Elements in otoliths may elucidate the contribution of estuarine recruitment to sustaining coastal reef populations of a temperate reef fish

Abstract

Estuaries and associated seagrass habitats are thought to be important nursery areas for many fishes.There is, however, no direct evidence for movement of fish from estuaries to reefs.The alm of this study was to determine if populations of Achoerodus viridis (Labridae) on rocky reefs were sustained by (1) recruitment to estuarine seagrass habitat followed by m o \ i e ~~~c n t to rocky reefs, (2) direct recruitment to rocky reefs, or (3) a combination of the two.Recruits were collected from estuarine seagrass and rocky reef habitats and elements in their otoliths analysed by inductively coupled plasmamass spectrometry (ICP-MS) to determine if d~fferent 'elemental fingerprints' could be found.Higher concentrations of Zn, AI, Pb, Mn, Ba and CO were found in otoliths of recruits from estuar~ne seagrass habitat than In otoliths of recruits from coastal reefs, the latter 3 elements showing sign~ficant differences.Strontium occurred in significantly h ~g h e r concentrations in otoliths of recruits from coastal reefs.Differences in concentrations of some elements In the otoliths of recruits allo\ved fish from the 2 env~ronments to be dlstinyuished 1 ~1 t h a high degree of dccuracy, enabling the contribution of estuarine recruitment to sustaining reef populations to be determined.Elemental composition of the juvenile core of otoliths from adults on reefs was related to the composition of otoliths of recruits from each environment to identify historical recruitment environments.Discriminant function analysis showed that 41 % of adults had recruited to estuaries and 59%) had recruited to reefs, but these figures may be overestimated because adults must be assigned to 1 of the 2 groups.There was evidence to suggest that some adults may form a third intermediate group.Further validation (e.g.comparison w ~t h laser or probe based methods and tagging techniques) of our a p p r o ~~c h is warranted.Elemental techniques may have great potential for resolving fisheries problems and identifying broader scale effects of environmental degradation.