Oreos—once bitten...

Figure 1. An X-ray scan of a spiky oreo.

This post is about oreos: the deep-sea fishes, not the cookies. I did wonder for a while which came first and perhaps that one was named after the other, especially since the eyes of some oreos actually look a bit like the cookies. Oreo means mountain in Greek and the Family name of the fish, Oreosomatidae literally means 'mountain-body'; referring to the large (dorsal) ridge found on the top of many species. As for the cookies, it turns out that oreo cookies were invented in 1912 and at one time were described as a 'mountain of a cookie', although apparently the history of the name is unclear.

Spiky oreo are a species of deep-sea fish (Neocyttus rhomboidalis Gilchrist, 1906, Family: Oreosomatidae), found off the coast of New Zealand and around the southern hemisphere at about the same latitude. Live oreos are not normally seen or caught by your average punter, as they are found between depths of 200–1200 metres. However, they are taken as bycatch in deep-sea fisheries, particularly those for orange roughy (Hoplostethus atlanticus, Collett, 1889).

There are commercial fisheries for black and smooth oreo and broadly speaking these fisheries are in similar places and depths as the orange roughy fisheries, although they tend to be further south. There are four common oreo species at these sorts of depths: black, smooth, spiky, and warty oreo. Spiky and warty oreos are the least common of the four and have a more northerly distribution.

For management purposes in NZ waters all four species are treated as one thing under the quota management system (Ministry of Fisheries 2014). I guess this makes it easier for the fishers, as they look similar. However, this is not so great for the fish themselves, as there is no way to know if one of the four species is being over-exploited if they are all recorded as the same thing.

Of the four species, the ecology of spiky oreo is arguably the least well known. Oreos have a gas-filled swim bladder and this expands rapidly as the fish is brought to the surface (a bit like the bends). As a consequence they suffer quite badly from stomach eversion; their stomach is forced inside out through the mouth by the expanding swim bladder (the expansion is caused by the change in water pressure and a particularly gruesome way to die I would image).

The only study I could find describing their diet recorded an eversion rate of ~94%. Lyle and Smith (1987) suggested that spiky oreo diet was dominated by zooplankton, particularly salps; although crustaceans,  fish, and cephalopods were also frequent food item. This is not a very helpful level of detail. However, this kind of diet suggests that spiky oreo feed in the water column and not from the seabed, which at least tells us something.

Anyway, I was going through some old photos the other day and came across a scan of a spiky oreo x-ray taken in 2004. These photos (Figures 1–3) are most interesting for the damage shown to the spine of this individual (Fig. 2). Predatory attacks on fish aren't always fatal, so I’m guessing this is either the result of an attack, or a malformation.

Figure 2. Note the repaired spinal damage.

Figure 3. A close-up of the dorsal spine.

Speaking of surviving attacks, Figure four is a picture of a warty oreo (Allocyttus verrucosus (Gilchrist, 1906)) with a large bite mark on it and Figure five is a close-up of the same bite mark. It’s not really possible to ascertain the size of the fish that made the bite mark, as the oreo may have grown since the bite. However, when the photo was taken the bite mark was about 50–60 mm across. I’ve been told that these bite marks are reasonably common and are often found in the same place—dorsally. The reasoning being that the oreos are not necessarily only being bitten in this area, but that bites elsewhere are fatal. I've not included data regarding the diet of warty oreo, as this is part of a paper I'm currently writing.

Figure 4. A warty oreo from Chatham Rise.

Figure 5. If you look carefully you can see the semi-circular scar.

This particular warty oreo was caught in 1062–1117 metres of water on northeastern Chatham Rise (same trawls as Jones 2008). I’m going to speculate that a deep-sea shark of some kind made the bite, as there are several likely candidates down at that depth. I wonder if it's possible to match the shape of the bite mark to a potential predator?


I'd like to acknowledge Steve O'Shea, as I think it was he who did the original scan of the spiky oreo. I honestly can't remember, but it seems a shame to not share the imagery, so I guess I'm doing it without permission. I'd also like to thank NIWA for retaining the fish for me; they came from the TAN0404 cruise.

References

Lyle, J.M. and D.C. Smith, 1987. Abundance and biology of warty oreo (Allocyttus verrucosus) and spiky oreo (Neocyttus rhomboidalis) (Oreosomatidae) off south-eastern Australia. Marine Freshwater Research 48: 91–102.

