Abstract
Settlement is a key process for meroplanktonic organisms as it determines distribution of adult populations. Starvation and predation are two of the main mortality causes during this period; therefore, settlement tends to be optimized in microhabitats with high food availability and low predator density. Furthermore, brachyuran megalopae actively select favorable habitats for settlement, via chemical, visual and/or tactile cues. The main objective in this study was to assess the settlement of Metacarcinus edwardsii and Cancer plebejus under different combinations of food availability levels and predator presence. We determined, in the field, which factor is of greater relative importance when choosing a suitable microhabitat for settling. Passive larval collectors were deployed, crossing different scenarios of food availability and predator presence. We also explore if megalopae actively choose predator-free substrates in response to visual and/or chemical cues. We tested the response to combined visual and chemical cues and to each individually. Data was tested using a two-way factorial design ANOVA. In both species, food did not cause significant effect on settlement success, but predator presence did, therefore there was not trade-off in this case and megalopae respond strongly to predation risk by active aversion. Larvae of M. edwardsii responded to chemical and visual cues simultaneously, but there was no response to either cue by itself. Statistically, C. plebejus did not exhibit a differential response to cues, but reacted with a strong similar tendency as M. edwardsii. We concluded that crab megalopae actively select predator-free microhabitat, independently of food availability, using chemical and visual cues combined. The findings in this study highlight the great relevance of predation on the settlement process and recruitment of marine invertebrates with complex life cycles.
Highlights
Settlement is a key process in the life cycle of meroplanktonic organisms as it determines the distribution of adult populations and community structure [1,2]
Exploring the Potential Food Availability – predatory Risk Trade-off In M. edwardsii and C. plebejus, results showed that predator presence had greater relative importance than food availability on crab settlement success (Figure 3; Table 1)
For M. edwardsii, free predators treatments showed only 57% of the settlement observed in treatments with no predators (LSD test, p#0,001), and 75% compared to chelae-secured treatments
Summary
Settlement is a key process in the life cycle of meroplanktonic organisms as it determines the distribution of adult populations and community structure [1,2]. This is mainly because settlers undergo high mortality rates as a consequence of their extreme vulnerability to a variety of factors during this period [3]. Selective pressure promotes a pool of the morphological traits and larval behavioral strategies that could drive settlement in microhabitats with high availability of food and refuge from predators [6,7]. In most marine meroplankton selection of settlement habitat is not a random choice. Preference for settlement in microhabitats with abundant organic matter has been reported and direct or indirect signals of food availability can be a strong settlement cue [7,9]
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