For studying rock-pool and littoral fauna and flora, it’s essential to visit the shore at low tide and the lower the tide the better. The lowest low tides (and highest high tides) are when the Sun and Moon are in line - ie at the Full or New Moon. These extreme tides are called "Spring tides" (whatever time of year they fall!) while the smaller tides when Sun and Moon are out of alignment are "Neap tides".

Tides at the New Moon are generally slightly better than those at Full Moon, but the best Spring Tides (ie when the low tides go out furthest) are those near the Spring and Autumn equinoxes (when the Sun and Moon are most nearly in line.) Of course different organisms are on the shore at different times of year, so it’s worth visiting during any Spring Tides.

Note that the times of high and low tides move round the clock on a two-weekly cycle (c25mins later per day) and also differ at different places along the coast. However, at any given spot the high and low tides fall at the same time each Spring Tide.

The present site offers a Moon-phase calculator for any month and year - useful for estimating when Spring tides are for planning ahead or if you don’t have the relevant tide table. Obviously the appropriate local tide tables will be more accurate, will give times of low and high tides and precise tidal estimates, but the published guides tend to be only available locally and the online guides only cover a short time ahead (eg BBC: 1 week, Proudman Labs: 28 days).