Ecology of the Von Damm Hydrothermal field, Cayman Trough, Caribbean

Abstract

Within this study it has aimed to analyse the ecology and distribution of major species at the

newly discovered Von Damm Hydrothermal vent site. From video analysis obtained using an

remote operated vehicle (ROV) it was found that a new species of Rimicaris shrimp is the

most abundant species present at the vent site, however tube worms were also present but

sparsely populated. This shows closer links to Mid Atlantic vent sites than previously thought

East Pacific Rise vents as a result. Zoarcidae fish and Lebbeus shrimp were also present

amongst the Rimicaris but less abundant also. Other species found at the vent site include:

Gorgonians, Cnidarians, Holothurians, Porifera, Galathea, Ophiuroids, Gastropods, a Sea

Dandelion and Anemone. The ecology of the vent site has shown that the Rimicaris is the

most dominant at the Vent site but is fed upon by the Zoarcidae, Lebbeus and Galathea of

which are distributed similarly. Due to this dominance it has forced the Vestimentiferans

further down the slope into weaker vent flows causing reduced abundance and distribution as

they are outcompeted.

Introduction

The discovery of hydrothermal vents is fairly recent and they have been found to be hotspots

for biological activity where animals have adapted to utilise sulphur to support their food web

instead of most species which undergo photosynthesis (Corliss et al. 1979). This is due to no

sunlight within the deep ocean. However the hydrothermal vents fluid contains sulphur which

is then used by chemoautotrophic bacteria to produce energy, which supports the food webs

of these communities. The existence of these new diverse ecosystems has been a topic of

scientific interest as it has revealed a diverse new ecosystem and thus disproving the Azoic

theory of Edward Forbes which stated that the deep oceans contained fewer and fewer

animals the deeper you go (Anderson and Rice, 2006). Understanding the ecology of the

hydrothermal vent fields is important as the impact of humans on the globe is causing

deleterious effects on ecosystems around the globe, by understanding the ecosystems such as

hydrothermal vent fields and the ecology of them will help to inform us on how to conserve

them and what management protocols are needed in order to achieve this. Furthermore this

will also help to maintain biodiversity which is important for ecosystem services and

diversity management (Schneiders et al. 2012).

Further reasons for studying the ecology of hydrothermal vents is due to the discovery of this

ecosystem being supported by chemosynthesis and not photosynthesis it raises energetic

questions such as how energy is transferred through the food web, how much energy is

required to support the communities large biomasses and the requirements of the specially

adapted animals living at the vent sites (Dover and Lutz, 2004). In addition as vent species

use chemosynthesis rather than photosynthesis it has been useful in evolutionary studies in

understanding how first life may have evolved (Muller, 2012). This is because it is believed

that life first originated from bacteria, with hydrothermal vents being one of the most diverse

environments for bacteria making them good locations to study evolution and their study may

further develop medical treatments through the discovery of new species. More over

hydrothermal vents have extreme temperatures and one of the biggest temperature gradients

on the planet and is an extreme environment, studying how organisms have adapted to cope

with these changes is important. In addition hydrothermal vents are also future targets for

mining of precious metals therefore the study of these vents will indicate how mining

operations may affect these communities (Glowka, 2003).

The hydrothermal vent fields within this study is the Von Damm Hydrothermal field, within

the Cayman Trough, this area is an area of interest as it became isolated with the loss of the

land bridge 3Ma, since then isolation will have has evolutionary implications such as

speciation, therefore understanding the ecology of the Cayman vent fields is an important

area for studying the evolution of species and divergence rates, furthermore it may reveal

information how the isolated vent systems continue to persist and spread from vent to vent as

it may help to better understand reproductive dispersal strategies (Tyler et al. 2002).

The aim of this report is to describe the distribution and to identify the major species present

at the Cayman hydrothermal vent field in order to analyse the ecology of the vent site and

further our understanding of these unique oases of life.

Methods

The Videos were collected from the Cruise of Okeanos Explorer In August 2011 using an

ROV. The videos used for this ecological analysis are from Dives 1, 3, 4 of the cruise. They

were analysed by observing the dive videos and recording down the times at which species

were visible on the video screen and then obtaining the time from the video timestamp where

the ROVs latitude and longitude positions at that particular time was used as positional

indicators of the species which was transferred into ArcGIS and overlaid onto a bathymetric

map of the seabed to show the position of the species found relative their position on the

seabed. This can then be used for the ecological analysis. For areas where animals were in

patches such as shrimp the latitude and longitude was recorded every second the shrimp or

animals was visible on the video to show multiple data points on the map in order to show an

approximate size of the patch. It is therefore important to remember that the results do not

indicate how abundant a species is at the vent site, but rather where they are present or absent

at the vent site.

