Faunal Colonization

In terrestrial environments, wounds are the most attractive to arthropods, followed by the natural orifices. The only wounds on the experimental carcasses were the head wound inflicted by the pin-gun, as well as various cuts and sores that had been present in life. Only the spring carcasses were observed for the first few weeks after submergence. Very shortly after submergence, a periwinkle, the wrinkled amphissa (Amphissa columbiana Dall) were attracted to the head wounds at 15.2 m (Anderson and Hobischak 2002). However, after that the wounds and orifices did not appear to be any more attractive than undamaged areas. Periwinkles are grazers and usually feed on algal films although they have been found to scavenge corpses of humans, marine mammals and fish (Sorg et al. 1997). It has been suggested that they are not feeding directly on the carrion, but rather on the algal films developing on the carcass (Sorg et al 1997). However, such early arrival suggests they are directly attracted to the carcass.

The carcasses at 15.2 m were more rapidly attractive to fauna than those at 7.6 m, but within 19 h, both sets of carcasses were attracting a variety of species (Table 12.3). The remains became covered in silt within hours of death and much of the faunal activity appeared to be related to this, presumably feeding on microbes, and micro flora and fauna within the silt. Many of the larger invertebrates caused abrasions or deep openings into the remains. In the spring experiments, within 24 h of submergence, some feeding damage was noted and by 3 days post submergence, the ears of most of the carcasses had a 'frayed' appearance, suggesting feeding activity also. Table 12.3 lists the species present on the carcasses from the spring experiments over time.

In the first 24 h, a green sea urchin (Strongylocentrotus droebachiensis (Müller)) and red or vermillion sea stars (Mediaster aequalis Stimson) were seen on some of the deeper carcasses, with more sea stars actively moving towards the deeper carcasses. A large sunflower sea star, Pycnopodia helianthoides (Brandt) was attracted shortly after death to the deeper carcasses only and was rapidly joined by several others that completely enveloped several carcasses. Several of these sunflower sea stars were seen moving rapidly towards the carcasses, actively attracted. On only one occasion was this sea star collected from remains at the shallower location and this at the remains stage. Some larger sea stars are known to feed on carrion as well as invertebrates (Sorg et al. 1997). After the sunflower sea stars had left, there appeared to be large grazed or damaged areas left behind. It may have been caused by the sun star when grazing on epifauna on the surface of the pig (Sloan and Robinson 1983). These sunflower sea stars were attracted from immediately after submergence until only bones remained. At one point, when only bones and skin remained, the sea star was found inside the bag of skin.

Other fauna noted on the remains within 24 h of submergence included the Western Lean Nassa (Nassa mendicus (Gould)), marine Oligochaetes (family Enchytraeidae), copepods, proboscis worms (Glycera sp.), bloodworms (Euzonus sp.), red rock crabs (Cancerproductus L.), blue mud shrimp (Upogebia pugettensis Dana), coon striped shrimp (Pandalus danae Stimson), Oregon triton (Fusitriton

Table 12.3 Species collected in the spring experiment. S resulting in a more detailed collection

= 7.6 m, D = 15.2 m. At 140 days post submergence, the remains were recovered and examined very carefully

Species

13.5H 19.5H 28.5H 3D 11D 30 D 40 D 47 D 54 D 116 D 140D

Phylum Arthropoda

Alaskan pink shrimp Pandalus eons Makarov Hermit crab Pagums beringanus (Benedict) Pacific red hermit Elassochirus gilli (Benedict) Barnacles (Balanus sp.) Small amphipods

Red rock crab Cancer productus L. Pacific lyre Crab Hyas lyratus Dana Blue mud shrimp Upogebia pugettenis Dana Large amphipods

Coon striped shrimp Pandalus danae Stimson Sitka shrimp Heptacarpus sitchensis Brandt Ostracod

Diastylis rathkei Kroyer Copepods Phylum Annelida

Marine oligochaetes Family Enchytraeidae

Proboscis worms Glycera sp.

Bloodworms Euzonus sp.

Pile worms Nereis vexillosa Grube

Marine worms Nereis sp.

Scaleworm Arctonoe sp.

