Realized connectivity: Larval source affects postsettlement survival Scott Hamilton, Bob Warner
The importance to recruitment of some retention of local production has been stressed in several papers: “Up to 60% of recruits come from local production” “Large recruitment pulses tend to be retention events” - but these are based on numbers at settlement
How do we know larval history? Otoliths and statoliths incorporate trace elements and can be used as environmental recorders Larval uptake Dissolved trace elements Otolith incorporation SUCCESSIVE LAYERS HAVE INFORMATION ON LARVAL PATHWAYS CORE HAS A NATAL SIGNATURE
Core (Embryonic period) Early larval period Near time of capture Otoliths and statoliths also record age, growth, and condition at settlement
Waters near islands tend to be more productive and are enriched in many trace elements
Recruits to St. Croix fall into two groups: high Pb over the entire larval life (nearshore) and low Pb in middle part of larval life (offshore)
Metamorphic band width (an otolith character) correlates strongly with condition at settlement
Recruits from offshore had significantly wider metamorphic bands than did recruits from nearshore
Recruits from offshore had grew significantly faster at the end of larval life than did recruits from nearshore
Recruits from nearshore (local retention) settled in high numbers (45% of total), but tended to be in lower condition. They subsequently suffered much higher selection intensity, and comprised only 23% of the recruit cohort after a month.
The intensity of selection was much greater for fish that developed in nearshore than offshore waters, potentially because only exceptionally strong performers from offshore waters made it back to reefs (nearshore larvae had it easy). Given this potential for asymmetrical post-settlement source-based survival, we may need to pay attention to ‘realized connectivity’ on ecological scales, that is, the proportion of individuals from different sources that survive to reproduce. We may also be wrong about the importance of local retention – it can lead to large numbers, but they may not survive well after settlement.