Results

From the analysis of the videos the major species and their distribution at the Von Damm

Hydrothermal vent field are as follows:

Fig1. Distribution of all species found at the Von Damm Vent Site different colours representing different taxonomic groups.

From Figure 1, the majority of species can be found on the slopes of the vent, mainly towards

the top of the vent where fluid is being expelled from the vent. However there are animals

found further away from the vent shown by the patch on the left of Figure 1.

Fig2. Dive tracks from the cruise showing the area surveyed by the ROV

Comparing where the species were found within figure 1, and where the ROV searched

within figure 2, it shows that the animals were found mainly on the slopes of the vent only

and the surrounding areas had no visible signs of animals present, as the outer yellow dive

tract has very little species present surrounding the vent.

Fig3. Distribution of Rimicaris shrimp species at the vent site, the most abundant species at the vent site (left) and image of

Rimicaris shrimp patch (right).

The most abundant species at the vent site was a new species of the Rimicaris shrimp, which

were mainly found in large patches around vent openings shown in Figure 3, as they try to get

as close to the vent fluid for their chemoautotrophic bacteria to feed upon. They can also be

found near most other species at the vent site as other species distributions overlapped the

Rimicaris distribution. Furthermore from Figure 3 they are also the most widely distributed

and most densely populated species that was found at the vent site.

Fig4. Distribution of Zoarcidae fish at the vent site (Left), image of Zoarcidae fish (right).

The abundance of the Zoarcidae fish are a lot less abundant than the likes of Rimicaris

shrimp as shown within figure 3, yet they are mainly found amongst the shrimp as shown

within figure 4. This is also replicated within the distribution as it overlaps with the shrimp

distribution.

Fig5. Distribution of the Shrimp Lebbeus virentova (left), image of Lebbeus (right).

The distribution of a second species of shrimp found at the vent site Lebbeus (Nye et al.

2012) was less abundant than the Rimicaris but were also found within the same location as

well as with Zoarcidae, as the Lebbeus and Zoarcidae are distributed similarly to Rimicaris

there may be links between them that cause this similar distribution.

Fig6. Distribution of Vestimentiferans at the vent site (left), image of Vestimentiferan tube worm (right)

The Distribution of tube worms at the vent sites of the Von Damm were low in abundance

and sparsely distributed. They were also distributed differently to the abundant shrimp and

were not found near the vents which could be a function of the shrimp out-competing the vent

openings as they both feed using chemoautotrophic bacteria.

Fig7. The distribution of Galathea Squat lobsters at the vent site (left), image of squat lobster (right)

The distribution of the Squat lobsters was also similar to the shrimp and fish but like the fish

and Lebbeus they are less abundant and were usually found on their own with the exception

of the above picture.

Fig8. The Distribution of Gastropods at the vent site (left), image of Gastropods (right).

Also found on the slopes of the vent site near the vent openings were small gastropods of

which in figure 8 are the small white dots, their distribution was also found within the same

location as the shrimp. All of the above species described in figures 2 to 8 with the exception

of the tube worms have similar distributions which could indicate interactions between the

species and they may depend on each other to maintain this distribution.

Fig9. The distribution of less abundant species at the vent site (top left) of which are: Gorgonian (top right), Sea Dandelion

(bottom left), Anemone (bottom middle), Jellyfish (bottom Right) and Holothurians, Ophiuroid, Sponge and Bivalves

Figure 9 shows the less abundant species found at the vent sites and singular individuals

found such as the jellyfish and sea dandelion. These species were distributed differently to

the major species found at the vent sites, and were found at the bottom of the slopes or not on

the slopes of the vent which may indicate they do not rely on the vent fluid for survival and

more likely depend on nutrient fluxes from the surface such as the Gorgonians, and

Anemone. The jellyfish also has the ability to move freely through the water column as no

polyps were found within the video it is unclear whether it is residentially distributed near the

vent or just moving with the water current.

Discussion

The ecology of the Cayman Trough hydrothermal vent fields is relatively low in diversity for

macrofaunal species as only 12 were observed during the videos however this is

characteristic of a hydrothermal vent community, on the other hand the microbial community

is most likely very large and diverse as it is supporting large abundances of animals at the

vent site seen within the results and videos (Glowka, 2003). In addition the most dominant

species at the vent site were large aggregations of the Rimicaris shrimp which were found

close to vent openings with Zoarcidae amongst them most likely Pachycara (Connelly et al.

