EFFECTS OF HURRICANE CARLA ON THE ECOLOGY OF REDFISH BAY, '

CARL H. OPPENHEIMER Institute of Marine Science, University of

ABSTRACT Hurricane Carla hit the Texas coast at Port O'Connor on September 8, 1961 with wind velocities up to 175 mph causing tides to 18.5 feet. A study of the effects of the storm immediately afterwards on Redfish Bay, 60 miles to the south of the storm center, showed the erosional effects caused by the water movement. The general ecological environments in the bay were not grossly affected by the storm. The sediments were disturbed to only a few mm and the grass beds were not damaged.

Redfish Bay, Texas (Figure 1), located about 30 miles northeast of Corpus Christi, is one of a series of inland bays formed by barrier islands characteristic of the coast of Texas. The shallow bay and mud flat environ- ments of Redfish Bay had been studied for coastline distribution of sedi- ment types, microflora, oxidation, reduction potentials, pH, and bottom communities, for approximately three years prior to hurricane Carla (Oppenheimer, 1960). Port Aransas is located on the north end of Mustang Island at the en- trance to the only pass (Aransas Pass) through the barrier islands between Pass Cavallo at Matagorda Bay in the north, and Port Mansfield in the South. Aransas Pass is stabilized by two jetties which extend several thousand feet into the Gulf. The channel is dredged from the jetties into Corpus Christi. A channel also has been dredged between Aransas Pass and the town of Aransas Pass on the mainland. Along this channel is the Aransas Pass Causeway. A description of the area can be obtained from Collier and Hedgpeth (1950) and Shepard and Moore (1955). The area is quite productive (Odum and Hoskins, 1960) and provides a growing area for mullet, red- fish, and other fishes, and a breeding ground for shrimp, the food of many of the fishes of the Texas coastal area. The last major hurricane occurred in 1954, when the water rose to 6.5 feet in the Port Aransas area. Hurricane Carla began to build up water along the Gulf coast on Sep- tember 8, 1961. The survey reported here was made approximately four days after the eye of hurricane Carla struck the coast at Port O'Connor, 60 miles north of Port Aransas (Figure 1). Reliable observations were

