Abstract
Mortality is very high during the pelagic larval phase of fishes but the factors that determine recruitment success remain unclear and hard to predict. Because of their bipartite life history, larvae of coastal species have to head back to the shore at the end of their pelagic episode, to settle. These settlement-stage larvae are known to display strong sensory and motile abilities, but most work has been focused on tropical, insular environments and on the influence of coast-related cues on orientation. In this study we quantified the in situ orientation behavior of settlement-stage larvae in a temperate region, with a continuous coast and a dominant along-shore current, and inspected both coast-dependent and independent cues. We tested six species: one Pomacentridae, Chromis chromis, and five Sparidae, Boops boops, Diplodus annularis, Oblada melanura, Spicara smaris and Spondyliosoma cantharus. Over 85% of larvae were highly capable of keeping a bearing, which is comparable to the orientation abilities of tropical species. Sun-related cues influenced the precision of bearing-keeping at individual level. Three species, out of the four tested in sufficient numbers, oriented significantly relative to the sun position. These are the first in situ observations demonstrating the use of a sun compass for orientation by wild-caught settlement-stage larvae. This mechanism has potential for large-scale orientation of fish larvae globally.
Highlights
Dispersal and connectivity are crucial for the persistence and resilience of marine populations [1]
To detect orientation behavior that may be an artifact related to the Drifting In Situ Chamber (DISC) structure itself, we identified deployments where the DISC rotated at least 180° and where positions were much more concentrated in the reference of the chamber than in a cardinal direction
Orientation analysis was restricted to C. chromis, D. annularis, S. smaris, and O. melanura for which ! 30 individuals were observed
Summary
Dispersal and connectivity are crucial for the persistence and resilience of marine populations [1]. Most demersal fish species disperse during a pelagic larval phase and drifting pelagic eggs and larvae can be transported over hundreds of kilometers by ocean currents [2]. Despite this potential for long distance transport, self-recruitment has been found to be consistently high (often > 30%; e.g., [3, 4]). The behavioral abilities of fish larvae are well developed: at least at settlement-stage, they can sense their environment, swim vertically and horizontally, and orient [5] Such behaviors are often invoked to explain how larvae can influence their dispersal.
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