Interactive Effects of Endogenous and Exogenous Nutrition on Larval Development for Crown-Of-Thorns Starfish

Abstract

Abstract:Outbreaks of crown-of-thorns starfish are often attributed to step-changes in larval survivorship following anomalous increases in nutrients and food availability. However, larval growth and development is also influenced by the nutritional condition of spawning females, such that maternal provisioning may offset limitations imposed by limited access to exogenous sources of nutrients during the formative stages of larval development. This study examined the individual, additive, and interactive effects of endogenous (maternal diet: Acropora, Porites, mixed, and starved) and exogenous (larval diet: high concentration at 10 4 cells·mL −1 , low concentration at 10 3 algal cells·mL −1 , and starved) nutrition on the survival, growth, morphology, and development of larvae of the crown-of-thorns starfish. Female starfish on Acropora and mixed diet produced bigger oocytes compared to Porites-fed and starved treatments. Using oocyte size as a proxy for maternal provisioning, endogenous reserves in the oocyte had a strong influence on initial larval survival and development. This suggests that maternal reserves can delay the onset of obligate exogenous food acquisition and allow larvae to endure prolonged periods of poor environmental nutritive conditions or starvation. The influence of exogenous nutrition became more prominent in later stages, whereby none of the starved larvae reached the mid-to-late brachiolaria stage 16 days after the onset of the ability to feed. There was no significant difference in the survival, development, and competency of larvae between high and low food treatments. Under low algal food conditions, larvae compensate by increasing the length of ciliated feeding bands in relation to the maximum length and width, which improve food capture and feeding efficiency. However, the effects of endogenous nutrition persisted in the later developmental stages, as larvae from starved females were unable to develop larger feeding structures in response to food-limiting conditions. Phenotypic plasticity influenced by endogenous provisions and in response to exogenous food availability may be an important strategy in boosting the reproductive success of crown-of-thorns starfish, leading to population outbreaks.

30 Years of Research on Crown-of-thorns Starfish (1986-2016): Scientific Advances and Emerging Opportunities

“…Laboratory experiments by Wolfe et al (2015aWolfe et al ( , 2017 demonstrated high larval survival and settlement success across a broad range of nutrient levels, and most importantly, below the lower threshold levels previously suggested by Fabricius et al (2010). The robust nature of larvae, even in oligotrophic conditions, may be driven by increased investment in provisioning of eggs by well-fed adults ) and the morphological plasticity of larvae to respond to changes in the availability of exogenous prey (Wolfe et al 2015b;Caballes et al 2017a). …”

“…solaris, based on contrasting diets (e.g., Acropora versus Porites), have a major bearing on the growth and performance of their progeny. Well-fed females provision their offspring with increased levels of endogenous energetic reserves, which not only allows larvae to withstand prolonged periods of starvation, but also enables them to grow larger and feed more efficiently (Wolfe et al 2015b;Caballes et al 2017a). Larval survivorship in the wild will also be limited by competition, predation and environmental constraints on development (see sections 2.13 and 2.14).…”

“…3) is extremely challenging. In culture, concentrations of CoTS larvae steadily decline with time (Wolfe et al 2015a;Caballes et al 2016Caballes et al , 2017aPratchett et al 2017b), indicative of significant rates intrinsic larval mortality (Rumrill 1990), which depend on food availability (section 2.1) and food quality (section 2.3). Mortality rates recorded for larvae in laboratory cultures ranged from 19% to 45% after 10 days (Wolfe et al 2015a).…”

“…It is also now understood that the algorithms used in the GBR to estimate chl-a from satellite remote sensing, in particular the MODIS satellite with the Aqua sensor, can give inaccurate and biased results; and therefore usage should be avoided for absolute measures of chl-a (King et al 2013). In-situ monitoring of nutrients, phytoplankton assemblages, and CoTS larvae, to relate size, abundance, condition larvae to local biological and environmental conditions (e.g., Wolfe et al 2015b;Caballes et al 2017a) in the lead up to the next outbreak of A. cf. solaris on the GBR, would clearly establish whether CoTS larvae can develop and settle even in the absence of nutrient plumes and phytoplankton blooms.…”

“…This special issue (Biology, Ecology and Management of Crown-of-Thorns Starfish) reflects the latest resurgence in scientific interest and research on Acanthaster spp., unequivocally focused on better understanding the initiation and spread of outbreaks, as well as refining the capability and capacity for effective management. In all, the papers presented in this special issue address: i) environmental drivers of fertilization and early development (Allen et al 2017;Caballes et al 2017b); ii) larval nutrition, larval development and implications for the 'nutrient enrichment hypothesis ' (Nakajima et al 2016;Brodie et al 2017;Caballes et al 2017a;Mellin et al 2017;Pratchett et al 2017b); iii) predation and implications for the 'predator removal hypothesis ' (Cowan et al 2016a' (Cowan et al , 2017Messmer et al 2017); iv) factors influencing settlement (Cowan et al 2016a;Pratchett et al 2017b); v) dispersal and genetics ; vi) longevity, growth, and size-and-age relationship (Wilmes et al 2016;MacNeil et al 2017); vii) movement (Sigl and Laforsch 2016); and viii) control and management (Buck et al 2016;Nakamura et al 2016).Aside from ongoing research to address critical issues related to the effective management of CoTS outbreaks, there have also been some fundamentally new directions for CoTS research in the last decade, enabled by advances in research methods and analytical capabilities. Therefore, this review also considers some of the foremost new directions for CoTS research, related to i) systematics and biogeography, ii) genetic and genomic sampling, iii) ecological modelling and iv) projected effects of environmental change.…”