IContribution No. 453 from The Marine Laboratory, Institute of Marine Science, University of Miami. Support for this survey was provided by the Fish and Wildlife Service, Bureau of Commercial Fisheries, St. Petersburg, . 60 Bulletin of Marine Science of the Gulf and Caribbean [13(1) obtained for tidal heights, and radar pictures located the storm center. Actual conditions of rain, wave height and direction, and water height within the area were not easily obtained because the large amount of water carried by the high-velocity winds limited visual observation and damaged most instruments. Information for water level and movement was obtained from personal accounts of witnesses who remained at the storm site, and from official data of the U. S. Weather Bureau at Corpus Christi, Texas. The area surveyed consisted of a triangle between Corpus Christi, Port Aransas and Rockport, Texas. The ecological conditions were observed by aerial survey, bottom sampling and microscopic observation, and com- pared with observations and photographs made during the previous three years. Photograph locations are indicated on the chart in Figure 1. Salini- ties may be obtained from the Texas Game and Fish Commission, Rock- port, Texas. As hurricane Carla moved west through the Gulf, the tide started to rise at Port Aransas on the evening of September 8. On September 11 at approximately 3 P.M. Carla hesitated in its westerly movement for about five hours, the eye being located off Port O'Connor approximately 70 miles north of Port Aransas. At 2 P.M. September 12, the eye moved in over Port O'Connor and at 4 P.M. progressed up Matagorda Bay. The small town of Port O'Connor was completely destroyed. The wind velocity (registering 150 mph before the anemometer blew away) was estimated at 170 miles per hour, and tides of 18.5 were recorded. The eye of the storm was about 30 miles in diameter, with its northerly edge at Port O'Connor, as it passed directly up Matagorda Bay. The effects were felt from Brownsville, Texas, to Cameron, . The lowest barometer reading was 27.5'0. Redfish Bay and vicinity, approximately 60 miles south of the eye of the hurricane, presented a unique situation with respect to change in wind direction and movement of wind-driven water because of the cyclonic wind movement. The waves and water moved coastward as the storm progressed to the west, causing the tides at Port Aransas to rise to 10.3 feet above mean low water, with waves and surges up to 40 feet. The Gulf water, moving westward, pushed into the bays behind the Barrier Islands. High waves and water progressed up the Corpus Christi ship channel toward Aransas Pass and Aransas Bay, causing a small amount of erosion along the channel edges and spoil banks. Sometime during the early hours of Monday, September 11, as the storm passed to the north, the wind shifted to the northwest and effectively counteracted the inward flow of tide into the bays and the wave action coming from the Gulf. This created a stabilizing effect upon the waves in this part of the Bay system and minimized erosion effects and as the storm progressed inland the wind velocity and wave action decreased. At the 19631 Oppenheimer: Effects of Hurricane Carla 61 same time, large amounts of rain fell which entered the Bay system, thus dropping the salinities and adding water to the Bay. The highest official tides and winds recorded were: Feet above Wind Velocity Rainfall MLW MPH (inches) Rockport 7.8 90 Corpus Christi 6.8 90 5.5 - 15 Port Aransas 10.9 125-(170 est.) Austwell 9.0 100-(1 SO est.) Observers noted that the wave action within the bays was not extensive. The highest waves were created by the storm moving inland, causing the Gulf waves to come into the bays for a limited distance. When the wind shifted to the northwest it formed waves which passed southward along Lydia Ann Channel toward Port Aransas. These, plus the Gulf waves which were coming in the Pass, caused considerable damage to the town waterfront. Although visual observations were limited, it is estimated by witnesses and from damage and erosion that the wave heights within Redfish Bay were less than three feet. As the storm moved inland the water moved out of the bays back to the Gulf, scouring out areas along Port Aransas, Aransas Pass Channel and Causeway, and the west spoil banks along Corpus Christi ship channel adjacent to Port Aransas. Four days after the storm this muddy water could be traced three to four miles into the Gulf as it passed out of Aransas Pass. (See Figure 12, which shows sedi- ment-filled water moving out of the shallow mud flats.) The fourth day after the storm the tide was still one foot above normal, and the mud flats and small islands behind the barrier islands were still flooded. Large expanses of normally exposed mud flats containing blue- green algae were still covered with water. The water in Redfish Bay, relatively fresh due to the rainfall, continued to move out of the Bay. The greatest effects of the storm were noted along the beach fronts of the many islands in Redfish Bay. The high tide and wind washed considerable material from the mud flats and the many spoil banks near the dredged channel, Aransas Pass and Padre Island causeways. Aerial observations were supplemented by photographs which may be compared with the aerial photographs taken prior to the storm. Figures 2 to 5 illustrate the extent of damage to the beach along the Gulf adjacent to Port Aransas. Figure 2 is of the north jetty. The beach front is cut back and the white sandy area shown was previously covered with dunes 10 to 25 feet high, similar to the few remaining dunes shown in the right center. Figure 3, taken a few hundred yards north of Figure 2, shows the result of the storm waves which passed over St. Joseph Island, almost leveling the high dunes which were previously present. The strip of beach at the top of 62 Bulletin of Marine Science of the Gulf and Caribbean [13(1) the photograph is St. Joseph Island. The water in the center is Lydia Ann Channel which connects Aransas Bay at the north with the Port Aransas channel. The mud flats in the bottom of the photograph will be referred to later. Figures 4 and 5 were taken of the South Jetty Beach before and after the storm. The beach has been badly eroded and the high dunes back of the beach have been leveled for about 300 feet from their previous location. Between dunes the hollows are filled with water. The pier has been partially destroyed and the line of waves indicates the typical bar structure of the area. Each line of waves represents an offshore bar. Two bars are shown in Figure 4. Figure 5 also shows the presence of two bars, the second bar not being as well defined as in Figure 4, which indicates that the bars did survive the storm or were immediately re-formed. Figures 6 and 7 were taken at the same location along the southeast shore of the Corpus Christi Ship Channel before and after the storm, respectively. Although the water level was higher in the photographs after the storm (Figure 7) no marked erosion can be detected. This is represen- tative for the area on the southeast side of the channel. However, on the northwest side of the channel the water moving out of Redfish Bay, and waves caused by the change in wind to the southeast, washed large sections of the old spoil bank away. Figure 8 was taken after the storm, showing the area of Figures 6 and 7 at the far right. The vegetation here is typical of the areas on the island having about 3 to 5 foot elevations which are not normally covered by water. Very little erosion was detected in this and smaller areas, due to the stabilizing action of the vegetation. The storm water did cover most of this area, as evidenced by large amounts of wreckage deposited, and the water-swept appearance due to removal of the old dead plant material. Figure 9 represents a large area of normally alternately exposed tidal flats containing a bluegreen algal cover. Although it is now shown covered by water just after the storm, the typical dark color of the mat is still visible and is intact. Even the old marsh buggy tracks over the flat were preserved. These thick algal mats of entwining bluegreen filaments usually form a tough cover over the sand. However, when they are covered with water, gas bubbles from photosynthesis will form within the mat and effectively float large pieces of it to the surface. At the time of this obser- vation the mat was still intact but could have been damaged if the water remained for a longer period of time. The storm apparently was not active enough to remove the algal mat, except perhaps in the few places where the white sand shows through. Figure 10 represents an area of the bay recently dredged for the Intra- coastal Waterway. The spoil banks are evident as white areas, surrounded by white, flocculent, clay-discolored water resulting from material washed from the spoil banks. The dark areas in the water represent communities of

