Tide-related periodicity of manta rays and sharks to cleaning stations on a coral reef

Although the movements of fishes on coral reefs have been well studied, there are few data on the movement of elasmobranchs on and around cleaning stations. The visitation to cleaning stations by elasmobranchs was documented by direct observation and remote video capture at an oceanic reef in the Coral Sea and the outer Great Barrier Reef at time scales of hours to weeks. Cleaning was only observed at Osprey Reef and duration of occupancy was recorded for all elasmobranch clients. Strong tidal patterns were detected, with 49% of sharks and 59% of mantas engaging in cleaning interactions on ebb tides. Forty-four per cent of non-cleaned sharks were also observed on ebb tides. Some manta rays (n = 19) were individually identified through ventral skin pigmentation to determine site fidelity; three were seen more than once with repeat observations occurring within days. This was consistent among weeks and days within weeks, regardless of time of day. Hypotheses for tidal behaviour are discussed and we argue that these observations are critical in elucidating previously unknown behaviours in elasmobranch ecology. Our study indicates that observations of large elasmobranchs at cleaning stations are another tool to elucidate elasmobranch ecology

Geochemistry of the Serifos calc-alkaline granodiorite pluton, Greece: constraining the crust and mantle contributions to I-type granitoids

The Late Miocene (11.6–9.5 Ma) granitoid intrusion on the island of Serifos (Western Cyclades, Aegean Sea) is composed of syn- to post-tectonic granodiorite with quartz monzodiorite enclaves, cut by dacitic and aplitic dikes. The granitoid, a typical I-type metaluminous calcic amphibole-bearing calc-alkaline pluton, intruded the Cycladic Blueschists during thinning of the Aegean plate. Combining field, textural, geochemical and new Sr–Nd–O isotope data presented in this paper, we postulate that the Serifos intrusion is a single-zoned pluton. The central facies has initial 87Sr/86Sr = 0.70906 to 0.7106, εNd(t) = − 5.9 to −  7.5 and δ18Οqtz = + 10 to + 10.6‰, whereas the marginal zone (or border facies) has higher initial 87Sr/86Sr = 0.711 to 0.7112, lower ε Nd(t) = −  7.3 to − 8.3, and higher δ18Οqtz = + 10.6 to + 11.9‰. The small range in initial Sr and Nd isotopic values throughout the pluton is paired with a remarkable uniformity in trace element patterns, despite a large range in silica contents (58.8 to 72 wt% SiO2). Assimilation of a crustally derived partial melt into the mafic parental magma would progressively add incompatible trace elements and SiO2 to the evolving mafic starting liquid, but the opposite trend, of trace element depletion during magma evolution, is observed in the Serifos granodiorites. Thermodynamic modeling of whole-rock compositions during simple fractional crystallization (FC) or assimilation-fractional crystallization (AFC) processes of major rock-forming minerals—at a variety of pressure, oxidation state, and water activity conditions—fails to reproduce simultaneously the major element and trace element variations among the Serifos granitoids, implying a critical role for minor phases in controlling trace element fractionation. Both saturation of accessory phases such as allanite and titanite (at SiO2 ≥ 71 wt%)(to satisfy trace element constraints) and assimilation of partial melts from a metasedimentary component (to match isotopic data) must have accompanied fractional crystallization of the major phases