Jones MRL 2008. Dietary analysis of Coryphaenoides serrulatus, C. subserrulatus and several other species of macrourid fish (Pisces: Macrouridae) from northeastern Chatham Rise, New Zealand. New Zealand Journal of Marine and Freshwater Research 42: 73–84.

Ministry of Fisheries 2014. Oreo Fisheries Plan Chapter. ISBN: 978-0-478-43202-2 (online), pp1–53.

Helmets...

Some observations on sea-shells...

Helmet shells are attractive orange and brown sea-shells and belong in the family Cassidae. They are found in temperate and tropical waters worldwide. People mostly know of them from cameo broaches. Cameos are often made from tropical helmet shells; the designs being carved out the external shell layers.

In New Zealand the most commonly seen helmet shell doesn't really have a common name, apart from well, helmet shell, which makes it difficult when there are actually more than one species... Semicassis pyrum is the New Zealand species most people are likely to encounter and are frequently washed up on exposed sandy beaches (Figure 1). In the north the much scarcer S. labiata is also found. There are several other species of helmets, but most are rare, and only found in the north or in deep water (see Powell 1979; Spencer et al., 2009). Semicassis labiata is generally narrower than S. pyrum, and can often be a much darker colour, but they can often be quite similar-looking (see figures 1 and 2).

Figure 1. Helmet shell (Semicassis pyrum). Pilot Bay, Mt. Maunganui, August 2015.

Figure 2. Helmet shell (Semicassis labiata). Pilot Bay, Mt. Maunganui, August 2015.

Their ecology
Both species have quite a broad distribution, with S. pyrum also found in southern Australia, while forms of S. labiata are found in both southern Australia and South Africa. It is thought that this wide distribution is due to a relatively long planktonic larval stage (Beu 1976) (the larvae swim around in the sea for ages and this enables them to be spread far and wide).

The feeding ecology (what they eat) of these two species is not that well known, although it is thought that they feed on echinoderms, particularly heart urchins (Echinocardium spp.). Oddly enough, I've not been able to find any published data confirming this, just anecdotal information, so at the moment it seems to be assumed. Interestingly, I did find some speculation in a 1967 paper that suggested that S. pyrum could be responsible for the predation of offshore toheroa (Paphies ventricosa) populations off the west coast of the North Island (Waugh & Greenaway, 1967). However, other members of this family are known to feed on heart urchins, so this is something that could use further exploration.

Typically these two helmet shell species turn up in wash-ups on sandy beaches, after storms, so it was with much surprise that I recently discovered both species live in the intertidal zone of Mt. Maunganui’s Pilot Bay. To find both species, virtually together, and poking up through the sand was quite unusual. It was something I had not seen in my many years of fossicking around the base of the Mount. Here are some pictures...

Semicassis pyrum

Figure 3. Semicassis pyrum. Pilot Bay, Mt. Maunganui, August 2015.

Figure 4. Semicassis pyrum. Pilot Bay, Mt. Maunganui, August 2015.
My foot for scale.

Figure 5. Semicassis pyrum Pilot Bay, Mt. Maunganui, August 2015.
Showing the area of Pilot Bay where this shell was found.
The arrow points to the location of the half-buried shell

Figure 6. Semicassis pyrum). Pilot Bay,
Mt. Maunganui, August 2015.
This is a different shell taken a day later in a another part of Pilot Bay.

Semicassis labiata

Figure 7. Semicassis labiata Pilot Bay, Mt. Maunganui, August 2015.
This is the shell in-situ. 

Figure 8. Semicassis labiata Pilot Bay, Mt. Maunganui, August 2015.

Figure 9. Semicassis labiata. Pilot Bay, Mt. Maunganui, August 2015. Same day as Fig. 6.

What does all this mean?

What were they doing there? As mentioned above, I'd not seen them here before and S. labiata is never common. I remember being told in the 1980’s that they could be found around the side of the Mount. However, I didn't see one live until August 1995. This could mean that they don't do this very often, perhaps it only happens in winter, and not every winter. Perhaps this could be a case where viewing the occurrence is rarer than the occurrence itself.