19631 Oppenheimer: Effects of Hurricane Carla 65 Thalassia and Diplanthera. Figure 11, taken just south of Figure 10, clearly shows the dark areas of bottom grass communities of Thalassia, Diplan- thera and other attached algae. These communities are growing in about two to three feet of water and demonstrate their apparent stabilizing effects on the bottom sediments. No evidence of extensive bottom damage caused by the storm was found. Small areas (five to ten feet in diameter) may have been eroded, but these may be normal and thus difficult to relate to storm effects. The spoil banks shown in Figure 11 were all older, with protective foliage, and very little erosion was detected in contrast to the new spoil banks shown in Figure 10. The water was not muddy. Figures 2 and 12 are of Lydia Ann Channel just one mile north of Port Aransas. Port Aransas can be seen in the background of Figure 12. Although the barrier islands were badly damaged (Figure 2, top), the large expanse of low-lying islands was not damaged. These islands were overgrown with a cover of Spartina, Salicornia and Black Mangrove (behind the barrier islands). At time of extra high tide these areas are covered with an ineh or more of water; otherwise they are a few inches above water. The structure in the center is the old Coast Guard Lighthouse which was originally the site of the Corpus Christi Channel before the jetties and dredging stabilized the movement of the Pass. Figure 13 was taken before the storm, which shows that the typical pattern of the islands was not changed by the storm. Except for a few places, the water within the bays was still quite turbid and characteristic of the area during the normal wind storms and high productivity of the summer months. The storm did cause considerable amounts of silt to be redistributed by the water, because all areas examined after the storm had a fresh cover of fine silt. This silt was examined by phase microscopy and found to contain a large population of living blue- green algae, flagellates. diatoms, nematodes, bacteria and ciliates. It is apparent that the organisms suspended during the storm action and those normally growing in the water reinoculated the newly deposited material. No apparent gross differences in populations could be detected in compari- son with previous observations (although no attempt was made to separate species of living organisms). The Thalassia and Diplanthera beds of previously studied stations were quite within normal apoearances, and the growth appeared more luxuriant than during the same time of year for the three previous years. The edges of the bays did not have unusually large deposits of grasses and algae except in a few places where such materials were accumulated because of being deposited by the receding tide, or where it was entrapped within a bay. These accumulations were rare. In some places, such as at Mud Island about seven miles north of Port Aransas, considerable algae and detached grasses (living and dead) were accumu- lated on the bottom in about one foot of water near the islal1d. However, 66 Bulletin of Marine Science of the Gulf and Caribbean fl3(1)

FIGURE 2. North jetty, Aransas Pass Ship Channel. At upper left channel to town of Aransas Pass. Lydia Ann Channel in center. After hurricane.

FIGURE 3. St. Joseph Island (Barrier Island) Lydia Ann Channel and small island approximately one mile north of Port Aransas. After hurricane. 19631 Oppenheimer: Effects of Hurricane Carla 67

FIGURE 4. South jetty, Port Aransas. Before hurricane.

