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Marine Life & Conservation Blogs

The Sergeant Major Fish: Underdog to Super-Dad

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You’re on a dive, minding your own business when suddenly, your mask is being bombarded by a frantic and extremely angry creature. In shock you reverse, exiting the firing line when you realise that the monster in question is none other than the Sergeant Major Fish.

If your biggest fear in the ocean is the ‘dreaded shark’, think again, it’s the Sergeant Major you really have to worry about!! In disbelief you take a second glance and notice that the creatures you once thought were small and peaceful are all behaving in this manner to anything crossing or invading their path.

Why do they behave like this? And why have you never noticed this before?

Background Check

Abudefduf is from the Arabic; abu “the one with”, def “side”, and duf “prominent”. Its name, referring to the vertical black bars on its side, roughly translating to “the one with prominent sides”. This is also where its gets its common name “Sergeant Major,” as the stripes resemble the bars on a military uniform. Despite the general common name Sergeant Major there are up to 20 species of this damselfish, part of the family Pomacentridae, that you can be found worldwide. Generally, their bodies are deep, oval and compressed with a continuous dorsal fin and a forked caudal fin, but each species varies in size and the number of dorsal fins, dorsal soft rays, anal spines and anal soft rays.

Meet the Locals

Here in the UAE we have the Indo-pacific Sergeant Abudefduf vaigiensis. Widely distributed throughout the Indo-Pacific: Red Sea, Indian Ocean to eastern Africa, north to southern Japan, and south to Australia. In 1991, it was even discovered in the Hawaiian Islands, possibly floating marine debris such as abandoned fishing nets, where it now coexists with the Hawaiian Sergeant Abudefduf abdominalis. They form large aggregations while feeding during the day and play hide and seek by themselves at night on coral reefs, tidal pools and rocky reefs at depths between 1 to 15 m. The Indo-pacific Sergeant can grow up to 20 centimetres long, feeding on zooplankton, benthic algae and small invertebrates.

The Interesting Part!

So now you have the Sergeant Major’s background check. Here’s the fascinating part!

Between March and August, the Sergeant Majors congregate in large numbers to reproduce. To start the process, the males prepare temporary nesting sites by coating patches of rocks, shipwrecks and corals with an adhesive substrate. The females then wander around looking for that special partner to mate with. When a female is near, the male will try to attract the female by preforming a unique and intriguing dance which involves moving up and down erratically, like the local dance club. If she’s digging his moves she will deposit up to 20,000 eggs. Once the eggs have dispersed, they attach themselves to the substrate the males prepared and will then be fertilized.

After all the fun, the females eventually take off leaving the males with all the responsibility of protecting his little patch. The male is extremely attentive by continuously aerating his eggs stopping fungus build up. He will also turn a darker bluish colour which most likely acts as a warning colour to predators or even possible camouflage. Any fish that comes too close are aggressively chased away and divers are left in bewilderment.

The eggs start as solid red ovals around 0.5-0.9mm. Once they are fertilised they start to turn a green colour with a deep red yolk leaving the surfaces as a patchwork. After 4-5 days the eggs will hatch an hour after sunset. If you are able to see the hatching, it can be amazing to watching as they wiggle out from the substrate and break free. Once hatched they are around 2.4mm in size and set off to tackle the big blue ocean.

I have been very privileged over the last few weeks to witness parts of this process and they are amazing to watch. The reef has literally been covered in patches of varying shades of red and green. The determination of the male Sergeant Major whilst hilarious to watch is also impressing for such a small creature to display. With my new camera I was able to catch some of these processes, but my next goal is to capture the courtship ritual and hatching (I may need a bigger camera though).

Next time you are out diving, make sure you don’t overlook the little guys, and look out for the patchwork of the ocean created by the Sergeant Major Fish.

Find out more about Kayleigh at www.followthewhitefin.com

Originally from the UK, Kayleigh has spent most of her life traveling all over the world. She is a PADI Master Scuba Diver Trainer, IYT Dive Boat Mate and International Association for Handicapped Divers (IAHD) Instructor. She taught scuba diving in the UK for 2 years but swapped the dry suit for warmer climates in the Caribbean and the U.A.E. and started blogging along the way.

Marine Life & Conservation Blogs

Creature Feature: Undulate Ray

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In this series, the Shark Trust will be sharing amazing facts about different species of sharks and what you can do to help protect them.

This month we’re looking at the Undulate Ray. Easily identified by its beautiful, ornate pattern, the Undulate Ray gets its name from the undulating patterns of lines and spots on its dorsal side.

This skate is usually found on sandy or muddy sea floors, down to about 200 m deep, although it is more commonly found shallower. They can grow up to 90 cm total length. Depending on the size of the individual, their diet can range from shrimps to crabs.

