The severity of reduced arm or body length is less straightforward than abnormal development. Smaller pluteus larvae might be at greater risk of predation (Morgan 1995, Marshall & Keough 2008). Furthermore, plutei use their arms to feed and an increase in arm length leads to an increase in feeding rate (Strathmann 1971). Indeed food limitation studies on echinoderms showed that plutei respond to food limitation by elongating their arms to attempt to increase feeding rate (Strathmann et al. 1992,Fenaux et al. 1994, Sewell et al. 2004). Early stunting is therefore likely to have a cascading effect, leading to lower growth rate throughout the larval stage and beyond.Studies on mussels found a cascading effect of low food on larval and juvenile growth, with smaller larvae metamorphosing into slower growing juveniles, thus further increasing the size difference and mortality rate in the juvenile stage (Phillips 2002, 2004).
Metal pollution may impact larvae physiologically in ways that do not result in gross developmental or size abnormalities, which would be unnoticed in this study. More sensitive measurements such as levels of metallothionein proteins have been proposed(Damiens et al. 2006, Geffard et al. 2007). Despite being a sign of metal-induced stress, elevated metallothionein might have no negative impact on short- or long-term growth and survival, and may not necessarily be present as invertebrate physiological responses to metals vary between species (Eisler 2007). Therefore, more research is needed to determine the relevance of such measurements at individual- and population-levels.