Reproduction and adapted histology for Yellow Hedgehog sponges. A study of Polymastia boletiformis in the Koster Sea.

Abstract

The Koster Sea is Sweden's most sponge rich area, hosting around 160 sponge species. Sponges are filter feeding invertebrates that belong to one of the oldest animal phyla on earth, Porifera. Concerning their body structure, they are regarded to be the simplest of multicellular animals, built up by rather independent cells with a low degree of specialization. This study has been looking into reproduction among the Polymastia. A genus with two known species in Swedish waters – Polymastia mamillaris and Polymastia boletiformis. So far, there has been no detailed reproductive study for either of those commonly found species in this region. Also, no knowledge of specific asexual reproductive structures is documented for the species. Major aims for this study were to identify collected sponges to species and to troubleshoot a repeatable methodology for histological processing of reproductive material in Polymastia. Reproductive studies in sponges are rare, and so methodology for good histology is still cryptic. Polymastia specimens collected in the Koster Sea during 2023 were examined histologically to see if there were any differences in reproductive structures (asexual as sexual) regarding size, location in sponge bodies and seasonality. Together with Polymastia specimens from Gothenburg Museum of Natural History all sponges were examined for signs of asexual reproduction. Sponges collected in this study belonged to the same species, the yellow hedgehog sponge P. boletiformis. Three specimens were identified as reproductive females with early oocytes with significantly different sizes. They were collected in April and the presence of small oocytes indicated that the species might reproduce during summer in the Koster Sea. No signs of asexual reproduction were found among the collected specimens nor the museum specimens. This study contributes to the field of basic science within sponge reproduction with a fully adapted histology protocol for P. boletiformis. Furthermore, it contributes with the first observations of reproductive Polymastia individuals in Swedish waters.