Although sometimes called the Undulate Ray, this is actually a species of skate, meaning that, as all true skates do, they lay eggs. The eggs are contained in keratin eggcases – the same material that our hair and nails are made up of! These eggcases are also commonly called mermaid’s purses and can be found washed up on beaches all around the UK. If you find one, be sure to take a picture and upload your find to the Great Eggcase Hunt – the Shark Trust’s flagship citizen science project.

It is worth noting that on the south coasts, these eggcases can be confused with those of the Spotted Ray, especially as they look very similar and the ranges overlap, so we sometimes informally refer to them as ‘Spundulates’.

Scientific Name: Raja undulata

Family: Rajidae

Maximum Size: 90cm (total length)

Diet: shrimps and crabs

Distribution: found around the eastern Atlantic and in the Mediterranean Sea.

Habitat: shelf waters down to 200m deep.

Conservation Status : As a commercially exploited species, the Undulate Ray is a recovering species in some areas. The good thing is that they have some of the most comprehensive management measures of almost any elasmobranch species, with both minimum and maximum landing sizes as well as a closed season. Additionally, targeting is entirely prohibited in some areas. They are also often caught as bycatch in various fisheries – in some areas they can be landed whilst in others they must be discarded.

IUCN Red List Status: Endangered

For more great shark information and conservation visit the Shark Trust Website


Image Credits: Banner – Sheila Openshaw; Illustration – Marc Dando

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Guarding Against Coral Invaders

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Protecting (Dutch) Caribbean Reefs from Unomia stolonifera

Recent reports highlight the concerning spread of the invasive soft coral, Unomia stolonifera, currently devastating Venezuela’s marine ecosystems and detected in Cuba. With the potential threat of its expansion to the (Dutch) Caribbean islands, urgent action and awareness are essential to safeguard marine biodiversity and local economies from possible catastrophic consequences.

Invasive species are animals or plants from another region of the world that don’t belong in their new environment. These species can have major ecological effects by decimating native flora or fauna. They can also cause large economic losses and impact human health. Invasive species also pose a significant threat to marine ecosystems worldwide, including the Dutch Caribbean. Among these invaders is the octocoral species Unomia stolonifera or “Pulsing Xenia”, originally from the Indo-Pacific. With its rapid growth and lack of natural predators, this species can outcompete native species and disrupt fragile marine habitats such as seagrass beds and coral reefs.

Background

The invasive soft coral U. stolonifera was first identified in 2014, off the coast of Venezuela. It is believed to have been introduced via the illegal aquarium trade.  Since this species can reproduce sexually and asexually (or fragment), even small pieces can regenerate to spread.  Once introduced it quickly took over shallow reefs and hard substrate at depths of 0-50 meters, outcompeting local corals and seagrass for space.  Follow on surveys found that this coral species exhibited average percentage cover as high as 80%, vastly outcompeting native corals. In highly colonized areas, fish are disappearing due to loss of habitats.

In 2022, during a survey conducted in Cuba by the University of Havana, an unknown octocoral was discovered which was later identified as the invasive Unomia stolonifera. It is suspected that the coral larvae arrived in ballast water from fossil fuel ships originating from Venezuela, as nearby sites adjacent to Venezuelan ports have been heavily affected by the invasion.

How to help

Prevention through continuous monitoring, particularly in high-risk areas such as marine harbors and oil facilities, is paramount. Early detection plays a pivotal role in mitigating the threat posed by Unomia stolonifera.

The public’s involvement and awareness are also vital. Local communities, recreational divers, tourists, and all stakeholders are urged to participate in early detection efforts by reporting sightings (photo, location and date) of this invasive coral to their respective Protected Area Management Organization (PMO’s)- the Fundacion Parke Nacional Aruba (FPNA)STINAPA BonaireCARMABI Curaçao Saba Conservation Foundation (SCF)Nature Foundation St. Maarten (NFSXM) and St. Eustatius National Parks (STENAPA). If an invaded area is confirmed, follow the recommendations by the local PMO’s.

Keys to Success

Despite the challenges, early detection is key to mitigating the threat posed by Unomia stolonifera. With continued vigilance, research, and community engagement, there is hope for containing this potential issue before it becomes a major threat.

About the DCNA

The Dutch Caribbean Nature Alliance (DCNA) supports (science) communication and outreach in the Dutch Caribbean region by making nature related (scientific) information more widely available through amongst others the Dutch Caribbean Biodiversity Database, DCNA’s news platform BioNews and through the press. This article contains the results from several scientific studies but the studies themselves are not DCNA studies. No rights can be derived from the content. DCNA is not liable for the content and the in(direct) impacts resulting from publishing this article.

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