It has been relatively quiet in the bays over the last week. The water is noticeably cooler now, but still fine for swimming if you don’t mind it being a bit fresh when you first get in.

This week I’ve been lucky enough to see one or both green turtles (Chelonia mydas) every time I’ve been out in the channel off the Salt House.

But the most noteworthy thing was that the adult sand mullet (Myxus elongatus) moved out of Emily Bay and formed a large school just above the reef off the Salt House. They were swimming around just beneath the surface and weren’t feeding, and stayed a few days before disappearing. Looking back through my photos from last year, they did the same thing in the same first week of July, which I find fascinating (see the images below). I am speculating that they were congregating in a large school prior to maybe leaving the bay to spawn.

I also saw a mature female elegant wrasse (Anampses elegans) a few times. Like many other wrasse species, juvenile elegant wrasse are female. They tend to move around in a school, but this dominant, alpha, female was on her own, and will, in all likelihood, be the one that changes sex to a male and controls a school of female fish if the male inside the lagoon disappears. This changing of sex is known as sequential hermaphroditism. I’ve only ever seen the male a couple of times and have included a photo here so you can see the difference. Males, which are territorial, cannot generally change back to females, which is why they are called ‘terminal males’. However, you may be interested to read on about the dangers of some sunscreens, below.

Sunscreens

On 8 July, Maui Nui Marine Resource Council ran a presentation on the use of sunscreens and their effect on coral reefs. Sunscreen is highly toxic; from 1 January this year, Hawaii has banned sunscreens containing the reef-harming chemicals oxybenzone and octinoxate. This presentation reviews the science and governance around the new law, and how effective it has proved in protecting their coral reefs and marine animals.

The presentation is quite long (over an hour) but it is a salutary exposé of how intense tourism and the use of unsafe sunscreens can cause ecological ruination to nearby coral reefs, and I can highly recommend it to anyone with a passing interest.

The main take-out messages are:

• Using an average dollop of sunscreen, swimmers at the beach can contribute 36 g of sunscreen every two hours per person into the environment.

• Thirty minutes after the application of sunscreen, it can be detected in urine.

• The sunscreen residue on skin washes off in the shower and eventually finds its way into the environment.

• Oxybenzone is an endocrine disruptor causing male fish to be less aggressive or less willing to mate. I mentioned the female elegant wrasse, Anampses elegans, above, which I saw in the bay this week and how she may end up as the male. Where there are sufficient concentrations of oxybenzone in the water, it can prevent this process of sequential hermaphroditism from occurring. Males can turn back into females; or it can prevent the mature alpha female from becoming a terminal-phase male, and consequently effecting the reproductive capacity of that species because there are no males to breed with.

• The chemicals in sunscreen can cause either the sterility of corals and fish, or for them to produce unhealthy offspring. They may look healthy but they become known as coral reef zombies.

• Oxybenzone can be toxic to the larval stage of fish.

• When something happens to kill off the reef (increased sedimentation, or bleaching, for example) a generally healthy reef will bounce back. However, reefs affected by the chemicals in sunscreen won’t necessarily have the capacity to do this.

• Sunscreen is extremely toxic to lawns and is a herbicide. Some golf courses rule that there must be no sunscreen application while players are out on the greens because it will kill the turf. Likewise, it kills underwater algae that is food for turtles.

• Oxybenzone decreases the temperature at which corals bleach, and therefore decreases a coral reef’s resilience to climate change.

Obviously, a lot more was covered in the time of the presentation. If you want to watch it, you can find it here. Please note that the presentation starts after a short gap of just over a minute. The Maui Nui Marine Resource Council also has a great page with steps you can take to help.