This first thing that occurred to me was that maybe they had come into the shallows to breed. However, I didn't see more than one shell at any one time, so this seems unlikely. More likely would be coming up the beach to lay eggs. Laying eggs in winter would make sense, as then the eggs could develop and hatch in spring, which would enable the larvae to take advantage of springtime plankton blooms. Cutting them open to see what sex they were would have answered this question, as all of them were large and probably adult, but I wasn't going to kill them just to satisfy my curiosity. On further recollection, the one I found in 1995, I did collect, and on inspection was found to be male. This is contrary to expectations, so maybe there's another reason…

What I do know is that I didn't see enough of them to draw any firm conclusions, so I'll have to make sure that I'm there next year to see if they turn up again...



References

Beu, AG 1976. Arrival of Semicassis pyrum (Lamarck) and other tonnacean gastropods in the    Southern Ocean during pleistocene time. Journal of the Royal Society of New Zealand, 6(4) 417.

Powell AWB 1979. NZ Mollusca. Collins.

Spencer, HG, Willan RC, Marshall B, & Murray TJ.  2014.
   Checklist of the Recent Mollusca recorded from the New Zealand Exclusive Economic Zone.

Waugh, GD, Greenaway JP 1967. Further evidence for the existence of sublittoral populations of    toheroa, Amphidesma ventricosum Gray (Eulamellibranchiata), off the west coast of New Zealand.    New Zealand Journal of Marine and Freshwater Research 1 (4): 407–411.

Marine invaders from Australia...

More things from Oz we didn't ask for… 

In New Zealand marine ecology there is a long history of introduced species. For example, anyone who's spent time in either the Waitemata and Manukau Harbour's will have seen the banks of the Pacific oyster – Crassostrea gigas. Especially anyone who's had the misfortune to fall on them; these oyster shell banks did not exist before the 1960's. Marine invaders can be difficult to spot until they are established and their potential effects can be challenging to ascertain.

In 2009, Burchard’s whelk (Nassarius (Plicarcularia) burchardi (Dunker in Philippi, 1849)) appeared  in a survey of marine life in Auckland’s Waitemata Harbour (this survey is part of an ongoing monitoring programme) (Townsend et al. 2010). Burchard’s whelk is a small snail (~12 mm long) and is originally from southern and western Australia, where it is quite common. The habitat of this whelk tends to be sheltered, muddy areas (Figure 1).

Figure 1. Intertidal mud-flats at Point Chevalier, Waitemata Harbour, Auckland, New Zealand; habitat for Burchard’s whelk (Nassarius (Plicarcularia) burchardi).

Burchard’s whelk is most likely to have turned up from Australia as a result of ballast-water discharge. Nassariids are known to have a planktonic larval stage, so it seems plausible that larvae lived long enough to be transported across the Tasman Sea in the ballast water of a vessel, but not long enough to drift across through natural vectors. Otherwise, they’d be here already and would probably have been recorded before 2009. Although diminished in recent years, there has been a rich history of shell collectors in NZ  and it is very unlikely that this whelk would have escaped their notice.

I first searched for this species in December 2010 and found it at Point Chevalier (mid-way up the Waitemata Harbour, Figure 1). In June 2015 I revisited the same location (Figure 3) and this whelk was still common, so it doesn’t seem to be going away. If anything, it's range has expanded as Burchard’s whelk has recently been found in the northern port of Whangarei (NZMollusca n.d.).

Figure 2. Burchard’s whelk, Point Chevalier, Waitemata Harbour, Auckland, New Zealand, 4/12/10.

Figure 3. Burchard’s whelk, Point Chevalier, Waitemata Harbour, Auckland, New Zealand, 14/06/15.

Ecological implications...

There are some closely related New Zealand whelks that are in the same family as Burchard's whelk (Nassariidae), but these are mostly found offshore or in much sandier conditions (and one in the deep-sea) (Powell, 1979). None of the NZ nassariids are particularly common and very little is known about their ecology. Other closely related species overseas are considered to be scavengers, so assuming that this invader is also a scavenger would be a good place to start.

Burchard’s whelk appears to share a common ecological niche with at least one other NZ whelk species (mud whelk (Cominella (Josepha) glandiformis, and speckled whelk (C. adspersa), both common intertidal whelks in sheltered waters (Powell, 1979). Burchard’s whelk appears to be quite a fast mover (for a snail), so it has the potential to get to food sources before local species. This means that Burchard’s whelk has the potential to compete with these local species for food and possibly other resources. At some stage Burchard’s whelk may replace the local whelk species in areas where they both occur. In addition, these local species may perform other ecosystem services that the newcomer does not. Predators may not recognise the newcomer, as they may look/smell/act differently to the local species and 'fly under their radar'. As such the invasion of this new species may upset the balance/functioning of the intertidal ecosystem.