2012) The shrimp are also likely out-competing the Vestimentiferan tube worms which were

found further down the slopes and not near vent openings where strong vent flow is needed to

sustain them. The tube worms were also low in abundance compared to other vent sites found

at the East Pacific Rise where they are found in large abundances, considering that they are

within a different zone of the vent than where they are usually found, the presence of the

shrimp may be preventing settlement near the strong vent flow areas, which as a result allows

the Rimicaris to dominate the vent (Hunt et al. 2004). Found amongst the Rimicaris were

Zoarcidae and Lebbeus shrimp, and Galathea Squat lobsters were also distributed similarly

to the Rimicaris but were less abundant, this would indicate that these species feed upon the

abundant Rimicaris shrimp which utilise the chemoautotrophic bacteria, this would explain

smaller abundances as multiple Rimicaris individuals are required to sustain an individual. It

also explains the similar distribution as they stay close to their food source (Ferry, 1997;

Colaco et al. 2002). Of the species described above they are the major taxa found at the

hydrothermal vent as a result it is not a very diverse community and significant impacts upon

the system could have destabilising effects or could completely restructure the community as

there are not many alternative food sources if a species is lost from the system as diversity

maintains ecosystem services (Schneiders et al. 2012).

The ecology of the minor species found at the vent such as the sea dandelion, and jellyfish

may promote health towards the community by increasing the diversity but the likelihood that

they are residential to the vent considering they were found singularly is doubtful and are

most likely moving with the water current in a migratory pattern (Burd and Thomson, 2000).

Similarly other species found such as Anemones, Ophuiroids, Holothurians and Gorgonians

were found. There were distributed away from the vent on the peripheral slopes, showing a

zonation between these and the patches of Rimicaris shrimp. However these animals most

likely do not depend directly upon the vent as Gorgonians most likely filter feed and

Holothurians deposit feed, they more likely depend on organic matter falling from the surface

and other particulates found in the water column driven by the currents caused by the vent

fluid. Due to the decreased dependency on the vent fluid they can inhabit further away from

the vents as they are outcompeted near the vents which causes zonation in terms of proximity

to vent openings. This also explains decreased abundances as there is less food available to

these peripheral vent species (Kim and Hammerstrom, 2012).

The Cayman community is also important biogeographically as it is isolated, as a result

different fauna exist here and from the cruise a new species of Rimicaris shrimp was

discovered as a result, the discovery of this new species also shows that vent systems are still

widely poorly understood and further research is needed towards them to understand

processes taking place (Connelly et al. 2012). The Cayman Trough vent site biogeography is

more likely more closely related to vents near the Mid Atlantic Ridge than vents at the East

Pacific Rise due to the dominance of shrimp species instead of tube worms found in the

pacific (Hunt et al. 2004; Zbinden et al. 2008). This is unusual for vent sites found at the

Cayman Trough as their assemblages are usually similar to those of the northern Pacific

(Tyler et al. 2002). This raises questions as to how isolated are the vent sites of the Cayman

trough and why there are differing dominances of species within the same geographical

location (Embley et al. 1990). In addition at the Von Damm site the presence of the Lebbeus

shrimp is one of the first recordings of them outside the Pacific, indicating there must be

some dispersal from the Pacific to the Caribbean which is further reinforced by the presence

of tube worms. It would therefore appear that although the Von Damm site is supposedly

isolated tectonically it has similarities to both Atlantic and Pacific vent sites asking the

question how isolated is the Von Damm site and further reinforcing the need to learn about

larval dispersal of hydrothermal species (Connelly et al. 2012).

To summarise the Von Damm vent field site is a uniquely inhabited by new fauna not seen at

any other vent which could be explained by influences from both Atlantic and Pacific

ancestors. There is two zones of zonation with dominant vent dwelling species such as

Rimicaris, Zoarcidae, Galathea, Lebbeus in close proximity to vent openings which are

found on the slopes of the vent and less species such as Gorgonians, Holothurians,

Anemones, Ophiuroids which do not directly depend on the species or vent fluid found on the

slopes that inhabit the surrounding area of the vents. In addition from the dive tracks of the

survey area the peripheral region was not covered in full as a result there could be possible

gaps in data as the ROV did not visit those areas, for which in future expeditions surveying

the peripheral regions more thoroughly may reveal new ecological patterns regarding

zonation and species distribution.

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