character and dynamics of the fishery population. Such an approach, and the information it provides, is necessary to successful rehabilitation of essential habitat or restocking of natural populations. Moreover, conducting basic research can help prevent the waste of precious time, funds, income, and human effort that typically has occurred in past failed attempts that were undertaken with insufficient knowledge. We urge the fisheries-ecology discipline and support agencies to promote strongly the primacy of research on basic processes.