Polychaetes Ammotrypane aulogaster Rathke

(continued)

Table 12.3 (continued)

Species_13.5H 19.5H 28.5H 3D IIP 30 D 40 D 47 D 54 D 116 D 140D

Phylum Mollusca

Oregon triton Fusititron oregonensis (Redfield) D S, D

Aleutian macoma Macoma lama Bartsch S

Sitka periwinkle Littorina sitkana Philippi S

Periwinkle Littorina scutulata Gould S

Wrinkled amphissa Amphissa Columbiana Dali DD S

Pandora sp.

Western lean nassa Nassarius mendicus (Gould) DD S

Giant western nassa Nassarius fossatus (Gould) D

Mussels S S

Phylum Echinodermata

Leather star Dennasterias imbricata (Grube) S

Mottled sea star Pisaster brevispinus (Stimson) S

Sunflower sea star Pycnopodia helianthodes (Brandt) DD DD DD

Red sea star Mediaster aeqalis Stimson D D D D D

Green sea urchin Strongylocentrotus droebachiensis D

(Müller) Phylum Chordata

Gobies Family: Gobiidae D

Sculpins Family: Cottidae D

Ling cod Ophiodon elongatus Girard D

Pacific halibut Hippoglossus stenolepis (Schmidt) D

Sand dabs Citharichthys sp. S. D

Larval herring Family: Clupeidae S. D

Phylum Nematoda S. D

oregensis (Redfield)), Alaskan pink shrimp (Pandalus eous Makarov) as well as larval herring (Clupea sp.) and two species of small amphipods, which were not caught for identification (Anderson and Hobischak 2002). The majority of the fauna were seen on the deeper carcasses (Tables 12.3 and 12.4). There was a stronger current at the shallower sites which may have accounted for the lower numbers of animals seen. Some of the fauna were clearly predating on other fauna, while some appeared to be feeding on the carcass. In most cases, only one or two members of each species were found on the remains, and no species was found in large numbers. On several examination days, some carcasses at 7.6 m had no visible fauna present, although feeding damage was evident.

When the remains sank, they fell randomly on either a sandy silt seabed or on rocks. This appeared to influence the fauna, with sea stars (Henricia sp), coon striped shrimp (Pandalus danae), sand dabs (Citharichthys sp.) and gobies found almost exclusively on carcasses on sand, while sunflower sea stars, pile worms (Nereis vexillosa Grube), sea strawberries (Gersemia rubiformis (Erhrenberg)), Oregon tritons, smooth cockles (Clinocardium blandum (Gould)), leafy hornmouth (Ceratostoma foliata (Gmelin)), chalky macoma (Macoma calcarea (Gmelin)), mussels and oysters were more common when the carcass rested on a rocky substrate (Anderson and Hobischak 2004).

When the bones were recovered at the end of the spring experiment, a more exhaustive examination of the remains could be made and marine oligochaetes (Family Enchytraeidae), bloodworms (Euzonus sp.), juvenile red rock crab, blue mud shrimp, pile worms (Nereis vexillosa), Nereis sp., Pandora sp., scaleworm, Aleutian Macoma (Macoma lama Bartsch), Sitka periwinkle (Littorina sitkana Philippi), Diastylis rathkei Krayer, Ammotrypane aulogaster Rathke, copepods, nematodes, ostracoda, wrinkled amphissa, Sitka shrimp (Heptacarpus sitchensis Brandt)) were found on the shallow remains (Table 12.3). On the remains at 15.2 m a Red rock crab, Pacific lyre crab (Hyas lyratus Dana), Pacific red hermit (Elassochirus gilli (Benedict)), proboscis worms, copepods, bloodworms, marine oligochaetes (Family Enchrytraeidae), scaleworms, giant Western Nassa (Nassarius fossatus (Gould)), Ammotrypane aulogaster, juvenile red rock crab and nematodes were recovered (Table 12.3) (Anderson and Hobischak 2002). However, at this time, only bones remained and the remains had been skeletonized for some time, so many of these species may have only been incidentally associated with the remains.