FIGURE 5. South jetty, Port Aransas. After hurricane. 68 Bulletin of Marine Science of the Gulf and Caribbean 1/3(1)

&. ...•• -

FIGURE6. Section of southeast shore of Corpus Christi Ship Channel about one mile from Port Aransas. Before hurricane.

FIGURE7. Same location as Figure 6. After hurricane .

.~. 19631 Oppenheimer: Effects of Hurricane Carla 69

FIGURE 8. Looking south along southwest shore of Corpus Christi Ship Channel about one mile from Port Aransas. After hurricane.

FIGURE 9. Redfish Bay mud fiats with blucgreen algal mat. After hurricane. 70 Bulletin of Marine Science of the Gulf and Caribbean [13(l)

FIGURE 10. Northwest edge of Redfish Bay showing mainland about five miles north of Aransas Pass. The Intracoastal Waterway runs parallel to the coast just to the right of the spoil banks. After hurricane.

FIGURE 11. Northwest edge of Redfish Bay showing mainland about one mile south of Aransas Pass. Aransas Pass Causeway to Port Aransas at the top. The Intracoastal Waterway runs diagonally from right to top, passing through Miller Bridge of the Causeway. After hurricane. 19631 Oppenheimer: Effects of Hurricane Carla 71

FIGURE 12. Looking southeast along Lydia Ann Channel toward the town of Port Aransas. After hurricane.

FIGURE 13. Looking toward the mainland from 51. Joseph Island. Before hurricane. 72 Bulletin of Marine Science of the Gulf and Caribbean \13(1) similar material was always present in the same location before the storm, indicating that the material found after the storm either remained or was accumulated immediately. These bottom accumulations provide a living environment for many small crabs and other crustaceans, and small fishes.

CONCLUSIONS It was immediately apparent that the effects of the hurricane in this area just south of the eye were not as severe as anticipated. Major erosion effects were present only near the beach areas adjacent to the Gulf and on spoil banks within the Bay. The grass flats remained intact, and the wave and water motion apparently cleaned out the old and the unattached grasses and algae which were deposited on the banks in many places, leaving clean, fresh-appearing grass flats covered with a fine deposit of new material. The bottom microflora was apparently not changed and showed a large amount of activity, as evidenced by cell movement and chlorophyll, prob- ably as a result of fresh materials which were deposited. No immediate detrimental effect for the shallow water spawning and breeding grounds could be detected during these preliminary examinations. The grass flats appeared more healthy than at any time during the previous three years in which the same area was studied. These conclusions are in agreement with those of Thomas, Moore and Work (1961) who stated that the damage caused by to the Thalassia beds in Biscayne Bay, Florida, is considered light and a rapid growth rate may contribute to early recovery from storm damage; and with Tabb and Jones (1962) who stated that they had no evidence that the aquatic fauna of north Florida Bay suffered any permanent damage due to hurricane Donna. LITERATURE CITED COLLIER, A. AND J. W. HEDGPETH 1950. An introduction to the hydrography of tidal waters of Texas. Publ. Inst. Mar. Sci. Univ. Tex., 1: ]21-194. ODUM, H. T. AND C. M. HOSKINS 1958. Comparative studies on the metabolism of marine waters. Pub!. Inst. Mar. Sci. Univ. Tex., 5: 16-46. OPPENHEIMER, C. H. 1960. Bacterial activity in sediments of shallow marine bays. Geochim. et Cosmochim. Acta, ]9: 244-260. SHEPARD, F. P. AND D. G. MOORE 1955. Central Texas coast sedimentation: Characteristics of sedimentary environment, recent history and diagenesis. Bull. Amer. Ass. Pet. Geo!., 39: ]463-]593. TABB. D. C. AND A. C. JONES 1962. Effect of Hurricane Donna on the aquatic fauna of North Florida Bay. Trans. Amer. Fish. Soc., 9] (4): 375-378. THOMAS, L. P., D. G. MOORE, AND R. C. WORK 1961. Effects of Hurricane Donna on the turtle grass beds of Biscayne Bay, Florida. Bull. Mar. Sci. Gulf & Caribbean, II (2): 191-197.