Juvenile Urchins Research Articles

Distribution patterns of Tetrapygus niger (Echinodermata: Echinoidea) off the central Chilean coast

We investigated spatial distnbution and temporal occurrence patterns of Tetrapygus niger in the subtidal zone off the central Chilean coast from March to November 1990. The shallowest portion of the subtidal zone and the shallowest edge of the kelp forest of Lessonia trabeculata appeared to be important recruitment zones for this species We found a s~gnificant number of recruits along the bed border, and a marked decrease of u rchn abundance toward the center of the kelp Data obtained in September and November outside the kelp bed showed juvenile urchins [i.e. <24 mm test diameter (TD)] strongly associated with crevices. Size-frequency distributions at 2 m depth for those months also showed a large trough of intermediate-sized individuals (i.e. 15 to 30 mm TD). Temporal analysls of size-frequency distributions of individuals collected outs~de the kelp showed a relatively slow shift of modes between March and September and a malor modal shift from September to November. Density values of urchins found in November were relatively low; however, the individuals appeared aggregated.

Recruitment characteristics of the commercially harvested red sea urchin Strongylocentrotus franciscanus in Southern British Columbia, Canada

The test size frequencies of red sea urchin, Strongylocentrotus franciscanus (Agassiz), populations from British Columbia revealed low recruitment overall (≈9.5%) compared with populations from lower latitudes. Juvenile urchins tended to shelter under adult conspecifics. On a fine scale, i.e. over 0.5–8.0 km, high variability in recruitment was evident. Possible effects of commercial harvesting are discussed. Site-specific harvest controls based on local habitat and urchin population (size-frequency) data are desirable as a fishery management tool, but would be too costly to gather over such an extensive coastal area.

Electrical activity at metamorphosis in larvae of the sea urchin Lytechinus pictus (Echinoidea: Echinodermata)

AbstractTwo types of electrical potentials were recorded from competent echinopluteus larvae of Lytechinus pictus. The first was associated with reversal of cilia that line the ridges of larval epaulettes. Ciliary reversal potentials were recorded from all parts of the larvae and from isolated body parts. Estimated conduction velocity of ciliary reversal potentials was 10–20 cm/s. The second type of potential was largest when the electrode was placed over the urchin rudiment. Rudiment potentials could not be recorded from isolated epaulettes and could not be correlated with any obvious behavior of the larva.Both potentials increased in frequency when a larva was brought in contact with a “conditioned” substrate. Ciliary reversal potential frequency increased six‐ to seven fold within a minute or two of contact and remained elevated until the point of partial tissue collapse during metamorphosis. Rudiment potential frequency also increased, but only three‐ to five fold and with a longer latency (3–6 min to peak frequency). Rudiment potentials maintained an elevated level of firing through total tissue collapse, at which time the larvae were electrically silent. Attempts to record from juvenile urchins, to determine the fate of the rudiment potential system in the final stage of metamorphosis, were unsuccessful.