Reproduction of sympatric populations of Patiriella gunnii, P. calcar and P. exigua in New South Wales, asterinid seastars with direct development

Abstract

Three asterinid seastars, Patiriella gunnii (Gray), P. calcar (Lamarck) and P. exigua (Lamarck) are sympatric in southeast Australia and form part of a series of Patiriella species endemic to Australian shores. Reproduction of co-occurring populations of P. gunnii, P. calcar and P. exigua was investigated in New South Wales from December 1988 to February 1991. Their reproductive cycles were documented by the gonad index (GI) method and by histological examination of the gonads. The annual cycle of the pyloric caecae was also documented and the relationship between the two indices was examined. Oogenesis and spermatogenesis are described in histological detail. The three species produce large yolky eggs and have direct development. Vitellogenesis and weight-gain by the ovaries results from accumulation of periodic acid Schiff (PAS +) material by the oocytes. P. gunnii and P. calcar are gonochoric and have well-defined reproductive cycles, spawning in spring and summer. There was a sharp decline in the GI of P. gunnii in December due to potentially synchronous spawning. Histological examination revealed that initiation of gamete release occurred in August. Gamete release by P. calcar also started in August, with episodic spawning through December. P. gunnii and P. calcar have coincident 3 to 4 mo breeding seasons. In general, P. exigua is protandrous with a broad size range over which sex change occurs. Some P. exigua, however are simultaneous hermaphrodites at the outset of gonad formation and become increasingly female with growth. This species has continuous gametogenesis and oviposits its eggs on the undersides of intertidal boulders, with enhanced oviposition during winter and spring. Newly metamorphosed P. exigua occupy intertidal microhabitats and were located in the field from August to October. It is suggested that increasing sea temperature during spring may serve to cue gamete release by P. gunnii and P. calcar and that enhanced oviposition of P. exigua in winter may be in response to conditions optimal for development of the egg masses at this time. The GI of male and female P. gunnii and P. calcar did not differ, while male P. exigua had a significantly lower GI than the females. Small males are characteristic of this latter species, and it is suggested that the decreased male investment in P. exigua is associated with its non-planktonic development. The gonad and pyloric caeca (PCI) indices of P. gunnii exhibited a reciprocal relationship, indicating that the transfer of nutrients from the caeca to the gonads supports gametogenesis. These indices were partly reciprocal in P. calcar. It is suggested that gonadal growth in P. calcar may be less dependent on caecal reserves than that in P. gunnii. The PCI of P. exigua maintained a similar level throughout the year and was higher than the GI. Although the Patiriella species have coincident breeding periods, temporal differences in the intensity of spawning appears to reproductively isolate them in the field.