However, there are many things that are as yet unknown… 

 • We don’t whether Burchard’s whelk is increasing in population, nor do we know it size or range.
 • We don’t what it eats, although it is likely to be a scavenger feeding on carrion.
 • We don’t what, if anything, eats it.
 • We don’t know how Burchard’s whelk competes with local species for resources.

A recent conversation with Michael Townsend (NIWA), who authored the paper describing the first record of this species in NZ (see reference below) revealed that Burchard's whelk does indeed reach food before the local species. He is is currently researching the ecological effects of this invader, so it will be interesting to see what he finds out…


References

Powell 1979. New Zealand Mollusca. Collins.

Spurgeon A, n.d. New Zealand Mollusca. Nassarius (Plicarcularia) burchardi (Dunker in Philippi,          1849). http://www.mollusca.co.nz/speciesdetail.php?speciesid=2798&species=Nassarius%20(Plicarcularia)%20burchardi Accessed 5/08/15.

Townsend M, Marshall BA, Greenfield BL, 2010. First records of the Australian dog whelk, Nassarius (Plicarcularia) burchardi (Dunker in Philippi, 1849) (Mollusca: Gastropoda) from New Zealand. New Zealand Journal of Marine and Freshwater Research 44: 343–348.

Weird things found inside the stomachs of deep-sea fish #1.

Figure 1. A basketwork eel.

This is post started out as a description of something that came out of the stomach of a basketwork eel (Diastobranchus capensis Barnard 1923), but expanded to be about the eels themselves and their potential role in the deep-sea ecosystem they inhabit. 

Basketwork eels are a deep-sea species that are mostly found at depths of between ~800–2500m, in oceanic waters of the southern hemisphere. They belong in the family Synaphobranchidae (cutthroat eels). We only really know about them because they are taken as bycatch in deep-water fisheries, particularly those for orange roughy (in New Zealand waters). Once caught, almost all basketwork eels are discarded (dead or dying) back into the water. As a they have no commercial value their ecosystem role is not very well known.

Their role in the deep-sea ecosystem

For reasons I'm not going to go into here, the deep-sea ecosystem I'm talking about is an abstraction with rather vague boundaries. There are many deep-sea ecosystems, so in some ways it would be more accurate if I talked about a fishery, rather than an ecosystem. Assume when I say ecosystem I'm talking about the depth range between about 800 and 1200 m. This is because even though basketwork eels can live deeper than this, not much commercial fishing for orange roughy occurs deeper than 1300 m and this is the source of most of the data.

Basketwork eels feed on (in decreasing order of importance) fishes, squids, crustaceans, and whatever else will fit in their mouths. They are likely to be opportunistic scavengers and could perform an important role in deep-sea ecosystems cleaning up carrion. This is a good thing, as there have been concerns that dead animals (particularly fisheries discards) left on the seabed, will then decompose, use up the available Oxygen, and possibly create dead zones in the deep-sea. However, the evidence for them being scavengers is largely circumstantial; previous reports have suggested that they might scavenge, and they frequently turn up to deep-sea baited camera deployments. However, they are probably also predators, as the line between scavenging and predation is a blurry one and it can be very difficult to discern the difference between the two modes of feeding.

Figure two. The stomach contents of a basketwork eel.

Discerning their mode of feeding matters on an ecosystem-scale, because if they are mainly scavengers, then they may benefit from influxes of discarded fisheries bycatch. However, if they don't scavenge, (like orange roughy - a mid-water predator which only seems to take live prey), then discarded bycatch may not be of benefit to them. The answer to this question has implications for the structure of deep-sea ecosystems in response to fishing activity. 

For example, if basketwork eels benefit from bycatch, then their population could increase at the expense of other bycatch species (which may occupy a similar niche), and in turn change the structure of the ecosystem (called a trophic cascade). Which could possibly lead to a break down in the normal functioning of this ecosystem. And when I say normal functioning of the ecosystem. I really mean 'it stops giving you anymore of what you were extracting from it'.

Figure three. A basketwork eel with a distended stomach, containing the remains of a lighthouse fish (Phosichthys argenteus).

