Fronts and eddies as key structures in the habitat of marine fish larvae: opportunity, adaptive response and competitive advantage

Abstract

SUMMARY: Surface fronts and mesoscale eddies are two classes of ocean structures that engender significant pattern in the habitats of marine organisms. Both are sites where mechanical energy of the physical system may be accessible for augmenting trophic energy available to biological organisms. Accordingly, they may offer opportunities for exceptional local productivity and growth of species particularly adapted to excelling in such highly-productive rapid-growth/high-mortality situations. The major relevant physical mechanisms involved are presented. A widespread attraction of many types of fish to floating objects drifting in the ocean is cited as an apparent adaptive response to the desirable aspects of surface fronts. An apparent contrary tendency for certain important marine fish species to be particularly successful in relatively poorly productive situations, where slower growth may be offset by much lower early life predation mortality, is also noted. Competing tradeoffs between (1) early life nutrition and resulting growth, and (2) mortality of early stages due to predation are suggested. These tradeoffs are posed and illustrated via a "predator pit" conceptual framework. Illustrations of the evident reproductive habitat choices of several populations of large temperate tunas are briefly presented. It is concluded that the time may have come for a general shift in the approach of at-sea fish larval ecological investigations from the conventional focus on associations with environmental properties on a "macro" scale to intensive investigations of the real-time progressions of linked physical-biological interactions occurring on a "meso" (and smaller) scale.Keywords: population dynamics, fisheries oceanography, convergence zones, divergence zones, upwelling, predator pits, ecological succession, tuna spawning areas. RESUMEN: FRENTES Y REMOLINOS COMO ESTRUCTURAS CLAVE EN EL HABITAT DE LAS LARVAS DE PECES MARINOS:OPORTUNI-DAD, RESPUESTA ADAPTATIVA Y VENTAJA COMPETITIVA. -Los frentes superficiales y los remolinos de mesoescala son dos tipos de estructuras de mesoescala que producen patrones significativos en los hábitats de los organismos marinos. Ambos son notables por ser lugares en los que la energía mecánica del sistema físico puede ser accesible para aumentar la energía tró-fica disponible para los organismos biológicos. Por consiguiente, pueden ofrecer oportunidades para que se produzcan producciones y crecimientos localmente excepcionales de especies particularmente adaptadas a sobresalir en tales situaciones de alta producción/rápido crecimiento/alta mortalidad. Los mecanismos físicos de mayor relevancia involucrados son elaborados. La amplia atracción de muchos tipos de peces por objetos flotantes que derivan en el océano ha sido señalada como una aparente respuesta adaptativa a los aspectos deseables de los frentes superficiales. Existe una tendencia aparentemente contraria para ciertas importantes especies de peces marinas que son particularmente exitosas en situaciones productivas relativamente p...

The Capricorn Eddy: a prominent driver of the ecology and future of the southern Great Barrier Reef

“…However, beyond the band of maximum circumferential velocity of the eddy in the sectors that are not driven by direct frictional coupling to the EAC, a band of downwelling will typically exist due to flow convergence (Bakun 2006). This is in response to progressive reduction from the eddy center of the outward-directed coriolis and centrifugal forces in the coastward (outer) zone where frictional retardation is increasing.…”

“…This represents an anti-cyclonic (anti-clockwise) torque being exerted by the rotating eddy on the less rapidly rotating waters beyond the zone of maximum circumferential velocity around the eddy (Bakun 2006). In this zone, the outwardly directed centrifugal and coriolis forces are declining rapidly with increasing distance from the eddy center, producing convergence and associated downwelling in the induced water flow.…”

Mesoscale eddies influence distribution and aggregation patterns of micronekton in the Mozambique Channel

“…Eddies are known to play a key role in the biological processes of pelagic ecosystems by converting physical energy into trophic energy (Bakun 2006). Eddies are pervasive and long-lived turbulent swirls in the ocean on scales of 10 to a few 100 km (Rhines 2001).…”

“…Several studies have demonstrated that eddies markedly enhanced geochemical transformations and primary production in the subtropical Pacific Ocean (Seki et al 2001, BenitezNelson et al 2007, in the Atlantic Ocean (McGillicuddy et al 1998, Garçon et al 2001, in the Bering Sea (Mizobata et al 2002) and in the Indian Ocean (Quartly & Srokosz 2004, Waite et al 2007). Mesoscale eddies also affect the upper-trophic-level organisms by influencing the horizontal and vertical distribution of mesozooplankton and fish larvae (Bakun 2006, Muhling et al 2007, affecting movement patterns of turtles (Polovina et al 2004, Lambardi et al 2008, attracting tuna (Young et al 2001) or swordfish (Seki et al 2002), and influencing the foraging strategy of seabirds (Nel et al 2001, Weimerskirch et al 2004, Hyrenbach et al 2006.…”

“…Various mechanisms explain how eddies can fuel biological production in open-ocean ecosystems, leading to patches of enhanced productivity in zones of low primary production. Cyclonic eddies can generate upwelling of deepcold-nutrient-rich waters towards upper euphotic surface layers in their centre (McGillicuddy et al 1998, Bakun 2006, enhancing local primary production (Seki et al 2001, Mizobata et al 2002, Benitez-Nelson et al 2007). Anticyclonic eddies can also generate an upward movement of rich waters, but located around their edge, where phytoplankton enrichment has also been observed (Mizobata et al 2002, Quartly & Srokosz 2004.…”