Hard time to be parents? Sea urchin fishery shifts potential reproductive contribution of population onto the shoulders of the youngest
- Subject Areas
- Conservation Biology, Ecology, Marine Biology
- gamete output, fishing, population structure, gonadosomatic index, reproductive potential, gonads, sea urchins
- © 2016 Loi et al.
- This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ Preprints) and either DOI or URL of the article must be cited.
- Cite this article
- 2016. Hard time to be parents? Sea urchin fishery shifts potential reproductive contribution of population onto the shoulders of the youngest. PeerJ Preprints 4:e2502v1 https://doi.org/10.7287/peerj.preprints.2502v1
Background. In Sardinia, as in other regions of the Mediterranean Sea, sustainable fisheries of the sea urchin Paracentrotus lividus have become a necessity. At harvesting sites, the systematic removal of large individuals (diameter ≥ 50 mm) seriously compromises the biological and ecological functions of sea urchin populations. Specifically, in this study, we compared the reproductive potential of the populations from two Mediterranean coastal sites which have different levels of protection. The sites were Su Pallosu, where fishing pressure is high (take zone) and at Tavolara-Punta Coda Cavallo Marine Protected Area (no-take zone) where the pressure is negligible. Methods. Reproductive potential was estimated by calculating Gonadosomatic Index (GSI) from June 2013 to May 2014 both for individuals of commercial size (diameter without spines, TD ≥ 50 mm) and the undersized ones with gonads (30 ≤ TD < 40 mm and 40 ≤ TD < 50 mm). Gamete Output was calculated for the commercial-size class and the undersized individuals with fertile gonads (40 ≤ TD < 50 mm) in relation to their natural density (Gamete Output per m2). Results. The reproductive potential of populations was slightly different at the beginning of the sampling period but it progressed at different rates with an early spring spawning event in the take zone and two gamete depositions in early and late spring in the no-take zone. For each fertile size class, GSI values changed significantly during the year of our study and between the two levels of protection. Although the multiple spawning events determined a two-fold higher total Gamete Output of population (popTGO) in the no-take zone, the population Mean Gamete Output (popMGO) was similar in the two zones. In the take zone, the commercial-sized individuals represented approximatively 5% of the population, with almost all the individuals smaller than 60 mm producing an amount of gametes nearly three times lower than the undersized ones. Conversely, the high density of the undersized individuals released a similar amount of gametes to the commercial-size class in the no-take zone. Discussion. Overall, the lack of the commercial-size class in the take zone does not seem to be very alarming for the self-supporting capacity of the population, and the reproductive potential contribution seems to depend more on the total density of fertile sea urchins than on their size. However, since population survival in the take zone is supported by the high density of undersized sea urchins between 30 and 50 mm, management measures should be addressed to maintain this size and to shed light on the source of the larval supply.
This is a preprint submission to PeerJ Preprints.
Results of PERMANOVA analysis
p-values were obtained using 9999 Monte Carlo samples from the asymptotic permutation distribution. Significant results are in bold.
Results of fertility tests
Mean percentage (± standard deviation) of fertilized eggs and four-arm echinoplutei obtained from tests of fertility performed on US individuals from both zones during the months of maximum gonadal development.
non-metric Multi-Dimensional Scaling for algal cover
nMDS ordination on algal cover of all replicate quadrats. White plots = take zone; black plots = no-take zone; triangles = July ’13; squares = January ’14; circles = May ’14.
Sea surface temperatures
Mean values (± standard deviation) of water temperature (SST) registered from June 2013 to May 2014. Squares = take zone; circles = no-take zone.
Data used for GSI analysis
Database of fertility tests conducted on undersized sea urchins (US)
Sea surface temperatures
Dataset of algal groups
Dataset used to calculate the percentage cover of conspicuous algal taxa or morphological groups.