As an aside, this ecosystem has already had signficant alteration through a, the selective removal of ~70-90 % of the orange roughy through fishing, and b, the destruction of bottom habitat (large, erect corals, sponges etc...), also through fishing. These impacts mean that regardless of what research is done now, we are not looking at a pristine, unaltered ecosystem.


However, trophic cascades are complex phenomena and not very well understood, especially in the deep-sea. For the eels to benefit from the fisheries discards the assumption would have to be made that they could reproduce faster than they themselves were being taken as bycatch. I would hasten to add that there is at the moment no evidence for trophic cascades in the deep-sea, but this may only reflect a lack of data.

Figure two shows the stomach contents of a basketwork eel from northeastern Chatham Rise, New Zealand (from between 1062 and 1117 m depth). At the time I called it seaweed, as I had found brown seaweed in the stomachs of eels I had previously dissected (see below). As for this particular identification, I'm not so sure anymore… However, if it's not seaweed, what is it? I'd be interested to hear suggestions.

Figure four. The remains of a lighthouse fish taken from the stomach of a basketwork eel.

Figure three and four are of half a lighthouse fish; what it looked like before I opened the eel's stomach and after I had removed it.

The question here is, did the eel predate the fish; bite though it and lose the other half. Or did it just pick up half a fish that something else had bitten through? Or perhaps there is an alternative explanation? It's an interesting question and not one easily answered.

Figure five shows seaweed taken from the stomach of another eel. This is seaweed in the stomach of a fish caught in 1117 metres of water. So either this fish swam to the surface (not very likely), or the seaweed sank over a kilometre to the seabed and was consumed once on or near the bottom. recent work in Mediterranean has shown that deep-sea fish do actually consume vegetable matter It is not known whether the eels selectively target vegetable matter, or if these are just small items that fit in their mouths.

Figure five. The green material below the eel is seaweed.

After looking at the stomach contents of about 135 eels I reasoned that scavenged material could be defined as: anything that the eel would not normally have access to e.g., fragmentary animals that lived further up in the water column (as far as we know this eel stays close to the bottom throughout its adult life*); plant matter as mentioned earlier; and fragments of animals larger than the eel itself. Anything else was probably/possibly prey. 

Using those conditions it turns out that about 30% by weight of the food of basketwork eels (from northeastern Chatham Rise, New Zealand) was scavenged material. This suggests that these eels play an active role in cleaning up the deep-sea through the consumption of dead material. Interestingly there was no evidence of any kind of change in diet as the eels got larger. Usually as fish get bigger they are able to handle larger prey, so their diet changes (called an ontogenetic shift in diet). This lack of an ontogenetic dietary shift could be interpreted as further circumstantial evidence for scavenging, since a smaller eel could tackle a large chunk of carrion without having to catch it as prey. 

To conclude, what I found suggests that any influx of carrion in the form of fisheries discards is likely to have some sort of effect on the basketwork eel population and in turn the ecosystem they inhabit. However, without further longer term monitoring the form those impacts could take are unknown. This is an area of deep-sea research which really interests me.


References
Drazen, J.C., Bailey, D.M., Ruhl, H.A., Smith, K.L., 2012. The role of carrion supply in the abundance of deep-water fish off California. PLoS ONE 7, e49332

Fujiwara, et al., 2007. Three-year investigations into whale-fall ecosystems in Japan. Mar. Biol. 28, 219–232.

Jefferies, R.M., Lavaleye, M.S.S., Bergman, M.J.N., Duineveld, G.C.A., Witbaard, R.,2011. Do abyssal scavengers use phytodetritus as a food resource? Video and biochemical evidence from the Atlantic and Mediterranean. Deep-Sea Res. I 58,415–428.

Jones M.R.L., Breen, B.B., 2014. Role of scavenging in a synaphobranchid eel (Diastobranchus capensis, Barnard, 1923), from northeastern Chatham Rise, New Zealand. Deep-Sea Res 1 85, 118–123.

Zintzen, V., Anderson, M.J., Roberts, C., Harvey, E.S., Stewart, A.L., Struthers, C.D., 2012. Diversity and composition of demersal fishes along a depth gradient assessed by baited remote underwater stereo-video. PLoS ONE 7, e48522

*we don't really know for certain, but this species doesn't turn up in shallower water fisheries as bycatch, so it's not a bad assumption.

