Nursery Function Drives Temporal Patterns in Fish Assemblage Structure in Four Tropical Estuaries

Abstract

Despite estuary-to-estuary differences in assemblage composition, fish faunas of tropical Indo-Pacific estuaries show parallel patterns of temporal change suggesting a common set of ecological drivers. One potentially important driver is the interaction of different patterns of occupancy by functional groups that display different life-history patterns. However, most studies that have considered temporal change lack the detail needed to understand life-history utilisation. Most have focussed on changes in CPUE or probability of encounter, with only one study going further and investigating changes in size structure, and then only for a single estuary. One of the reasons for this lack of detail is the large volume of work needed to collect comprehensive data on size structures of species rich assemblages across multiple estuary systems over time. To overcome the logistical limitations on data collection, we used joint patterns of change in CPUE and mean biomass per fish (BPF) as proxies for changes in size structure. We investigated how different life-history strategies contributed to overall temporal patterns of assemblage change across 4 tropical Indo-Pacific estuaries. The 3 lifehistory strategies displayed characteristically different patterns in CPUE, BPF, and the relationships between CPUE and BPF that reflect differences in the way that the 3 groups use estuaries. These different patterns interacted to produce complex assemblage patterns that are likely to be sensitive to location-specific differences in the mix of species from each group, providing at least part of the explanation for the site specific fish assemblage structures that are characteristic of tropical estuarine fish fauna.

Why are there so few freshwater fish species in most estuaries?

“…Although estuarine fish assemblages tend to be numerically dominated by small estuarine resident species and the juveniles of marine species that use these systems as nursery areas (Harrison & Whitfield, 2008;Sheaves et al, 2013), there are also considerable numbers of small and large piscivorous fishes that are attracted to estuaries (Whitfield & Blaber, 1978b;Baker & Sheaves, 2005). Some of these euryhaline marine piscivores may even extend their range into the low salinity upper reaches of these systems (O'Connell et al, 2007).…”

Influences of environmental conditions in the fish assemblage structure of a tropical estuary

“…The estuaries are characterized by their high geomorphological and environmental complexity, which is reflected in their high physicochemical variability (Elliott and Quintino 2007;Day et al 2012), which is strongly related to hydrological circulation patterns, mainly due to changes in the discharge of freshwater into the system (Wolanski et al 2004(Wolanski et al , 2006Sun et al 2009). These environmental variations generate different responses from the community of estuarine organisms (Chícharo et al 2009;Teichert et al 2017), related to the characteristics of their life cycle, the possibility of taking advantage of shelter and food opportunities, and their physiological characteristics (Sheaves et al 2013;Potter et al 2015;Winemiller et al 2015). This generates individual distribution patterns of organisms, which is evidenced by changes in density and biomass (Able 2005;Sheaves et al 2013).…”

“…These environmental variations generate different responses from the community of estuarine organisms (Chícharo et al 2009;Teichert et al 2017), related to the characteristics of their life cycle, the possibility of taking advantage of shelter and food opportunities, and their physiological characteristics (Sheaves et al 2013;Potter et al 2015;Winemiller et al 2015). This generates individual distribution patterns of organisms, which is evidenced by changes in density and biomass (Able 2005;Sheaves et al 2013).…”

“…Lima et al 2015), but also for the high food availability (Nagelkerken et al 2008;Lima et al 2015;Ferreira et al 2016). Other factors include the use of the estuary as nursery grounds (Sheaves et al 2013) and shelter during different stages of their life cycle Sheaves et al 2013;Potter et al 2015), which lead to changes in species composition, density, and biomass along the estuary (Blaber et al 1989;Sheaves et al 2013;Ferreira et al 2016). On the other hand, the supply of resources and competition (Blaber et al 1989;Day et al 2012;Le Pape and Bonhommeau 2015;Whitfield 2016;Teichert et al 2017), along with tolerance or preference for specific environmental conditions (Blaber et al 1989;Able 2005;Sheaves and Johnston 2009;Whitfield et al 2012), also influence the use that fish have of estuaries, which is reflected in variations of the fish assemblage, spatially and temporally.…”

Food from the Sulawesi Sea, the need for integrated sea use planning

“…Hence, fishermen have an incentive to increase their wild shrimp catches by increasing their fishing effort, using a variety of fishing gears. However, these catches also depend on the abundance of adult shrimp stock, and shrimp sizes (Sheaves et al 2013, Baker et al 2014. The distribution of shrimp is affected by a range of environmental factors and spatial attributes that affect the growth and survival rates of juvenile shrimp in different habitats (Primavera 2005a, Barbier 2007a, Chong 2007.…”