Photoperiod, temperature, and food availability as drivers of the annual reproductive cycle of the sea urchin Echinometra sp. from the Gulf of Aqaba (Red Sea)

Abstract

In spite of the efforts invested in the search for the environmental factors that regulate discrete breeding periods in marine invertebrates, they remain poorly understood. Here, we present the first account of the annual reproductive cycle of the pantropical sea urchin Echinometra sp. from the Gulf of Aqaba/Eilat (Red Sea) and explore some of the main environmental variables that drive echinoid reproduction. Monthly measurements of gonado-somatic indexes and histological observations of 20 specimens revealed a single seasonal reproductive cycle, with gametogenesis in males and females being highly synchronized. Gametogenesis commenced in June and peak spawning occurred between September and October. Gonado-somatic indexes were significantly correlated with seawater temperatures but not with photoperiod. The latter cycle lagged behind the gonado-somatic cycle by two months, suggesting that the onset of gametogenesis corresponds to shortening day length, while spawning may be driven by warming seawater temperatures. Gonads remained quiescent throughout the winter and spring (January through May) when temperatures were at their lowest. Chlorophyll-a concentrations increased significantly in the months following spawning (October through January). These high concentrations are indicative of high phytoplankton abundance and may reflect the increase in food availability for the developing larvae. Of the external test dimensions, length presented the highest correlation to body weight, indicating length as the best predictor for body size in Echinometra. Neither sexual dimorphism nor size differences between males and females were detected, and the sex ratios were approximately 1:1 in three distant Echinometra populations. Environmentally regulated reproduction, as occurs in sea urchins, might face severe outcomes due to anthropogenic disturbances to the marine environment. Consequently, there is a need to deepen our understanding of the mechanisms that drive and regulate this process in broadcastspawning species.

Temperature influences the reproduction of fiddler crabs at the southern edge of their distribution

“…The breeding season, for example, tends to be continuous or prolonged in tropical populations, and restricted to warmer months in temperate ones (Clarke 1987;Hines 1989;Bauer 1992;Defeo & Cardoso 2002;Hartnoll 2006;Luppi et al 2013;Stocks et al 2015;Bi et al 2016). Other traits that influence reproduction and can be affected by variation in climatic conditions (e.g., temperature, photoperiod) or availability of resources along the latitudinal gradient include size at the onset of sexual maturity, ovary maturation, synthesis of vitellogenin, and the number and size of broods (P€ ortner et al 2007;Hirose et al 2013;Bronstein & Loya 2014;Thongda et al 2015;Thatje & Hall 2016). Understanding the spatial patterns of reproductive biology might allow prediction of species fitness and population stability in different locations within the geographical range of a particular species (Lester et al 2007;P€ ortner et al 2007;Stocks et al 2015).…”

Reproduction of the long-spined sea urchin Diadema setosum in the Gulf of Aqaba - implications for the use of gonad-indexes

“…High TBT concentrations, on the other hand, have been measured in the past from sites adjacent to the current sampling locality 32 . Interestingly, sex ratios in Echinometra sampled in the same locality on the exact same dates, showed equal proportions of males and females 33 – possibly indicating differential susceptibility to pollutants. Specimens of Tripneustes gratilla elatensis , again from the same sampling site, showed mass skeletal deformations that are thought to have been caused by chemical pollutants 34 , while other echinoid species in the area, including Diadema and Echinometra , showed no signs of deformations.…”

“…Production of a large number of excess oocytes consequently leads to phagocytosis of the unspawned portion, producing a bimodal oocytes size frequency distribution 25 . In contrast, when only a low number of excess oocytes are being produced, the continuous progression of small to large oocytes is manifested as a unimodal distribution 33 35 . In this respect, Diadema from the GOA seem to produce few excess oocytes per gametogenetic cycle and their spawning is most likely exhaustive.…”

“…A similar tendency of gametogenesis initiation triggered by the onset of shortening day length was also reported in other echinoid species, such as Strongylocentrotus droebachiensis 49 , Eucidaris tribuloides 51 , as well as Echinometra sp. from the GOA 33 .…”

Predicting spawning date of nyale worms (Eunicidae, Polychaeta) in the southern coast of Lombok Island, Indonesia

“…Reproductive synchrony is therefore very much important to maximize reproductive output. Such asynchrony may be achieved by using natural cues from annual cycles of temperature (Olive 1980;Willis et al 1985;Babcock et al 1986) or photoperiod (Olive 1995) or both of them (Babcock et al 1994;Olive 1995;Brownstein and Loya 2015), and lunar or tidal cycles (Fong 1993). Coral reproduction in the Great Barrier Reefs has long been accurately predicted to species level and hours of spawning time (Willis et al 1985;Babcock et al1986) since it has been known that their spawning date and time are strongly linked with temperature, moon phase, and tidal cycles.…”