One fish, two fish... Well, one really

What you can do with one deep-sea fish…

In the deep-sea there are many species for which there is limited amounts of biological information. It's safe to assume that if there's no money to be made from it, then there's not likely to be all that much in the way of research regarding it. In June 2014 I had the opportunity to dissect a banded bellowsfish that had come to us mixed up with one of the giant squids we were dissecting for a live webcast. It turns out that this is a species of deep-sea fish that not really all that much is known. I was able to look in both its stomach and intestines, describe what this particular fish had recently been eating, and make some comments regarding it's ecological role.

Figure one. A banded bellowsfish possibly feeding from the seabed off the Wairarapa coast in approx. 300–400 m (image courtesy of the Ministry for Primary Industries. The black bar indicates 20 cm).

A brief summary of current level of knowledge regarding banded bellowsfish

The banded bellowsfish (Centriscops humerosus (Richardson 1846)) is a small fish (to ~30 cm) with a circumglobal distribution in temperate waters of the southern hemisphere. Commonly encountered between depths of 300–600 m (Froese & Pauly 2014; Francis et al. 2002). In New Zealand waters it is found on the continental slope, with a preferred depth of ~460 m (Francis et al. 2002). Because it’s a small fish, that lives in quite deep-water, nobody really knows all that much about it.

However, banded bellowsfish have been reported as bycatch in some New Zealand upper-slope fisheries, particularly those for hoki (Macruronus navaezealandiae Hector 1846) and scampi (Metanephrops challengeri Balss 1906) (Francis et al. 2002). Despite this, very little is known regarding their ecology, especially in New Zealand waters. 

Observations based on both still (Fig. 1, 2) and video footage suggest that they swim in close proximity to the bottom and are adverse to light (Pakhorukov and Parin 2012). Globally, little is known of their feeding, although off Tasmania they were found to feed mainly on brittle stars (Ophiuroidea) (Blaber & Bulman 1987). This feeding coupled with their proximity to the bottom, suggests that they may feed from, or near the seabed (benthic feeders). Incidentally, there are also anecdotal reports of banded bellowsfish in captivity breaking the surface and shooting water out of their mouths (Hannam pers. com.). This latter behaviour suggests that they might use jets of water to disturb or expose prey from the seabed. Pakhorukov and Parin (2012) also found that this species is more common around areas of three-dimensional complexity, e.g., coral, sponges etc… It is well known that in the deep-sea areas of increased structural complexity yield higher species-richness, so this could suggest that they could be utilising these areas for feeding or refuge.

Figure two. Two banded bellows fish swim in close proximity to the seabed, off the Wairarapa coast in approx. 300–400 m (image courtesy of the Ministry for Primary Industries. The black bar indicates 20 cm).

New data and conclusions

This is what I found: in the stomach there were three different valviferan isopods (a marine variety of slater). There was much more variety in prey in the intestinal contents; valviferan isopods, sections of sedentary worm tubes (and their remains), amphipod remains (a bit too digested to really tell much more), a nuculanid bivalve (clam), and a small (~3 mm) gastropod snail (?Rissoid-like). All these food items are consistent with a benthic-feeding mode. 

One of the interesting things I've found looking in the stomachs and intestines of deep-sea fish is that they often contain different things, and often the same fish can have different items in their stomachs and intestines (a topic I will write more on in the future).

While this is interesting dietary information, I was only looking in one fish, and it would be quite bad science to try and conclude too much from these data. However, it is a diet that is consistent with what little data exists. and what it does suggest is that there is an interesting project here for someone; not just describing the trophic role of this species, but analysing it’s size and age structure, as it’s probably safe to assume that this not been done.

References

Blaber SJM, Bulman CM 1987. Diets of fishesof the upper continental slope of eastern Tasmania: content, calorific values,dietary overlap and trophic relationships. Marine Biology 95: 245–356.

Francis MP, Hurst RJ, McArdle BH, Bagley NW, Anderson OF 2002. New Zealand demersal fish assemblages. Environmental Biology of Fishes 65: 215–234.

Froese RD, Pauly D. Editors. 2014. FishBase. World Wide Web electronic publication. http://www.fishbase.org, version (11/2014).

Pakhorukov NP, Parin NV 2012. Visual observations of fish at the Whale Ridge (Atlantic Ocean) from the Sever-2 manned underwater vehicle. Journal of Ichthyology 52 (9): 579–591.

Why here and then?

