MEPS 233:157-168 (2002)  -  doi:10.3354/meps233157

Gametogenesis and reproductive behavior in the echinoid Lytechinus variegatus

Daniel A. McCarthy*, Craig M. Young

Department of Larval Ecology, Harbor Branch Oceanographic Institution, 5600 US Hwy 1 N., Ft. Pierce, Florida 34946, USA

ABSTRACT: Gametogenesis and behavior facilitating reproduction were studied in the echinoid Lytechinus variegatus (Lamark 1816), found off Key Biscayne, Florida, during 1993. Oocyte diameters and qualitative staging of gonad sections indicated a sustained peak in reproductive state from April to June followed by a decrease in reproductive state by August and a shorter reproductive peak by November. Ripe females censused during both reproductive seasons showed substantial variation in oocyte size suggesting that sporadic, small scale spawning events commonly occur in this population. Counts of urchins in nested quadrats showed that L. variegatus aggregates at no fewer than 4 different spatial scales (0.0625, 0.25, 1.0 , and 2.0 m2 ) with aggregations at larger scales being most common, especially prior to reproductive seasons. A noticeably higher amount of food in guts at these times suggests that these aggregations may be formed during random encounters during periods of increased feeding activity, which may also build up energy reserves for reproduction. Marked urchins were arranged in artificial aggregations of various sizes to investigate potential reproductive interactions. Most urchins moved 1 to 3 m d-1 throughout the year. Most encounters among urchins were of short duration and occurred randomly. Urchins placed in the largest aggregations dispersed most slowly during April and June, the periods with the highest mean oocyte diameters. The incidence of heterosexual pairing among naturally occurring pairs of urchins was random, suggesting that L. variegatus may not be able to distinguish gender. Sex ratio of the population was skewed in favor of males. The data suggest that numerous small scale spawning events take place during an extended reproductive season and that intraspecific encounters occur during this season entirely by chance. This method of spawning may enhance outcrossing.

KEY WORDS: Aggregations · Behavior · Lytechinus · Gametogenesis · Movement · Echinoid

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