Relationships between fish larvae and siphonophores in the water column: effect of wind-induced turbulence and thermocline depth

Abstract

Sanvicente-Añorve, L., Alatorre, M. A., Flores-Coto, C., and Alba, C. 2007. Relationships between fish larvae and siphonophores in the water column: effect of wind-induced turbulence and thermocline depth. – ICES Journal of Marine Science, 64: 878–888. The relationship between the abundance of fish larvae and siphonophores in relation to wind-induced turbulence and thickness of the mixed layer in the southern Gulf of Mexico were studied during two periods of different wind conditions: April (5.25 m s−1) and October (6.5 m s−1). The Spearman correlation between fish larvae and siphonophores revealed a random relationship in the 0–10 m layer during April and in the 0–20 m layer in October. This structure presumably persists while turbulent forces remain at sufficient strength. Positive patterns were observed deeper in the water column. Whereas thermocline position did not correspond with the depth separating random and positive relationships, low turbulence values did. Observations indicate that turbulent kinetic energy values above 4 × 10−4 J kg−1 might promote a random distribution between potential prey and predator zooplankton taxa. In surface waters, contact rates between siphonophores and fish larvae showed that turbulence enhances encounters 2.5 (1.2) times in April and 3.3 (1.3) times in October for prey velocities of 0.003 (0.011) m s−1. The positive relationship between fish larvae and siphonophores could be caused by a high degree of spatial overlap, enough food for both groups, and limited predation on larvae in the presence of alternative prey. Seasonal variability in the vertical structure of distribution patterns was attributed mainly to aggregative feeding behaviour of organisms and disruption of patches as a consequence of small-scale water turbulence.

Encounters in the Zooplankton: Implications for Pelagic Ecosystem Dynamics

“…Even when fish larvae constitute only a small fraction on the diet of gelatinous and soft-bodied zooplankters, in some cases predation on fish larvae can significantly reduce the abundance of a cohort, affecting the recruitment of juveniles to adult population [37,38]. In an attempt to understand the predatory impact of siphonophores on fish larvae in the southern Gulf of Mexico, Sanvicente-Añorve et al [39] estimated and compared the predatorprey encounters in relation to the wind-induced turbulence during two contrasting wind periods.…”

“…The study of Sanvicente-Añorve et al [39] was carried out in the southern gulf (Figure 1) during two months: April (wind speed 5.25 m s −1 ) and October (6.5 m s −1 ) of 2001. A total of 149 zooplankton samples were collected in six vertical strata of the water column (0-10, 10-20, 20-30, 40-60, 60-80, and 80-100 m) using a multiple opening-closing net equipped with 75-cm diameter and 500-μm mesh size.…”

Population structure and mating encounter rates in a marine pelagic invertebrate, Firoloida desmarestia (Mollusca)

“…Heteropod populations are often low in density. Low population densities appear as a limitation on the encounter of mates (Kramer et al 2011), but wind-induced turbulence can increase encounters among plankton specimens (Saiz et al 2003, Sanvicente-Añorve et al 2007. Further, Kiørboe & Bagøien (2005) stated that mating encounter rates depend on the swimming speeds of males and females, their concentrations, and the effectiveness of remote male detection.…”

“…Wind-induced turbulence may influence planktonic populations with either favorable or deleterious consequences, depending on its magnitude (MacKenzie et al 1994). For instance, the moderate velocities of small-scale turbulent flows increase encounter rates between predators and prey (Rothschild & Osborn 1988, Dzierzbicka-Glowacka 2005, Sanvicente-Añorve et al 2007 and between potential mates (Schmitt & Seuront 2008). However, higher velocities may re -duce feeding rates of zooplankters and also affect the type of captured prey (MacKenzie et al 1994).…”

Distribution of planktonic cnidarian assemblages in the southern Gulf of Mexico, during autumn

“…Knowledge of this group of organisms in the Gulf of Mexico is as yet limited, despite several recent studies that have informed on the relationship between the assemblages of medusae or siphonophores and the local oceanographic conditions (Loman-Ramos et al 2007;Sanvicente-Añorve et al 2007a, 2007b. Considering the intense water mass transportation that takes place in the Campeche Bay during the autumn-winter, it would be expected that the structure and composition of the planktonic cnidarian assemblages reflect the oceanographic conditions.…”