This blog post is another regarding a small New Zealand invertebrate (in this case a small marine snail) that not all that much is known about. It's also about finding things when you didn't expect to, and then finding them again in the same place (and at the same corresponding time) nearly thirty years later. There is also some speculation regarding how and why this might have occurred.

Often, when you are looking for marine animals you will find the remains of dead ones before you find living examples. This is almost universally true when it comes to shell collecting. Thanatocoenosis is a term to describe these death assemblages (it’s more of a paleontological term, but I just wanted to use a really big word). Also, in these assemblages you will tend to find a variety of sizes, from small juveniles to adults. Anyway, this brings me back to the topic of this post, which is when the opposite occurred; I found live ones before I found dead ones.

Margin shells are from the family Marginellidae, and in New Zealand waters we have quite a few endemic species. They live from the intertidal down to quite deep water. For example, I've taken one from the intestines of a white rattail that was caught in 901 metres of water (Jones 2008). As a family, they are characterised by having very small, quite polished shells. Many species, although small, are quite pretty (if you are that way inclined). 

Mesoginella koma (Marshall, 2004) is arguably the most common New Zealand margin shell. It is a small (6 mm) gastropod (snail) found throughout New Zealand in shallow water (Powell, 1979). It does not have a common name (to my knowledge) and was formally more well known as Marginella pygmaea Sowerby, 1846. Anyway, this is a species I’ve never found at Mt. Maunganui, well, I should say I’ve never found a dead one. So, going way back to the 21^st of August 1982, I was collecting shells on the beach that is on the Matakana Island side of the Mount (see pictures below). It was a low tide in the afternoon and I noticed that the surface of the sand was being broken by something coming up through it. It turned out to be this small snail. The interesting thing was that these were all live, and all adult. I know this area well, and often came here at other times of the year in similar conditions, but never found them (dead or alive).

So if we leap forward to the 11^th of August 2010, I was again looking in the same place, in the afternoon, at low tide and I found them again, coming up through the sand. This time I took pictures:

This is the side of Mount Maunganui, looking north and showing the sample area.

Looking south across Tauranga Harbour showing the rocks, between which I found the M. koma.

A close-up of Mesoginella koma (~ 6 mm).

Mesoginella koma coming out of the sand.

Another picture of a M. koma coming out of the sand.

Another close-up of M. koma. 

I thought that these occurrences raised some (possibly only to me) interesting questions. For instance, why only live adults? Why only here? Why this time of year?

So here are some speculative thoughts…

As to why only in that location, I wonder if there is a small population of this species in the Tauranga Harbour entrance, and they live in slightly deeper water, just beyond the intertidal zone? I’ve never found them anywhere else in the Mt. Maunganui area. This species is really common in the north, so perhaps this is a small isolated population?

As to why only adults and only at this time of year is probably easier to speculate over. My best guess is that they are coming in to shallower water to breed or spawn. They could be doing this in the evening during winter, as the hours of daylight are less and presumably they would have less chance of being eating or drying out, especially if they live most of their lives below low tide. This would explain both their adult size and the timing. I do recall hearing somewhere that they might be nocturnal, which would make sense. However, this doesn’t explain why I never seen dead ones of any size. The harbour channel rapidly descends to about 30 m depth in the middle, so perhaps the severe depth gradient and high current environment washes away smaller and/or dead shells into deep water?

There is always is the possibility that since these are chance observations, that I am just seeing what I want to see here. However, I used to come to this part of the beach a lot in the 1980's (not a lot for a teenager to do in the Mount back then) and I never found dead examples of this species; something I would have expected if it were living in the intertidal or just offshore there. So, more questions to be answered here...  I would suspect that since this species is far more common further north that it wouldn't be that hard to work on. It would be interesting to understand more about the role this species plays in the sub-tidal ecosystem.

Cheers

Dr. Matthew Jones

References

Jones, M.R.L., 2008. Dietary analysis of Coryphaenoides serrulatus, C. subserrulatus and several other species of macrourid fish (Pisces: Macrouridae) from northeastern Chatham Rise, New Zealand. New Zealand Journal of Marine and Freshwater Research 42: 73–84.

Marshall, B.A., 2004. New names for four common Marginellidae (Mollusca: Gastropoda) from northern New Zealand. Molluscan Research 24: 7–20.

Powell, A.W.B., 1979. NZ Mollusca.