Very low numbers of animals were seen on the fall carcasses, although again, the deeper remains were more attractive (Table 12.4). When the bones were recovered at the end of the fall experiment, both shallow and deeper remains were found to have shrimp, small amphipods, marine oligochaetes, sunflower sea stars, and a large number of mollusks, although by far the greater number of mollusks were found on the deeper remains (Table 12.4). A mussel bed and a kelp bed had developed near the remains of one of the shallow carcasses. Many more mollusks were found on the fall carcasses than on the spring carcasses. A large sunflower sea star was seen on the bones at 225 days on a shallow pig, the first time this species was recorded on a carcass at 7.6 m. This species appeared to be much more attracted to

Table 12.4 Species collected in the Fall experiment. S = 7.6 m, D = 15.2 m. At 225 days post submergence, the remains were recovered and examined very carefully resulting in a more detailed collection. At 35 D, only one carcass, from 7.6 m, was brought to the surface for examination and at Day 48 a carcass from 15.2 m was brought up for examination then returned

19 225 D

Phylum Arthropoda

Shrimp Pandalus sp. S, D

Barnacles (Balanus sp.) S

Small amphipods S S, D

Diastylis rathkei Krayer S

Copepods S

Phylum Annelida

Marine oligochaetes Family Enchytraeidae S D S, D

Proboscis worms Glycera sp.

Bloodworms Euzonus sp. S D

Pile worms Nereis vexillosa Grube S

Marine worms Nereis sp. S

SandwormsNephtys sp. S

Polychaetes Ammotrypane aulogaster S

Rathke Phylum Mollusca

Three rib chiton Lepidozona trifida S,D

(Carpenter)

Copper's chiton Lepidozona cooperi (Dall) D

Wrinkled amphissaAmphissa S

columbianaDall

Smooth cockle Clinocardium blandum S, D

(Gould)

Wrinkled slipper-shell Crepidula lingulata D

Gould

Pacific blue mussel Mytilus edulis L. D

Smooth pink scallop Chlamys rubida D

Hinds

Thin shell littleneck Protothaca tenerrima D

(Carpenter)

Red turban Astraea gibberosa (Dillwyn) D

Hooded puncturella Cranopsis cucullata D

(Gould)

Tucked margarite Margarites succinctus D

Carpenter

Smooth margarite Margarites helicinus S

(Phipps)

Chalky macoma Macoma calcarea S, D

(Gmelin)

Macoma Macoma sp. S, D

Hind's mopalia Mopalia hindsii (Reeve) D

Oyster Ostrea sp. D

Edible flat oysters Ostrea edulis L. S

Olympia oyster Ostrea conchaphila S

Carpenter

(continued)

Table 12.4 (continued)

Sitka periwinkle Littorina sitkana Philippi D

Slender bittium Bittium attenuatum D

Carpenter

Abalone piddock Penitella conradi D

Valenciennes

Variegated chink-shell Lacuna variegata S

Carpenter

Leafy hornmouth Ceratostoma foliata S

(Gmelin)

Tusk shells Family Dentaliidae D

Mussels S, D

Phylum Echinodermata

Sea star Henricia sp. D D

Feather star Florometra serratissima D D

(Clark)

Sunflower sea star Pycnopodia D S, D

helianthodes (Brandt)

Brittle star Ophiopsilla sp. D

California sea cucumber Parastichopus S

californicus (Stimson)

Phylum Chordata

Gobies Family: Gobiidae D

Phylum Nematoda S

Phylum Cnidaria

Sea strawberry Gersemia rubiformis S, D

(Erhrenberg)

carcasses placed out in spring rather than those in fall, actively moving rapidly towards the carcasses, and preferred the carcasses at 15.2 m, obviously preferring the slightly deeper waters. Although a larger diversity of fauna was collected when the skeletal remains were recovered, many species were only represented by a single specimen, or two or three specimens.

A much greater diversity of species were recovered on the carcasses placed out in spring rather than those in the fall, although a large number of species of mollusks were recovered 225 days after submergence in the fall experiment, but many were probably incidental, merely settling on a substrate (Tables 12.3 and 12.4). At no time were very large numbers of animals found on the remains in either season. As well, due to inclement weather and difficulty in getting vessels, the fall experiments were sampled much less often than in spring.

In many cases, only one or two specimens of a species were present at any time. As can be seen from Tables 12.3 and 12.4, on many occasions, no fauna were observed on the remains at all. The large diversity of specimens collected when the bones were recovered suggests that many of the invertebrates were missed by divers, or dispersed due to disturbance.

12.2.4 Discussion

Pig carcasses are commonly used in forensic entomology studies as they have been found to decompose in a very similar manner to that of humans on land (Catts and Goff 1992). Our work has shown that pigs also decompose in the aquatic environment in a similar manner to submerged humans (Petrik et al. 2004; Hobischak and Anderson 1999; Hobischak 1998).

