I examined patterns and timing of ontogeny and relative growth in five species of blenny (Teleostei: Blenniidae) from the northern Gulf of Mexico by assigning a suite of discrete character state scores to ontogenetic events (10 external traits; 218 total specimens). This is the first study to evaluate developmental patterns in reef-associated fishes relative to the timing of metamorphosis and settlement by applying scaling techniques and statistical methods to quantify, differentiate, and select criteria for defining intervals of development across taxa.
Blennies settle at a common state of ontogeny and share a common pattern of body and fin/cirrus growth. Three 'natural' intervals of development (labeled 'larvae', 'metamorphs', and 'settlers') were consistently identified based on scoring and summing character states, and cluster analysis. Shape differences separate larvae from metamorphs, but not metamorphs from recent settlers. The common growth pattern consists of a general deepening of the head and abdomen, a narrowing of the interorbital region, and elongation of the pectoral and pelvic fins. These changes during metamorphosis produce the common shape and basic adult body form at settlement. Differences in shape show little relationship to phylogenetic distance.
Estuarine blennies settle at a smaller size but similar state of ontogeny as coastal/shelf species, which suggests the timing, rate, and state of ontogeny at important periods of ecological transition, may influence survival. The smaller size at settlement in estuarine blennies is consistent with natural selection emphasizing rapid ontogeny in species or areas where competition for available habitat or resources is great. Differences in fin and body pigmentation patterns and in the number of teeth between estuarine and coastal/shelf blennies suggest that development reflects adaptive convergence to similar ecological niches and habitats, rather than revealing any evolutionary relationship.
In blennies, ontogeny progresses gradually and continuously rather than in a stepwise fashion, as postulated by saltatory theory. Differential growth rates of individual body parts provide a similar conclusion. Variability in the timing and magnitude of ontogeny make recognizing proposed thresholds between 'steps' difficult, if not impossible. Blennies are not juveniles at settlement as commonly accepted for many other demersal and reef-associated species.