In these experiments, the carcasses decomposed much more slowly than was expected. Public safety divers frequently report complete or partial skeletonization of a body within hours of death in certain situations (Teather 1994), so the slow decomposition and lack of anthropophagy were unexpected. Surprisingly, although a number of different species did colonize and feed on the remains, the actual numbers of animals present on the remains were extremely low at all examination times, at both depths and in both seasons. Scavenging and feeding damage was seen on the carcasses but most tissue loss seemed to be due to decomposition, current action, tidal action, and movement of the carcasses against the substrate. The lack of numbers of animals may have been due to disturbance by divers, as scavenging did occur, even when carcasses seemed to be relatively free of invertebrates. However, the much greater numbers of animals seen in the next set of experiments suggests that disturbance was not the only reason for such low numbers. It is quite possible that many species were missed, either due to disturbance, or lack of visibility as many more species were collected when the bones were recovered at the end of each experiment, and on the two occasions when remains were brought to the surface briefly.

Adipocere formation was visible to the naked eye by Days 33 and 40. Adipocere is the result of the saponification or hydrolysis and hydrogenation of the adipose or fatty tissue and occurs most commonly in moist anaerobic situations (Lo 2007). It has been reported that the timing of adipocere formation can be used to estimate elapsed time since death (Mellen et al. 1993) particularly when temperature is known (Kahana et al. 1999). It was generally believed that adipocere took several months to form unless in very warm conditions (Simonsen 1977). However, in a study of 15 bodies recovered over a period of months from a ship wreck, adipocere formation was seen in 38 days after submergence, despite cold waters (Kahana et al. 1999), and in a study of aircraft accidents in the ocean, adipocere formation was seen after 34 days in the Mediterranean Sea at a depth of 540-580 m (Dumser and Turkay 2008). A recent review of the literature has shown that the timing of onset of adipocere formation is very variable. (Lo 2007; O'Brian 1994).

There was no evidence of any clear successional patterns at either depth or season and most animals seemed to be opportunistic feeders, feeding on many kinds of food, including carrion if it was present and on its' microfauna and flora. No species appeared to be carrion dependent, as is seen with many carrion insects on land. Most of the species were not time dependent and were found on the carcasses at any time from fresh to the remains stages.

In both seasons and depths, the carcasses sank at first, then refloated with bloat, but surprisingly, remained floating for a considerable period of time, due to gases in the tissue and, when almost skeletonized, in the remains of the organs, which appeared to act like balloons. In contrast, pig carcasses in both still and running freshwater remained bloated from 9 to 35 days in the same geographic area (Hobischak 1998) and 2-10 days in nearby terrestrial environments (Anderson and VanLaerhoven 1996). This prolonged flotation was also noted in brackish waters (Zimmerman and Wallace 2008).

A much greater diversity of fauna was seen at 15.2 m, and some species seemed only to be attracted to the deeper carcasses, although this was less apparent in the fall experiments. In general, the difference in depth did not seem to have as much impact as flotation of the remains. Those carcasses that remained floating for much of the experiment were much less scavenged than those that had contact with the sea bed. The seabed at this site was very variable with rocky areas close to sandy areas. For those carcasses that remained in contact with the seabed, or sank down, those that fell onto sand or silt were much more rapidly scavenged than those that fell to rock. This is presumably related to the greater abundance of fauna within the silt rather than on rocks and the accessibility of the carcass, with those floating only being accessible to fauna that can swim.

The obvious limitation with this study is that divers and boats were required to attend the scenes. This is limiting financially and was dependent on divers who donated their time to this project and the availability of RCMP, Canadian Coast Guard, Vancouver Aquarium Marine Research Centre and Canadian Amphibious Search Team vessels, whose time was donated. This meant that the carcasses could not be examined as frequently as is desirable and this was particularly true in experiments begun in October, when weather conditions were less favourable than in summer. It is also limiting with regards to human safety, as bad weather conditions prevented diving, and diver safety also limited the depths and situations that could be examined. As well, divers approaching and examining the remains may have disturbed the fauna on the carcasses. These problems were alleviated in the next set of studies which were performed with the Victoria Experimental Network Under the Sea (VENUS).

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